INDUSTRIAL A N D ENGINEERING CHEMISTRY
36
Vol. 17, No. 1
Effect of Sulfides on the Alkaline Hydrolysis of Skin and Hair' By Henry B. Merrill A. F. GALLUN& SONSCo., MILWAUKBE, WIS.
N A previous communication2 the comparative hydrolysis Sulfide Absorption and Hydrolysis of Skin and Hair of skin and hair was studied as a function of pH value, In comparing the action of sulfides on skin and hair, series time, and temperature. The extent of hydrolysis in any given experiment was taken as the per cent of the total nitro- were run in which increasing amounts of NaSH or Ca(SH)* gen in the sample which passed into solution during the course were added to saturated Ca(OH)2 containing an excess of of the experiment. The materials used were purified calf solid lime. The digestion period was one day, and the hair and purified calf skin. It was shown that hair is some- temperature was 2 5 O C. The results of these experiments what more readily hydrolyzed than skin by alkaline solu- are given in Tables I and I1 and in Fig. 1. Attention is called to the tions. Between the DH striking difference between values 7 and 13 (appr;xiSulfides have no influence on the hydrolysis of skin, exthe behavior of hair and mately) the rate of hydrolcept in so far as they alter the alkalinity of the solution. skin. In the case of hair, as ysis of both materials is In the case of hair a t any given alkalinity the rate of hythe concentration of the sdsmall and nearly independrolysis increases with the concentration of sulfide, and fide is increased the amount dent of pH value, but as a t any given sulfide concentration the rate of hydrolysis of hair hydrolyzed is the pH value is increased increases with the alkalinity. The rate of hydrolysis of markedly augmented; with above a critical value the hair by alkali alone is very much increased if the hair is skin, on the other hand, rate of hydrolysis increases previously treated with alkali sulfide for a short time. there is scarcely any invery abruptly. If the per It is concluded that the hydrolysis of hair in alkaline crease in the per cent of cents of the total nitrogen solutions containing sulfides takes place i n two steps: h y d r o l y s i s , except when dissolved a r e plotted (1) a reaction between hair and sulfide, and (2) a reaction verylarge amounts of NaSH against pH values, the rebetween altered hair and hydroxide. This conclusion has are added to the lime. A sulting curves lie almost been verified by experiment. second important difference Darallel to the horizontal lies in the fact that in the ;xis until the critical pH value is reached and then turn upward at an angle of nearly case of hair considerable amounts of sulfide are absorbed or 90 degrees. If the temperature is increased, or the time otherwise removed from the solution, whereas in the case of of digestion lengthened, the principal effect is to shift the skin no sulfide is taken out of solution. The apparent conclusion is that the hydrolysis of hair in sulfide liquors is critical pH towards the region of lower alkalinity. In the experiments described in this paper, the work on the connected with the absorption of sulfide from the solution. comparative hydrolysis of skin and hair has been extended I-HYDROLYSIS OF SKIN AND HAIRIN SOLUTIONS OB C A ( O H ) Z + NASH t o include the effect of sulfides on the hydrolysis. The object TABLE (Time, 1 day: temperature, 25' C.) was, first, to obtain exact data on the effect of sulfides on the -KINr HAIR (SH) - PER LITER Per cent M o w (SH) - PER LITER Per cent hydrolysis under definite conditions of hydrogen-ion concen- MOLS Before After hydrolyzed Before After hydrolyzed tration, time, and temperature; and, second, to learn from None None 1.62 None None 1.56 0.01 0.01 0.76 0.01 0.005 1.85 these data as much as possible concerning the mechanism 0.038 0.036 1.62 0.05 0.05 1.62 0.05 0.037 5.17 of the action of sulfides on skin and hair. 0.094 2.65 0.094
I
Experimental Methods
The method was the same as that employed in the previous study. A definite quantity of purified hair or skin was treated with a definite quantity of the sulfide liquor under sexamination, for a definite time, a t a definite temperature. After digestion, the nitrogen which had passed into solution was determined in an aliquot of the filtered liquor, and the per cent of the total nitrogen which passed into solution was taken as a measure of the hydrolysis. The amount of sulfide absorbed was determined by analysis of the liquor before and after digestion, using the volumetric zinc-precipitation method with nitroprusside indicator. The solutions employed were (1) NaOH NaSH; (2) .Ca(OH)z NaSH; and (3) Ca(OH), Ca(SH)2. NaSH was prepared by passing pure HzS into 2 N NaOH, until the solution contained Na+ and (SH)- in equivalent amounts, as shown by analysis. Ca(SH)2 was prepared in a similar manner by passing HpS into a suspension of Ca(0H)S.
+
+
+
1 Presented before the Division of Leather and Gelatin Chemistry at Septemt h e 68th Meeting of the American Chemical Society, Ithaca, N. Y., ber 8 to 13, 1924. a Merrill, THIS JOURNAL, 16, 1144 (1924).
0.10 0.120 0.15 0.20 0.25 0.30 0.40 0.50 0.75
i:oo
0.10 0.126 0.15 0.20 0.25 0.30 0.40 0.50 0.75 1.00
1.40 1.70 1.74 1.52 1.90 2.09 2.37 2.75 4.47 6.75
0.10
0.076
11.37
0.15 0.20 0.25 0.30 0.40 0.50 0.75 1.00
0.120 0.134 0.188 0.240 0.350 0.440 0.640 0.90
24.75 43.52 59.03 66.93 77.25 79.10 81.69 84.86
Hydrolysis of Hair and Concentration of Sulfide
Here we are confronted with the difficulty that it is not possible to change the concentration of sulfide without a t the same time changing another very irnportant variable, the hydrogen-ion concentration. Moreover, the magnitude of the change in pH value produced by the addition of sulfide to a lime liquor cannot be accurately measured in the presence of large amounts of sulfide, owing to the poisoning action of the sulfide on the hydrogen electrode and the color reactions which sulfides seem to undergo with aU the indicators suitable for the pH range in question. This difficulty was overcome by the following procedure: A series of solutions was prepared, all containing the same amount of NaSH, and containing increasing amounts of NaOH. The amount of sulfide was made small in order that the effect on the pH value might
January, 1925
INDUSTRIAL A N D ENGINEERING CHEMISTRY
be as small as possible. The pH values of these solutions were calculated from the concentrations of NaOH and NaSH. and the hydrolysis constant of NaSH. The results obtained'with such a series gave the effect of increasing OH concentration on the hydrolysis of hair, at a constant SH concentration. Other series were run a t different concentrations of sulfide. The results of these series, when per cent of hydrolysis was plotted against pH value, gave a series of curves, and the vertical distance between any two curves gave the difference in per cent of hydrolysis caused by a difference in sulfide concentration, a t a constant pH value. The results of these experiments are given in Table I11 and Fig. 2. It will be seen (1) 1 that a t any given sulI fide concentration the rate of hydrolysis increases with increasing I pH value, and (2) a t , any given pH value the rate of hydrolysis increases with increasing I sulfide concentration. I We may now discuss the curves in Fig. 1representing the hydrolysis of hair as a function of sulfide concen4 so t tration, in solutions (1) of saturated Ca(OH)% NaSH, and (2) of 20 2 saturated Ca(OH)2 Ca(SH)Z. I n t h e 10 I t former case both the p H value and the sulfide concentration are increased as the conlsx~-. pel. l i t e r FIQ. HYDROLYSIS OF SKIN AND HAIRA S A centration of NaSH is FUNCTION OF SULFIDE CONCENTRATION increased. This reTime, 1 day sults in a very rapid inTemperature, 25' C. crease in the per cent of hydrolysis with increasing sulfide concentration. In the second case the pH value is decreased as the concentration of Ca(SH)Z increases, owing to the repressive action of the added calcium salt on the solubility of lime. We thus have a system in which two factors, having an opposite effect on the hydrolysis of hair, are being varied simultaneously, and the result is the irregular curve shown in the figure. It should be stated that this curve is the result of two entirely independent sets of measurements, so that the maxima are not the result of experimental-error.
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Sulfide Absorption and Hydrolysis of Hair as a Function of Sulfide Concentration
We have seen that in solutions of NaSH or Ca(SH)2 the hydrolysis of hair increases with increasing sulfide strength, at a given pH value. We have seen that sulfide is absorbed by hair and is not absorbed by skin, upon which the sulfide seems to have no action. The conclusion might be drawn that the sulfide exerts a direct solvent action on hair, and that the amount of sulfide absorbed should bear a definite ratio to the amount of hair dissolved. TABLE 111-HYDROLYSIS OF HAIRAS
A FUNCTION OF PH VALUE, AT DIFFERCONCENTRATIONS OF (SH) (Solutions, NaOH NaSH; time, 1 day; temperature, 25' C.) MOLS(SH) PER LITBR Per cent pH value Before After hydrolyzed 12.00 None None None 12.4 None None None 12.7 None None 0.35 13.0 None None 0.80 11.5 0.018 0.011 1.56
ENT
+
12.0 12.4 12.7 12.85 13.0 11.5 12.0 12.4 12.7 12.85 13.0
1
! I
-
-
0.018 0.018 0.018 0.018 0.018 0.047 0.047 0.047 0.047 0.047 0.047
0.011 0.010 0.010 0.010 0.011 0.029 0,030 0.029 0.029 0.029 0.029
1.29 2.15 2.15 3.03 7.04 2.05 3.03 5.48 8.95 11.75 14.52
J.4
+
+
MOlS
S K I N AND HAIRIN SOLUTIONS OF C A ( O H ) z f Cn(SH)z (Time, 1 day; temperature, 25' C.) 7 SKIN HAIR-MOLS(SII) PER LITER Per cent MOLS(SH) - PER LITERPer cent Before After hydrolyzed Before After hydrolyzed None None 1.62 None None 1.79 0.004 0.003 1.17 0.011 0.006 2.09 0.011 0.005 1.44 0.027 0.022 3.42 0.025 0.010 1.97 0.038 0.026 2.54 0.052 0.055 3.04 0.050 0.034 3.48 0.064 0.044 3.52 0.078 0.082 3.23 0.075 0.052 2.29 0.086 0.064 2.93 0.104 0.112 2.00 0.100 0.078 2.35 0.180 0.132 2.00 0.124 0.098 3.42 0.144 0.116 7.44 0.160 0.160 3.04 0.150 0.124 3.42 0.180 0.188 2.09 0.200 0.200 1.78 0.200 0.156 8.29 0.255 0.260 1.91 0.300 0.300 2.00 0.300 0.255 10.35 0.324 0.287 10.57 0.365 0.322 9.99 0.40 0.40 2.19 0.40 0.360 9.50 0.50 0.50 2.46 0.50 0.420 10.40 0.59 0.536 12 73 0.64 0.64 1.43 0.64 0.610 14130
TABLEIV-RELATION BETWEEN SULFIDE ABSORPTION AND HYDROLYSIS OB' HAIRAT DIFFERENT SULFIDE CONCENTRATIONS (Solutions, NaSH Ca(0H)t; time, 1 day; temperature, 25' C.)
+
---MOM Before 0.01 0.05 0.10 0.15 0.20 0.25 0.30 0.40 0.50
-
(SH) PER LITERAfter Absorbed 0.005 0.005 0.037 0.013 0.076 0.024 0.120 0.030 0.134 0.066 0.188 0.062 0.240 0.060 0.350 0.050 0.440 0.060
Ratio absorbed sulfur to dissolved nitrogen 1.25 1.16 0.980 0.554 0.701 0.487 0.407 0.299 0.350
Mols nitrogen dissolved per liter 0.0040 0.0112 0.0246 0.0541 0.0942 0.1280 0.1470 0.1673 0.1713
In Table IV data have been collected to show the absorption of sulfide and the amount of hair hydrolyzed at different initial sulfide concentrations. It will be seen that, in general, the amount of sulfide absorbed increases with increasing sulfide concentration, as does also the amount of hair hydrolyzed. However, when examining the ratio between the sulfide absorbed and the hair dissolved, it is seen that no constancy exists; neither does the amount of sulfide absorbed stand in any simple relation to the initial sulfide concentration.
TABLE11-HYDROLYSIS OF
-
12.2 12.4 pH Value
FIG.2-HYDROLYSIS
12.6
12.8
OF HAIRAS A FUNCTION O F pH VALUE INITIAL CONCENTRATIONS OF SULFIDE Solutions, NaOH f NaSH Time, 1 day Temperature, 25' C.
AT
DIFBERENF
INDUSTRIAL A N D ENGINEERING CHEMISTRY
38
It cannot be assumed then, that the mechanism of the hydrolysis of hair in solutions containing sulfides is a direct reaction between hair and sulfide, resulting in the formation of soluble decomposition products of the keratin, with concomitant using up of the sulfide ion. Sulfide Absorption and Hydrolysis of Hair as a Function of Time
The conclusion drawn in the last paragraph is borne out by the results obtained when sulfide absorption and hydrolysis of hair are studied over varying time intervals. The results of such a series of experiments are found in Table V and in Fig. 3. The hydrolysis of hair is practically a straight-
90 83
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Vol. 17, No. 1
TABLE VI-EFFECT
OF R A T I O OF HAIRTO SOLUTION ON HYDROLYSIS 01 HAIRAND ABSORPTION OF SULFIDE (Solutions, Ca(0H)a Ca(SH)r; time, 1 day; temperature, 2S.O C.) Hair Solution MOLS(SH) PER LITER-GRAMS NITROGEN-Per cent Grams Cc. Before After In sample Dissolved Lrdrolyzed 0.25 150 0.124 0.116 0.0358 0.0059 16.48 150 0.124 0.114 0.5 0.0716 0.0088 12.81 150 1.0 0.124 0.108 0.1430 0.0143 10.00 150 0.124 0.108 2.0 0.2860 0.0227 1.94 150 0.124 5.0 0.104 0.7160 0.0370 5.17
+
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Mechanism of the Action of Sulfides on Hair
In the preceding discussion, the following facts hare been brought out: 1-Sulfides increase the hydrolysis of hair at a given pH value, but have no appreciable hydrolytic action on skin. 2-Sulfide is absorbed by hair but not by skin. 3-No definite relation has been found between the amount of sulfide absorbed and the amount of hair hydrolyzed, 4-In the absorption of sulfide, equilibrium is established in a few hours. The hydrolysis of hair, on the other hand, continues at a nearly uniform rate for days. 5-In the presence of sulfide, the effect upon the hydrolysis produced by increasing the pH value of the solution is very much greater than in the absence of sulfide.
These facts lend themselves to the following interpretation: 1-There is a reaction between keratin and the SH ion.
2-This reaction so alters the structure of the protein that the residues are more readily attacked by the OH ion.
Stiasnys long ago showed that the unhairing of skins was dependent upon both the sulfide and the hydroxide concentraHe found that the best results were obtained in the FIG.3-HYDROLYSIS OF HAIRA N D ABSORPTION OF S U L F I D E AS A FUNCTION tions. OF TIME presence of equivalent amounts of SH and OH, and that inSolutions, Ca(SH)r 4- Ca(0H)a creasing SH beyond this ratio had an inhibiting influence on Temperature, 25O C. the unhairing. This is true over a small range of sulfide line function of time, but practically all the absorption of sul- concentration, as is shown in one of the curves of Fig. 1. fide takes place in the first half hour. From this it is clearly The effect, however, is due to the diminution of the pH value. evident that the solution of the hair is not determined by the If the concentration of OH ions is maintained constant, the effect of increasing sulfide concentration is to increase the absorption of sulfide alone. amount of hair dissolved, no matter what the ratio of OH to SH may be. TABLE V-HYDROLYSISOF HAIRAND ABSORPTION OF SULFIDE AS A FUNCTION 2
4
Tlme
- 6days
OF
(Solutions, Ca(0H)r Per cent Time hydrolyzed Before 15 min. 2.06 0.136 30min. 1.66 0.136 lhour 1.37 0.138 2hours 2.84 0.136 2.06 0.136 4hours 8hours 3.33 0.136 16hours 6.17 0.136 lday 7.54 0.136 2days 12.68 0.136 4days 28.80 0.136 14days 88.00 0.136
lo
8
12
14
TIME
+ Ca(SH)e;temperature, 25’ C.) MOLS(SH) - PBR LITER -ABSORBEDAfter 0.124 0.112 0.120 0.112 0.112 0.112 0.106 0.106 0.104 0.100 0.089
Total 0.012 0.024 0.016 0.024 0.024 0.024 0.030 0.030 0.032 0.036 0.047
By blank By sample 0.000 0.012 0.000 0.024 0.000 0.016 0.000 0.024 0,000 0.024 0.000 0.024 0.001 0.020 0.001 0.029 0.002 0.030 0.004 0.032 0.015 0.032
Absorption of Sulfide and pH Value
As will be seen from Table I11 the amount of sulfide absorbed is independent of pH value, at a given initial sulfide strength. Hydrolysis and Sulfide Absorption as a Function of the Ratio of Solution to Hair
When increasingly large doses of hair are treated with equal volumes of solution, the amount of nitrogen dissolved increased with the size of the sample, as might be expected (Table VI). The per cent of the total nitrogen digested, however, decreases with increasing ratio of sample to solution. This has obvious practical bearings, since, presumably, a certain fraction of the hair and epidermal system must be hydrolyzed before satisfactory unhairing will take place. The quantity of the sulfide absorbed by the hair increases with increasing quantity of hair present, but not nearly in the same proportion.
Test of the Theory
From the hypothesis suggested to explain the facts observed
to be connected with the action of alkaline sulfides on hairnamely, that the action goes on in two steps, the first being a rapid reaction between keratin and sulfide and the second being the hydrolysis of the altered keratin by the hydroxide-a prediction may be made. If this hypothesis is valid, after the reaction between hair and sulfide has occurred the further hydrolysis should go on just as well in a solution free from sulfide as in the solution in which the initial sulfide-keratin reaction took place. This prediction was tested by the following experiment: Two samples of hair were treated with the same solution of Ca(0H)z and Ca(SH)a. Sample A was digested for 24 hours. In the case of Sample B, however, four-fifths of the sulfide solution was replaced by limewater after one hour. The digestion was then continued for the 24-hour period. Nitrogen determinations were made on the removed liquor from 3,and on the final solutions obtained from A and B. Sulfide determinations were made on the same solutions. A third sample, C, was digested with a lime-sulfide solution made so as to have the same final sulfide concentration as the solution in contact with B, after the replacement of the initial solution with lime water. The nitrogen dissolved in the period between the end of the first hour and the end of the twenty-fourth hour was oalculated. The results are given in Table VII. : G @ b n , 84 (1906); J . Soc. Leuthn Trades’ Chem., 8, 129 (1919): Scrcncc, 57, 483 (1923).
INDUSTRIAL A N D ENGINEERING CHEMISTRY
January, 1925 TABLEVII-EFFECT
OF CONCENTRATION O F S U L F I D E ON
HYDROLYSIS OF
HAIRAFTER INITIAL DIGESTION (Solutions, Ca(0H)z 4- Ca(SH)*; temperature, 25' C.)
-GRAMS NITROGEN DIGESTEDIn period -?VIOLS (SH) PER LITERStart 1 hour 24 hours 1 hour 1 to 24 hours 24 hours 0 0971 0 1102 0 0131 0 119 0 098 0 098 0 019 0 0131 0 0801 0 0932 0 119 0 098 0 019a 0 0013 0 0097 0 018 0 0084 0 018 0 026 a 120 cc. of liquor replaced by Ca(OH)*solution after 1 hour
Sample A B
c
-
I n general, the results of this experiment are in accordance with the theory. This is certainly true in a qualitative sense. The amount of nitrogen dissolved between the end of the first and twenty-fourth hours is very nearly as great in the case of Sample R, where the bulk of the sulfide
39
solution was removed after one hour, as in Sample A , where the entire quantity of sulfide was left in contact with the sample for the full digestion period. On the other hand, the nitrogen digested in this period in Sample B is sixty times as great as in a solution of the same sulfide concentration, Sample C, in contact with hair which had not been previously treated with stronger sulfide. Acknowledgment
The avthor wishes to acknowledge his indebtedness to J. A. Wilson, under whose direction this work was carried out, for his many helpful suggestions and kindly criticisms during the cohrse of this investigation.
Effect of Some Inorganic Salts on the Polarization of Sugar Solutions' Preliminary Data2 By Robert J. Brown GREATWESTERN SUGAR Co., DENVER, COLO.
showed that the effect of a Within the limits o€ analytical error, the effect of certain salt on the polarization of polarization of sucrose salts on the polarization of sugar in solutions of the conin solution is at times sucrose was proportional to centration of thin juices is proportional to the amount of afferted by the presence of the amount of sugar present both the salt and the sugar present. as well as to the amount of nonpolarizing impurities, It would appear possible to determine the effect of insalt present, when working the inorganic compounds organic salts on the polarization of sugar solutions, of low with solutions having a conapparently having greater concentration, by determining the value of K a t high coneffect than the organic comcentration of as low as 5 centrations, thus reducing the relative error. pound. The extent of this grams of sugar per 100 cc. As yet no salt has been found which, when present in the effect, especially with inorThe writer has therefore amountof 5 per cent on sugar in a solution of the concenganic salts, was of interest attempted to check Jackson tration of thin juice, affects the polarization to the extent in connection with the deand Gillis' later results, of 0.01 degree, when using not more than a normal weight working with solutions of velopment of a method of of the solution made to 100 m l . analysis whereby the purity still lower sugar concentraIf, as is indicated by results of Jackson and Gillis, the of a thin juice may be detion, and to prove that the effect of any salt on the polarization of 'invert sugar is termined with an accuracy effect of a salt on the polarsomewhere near double its effect on that of sucrose, the ization of sucrose in solution of * 0.1 per cent. This actrue sugar in thin juices may be determined by enzyme is proportional to both the curacy in purity requires inversion without taking the effect of the salt into account. amount of salt and amount that the sugar be deterof sugar mesent. If this is mined with an accuracy of = t O . O l Der cent. true, the writer's formula for determining the per cent sugar The fiterature on this subject is somewhat limited. The present will resemble that of Jackson and Gillis, their constant, data are apparently confined to three sources. Bodenben- K , for salt being divided by 100 and the formula being der and Steffen3showed the effect of a salt on the polarization Per cent sugar = P KPM of sucrose to vary with the concentration of both the salt and when P is the polarization, and M the weight in grams of the the sucrose, but failed to show any mathematical relationship. salt present in 100 ml. of the solution as read in the polariJackson and Gillis4showed that when keeping the concentration of sugar constant a t 26 grams per 100 cc., the effect of a scope tube. given salt on the polarization of the solution was proportional Apparatus and Experimental to the amount of the salt present in the solution. Later, in a [discussiontouching upon this subject carried on between 811 polarizations were made using a Bate's type Fric Jackson and Gillis6 and C. A. Browne,B Jackson and Gillis polariscope, using only one 400-mm. jacketed polariscope 1 Presented before the Division of Sugar Chemistry a t the 67th Meeting tube, all readings being made at 20' *0.1' C. of the American Chemical Society, Washington, D. C., April 21 to 26, 1924. The work was done on 12- to 15-degree sugar solutions, the 2 The primary object in presenting data a t this time is to obtain an amount taken for polarization ranging from 0.5 to 4 N weight exprerision from others as to the effects which they have found, and thus of solution. In some cases sugar was weighed directly into save cluglication of work. 3 Browiie, "Handbook of Sugar Analysis," p. 184. the flask in the desired amount, but generally a standard 4 B u r . S t a n d a r d s , Sci. P a p e r 375. sugar solution was used. The salt was added by pipetting the 6 L o u i s i a n a Planter, 66, 141 (1921): Facts about S u g a r , 13, 10 (1921). desired amount from a standard solution. Solutions were @ L o u i s i a n aPlanter, 66, 109 (1921); Facts about S u g a r , 12, 230; 13, made to volume by a carefully standardized mark, or by 50 (1921). See also Hinton, I n t e r n . S u g a r J.. 24, 420 (1921).
I
'IF IS well known that the
+
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