The Silk-Soaking Process*

action between the silk sericin and the soap-alkali. There is developed at the same time, probably as a result of the decomposition of the soap by the...
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980

INDUSTRIAL AND ENGINEERING CHEMISTRY HNOI

GALACTOSE

Mol 0.056 0.056 0.111 0,222

Mol 0.386 0.386 0.386 0.386

_____

CONCN.OF HNOi

Per cent 33.6 33.6 33.6 33.6

Table VII-Oxidation CONCN. OF

”0s

Mol 0.111 0.222

Mol 0.386 0.388

Percent 33.6 33.6

TIME OF HNOa LEFTIN HNOs DRIVENFROM Loss OB OXIDATIONMOTIIER LIQUOR OXIDATION VESSEL HNOa

Hours

1 2.3 1 1

Mol 0.255 0.197 0.179 0.082

Mol 0.131 0.189 0.207 0.304

Mol 0.018 0.048 0.038 0.070

Loss OF

M

~

$MUCIC ~ACID ~

HNOa

Moruna T,mrrna

PPI’.

Per cent 4.57 12.46 9.92 18.22

Mol 0.078

Md 0.010 0.016 0.019 0.015

0.088

0.145 0.248

of Glucose: Effect of Various Factors on Nitric Acid Loss a n d Organic Acid Yield

TIMEOF HNOa LEFTI N “Os Loss OF OXIDATIONMOTHER LIQUORF R o ~ ~ ~ ~ rHNOa l o M

Hours 1 1

Vol. 22, No. 9

of Galactose: Effect of Various Factors on Nitric Acid Loss a n d- Oreanic A r i d Yield ~.~~ _~__.~..

Table VI-Oxidation

Mol 0.110 0.039

Mol 0.276 0.347

sugar acid into oxalic and other acids of small molecular weight. However, fair agreement of the molar sums for each group of experiments in which the amount of xylose taken wa.s constant indicates that the relative amounts of monobasic and dibasic acids can be approximately ascertained by the procedure used. For more accurate analyses of the mother liquors the pure acids must be studied electrometrically and their ionization constants determined in order to select, if possible, indicators which will effectively reveal the respective amounts o€ monobasic and dibasic acids present. The probability of the presence of other oxidation products of these acids, such as oxalic acid, or of the original sugars must also be considered. Further experiments are under way on a study of the mother liquors from the oxidation of these sugars, particularly xylose, to include means of separating the acids and identifying them and of developing methods for control analyses on the oxidation process.

Mol 0.044 0.071

TITEROF ORACIDSIN

HNOa

OF

M~~~~~ L~~~~~

Per cent 11.40 18.42

MI. 10 N N a O H 17.55 25.13

GANIC

MONOBASIC ACIDIN

DIBASIC ACIDIN

M~~~~~ LIQUORMOTHER LIQUOR Mol 0.146 0.113

Md 0.015 0.069

Oxidation of Galactose and Glucose

For comparative purposes a few oxidations of crude galactose and pure glucose were carried out. The results are set forth in Tables IV, V, VI, and VII. The procedure used was the same as that of the experiments with xylose, except that in the case of galactose the dibasic acid, mucic acid, precipitated, and was separated from the mother liquor by filtration before dilution. The losses of nitric acid and the organic acids produced .are found to be dependent upon the same variables that affected the xylose oxidations. Literature Cited (1) Acree. British Patent 160,777 (March 18, 1921); C. A . , 16, 2545 (1921). (2) Burdick and Freed, J . A m . Chem. Soc., 43,518 (1921). (3) Hall, Slater, and Acree, Bur. Standards J . Research, 4, 152 (1930): Schreiber, Geib, Wingfield, and Acree, IND.ENO.CHBM.,sa, 497 (1930). (4) Markley and Hann, J . Assocn. Oficial Agr. Chcm., 8,455 (1925). (5) Tollens, “Kurzes Handbuch der Kohlenhydrate,” p. 731,Leipzig, 1914.

The Silk-Soaking Process* I-Effect of Soap and Other Alkali on Silk Sericin Ralph Hart THE HARTPRODUCTS CORPORATION, 1440 BROADWAY, ~ ‘ E WYo=, N, Y.

It was shown that, when raw silk is soaked in a solution of soap, there is a marked decrease in the concentration of fatty matter and particularly of alkali in the solution. This is due to an adsorption by the silk and to the interaction between the silk sericin and the soap-alkali. There is developed at the same time, probably as a result of the decomposition of the soap by the sericin, a large amount of free fatty acids. Consequently the treated silk, as well

as the spent liquor, contains a considerable amount of free fatty acids. The quantitative distribution of the ingredient after soaking is given and the results graphically represented. It is also indicated that a small but constant fraction of the sericin is capable of reacting with excess alkali in the cold and that ita combining weight with alkali is probably on the order of fatty acids.

.............. HE cocoon of the silkworm produces simultaneously two continuous filaments which immediately upon spinning are cemented together into a single fiber by natural gum substance called “silk gum” or “sericin.” The fiiament proper or fibroin and the sericin are proteins of practically identical ultimate composition and somewhat similar chemical properties, though they differ greatly in physical characteristics. To produce the raw silk skein of commerce a number of cocoons are heated in hot water to soften the gum, their ends joined together, and the cocoons unwound simultaneously. They are then twisted to increase the “cohesion” of the individual fibers, and finally reeled on a swift,

T

1

Received May 19, 1930.

producing a skein of strands which is stronger, heavier, and more uniform than the individual filaments. The quality and strength of the thread, however, reeled at the filature is still insufficient for the purpose of knitting or weaving, and hence is subjected to a series of mechanical operations known as “throwing,” which consist of re-winding the silk on suitable holders, cleaning and in other ways rendering the fibers more uniform, and finally of doubling and spinning, or twisting a number of threads together. As a preliminary to throwing, the yarn is nearly always treated with an emulsion of oil and soap or their equivalents, which treatment may be done either by spraying or soaking. The function of the oil seems to be entirely physical and

~

September, 1930

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I N D U S T R I A L ‘4N D ENGINEERING CHEMISTRY

mechanical. Those suitable for the purpose should be good lubricants with little tendency to oxidize, gum, or turn rancid, and should be readily removed in the degumming process. The soap, on the other hand, besides displaying its familiar colloidal properties such as emulsification, penetration, adsorption, etc., seems to enter also into a true chemical reaction with the sericin or silk gum. This investigation was undertaken a t the request of a prominent throwster, who wished t o standardize the soaking operation in his plants as well as to acquire more fundamental knowledge about the process. That part of the investigation dealing with the effects of soap on the silk-gum forms the subject of this paper. Experimental Procedure

A skein of raw silk was heated to constant weight in a conditioning oven a t 110’ C. and then soaked for 24 hours a t room temperatures (28-30’ C.) in a water-tight container with five times its weight of a solution containing about 2.25 per cent anhydrous soap. The excess liquid was then removed by vigorous hand wringing, and the skein immediately weighed and again dried to constant weight. The liquor before and after soaking, as well as the dry soaked silk, was then analyzed for acidity, alkalinity, and total fatty matter. For the sake of simplicity the results given in this paper, unless otherwise stated, have been calculated on a basis of 100 grams original soaking solution and 20 grams of absolute or bonedry unsoaked silk. The yarn used throughout this work was a high-grade Japan silk, commercially known as Special Grand XX Pagoda Chop, 13/15 denier, and a product of the silkworm Bombyx mori. Because of the compartness of the sericin in this type of silk, producing a certain buoyancy upon soaking as well as resistance to degumming, it is also known as a hard-natured silk. The soap was illerck’s powdered sodium oleate, neutral, and distilled water was used in making the solutions.

compared with the adsorption by the silk, calculated as shown in Table I. The loss was found to be 0.41 gram, against an adsorption of 0.43 gram. The adsorption was equal to 2.1 per cent on the weight of the dry silk. Table I-Adsorption of Fatty Matter Fatty matter in 100 grams soaking liquor: Total fat as soap before soakmg, grams.. . . . . . . . . . . . . . . . . 2 . 3 8 Total fat as soap after soaking, grams.. . . . . . . . . . . . . . 1.97 0.41 Loss in fat as soap, grams.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fatty matter in 20 grams silk: Total fat as soap, grams.. . . . . . . . . . . . . . . . . . . . . . . . 0.99 Liquor absorbed, grams. . . . . . . . . . . . . . . . . . . . . . . . . . 2 8 . 2 Fat as soap in liquor, per cent . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.97 Total fat as soap due to absorbed liquor, grams.. . . . . . . . . . 0 . 5 6 Fat as soap adsorbed by silk, grams (0.99 0.56). . . . . . . . . . 0 . 4 3 2.15 Fatty matter as soap adsorbed, per cent of dry silk

-

Decomposition of Soap

Although in Table I the fatty matter is given as soap, this is true only in the case of the original soap solution, as the fat in the liquor after soaking and in the soaked silk was found to consist of a mixture of soap and fatty acids, formed apparently by the decomposition of the former during soaking. Takanashi (7) states that the fatty acid or acid soap liberated by the action of sericin during the degumming process is adsorbed on the fiber and protects the fiber better from the further action of alkali. Bray ( I ) investigated the effect of soap on wool, which, like silk, is a protein material, and finds that there is a chemical combination between the wool and alkali liberated by hydrolysis of the soap; also that the alkaline portion of the soap is adsorbed by the wool, leaving the fatty acid free either in the bath or deposited on the fiber. Sadtler and Lathrop (3) state that the pH value of the spent liquor from the silk soaking process is less than before soaking, and for re-use they add alkali to raise the pH value. They do not, however, explain the acidity. Scott (4) reports that, after degumming successively two batches of raw silk in the same bath, containing originally 2 per cent soap, the pH value of the solution dropped from 8.8 to 8.4, no degumming taking Determination of Fatty Matter place when the solution reached the lower pH value. He In determining fatty matter in the liquor after soaking, restored the degumming efficiency of the spent bath by adding by acidifying and extracting with ether, considerable difficulty 0.01 N caustic soda solution, having a pH value of 12.12. was experienced due to troublesome emulsions, apparently He attributes the buffer action of the spent degumming liquor caused by the sericin in solution. Shelton and Johnson ( 6 ) or gum suds, which is used as an assistant in dyeing silk, to observed that when a liquid immiscible with water i s shaken the dissolved sericin. It now seems that the buffer action with an aqueous solution of sericin a very stable emulsion may be due to the sericin only indirectly, and that the resresults, which upon standing or centrifuging creams in a toration of the degumming power to the bath by the addition separate layer. Both layers contained proteins, which, how- of alkali is probably due to the conversion of the fatty acids ever, differed distinctly in their physical behavior. I n this into soap. work it was found that upon shaking an acidified aqueous Under the conditions of the present experiment the acidities solution of sericin with ether, it separated into a clear, lower per gram of the liquor after soaking and of the soaked silk water layer and an upper, viscous emulsion that separated (Table 11)were 1.30 mg. and 2.65 mg. KOH, respectively, or, very slowly. Upon drawing off the lower layer and adding in terms of oleic acid, 0.65 and 1.33 per cent. That the acidity about 5 cc. of alcohol to the remainder with gentle mixing, was due to fatty acids was later confirmed by extracting the the emulsion liquefied immediately and separated into a turbid liquor (made 50 per cent alcoholic) with petroleum ether and lower layer, containing apparently a fibrous precipitate and an examining the residue upon evaporation. Persistent emulupper clear ether-layer. Boiling the solution for 1 hour with sions made it difficult to extract the liquor direct. It was about 25 cc. of strong hydrochloric acid practically eliminated therefore evaporated to dryness, dissolved in alcohol, filtered, the tendency to emulsify and was the procedure followed in the filtrate made 50 per cent alcoholic, and the fatty acid exthese experiments. tracted with petroleum ether. The reaction between the soap and raw silk with the formation of free fatty acids is probably Adsorption of Fatty Matter complete as soon as the silk is thoroughly wetted by the soluIt was found upon analysis that the total amount of fatty tion, for the acidity of the liquor after soaking 15 minutes matter deposited on the silk was considerably greater than was practically identical with that after soaking 10 days. that calculated from the quantity and the original concentraEvidently the formation of free fatty acids is the result of tion of the liquor retained by the silk after soaking. A care- an interaction between the alkali due to hydrolysis of the soap ful check of the liquor before and after soaking showed a and the silk sericin. The results given in Table I1 indicate definite decrease in concentration of the fatty ingredients; that part of the alkali in combination with the sericin remains hence, the excess deposited on the fiber is due either to a chemi- on the fiber while the rest diffuses in the liquor. Thus, in cal reaction or to an adsorption, most likely the latter. The the extraction procedure for free fatty acids described above, loss of fatty ingredients in the liquor was determined and the residue upon the filter paper, apparently the alkali-sericin

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INDUSTRIAL AND ENGINEERING CHEMISTRY

compound, was thoroughly washed with hot alcohol and ether, then dissolved in hot water and the total alkalinity of the solution determined, which was found to be 35.9 mg. KOH. The alkalinity could not be due to soap, since upon extracting the acidified solution with ether no fatty matter was obtained. I n the case of the soaked silk the sample, after thorough extraction with alcohol and ether to free it from soap and other fatty matter, was boiled in hot water and the total alkalinity of the water extract determined and found to be equal to 98.0 mg. KOH. According to Table 11, the combined alkalinities of the alcohol residue and the extracted silk were approximately equal to the total acidity developed-namely, 133.9 mg. KOH compared with 146.3 mg. KOH. The discrepancy is probably due to errors in the alkalinity determinations, since owing to lack of time, the method was not thoroughly investigated. It will also be noticed that the silk decomposed 31.6 per cent of the original soap, or about 3.7 per cent soap of its own weight. T a b l e 11-Alkalinities of Alkali-Sericin C o m p o u n d s Compared w i t h Acidities of Liberated F a t t y Acids; Percentage Decomposition of S o a p Alkalinitv of alcoholic residue from liauor: Weighi liquor, grams.. . . . . . . . . . . .-. . . . . . . . . . . . . . . . . . . . . 71.8 Alkalinity, mg. K O H per gram liquor.. . . . . . . . . . . . . . . . . 0.5 Total alkalinity, mg. K O H . , ....................... 35.9 Alkalinity of extracted silk: Weight silk, grams. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 0 . 0 Alkalinity mg. K O H per gram silk.. . . . . . . . . . . . . . . . 4.9 Total alkhnity, mg. KOH... . . . . . . . . . . . . . . . . . . . . . . . . 98.0 Combined total alkalinity, mg. K O H (35.9 f 9 8 . 0 ) . . . . . . . . . . 1 3 3 . 9 Acidity of liquor after soaking: Weight liquor, grams.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71.8 Acidity mg. K O H per gram liquor.. . . . . . . . . . . . . . . . . 1,30 Total aLdity, mg. KOH... . . . . . . . . . . . . . . . . . . . . . . . . 93.3 Acidity of soaked i l k : Weight silk, grams.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20.0 Acidity, mg. K O H per gram s i l k . . . . . . . . . . . . . . . . . . . . . 2 . 6 5 Total acidity, mg. KOH... . . . . . . . . . . . . . . . . . . . . . . . . . 5 3 . 0 Combined total acidities, mg. K O H (93.3 f 53.0). . . . . . . . . . 1 4 6 . 3 Decomposition of soap: Total alkalinity in liquor before soaking, mg. KOH... . . . . . 4 6 2 . 0 Per cent soap decomposed loo).. . . . . . . . . . . . . . 3 1 . 6 146.3 Soap decomposed, per cent of silk (200a 2o x 100) . . . . 3.7

(146.iG

-

a

Neutralization value of oleic acid in mg. KOH.

Another indication of the loss in soap and the presence of free fatty acids is the great drop in the surface tension of the liquor after soaking. This was determined with a Traube stalagmometer against a light viscosity medicinal mineral oil, and the results were as follows: water value, 13 drops; before soaking, 1235 drops; after soaking, 202 drops. Many throwsters, for fear that acidity may cause rusting, limit the free fatty acids in their soaking oils to a very low percentage, usually less than 0.1 per cent based on the silk. It was shown above that the fatty acids deposited on the silk as a result of the decomposition of the soap amounted to 1.33 per cent. This is more than ten times the quantity usually due to the soaking oil. The free fatty acids of the soaking oil, therefore, even if considerably in excess of the most liberal specification, can exert only a minor effect in comparison with the fatty acids due to the decomposition of the soap. However, in so far as the low fatty acid content is a criterion of the quality of the oil, it is a desirable specification. The soap most favored by throwsters is made either from olive oil or red oil (oleic acid). I n view of the appreciable quantity of free fatty acids deposited on the fiber after soaking (as a result of the decomposition of the soap), their tendency to oxidize or gum becomes of considerable importance. Red oil, in common with other fats of animal origin, is more objectionable in this respect than a vegetable product with a similar iodine number. The sgne objection would hold in case of the triethanolamine soap of red oil. Recent research (2) indicates that this tendency may be greatly reduced by introducing antioxidants in the oil. The foregoing statements are made with no personal experience as to the rela-

Vol. 22, No. 9

tive merits of the two kinds of soap in so far as their oxidizing or gumming properties are concerned. Adsorption of Alkali

As already mentioned, Bray (1) observed that wool absorbed alkali. He soaked a skein of wool in a 0.3 per cent solution of sodium oleate for 1 hour a t 130' F. (54.5' C.) and found that the concentration of alkali in the solution was r e duced 12.7 per cent. He attributes the absorption entirely to a chemical reaction between the wool substance and the alkali liberated from the soap by hydrolysis. Thus, less alkali was absorbed from a soda soap than from a potash soap solution, since the latter is supposedly more hydrolyzed. I n the case of silk, the loss of alkali concentration in the solution (under conditions of these experiments) was about twice as great as Bray reported for wool (see Table IV). In this connection i t is to be noted that the loss in concentration of alkali in the liquor is due to two factors-namely, to an adsorption of soap by the silk and to the alkali-sericin compounds remaining on the fiber. I n Table 111an attempt is made to account for the original alkali after the soaking. It will be observed that the alkalinity in the original solution amounted to 462 mg. KOH, compared with 475.8 mg. KOH, the total alkalinity recovered in the liquor and silk after treatment. It will also be noted that the drop in concentration of alkali in the liquor after soaking amounted to 27.7 per cent, and that the silk adsorbed 0.64 per cent alkali, expressed as caustic potash. Table 111-Distribution of Alkali after Soaking Alkali in liquor before soaking: Weight liquor, grams. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .100 Alkalinity, mg. K O H per g r a m . . . . . . . . . . . . . . . . . . . . . . . . 4.62 462.0 Total alkalinity, mg. KOH.,. . . . . . . . . . . . . . . . . . . . . . . Alkali in liquor after soaking: Weight liquor, grams., . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71.8 Alkalinity, mg. K O H per gram.. . . . . . . . . . . . . . . . . . . 3.34 Total alkalinity, 239.8 . . mp. - KOH... . . . . . . . . . . . . . . . . . . . . . Alkali in soaked silk: Weight silk, grams. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20.0 Alkalinity extracted fatty matter, mg. K O H per gram silk. 6.90 Total alkalinity in extracted fatty matter, mg. K O H 1 3 8 . 0 4.90 Alkalinity fat-free silk, mg. K O H per gram s i l k . . . . . . . . . . 98.0 Total alkalinity fat-free silk, mg. K O H (20 X 4.90). . . . . . . Combined total alkalinity, mg. K O H (138 f 98). . . . . . . . . . 236,O Combined alkalinities in liquor after soaking and in soaked silk, mg. K O H (239.8 236). . . . . ~. . . ; . . . . . . . . . . . . . . 4 7 5 . 8 Decrease in concentration of alkali in liquor, per cent 27.7 (4.624;23.34) x loo] ............................

+

[

Alkali adsorbed by silk, (4.62 3.34) 100

-

2o

as

per

cent

caustic

potash

...................................

1o

0.64

Table IV gives the rate of absorption of alkali by 20 grams of raw silk soaked in 100 grams of soap solution. The maximum absorption, it will be noted, was about 28 per cent of total alkali. Equilibrium was practically reached after 8 hours' soaking, and the absorption after 15 minutes was about 50 per cent completed, whereas beyond 24 hours there was practically no change. Table IV-Rate

of Absorption of Alkali by Raw Silk f r o m S o a p Solutions, at R o o m Temperatures

ALKALINITY OF N ~ , ORIGINAL

I

MFg%H

SOAKING

PER

GRAM

ALKALIABSORBED Mg. K O H per gram of s o h .

Per cent in soln.

Per cent of av. absorption after 24 hours

0.64 0.88 0.88 1,18 1.32 1.20 1.15 1.10

14.1 20.0 20.0 24.5 27.9 28.3 26.8 27.0

50.5 71.6 71.6 87.8 100.0 101.2 96.0 90.7

-

oig$

Distribution of Ingredients

The quantitative distribution of the soap and the products of reaction in the liquor and on the fiber after soaking, enumer-

I-VDUSTRIAL .4ND ENGINEERING CHEMISTRY

September, 1930

ated in Tables I to IS’, inclusive, is summarized in Table VI in which are also given the respective quantities adsorbed and absorbed by the silk. It will be observed that the raw silk adsorbed 0.4 per cent oleic acid and 1.6 per cent soap, or a total of 2.0 per cent, based on its own weight. The same data, calculated per 100 mg. KOH of total alkalinity in the original solution, are shown graphically in Figure 1. Table V-Distribution

of Ingredients after Soaking TOTAL QUANTITY

&E. K O H % Acidity in solution after soaking.. , . , . , . . 93.3 Alkali in solution: Original solution.. . . . . . . . . . . . . . . . . . 462.0 After soaking.. . . . . . . . . . . . . . . . . 239.8 As alkali-sericin compounds. . . . . . . . . . 35.9 As soap, by difference... . . . . . . . . . . . . 203.9 Acidity in silk: Total . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53.0 1.3” Absorbed (28.1 X 1.3).. . . . . . . . . . . . . 36.5 O.ga Adsorbed, by difference.. . . . . . . . . . . . . 16.5 0.4a Alkali in silk: As soap: Total ............................ 138.0 3.5s 74.2 1.9b Absorbed 128.1 (1.97X 2 1.3)).. . . 1.6b Adsorbed, by difference., . . . . . . . . . . 63.8 A s alkali-sericin compounds: .i.. . . 98.0(*) Total. ..................... -4bsorbed (28.1,X 0.5).. . . . . . . . . . . . 14.1 Adsorbed. bv difference.. . . . . . . . . . . 83.9(*) 0 Oleic acid equivalent based on weight of raw silk b Sodium oleate equivalent based on weight of raw silk

-

inn

P... ~...R . MG. KOH

ORIGINAL SOLN. M E . KOH 20.2 100.0 51.9 7.8 44.1

983

of solution, or 250 mg. per 100 grams of original liquor. The liquor after soaking, however, was still strongly alkaline and, in spite of its high p H value, no more alkali was adsorbed. There was considerable swelling of the fibers during the caustic soda soaking, which was evident from the fact that the amount of liquor retained by the silk aftJervigorous wringing was about 200 per cent of the weight of the dry silk, compared with a p proximately 130 per cent, the average for soap soakings. When soaked in sodium carbonate solution, the results were similar to soakings in straight soap solutions. I n the soda ash soaking the alkalinity was reduced from 5.60 mg. to 4.13 mg. KOH per gram of solution, or a total decrease in alkalinity of 147 mg. KOH per 100 grams of original liquor, compared with 146.3 mg. KOH, the amount of alkali absorbed by the sericin in a soap soaking.

11.5 7.9 3.6 29.9 16.1 13.8 21.2(==) 3.1 18.l(==)

Nature of Alkali-Sericin Compounds

During the course of this work there were indications that the quantity of sericin that reacts with excess alkali in the cold varies only within narrow limits. According to Table I1 the total free fatty acids in the liquor and on the fiber after soaking were equivalent to 146.8 mg. KOH, which also represents approximately the amount of alkali adsorbed by the sericin. This figure probably does not measure the total amount of alkali with which the sericin is capable of reacting, since the liberated fatty acids undoubtedly suppress the hydrolysis of the soap before the adsorption or neutralization is completed. The raw silk was therefore soaked in mixtures of soap (same concentration as heretofore) and caustic soda, giving solutions of higher pH values than straight soap. T’arious amounts of caustic soda were added until the liquor after soaking for 24 hours showed only a trace of free fatty acids. This was taken to indicate that there was sufficient free alkali present to satisfy adsorption by the sericin. The alkali necessary to attain this result was found to be 2.4 mg. KOH per gram of solution, or a total of 240 mg. KOH for the 20 grams of silk or 100 grams of the original liquor. A similar result was obtained by a different method. A sample of the previously soaked silk was extracted with alcohol, dried, and soaked again in fresh soap solution, under the same conditions as the original soaking. The liquor after the second soaking was then tested for acidity and found to contain 0.7 mg. KOH per gram, compared with 1.3 mg. KOH after the first soaking. This procedure was repeated on the same sample of silk and the acidity of the liquor after the third soaking determined. This was found to be practically nil, indicating that the adsorption had probably been completed by the successive treatments. The total acidity in the various solutions and on the silk was then calculated with the following results: after first soaking, 146.8 mg. KOH; acidity after second soaking, 82 mg. KOH; acidity after third soaking practically none, or a total of 228 mg. KOH compared with 240 mg. by the previous method. A somewhat sirmlar decrease in the amount of alkali was observed when the silk was soaked in straight caustic soda solution, having a concentration of 4.58 mg. KOH per gram of solution. The concentration after treatment was reduced to 2.02 mg. KOH or a loss of 2.56 mg. KOH per gram

///CUhS

g

a

0 .

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/‘

udrrcrbed

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Concentration soap solution e4.62 mg. KOH Ratio soap solution to silk = 5:l Figure’l-Distribution of Ingredients in Silk a n d Liquor after Soaking, per 100 mg. KOH of Original Solution

During this work there were occasions to determine the amount of sericin dissolved in the liquor after soaking (under the usual conditions, the dissolved gum amounted to less than 1 per cent of the weight of the silk), and its adsorption or neutralization equivalent seemed to be on the order of fatty acids. It would be interesting to know the relation between the alkali-sericin compounds as obtained in these experiments and the two fractions of sericin mentioned by Shelton and Johnson (6). Acknowledgment The writer acknowledges his thanks and indebtedness t o George W. Searell, chief chemist for Kahn & Feldman, Brooklyn, N. Y., throwsters and silk merchants, for suggesting this investigation and particularly to Herman Feldman, treasurer of the same company, for extending the facilities of their plant and laboratory for this work. Literature Cited (1) Bray, A m . Dya5lu.f Rept., 18, 24 (1929). ENG.CHEY.,22, 341 (1930). (2) Mattill and Crawford, IND. (3) Sadtler and Lathorp, U . S.Patent 1,671,786(May 29, 1928) (4) Scott, Am. Dyesluf RePf., 14, 145 (1925). (5) Shelton and Johnson, J. Am. Chem. Soc., 47, 412 (1925). (6) Shelton and Johnson, IND.END.CHBY.,22, 387 (1930). (7) Takanashi, through C. A , , 22, 2843 (1928).