Electrical Stabilitv of MineralOil-Treated Dielectrics Influence of Refining Technique F. M. CLARK AND E. L. RAAB General Electric Company, Pittsfield, Mass.
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The suitability of mineral oil for use as an impregnant of cellulose dielectrics is best gaged by a study of the treated insulation. “Beaker” studies of the oil are frequently misleading. The common danger in the manufacture of mineral impregnating oils for dielectric use is that of overrefining. This results from the fact that the chemical and dielectric properties of the oil, per se, improve with exhaustive acid treatment of the distillate, in contrast to the behavior of the oilimpregnated cellulose insulation which reaches its maximum dielectric stability after only a limited refining treatment. The object of the refining treatment is to eliminate as completely as possible the olefin type of chemical unsaturation in the crude oil without
severe reduction in its aromatic unsaturation. For the type of distillate studied, the greatest dielectric stability of the treated insulation is obtained when the aromatic unsaturation content of the oil is in the range from 22 to 23 per cent corresponding to a specific dispersion value of 115 to 117. To acid refine the distillate oil to its greatest impregnating dielectric stability, the treating temperature is preferably around 20” C., and 96 per cent concentrated sulfuric acid is used in the ratio of 3.5 to 5.5 pounds per gallon of oil. Increased treating temperature, with or without variation in the concentration and the amount of acid used, yields a product of inferior qualities when the dielectric stability of the impregnated cellulose is studied.
HE refining of mineral oil for application as a dielectric impregnating medium in high-voltage apparatus begins with the fractional distillation of the crude oil. The distillation products obtained are so unstable that they are entirely unsuited for electrical use without further chemical treatment. Among the refining agents used to eliminate the unstable hydrocarbons and the asphaltic and resinous materials present in the distillate is sulfuric acid. Although the exact treatment best adapted to produce the most stable dielectric product will vary with oil from one crude source t o another, one of the objects of this paper is t o demonstrate the general type of sulfuric acid refining treatment best suited t o the manufacture of an impregnating oil from Gulf Coast crude for use in high-voltage apparatus. The problem of determining the suitability of a mineral oil for electrical application is made difficult because of the peculiar nature of its application. The oil is rarely used alone but as an impregnant of solid insulation, usually cellulose, in the form of paper sheets or pressboard. Just as the combined use of the oil and solid affects the dielectric properties of each taken individually, so also does such use affect the problem of chemical and electrical stability. A previous article ( 2 ) described the difficulty of predicting the suitability of an oil from a “beaker” study of its properties. The present paper further emphasizes the difficulties and dangers involved in the use of beaker tests as a basis of oil selection. The selection of mineral oil for dielectric use must recognize the fundamental differences which exist in this type of application as contrasted to the more common use of the oil as a lubricant. Mineral oil as a dielectric is expected to have an unlimited life a t temperatures of application normally below 100” C,, under conditions of high-voltage stress and oil oxidation. Because it is impossible t o withdraw the oil
for reconditioning or replacement in most of its impregnation applications, minor but cumulative chemical and dielectric changes in the oil may ultimately determine the useful life of the apparatus. Although the cause of this type of change is of great importance in commercial practice, it may be entirely overlooked or even absent in the usual laboratory examination of the oil itself because of adsorption by the cellulose in combination with which the oil is used. For this reason the study of the oil-impregnated cellulose insulation has been advocated (2). The present paper gives further substantiation of the value of such studies.
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Oil Refining Technique A uniform oil refining technique is used throughout this study. The distillate oil was from a Gulf Coast crude stock of the type generally used in the manufacture of a mineral insulating oil’ adapted for hi h-voltage cable and ca acitor use (viscosity 100 seconds Saybok Universal at 37.8” C . r The oil was cooled or warmed t o the desired treating tem erature which was carefully maintained throughout the acia treating process. When less than 2 pounds of acid per gallon of oil was used, the acid wm added in small amounts with continuous shaking of the oil t o secure intimate contact and to maintain the treatin temperature at the desired value. When more than 2 pouncfs of acid per gallon of oil was used, the treatment was stopped after this amount of acid had been added in order t o allow the acid sludge t o settle for separation. After its separation, the addition of the acid was continued until another 2 pounds per gallon had been added; then the acid sludge was again removed and the procedure repeated until the desired quantity of acid had been used, the oil temperature being carefully maintained at the desired value. The acid-treated oil was then washed with a dilute (3 per cent) caustic solution until neutral, washed with water, and dried. The oil was then treated with 80-300 mesh, dried fuller’s earth. Two per cent by wei ht of fuller’s earth was used, and the treatment maintained for 28 minutes at 50” C. The o!l after filtration to remove the adsorbent was then ready for dielectric me. 110
INDUSTRIAL AND ENGINEERING CHEMISTRY
January, 1942
Testing Procedure In determining such oil properties as color and acidity, the testing procedures of the American Society for Testing Materials were used. The power factor of the oil was determined a t 60-cycle voltage under a dielectric stress of 30 volts per mil with concentric electrodes having a 0.100-inch gap spacing. To determine the dielectric stability of the oil-treated insulation, a vacuum-dried and impregnated test pad was used, as described later. The dielectric stability was gaged by the power factor value of the treated insulation measured a t 30" and 75" C. under 60-cycle voltage a t a dielectric stress of 500 volts per mil after 10 weeks on life test a t 75' C. under a 60cycle voltage a t 812 volts per mil. Valuable information concerning the chemical character of the oil was obtained by the determination of the olefinic and aromatic value. The procedure used was based on Kattwinkel (4). I n a previous publication (2) the importance of the unsaturation value of the oil was emphasized, but technical errors in the manipulation of the test as previously described are now recognized to have resulted in an erroneous
111
relation between the real unsaturation value and the dielectric instability of the oil-treated insulation. The test procedure used throughout the present study is as follows: Ten milliliters of oil at 25" C. are cooled to 15" C. in a Babcock sulfonation bottle, the neck of which is graduated for 10 ml. in 0.20-ml. divisions. To the oil is added a cold acid mixture consisting of concentrated (96 per cent) sulfuric acid containing 30 grams of phos horus pentoxide per 100 ml. This acid mixture is added in the &lowing portions until a total of 30 ml. have been added to the oil: 1 ml., 1 ml., 1 ml., 2 ml., 5 ml., 10 ml., 10 ml. After each acid addition the oil is shaken vigorouslyfor 15seconds and the mixture cooled to 15' C. After the acid mixture has all been added, the oil is allowed to settle for one hour at 15-20' C. Sufficient concentrated sulfuric acid is carefully added to bring the oil level within the ran e of the graduated scale of the bottle. The acid mixture is then aflowed to settle overnight. The total unsaturation of the oil is determined as follows:
% total unsaturation
=
ml. of oil absorbed original vol. of oil used
The olefinic unsaturation is determined in the same manner, except that an acid mixture containfng 5 grams of boric acid in 100 ml. of concentrated sulfuric acid (96 per cent) is substituted for the phosphorus pentoxide-acid mutture. The aromatic unsaturation is determined as the difference between the total unsaturation and the olefinic unsaturation values obtained.
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I n general, the amount of acid required in the treatment of an oil depends on the character of the oil and the degree of refinement desired. The common danger in the manufacture of dielectric impregnating oils is that of overrefining. Excessive treatment will remove those products which have been found most necessary for the greatest dielectric stability of the oil-treated assembly. The properties of the oil as usually studied are of little value and may be grossly misleading. When 96 per cent concentrated sulfuric acid is used at 20" C. to refine the crude distillate, the character of the refined product, as judged by the usual tests; changes with the increased quantity of acid used. To best illustrate this, the properties of the oils obtained are shown in Figure 1; 500 ml. of the oil, after the acid-refining treatment, were aged for 96 hours a t 100" C.in a 600-ml. Pyrex beaker, placed in an
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FIGURE 1. EFFECT OF REFINING TREATMENT ON OIL STABILITY
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INDUSTRIAL AND ENGINEERING CHEMISTRY
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air oven with a constant supply of conditioned air. The stability of the oil as gaged by its color, acidity, and power factor after the aging treatment increases with the increased quantity of sulfuric acid used. It has already been demonstrated (2) that the presence of chemically unsaturated hydrocarbons plays a major part in determining the dielectric suitability of mineral oil as an impregnant for cellulose insulation in high-voltage use. Unsaturated hydrocarbons such as the olefins, diolefins, and acetylenes are, in general, readily attacked by sulfuric acid.
The aromatic hydrocarbons are less easily attacked, although they are considerably more reactive with sulfuric acid than are the paraffins. As the quantity of 96 per cent sulfuric acid is increased at 20' C., the unsaturation of the oil decreases with respect to both the olefinic and aromatic types of unsaturation (Figure 2). There is, however, no critical value in the relationship which could be accepted as a guide to the proper amount of refining treatment to yield the most suitable product for dielectric use. On the other hand, since it has already been demonstrated (2) that the presence of olefin unsaturation is objectionable, the conclusion might be drawn that the best product obtainable would be that involving the use of excessive amounts of sulfuric acid. From the data submitted, such an oil product would have the maximum stability in color, acidity, and power factor, and would be most free from the objectionable olefinic hydrocarbons. If applied, however, this conclusion would lead to the manufacture of a dielectric product ill-suited for commercial use. This is best illustrated by reference to the behavior of the cellulose insulation treated with oils prepared by the use of varying quantities of 96 per cent sulfuric acid a t 20" C. The impregnated test specimen used in demonstrating the fundamental differencesbetween mineral oils of varying types of refinement as impregnants for high-voltage cellulosic dielectrics is designated as a stamp capacitor. In its simplest form, as used in this paper, the stamp capacitor has a dielectric pad consisting of eight sheets of 0.0127-mm. linen paper giving a total thickness of 0.102 mm. The dielectric is assembled between 0.0762-mm. aluminum foil electrodes, the edges of which are carefully prepared to eliminate burrs. The whole is assembled between glass plates and held in position by means of phosphor bronze clips. The dielectric pad is 7.62 X 5.07 cm. in area. The electrodes are 5.72 x 3.18 cm. After assembly the stamp capacitors are dried a t 100' C. for 48 hours under a pressure of less than 0.3 mm. of mercury, after which the capacitors are impregnated with the degassed mineral oil a t the same temperature and pressure. The power factor values reported are the test average
75.C CAPACITOR
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Vol. 34, No. 1
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DIELECTRIC
January, 1942
INDUSTRIAL AND ENGINEERING CHEMISTRY
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A typical set of results showing the change in the 60cycle power factor of the oil-treated insulation as affected by 4.0 the refining treatment used in the preparation of the mineral 4.0 3.8 oil is given in Figure 3. Since the ultimate dielectric stability 3.8 of the treated insulation can best be analyzed from a study 3.6 3.6 of the 10-week power factor value, families of curves of the g-1 3.4 3.4 type illustrated in Figure 3 are not reproduced here. A g 3.2 3.2 study of the dielectric stability of the oil-treated insulation 3 3.0 3.0 is made using the 28 za 10-week life test5 2.6 4.2 power factor as the 2.6 2.4 gage. Such studies 4.0 2.4 9 2.2 clearly illustrate the 3.8 22 2.0 fallacy of conclusions 3.6 2.0 = 1.8 based on the beaker 3.4 1.8 1.6 type of laboratory $ 3.2 I.6 test analysis. 6 1.4 3.0 1.4 Figure 1 (upper 2 1.2 12 graph) illustrates the g E 1.0 1.0 improvement in oil P $ .8 .8 color stability which 6 accompanies the exe2 6 .4 4 haustive treatment of .P the crude distillate .2 with 96 per cent conb 1.6 0 0 16 17 18 19 2 0 21 22 23 24 25 0 1 2 3 4 5 6 7 8 9 c e n t r a t e d sulfuric 1.4 % AROMATIC UNSATURATION PERCENT OLEFINIC UNSATURATION 6 acid a t 20" C. The s 1.2 FIGURE 5. EFFECT OF OLEFINIC AND AROMATIC UNSATURARON life-test dielectric sta1.0 ON DIELECTRIC STABILITY OF CELLULOSE IMPREGNATED WITH bility of the treated g TREATED OIL insulation, however, bQ .6 contradicts such an IO4 106 108 110 I12 114 116 118 120 observation. Figure SPECIFIC DISPERSION, 25.C. of five individual capacitors measured a t 60 cycles and 500 ( l e f t ) indicates FIGURE7. RELATIONBETWEEN that a n i m p r o v e volts per mil (19.68 kv. per mm.). Life endurance tests are SPECIFIC OPTICALDISPERSION OF ment in the dielecTHE OIL AND DIELECTRIC STABII~ carried out a t 75" C. and 812 volts per mil (31.9 kv. per mm.) tric stability accomITY OF OIL-TREATED INSULATION with the stamp capacitor always immersed in the oil, the panies the decrease in surface of which is exposed to 75" C. air with full freedom oil color only to a of oxidation. Linen capacitor paper is used as the solid l i i i t e d degree, beyond which further decrease in oil color. dielectric because it is free from contaminating materials and is accompanied by a decreased dielectric stability of the it can be obtained in thin sheets; the need for extremely high treated insulation. Figure 1 (center graph) indicates that the tendency to acid generation in the'oil is decreased with the increased treatment of the distillate with 96 per cent concentrated sulfuric acid a t 20" C., a t least to the point that 4.4pounds of acid per gallon of distillate are used. Beyond this point the lack of sensitivity of the acidity test used prevented distinction between the relative acid-forming tendencies of the oils examined. However, Figure 4 (center) clearly indicates that the dielectric stability of the treated insulation is seriously impaired as the acid treatment of the oil is carried beyond the ratio of 4.4 pounds per gallon distillate. Figure 1 (lower graph) illustrates the fact that the power 217 I < I factor of the mineral oil after a 96-hour aging test a t 100' C. 16, improves with exhaustive acid treatment. The improved oil power factor, however, is not reflected in an increased dielectric stability of the treated insulation. Figure 4 (right) demonstrates that, as the oil itself decreases in power factor after the 96-hour oxidation test at 100" C. as the result of a more severe acid treatment, the improvement is reflected in the greater stability of the oil treated-insulation during the 10-week life test only to a limited extent. A rapid decrease in the dielectric stability of the treated insulation is observed beyond a refining treatment of about 6.6 pounds of acid per voltages to secure the dielectric stress desired is thus eliminated. The life-test voltage stress applied is such that no gallon of distillate even though further acid treatment does dielectric breakdown normally occurs during the investigaresult in a greater dielectric stability of the oil itself when tested alone. tion. The 60-cycle, one-minute step-up, dielectric strength test of the oil-treated capacitor so prepared is from 2000 It is important to observe that an oxidation run of only ko 2500 volts per mil. 96 hours a t 100' C. gives but mild oxidation. It might be 4.4 4.2
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FIGURE 9. EFFECT OF TEMPERATURE OF ACID TREATMENT ON DIELECTRIC STABILITY OF OILIMPREGNATED PAPER
The same sort of critical behavior is observed when the unsaturation of the oil is studied, The olefinic and aromatic unsaturation values are each reduced by exhaustive acid treatment of the oil (Figure 2 ) . The stability of the oiltreated insulation, however, is not correspondingly improved. The suggestion has already been made that the principal cause of dielectric instability in oil-treated paper is the presence of the olefinic type of unsaturated compound (3). The
Vol. 34, No. 1
presence of aromatic hydrocarbons has been found to give increased dielectric stability to the oil-treated dielectric ( I , 3). The problem in the practical refining of the oil is to reduce the amount of olefinic unsaturation below the dangerous limit without severe reduction in the quantity of the aromatics present. The oil-treated insulation of this study (Figure 5) reaches its greatest dielectric stability with an olefin unsaturation corresponding to approximately 2 per cent and an aromatic unsaturation of about 22.5 per cent. These data are not accepted as demonstrating that it is undesirable to remove olefinic unsaturation below the 2 per cent value, but rather that to do so reduces the aromatic content of the oil t o a 5.5 v a l u e which decreases the stability 5.0 of the treated insulation. & 4.5 I n discussions concerning the con5 tent of aromatic hyf 4*, drocarbons in mineral oil, the specific dispersion value is 3.5 4 f r e q u e n t l y used. 3.0 The relation established between the specific dispersion value and the aromatic unsatura2.0 tion value as deB termined by the 1.5 method already de5 scribed is illustrated 11.0 in Figure 6. Such a relation leads to .I the conclusion illustrated in Figure 7 0 that the oils showing 0 10 20 30 40 50 60 70 80 90 I O 0 the greatest dielecACID TREATINQ TBYPERATLRB C. tric stability in the FIGURE 10. EFFECT OF INCREASED treated insulation TEMPERATURES OF REFINING ON are those having a DIELECTRICSTABILITYOF OILspecific dispersion IMPREGNATED PAPERVSING 0.73 value in the range POUXD OF 96 PER CENT CONCENTR4TED SULFVRIC ACIDPER GALLON of approximately OF O I L 115 to 117. Since the specific dispersion value. however. does not give proper recognition to the important effects accompanying the presence of olefinic compounds, the use of the experimentally determined aromatic and olefin unsaturation values are preferred. In view of the important differences between the stability of mineral oil when tested alone and in the form of the treated insulation, it is concluded that, from the standpoint of practical utility, final decision must be made on the basis of the behavior of the oil-impregnated insulation; it is in this combination of materials that the most critical demands are imposed on the oil in high-voltage commercial use. Such a decision leads to the conclusion (Figure 8) that, when Gulf Coast crude distillate of the type studied is refined by 96 per cent concentrated sulfuric acid a t 20" C. for use as a dielectric impregnant in high-voltage apparatus, the treatment should be 3.5 to 5.5 pounds of acid per gallon of oil. Refining of the oil distillate to this extent gives the maximum dielectric stability t o the treated insulation even under severe conditions of oxidation and electric stress. Such an
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INDUSTRIAL AND ENGINEERING CHEMISTRY
January, 1942
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FIQURE 11. EFFECT OF CONCENTRATION OF FURIC ACID AT Two TEMPERATURES ON DIELECTRIC STABILITY OF OIL-TREATEDCELLULOSE INSULATION
The temperature of the oil refining process is of great importance in attaining the most stable dielectric product. Higher temperatures are effective in removidg the desirable aromatic hydrocarbons as well as the objectionable olefins and asphaltic substances present in the oil. Furthermore, the sulfonation of the aromatics and' esterification of the olefinic compounds proceeds more rapidly a t the higher treating temperatures. Since such products are objectionable for the best dielectric stability, the problem of obtaining an improved dielectric impregnating oil can be made more difficult by the application of an indiscriminately selected temperature for the oil treatment. Using 4.4 pounds of 96 per cent concentrated sulfuric acid per gallon of oil, the most stable product is obtained when the acid treating temperature is approximately 20" C. Figure 9 illustrates t comparative life-test stability of the treated insulation afte impregnation with oil which has been acid-treated at 20" and 50" C. using 96 per cent concentrated sulfuric acid. The advantages of the lower temperatures are obvious
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FIQURE 13. EFFECT OF FULLER'S EARTH TREATMENT OF OIL ON DIELECTRIC STABILITY OF IMPREONATED CELLULOSE INSULATION
The application of mineral insulating oil is not closely associated with oil color but is associated with resistance t o oxidation. The special nature of the oxidation resistance, however, is evident; for unlike the relation illustrated in Figure 9, the refining of oil for lubricating uses can frequently be carried out at moderately high temperature with economic advantage and without loss in oxidation resistance (6). FIQURE 12. COMAttempts to prepare mineral impregnating oil a t higher PARATIVE STABILITY OF CELLULOSE IN- temperatures than 20" C. have invariably resulted in a prodSULATION AT 30" AND uct more unstable dielectrically even though the quantity of AT 75' c. AFTER IMacid has been greatly reduced below that found most adPREqNATION WITH vantageous a t the lower treating temperature. Figure 10 D,IS,TI L L A T E 0 I L WHICH HAS BEEN illustrates the dielectric instability after an oil is treated with REFINED WITH FUM96 per cent concentrated sulfuric acid in limited amounts INQ SULFURIC ACID (0.73 pound per gallon), above 20' C. The dielectric stability (2 P O U N D S P E R of the product is in no instance comparable with the stability GALLON OF OIL) AND WITH 96 PERCENT obtained when the same crude distillate is treated with 96 ACID (4.4 POUNDS per cent acid a t 20" C. in the ratio of 4.4 pounds per gallon PER GALLON OF OIL) (Figure 8).
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The concentration of the acid used for treating a distillate depends upon the purpose for which the refined oil is intended. As an impregnant for high-voltage dielectrics, 96 per cent concentrated acid is most effective in reducing the undesirable olefinic type of unsaturation without excessive reduction in the aromatic hydrocarbon content whose presence appears essential in order to obtain maximum dielectric stability.
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INDUSTRIAL AND ENGINEERING CHEMISTRY
Figure 11 (left) correlates the power factor for the vacuumdried capacitor after impregnation with the oil refined at 20” C. with sulfuric acid varying in concentration from 96 to 70 per cent. .I n each instance 4.4 pounds of the acid were used per gallon of oil treated. The dielectric instability of the oil-impregnated cellulose after the use of the weaker acid a t 20” C. is not eliminated when the acid-refining treatment is carried out a t a higher temperature. The data in Figure 11 (right) show the behavior of the capacitors impregnated with oil treated with sulfuric acid of varying concentration a t 50” C., using 4.4 pounds of acid per gallon of oil. Fuming sulfuric acid (20 per cent SO3) has not been found advantageous for the treatment of insulating oil. Despite its more efficient action in removing the dielectrically unstable olefin hydrocarbons, its drastic action on aromatic hydrocarbons is difficult to control. The reduction in the aromatic content of the oil has invariably been too severe to obtain the greatest dielectric stability. Typical results are illustrated in Figure 12 which compare the life test behavior of capacitors treated with the distillate oil after refining treatment with 96 per cent concentrated acid and with fuming sulfuric acid. As usual in dielectric tests of this type, the greatest instability of the dielectric appears in the tests a t the higher power factor testing temperature.
Vol. 34, No. 1
nated insulating oils is well known. One of the common adsorbents in commercial use is fuller’s earth. Under its influence, olefinic compounds can be removed by adsorption without drastic effect on the aromatic hydrocarbon content. Figure 13 compares the dielectric stability of capacitors impregnated with an oil prepared with 4.4 pounds of 96 per cent sulfuric acid per gallon of oil a t 20” C., followed by the “standard” fuller’s earth treatment already described, and the stability of capacitors prepared with the same oil after a similar fuller’s earth treatment applied five consecutive times. The additional earth treatment reduced the olefinic concentration from 3.5 to 2.5 per cent without significant change in aromatic unsaturation. The result is increased dielectric stability for the treated insulation. However, since exhaustive treatment of the oil with an adsorbent such as fuller’s earth has been found to remove, or a t least to reduce, the aromatic hydrocarbon content, excessive and uncontrolled treatment of the oil with the adsorbent must be avoided if the maximum dielectric stability is to be obtained.
Literature Cited
Use of Adsorbents
(1) Berberioh, L. J., IND.EN@. CHEIII., 30, 280-6 (1938). (2) Clark, F. M., Ibid., 31, 327-33 (1939). (3) Clark, F. M., Proc. Am. Sac. Testing Materials, 40, 1213-34 (1940). (4) Kattwinkel, R., Brenmtof-Chem., 8, 353-8 (1927). (5) Typke, K., Petroleum Z.,22, 751-6, 774-8 (1926).
Adsorbents are extensively used in the petroleum industry. The use of these materials for the reclamation of contami-
PREISENTED as part of the Symposium on Electrical Insulation Materials before the Division of Industrial and Engineering Chemistry a t the 102nd Meeting of the AMERICAN CHEMICAL SOCIETY, Atlantic City, N. J.
Amino Acid Composition of
Cottonseed Globulin Preparations T. D. FONTAINEI, H. S. OLCOTT2,AND ALEXANDER LOWY hlellon Institute and University of Pittsburgh, Pittsburgh, Penna. A CONTINUATION of the studies on the preparation and properties of the cottonseed proteins ( l a , IS,I J ) , a partial analysis of the amino acid composition of the globulin fraction has now been completed. In the light of recent developments in new methods of isolation and new uses for the vegetable proteins, the composition of the protein potentially available in the largest quantities assumes increasing importance. Calculated for the yields here recorded, the 4,000,000 tons of cottonseeds processed in 1940 contained 400,000 tons of globulin. Furthermore, the recent innovations in amino acid procedures have made possible the determination of some components not previously described. #Finally,detailed information on the amino acid make-up of a protein moiety is instructive in the determination of protein structure and nutritive properties. Previous studies on the amino composition of the cottonseed globulins were reported by Abderhalden ( I ) , Friedmann (6),Jones and Csonka (7), and others, and will be referred to in the experimental part. After unsuccessful attempts to 3
Present address, Southern Regional Research Laboratory, New Orleans,
La. Present address, Western Regional Research Laboratory, Albany, Calif.
prepare a crystalline globulin, it was decided that an analysis of the whole globulin would be as useful as a series on preparations obtained by salt fractionation methods. Unpublished observations indicate that the proteins analyzed contained a number of separable globulin fractions. Jones and Csonka (7)described the fractionation of a cottonseed globulin preparation.
Preparation of Protein Fractions Three globulin preparations were compared. Two were obtained by acid precipitation of an alkaline extract of cottonseed meal in a modification of the method described by Nickerson (12);the second differed from the first only in that further steps of re-solution and re-precipitation were involved. The third preparation was obtained by dilution of a salt extract of cottonseed meal. Dehulled cottonseed meats from the 1939 crop were obtained through the courtesy of W. H. Jasspon of the Perkins Oil Company, Memphis. They were ground in a burr mill to pass a 20-mesh screen and then extracted with ethyl ether in a large-scale Soxhlet-type extractor (18 pounds capacity) for 3 to 4 days. The oil- and gossypol-free meats were dried
