OCTOBER, 1939
INDUSTRIAL AND ENGINEERING CHEMISTRY
Literature Cited Bauer, F. W., Ber., 37, 3128 (1904). . , 720 (1923). Bedford, C. W., and Gray, H., IND.EXG.C ~ M 15, Brazier, S. A,, and Ridgway, L. R., J. SOC.Chem. Ind., 47, 351T (1928). Brown, J. R.,and Hauser, E. A,, IND. ENG. CHEM.,30, 1291 ( X938\. B&se: W.F., Ibid., 24, 140 (1932). Cotton, F. H., Trans. Inst. Rubber Ind., 6, 501 (1931). Cramer, H. I., private communication, Sept. 17, 1938. Denighs, G., Compt. rend., 108, 350 (1889). Faragher, W. F.,Morrell, J. C., and Monroe, G. S., IND.ENQ. CHEM..19. 1281 (1927). Grote, I . 'W.,'AnaZyst, 56,' 760 (1931). Gutmann, A., Ber., 56, 2365 (1923). Liebermann, C., Ibid., 20, 3231 (1887).
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(13) Lindsly, C. H., IND.ENQ.CHEM.,Anal. Ed., 8 , 179 (1936). (14) Meyer, K. H., and Hohenemser, W., Helv. Chim. Acta, 18, 1061 (1935). (15) Midgley, T., Heme, A. L., Shepard, A. F., and Renoll, M., J. Am. Chem. SOC.,56, 1325 (1934). (16) Rheinboldt, H . , Ber., 60, 184 (1927). (17) Rossem, A. van, India Rubber J . , 92, 845 (1936). 119'1 Rossem, A. van, and Dekker, P., Ibid., 95, 682 (1938). Stair, R., and Coblentz, W. W., Bur. Standards J . Research, 15 295 (1936). (20) Staudinger, H., India Rubber J . , 95, 646 (1938). (21) Stevens, H. P., AnaZyst, 40, 275 (1915). (22) Williams, I., India Rubber J. (London Conf. Suppl.). May, 1938.
i;;;
PRESENTEDbefore the North Jersey Section of the American Chemical Society.
Cottonseed Hulls as an Industrial Raw Material D. M. MUSSER
AND
R. F. NICKERSON
Mellon Institute, Pittsburgh, Penna.
I
N An' average year the United States produces about a million and a quarter tons of cottonseed hulls as a byproduct of the cotton crop. During the past few years unusually large crops have increased that figure. Although the utilization of agricultural products in general as industrial raw materials has been promoted extensively in recent, years, the possible uses of cottonseed hulls have received but scant attention. As one part of a broad research program to develop new uses for the cotton plant, the available literature and all other sources of information on this low-priced waste product have been searched for chemical facts and ideas regarding practical applications. In collating this knowledge, we have maintained a constantly critical attitude.
Production The hull of the cottonseed is the horny, external covering which encloses the seed kernel or meat. During the growth season of the plant the hulls contain the cells which give rise to the cotton fibers or hairs. After the cotton has been picked, the seeds are ginned out of the lint, but in most American varieties the ginned seeds are covered with an adherent fuzz consisting mostly of short fibers. Subsequent processing by delinting machines removes the greater part of this fuzz, which is then marketed as cotton linters. The hard, dark brown hull is cracked off and removed from the kernels in a series of operations. It is frequent practice to pass the hulls so obtained through a beater, which breaks them down to hull bran and facilitates the removal of hull fibers, the very short cotton which escaped the delinting processes. Several methods have been reported for removing the fibers from the hull bran. Dorner (9)obtained a patent on a process for powdering the hulls and separating them from the hull fibers with an air blast. Chetverikov (7) effected the separation by boiling the hulls for several hours with a solution of sodium hydroxide. Kao and Yu (26) separated the linthull mixture by the action of hydrogen chloride gas. More
recently Earle (10) patented a method employing froth flotation for dividing the fibers and hulls. As cotton is picked, the cottonseeds represent about two thirds by weight of the crop, or about a half ton of seeds for each bale of lint. Harrington (19) found the ratio of hulls to meats in nine common varieties to be approximately 1 to 1, with very little variation. Thus the hulls constitute approximately one third by weight of the total crop. Woolrich and Carpenter (66) give an excellent discussion of the production and processing of cottonseed.
Chemical Composition Harrington (19) reported the following data on the composition of hulls from seventy-three varieties of cotton: Water Protein Fat N-Free Ext.a Fiber Ash 41.2 2.4 8.18 1.62 0.12 34.8 Minimum, % 9.97 5.18 1.05 42.1 47.9 2.8 Maximum, yo a Nitrogen-free extract ie for the most part pentosans. Exoept for some minor variations these data agree with the results compiled by MoBryde (51).
Analytical determinations on cottonseed hull bran have been carried out in our study and have been treated in detail elsewhere (36). The standard methods for wood technology have been applied in the analyses for the following constituents: cellulose by the procedure of Cross and Bevan (8); lignin by the method of Ritter, Seborg, and Mitchell (43); furfural, pentose, and pentosans according to the standard A. 0. A. C. procedures (4); hydrolysis number by the method of Hawley and Fleck (20);and methoxyl, acetic acid, ethersoluble material, one per cent sodium hydroxide-soluble material, cold-water soluble material, hot-water soluble material, ash, and moisture as suggested by Schorger (46). The hull bran analyzed was first freed as completely as possible from hull fibers and then ground to 40 mesh. Samples of this material were then used for the following determinations, given in per cent on an oven-dry basis:
1hl)USTRIAL AND ENGINEERING CHEMISTRY
1230
Moisture Cold-water sal. Hot-wster sol.
Ether-sol. i&dkali-sol. Methoryl
s.11 1.87
7.52 0.27 20.22 2.28
2.16
Lignin Total pentassm Furfural
23.40 38.4U
Celluloee Aaetiu soid by hydrolyssis
22.50 53.40 4.88
Hydiolysia No.
33.40
In addition to gross ardyses, McBryde (3'1) reported analyses on tlie ash of cottonseed l i n k Later McIlargue (SZ) gave more extensive data which agreed well with the comparable values of McBryde; they represent the mineral constituents oE cottonseed hulls as perccntapcs of dry matter : K
Ne
1.143 0.877
Ca 0.131 M g U.0248
Fe
0.0138
M n 0.0138
CuU U014 ZnU.002
PU.058
8 0.038
Ash analyses by Sheets and Thompson (48) showed 9 per cent phosphoric acid, 23.4 per cent potash, and 8.85 per cent lime. Lishkevicli (99)concluded that 70 per cent of the phosphorus of hull bran was organically combined. The commition of the ash of cottmseed hulls has licm
VOL. 31, NO.110
per cent of an insoluble substance. More recently Anderson, Hechtman, and Reeley (f) succeeded in preparing a white hemicellulose from cottonseed hull bran.
Suggested Uses The literaturc does not reveal many practical tonnage uses for cottonseed hulls. Although these hulls are comparatively cheap, with xn average price (87) of xhout 5-6 dollars per ton, industry consumes a rather limited amount. Prior to 1900 hulls uere commonly burned as fuel; the ash, because of its high potash content, was used as a fertilizer. Hoffman (88) described an apparatus and the conditions for obtaining high fuel value from hulls. CARBOKIZATION Axn DISTILLATION. When hulls are carbonized in an iron retort in tlie absence of air, and the inorganic ingredients are removed by subsequent treatments with acid and alkali, the pyrolytic residuum is chimed (Zf) to be 99.5 per cent pure carbon. I t is stated that this product may be employed as a pigment in oils and paints, and that i t may he utilized for the manufacture of other carbon products such ILR electrodes
OCTOBER, 1939
INDUSTRIAL AND ENGINEERING CHEMISTRY
Basore and Schweickhardt (6) developed a method for producing B high-grade decolorizing carbon from extracted cob tonseed hulls. The residue remaining after the extraction of xylose from cottonseed hulls was airdried, mixed with calcium oxide, and heated to 1800" F. The carbon was rendered free of calcium oxide and activated at lfiOOo F. by air. The end material possessed high absorptive properties and might he of interest to sugar technologists. An investigation of the production of activated carbon from hull bran as part of our program has yielded promising results. The products formed when hulls are destructively distilled in the absence of air were studied by Randolph, Grove, and Tucker (48). Their examinations showed 29 per cent of gas, which had a calorificvalue of 300 B. t. u. per cubic foot; 41.5 per cent of liquid condensate, which was divided into aqueous solution (35 per cent) and tar (5 per cent), and 29.5 per cent of a charcosl with a heat value of 12,500 B. t. u. per pound. The aqueous solution contained enough acetic acid to warrant industrial consideration. The tar was found to be hard drying, unusually resistant to common chemical reagents, and high in phenol content, which suggested its possible value as a preservative for hardwoods. XYLOSE.Eulcr (11) first pointed out that xylose can he made commercially from cottonseed hulls. Hudson and Harding ($3) showed that yields of 8-12 per cent xylose can be obtained by treating hulls with ammonia, extracting with sulfuric acid, and subsequently crystallizing the xylose from an alcohol solution. Sherrard and Rlanco (49) used a similar process for obtaining xylose but made the extractions a t higher pressures. Hall, Slater, and Acree (18)developed an improved method by which hull bran is given chemical pretreatment to remove inorganic constituents, gums, and other impurities. Extraction of xylan and its hydrolysis to xylose is effected with hot sulfuric acid under steam pressure. The extract is treated with lime to remove the sulfuric acid, concentrated, and allowed to crystallize. No alcohol is used in the process. This procedure was carried ant experimentally on a semicommercial scale and described in detail by Schreiber and collaborators (47). The principal product of the hydrolysis of FURFURAL. pentosans is furfural, which can he obtained in higher yield from cottonseed hull bran than from any other known plant material (47). From air-dried hull bran Markley (S3) recovered 22.3 per cent furfural, and an equivalent yield was obtained in our laboratories. Zakoshehikov sad co-workers (58)suggested that even higher yields of furfural may bo produced from cottonseed hulls if tannins and lignin are first removed by chlorination and washing with water. For these reasons cottonseed hull may vrell play an important part in the future production of the furans. A?a result of the work of Miner and his associates, furfural is now prodnced in the United States almost entirely from oat hulls. Commercial production from this raw material was begun in 1921 and in subsequent years has shown a steady increase through the discovery and development of new applications, Acfording to government statistics (50) for the period 1929 to 1933, inclusive. the average annual output of furfural %vasabout 2,000,000 pounds. With increased production the cost of furfural would probably be reduced and its industrial ntilization correspondingly extended. Peters (39,40) recently made a critical review of the uses suggcsted for furfural and its derivatives. In general, forfural is a highly reactive compound and possesses many properties which give it commercial utility. The most important applications a t present appear to be in the manufacture of plastics and resins and in solvent refining processes. Other possibk industrial outlets are in the fahri-
1231
cation of dyes, fungicides, tanning agents, preservatives, and antioxidants. Sherrard and Blanco (49) pointed out FERMENTATION. that acid hydrolysis of cottonseed hnlls yields xylose but almost no fermentable sugars. Although xylose will not undergo alcoholic fermentation hy yeast, it can he fermented with butyl-acetone organisms (16, 41, 44, 51, 68, 55). By the addition of corn mash normal yields of butyl alcohol, acetone, and ethyl alcohol are obtained (63). Moreover, Fred and Peterson (14) showed that pentose sugars treated with a suitable nutrient material arc acted upon by Lactobaeillvs penloaeetius to give almost quantitative yields of acetic and lactic acids. Xylonic, succinic, citric, oxalic, propionic, formic, and butyric acids, carbon dioxide, hydrogen, acetone, acetylmethylcarbinol, ethanol, 2,3-butylene glycol, and n-butanol were reported as products of the action of microorganisms on xylose (16). It is thought that fermentation studies along these lines will open a wide range of possibilities not yet explored. FEED FOR DOMESTIC ANIMALS.At present hulls are used chiefly as roughage for beef and dairy cattle. They are not very nutritious, being equal in feeding value to prairie or Johnson grass hay, but serve as a carrier for ground grain and cottonseed meal. Furthermore, they are useful in regulating the nitrogen content of cottonseed meal and cake. It has been suggested that chemical treatment might increase their usefulness as a stock feed (85,S.Y). Supplemented with calcium, green feed, and protein, hnlls are said to be sirperior to hill-land carpet and Bermuda grass hay (80).
cour1esy. come, cotion Gin company
MACnINE FOR DEHULLINQ COTTONSEED There is no ready market, for large qusntiFERTILIZEK. ties of hulls; consequently they oft,en accumulate as so much waste material a t the niimerons oil mills and may eventually find use as a cheap fertilizer. The value of liulls for this purpose is indicated by the statement (45) that l ton of cottonseed hull ashes is equivalent to 4.5 tons of average hardwood ashes and to 15 tons of leached hardwood ashes. Anderson, Swanbaek, and Street (3) carried out experiments on the use of cottonseed hull ashes as a sourco of p o h h for tobacco
INDUSTRIAL AND ENGINEERING CHEMISTRY
1232
. plants. Their results did not show any improvement in yield or grading from the substitution of hull ashes for other carriers of potash. The foregoing analyses indicate that the nutrient value of hull ashes can be attributed to the presence of a variety of metallic oxides. Although unashed hulls contain only a small percentage of nitrogen, the high content of insoluble carbohydrates suggests their use as a source of humus in addition to the slowly available metals. Thus the utilization of hulls as a mulch might well be extended beyond their present application to strawberries (64).
DIRECTION OF
Courtesy, Carver Cotton Gin Company
SCHEMATIC ILLUSTRATION OF THE OPERATION OF MACHINE
A
LINTER
The base-exchange capacity of cottonseed hulls and cottonseed hull bran has been investigated in this laboratory. The results are recorded in the following table, together with comparable values found by Muller (35) for a variety of organic materials, as milliequivalents per gram of dry weight: “Natural humus” German eat mom Hyper-fumus” Leaf mold Sphagnum mose Michigan peat Brown rot Oak leaves
1.73 1.43 1.39 1.18 1.12 1.07 1.07 0.95
Dehvdrated manure BarFbog peat Cottonseed hull bran Cottonseed hulls Cow dung, dried 105’ C. Bagaeae Rye etraw Wood shavings
0.73 0.66 0.40 0.38 0.24 0.13 0.00 0.00
The appreciable base-exchange capacities of hulls and hull bran suggest their use as a bedding material for domestic animals. Hulls may be treated with pine oil (68) and other oils or materials to prevent their clinging to animals. The soiled bedding plus manure may then be used as a fertilizer. FILLING.Hulls have been employed to a limited extent RS packing and stuffing material-for example, in the manufacture of baseballs and horse collars (6). They are practically free from dust and siliceous matter and have fairly good insulating qualities (18). Their usefulness as heat-insulating and packing materials in the construction of houses is being investigated by the Department of Agriculture. For these experiments the hulls are rendered fireproof by ammonium sulfate. Preliminary results indicate that cottonseed hulls may prove satisfactory for this use. Future developments in this field may lead to a treatment which will render the hulls simultaneously fire- and rodentproof a t low cost. It has been suggested also that cottonseed hulls may be combined with a suitable binder to make cork substitutes, linoleum, light-weight boards, and similar products (16,24). An objection to this use of hulls is their brown color. However, a method of remoying the coloring matter was proposed by Muller ( S 4 ) , who suggests the use of the colored extract in paints for glass and metal. Gill and Greenup (17)
VOL. 31, NO. 10
investigated this pigment further and reported the isolation from an aqueous extract of a resinous or pectinlike substance which charred a t 320’ C. and corresponded approximately to C I Q H ~ ~ O X . MISCELLANEOUS. Sawdust, rice hulls, and similar bulky substances are used as the chief component of several sweeping compounds. A superior product (38) in which cottonseed hulls are the principal constituent was recently developed in the work of this fellowship. Fenton ( I S ) described the use of cottonseed hulls as a poison carrier in grasshopper control, and Ward (64) reported considerable application for this purpose during the past year. At the same time Ward noted the use of hulls as a side-wall filler in oil-well drilling and as a material for caulking the thermal joints between concrete highway slabs. Several years ago a patent was granted to cover the use of hulls for putting greens on golf courses (16). At the height of the miniature golf fad considerable quantities were used in the construction and maintenance of courses. So far as is known, this application has not been extended to regular golf greens, where the control of worms, insects, and blight is highly desirable. Hull fibers are potentially a valuable source of quality cellulose. A process (27) was developed recently for the conversion of cottonseed hulls into a pulp which, it is claimed, is superior to that obtained by the usual methods. Hull fibers and pulps find use in the manufacture of paper, cellulose, and derived products.
Literature Cited Anderson, E., Hechtman, J., and Seeley, M. J., J. Biol. Chem., 126,175 (1938). Anderson, E., and Kinsman, S., Ibid., 94,39-47 (1931). Anderson, P. J., Swanback, T . R., and Street, 0. E., Conn. Agr. Expt. Sta., Bull. 386,475(1936). Assoc. Official Agr. Chem., Official and Tentative Methods of Analysis, 1935. Basore, C. A., and Schweickhardt, W. K., Bull. Alabama Polytech. Inst., No. 2,29 (1931). Boynton, A. W., U. S. Patent 288,766 (1883). Chetverikov, N., Maslobolno-Zhirovoe Delo, 2, 34-9 (1932). DorBe, C . , “Methods of Celluiose Chemistry,” p. 331, New York, D. Van Nostrand Co., 1933. Dorner, B., U. S. Patent 1,789,354(1931). Earle, T.. Ibid., 2,122,607(1938). Euler, H., “Grundlagen und Ergebnisse der Pflanzenchemie,” p. 44 (1908);J . Am. Chem. SOC.,39, 1038 (1917). Fairbairn, T . M., Valdespino, A. S., and McCart, R., U. S. Patent 1,559,520(1925). Fenton, F. A., Am. Cotton Grower, 3, 37 (1937); Cotton Literature, 7, 422 (1937). Fred, E. B., and Peterson, W. H., U. S. Patent 1,485,844 (1924). Freeman, W. K., Ibid., 1,175,427(1916). Fulmer, E. I., IND.ENG.CHEM.,28, 778 (1936). Gill, A. H., and Greenup, H. W., Oil & Fat Industries, 5 , 288 (1928). Hall, W. L.,Slater, C. S., and Acree, S. F., Bur. Standards J . Research, 4, 329 (1930). Harrington, M. T., Texas Agr. Expt. Sta., Bull. 374 (1928). Hawley, L. F., and Fleck, L. C., IND.ENG. CHEM.,19, 850 (1927). Hershman, P.R., U. S. Patent 1,188,936(1916). Hoffman, G.,Power, 77,462(1933). Hudson, C.S.,and Harding, T. S., J . Am. Chem. SOC.,39, 1038 (1917). Hurst, I. A., U. 9. Patent 1,863,540(1932). Ivanova, V. T.,and Kurennova, A. M., Trest Khlopkochistitel. Prom., Collection of Papers, No. 1, 115 (1933). Kao, Chang-Keng, and Yu, Chi-Hsing, J. Chem. Eng. China, 3, 331 (1936); Cotton Literature, 8,95 (1938). KoraheniovskiI, G. A., and Raskina, R. L., Trest Khlopkochistitel. Prom,, Collection of Papers, No. 1, 124 (1933). Lapp, W.H.,U. S. Patent 2,014,900(1935). Lishkevich. M..Maslobolno-Zhirovoe Delo. 13,20 (1937). Lush, R. H., Staples, C. H., Fletcher, J. L., and Stewart, S., La. Agr. Expt. Sta., Bull. 238, 1 (1933). (31) McBryde, J. B.,Tenn. Agr. Expt. Sta., Bull. 4, No. 5 (1891).
OCTOBER, 1939 (32) (33) (34) (35) (36)
.-
137) I
(38) (39) (40) (41) (42) (43) (44) (45) (46) (47) (48)
INDUSTRIAL AND ENGINEERING CHEMISTRY
MoHargue, J. S., J . Am. SOC.Agron., 18, 1076 (1926). Markley, K. S., Ibid., 20, 1102 (1928). Miiller, O . , U.S. Patent 930,874 (1909). Muller, G. F., doctorate thesis, Rutgers Univ., 1930. Musser, D. M., J. Assoc. Agr. Chem., 22, 421 (1939). National Cottonseed Products Assoc.. “Cottonseed and Its Products,” 1937. Olcott, H. S., Soap, 14, 105 (1938). Peters, F. N., IND. EXQ.CHEM.,28, 755 (1936). Peters, F. N., Ibid., News Ed., 15, 269 (1937). Peterson, W. H.. Fred, E. B., and Schmidt, E. G . , J. Biol. Chem., 60, 627 (1924). Randolph, E. E., Grove, C. S., and Tucker, R. C., J . Elisha Mitchell Sci. SOC., 48, 26 (1932). Ritter, G. J., Seborg, R. M., and Mitchell, R. L., IND. ENQ. CEEM.,Anal. Ed., 4, 202 (1932). Robinson, G. C., J . Biol.Chem., 53, 125 (1922). Sadtler, 9. P., and Matos, L. J., “Industrial Organic Chemistry,” p. 89, Philadelphia, J. B. Lippincott Co., 1923. Schorger, A. W., IND. ENQ.CHEM.,9,556 (1917). Schreiber, W. T., Geib, N. V., Wingfield, B., and Acree, 9. F., Ibid., 22, 497 (1930). Sheets, E. W,, and Thompson, E. H., U. S. Dept. Agr., Farmers’ Bull. 1179 (1920).
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(49) Sherrard, E. C., and Blanco, G. W., IND. ENG.CHEM.,12, 1160 (1920). (50) Skinner, W. W., McCall, M. A., Post, R. E., Blanck, F. C., Veitch, F. P., and Herrick, H. T., “Preliminary Estimates of Farm Products, By-products and Wastes Available for Industrial Use.” D. 9. U. S. Dent. Am.. 1935. (51) Speakman; H. B., J . Biol. hhek; 58, 395 (1923). (52) Underkofler, L. A., Fulmer, E. I,, and Rayman, M. M., IND. ENG.CHEM.,29, 1290 (1937). (53) U. S. Dept. +4gr., Preliminary Statement of a Cotton Research Program, 1935. (54) Ward, A. L., Cotton and Cotton Oil Press, 39, No. 31, 3 (1938). (55) Weinstein, L., and Rettger, L. F., J.Bact., 25, 201 (1933). (56) Woolrich, W. R., and Carpenter, E. L., “Mechanical Processing of Cottonseed,” Knoxville, Univ. Tenn. Press, 1935. (57) Zakoshchikov, A. P. Ivanova, V. T., Korzheniovskil, G. A., and Xurennova, A. M., Trest Khlopkochistitel. Prom., Collection of Papers, No. 1, 102 (1933). (58) Zakoshchikov, A. P., Ivanova, V. T., and Kurennova. A. M., Trest Khlopkochistitel. Prom., Collection of Papers, No. 1, 87 (1933). CONTRIBUTION from the Multiple Industrial Fellowship of the Cotton Research Foundation at Mellon Institute.
Electrodeposition of Svnthetic Resins J
ANDREW GEMANT University of Wisconsin, Madison, Wis.
metals of synthetic resinous materials is described. The novel feature is the use of hydrophobic insulating liquids, chiefly mineral oils, as the dispersing phase of the necessary suspensions. Because of the absence of electrolytic products as well as traces of water in the deposit, the method seems to be especially suitable for making electrically insulating layers on metals.
The deposition from insulating liquids has the advantage of avoiding complications due to electrolytic products, since the conductivity of the system is negligibly small. The deposition proceeds without enclosure of water between the solid particles, which is highly desirable from the standpoint of the insulating qualities of the deposit. This paper presents some results of the research carried out in connection with the development of the process (4). Four synthetic resins were used: polymeric styrene (PS), supplied by the Bakelite Corporation; methyl methacrylate polymer (MM), butyl methacrylate polymer (BM), and an alkyd modified urea-formaldehyde resin (AU), all supplied by E. I. du Pont de Nemours & Company, Inc.
RECENT paper (3)described some quantitative results concerning the cataphoresis of resinous materials in insulating liquids, By measuring the cataphoretic mobility it has been possible to compute the electric potential difference across the boundary between the two phases. A microscopic method has been used for the measurements. The progress of cataphoresis can be followed also by visual observations of deposits of the resin on metals. In continuing research along this line, the author has found that the deposits have sufficiently high insulating qualities to warrant the development of a method of depositing insulating resins for industrial purposes. Deposition from aqueous suspensions of insulating materials is already known, especially for rubber ( I ) , but the corresponding method for hydrophobic insulating media has not previously been suggested. Indeed, very little scientific research in this special field has been done, and that has been merely qualitative (6).
Preparation of Suspensions The general principle of preparing the necessary suspensions was that of slow precipitation from real solutions. Synthetic resins can be dissolved in certain insulating organic solvents, and these systems present all the characteristics of real solutions, in spite of the fact that the unit molecules are extremely large so-called macromolecules. On the other hand, the solubility in mineral oils of these resins is rather limited; accordingly it is possible to obtain fairly stable suspensions if mineral oil is added to the solutions. The solutions themselves do not show any sign of cataphoresis, as explained previously ( 3 ) ; nor are mixtures containing about equal parts of solvent and mineral oil effective. The right proportion between solvent and oil is one of the essential points. The correct solvent-oil ratio is in the range 1:2 to 1:3. A larger proportion of oil is not advisable, since the suspensions become too labile. For the same reason it was not possible to increase the concentration of the resin beyond a comparatively low limit.
A new process of electrodeposition on
A
