Document V3LXd23xLB9wJE7v11319k1z8

THE JOURNAL SERIAL - V- \ Society of Chemical 3nbustry YOL. XIZ. -- 1900, INDEX. LONDON: EYRE AKD SPOTTISWOODE, HIS MAJESTY'S PRINTERS, EAST HARDING STEEET, FLEET STBEET E.O. N41533 March 31. woo.] THE JOURNAL OP THE SOCIETY OF CHEMICAL INDUSTRY. 213 qua naphthalene, a previous deposit of naphthalene might sition of naphthalene, rather supported his own view. A be moved so as to block a pipe. If, as Mr. Ilehner had hot day was just the time when the benzene would uot said, there was a deposit of naphthalene in an old pipe, it condense out, and the conditions then might be those might be moved so as to choke up a local service. If necessary for the formation of the naphthalene in the gas. anyone present could say whether Mr. Leather had had a Other references had been made to the way in which perfectly clean main to experiment on in a new district abrupt bends seemed to facilitate the formation of naph with washed coal gas, that would be a help towards uuder-. thalene. On the hypothesis that the gas and pipes were standing the paper from their poiut of view, and could be mutually electrified by the friction of the gas passing along, claimed by Mr. Allen in support of his theory. it was conceivable that the naphthalene molecules, being Mr. H. Le ic es t er Gr e v il l e said that the tendency of the heaviest oues present in the gas, might be attracted by naphthalene to accumulate in bends and angles of pipes the oppositely charged iron of the pipes, and held fast at was probably due to friction, though moisture probably had the bends, where a sort of back eddy might be produced influence on the formation of deposits. The statement in ia the gas. He had endeavoured to test this by highly the paper, that gas normally left the works free from electrifying the gas as it passed along a tube presenting naphthalene vapour, would require corroboration, con many obstacles to its passage, but could obtain no result, sidering that the presence of naphthalene in quantity was although both high alternating currents and large static so evident at all points of the manufacture. That naphtha charges were employed to electrify the gas. lene--a substance always regarded as essentially a product The Ch a ir ma n remarked that the subject was one of of high temperature--could be absolutely produced in the the highest importance to coal gas makers, and it only gas at the ordinary temperature of the air, would also remained for him as Chairman, in tendering to Mr. Allen require a large amount of confirmation. If naphthalene the thanks of the meeting, to endorse the suggestion which could possibly be permanently retained in the gas instead had been made by Prof. Clowes, that the author should of being deposited, it would be a great boon to gas companies continue his investigations and endeavour to obtain some on the ground of its great value asau iUuminant. experimental proof of the revolutionary view of the genesis Mr. R. W. Al l e n , in reply, said he had treated the of naphthalene iu coal gas which hud been submitted to matter purely from the scientific standpoint. For the them that evening. statements he had made about the deposits in the mains he had the authority of Prof. F. D. Brown, Chairman of Directors of the local company, and also of the Chief Eugineer. The work extended over a year, and that to a very great extent eliminated any variations that other wise might have been supposed to exist in the amounts of naphthalene in the gas as it issued from the mains. Reference had been made to Mr. Leather. In a paper on " Naphthalene Deposits " read by him before the Gas Institute (see Journal of Gas Lightiug, 73, 1754) be bad stated that gas which contained at the most only 14 grains of naphthalene per 100 cb. ft.--an amount insufficient, as be (Mr. Allen) had shown, to saturate the gas at a very much lower temperature than it was likely to be subjected to in the mains--vet deposited naphthalene, la reply to Mr. Watson Smith he might say that he made no effort to prevent the benzene being removed along with the naphthalene, but experimented afterwards with gas from which the naphthalene was carefully removed and the ben zene reintroduced in a quantity insufficient to saturate it at the temperature of the bath. Mr. Hehner had asked why he did not convert the frozen-out naphthalene into picrate of uaphthaiene. It was because the benzene would THE IODINE VALUE OF OILS. nr ARTHUR MARSHALL, F.O.S., A.I.C. Al t h o u g h there is an extensive literature ou the subject of the determination of the iodine value of oils, yet the exact nature of the reactions taking place in the various methods that have beeu proposed is still somewhat obscure. A great advance in the practical carrying out of the determination has beeu made by Wijs (Beriehte, 1898, 31, 750), who has- proposed to employ a solution of iodine monocliloride in acetic acid iu the place of Hubi's solution of iodine and mercury bichloride in alcohol. Wijs's solution possesses the two great advantages that it is rapid in its action, and that it alters very little in titre. Lewkowitsch has shown that it gives the same iodine values as Hubbs solution, if the latter be properly applied (Analyst, 1899, 257). In opposition to Ephraim (Zeit. uugew. Chem. 1895, 254), and his own previous opiniou (Zeit. anal. Chem. 1898, 277), Wijs considers that with Hubbs sohitiou, iodine mouochlorkle is not added on to the unsaturated acid radicles directly, but that the iodine chloride formed reacts with water,, producing hypoiodous acid-- also have beeu converted into solid picrate, whereas by ICl + H-0=IUO - HC1 (1), first converting the mixture into nitrobenzene and nitrouaphtbaleue and oxidising this with chromic acid, the nitronaphtbaleue formed nitrophthalic acid, which separated out oil cooling, whereas the nitrobenzene did not give a and that this is added on to the oleic acid or other unsaturated substance--- Cl7Hx.CO.:H + HIO = HOLCl7H:iaCU2a (2). similar compound. Mr. Hehner had also remarked that he (Mr. Allen) had worked with much too small a volume of gas to ensure accuracy. It was true that the volume of gas was comparatively small, but he had the utmost That this addition product then reacts with the hydrogenchloride formed according to the previous equation (l). HO 1Ci-H;9COH r HOI - t;iU:,rH;aCO..H + H.,0 (3). confidence that his weighings were correct in every instance In support of this view Wijs states that, if hydrogen, to, say, a tenth of a milligramme, aud the total errors were chloride be added to Hiibl's solution, it retards its action. probably uuder l per cent. The weight carried over by Hydrogen chloride, he says, would increase the amount the volume of gas he worked with was 0*0050 gnu. at the of iodine chloride in the solution, but would, to some extent, lowest temperature employed, 8*0 0.--a perfectly appre prevent the formation of hypoiodous acid, as shown in equa- ciable quantity, capable of being weighed accurately, : tioa (l). It is true that it has this effect, for, if iodine and especially when account was taken of the great care he mercuric chloride be dissolved iu alcohol in suitable pro took to prevent the (J-tubes of naphthalene absorbing portions, and if then, hydrochloric acid be added, the brown moisture. The large number of experiments made at each colour of iodine disappears aud ouly the yellow colour of temperature also tended to reduce errors to a minimum. iodine chloride remains. It is, however, practically impossible He also stated that he never had had a doubt but that to predict what effect the hydrogen chloride would have the weight of uaphthaieue required to saturate hydrogen, upon the reaetiou between iodine chloride and oleic acid, &c. coal gas, carbon dioxide, air, &c,, was exactly the same. Wijs then proceeds to show that freshly prepared hypoiodous This is uot the point; the doubt--one held by many men acid is absorbed to the full extent by arachis oil practically of note--was whether all these gases would saturate them instantaneously. He, however, omits to show that hypo selves completely with uaphthaiene with equal rapidity, iodous acid is present in Hiibr.s solution in any quantity. aud what the speed of complete saturation was. Iu reply As it is an extremely unstable substance, there is probably to Mr. Helps' question he regretted to say he could not never more than a very small quantity present. x\s soou as- throw any light on the point, as he was uot a practical it is formed it must be converted into iodic acid. In order man. But it seemed to him that the statemeut made by to prove that hypoiodous acid does not necessarily take any Mr. Helps, that a hot summer's day increased the depo part in the action, it is only requisite to show that th* 5214 THE -TOmR/NTAT, OF THE SOCIETY OF CHEMICAL LNDUSTBY. [March 31, im addition takes place equally well, where there cannot ! there is present a considerable excess of both iodide and possibly be any present I prepared a solution of iodine j iodate. monochloride in dry carbon tetrachloride. The solution \ Wijs has stated that with Hubl's reagent the oil, after was kept over fused catcium chloride to prevent the j absorbing iodine and chlorine, splits oft' a certain amount of presence of any trace of moisture. The iodine values of j hydrogen chloride (Zcit. anal. Chern. 1898, 277), thus :-- some samples of oil were then determined by means of this j solution, and also by means of a solution of iodine chloride C02HCJ7H33ICI - COMC^l + HCi. in glacial acetic acid. ] and the experiments he cites makes this appear very probable. Iodine Value. From what I have said above, it is evident that this does Time. i j Oil. ICI in CH3COOH. ' IClinCCl. not take place in the carbon tetrachloride solution. Hiibl, in his original paper (Uingler's polyt. Journ. IfiSl, 281), mentions that with his reagent he obtained a product Mins. lo 1<* lu 10 1 3u' j j j j i ! Rape M . | 103*0 ; 103*8 102*0 i 103*0 102*0 103*2 102*2 i 10t*2 i 102*8 i 104*8 having the composition CjgHgiCLICl. Further evidence that iodine .and chlorine are added on in these simple atomic proportions is.given by the colour of the carbon tetrachloride solution, which remains unchanged during the addition. If, however, the mixture be allowed to remain sufficiently long for substitution to take place, the purple colour can be seen to develop. 10 Linseei 1<> 1 178 *u 178..*5 178*0 178*9 17S*0 I think that the above experiments make it clear that the so-called " iodine absorption " consists simply in the addition of iodine chloride directly to the double linking of the unsaturated acid, and that no other reaction takes place It is evident from these figures that iodine chloride acts i to any appreciable extent. in exactly the same way in the absence of water as it does That the absorption is complete in the case of the ordi in the presence of it. If anything, it acts more euergeticallj', nary unsaturated fatty acids is proved by the following for Wijs found that the action on linseed oil of a solution ( facts:-- in acetic acid containing 5 per cent, water took about seven . (1) That iodiue absorptions demanded by theory have minutes, whereas, with carbon tetrachloride, it is apparently ; been obtained in the case of oleic, isoleic, brassidic, and completed in one minute. I doubt, however, whether the . isoerucie acid. addition ceases immediately potassium iodine solution is (2) That the same values are obtained with HtibFs added. From the colour of the carbon tetrachloride beneath ; solution, with Wijs's solution, with a solution of iodiue the aqueous layer, it is evident that it contains no free chloride in alcohol (Ephraim, Zeit. angew. (.'hem. 1895, iodine, but a considerable quantity of iodine chloride, which 254), and with iodine chloride in carbon tetrachloride. no doubt acts further upon the oil whilst the titration is (3) That in the case of Wijs's solution the iodine value proceeding. obtainedis unaffected by the excess of tbe reagent employed The colour of the carbon tetrachloride solution gives (Lewkowitscb, Analyst, 1900, 34). considerable information of what is proceeding in it, for, if it contain free iodine, it becomes brilliant purple, whereas ; iodine chloride colours it a pale brownish yellow. When substitution takes place, iodine is at once set free in accord- j ar.ee with the equations-- j Mclihinev in a recent paper having endeavoured to resuscitate the bromine value " (Journ. Anier. Chem. Soe. 1899, 1084), I thought that it was of interest to determine the bromine value of the same sample of linseed oil, with which the above experiments were made. I made a solution 1UI 4- ICi = BC1 + HI; and of bromine in carbon tetrachloride of about N/5 strength (Me- HI 4- ICI = HC1 + 21. Ilhiney recommends N/3 strength) and proceeded in the usual way. Calculating the result as iodine, I obtained the If, therefore, a considerable amount of substitution take j following results :--In 10 mins., 140*2 per cent, of iodine ; place, it will become apparent to the eye. There is, how- : in 20 mins., 141*3 per cent, of iodine. The mean of the ever, a more delicate test for substitution, viz., the acidity 1 results with iodine chloride was 178*3. It is therefore of the solution. This can be very conveniently estimated evident that under these conditions the absorption is far iodometrically.. After the iodine has been titrated with from complete. There was no evidence of substitution. thiosulphate in the usual way, potassium iodate is added to ; Mclihinev also obtained values lower than those given by the solution. When this is done every equivalent of acid HiibFs method. He states that substitution takes place, present liberates an equivalent of iodine-- ; and that the addition is instantaneous. GHCl + KIO;, + SKI = 6KC1 + 3H.O + GI (!.) ! 1 also bromine tried were the effect of iodiue dissolved in carbon bromine. Iodine tetrachloride and and the. The iodine is then titrated with thiosulphate. This was j operations carried out as usual. In ten minutes I obtained carried out with the oils above, but in no case did potassium j an iodine absorption of 167*0, i.e. 11*3 below the true iodate bring back the colour when proper precautions had value. It is evident from these experiments, that iodine been taken to exclude moisture. ; chloride must not be replaced by either bromine or bromine A mere, trace of water in the carbon tetrachloride solution iodide. rapidly produces the change-- Both Wijs and Lewkowitscb have made statements as to 3IC1 + 3H;0 = HIO;i + 3HC1 + 2HI (2.) 1 the effect of time on the iodine chloride-acetic acid solution. Wijs (Berichte, 1898, 752) stated that a solution in v5 per cent, acetic acid lost only 0*3 per cent, of its titre in the The bydriodic acid then 1 eacts with more iodine chloride liberating iodine, as becomes evident to the eye-- j first 96 hours. Lewkowitscb with acid of the same strength found a decrease of 4 per cent, in 80 hours, hut with 99 per 2HI + 2ICI * 2HC1 + 21 (3.) \ cent, acetic acid he found the solution unaltered after two months. The solution at the same time becomes cloudy in con- { I have not found the titre to keep as constant as is stated sequence of the separationof iodic acid, which is insoluble, in , by Lewkowitscb, although it does not vary sufficientlv carbon tetrachloride. If the solution be dried over calcium j rapidly to cause any inconvenience. Even when new the chloride, it becomes clear once more. j titre does not alter so rapidly as to prevent use at once, From the above equations it will be seen that for every j but after months it still continues to decrease slowly. molecule of iodic acid formed there are also six equivalents j In order to investigate this point I further purified n;v of acid, which, it might be supposed, should be sufficient to j acid -by recrystallisiug twice, and pouring off part of the convert the iodic acid into iodine again in accordance with j acid each time. I then placed 25 c.c. in a dry stoppered equation (1). This action is, however, only complete when | bottle with 25 -cCi~of my solution of iodine chloride in March31,19000 THE JOURNAL OF THE SOCIETY OF CHEMICAL INDUSTRY. 21", carbon tetrachloride. After 10 minutes potassium iodide Dr. Le w k o w it s c h said that perhaps Mr. Kay would was added, and the iodine was titrated in the usual wav. like to know that a stili,5tnore convenient way of preparing It required only 90*6 c.c. of thiosulphate, whereas the the solution was to accurately weigh off quantities of iodine and iodine trichloride. iodine chloride used should have required 95 75 c.c. There Mr. Ma r s h a l l added that iodine monochloride itself was an absorption, therefore, equal to 5*38 per cent, of the could be prepared without difficulty in a sufficiently pure original amount in 10 minutes. This experiment was repeated, state, and might even be bought so. He had prepared with allowing the action to proceed for 12 hours. There was it the solution of carbon tetrachloride with which the above then an absorption of 22*9 per cent, of the halogen present. experiments were performed. In a similar experiment, in which a few drops of water were The Ch a ir ma n said that he thought that the Committee added, there was an absorption of 24*1 per cent, in 12 were justified in extending a hearing to papers of this hours. In all these cases the bottles were kept in a dark description, which contained carefully recorded statements cupboard during the action. of actual results obtained in painstaking work. It is well known that chlorine acts upon acetic acid in the presence of iodine quite readily if the liquid be warmed, producing cbloracetic acid. From the above experiments it iftanchocter datum. is evident that the action takes place also iu the cold, though slowly. This substitution must gradually weaken the solution under ordinary circumstances, though it is evident from Lewkowitsch's statement, that this does not always Meeting held on Friday, March 2nd, 1900. take place. In any case the action is too slow to seriously interfere with the value of the method. DB. J. GROSSMANN IN THE CHAIR. The weakening of. the solution must depend to a large extent upon the amount of cbloracetic acid formed in the preparation of the reagent, and this may account for the THE NATURE OF INDIA-RUBBER. differences observed by different observers. BY DR. CARL OTTO WEBER. In conclusion I wish to say that I do not propose to ` substitute carbon tetrachloride solution in the place of that proposed by Wijs for general use, but in some cases it will he found more useful. On the whole, acetic acid is more Th e great experimental difficulties encountered iu the investigation of colloidal bodies are responsible for the slow development of the chemistry of these substances. convenient to work with than carbon tetrachloride. Their physical constants are highly indeterminate; and instead of melting points, boiling points and solubility', Dis c u s s io n . they simply exhibit a gradual merging of one state into another. Thus the characterisation of the colloids and their Dr. Lf .w k o w it s c h said that he did not think that the derivatives, and their isolation and purification from reaction paper added much to their knowledge. The literature on the mixtures is generally a matter of the very greatest difficulty. subject of iodine values was so startling in its proportions that These difficulties are met with in a pronounced degree in he had himself stated in that room that he congratulated the chemical investigation of india-rubber, which forms the any* chemist who did not add to it. It was true he had most important raw material of a large and, though perhaps himself lately committed a few ideas on the subject to print, only in a mechanical sense, highly developed industry. In but his excuse was that WijsJ beautiful method had deed, not even is the empirical formula of india-rubber appeared meanwhile, and this method had, in his opinion, established with certainty; the question as to whether it completely cleared the air. Stability of Wijs5 solution was ; should be regarded as a practically uniform substance, a demonstrated for at least five months, and no one could : hydrocarbon, an oxygenated product, a mixture of isomeric complain if alterations should occur after that time. or polymeric compounds still being open to discussion. It Mr. 1\ Iy ay asked what was the best way of preparing is thus not surprising that we should be entirely in the dark Wijs1 solution. The ordinary method of finding the respecting the question of the cause and nature of the differ strength by titration was inconvenient, and he would like to ence exhibited by the numerous varieties of india-rubber know if there were any physical sign to guide one as to obtained from plants belonging to very different botanical when the combination with chlorine was complete. families. Mr. A. Ma r s h a l l , replying to the last speaker first, said If unworked, crude rubber* be treated with chloroform that it was quite easy to stop the passage of the chlorine at or carbon bisulphide, partial solution gradually takes place ; the correct time without titrating. The solution of iodine and it was very early observed that, by this treatment, in acetic acid was dark brown in colour, whereas the the rubber was separated into two parts, the one being solution of iodine monoeliloride was light yellow. The soluble, the other insoluble, and presenting a peculiar chlorine should therefore be passed in until this change of reticulated appearance under the microscope. Very- colour took place. The final change took place at quite a divergent statements are to be found respecting the. relative sharp point. He could not agree with Dr. Lewkowitsch as to proportions in which these two constituents occur. In one the want of necessity for this investigation. No doubt Wijs' case the amount of the insoluble body is given as varying method for the determination of the iodine value would be from 30 to 70 per cent. (Ladenburg's Handworterbuch, generally adopted by chemists. There would consequeutly Bd. V,, 479). but on the other hand Gladstone and Hibbert l>e a tendency to adopt Wijs5 theory as to the nature of the (Jour. Ohem. Soc. Trans. 1888, 679) found in Para rubber reactions taking place. He thought it was a matter of 4 per cent. only. For this reason I have thought it desirable importance that the exact meaning of the term " iodine to re-examine this point. value M should be known with certainty. Gladstone and Hibbert suggested that the insoluble As to the keeping properties of Wijs' solution, he *' modification " of india-rubber was produced during the thought it was remarkable that the solution prepared by drying of the juice, because they observed that by heating l)r. Lewkowitsch should retain its strength so much better the soluble part it was more or less changed, and less than those prepared by Wijs or himself. He suggested susceptible of subsequent solution. They found this heat that perhaps Dr. Lewkowitsch's solution had been prepared effect to increase as the temperature was raised and also on a hot day, and that consequently a great part of the with the length of time during which the heat continued. acetic acid had been converted into ehloracetie acid during For this reason I employed for my experiments, not washed the preparation of the solution. and dried rubber, but the thin films into which the inner Dr. Le w k o w it s c h remarked that, on the contrary, it parts of a crude loaf of rubber can be split. These films was a very cold day. contain a considerable proportion of water which was got Mr. Ma r s h a l l , continuing,said that possibly chlorination rid of by often repeated treatment with acetone. During of the acetic acid would not occur if the solution were quite this operation the films, which were w*hite at first, assumed free from...water. In consequence of the hygroscopic character of glacial acetic acid, it could not he kept an * All the following statements refer to Para rubber, unless som hydrous unless access of damp air were prevented. - other variety is expressly stated.