Document nkGZoOY8XgDD3RrG6YkNeN0pm

$| ORIGINAL COPY | ' ` P'-'p ^ STATUS REPORT ^' . Authors: INORGANIC POLYMERS: IMPACT MODIFICATION OF ASBESTOSPHOSPHORIC ACID .COMPOSITION BOARD G. D. Jacobs J. A. Faucher Dote: July 6, 1964 Project Ko.: 191G31 FlU No.: '2777. SUMMARY: The work on this project has been concerned mainly with the inorganic mineral chrysotile, a form of asbestos currently being mined by the Nuclear Division at Coalinga, California. Attempts have been made to impact modify an asbestos-phosphoric acid- water composition board (code designation P-38) originally produced by the Nuclear Division. Previous experience here had shown that impact strength correlated well with low temperature ,,transitions,, in the mechanical loss spectrum of organic polymers, and it was felt that the incorporation of one of these organic polymers in the asbestos board might lead to the desired product. To date, however, the addition of a rather large number of organic polymers in various percentages has not improved the strength of the board to any great extent. It is now felt that some material will be necessary that is capable of chemically reacting with the hydroxyls of either the asbestos or the phosphoric acid. Very little is known about the chemical reaction between the asbestos and phosphoric acid. In fact, the physical characteristics of the asbestos fibers are still open to controversy and a great deal of basic research is currently being carried out on this material. A brief sampling of some of this work is given in this report. Present work on this project to modify the P-38 composition is-concerned with the possibility of adding fibrous organic polymers to the mixture. This phase of the'work is a direct result of the work carried out by the U.S. Army on the addition of nylon fibers to cement in which they were able to improve the impact strength of cement by a factor of twenty-seven. Preliminary work with asbestos shows an increase in impact strength, although not nearly as large as in the case of cement. Projected work includes the use of poly carbonate and polyhydrcxyether fibers as additives. INTRODUCTION: Asbestos is the generic name given to a number of - mineral silicates varying quite widely in chemical composition. These silicates are divided into two mineral classes; serpentine and amphibole. A list of the more common types is pre sented in Table I along with their chemical formulae. Research ond Development Deportment Chemicals Division Union Carbide Corporation I I i 2 By far the most important single type of asbestos is chrysotile, accounting for nearly 90% of world production. Certain ones of the amphibole group, noteably crocidolite (blue asbestos), amosite. and anthophylite, do find use in specialized plastics appli cations^*^) . The major portion of this report is concerned with a chrysotile variety being mined by the Nuclear Division at Coalinga, California. Table II is a comparison of the physical properties of a general chrysotile asbestos with the high-purity grade UCC Coalinga fiber.* The unique properties of the Coalinga fiber are attributed to its greater specific surface area and adsorption properties as shown in the table. Chemically, chrysotile has been described as a hydrated basic silicate of magnesia. Normally, some magnesium carbonate and hydroxide are associated with the fibers in the form of dolomite and brucite. Table III gives the chemical and mineralogical compositions of a general chrysotile fiber as compared to the Coalinga fiber. Until a few years ago the formula for chrysotile was written as 3MgO 2SiOa 2H..O, implying a di-hydrate. As a result of recent research efforts^*4 ', it is now felt that a better representation of the "molecule'' is given by the formula MggSigO- (OH) >, where the previous water molecules are now present in the form of hydroxyl groups. The individual fibers are pictured as layers of silicon-oxygen tetrahedra (Si.O.Q-4) condensed onto magnesium hydroxide layers. Each of the silicdn=oxygen/magnesium hydroxide layers is superimposed upon layers of similar composition, but no chemical bonding is thought to occur between the layers. A schematic drawing of a portion of the curved wall layer of a chrysotile fiber is shown in Figure 1- (5). Another view is shown as Figure 2. A controversy has also arisen over the physical structure of the individual fibrils. Pictures taken with the electron micro scope seem to indicate that the fibers are in the form of "hollow. tubes"(6). Recent evidence from X-ray diffraction measurements'?' and density determinations *' has thrown doubt on this theory and the present proposed picture is that the central portion of the tubes is filled with amorphous or partially oriented material. As pointed out by Dr. E. J. ff. Whittaker this filling of the tubes with amorphous material would lead to an appearance of emptiness under the electron microscope due to the contrasting effect between the walls of the fiber and the filling material. A recent study using ultrasonics'' also provides evidence that the material filling the voids between fibers is amorphous. Chemical reactions of chrysotile are also now being in vestigated. X-ray methods serve as the principal tool for studying these hydrothermal reactions, which are found to be predominantly topotactic. Being topotactic implies that the normal reaction involves the migration of cations, including silicon, while having little effect upon the oxygen framework'9*. * Three product grades of asbestos are currently available from the Nuclear Division: Standard Grade. Hierh Purity Grade, and Colloid -3 - The preceding paragraphs should serve as a general intro duction to the nature of the mineral asbestos and give some idea of the research being done on this material. Further specific information may be found in the references cited as well as in the four books listed in the bibliography. Due primarily to the large supply available and to the unique characteristics of Coalinga fiber, "the Nuclear Division initiated work on finding saleable products which utilized their asbestos. One of the materials produced was an asbestos-phosphoric acid-water composition board (code designation This material suffered, however, from a lack of impabt strength as well as poor weatherability. The Nuclear Division also developed an asbestos-phenolic composition (code designation F-100) which showed both improved strength and weatherability'-12) . Efforts at Tuxedo have since been directed primarily at improving and marketing the F-100 composition in the form of pipe. Since previous experience was available on impact strength of organic polymers, as evidenced by studies on the low temperature loss peaks in the mechanical loss spectrum, it was decided to look again at the P-38 compositon with the thought of adding an impact modifying filler to the composition. Experimental The Coalinga asbestos used throughout these investigations was the high-purity grade - i.e. the material has been defilibrated and the magnetite removed. Early experiments were concerned with finding the best ratio of asbestos-phosphoric acid-water for easy mixing and extrusion. After several trials using various ratios,it was found that the following proportions were most satisfactory: 70 parts asbestos 35 parts water 30 parts 85% phosphoric acid The dry, powdery asbestos is loaded into a Cincinnati MixMuller* and the phosphoric acid-water solution added through a funnel provided with the mix-muller. The time taken for addition of the phosphoric acid-water solution is rather critical in that water is apparently lost from the mixture for both short times of addition (causes heating of the mix) and also by evaporation if excessive'time is involved. We have found, in agreement with the Nuclear Division, that a fifteen-twenty minute period for addition of ingredients is best. Additional ingredients were normally added after the phosphoric acid-water solution and in certain cases (liquid fillers) a proportionately smaller amount of water was necessary in order to acquire an extrudable product. The final product, ready for extrusion, is of a putty-like consistency. Cincinnati Muller Co., Cincinnati, Ohio; Previous experiments had shown that a Hobart blender did not give adequate mixing on this c"n^ fO 1 a^ \ 4- The first experiments (before acquisition of an extruder) with the P-38 composition consisted of pressing the material into disc-shapes at 10,000 psi. Tests on these discs showed, however, that in order to obtain material with any strength whatever it would be necessary to extrude the composition. Previous work by the Nuclear Division (see reference 11) had shown that a ram-type .extruder was best suited for the P-38 composition. The ram extruder now in use was designed by Mr. Gene LeRoy of the Research and Development Department Special Projects Division, Machine Design. An Ener Pac* hydraulic, power-operated, pump and cylinder are incorporated in the design. The exit die is of a rectangular shape with dimensions 3" x 1/4". The P-38 composition is loaded into the extruder and then the ram moved forward to seal-off the chamber. The chamber is evacuated for several minutes before the extrusion is started. Starting with two pounds of asbestos, an extruded "board" approximately four feet in length is obtained (3" in width, V4" in thickness). Normal extrusion pressure is 2000-3000 psi. The "board" is cut into six and twelve inch lengths. The six inch lengths are rolled out (transverse to direction of extrusion) into pieces l/o" in thickness, using several passes through a large roll mill. All the pieces are then subjected to a room temperature cure followed by a cure at either 110C or 150C depending on the type of filler used. It is necessary during the cure-cycle to sand wich the asbestos strips between expanded-metal sheets in order to prevent warping. After curing, the boards are removed from between the metal sheets and cut into small pieces for testing. The 1/g" thick samples are given flexural strength and flexural modulus tests (ASTM D790-61) while the I/4" specimans are subjected to the Izod impact test (ASTM D256-56). The Gardner impact test proved unsatisfactory for testing these specimans. All samples are tested in both the parallel and transverse directions (designated P and T respectively in the tables). DISCUSSION: The first experiments with the P-38 blend were concerned with finding the best ratio of ingredients and optimum ~ mixing time, as pointed out in the ejqperimental section of this report. A short study was also conducted to determine the function of room temperature curing time on the strength of the final board. Previous studies by the Nuclear Division had shown that both a room temperature cure and a final curing at an elevated temperature were necessary for a high-strength board. The results of our room temperature cure time study are given in Table IV and shown plotted in Figure 3. From these results, it was concluded that a room temperature cure of at least sixteen hours was required. The three points shown plotted for a sixteen hour cure were taken as an indication of the deviation which can be expected from one batch to the next. Several runs were also made using different curing temperatures as well as different amounts of time at this elevated temperature but * Blackhawk Industrial Products Co., Butler, Wisconsin. - 5- ail seemed to indicate that 16+ hours at room temperature followed by 4 hours at 150C gave the best results. The next step in the project was to investigate the effect which various additives would have on the strength of the P-38 composi tion. The rest of the discussion section will be sub-divided into sections dealing with the various additives thus far investigated. DQDA 3269 (72/28 ethylene/vinyl acetate copolymer) An informal report by Dr. G. H. Potter (Project No. 399M20; dated 16 December, 1963) reported the possibility of cross-linking or reaction of some type between asbestos and ester-containing polymers, after mixing on a hot roll-mill. Unfortunately this method coats the asbestos fibers so that they are no longer available for attack by the phosphoric acid-water solution used in the P-38 composition. Even prolonged extraction with toluene did not remove enough of the excess polymer so that the fibers could undergo further chemical reaction. An attempt was also made by first reacting approximately one-half of the phosphoric acid-water solution with the asbestos and then placing the material on the mill with DQDA. However, the DQDA would not react in this case and was present in the extruded board as an inert filler. Adding pulverized DQDA to the mixture in the mix-muller was also unsuccessful. One further step was taken with this type polymer. Granulated AYAT was added to the dry asbestos in the mix-muller followed by the phosphoric acid-water solution. The AYAT appeared to be present as an inert filler also. Hercules "Aquapel" (364 and 380) The next material tried was "Aquapel", an alkylketene dimer manufactured- by Hercules Powder Company. The dimer was added both in the form of dry flakes and as an emulsion in water. As can be seen from Table V, no significant increase in the strength of the P-38 composition was obtained. Cationic Wet-Strength Resin A cationic wet-strength resin consisting of poly Q-asparagine polyamine partially crosslinked with epichlorohydpin (14.2 '% total solids) was obtained from Dr. P. M. Westfall and added to the standard P-38 mixture. The material before curing is very difficult to break apart but as shown in Table V, after curing it shows no great im provement in strength or impact. Gantrez AN-139 Copolymer As a result of reading U. S. Patent 3,113,064 entitled, "Asbestos paper containing vinyl alkyl ether-maleic anhydride copolymer and method of forming same", we decided to try adding one of these copolymers to the P-38 mixture. The one chosen was Gantrez AN-139, a copolymer of methyl vinyl ether and maleic anhydride manufactured by General Aniline and Film Corporation (gaf). The copolymer was -6- added both in the dry state and in the form of a water dispersion. There was some improvement in the strength of the cured P--38 board but not a significant amount. (see Table V). Polyox - Carbopol 940 Carbopol 940 is a water-soluble, high molecular weight poly (acrylic acid) manufactured by the B. F. Goodrich Chemical Company. The Polyox and Carbopol were added to the asbestos in the mix-muller both in the dry state and as a mixture in water. A combination of Polyox and Carbopol was also tried but did not give any great improve ment in strength as seen in Table V. Latexes Since the best way to obtain good dispersion of the filler material and at the same time enhance the possibility for any reaction between the filler and the asbestos is to add the filler as a water solution, the use of latexes becomes a logical possibility. After a few batches were prepared,it became apparent that a new study of strength as a function of curing time and temperature was needed. A series of mixtures were prepared using as a filler 10.4% of a 60/40 styrene/butadiene latex containing 48% total solids. The variables included room temperature cure times of from 0 to 36 hours and high temperature cures (110C) of 4,8,16, and 32 hours. The results are tabulated in Table VI and shown plotted in Figure 4. As a result of this study, the remainder of the runs using latex fillers involved room temperature cure times of 30+ hours followed by 24 hours at 110C. As can be seen from Table VII, various types and percentages of latexes were studied, including styrene/butadiene, polyethylene? acrylic acid, phenoxy A, and a carboxylic modified butadiene/acryloni trile copolymer (a product of the Chemical Division of The Goodyear Tire and Rubber Company, known commercially as Cheraigum Latex 550). Again, however, no really outstanding improvement in strength was obtained for any of the latexes used as fillers. Di-(2-ethylhexyl) phosphoric acid In place of a portion of the phosphoric acid used in the P-38 composition, di-(2-ethylhexyl) phosphoric acid was substituted. It was hoped that some cross-linking could be promoted by using this material but in all the mixes prepared, the cured board was extremely weak. The use of superphosphoric acid was also investigated but it proved unsuccessful. No testing of these samples was attempted. Fibrous fillers The use of fibrous fillers has proved to be the best choice to date. As shown in Table VIII, crocidolite (Cape blue asbestos), glass, and nylon fibers have been tested and they all seem to increase impact strength, especially the nylon. The work on nylon stems from I -7 a report by the U. S. Army^ ^ on the addition of nylon fibers to cement. The impact strength of cement is reported to be increased by a factor of twenty-seven. Further work is being planned along these same lines using as fillers, nylon (different denier), polycarbonate, and polyhydroxyether fibers. F-100 Composition For comparison purposes,a batch of the F-100 composition was prepared and tested. The ingredients were as follows: 60 parts asbestos, 15 parts water, and 25 parts BRL 1100 (water soluble phenolic predominating in dimerized trimethylol phenol with some residual monomer; 64-68% solids content). The test results are listed in Table VIII. REFERENCES Q 1. Modern Plastics (Encyclopedia Issue for 1964) 41/No. 1A, 525 (1964). 2. V. E. Barrable, A. Bennett, and A. F. Jerome, I and EC Product Res. and Dev. 2, 186 (1963). 3. Handbook of Asbestos Textiles, Asbestos Textile Institute, Philadelphia, Pa., 2nd edition, p. 3 (1961). 4. F. L. Pundsack, J. Phys. Chem. 59,. 892 (1955). 5. after E. J. W. Whittaker, Chem. and Eng. News, p. 35, 30 Sept. 1963. 6. T. F. Bates, L. B. Sand, and J. F.Mink, Science 111, 512 (1950); in addition, reference 12 contains a picture of some Coalinga fibers taken with an electron microscope. 7. F. L. Pundsack, J. Phys. Chem. 60, 361 (1956). 8. E. Martinez and J. J. Comer, The Am. Mineralogist 49, 153 (1964). 9. M. C. Ball and H. F. W. Taylor, J. Appl. Chem. 13, 145 (1963). 10. L. S. Dent Glasser, F. P. Glasser, and H. F. W. Taylor, Quart. Revs. 16, 343 (1962). 11. Nuclear Division, Research Report No. 39: Development of New Building and Pipe Materials From Coalinga Fibers, G. S. Jordan and N. J. Setter. 12. Nuclear Division, F-100 Data Book, G. S. Jordan, H. F. Reichard, and N. J. Setter. 13. Technical Report 1757~TR, "Plastic Fibrous Reinforcement for Portland Cement", prepared by S. Goldfein, U.S. Army Research and Development Laboratories, Ft. Belvoir, Virginia. - 8- BIBLIOGRAPHY (1) Asbestos, From Rock to Fabric, The Textile Institute, Manchester, 1956. (2) Asbestos, Its Industrial Applications, D. V. Rosato, Reinbold Publishing Co., 1959. (3) Handbook of Asbestos Textiles, Asbestos Textile Institute, 2nd edition, T551--------------------------- (4) Asbestos Fundamentals, B. Berger, Chemical Publishing Co. Figure 1 silicon OO magnesium oxygen 0 hydroxyl Chem. and Eng. News. p. 35, 30 Sept. 1963 This drawing represents a portion of the curved wall layer of a fiber of chrysotile asbestos. The fiber walls are composed of 12 to 20 such layers; each layer being about 7.3 a thick. of tne w pixels one o* T Pa*aJ- in ?iSr  /S A ou /"\ u /N u o N 00 S tre n g th as a F u n c tio n o f C u rin g Tim e Tim e a t Room T e m p e ra tu re ( h r s ) VrJ u oo oo oo to o' (xsd) i^Sua-i^g H3jnxaij[ o oo o (rsd) qq.2usjq.g t-*nxaT.i F le x u r a l S tre n g th vs Tim e a t Room T e m p e ra tu re Tim e a t Room T e m p e ra tu re ( h r s ) Classification Serpentine Amphibole** TABLE I Common .Name Chrysotile* Crocidolite Tremolite Actinolite Anthophyllite Amosite Formula "83Si25COH)4 1'2Fe5St822(0H)2 C2HSSS1822(0H)2 Ca(MgFe)sSipOp^(OH) (11^6)781^0^ (OH) (MgFe)6Si8022(0H)2 chrysotile exists in at least three modifications depending upon the form of the crystal lattice. The following four papers are recommended for the interested reader. . ,1 E. J. W. Whittaker, Acta Cryst. 6 747 (1953) 2. E. J. W. Whittaker, Acta Cryst. 9, 855 (1956) 3. . E. J. W. Whittaker, Acta Cryst. 9, 862 (1956) 4. E. J. W. Whittaker, Acta Cryst. 9, 865 (1956) ** see: for more information on the crystal 5. E. J. W. Whittaker, Acta Cryst. chemistry of amphiboles l 291 (1960) Property Density, g/cc Hardness g Specific Surface m /g Oil Adsorption g/lOg Water Retention g/20g Bulk Density Wet cc/5go Dry lb/ft*5 Refractive Index Luster Color Brightness (% of MgO) Electrical Charge Acid Resistance Alkali Resistance Specific Heat BTU/lb-F Tensile Strength lb/in2 Temp, of Max. Loss Temp, of Struct. Loss TABLE II* General Chrysotile Asbestos 2.25-2.75 2.5-4.0 10-50 4-5 32-34 10-15 1.50-1.55 silky green-gray positive poor good 0.266 80,000-100,000 800C 600C UCC Coalinga Asbestos (high-purity grade) 60-70 14-16 175+ 3-5 white 75-80 * Table taken from letter of W. H. Dresher, Nuclear Division TABLE III* CHEMICAL COMPOSITION Compound General Chrysotile Asbestos MgO Si02 Fe34 Fe23 FeO H_0 Total Combined 30-44% 35-44 0.5-5.0 0-6.0 0-6.0 12-15 Mineral MINERALOGICAL COMPOSITION General Chrysotile Asbestos chrysotile brucite magnetite hydrotalcite major moderate 0.5-5.0% -- UCC Coalinga Asbestos (high-purity grade) 42 42 <1.0 -- 0.3-1.6 16.0 13.5 UCC Coalinga Asbestos (high-purity'grade) major minor <1.0% minor * Table taken from letter of W. H. Dresher, Nuclear Division ft r-s H CD O 3 to Q id 3< co co t- r- co n i)i Tf (o io n o rlHHHHHH CO o o ft <W ft (N rH CO t> U< 3* O HB H rl HHN #* ooooooo ID CO 3* 3* CO CO 00 rtri rl H H rtN oo oo o oo bO s H U 3 CD O r-4 d (0 iH <H o V3i 3 r-l X3 3 O 3 iH o O *r( ft S3 ft P' >o 3 3 UW $ IS CO df d bO/-v ft,ft Vi 3 -H 3 m u x u 04 3 ft " r-l CO fUt ft k>; H o >J o' f3t CO 3 (O IO 01 H D1 ro CO t O CO r-l CO d* H I-. 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OM ao 0X Mo Cn mp TABLE V oo ooo o ooo * oo oo to* to to to M to to to M M M M CO CO cn * oo *4 4 to * cn o> -4 *4 o ooo o ooo o o OO M M HHH M to M M MM M M 9 tP 00 coo to *0 00 <P P jPM M M M M M M PHH M M M M cn cn to M 9 99 CO 00 to cn cn cn cn tO -40 cn cn cn cn tP tP CO iP N Oa s 3 a M rt < P -38 C o m p o sitio n P lu s A d d itiv e s a sa 60 ^^i^i*ioiAtAioiA<oiAtAiAiA HHHHHHHHHHHrtHH 9 o CO o C4 CD fa 3 9M K *3D H o U) a rh*ahOwOwtt*'n0*n'f~wIQOhPtdflOhOhOnOO ^*a**** oooooooooooooo ctctocqcittdeittcittttctc* oooooooooooooo C')tO^tO-l^H`CHO<O'*<OO'*H<0NC^OWO-'r*jCsfftr-4 hhwnnnnncqnnnmn ^irPtHJONt>lOCC'PJJNHWWNNOTftW'O0 0*6*01040)0104010*0404010)0 9fa b3D*'*H* S4Ofa*' CaD' CO I 9 4 3 Q CD \*o Cfa HOo CO d oo >\ rl O fcft P CO CO d < H X O 4-> 6ft d p-4 r-4 3 tti cfwa 3 o 0^*^*-fNiinrCN^A0o<tNPo0*NAo1<CoO^0c<0o01<t^H-OCOOO0j-CHC0OCOO<^--OWcOCi^0roCCto^O0 lA i^p^w^coNcoOnn^r-^Hi-cHcofnoMoicoo>^^HOONONO CfaO o *c CO co co CO CO CO GO <H 00 00 eH CO iH^QOrHQOiHOQ H a if fa e OOC4^CfH04H0H4 OHl HCOC004QCC9* ofa *o Cf 00 faO 00 VI lA s crcOO4 04H^O)HCrHfl0t*<O( I I NI ttI ffIiOt OI t*I I I I I I t 60 s fHa 3o fa o M 3 ri *o afa 60 c fMa d <o3 3o o n -d fa d a to d4 3 foa o. 4>-> oo 03 tc cw <pH0 oo I*s0** pH pH H ^to to * HH to to in to HHH CO ^ to lO HH to CM CO tO lO to Hf ^ pH pH rH rH rH rH rH N'fl'HN lO tO rH pH O pH t" t** CO pH iH CO CO h rH rH oo W d> rH H rH CM oo t- CM rH oo CD 00 * ^ tw ,h to CM CM rH pH pH pH rH pH rH CM rH oo o OO TOJ 00 OCM CO CO CM CO CM rH CM CM CM rH CM CM CM 'M* CM CM A O O O O O O o h* CM CM O CM O CM 00 rH CM CM rH O O pH CM 04 rH O o d CO >4 3 K 3H X *30 *H oa F = 0< 2 .7 3 2 .3 5 1 .7 2 2 .2 2 2 .3 6 2 .7 3 2 .3 4 1 .4 6 2 .7 6 2 .3 4 2 .2 8 2 .1 4 1 .4 8 2 .2 7 > 2 .4 0 2 .4 0 2 .2 0 1 .3 8 2 .5 4 1 .8 9 3.21 3 .1 0 2 .5 0 2.34 to CO r-( oo t* CM to rH t- r ift C** 0 CM CM rH rH rH rH rH rH H O CM CM rH HHH tJ* rH CO ^ rH ^ * CM CM CM rH b0 C H u 3 U > rl Ho rH A +* U tOr-N < 0) 3ax> auC> -arHo 3 rH 4H W 44 8600 8361 5833 5629 6954 8156 7427 4682 9444 7746 9415 8874 7360 7535 5062 4908 6835 7850 6827 4824 8434 6812 7842 8524 COo tj* to c r*- rH c- o rH CO CO o^on C- CM C* CO ^ T? to pH C** CO c- CM to c- ^^ rH CO O CO O O u 0 <H 01 A 0) *H w 01 44 COI Ck * mn a> >X H 0) 44 44 tH rt O rH O w < J<5 O OC 1 o Ah o> 4-> CM O 0) a p*^i (0 0) cn *D TJ *0 H tH *H rH pH pH 00 0} a3 to 44 44 44 00o 44 +4 44 6*6*6* rr rr rf \ 10(0X0 U 3 <H O pH C3 CM CO C * tJ* CM \ C0 CO 0) 03 0*0*0 H tH tH HHH ooo 03 01 0) rH rH rH ddd 4J 4J ooo 44 44 4-> 6*6*6* * pH rH rH \\\ xoxoxo 03 TJ H pH O' 03 pH d 44 o 4-> 6* o CQ ffl SS. 'sv KO (O ^ \\ o ooo \\\ 6*6*6* ^* t-- N OO pH CM 6*6* CM o pH 6*6*6* ^ f* CM pH CM 6*6* rf CM rH 03 X TJ a> *h 44 rH dO pH 0) C: *0 pH *h d O +> do 44 o H rH > u t- C 0 d 1 -v C H O pH rH >v >* u JS o d rH --> d O ** hj o bR o tR <3< ^3* y H O rH -H >>rs pH /n h 03 >> 0) O TJ h *0 d Tt u **H 6* O 0 in to6* ifl rH <0 ^ rH Is- 1 1 ow M W Ct, ft D 6*6* 6* to rt*tO ^ 09 CM O rH rH r*N rsr\ (0 0) 03 *0 TJ *0 **H HHH rH pH 0 0 0 03 03 03 pH HH d dd 43 0 OO" M 4- 6* CO CO ^ w X X X ft) 0) 0) **J 4J 44 d d d rH rH rH >> >v ^ X XX 0 ooc cc o a> a> a XS A Oi a g. 6* 6*6* CM CM rH rvrs 0) 03 03 *0 O T3 H *H H HH O O O 03 03 03 rH pH pH d d rt 4-> 44 44 O O O * 44 44 O 6* C bRfeRrH cm rH pH * 00 6* CM *-" ^ + EE D3 p 0 uu Ed 5j-h <h h tH E E E EO a> ci a .xi rruo oo ,, ,, 6*6* (O C* >00 . . . CM rH rH CM rH 1t CM CM ^ pH t1 CO CO to pH CO CO I11 Tf ^ pH H CM rH rH I1 11 1 [* CM M* "*3< rH CM HHH c-1- r rH till C-- ft C tt c a> H TJ O h to c *H *H O 0) tn u d A o pH d H c H c 0 *o a> 03 d A O U id i 03 i 0) i tfi td i 44 ic I0 to ih iO ta i t* i t i i S3 oo o *t* CO HHH rH 04 CD CO HH to CO C4HH * ooo t- 04 rH tO OO 05 to rH 04 04 O co ^ co CO 04 CO ooo 04 01 n* oo 04 o <0 o <k0 3to X 3X r3H H *Q ._ o a i< 2 P 05 CO CO r-tCOt- C4 w4 O t- Cf5 COt t o NWrl rf yfi CO 01 04 04 CO CO CO 05 04 04 V <c tn 3 rH P wd o Q < H H 0) o o o 0o0o p* b0^* DK d *H a> jh a H4JW CQ >. W P H o o < rH CO CO 05 O^fCO to CO 04 05 CO o CO 0- 05 CO CO CO PI rH 05 00 00 to to to V (0 0 p to XJ to ctf (0 3 r^H o ' *W JQ Q) H P H rH OH (t O fafliH ho t bO oh\t QrH rH fcSbfcb* 00 00 00 04 04 04 ** * CO CO CO CO CO 00 uu H H 3 C o o oo wH rH U U .a .Q H *H <H <M ad oo H>v HX ca coi coi to CO OO rH 05 H CO CO 04 04 CtoO 04 rH 04 rH 05 * CO rH to o a O o o 0 rH 1 f*4 .X 0o) ^C I GO U O00 co o P <H lO fed* rH 04 rH III ID ID O Ol 03 CO rHI 04I 00 00 CO co I 5 Distribution J. W. Biddle, 511 F. E. Bailey, 511 D. L. Engle, 511 J. 0. Koehler, 511 J. V. Koleske, 511 R. D. Lundberg, 511 C. W. McGary, 511 A. E. Montagna, 511 A. W. Myers, 511 G. W. Rausch, 511 K. Smith, 511 J. J. Stratta, 511 W. N. Stoops, 511 L. H. Wartmen, 511 F. J. Welch, 511 C. E. White, 511 C. B. Witherell, 511 N. L. Zutty, 511 Ivey Allen, 312 A. Brown, 312 L. Imhof, 312 S. Jordan, Sterling Forest, N.Y. C. N. Merriam, 312 F. P. Reding, ERA H. F. Reichard, Sterling Forest, N.Y. Information Retrieval Authors (4)