Document O3V8xy7O8yoG7E0rgDLEyDknv

320 ARMSTRONG & KLEIN--PAINTS UNDER CONDITIONS OF PRACTICE. [April 15, 1913. The dish is gently heated over a low flame so that the liquid fumes moderately for three minutes. If a deep yellow colour is formed" before the end of the time the heating is at once stopped. When cool about 5 c.c. of water are added and the liquid is poured into a 50 c.c. Kessler cylinder, the dish being further washed with about 3 c.c. of water. 1 c.c. of a saturated solution of sodium sulphite is mixed with the liquid and then 10 c.c. of about 6 N ammonia are added while cooling. A brown colour indicates the presence of benzoic acid. Finally 2 c.c. of ammonium sulphide are added, when a deep red colour is producod. The liquid is then diluted with water to 50 o.c. and compared with standards prepared in the same manner. In a particular experiment standards of 3, 5, and 7 mg. of benzoic acid were made. A milk residue ~to which 5 mg. of benzoic acid had been added indicated T} :about 4*5 mg. , on comparison with them, 8 o Dis c u s s io n . / 5T a O Mr. 1/ H. Al c o c k said that, whilst examining a bottle /T7of medicine which was found, to contain both sodium CD benzoate and ammonium chloride, during the process Zp of evaporation the benzoate was dissipated and only 4 CD sodium chloride with the excess of ammonium chloride cr * ' remained. This suggested a method for determining CO o' Of the sodium benzoate in milk--the addition of ammonium i; chloride and submission to steam distillation. The of : j. dissociation would take place more readily than ever in acid solution, the whole of the benzoic acid being a i> CD f\fij CO CD found in the distillate and in less quantity than 600 c.c. of it. In the authors* process the latter might be con centrated by adding sodium carbonate to fix the benzoic acid before the acid and ether treatment, which would economise the amount of ether. He did not ,, regard as desirable the use of sulphuric acid with sodium benzoate, for fear of the formation of a sulpho derivative which would not be volatilised so readily, He favoured the less destructive phosphoric acid rather than hydrochloric or; sulphuric acid. ` ` Mr. Liv ee s e eg e , in reply to questions,5 said the pre servative was intended to prevent the milk going sour, and there was wisdom in including the sodium carbonate.; The alternative method suggested by Mr. ' Alcock was; certainly interesting. - . - 'iV London Section. >' i Meeting held at Burlington House, oh * Monday, February 3rd, 1913J ' * ` v;.;1'; PROP W. B. E. HODGKINSON IN THE CHAIR. ' ' THE BEHAVIOUR OF PAINTS UNDER THE CONDITIONS OF PRACTICE,' WITH SPECIAL REFERENCE TO THE ASPERSIONS CAST . UPON LEAD PAINTS. J ;; BY HENRY E. ARMSTRONG AND 0. A. KLEIN. , A communication was made to the Liverpool Section of this Society on May 3rd, 1911, by Prof. E. C. CL Baly, on " The Toxicity of White Lead,** which became widely known, though not published in the Journal of the Society, through the appearanoe of accounts of the meeting in various trade journals--notably >"The Oil and Colour Trades Journal** of May 6th, 1911, p. 1518 and'the Chemical Trade Journal, .May 13th, 1911. The finalconclusion arrived at in this communication was : " That; a definite volatile lead compound is given off in the drying of white lead paint. It appeared to be peculiar, to basic : carbonate of lead and to explain the prevalence of lead poisoning among painters.'1 We believe that before being presented to this Society, this conclusion had been brought under the notice of the Departmental Committees of the Home Office appointed February, 1911, .to consider; When requested, at the time of the appearance of the account of Prof. Baly's work, by a Committee of tho London Chamber of Commerce, to consider these state ments, one of us forthwith formed tho opinion that his conclusion was illogical, unwarranted by the facts and without justification; our experiments show thisifto be the case. I The opening sentence of tho Chemical Trades Journal report:--" Prof. Baly said the experiments which he made were with a view to ascertaining whether it was possible to obtain conclusive evidence as to the toxicity of white paint used by painters "--affords clear indication that Prof. Baly was inclined to assume toxicity, whatever that expression may include. The following sentences show this to be the caseEveryone is familiar with the characteristic smell of white lead paint when drying upon a newly painted surface, which was described by painters as the smell of lead. Painters have long ascribed'this characteristic smell to lead and it is noticeable that there is no such smell from zinc-white paint. It is well known, too, that while painters do suffer from lead poisoning, only in rare instances is poisoning known among workers in the manufacture and mixture of white lead. It was therefore decided to investigate and to obtain some definite pronouncement with regard to this so-called leady smell." The argument on which the experiments made by Prof. Baly were based is stated as follows :--" If, as painters insisted, some lead compound was given off in drying white lead, then there would bo absorption of light when light passed through the vapour into the spectroscope and so, on these lines, experiments were made." The question arises, first--have painters long asoribed the smell illogically to lead or logically to lead paint ? Then, is it true that they have insisted that " some lead compound ** is given off as white lead dries ? Was not this last statement a product of the speaker's imagination ? The one, serious suggestion which we have been able to find that a volatile compound of lead is given off from Eaint in drying is made in the Report presented in 1907 y M. Breton to the. French Chamber of Deputies. ,,We shall deal with this Report later on. ' The reason why Prof. Baly used a complicated photo graphic method, in the. first place, is. not far to seek. During the greater part of his career, he has been engaged not in chemical work but in taking photographs of the absorption spectra of substances in solution. He used the method both naturally and because, probably, he wished to show that the very elaborate, costly apparatus, at his disposal could be put to practical use. .. In the first experiment, a tube was coated inside with "stiff white.lead paste containing 7 to 8 per cent, of linseed piL" In the second, ." zinc white paint " ;paste was'used ; in the third " Purex lead paint. Some Hght was absorbed in the case of the white lead paint alone.. . The experiments .were then repeated with the three materials in tubes heated at temperatures varying from 60 to 150 C., photographs being taken at 5 intervals throughout this range we are told that:--" With zinc white there was no absorption of light up to 100 C,, after whioh there was a small increasing absorption probably due to the linseed oil beginning to vaporise at this point. In the case of white lead, absorption was apparent at 75 C., while purex behaved exactly the same as zinc white." But as it might be asked, " Why heat, the paint ? " in the next experiment, " a tube of glass was coated with white lead and placed in a copper tube overnight at 40 C. Upon passing a beam of light through it as before, absorp tion took place. Another tube smeared with purex treated in the same way showed no absorption. " We are left in doubt what is meant by " white lead '* here and when it was that the beam of fight was passed through the tube which had been placed in the copper tube overnight. But we are only dealing with a report. Finally, to test whether a room painted with white lead paint would show the same result (as the tubes) under the spectroscope " two wooden boxes were made 7 ft. long N39031 Vol. XXXII., No. 7.] ARMSTRONG & KLEIN--PAINTS UNDER CONDITIONS OP PRACTICE. 321 were allowed to dry in a warm room and then each was photographed with the beam of light passing through. The result was definite absorption with white lead, none with purex." No definition of " paint" is given. Apparently actual paint was never used but merely mixtures of the solid material and linseed oil, without turpentine. The conclusion arrived at up to this point by Prof. Baly was that the. painter using white lead paint is exposing himself to volatile compounds ; this (apart from the fact that painter's paint is something different from Prof. Baly's mixture) is the only logical deduction that he was entitled to make, though by implication his hearers were probably led all through to regard the white lead as an incriminated article, capable of emitting vapour containing lead and presumably poisonous ; indeed the implied charge at once follows:--" Having arrived at these conclusions, the point to determine was, what these volatile compounds are. Though this point has not "been settled conclusively, enough evidence has been obtained to prove that a definite volatile compound'of lead does exist in white lead paint." Various distillation experiments are then referred to in which distillates were obtained containing lead when white lead had been used but free from lead when purox was substituted for the white lead. No word is said which indicates that any special precautions were taken to prevent tho lead from being carried over mechanically or, indeed, that Prof. Baly was in the least alive to the need of taking any precautions to prevent priming. Finally, the rapid action of litharge on linseed oil is referred to and the opinion expressed that action takes place in a similar manner between white lead and oil, though more slowly, the implication being that the primary volatile lead compound is produced because `-while grinders and mixers rarely* suffered from lead poisoning, painters frequently did, owing to the fact that the white lead paint was kept eight to nine months, during which time the reaction took place." ' *: In opening the discussion, Mr. Carey, the Chairman, said "that Prof. Baly had made a speciality of spectro scopic work and his contribution that evening had shown them one of the uses to which the speotroscope could be put." * We should prefer to say misuses rather-than uses. The following remarks made by two medical men present at the meeting, showing the impressioh produced, are of interest in more than one particular : " /; . \` "Dr. Coliis* said that doctors always ;argued that the poisoning of painters must be due to dust, while the pointers themselves always insisted that it was due to the ieady smell, as they called it, from white lead paint. Professor Baly had shown that the painter was right after all. He always thought that chemists could help doctors more than had been the case, , up to the present. His own personal opinion was that rather too much was made in these days of microbes. It was true that microbes did a great deal of damage, but he thought that in many cases it was due to the vitality of the human system having been previously lowered by other means before the microbes got to work." "'Dr. Buchanan,t a toxicologist, said that one of the surest indications of lead poisoning was the alteration in . the corpuscles of blood which took place half an hour after inhaling. He mentioned that he had drawn the attention of one of the district medical officers to this fact and he had let his daughter examine the. blood of patients\who came under his notice. After a time his daughter,^ who was quite healthy, showed signs of lead : poisoning by (on examination of her) red blood corpuscles. . The medical officer was at a loss to understand this, until %. it transpired that some painting had been done at her home. It is evident that Prof. Baly paid no attention to existing knowledge of the behaviour of drying oils---to the wellknown fact that the drying process involves more or. less ! oxidation of the oil and that volatile produots are formed; also that he in no way took into account the use of turpen tine or other volatile liquids in thinning paints and that the vapour of these is at once given off rapidly from the painted surface : even Drs. Coliis and, Buchanan, the medical men present, seemed to be unaware oftthis latter circumstance. ;: ^ ` Three questions were before us when we commen||d .our experiments:-- ; *^ 1 The#possible effect of the various constituents of paints taken singly; in other words, whether the symptonis supposed to be characteristic of lead poisoning were in reality due- to lead. ^ 2. The extent to which volatile substances were pro duced at any stage either during the preparation of lead paints or during their use by painters. ' 3. Whether volatile lead compounds were producible or .produced in the manner Prof. Baly had indicated. 1 It is well known to the chemist that the compounds of lead generally and also tho fatty oils used by painters are not volatile in any ordinary sense of the term. The few volatile compounds of lead, such as the? tetraethide (PbEt4), that are known are altogether peculiar substances arid there is no probability that such are formed from white lead and oil. But turpentine is well known to be a very volatile sub stance and a powerful irritant of the skin; those who have worked with it much are well aware that it produces head- ' ache and that it also affeots the stomach; different persons, however, are sensitive to its action in very different degrees and painters, as a rule, seem to become accustomed to'it early in their career. Russian turpentine ! is far more active than either French or American turpentine--prob ably owing to the presence of easily volatile products of destructive distillation.' V. . We were led at the outset of the inquiry to make the . suggestion that some at least of the symptoms ascribed to lead poisoning were to be attributed to the turpentine in the paint--especially the effect on blood corpuscles commonly regarded as symptomatic of lead poisoning. It is somewnat remarkable that, apparently, this point has escaped the notice of the medical experts. Dr. K. R. Goadby,one of the authorities on lead poisoning, has made < special experiments to test the validity of our contention which have led him to conclusions in entire agreement with * our suggestion. ,. ; 4 > Dr. Kenneth Goadby* has found that animals subjected to the vapours given offfrom white lead paste;atan elevated temperature, viz., 50 C., were quite unaffected after-over 300 hours' exposure, whilst those exposed to; the vapours produced at ordinary room temperature from a surface painted with any paint containing 'turpentine suffered from the outset. Whilst he was unable to distinguish between the physiological effects produced by paints con taining white lead, basic sulphate `.of lead;' zinc oxide or lithopone, it was obvious that the animals suffered through the agency of a common cause; further experiments showed that the ill-effects observed were due to turpentine vapours and could be reproduced^in other animals by subjecting them to turpentine vapour alone. , In determining whether and to what extent volatile products are formed from linseed or other oils and the ordinary materials used in making paints, we have sub stituted for the very complicated and expensive apparatus used by Prof. Baly, - a very simple and inexpensive test which it is open to every one to use. . This hasthe advantage of being a physiological test comparable with that afforded m by the human subject, comparable even with the blood * corpuscle, a test, moreover, the result of which cannot .well be misinterpreted--the leaf of the common shrub the Aucuba Japonica or spotted Japanese, laurel. When the leaf is exposed in an atmosphere of any volatile sub stance, it blackens more or less rapidly, as-the vapour which enters through the stomatal openings of the under surface rapidly induces the interaction of. a glucoside (aucubin) present in the leaf and a corresponding enzyme, the immediate product, of change being a substance which undergoes alteration in a manner not yet understood into an almost black substance. .. . * We believe the test is likely to prove of special value in examining oils to be used in maxing paints. All that * A Medical Inspector of the Home Office and a member of both the Departmental Committees referred to. t Professor of Toxicology, University of Liverpool. Lead poisoning and lead absorption, Legge and Goadby, p. 108, Arnold, London, 1912. 322 ARMSTRONG & KLEIN--PAINTS UNDER CONDITIONS OF, PRACTICE. [April 15, 1913. is necessary is to shut up the leaf along with, though are being given off from the substance or mixture to which, hot in contact with, the material to be tested, in. a large it is exposed. The behaviour of the Aucuba leaf and test tube, bottle or jar ; in order to hasten the action, the also of the ordinary laurel leaf when exposed to vapours charged vessel is best placed in an incubator at about blood has been fully discussed by one of us in conjunction with. temperature (35--37 C.). E. F. Armstrong.* ^ N othing happens when the Aucuba leaf is exposed during 24 hours in presence of either dry white lead or.of any of the Cu r v e II. soM materials used in paint making or of anyv of the oils OH used in, making paint; but the leaf blackens rapidly in the presence of turpentine, the effect being visible often after a few minutes and the blackening complete "usually ll within an hour. The leaf varies in sensitiveness, being most sensitive during the growing period. We are con p fident that all the liquids which can be used in, thinning paint would act similarly. Recently we examined several samples of turpentine substitute thinners now on the market and found all to be extremely active. .. ` The fact that turpentine and similar liquids produce the effect so rapidly is of special significance in connexion with the effects sometimes observed in newly .painted apartments. We believe that the vast majority;of com-; plaints that'are made against paints as: having caused . inconvenience or serious effoots are siinply and.solely due . to this capse alone.; It also foliow;s that the one necessary ! precaution to take is not to risk exposure to the vapour,; as the turpentine evaporates rapidly from a painted surface . it is not difficult to avoid being subjected to its influence. Those painters who are specially sensitive should not be allowed to undertake work (flatting) in which much turpen tine js used. To test the behaviour of paints in drying, a series of paints were made up so that each contained the same quantity of turpentine, i These were then applied to glass; and the weight determined at intervals. :. That an imme Loss in weight of paint films du^ to volatilization of thinners. After one hour paints began to dry so that volatiliza tion loss is balanced by drying. The above are four well-known; white lead substitutes. ; diate decrease in weight takes place. owing to, the rapid evaporation of turpentine is obvious ; and the induced; drying effect is clearly shown in the following curyes ,We may here state that all the materials used in our experiments were of good commercial quality as determined by analyses before: use. The. white lead used was of Cu r v e I. English manufacture---both stack and other process pro ducts ; the oxysulphate used was in part of French and in. part of English manufacture and consisted entirely of basic* sulphate of lead unadulterated with1 barium sulphate in the manner now practised in England. ; We have exposed leaves, at blood heat, in presence of a. great variety of mixtures.of solid materials with linseed oil- In all cases some effect has been visible sooner or later, whilst leaves exposed simply over water have undergone no* visible change during the same period. In the case of mixtures containing either white lead or sublimed oxy sulphate of English or French manufacture, blackening, has sometimes been complete after 3 or 4 days; but leaves exposed over mixtures made from either lithopone; or natural barytes or zinc oxide free from lead became* ... . Hours. , , Showing loss in weight of films of paint of ordinary thickness-- paint applied on glass. The drying . effect is seen. Paint contained 20% vol. thinners. more or less spotted in the same time; even lime and baryta have been found to hasten the production of the vapours. Eventually the leaves exposed over oil alone* have shown signs of blackening, proving that the oil is slowly undergoing oxidation ; leaves exposed over boiled It appears that practically the whole of the turpentine is oil blacken much more readily than those exposed over raw removed after a period of one hour and1 that there is little oil and when boiled is substituted for the unboiled oil in any difference in the behaviour of different paints, whatever the of the mixtures the blackening takes place more rapidly.f base ; obviously the effect of the turpentine i3 the same, ; whatever base be used.; It is to be noted that most of the substances introduced as substitutes for white lead require a > larger proportion of thinners. We have examined eight of the most advertised substitutes on themarket. These are; * The function of hormones in stimulating enzymic change in relation to narcosis and the phenomena of degenerative and regenerative change in living structures. Hoy. Soc. Proc., 1910, ,82 538. The function of hormones in regulating metabolism. ,Annals of Botany, 1911, 25 607. . sold either in paint or paste form and vary in volatile thinners from 5--22 per cent. : All these thinners are M'toxic tlkleaves. ` J; ^!V ' 2. Wheh an Aucubaleaf is exposed over a mixture of - white lead 'and linseed oil, it sooner or later shows signs r of being affected, black spots appearing here and there; after 2 or 3 days black patches are usually visible or it may be nearly black all over. When boiled linseed oil is used, this effect is produced more rapidly. Of course, the leaf is not so immediate a test of the presence of vapour as the spectroscopic test used by Prof. Baly; it is, however,; sufficiently rapid and not only has the advantage of being both simple and practical but is of special value, as it is a cumulative test which affords ocular demonstration of the rate at which and the extent to which volatile products t Nature of the volatile products produced from linseed, oil. It has long been known that considerable amounts of volatile products are formed in the process of drying linseed or any other drying oil.. Genthe (Zeits. f. ang. Chem., 1906,19, 208) states that the loss amounts to 15 percent, in the case of linseed oil drying at ordinary temperatures. . Heid (Joum. Soc. Chem. Ind., 1898,17,75) records that in the manufacture of linoleum (where large quantities of linseed oil are oxidised) a gain of only 10 per cent, is observed and ascribes the difference between this gain and the theoretical . gain to loss of volatile products. We have examined solidified oil obtained from the volatile products given off on boiling oil together with litharge, the samples being collected from areas where mechanical spraying was impossible; we were unable to find lead in these. Oil boiling is carried on at elevated temperatures and therefore the conditions are such as would be favourable to the formation of volatile organic lead compounds if such were possible. It is to be noted that Baly has also examined such products and has failed to find lead present. Vol.XXXII.,No.7.] ARMSTRONG & KLEIN--PAINTS UNDER CONDITIONS OF PRACTICE. 323: The behaviour of zinc oxide is variable ; sometimes the, leaves blacken rapidly over mixtures of this substance with linseed oil. The differences observed Jmay' ' be ascribed to the presence of lead or perhaps of manganese in varying amounts. It is welj 'known,1that,' excepting the New Jersey *brand, zinc oxide made from' the ' ore, generally contains from l. to 5 per cent, of lead, (as oxy-` sulphate); that made from spelter is usually free from load. It may be noted that certain standard English? specifications specify that zinc white shall not be blackened5 by sulphuretted hydrogen. ': Mixtures of linseed oilwith the various commercial driers all affect the leaves more or less' rapidly: we there-. fore think that the "Aucuba" test is one that may prove1 to be of value in testing the efficiency ofJdriers.: Nor is linseed oil peculiar in this respect : cornflower oil, crude and refined soya bean oil, menhaden oil and even olive oil give off vapours moderately rapidly, when mixed with either white lead or driers or both, on exposure to air; castor and China-wood oils are more slowly affected. There is no doubt that any oil that will dry. and can be used in paint will yield volatile produots during the process , of drying. # 3. Taking into account what isknown of the compounds of lead, it was inconceivable that the iVapodra given ofi- during the drying of lead paints should contain lead.^ From the experience gained from a! large number of. experiments we have made to test whether; lead as volati-? lised as Prof. Baly has asserted it is, we are able to state, positively that lead cannot be found in the. distillate from the distillation either of white lead or of basic sulphate of lead . when effective' ?precautions are taken to: prevent,;the contents of the distillation flask from being carried; over , mechanically into the distillate. It is astonishing,; however,, how easily priming takes place* when at mixture of .oil and ; white lead is heated and how difficult it> is to prevent/ particles of solid from being carried over when amixture of oil with any solid substance--not white lead alone--r is subjected to distillation in a current of steam. Oxy- sulphate (Purex), in our experience, is just as .".volatile*? as white lead. A: '-'A : Aw"r'r ; We have tried in many ways to prevent this priming effect and have found tho most effective preventative to be the use'of a length of half-inch block tin tubing, bent at an acute angle about one foot above the 'distillihg flask, as connecter and condenser, in the marinei* vadvocated j by Dr. Bernard Dyer for the determination of nitrogen by the Kjeldahl method. : ; : : ^; When a mixture of white lead with oil is heated, the' basic carbonate is decomposed and both steam and carbon 5 dioxide are given off: solid particles are easily earned forward in the spray that is formed by the .bursting of tho bubbles as tho gas escapes.' When the.distillation is effected under reduced,pressure, this effect is even exaggerated.; When basic sulphatp of. lead is heated, no gas is; produced and but little wat<& is. given off, so that there is far.less priming. , , .; O . It is necessary here to point out that no such spraying: effect or mechanical separation of particles as is observed in distillations can occur during the drying of paint under the conditions of ordinary practice! and therefore these experiments have been carried out under conditions' much more rigorous than obtain in practice. * - ; A proof of the inefficiency of glass traps in preventing priming is afforded by experiments made with the apparatus shown in Fig. I. A mixture of oil and the lead salt to be distilled in a current of steam having been put into a flask' about 800 c.c. in capacity, steam was passed into the mixture and afterwards through flasks 1 and 2 into the upright tower and thence through a condenser. '.' Dt*mLAT19N KXKKKIMKjm ' Fio. 1. Experiments were, made using (1) white, ,lead and (2) litharge, linseed oil and lead acetate being added in each I experiment.,/ No lead was found in . the. final distillate but the: contents . of' the. first receiving flask contained^ lead, whilst, the second receiving flask and. the tower were free from lead. Af v.,A '7 'A". i The presence of lead in the first receiver flask could be due to one or both of two causes--(1) to a volatile lead' compound soluble in water and volatile: in steam but not volatile at the temperature of No; 1 flask; land (2), to? the spraying over of the lead compound. >> 324 ARMSTRONG & KLEIN--PAINTS UNDER CONDITIONS OE PRACTICE. [April 15, 1913. In order to decide. between these alternatives, the experiment with litharge was repeated with the following alterations:-- (1) Flask No. 1 was heated by a boiling water bath so as to drive off any volatile lead compound in solution, it being obvious from the previous experiment; that if a volatile compound were "formed it was volatile at this temperature. (2) Flask No. 2 and the tower were exposed to the air. The distillation was continued during half an hour. On examining the distillates, lead was found in the first flask a but not a trace was detected either in the : second flask or in the tower or in the distillate--showing that, lead, had been carried from the distillation flask mechanic ally into, Flask No. 1 and that, a3though the liquid in this, was kept boiling, the lead cbmpound travelled no further: proof was thus obtained that the lead compound was spirayedj oyer from..thqifi^ PaintingExperiments. None of the experiments so far described nor, indeed, any other of the experiments that have been reported, can be said to be oxactly comparable with the practice of painting; the following experiments were made, therefore, to ascertain whether, under ordinary painting conditions, using an ordinary white lead paint, a volatile lead com pound could be isolated. It must be pointed out that these experiments are quite comparable. with the con ditions undor which the painter works and are of value in consequence. - t, } The apparatus used is shown in Fig. 2. ^ Apparatus used in paint drying experiment. "A**.is axi air-tight box,TO ft. long by^9 in. broad by 2 in. deep, arranged so that the air which ,was aspirated through it should travel over-the'surface of,the box by means of channels, the air thus travelling the length of the box four times, as shown. The box was fitted with a glass top, in order that the paint should dry under normal conditions as regards light. This feature has been omitted in; all. other reported experiments,' although the important influence of light in the drying of paint' is weU known. ' The: joints between`the top of the channels and thef glass ; were made by' laying thic k ' walled rubber tubing on the; top side of the partitions and tightly screwing down the: glass cover, so as to render it>air-tight, thereby compelling the air to travel through the 40 ft. of channel Thai box was painted with*an ordinary/ linseed oil (and turpentine paintand at once closed;; aspiration was then commenced,; the air passing through - the : various \ devices shown, am order to absorb, if possible, any volatile compound which might be formed. The outlet tube was fitted into the box- through a cork, so arranged that the tube was above the I painted surface. Where possible, all joints were of fused ~ glass; otherwise they consisted of paraffined cork. .... Area of painted surface, 20*80 sq. ft.=1*94 sq. metres.; 1 Weight of paint used for each coat, 130 grammes, approxi-p mately 67 grammes per square metre. Time of aspiration: x 1st coat ............................... A-J____ X ^............. .. hours. 48 lO 78 Rate of aspiration, approximately 300 c.c. per minute. Volume\of air aspirated through, at least 1400 litres. Three successive coats of paint were applied before the apparatus was disconnected. and the contents of . the scrubbers examined; therefore the apparatus had received the paint fumes from 390 grammes of paim covering, as a single-coat, an area of 62*5 square feet. Flasks l and2. Emptyodour of paint. ;^ Bulb 3. Contained 6 c.c. of colourless liquid, smelling of turpentine. When boiled with nitric acid, this became, yellow; on adding ammonia, there was no change; on adding acetic acid, no change; colourless when cold;1 sulphuretted hydrogen produced very slight straw dis colouration. Trap 4. 3 c.c. colourless liquid, smelling of turps. Tested as above, very slight straw discolouration; quantity,; if any, too small, to afford a positive result. Washer 6. Colourless liquid--free from lead. Wash bottle 6. . Yellow liquid; crystals on bottom; soluble in water. Sweet. ester-like smell. Free frbm lead. M. Wash bottle 7. Brownish-yellow liquid. Evaporated to dryness and ignited. Left a large quantity of carbon aceous residue. Extracted with. nitric acid--free from lead. Wash bottle 8. Very pale yellow--free from lead. Conclusion : Volatile lead compounds are not produced , in appreciable quantity when a freshly-painted surface is dried under normal conditions. . The experiment was repeated, but without obtaining any indication of: lead. ' Offset of age on.white lead ground in oil. ,, . Baly has suggested that the formation of volatile lead compounds in white lead and oil takes plaoe during the period of nine months. - This suggestion was based on indirect evidence and was rendered necessary by the fact * that workers7 engaged in the grinding of white lead do not suffer from lead poisoning. Lf, however, the volatile >. products were' formed at once-the occupation would. bo most deadly; as the temperature of grinding * is often higher than that at which Baly has stated volatile lead products are produced. ~> In order to investigate this suggestion experimentally we examined a sample of white lead pasto ground in September,. 1907, which meant a period of 61 months between time of > grinding and examination ; the results obtained were exactly the same as those obtained on using new white lead and linseed oil, showing that it is; impossible to detect any volatile lead compound in white lead paste which has been stored durirg STmonths, so that on experimental grounds the suggestion is' unsound;;-;'- ` n >' f: ; '*!' 1 Further, we have compared the rates of blackenings of leaves'exposed over white- lead paste 1 day, 9 months > and 65 months old and can find ho difference. > * ProfessorBah/ssecondcommunicalion. `i5;; A second communication ?on the toxicity* pf white lead.. paints was brought before the, Liverpool Section of this j. Society on March 13,1912, andwaspublished in the, Journal.. issued on June 15, 1912, 31, 515... r No word of reference.,' is to be found; in this to; the previous communication-- not the slightest apologyis, offeredtowhite lead for the - sluV previously casiupon-its cliaracter but it is subjected,. to a further damaging accusation : again, we think without justification.. . ..." ... - The opening sentences of this second pommunioation are somewhat more guapied than those, of the earlier paper-- moreover an interesting, indication is given of the true inwardness of the object Professor Baly had in view in making his experiments, as he states :" The matter was brought particularly under my notice during a discussion of the relative merits of the basic carbonate and basic \ sulphate of lead as pigments. Even without any previous experience I at once detected a most decided difference between the smell of the two substances when ground in linseed oil. It occurred to me that this matter could easily be put to a strict scientific test and in the present paper are contained the results of some experiments I have made in this direction. It may safely be said that any statements as to smell and even as to cases of poisoning are somewhat unsatisfactory unless there is forthcoming some proof of the exhalation pf poisonous vapour by the paint in question. It was to investigate whether or no any volatile and poisonous emanations truly occur that the present work was undertaken.** It is a little difficult to understand how the relative merits of carbonate and sulphate as pigments could be determined by the study of vapours given off from mixtures of the substance with oil: and the logic of the statement-- " I at once detected a most decided difference between the smell of the two substances when ground in linseed oil "-- is not easily perceived: what smell has to do with the merits of a substance as a pigment is not clear. Vol. XXXLI., mo. 7. ] ARMSTRONG & KLEIN--PAINTS UNDER CONDITIONS OF PRACTICE. 325 The spectroscopic observations described are obviously white lead was the only one, that gave at ordinary tem those described in the first communication. But at the peratures a measurable amount of'the aldehyde in my end of the account that is given of them, we read :--" It experiments. For this reason the conclusion must be may be of some interest to record the fact that the smell of drawn that danger attends the use of white lead paints!' the glass tubes after they had been heated in the above " The same must be said of red lead, for it seems that experiments was singularly nauseating, and in the case of. the poisonous volatile compound is;even more readily the tubes containing the white lead thevapours produced given off by this substance."* 5> ! : n : certain specific symptoms such as lassitude and "severe It is to be noticed that the nauseating vapours were only localised neadache followed by diarrhoea." obtained by heating the mixture of wnite lead and oil to ' Now it is well known that the smell of an expiring tallow candle is " singularly nauseating," yet we put up with it occasionally and are unhurt. Professor Baly must have gone very much out of his way to make himself ill and one would like to know exactly how he did it., The value of his evidence depends entirely on this---on his sensitiveness to impression and on proof being given that when his;health was disturbed the said vapours were the actual and sole , factors of the disturbance : their average effect rather than their Baly effect should have been determined--he may 60--65 and that apparentlysimilarvapours were obtained when Purex and zinc white were used, though only at higher tomperatures: Such results are clearly in no way comparable' with those obtained in practice when paint dries' at' atmospheric^temperatures--no one thinks of describing the smell then obvious as singularly nauseat ing. ..... t : `5 Objection may be taken, on similar grounds,1 to the Comparative experiments in which the relative amounts of silver reduced in equal times by the vapours given off well have: been subject to mental impressions during the from various niixi/ures were determined. ` . inquiry. V '"/'/ //` //"* The term " poisonous volatile compound " after all is We are interested in having our observation (that no a purely relative expression.! Chloroform is, a: most, volatile compound containing lead is given off on; heating poisonous volatile compound--yet people; are daily,'of set white lead with oil) confirmed by Professor Baly in the purpose^ subjected' to 'its yhpours and, as *a rule,1 are `but positive way in which it is confirmed in this second com temporarily affected;by *itlj Ammonia!' has extraordinary munication. As `the 1 following 'statement * shows, he is toxio ' powers and yet it is used; by' uromon all ` the world uncompromising in his admission but he might have had over as smelling salts and in recovering them from'fainting the candour to confess that he had repeated his experi ments because of our failure to confirm 'his results. ` "Comparative tests were made with'white lead and basic sulphate and ' in the earlier experiments distinct evidence seemed to be obtained that there was produced a small quantity of a volatile lead compound in the case of the white lead. More recent experiments did not con firm these results and therefore it was concluded that the* fits. Every known volatile substance is , more or * less toxic. Cheese is regarded'as a valuable food all-over the world, yet at times, in some people, it produces consider able stomach derangement. Clearly the poisonous vapour bogy has been' manufactured by Professor Baly as1 a means of escape from a difficulty in which he had'placed himself by discovering volatile lead where there was no lead and he has used it as a. stone to cast at white lead * M lead in the earlierexperiments must have been mechanically As a matter of fact, he. has adduced no more evidence carried over in the form of carbonate.-In order to. obtain in his second communication that white lead under more definite evidence as to the question of volatile lead tonditions of practice gives rise to an amount of vapour compounds, about 4 lb. of the stiff paste of white lead capable of producing effects'such as; would'justify'the and linseed oil was heated vacuo by an oil bath and the use of the term poisonous* than he has that lead itself is products condensed in a vessel cooled ky liquid air. On volatilised.1 ' / allowing the temperature of the receiver to rise, a con siderable quantity of gas was evolved, leaving about 30 c.c. of liquid. This liquid contained a large quantity of water and was tested for lead but no definite-evidence of the .presence of this metal was obtained."{ , The lead bogey being perforce thus cast aside, the nauseous vapour bogey is nbw: dragged^upon the scene; V It; was found that (the gaseous product possessed, an indescribably nauseous ' odour- andAwas undoubtedly poisonous, similar results being produced as those, already- ' described. . This experiment was repeated with basio lead .sulphate but little or. no distillate was obtained." . ' ; f > : Experiments are then: described to - establish the selfr 'evident proposition that when a hydrated1 substance;. is heated vapour of water is given off, and. that this does . In condemning white lead, moreover/^ has condemned .paints altogether... . As Mr. Morris saidin .tho discussion|:-- "^regards.,the" use of dryers, ;^as necessai^ Tor' the paint to dry quickly.,,* Howl,could they 'get ^ the commercial aspeot of the* case, by/using less dryers or; tto^e;at faU.T ^ . If a paint is.to be of;any..practical /use, .it must,tdry;: the nauseous substances of.Professor, Baly will arise: but every one .connected with the , industry--every / painter throughout the country--knows full.we^ that 'the rate at which. the change, takes place is so slow,,the quantity of va'pour given off so flight, that it is, quite,easy, in practice,, to ayoid. ill effects./ It is -oiniy necessary (to^entilate .^ little and to give the paint time'to..dry* if not happen when no water is present, as in; the .case, foI Paints cannotbe made^without oil,and, cannot well be basic lead sulphate. =. . o A. ; i:til applied unless thinned' by/;a; volatile liquid;and some Finally we read : " I cannot claim that the above ex- drying agent must be present in them. Whateveryolatile ?eriments represent the last word upon the, subject but. do feel that as far as they have gone they establish the fact that a poisonous volatile substance is given off liquid be used to thin a paint, it will be capable of pro ducing effects: such as - turpentine produces--in . Baly language, it will be poisonous.- Buti it .is perfectly, well paints made with white lead or red lead. * It seems to me to. be a necessary conclusion that we must recognise the. existence of qf source of poisoning in connexion with painting, that is to be differentiated from lead poisoning proper. \The symptoms described in the earlier portion of known that it is possible by. very simple precautions to grevent any serious effects arising--those. painters, who, . ke Professor Baly, .are specially sensitive to the irifluenco of vapours must not be allowed to flat large, surfaces in/ closed apartments. , this papervwere experienced by me both with the vapours And we must set on the other side/the. hygienic value- / of painting with an oil paint containing, a .drying,; agent. / seem impossible to, attribute them to . lead poisoning.' and a penetrating volatile substance- such.as.turpentine^ These symptoms, my experiments shew' are doubtless to V which Dr. Goadby, wo .believe, \has, drawn/speoial due to the evolution of unsaturated aldehydes>and these attention; no more effective, means--probably`>tno- 8uch are given off by any paint, containing oxidising agents, effective < means--of. destroying ,. micro-organisms ^can white lead or red lead. . The cases of poisoning which have possibly be devised. . If a room be ;wpll washed,down*,;then! (beennoted amongst people inhabiting roomsfreshly painted rewhitewashed and repainted^ especially if `it' be - shut/ 1 with white lead would seem therefore to be due to these tight while the paint is still fresh and left for the vapours : unsaturated aldehydes and not to be true lead poisoning. that are given off--both those of turpentine and1those of: * " It is perfectly possible to minimise the amount of this the Baly bogey--to. act!' antisepticallythe chance of; poison by utilising either basic lead 'sulphate- or zinc,* organisms surviving will jbeverysmafl.None of. the! white and by using as little drier as .possible: I say this conventional, recognised. fmethods; of; disinfectingpan . be! with the more confidence, because, of the white paints,^ so effective. **. AlAf,,:*; - m "326 ARMSTRONG & KLEIN--PAINTS UNDER CONDITIONS OP PRACTICE. I April 15, uui M. Ju l e s -Lo x t is Br e t o n 's Re p o r t . " Rapport fait au nom de la commission do l'hygieno publique ohargEe d'oxaminer le projct do ioi, adopte par ilo Senat, sur 1'emploi dos composes du plomb dans les travaux de la peinturo on batiments." Paris, Imprimerie do la Chambre dcs DeputEs, Mottoroz et Martinet, 7, rue ^Saint-Bonoit, 1907. This report is to bo regarded as of special importance, owing to the action taken by the French Government in legislating prospectively against the use of white lead even .for outside painting purposes. Probably everything that can be said against white load is to be found in its pages. Wo are concerned only with the chemical evidence adduced )by M. Breton himself, by M. Trillat and by MM. Heim and Hubert. Before referring to these, we may mention that it* is on ^record that tho great Stas, when questioned, in 1855, whether the symptoms sometimes, shown by delicate persons, after living in a room recently painted with white lead, could be due to lead poisoning, is said to have ireplied that experience showed that a recently painted (room could be inhabited with impunity. In giving evidence before the Chamber of Deputies, in 1903, Prof. Armand Gautier expressed the opinion that persons inhabiting rooms painted with white lead do not run any risk, as load paint does not emit either emanations or dust. M. Breton (Report, p. 334), in objecting to the removal of paint by burning off, which ho speaks of as provoking 4` la production d'Emanations plombiquos,*.* refers to an opinion expressed by M. Gautier to the effect that painters 4xre subject to poisoning from this cause " parco qu'ils no peuvent pas so soustraire aux poussieres plombeusos ainsi -produitos." It is noteworthy that he does not suggost "that lead is. ever volatilised during tho operation. M. Breton's experiments,--M. Breton gives details f(Report, p. 335) of experiments made by himself, in 1903, which he considers prove that a volatile compound of lead is produced during the drying of lead paint. He appears "to have arranged a series of freshly painted metallic boxes concentrically under a bell jar, through which he then -aspirated air, this air being afterwards bubbled through 10 per cent, solution of sulphuric acid. At the end of c, day lead was detected in the acid. M. Breton explicitly states, however, that the quantity of lead present was extrlmement rduite et que les rEactifs ordinaires du plomb ne peuvaient la rEveler." Ho based his assertion that lead was present on the use of Trillat's agent--which is not specifically a test for lead. M. Trillat, at his request, repeated the experiment but did not confirm the result. To this M. Breton objects that M. Trillat had only painted tho interior of tho bell jar " a.u lieu d'omployor notro dispositif do boitoa on chicano qni nous donnait uno trEs grando surfaco d'Emanation l " He then proceeds :-- " Cette disposition opEratoiro differente oxplique parfaitoment la drffErence des rEsultats obtenus; car, nous le rEpEtons, nous n'avons pu dans notre experience oonstator I'entrafnoment que de traces infinitEsimales et presquo indosables de plomb et la diminution, d'ailleurs consider able, de la surface demission dovait nEeessairement rendre impossible cetto constatation. " Mais, comme nous avons renouve!6 a plusieurs reprises, en prenant toutes les precautions possibles, et on controlant soigrieusomont tous nos rEactifs, 1'experience ci-dessus dEcrito et quo toujours nous sommes arrives au mftme rEsultat, nous pouvons assurer formellement que, quoique trEs faibles, ces Emanations se produisent rEellement. " Nous avons d'ailleurs varie notre dispositif en faisant barboter Fair dans la peinturo de ceruse contenue dans un ballon de vorre et avons pu constater do cette maniere Tentrainement du plomb en utilisant simplement les rEactifs ordinaires, acide sulfhydrique on monosulfure de sodium." With reference to this last experiment, we have no hesitation in asserting that the lead detected by M. Breton was carried forward mechanically; we have failed in obtaining evidence of the presence of lead, when the precaution was taken of preventing any spray that is formed as tho bubbles burst at the surface of the paint from being carried forward by interposing a scrubbing flask between that containing the paint and the receiving flask. And, as we have already stated, we have been unable to detect lead in air aspirated during hours through a box exposing a freshly painted surface which we imagfe was far in excess of that exposed in M. Breton's expelment with boiles en chicane. Heim and Hebert's experiments (Report, p. 339).--In 1907 MM. Heim and HEbert carried out a scries of experiments with the object of detecting and measuring tho amount of lead in the atmosphere of workshops where white lead was used. Ultimately they devised a method based on the use of Trillat's agent. In examining the air of workshops, the air was drawn through a plug of cotton wool (ouaie). They were struck by the fact that they very often found traces of lead in their absorption apparatus, even after such filtration of the air ; they therefore assumed that some portion of the lead in tho atmosphore was in a state of vapour and capable of passing through tho filtering plug without being caught by it. No proof was sought for that a larger or more tightly packed plug, if not a series of plugs, would bo effective. * They made various experiments, in which air scrubbed by passing through two vessels, one containing sulphuric acid, the other potash, was passed through a long tube 1-2 cms. in diameter containing the material to be tested. When the material was a powder, the two ends of this tube were pluggod with cotton wool. The air from tho tube, after passing through a U tube " bourrE do coton bien serrE, assurant sa filtration parfaito," was conducted through a Gautier absorber containing about 10 c.c. of dilute sul phuric acid. The rate of passage was from 3--4 litres per hour and the experiment was continued until 100 litres had been passed through the tube. In tho experiments with litharge and white lead, the tube contained a mixture of 150 grammes of emery with 11 grammes of the former and 15 grammes of the latter. The amount of lead carried forward in 100 litres of air was estimated to be as follows :-- Milligrammes, 0*15 {White lead at 15--20 ............................ 0*20 0-12 Litharge at 15--20.................................. J0-0.1 0*01 at 100* .................................. J0-01 10*01 We venture to think that if load was carried forward, of which the experiments afford no actual but merely inferential proof, it was carried forward in the form of dust. On making experiments in the manner described by Heim and HEbert, using sulphuretted hydrogen as the test for load, wo have found that dust may bo carried forward in the air stream unless particular caro bo taken in packing the cotton wool plug tightly, t Trillat's testfor lead.--This test is based on tho fact that when the compound formed by condensing formaldehyde and dimethylaniline is subjected to oxidation, it is con verted into the carbinol HO.CH(CaH4*NMe2)2, which gives coloured salts with weak acids, though those with strong mineral acids are colourless. The use of the diphenylmethane base as a test for lead depends on the fact that it is oxidised and converted into the carbinol by lead * The difficulty of constructing efficient filters to remove lead dust from air is recognised in the report of the Home Office Committee on the use of lead in potteries. tit is of interest that Baiy was unable to find any absorption took place when light from a cadmium arc was passed through tubes containing dry white lead and that this observation is cited by him to show that even spectroscopic methods allow of no volatilization of white lead being detected at ordinary temper atures. Finally, in the Report of the Medical Inspector of Factories, contained in the Annual Report of the Chief Inspector of Factories for the year 1911, Cd. 929 page 210, we find the following "Experiments were carried out in the laboratory of a lead smelt ing works in London to determine the temperature at which lead fumes arise from the surface of open baths of molten lead. They showed chat unless pure lead is heated to about 500 C. and at the same time stirred, no appreciable fume comes off. . . . When a bath of molten lead is not stirred at all it can be heated to over 740* C. without finding oxides in the air.'* This statement is not in agreement with the figures of Heim and Hubert who claim to have shown that lead volatilises at ordinary room temperatures. Voi. XXXII., No. 7.1 ARMSTRONG & KLEIN--PAINTS UNDER CONDITIONS OF PRACTICE. 32? peroxide ; but it is acted upon equally well in the same way by manganese peroxide and not a few other oxidising agents. To use the test, the solution of sulphuric acid supposed to contain lead is evaporated to dryness in a small dish and a drop or two of a solution of sodium hypochlorite is added to convert the lead sulphate into the peroxide ; according to Trillat, the excess of the hypochlorite is removed either by washing or by calcining. The agent is then added to the rcsiduo in the dish. The presence of lead is indicated by the appearance of a blue colour, either at once or on warming. Trillat recommends the use of acetic acid in preparing the agent but there are objections to this and Carney has proposed to substitute citric for acetic acid. We can support his recommendation.* We are in no way satisfied with the test as one suitable for the detection of minute amounts of lead, especially on account of the difficulty of removing any excess of hypo chlorite by washing; obviously calcining is out of the question, as it is likely to decompose lead poroxido. In our hands the results have been somewhat irregular and we are not inclined to rate it as much more if at all more sensitive than the sulphuretted hydrogen test. The results obtained by Heim and Hubert do not carry conviction. In tho first place, no blank experiments are quotod showing that they had tested all the materials they used, though it is to bo supposed that they took this precaution. They state that after passing 100 litres of air over lead filings at 18 C., they found as much as 0*5 mgrm. of lead to be volatilised ; when, however, the lead was heated to its melting point (335), the amount volati lised was only 0 4 mgrm. and fused type metal (m.p. 200) and plumber's solder (m.p. 224) gave only 0*2 mgrm. If lead volatilises under such conditions at all, it does not seem probable that there would be no increase in the amount volatilised on raising the temperature from 18 to over 300; the difference is scarcely accounted for by Heim and Hubert's contention that the surface exposed is greatly reduced by the fusion of the metal. Wo are inclined to think that the lead was carried forward as dust, as on repeating the experiment, using a tightly packed plug of cotton wool, we have not been able to detect lead by the sulphuretted hydrogen test. Triliat'a experiments (Report, p. 344).--M. Trillat's ex periments consisted in placing four Petri dishes at different heights under each of three sterilised bell jars of 10 litres capacity; these dishes contained Raulin's fluid inocu lated with a culture of Penicillium glaucum: Nothing else was put under the one bell jar but the second had in it a dish containing about 50 grammes of powdered white lead and the third one containing a paste of white lead and, linseed oil. In the case of the blank bell jar, growth set in at the beginning of the third day ; in the second, containing dry white lead, a slight retardation was noticeable; in the third, the retardation of the growth of tho organism was obvious. In a second set of experiments, Aspergillus niger, a more sensitive organism, was substituted for Penicillium. The experiment began on Jan. 15th ; on Jan. 19th a few colonies wero seen in the blank bell jar and in that containing dry white lead, though they were slightly less numerous and less compact in the latter. No growth had set in under the third bell jar at the end of 15 days, when the cultures under the two other jars were fully developed. An experiment carried out with oil alone showed that this had no influence in retarding tho growth of the organism. It was also found that a pasto made by mixing white lead with water had no appreciable effect. Precisely similar results wero obtained by Dr. Marie (Report, p. 340), using Ebert's bacillus. This observer also tried the effect of a mixture of zinc white and oil and found that the growth of the organism was " plus net et complex " than that in presence of tho mixture of oil and white lead, " rappelant celui de la premiere culture cn presence d'huile pure mais moins florissante bien que nettement plus vivace qu'avec le plomb." It is obvious, however, that such results in no way justify the conclusion that Dr. Marie draws when he says : " dies montrent Taction d'arrfit des vapeurs melalliques ,Comp* R* L Carney, J. Amer. Ohem. Soe., 34 p. 32, and Chem. News, May :n, 1912 par rapport aux ph6nomencs organiques vitaux 616mentaires." The very slight initial effect observed by Trillat, in a single case, on exposing organisms in presence of white lead alone, is of no significance in view of the irregularities often manifest in such experiments. M. Breton quotes an experiment (Report, p. 348) made 1 with a guinea pig, which was killed by exposure to air aspirated through a vessel containing a mixture of 300 grammes of white lead, 100 grammes linseed oil and 25 grammes of turpentine. After calling attention (Report, p. 349) to the opinion ex pressed by MM. Riban and Bouchardat that turpentine , exercises toxic effects, M. Breton then states that he had exposed a guinea pig in a precisely similar manner to the vapours given off from a mixture containing zinc white in . place of white lead and that no ill effects wero produced. Dr. Goadby, who has carried out an exhaustive series of experiments with various bacteria, similar to but far more extensive than those made by MM.. Trillat and Marie, has failed entirely in detecting any effect in the case of organisms exposed in presence of white lead alono. He has also shown that whether,the paint used be made from white lead, zinc white or lithopono, the vapours given off from painted surfaces ahvays affect guinea pigs more or less prejudicially. Tho fact that a guinea pig was unaffected by zinc white paint in the single experiment made by Breton can only be attributed to some accidental cause --guinea pigs, like painters, doubtless are not all equally sensitive to turpentine vapours. Such then is the caso against white lead. The French evidence that a minute amount of vapour containing load is given off under the conditions of practice is not only unsubstantial but wo have failed to corroborate it; and it is easy to see how the mistake arose. Prof. Baly's evidence, wo venture to say, is rebutted by our observa tions ; and he has himself admitted that he'was in error in asserting that volatile compounds of lead are produced on heating whito lead with linseed oil. Prof. Baly, however, has introduced a now terror into painting in asserting that poisonous volatile organic substances are given off during drying--unsaturated aldehydes and so forth. But practice shows and all knowledge of the subject confirms this experience that this danger does not exist. Under the ordinary conditions of practice, such vapours are given off at such rate and in such quantity that their effect is negligible: only ultra sensitive persons and those who are bent on being affected are likely to be disconcerted by them. The production of such vapours is in no way confined to lead paints--as Prof. Baly recognises, they are the necessary outcoino of tho drying process. At most, it can be said, that they are produced most rapidly from white lead paint because this dries most rapidly--a.circum stance which gives to white lead paint its special value. It is clear that the real sinner in paint is turpentine; . and any efficient substitute for turpentine that can bo used will produce effects similar to those which this hydrocarbon produces, because tho effects are thoso that aro produced by volatilo vapours generally. Obviously, tho only logical way to got over tho vapour difficulty will bo to abolish paints altogether. After all, the real difficulty is the old ,ono and on this point wo need merely quote the closing -sentences of tho General Editor's Preface to. tho roccntjy published authoritative work on Lead Poisoning and Lead Absorption by Dr. Lcggc. H.M. Medical Inspector of Factories, and Dr. Goadby :-- " Tho authors bring forward convincing evidence, experimental and statistical, in favour of tho causation of lead poisoning by tho inhalation of dust. This.makes prevention a comparatively simple matter and tho methods of prevention aro offcctivo and will contribute greatly to 4 the health of the workers and the prevention of phthisis, . which is so prevalent among lead-workers. . Exhaust fans and hoods or vacuum cloaners, for carrying away tho dust formed in tho various processes--these aro the simple means by which tho dust can be removed and tho workers* health assured." , In recent years, six European countries havo made the use of lead paints the subject of exhaustive inquiry and the o j si 328 ARMSTRONG & KLEIN--PAINTS UNDER CONDITIONS OF PRACTICE. [April 15,1613. French alone liavo decided to prohibit their use. The law is due to take effect on January 1, 1915 but it is signifi cant that it applies only to house painting and that its application is open to great latitude, being subject only to the ruling of a single Minister. There is doubt whether the law will bo enforced. Thus tho British Consul at Lille reported in August, 1912, as follows:-- " White load.--There was no sensible modification in tho white load industry. Tho law prohibiting its use for outdoor painting purposes, which comos into operation three years hence, does not appear to bo in favour with tho public. For the use thereof has not decreased, whereas substitutes such as lithopone, etc., are being gradually left aside as consumers begin to discover their inferiority to whito lead and it is doubtful whether the law will ever como into force." From the history of the French enquiries, it appears that since 1786 French ministers have decreed on nino occasions that the use of white lead was to be discontinued, so far without any permanent result. It can scarcely be doubted that, as a rule, hygienic interests have been subordinated to polemics and it is important to note that the quantity of whito lead used in France at the present time is greater than ever. Regulations affecting the painting industry have been introduced in Austria, Belgium, Germany and Switzerland*; Holland has not yet taken action though inquiries have been hold, in that country. ^ In our own country, it is difficult to judge of the danger attending the use of white lead, as the Home Office returns are particularly weak regarding the incidence of disease and the death-rate among painters, as notification is not legally compulsory. Judging from tho returns issued by the Registrar General, it would seem that the painter is in no way subject to any abnormal risk. It is beyond question that, in the past, symptoms have often been ut down to lead poisoning which were in no way caused y lead and that tho medical profession have much to learn in this respect. Now that the true sources of danger are understood, there should be no difficulty in reducing tho risk to a minimum. The -properties of paints which are ofpractical consequence. --In conclusion, wo venture to point out that those are broad issues to bo discussed in connexion with tho paint industry besides the question of possible toxicity, for is not the" time at hand when those who are connected with its various branches will be called on to consider whether they will regulate or whether they will merely allow themselves to bo regulated ? Wo are advancing into an ago when the "liberty of tho subject " may become an unknown quantity; when sentiment and the opinion of an uninstructed majority will more and more prevail over sense and intelligence: unless those latter elements are organised not merely in their own defence but in tho interest of tho unintelligent majority. We need in this country to get rid of the prevailing belief in tho ability of the so-called man of business to understand everybody's business besides his own and of his own absolute belief in himself ,* also wo must bo alive to the worse danger that is ahead of us, the calculating politician whose sole appeal will bo to Demos. In some wav or other, the belief in true expert knowledge, in the collective wisdom of men thoughtful and experienced, of knowing men, must be made to live among us and our proceedings must bo ordored more upon The following conclusions arrived at by a majority of the Swiss Commission are of interest:-- 1. Le danger d*intoxication par les composes de plomb, employes dans les travaux du Mtiment, a Gendve, est minime. 2. II est possible, par des mesures de police, applicables aux chantiers, de diminuer encore, sinon d'elhniner compl6tement le nombre des cas de saturnisine professionnel parmi les ouvriers peintres en b&fciments. 3. Le remplacement de la ceruse par l'oxyde de zinc mettrait l'industrie du b&timent a Genfive dans un 6tat d'inlteriorifcS injustice. 4. L'oxyde de zinc n'a pas les quality industrielles requises pour pouvolr remplacer avantageusement la edruse. 5. L'oxyde de zinc n'est pas si inoffensif qu'on veut bien le dire. En cherchant bien, on trouverait peut-0tre aussi quelques peccadilles a lui reprocher et pouvant motiver 1'horreur que MM. les entrepreneurs en g6n6ral et ceux de Gen6ve en particular 6prouvent a son endroifc. La Ceruse, etc. Geneve: W. KUndig et Fils. RueduVieuxCollege, 4. 1907. their advice than is now the case. Some sense of our individual ignorance must come upon us all. Through ignorance, democracy lias ruined many civilisations in the past; our one great chance of survival and improve ment is to organise and apply'Scicnce to neutralise igndfc- ance; if wo cannot do that, our science will not avail us iik tho ond. 1 It should be possible for a Society such as this to help in promoting the promulgation of a code of industrial ethics. Tho public will oxpoct the introduction into the code of articles protecting them more than is tho case a present against tho use of unfit materials, against tho bold and unblushing advertisement of rubbish. The special question wo would raise is whether it be not desirable to determine by collective action what arc truly fit materials for painters' use--whether it bo not to tho interest of the trade to promote systematic inquiry which will make it possible to offer sound advice, if not to lay down rules for the general guidance. The Americans aro already alive to this necessity and have conducted exten sive inquiries with paints. There are very many problems awaiting solution. The use of lead compounds in while paints.--Given tho undoubted fact that lead can be so used that it need be no source of danger to the user, the question still remains--is it essential ? Tho verdict of experience is undoubtedly strong if not absolute in its favour, as is shown for example by the following quotation from tho Report of the inquiry carried out by our Home Office twenty years ago " In the past a large amount of thought, labour, time and money have been expended by many experts in the search for a substitute for carbonate of lead. Several compounds havo beon mentioned to the Committee as being equal to white lead and capable of taking its place, if only the prejudice of middle-men and dealers could be removed so as to secure for them a fair field in tho paint market. One of these compounds and the one on which most stress has been laid is oxide of zinc. This has been used with success for internal decoration but for rough surfaces and for exposure to heat, cold and rain it does not possess the qualities for which white lead is conspicuous, namely, covering power and durability. Moreover, the price of oxide of zinc is greater than of carbonate of lead. With regard to all these so-called substitutes the Committee have invariably found that on closer inquiry of persons competent to judge and un prejudiced on either side, tho substance in question was in some particulars inferior; and they have come to the conclusion that there is at present no substitute that can tako the placo of carbonate of load.** In the interval, many improvements havo been effected and the various substitutes are greatly superior in quality to those formerly offered. Nevertheless, at the present time, it cannot bo maintained that any singlo pig ment is suitable for all purposes and it is scarcely probable that such a pigment will ever bo found. It is more probable that tho solution of tho problem will always lie in tho proper selection of tho pigment or pigments suitable for tho particular purpose in view /*1, i2t 3ha4s5been clearly shown that tho weakness of one pigftient can bo met by the addition of another or other pigments and that, in many cases, a mixture is advantageous. The white pigments now in use in considerable quantity are only four--basic lead carbonate, basic lead sulphate, zinc oxide and the mixture of zinc sulphide and barium sulphato known as lithopone. Basic lead sulphate.--This substance was introduced as a pigment by Bartlett in 1866--it has been used to a considerable extent in the United States of America during recent years. Lead sulphate has beon proved to bo a failure in practice. Tho oxy-sulphate apparently owes its value to the fact that, like white lead, it is a basic material. Being acted upon by acids, it is practically just as poisonous as white lead. Apparently it is less active than white load towards drying oils but it is just as readily blackened by sulphuretted hydrogen. Zinc white.--The use of zinc oxide as a pigment was first suggested by Courtois in 1780. It was introduced into commerco about 1846. Many improvements havo been made in the methods of manufacturing it and in its quality, Vol. XXXII., Ko.7j ARMSTRONG & KLEIN--PAINTS UNDER CONDITIONS 0P PRACTICE. 320 tho result being, that it now occupies a definito position as a pigment, but the statements that have been circulated of its superiority to white lead and in relative disparage ment of this latter are not merely exaggerated but often false. There are two types of zinc oxide on the market--tho one known as " indirect " prepared by burning spelter; the other termed " direct " prepared from the ore. The latter usually but not always contains lead (as basic sulphate), owing to the presence of galena in the ore; when lead is present, this variety often* has a bad colour owing to impurities other than lead contained in the ore. There is "no generally accepted opinion as to the superiority of the one or the other type but it is claimed by the makers of the direct product that the presence of a small amount of lead increases the stability of the paint film. In view of tho question wo have raised as to the possibility of " lead " promoting the oxidation of tho oil, this contention is well worth con sideration. In Europe, the production of zinc oxide is practically limited to Belgium, owing to the monopoly this country has of zinc. Lithopone.--This pigment is prepared by precipitating zinc sulphate with barium sulphido and is therefore a mixture of barium sulphate and zinc sulphido: but as it is subjected to furnace treatment to improvo its physical condition it often contains somo zinc oxide. One remarkable peculiarity of this pigment, which Horiously affocta its use, is tho m&nnor in which it changes in colour and darkens on exposure to light. Ready-mixed paints.--Tho direct sale of ready-mixed paints is increasing in this country though the bulk of the white pigment sold is in tho form of paste. In tho United States of America ready mixed paints are purchased on a large scale by tho painter. Tho paints sold are often composite, being mixtures of two or more of the follow ing :--Zinc sulphide, white lead, zinc oxide, leaded zinc, lithopono, gypsum, talc, silica, alumina, barium carbonate, barytes (natural and artificial), calcium carbonate, magnesite, china clay, French chalk, asbestos. It has been found necessary in certain States of America to introduce legislation with regard to tho labelling of such paints, requiring tho chomieal composition of tho paint to bo stated on every package so as to guard against fraud. Value and suitability of paints.--Tho valuo of a paint is necessarily tho outcome of a combination of more or loss delicately balanced factors. Tho nature of tho vohiclo is of great importance and the fact that pigments other than tho lead pigments require a larger proportion of oil is of fundamental significance in view of the well-known porosity of linseed oil films and of their tendency to shrink. The ease with which white lead may be applied is explained by tho changes which take place botween tho oil and white lead. During tho time of its storago as paste, chemical action takes place to a small extent and some lead is dissolved in the oil; this materially assists in the subsequent drying operations. In tho case of zinc oxido or alliod pigments, little or no change takes place, whilo the iqjxturo is in the form of pasto. Whon applied as a paint, in both cases the drying takes place by oxidation, although physically tho two products differ considerably. In tho case of lead paint, a film is obtained which has considerable elasticity, so that tho contraction and expansion produced by variation of climatic conditions do not result in fracture of tho film; whereas in tho case of zinc paint, tho oxidation product has a hard, brittlo, inelastic surface, which docs not change in unison with the surface on which the paint is applied. The ultimate product is hard and finally blisters and cracks or becomes translucent and peels off. Tho final result is a surface which is not so suitable for repainting as is that obtained when lead paint is used. We believe that for many purposes a mixture of white lead with zinc white is far superior to either singly. The physical condition of a pigment must also be con sidered in relation to its powers of lasting. White lead is not a powder of uniform size, being invariably graded to some extent, as is apparent when tho product is olutriatod. This gives the film mechanical stability. The condition is imitated to somo oxtont, in what aro termed " reinforced paints," which consist of the previously named white lead substitutes ground together with asbestos or other inert materials of largor size, in order to imitato as closely as possiblo tho condition naturally obtaining in white load. White lead substitutes aro invariably in an extremely fine state of division and regular in size; therefore, tho reinforced effect cannbt be obtained with these pigments alone. A practical rolult of this is the defect observed when tho mouldings on dobrs are painted with the substitutes for white lead. It is quite useless to attempt to determine tho painting valuo of any pigment on what might bo termod straight painting: the intricacies afforded by mouldings and similar structures aro the most conclusive tost. ' It is commonly objected that lead paints (both basic . carbonato and sulphate) aro blackened by sulphuretted hydrogen. But as a matter of fact, tho blackening of paint out of doors is rarely due to this cause, being usually effected by smoke and dirt; convincing proof of this fact has been afforded of late years, since the process of cleansing by stoam has been introduced. Tho groat cause of tho decay of paints exposed out of doors appears to bo the sulphurous and sulphuric acid in tho atmosphere, especially in towns. It is stated that no loss than 150,000 tons of sulphur aro projected annually into tho air of London, forming eventually somo 600,000 tons of sulphuric acid. Lead paints aro scarcely affoctod by sulphurous and sulphuric acids, which if they act at all sorvo only to convert tho oxido in tho basic material into insoluble sulphate; but zinc paints (zinc whito and lithopono) aro most seriously affected by the conversion of the zinc oxido or sulphide into zinc sulphate--a substance easily solublo in water; the change is fatal to tho painted surface. On this account, such paints are only suitable for use wherever rain has not access and should only bo used in dry situations. It is on points such as these we venture to think that tho public and oven painters need authoritative information: in tho end, it must bo to the interest of the trade as well as of tho public that proper materials should bo used and that tho work done should bo sound. Conclusions. In conclusion we submit that it is clearly shown:-- 1. That tho vapours produced during tho drying of white-lead pastes and paints do not contain lead. 2. That the vapours given off as paints dry consist of turpentine, for tho most part, together with oxidation products of tho oil and that these latter aro common to paints generally containing oil so treated that it will dry. 3. That the oxidation products formed from tho oil during drying aro harmless under tho conditions of practice, as has been shown by experiments with animals. 4. That tho toxic effects sometimes experienced from drying paints aro to bof ascribed to turpentino and that duo allowanco must bo made for this in dealing with tho hygienic phase of tho problom. Our inquiry also shows that in many cases offocts have been regarded as duo to u load poisoning " which aro attributable to other causes, especially to turpentine. 5. Tho whole available ovidenco indicates that tho dangers attending tho use of lead compounds are only the well-known mechanical dangers. 6. Thero is no foundation for the importation of a new olomont of dangor into tho consideration of tho question of paints. Lead paints are to bo objected to only on tho ground that they may enter into tho system through careless handling or in tne form of dust such as is producod by rubbing down old paint. Dis c u s s io n . Mr. Pear c e, M.P., said that there appeared to bo somo foar lest there might bo some legislative interference with white lead. Parliament acted carefully and with reluc tance in those matters, and looked to tho Departmental Committee for definito advico. If the question camo seriouslv before the House of Commons, the paper would be of great advantage to tho Membors. He was sorry that Professor Baly was not present; ho would like to have heard his views. They had no moans of judging c2 330 ARMSTRONG & KLEIN--PAINTS UNDER CONDITIONS OF PRACTICE. [April 15,1013. Professor Baly's case ; he was an authority on the subject. It was still inoro important from tho Houso of Commons' point of view that the Fronch Government had decided "to prohibit tho use of lead paint in 1915. If those two facts (although after tho Paper ho had heard they carried very littlo weight indeed, to his mind) had reached tho Houso uncontradicted and unchallenged, they might have led to somo legislative result, although oven then ho hardly thought so. At any rate Prof. Armstrong had rendered service by showing that white lead had been attacked unjustly. He was glad to know that a member of the Departmental Committee was present, and after what had been said and after tho Report had been received and tho Paper published ho would bo surprised if tho Houso of Commons were ever called upon to tako any action against white lead. Mr. Vic k er s said that for the last four or five years ho had boon periodically going to lectures on lead and zinc. One came away from ono lecture feeling that zinc was tho right and only thing, and from the next lecture that lead was the right and onlv thing. Manufacturers wanted to obtain durability. The question of inside painting presented little difficulty, but for outside work they always seemed to be faced with something. White lead always became chalky, with zinc there was hardness, and with lithophone there was no durability. A series of fences had been put up in America with' the idea of applying to them paints made of all sorts of materials, and then having them watched. Two or three years ago tho same suggestion was made to tho Paint and Varnish Society, but nothing had been done. Ho would bo very pleased to erect, and would give 150 guineas towards tho cost of putting up, fences wherever tho Paint and Varnish Society, the National Association of Master Painters, tho Society of Chemical Industry, tho Royal Institute of British Architects, the Socioty of Arts, or a combinod Committee of them all, might desire, and let thorn supervise tho fences and arrange what paints woro to be put on them. As manufacturers, they wanted to know which was tho most durable typo of paint for outdoor work, and perhaps some small experiments might be made at the same time on iron work. If tho Committee would accept tho offer to con tinue for a test for three years or longer, ho would be very pleased. Mr. No e l He a t o n said that all technical men looked upon Baly's paper as of no real practical importance. Unfortunately, however, it was likely to have a very damaging effect amongst people who had no technical knowledge of the subject. On that account they must bo grateful to Prof. Armstrong for so clearly putting before them tho many weak points in his arguments. He hoped that those who had been trying to asperso the character of white lead would pay as much attention to Professor Armstrong as they had to Professor Baly. But from his point of view ho did not think that tho section of the paper dealing with tho work of Baly was the most important part. To him tho conclusions at tho end of tho paper woro most valuable, and particularly the suggestions that were brought forward for tho necessity of collective inquiry into tho whole matter. During the past two years there had been far too much talk on this subject.. An enormous amount of evidence had been collected by the Departmental Committco. But very little had been done in tho way of getting at tho bottom of the matter on scientific and practical lines. A practical investi gation had been mado in the United States, to ascertain whether they could do without white lead or what were tho real facts about its use, and their results led inevitably to the conclusion to which Professor Armstrong had arrived, viz., that nothing could be substituted for it. Neverthe less they ought not to tako their results at second hand, and should do something over here, as after all, the two climates were not the same. In common with a good many others he had been agitating for practical experiment on an organised scale for a considerable timo, and he was indebted to Prof. Armstrong for putting forward the same proposition. From his own experience it was not possible to replace white load by any substitute without loss of durability. Mr. Da v id s o n said that Prof. Armstrong had well said that ono must bo very careful what deductions they made from the result of experiments. That it was proved conclusively that lead was not volatile in paints was of great service, and it was to bo hoped that with the experiments suggested, they ought to bo able to deal conclusively with the questions of efficiency and durability of the various paint pigments. Mr. Kimb b h referred to the tests carried out in American by H. A. Gardnor, which indicated that zinc and zinol compounds behaved differently in different oil media. Mr. Ro w el l said that if white lead or manganese dioxide were mixed with linseed oil, a peculiar smell was produced. If that smell or emanation were poisonous, men who were daily boiling oil and varnish with oxidising agents such as manganese dioxide and lead oxide should bo most subject to somo sort of poisoning corresponding to Professor Baly's symptoms: but it was a fact that in varnish houses and oil boiling shops poisoning of that description did not occur, so that it might bo said that emanations from paint, other than the turpentine smell, were not toxio in a marked degree. A member said that lie had had occasion to examine the deposit formed on the iron doors and ceilings in rooms where lead driers were used and on analysing he had found there was 10 per cent, of lead. Mr. Co s t b said that ordinary Russian turpentine was certainly very much more irritant and had very much more marked rubefacient properties than American turpentine. He had tried it by experiments. Dr. Mo l l w o Pe r k in said that if Russian turpentine were properly purified it was not so ; it was a splendid drier. Professor Ar ms t r o n g , in reply, said ho was very glad to hear of the willingness on the part of the trade to take up these matters and investigate them systematically ; the results were likely to be of extreme value to the industry. Chalking was one of the great objections to white lead; on the other hand there was a difficulty with zinc paint, that it gavo a very brittle film, and as had boon pointed out, it was known that by combination of tho two a very superior result was obtained. It ought to be possible by varying tho medium and by working more in tho direction of studying tho effects produced by oils, something could bo found which would get over the ono real objection raised to white lead paint. There was no doubt that tho medium played a very important part with zinc oxide, but tho subject had been very inadequately studied. As regards the volatilisation of lead in tho boiling house, he was certain if tho speaker who mado those remarks would look into the matter he would find there had been a mechanical transfer. It was very difficult to believe that anything like 10 per cent, of lead could ever be present through volatilisation. He thought ho might claim to have discovered Russian turpcnfcino somotimo in tho seventies ; ho used then to examine all tho turpontino that came into the Port of London to seo whether it was contaminated with petroleum. In tho paper ho had pointed out that Russian turpentine produced effects which the American and French did not; especially were its physiological effects much more marked. What Dr. Perkin meant by properly purifying he did not know. By fractionation it was possible to get a product very similar to the French and American. Its peculiar effect was due to the presence of small quantities of products of heat and of destructive distillation. He believed that during manufacture it was customary to heat to a point very much beyond that which was customary in the case of the extraction of French and American oils. Of late years the smell which distinguished Russian turpentine had been got rid of by somo method of treatment. Mr. Kl e in wrote that in England no organised attempt had yet been made to determine the relative efficiency of the respective paint bases on scientific linos and until that was done little progress could be made in solving "tho paint question." If it could be shown that tho use of white lead constituted an abnormal source of danger, to the user, and that at reasonable prices efficient substitutes were available then the case for prohibition might be considered to be on a sound footing. Recent work clearly showed that lead poisoning was readily amenable to regulations, and he had littlo doubt Vol. XXXII., No. 7.] EGERTON--THE HEAT TEST ON GUNCOTTON, &c. 331 that regulations of a reasonable typo would effect a real improvement amongst house painters. With reference to coach painting, he quoted the remarks of Dr. Collis (H.M. Medical Inspector of Factories) in the Annual Report of tho Chief Inspector of Factories and Workshops, for the year 1910 (Cd. 5693, p. 175), dealing with coach painting, stating that he had visited throe largo railway works : " At the third works lead paint is used generally, but great caro is exercisod to prevent plumbism, no surface covered with lead is sand papered, no burning off of lead paints is done, there is good lavatory accommodation and an excellent dining room and kitchen, whore food brought by the men is oooked, are provided. The general health of tho men is good.** Such a statement left no question as to tho efficiency of hygienic control in rendering coach painting a healthy occupation. At first sight prohibition would appear to be tho simplest and most effective method of dealing with problems of industrial hygione, but its logical application would provo the most effective barrier to progress yet devised, and its intorfereneo with chemical industries in particular would bo intolorablo. Mr.ding held at Burlington House on Monday, March 3rd, 1913. riU)F. W. ft. IS. UODGlvINSON IN TIIK CHAIR. THE HEAT TEST. I.--G UNCOTTON. II.--NITRO GLYCERIN AND CORDITE. IH.--THEORETICAL. BY ALFRED O. EGERTON. Introductory. The purpose of stability test is firstly to measure the extont of decomposition o? an explosive, and secondly to gauge its liability to decompose. The latter is especially important when the test is used for accepting a now explosive, wh lo both aro important when the extent of deterioration of an old explosive is being determined. A stability tost should be easy and quick to carry out and require an inexpensive apparatus. The test should be carried out under conditions similar to chose to which it is normally exposed; it must not be affected by moisture and other volatile products in tho explosive ; lastly, it should be suitable for all explosives. In review ing the many stability tests which have boon devised, it cannot be said that any one of them satisfies all these con ditions. A simple test is renuirod which will satisfy these requirements and combirio tlio good qualities of tho Abel tost, the Will tost, and tho Silver Vessel tost; and which will bo capablo of differentiating between an impure and an unstable explosive, and which can be used either as an acceptance test or as a test of decomposition. The present work started with an application to tho amount of nitrogen oxides liberated during an Abel test, of a method of analysis of small quantities of gases by moans of drops used "as indicators. In tho course of this analysis it was found necessary to investigate many features of the heat test not oxplainablo from previous work. Tho work points to a method of carryiug out tho Abel test which might make it a thoroughly reliable and efficient stability tost. From the rosult of many observations tho heat test has been found open to numerous orrors. There is difficulty in securing absoluto constancy in tfio reagents and in tho papor employed ; substances volatilising affect the reagent on tho papor, and moisture causes dilution. Moreover the time takon for tho test papor to bo affected doos not necessarily imply the rate at which tho explosive will decompose, especially if small quantities of unstable pubstapees are prosont; ifye assumption must be made with all due caution that these very slight decompositions mean that tho explosive is so unstable as to givo rise to dangerous decomposition on storage. Robertson and .Smart (this J., 1910, 130) Hhvo settled many points about the tost, but there still remains much to bo dono, so some of their experiments wcle repeated and new ones devised to settlo the more difficult points. Tho main points to be cleared up were:-- (1) What conditions affect tho rato of decomposition of an explosive, and what substances are evolved from it ? (2) What is the source of the nitrogen oxides ? (3) Whether tho indications of tho tost paper can bo relied on ? (4) What is tho relation connecting tho concentration of N02 with time of colouring of reagent ? Pa r t I. Experiments with paper reagents. To begin with, a largo number of heat tests wore made on samples of guncotton, the heat test tube and its contents wore kept in tho air out of tho bath for an interval of 20 minutes botwoon each tost; tests wore thus ropoatedon the same samplo many timos ovor. Tho experiments aro sot forth in dotail in tho complete papor. The main results arc, (a) that a test repeated a second time on guncotton is always lower than a first tost; (b) that evacuation, which tends to draw out the products of decomposition, may either cause a rise or fall of tho test depending on the condition of tho guncotton and the circumstances of the test; (c) that tho prosonco of moisture has a great deal to do with the time of the tost. A theory has been deduced from the experiments and it is probably a correct view of what occurs within tho tube, sinco it is found to afford explanation for so many apparently discordant results. The reaction may be due to :--(1) The nitrogen oxides produced by a true decomposition of the guncotton during the test; (2) The nitrogen oxides from incompletely removed impurities; 3 Tho nitrogen peroxido dissolved in tho guncotton. A proper stability tost should distinguish betwoen these throe possibilities and measuro the amount of nitric peroxido produced from each cause. Robertson and Smart describe experiments which show that normally prepared guncotton does not contain any appreciable quantity of peroxide in solution. The authors proceed to test tho view that impurities give rise to the nitrogen peroxide produced during the test. They perform a continuous test on guncotton and find a fall in tho test occurs, followed by a rise. Tho rise, according to them, doos not indicato that tho guncotton is getting more stablo by tho elimination of an impurity, but is simply due to the desiccation of tho papor by the dried and heated guncotton, for when a trace of moisture is added tho heat test again falls. Tho work here described shows that this is not the main cause of the rise in tho tost, though it agrees with the contention of Robertson and Smart that tlio heat tost of a normal guncotton is not duo to unremovod impurities. Robertson and Smart's viow, then, of tho heat tost is that tho nitrogon peroxide is produced by tho decomposition of tho oxplosiyo during the tost, that any nitrogen peroxide in tho tubo is readily removable and tliat it is this peroxide which tends to lower tho tost on repetition, and that prolonged tests on dry guncotton aro cluo to the desiccation of tho paper. During this work, it was found, on the contrary that evacuation always lowers tho test at first ; if it was only the nitrogen peroxido left in tlio guncotton which tends to lower tho test, evacuation must always increase it. The idea of tho actions in tho tube gloanod from tho work described in this paper is tho following:--That on heating tho guncotton nitrogon peroxido is evolved, some of the nitrogon peroxide is absorbod by tho moisture in tho guncotton, which latter also tends to vaporise and condonso on the papor and on tho walls of tho tubo, nitricand nitrous acids aro thus formed in the guncotton, on tho walls and on tho papor. It is in tho form of nitric acid that the guncotton absorbs ueasily removable nitrogon peroxido**; not so much an absorption by tho nitrocellulose itself as Robertson and Sprnrt seom to imply in experiment (loc. cit. p. 132) of thojr paper, but an absorption pf nitrogon