INDUSTRIAL AND ENGINEERING CHEMISTRY
February, 1927
243
for the production of these products is caused by lower tem- ripe sludge and fresh solids is kept correct and constant, diperatures and additions of lime, the protozoa are more numerous under these conditions. At higher temperatures and additions of lime, when these bacteria are rapidly replaced by other groups producing different intermediate compounds, protozoa numbers are necessarily low. P r o p e r Reaction In a previous publication4 it has been shown that exclusion of air induces liquefaction of the organic material. This liquefaction can be changed by proper reaction and proper temperature to gasification. With the increased rate of digestion, odors are naturally intensified. The digestion time in days for treated and untreated material a t different temperatures is as follows: 10°C. Untreated Limed
360 325
18'C. 200 150
24OC.
142 108
29.5'C. 61 54
35'C. 89 108
The figures represent the minimum time necessary for digestion of material before sludge drawing and not until digestion is complete. It must be borne in mind that these figures are given for unseeded material. If the relation of 6
New Jersey Agr. Expt. Sta., Bull. 427.
gestion time decreases again considerably. Summary Digestion is extremely slow a t temperatures below 10" C. Raising the temperature a few degrees above 10 has comparatively little effect. Digestion time is materially decreased with higher temperatures. Maximum digestion takes place at about 27-28' C . Definite quantities of organic material present in sewage produce about the same volume of gas a t all temperatures. The volume of gas produced from the same sewage sludge can be increased by changing the reaction of the medium and the composition of the gas changes due to a preponderance of different organisms. In a given time the average number of bacteria per gram organic matter in unadjusted sludge does not increase with increase in temperature, whereas the average numbers of bacteria in lime-treated sludge decrease with the increase in temperature. In a same given time protozoan numbers (mainly small flagellates) follow t.he bacterial numbers. Keeping the material a t the proper reaction (pH 7.3 to 7.6) decreases digestion time still further. The composition of the gas changes with the reaction of the medium.
Behavior of Formaldehyde-Tanned Hide Powder toward Chromium Compounds' By K. H. Gustavson WIDEN-LORD
TANNINQ CO.,
OMPARATIVE studies of hide protein proper in the form of hide powder, of the protein in different degrees of aggregation, and of hide powder pretreated with other agents resulting in structural alteration of the hide protein offer a promising method of attack of problems in protein chemistry in general and the mechanism of tanning processes in particular. This paper deals with the behavior of chromium compounds toward hide powder and toward the powder pretreated with formaldehyde. The nature of the action of formaldehyde upon proteins is, as most problems in leather chemistry, still a much debated but unsettled problem. Of all types of tannages, the one with formaldehyde is generally considered to be purely chemical in nature. The investigations of Bergmann and his collaborators* in regard to the nature of reaction products between amino acid, piperazines and related structures, and formaldehyde demonstrate the manifold possibilities of this reaction. Besides the primary amino groups, other basic groups seem to participate in the formaldehyde combination. From the view of the internal salt structure of aliphatic amino acids and types similar to diketo-piperazines as the elementary units in the protein aggregates, the action of formaldehyde may be considered to consist in a chemical combination with the basic groups and a simultaneously occurring breaking-up of the closed structure. Bjerrum3 has pointed t o the fact that the Sarensen amino acid titration is quantitative first
C
1 Presented before t h e Division of Leather and Geliitin Chemistry at the 72nd Meeting of the American Chemical Society, Philadelphia, Pa., September 5 t o 11. 1926. * Bergmann, Collegium, 1943, 210; 1914, 209; Bergmann, Jacohsohn, and Schotte, Ibid., 1923, 345; Bergmann, Ulpts, and Carnacho, Ibid., 1922, 352; Bergmann and Ensslin, Ibid., 1926, 493; Bergmann and Miekeley, Bcr., 67, 662 (1924). 8 Z. physik. Chem., 104, 147 (1923).
DANVZRS, MASS.
29. In the isoelectric state the aliphatic amino acids exist mainly as internal complexes: hence, only a slight fixation of formaldehyde can take place in this pH range. By activation of amino groups by the formation of the sodium salt (by addition of alkali), the reaction proceeds and is quantitative a t pH 29. Similar considerations may be useful in the treatment of the protein-formaldehyde problem. It is also a well-known fact that part of the formaldehyde is held in reversible combination with the protein. Secondary valency phenomena and adsorption reactions are probably responsible, a t least in part, for this particular behavior. The view of an inactivation of basic protein groups and activation of the acidic groups by the formaldehyde treatment is supported, among many facts, by the following findings: at pH
The isoelectric point of gelatin after this treatment is shifted toward the acid side with reference t o the original isoelectric point.' The combining capacity of such treated hide powder toward alkali hydroxide is increased and also the stahility of the resultant alkali compound, a fact in harmony with the view of activation of acidic groups as resulting from combination with formaldehyde.6 Acid dyestuffs show a marked decrease in their affinity toward formaldehyde-collagen as compared to collagen proper, indicating a less number of available basic protein groups for this reaction.6 Further indication of the justification of this concept is offered by the decrease in acid binding capacity of the hide powder after formaldehyde treatment, first observed by Stiasny.' His Gernwross and Bach, Collegium, 1922. 350; 1923, 377. Gerngross and Loewe. Ibid., 1922, 229. I Gerngross, Ibid. 1920, 565; 1921, 169. 7 Ibid.# 1908, 132. 4
6
244
I S D USTRIAL A N D ESGI-YEERING C H E X I S T R Y
finding was later confirmed by Gerngrosss and Fahrion 9 Stiasny was led by this fact to the belief that formaldehyde tannage is chemical in nature. This a t a time when this eminent investigator strongly advocated the colloidal or physical view of the mechanism of tannages.
VOl. 19, No. 2
solutions were added in 200-cc. portions. The reaction lasted for 48 hours. Comparative series were run a t the same time under exactly the same conditions. Electrometrical pH determinations were made on the residual solutions after separation from the tanned stock. The analytical procedure has been described in a previous paper.
It is thus evident that we possess most conclusive proof in favor of the view of the formaldehyde-protein combination being principally a chemical reaction affecting the basic protein groups. The fixation of formaldehyde by hide protein increases with concentration of the formaldehyde in solution, whose pH greatly affects the extent of combination. The difficulties encountered in quantitative evaluation of this fixation as a function of pH are evident from the paper of Thomas, Kelly, and Foster,'O where, also, an excellent critical review of previous work is given. The pH range between 6 and 8 is indicated to be most favorable for the formaldehyde tannage. This finding is supported by the industrial procedure in this method of tannage.I1 Reactions which are considered to involve principally the basic protein groups are as a rule retarded by this combination of protein with formaldehyde. The decreased fixation Grams CHiO in 100 cc. solution of pretannage of acid has previously been noted. Vegetable tannins and Figure 1-Effect of Increasing Formaldehyde-Tannage of Hide Powder (at pH = 8.0) upon Its Rate of Combination with acid dyestuffs show also a diminished rate of and capacity Chromium I-40.2 per cent acid chromic sulfate liquor of concentration 9.5 grams for combination.12 Simple ionic reactions taking place by CrrOs per liter. II-63 per cent acid chromic sulfate liquor of concentra. means of the acidic protein groups show increased reactivity, tion 14.0 grams crzo3 per liter. as, for example, the fixations of sodium and potassium hyResults droxides. The fixation of chromium from the common basic The effect of increasing concentration of formaldehyde in chromic sulfates is reported by Gerngross to be decreased by the formaldehyde tannage.13 The contrary behavior has the pretanning bath (at the optimal pH of 8.0) on the fixation also been reported.14 Similar contradictory statements in of constituents of chromic sulfate is shown in Table I and regard to fixation of tannins and other tanning agents are to illustrated graphically in Figure 1. be found in the literature. This unsatisfactory state of The formaldehyde tannage was carr;ed out in well-buffered affairs is probably due not solely to inaccuracy of methods solutions (KHzPOd + KOH) at p H = 8.0. A 40.2 per cent acid but also, as is made likely in this investigation, to the different chromic sulfate liquor (neutralized 63 per cent acid chrome and uncontrolled conditions of the pretreatment with formal- liquor) diluted t o a concentration of 9.5 grams CrlOa per liter immediately before the start of the experiment, possessing both dehyde. cationic and anionic chrome complexes, was employed in the Experimental Procedure
Portions of hide powder equal to 5.00 grams collagen were treated for 48 hours under continuous rotation with 100-cc. portions of formaldehyde solution, in concentrations and with initial pH of solutions as noted in the tables. The treated hide powders were then washed free from formaldehyde and alkali. The latter was removed with great difficulty from specimens tanned a t great alkalinity. Repeated washings and drummings for several days, however, secured a nearly ashless and completely alkali-free formaldehyde-hide powder, even under these conditions. Preliminary experiments showed that the degree of hydrolysis of hide protein in presence of formaldehyde was practically independent of the pH values of solution in the range employed in this investigation. Under identical conditions, the percentage of hydrolyzed hide protein based on the total amount was 1.4 and 1.7 for pretannage at an initial pH of 8 and 12.2, respectively. The treated hide powder specimens were finally taken to "dryness" on hardened filter paper in Buchner funnels and their moist weight ascertained. Fortions of hide powder equal to 5.00 grams collagen were used as blanks after soaking for 12 hours in 100 cc. of water and taken to about the same moisture content, All hide powders were brought to the same moist weight-the maximum recorded-by addition of the necessary amount of water, and the chrome Collegium, ieao, 2; 1921, 169, 288. Ibid., 1920, 125. 10 J . Am. Leather Chcm. Asroc., 11, 57 (1926). 11 Hey, J . Intern. Soc. Leather Trades' Chem., 6 , 131 (1922). I f Gerngross and Roser, Collegium, 1912, 1. 1) Ibid., isai, 489. $4 Griliches, Ibid., 192!4, 199, 286; Thuau, Cuir, 1, 201 (1909). 8
0
first series. A cationic liquor of 63 per cent acidity in a concentration of 14.0 grams Cr203 per liter was used in the second series. Table I-Influence of Increasing Degree of Formaldehyde Tannage of Hide Powder upon Its Fixative Capacity toward Chromic Sulfate .~ (DHof uretannane solution 8.0)
-
CC. Per cent Per cent Per cent Per cent 40.2 Per Cent Acid Chromic Sulfate (9.5 Grams CrrOa fief liter) Equal Cathodic and Anodic Migration 23.31 39.8 14.10 60.5 0 3.57 62.5 17.84 37.6 3.56 11.15 0.8 64.1 16.22 37.2 3.55 10.41 2.0 9.65 66.3 14.56 36.8 4.0 3.545 13.85 36.0 6.0 3.545 9.38 67.7 8.0 3.54 8.95 69.7 12.84 35.2 2 0 . 0 3 . 5 4 8 . 3 5 68.4 12.54 3 5.0 ~. .. Per Cent Acid Chromic Sulfate Liquor, (14.O Grams CrrOa per liter) Cathodic Migratran 11.43 59.8 69.4 3.03 7.93 0 10.44 58.2 70.3 3.02 7.34 0.8 9.94 57.4 70.3 3.01 6.97 2.0 9.32 67.6 70.7 3.01 6.59 4.0 9.06 56.5 71.0 3.005 6.43 6.0 8.86 56.8 72.0 3.00 6.38 8.0 8.62 56.2 71.5 20.0 3.00 6.16
Grams/100
1 2 3 4 5
6 7 63 1 2 3 4 5 6 7
The effect upon chrome fixation of the H-ion concentration during pretannage is treated in Table 11. These tests were made in well-buffered 2 per cent formaldehyde solutions. A 40.2 per cent acid sulfate liquor in concentration of 10.6 grams CrlOs per liter in freshly prepared state was used for the first series, while a 63 per cent acid chrome liquor containing 10.5 grams CrzOa per liter and treated under identical conditions gave the results reported in the second part of the
table. '5
Gustavson and Widen, THISJOURNAL, 17, 577 (1926).
I N D USTRIAL:ASD ENGINEERING CHEMISTRY
February, 1927
Table 11-E5ect of pH Values during Formaldehyde Pretannage upon Degree of Chrome Fixation by Formaldehyde-Collagen Compound PH O F SOI,CTIOS F O R PORNALDEHYDE TAKNACE
SO.
100
(>RAMS
40.2 Per Cent Acid Sulfate Liquor 2.45 7.0 8.0 10.0 11.0 Blank (regular hide powder) 6 3 Per Cent Acid Chrome Liquor 2.45 7.0 8.0 10.0 ii.0 Blank (regular hide powder)
COLLAGES
10.54 9.38 9.16 10.37 10.96 10.68
of C h r o m i u m by Hide Powder a n d hyde-Treated Powder
Grams CrzOs/liler
Formalde-
CRzOa COMBINED WITH 100 GRAMS COLLAGEN Hide powder Grams
pH
=
8.0
Grams
3.12 3.12
pH = 12.2 Grams
3.32 3.40
~~
1
3
4
5
FORMALDEHYDE POWDER
N ~ TRATION , OF So-
PH
= 8.0 PH = 12.2 CrzO3 Acidity O f on chrome- Crz03 on Acidity of CrzOa on Acidity of collagen collagen colchromecolchromebasis compound lagen collagen lagen collagen basis compound basis compound
Grams CnO, 9er liter Per cent Per cent Per cent Per cent Per cent 6 3 Per Cent Acid Chromic Sulfate Liquor" 6.2 10.40 57.2 9.88 53.2 10.92 12.12 12.4 11.20 12.60 57.9 53.6 12.82 18.7 11.88 13.62 58.5 53.4 13.20 24.9 12.42 13.87 58.8 55.2 12.65 13.57 37.4 59.4 54.8 14.88 12.52 13.10 62.3 60.7 55.2 15.00 12.14 93.5 12.22 14.38 62.9 56.7 10.79 155.8 11.36 13.94 66.7 58.2 37 Per Cent Acid Chromic Sulfate Liquorb 5.85 20.33 11.7 28.38 17.5 24.64 23.4 21.00 35.1 16.90 46.8 14.39
44.5 Per Cent Acid Chromic 7.4 8.25 14.8 10.08 27.7 12.29 37.1 12.60 74.2 13.41
Chloride 6.84 8.30 10.32 11.07 12.26
10.86 12.83 16.14 16.72 20.91
Some of the data obtained are given in Tables 111and IV. Graphs are shown in Figures 2, 3, 4, and 5. In Table V are given data from a series with different chromium compounds, using regular hide powder and the same formaldehyde-tanned with the use of buffers at pH values of 7.0 and 12.0 in 1 per cent formaldehyde solutions.
Per cent 54.3 55.5 55.7 56.1 56.0 57.9 57.4 57.8
a Sucrose reduced. b With NazCOa-neutralized 63 per cent acid chromic sulfate liquor in freshly prepared state.
Table V CRZOS COMBINED WITH 100 GRAMS COLLAGEN
CHROME LIQUOR Nature
Concentratior
FORMALDEHYDE HIDE POWDER
Hide powder pH
Grams Crz03 per liter Grams 40.9 per cent acid chrome liquor 10 0 22.87 in concentration g./l. CrzOa 15:0 20.74 10.96 607, acid chrome sulfate liquor 12.70 of concentration g./i. ~ r z ~ a 10.64 69% acid chromic chloride of concentration g./l. CnOs 12.5 5.61 60% acid chromic chloride of concentration g./l. CrzOs 9.5 6.93 44.57, acid chromic chloride of 7.55 concentration g./1. CrzOa 2; 16.06 15.03 11 2b Sulfito compounda 1315~ 27.24 Basic made sodium oxalatochromiated 10.0 5.90
{
{ {
i
=
7.0 pH = 12.0
Grams 21.83 16.80 9.85 11.67 10.99
Grams 27.58 29.04 11.48 13.53 12.68
4.60
6.58
6.21 6.42 14.36 10.77 24.65
7.29 10.21 21.75 18.48 35.46
4.36
4.48
63 per cent chromic sulfate containing 3NazS0~:CrtO~. b 5-week-old solution. e Freshly prepared. d pH 4.92 at equilibrium. (I
-
A basic aluminum sulfate solution of 66 per cent acidity and a concentration of 12.5 grams A1203 per liter in equilibrium gave the following amounts of 8 1 2 0 3 combined with 100 grams of collagen:
Formaldehyde hide powder
92.5 Per Cent Acid Chromic Suljate
2
HIDEPOWDER CONCENLUTIONS
23.16 15.86 15.10 22.74 23.40 21.94
Formaldehyde-tanned hide powder prepared in the pH range near true neutrality shows diminished capacity for chrome fixation. For extremely basic liquors of colloidal character and containing electronegative complexes besides the complex cations, high and low pH values of the solution for pretreatment leads to increased chrome fixation. The same applies to chrome liquors of acidities usually employed in practice and without any marked colloidal nature for hide powder pretanned at high pH values. Series buffered with sodium bicarbonate in pH range from 8 to 11.5, employing the above 40.2 per cent acid liquor, gave higher values for amounts of fixed Cr203 than the blank in the pH range from 10.2 to 11.5 with a maximum at pH 11.0. In comparing the action of sodium hydroxide and sodium bicarbonate at an initial pH of 12.0 it was found that the values of C1-203 for the solutions made alkaline with the hydroxide were greater than those obtained from the bicarbonate-treated stock, although an almost constant pH was maintained in the latter case and not in the first. This finding probably indicates a specific ion effect. In the following experiments with a number of chromium compounds the formaldehyde treatment was carried out in unbuffered solutions of initial pH of about 8 and 12.2, respectively, with only 1 per cent solution of formaldehyde in order to obtain conditions similar to those in practice. The formaldehyde was in all experiments brought to a pH of 8 before use by neutralization with sodium hydroxide. An 0.02 M sodium hydroxide solution served to give an initial pH of the solution with formaldehyde addition equal to 12.2.
hyo. CONCENTRATION of SOLUTIONS
of Chromium by Hide Powder a n d b y Formaldehyde-Treated Powder
C R 2 0 3 C l , M B l r ; E D N'ITII
Grams
Table 111-Fixation
Table IV-Fixation
245
Regular hide powder Formaldehyde-treated hide powder: pH = 7.0 pH = 12.0
Grams 8.03 7.08 7.95
A solution of hemlock bark extract, containing 30.5 grams total solids per liter and a pH of 4.18, gave the following amounts of tannin combined with 100 grams of collagen:
Regular hide powder Formaldehyde-treated hide powder: pH = 7 . 0 pH = 12.0
Grams 45.5 40.3 48.2
Table VI illustrates the relationship between pH of pretreatment with formaldehyde and the amount of chromium fixed from a sulfito compound prepared from a 60 per cent acid liquor containing 3NazS03:Cr203and in a concentration 10 grams CriO3 per liter (1-week-old solution).
.
INDUSTRIAL AND ENGINEERING CHEMISTRY
246 Table V I
PH on FORMALDEHYDE C R Z OCOMBINED ~ WITH PRETANNACE SOLUTION 100 GRAMSCOLLAGEN
Grams 22.01 17.79 20.12 24.67
Regular hide powder 7.0 11.0 12.5
The tanning action of several chromic salts in the presence of neutral salts is illustrated in Table VII. Table VI1 CHROME SALT Concentration
Nature
’
Grams CrzC fie7 iiler 379%acid chrome sulf i t e liquor 40.8 Same, 3 M NaCl 6 3 % acid chromic sulfate 25.2 Same, 0.5 M NalSOd 9 2 . 5 % acid chromic sulfate 14.5 Blank 0.25 M NazSO4 0 . 5 M NazSOi 2.5 M NaCl
HIDEPOWDER Crz01 Acidity of on chromecollagen collagen basis compound
>ORMALDEHYDE ’OWDER (PH =
HIDE 12.2)
CrzOs Acidity of on chromecollagen collagen basis compound
Per cenf
P w cent
Per ccnl
Per cent
15.91 9.61
46.3 45.5
32.36 22.83
38.9 40.1
15.08 8.05
61.3 72.5
16.32 10.53
56.1 65.8
3.13 2.52 2.09 1.16
118.1 136.4 152.7 140.6
3.15 2.87 2.48 1.84
87.0 105.4 116.3 82.4
Discussion of Results and Theory
In view of the micellar structure and ampholytoid nature of hide protein, and further in consideration of the different properties of chromium compounds in regard to charge of complexes, degree of dispersity and hydrolysis, the promulgation of a theory of chrome tanning with general applicability must include, as regulating factors, the participation of primary and secondary valency and also adsorptive forces. The experimental conditions, nature of the protein, and the composition of the salt principally determine the relative importance of any of these factors. In cationic chromium compounds, such as basic chlorides and sulfates of relatively great per cent acidity, reactions based on primary valency predominate. The formation of acido-hydroxo-chromi-collagen compounds by means of the acidic protein groups is indicated to be the mechanism of this reaction, extensively applied in practical one-bath chrome
6,
0‘
I,
J0
?,
Jo
in
A
b ,
A
-16
Concentration of solution in grams CrrOl per liter Figure 2-Fixation of Chromium from a 92.5 Per CentTAcid Chromic Sulfate Liquor by Hide Powder Proper and Hide Powder Formaldehyde-Tanned a t pH = 8.0 and 12.2 a8 a Function of t h e Concentration of Chromic Solution
tanning. It is very probable that forces of the nature of secondary valency are supplementary factors. In very basic chromic sulfates, the additional factor of the degree of aggregation of the chrome complexes enters, as the dispersity of the complexes is markedly decreased. Anionic complexes are generally also present; accordingly, both primary and secondary valency reactions occur simultaneously, besides those of adsorptive nature. The mechanism of fixation of anionic chrome complexes by hide protein is indicated to be chiefly a formation of molecular compounds by means of the basic protein groups.16 Such a simplified generalization is 16
Gurtavson, J. Am. Chcm. SOC.,48, 2963 (1926).
Vol. 19, No. 2
useful at the present status of our knowledge. The study of a number of chromium compounds in their behavior toward hide protein in different states has made such a classification very probable. The data demonstrate clearly that hide powder which has undergone formaldehyde treatment in the optimal pH range in the vicinity of the true neutrality (pH 6 to 8) possesses a diminished rate and capacity of combining with chromium compounds in general. As a rule, chemical inactivation or removal of basic protein groups leads to decreased fixation of chrome complexes. Thomas and Foster” report that pretanning of hide powder by means of vegetable tannins and quinone and the removal of primary amino groups by nitrous acid treatment leads to products with very markedly lessened affinity towards chromic sulfates. The conclusion was drawn that the basic protein groups play a significant part in the regular chrome tannage (the type of cationic chromium as a rule). The view of formation of molecular compounds by means of the basic protein groups, a type similar to the well-known ammin compounds of Werner, was suggested by these authors as a possible mechanism of chrome fixation. Upon a stricter examination, the inadequacy of such a view is realized. The tanning mechanism of basic chromic sulfates consists in two separate but mutually influenced reactions, the fixation of the complex cations by acidic protein groups and the fixation of the hydrolyzed acid (in equilibrium with the chromic salt) by the protein through its basic groups. Stiasny18 formulated this concept some eighteen years ago and no conflicting fact has been observed in later investigations. The formaldehyde-treated hide protein possesses a fewer number of basic groups than the regular hide powder and the same applies to the abovementioned collagen compounds studied by Thomas and Foster. Accordingly the fixation of hydrolyzed acid must be decreased. This in its turn will tend to depress the forthgoing hydrolysis of the chromic salt. As the fixations of “basic” and “acidic” constituents of the chromic salt by the hide protein are intimately connected processes, a retardation and decrease of the combination with sulfato-complexes results. This view, originally suggested by Gerngross,lg seems to be the nearest to hand and logical explanation, The rate of combination of formaldehyde-treated hide protein with bases, such as potassium hydroxide, is increased, a fact supporting the view that the formaldehyde-protein combination is associated with an opening up of the ring structure of the elementary units, probably also accompanied by a redistribution of valency. We would expect the final chrome compounds with formaldehyde-collagen to possess the same per cent acidity as that of regular hide protein if no activation of acidic groups is induced by this pretreatment. The data show, however, that the retardation of the acid fixation is more pronounced than that of chromium, as the per cent acidity of the formaldehyde-collagen-chromium compound is lower than that of regular hide powder. The findings are logical to the view of an activation of acidic protein groups taking place, leading to increase in amounts of sulfato-hydroxo-chromi complexes fixed by the hide protein. The latter have generally an acidity of 25 to 35 per cent, where on the other hand the chrome collagen compound from regular hide powder shows an acidity of about 50 to 60 per cent (including acid associated with protein). The retardation of the acidic and indirectly also of the chromium fixation, however, more than counterbalances the tendency of increase in Crz03 values resulting from the activation of acidic protein groups and the result is that formaldehydecollagen formed in the optimal pHrange givesjower chromium 17
J . A m . Chem. Soc., 48, 1312 (1926).
‘8
Collegium, 1908, 337. Ibid., 1921, 489.
19
February, 1927
.
INDUSTRIAL AND ENGINEERING CHEMISTRY
247
fixation than the regular hide powder. The view of the acidic groups of the protein chiefly being involved in the cationic chrome fixation is today not only a speculation but instead an hypothesis based upon experimental data from widely different types of reactions. In the pretannage with formaldehyde in solutions of great pH values-. g., 12.2-the formation of alkali collagenate leads to an increased activity of the acidic groups in the hide protein brought back after treatment to its isoelectric state. Further, a considerable
anionic complexes which in all probability react with the basic protein groups. Inactivation of the latter by formaldehyde leads to an inhibition of the fixation of anionic chromium. The more acid salt, containing chiefly cationic chrome is considerably less influenced in its reaction with formaldehyde-collagen-compound as in this instance only the indirect action of the reduced number of basic protein groups is manifested. The curves of chrome fixation by formaldehyde-tanned hide powder of pH = 8, compared with those of regular hide powder shown in Figures 2 and 4,are similarly explained. Addition of neutral salts leads to values in fixation of chromium showing greater differences. The theoretical treatment of this phase cannot yet be successfully carried out. Pretreatment with formaldehyde at low pH values, as pH = 2.5, is chiefly a process of peptization and activation of basic protein groups. Accordingly, the more acid chromic salts are not influenced in their reactions by this pretreatment, but the colloidal liquors give also here increased chrome fixation compared to regular hide powder. The anionic sulfito-sulfato-hydroxo-chromi-compound21is Concentration of solution in grams CrrO; per liter Figure &Fixation of Chromium from a 63 Per Cent Acid less taken up by formaldehyde-treated hide powder at pH Chromic Sulfate Liquor by Hide Powder Proper and Hide 7 and 8 than by regular hide powder. The fixation of these Powder Formaldehyde-Tanned a t pH 8.0 and 12.2 as a Function of the Concentration of Chromic Solution complexes is in part at least by means of basic protein groups. Thus their behavior is as would be expected. Formaldehydedeaggregation of protein occurs. Such changes are not un- collagen formed a t greater pH values, where the deaggregaexpected in light of the aggregation hypothesis of protein tion of the hide micelles is a prominent,factor, shows also structure. Participation of primary valency by the chemical greater affinity for sulfito complexes than recorded for regular interaction influences not only the primary valency but a re- stock. The liquors used were highly colloidal. The degree distribution of residual valency probably takes place, leading of dispersity of the complexes decreased considerably upon to changes in the specific surface potential of the treated pro- standing and in the five-week-old solutions a heavy turbidity tein. was noticeable. By these agglomeration processes, the Cationic chromium salts of crystalloid nature possess a tanning property is considerably decreased, probably on greater tendency of combination with the hide powder pre- account of formation of complexes possessing such high detanned with formaldehyde at pH of 12.2 than with regular gree of aggregation that their rate of penetration into the hide powder. It has been shown that treatment of hide protein gel is greatly retarded. These compounds show powder by certain neutral salts-e. g., thiocyanate-tends to behavior very similar to that of hide powder peptized by deaggregate the protein structure, thereby increasing the 60 fixation of colloidal tanning agents.20 The cationic liquors , employed in this investigation showed, however, practically complete independence of the neutral salt pretreatment in their reactions with the deaggregated specimens and hide powder proper. Accordingly, in the case under consideration, the deaggregation factor must be left out of consideration and the increased chrome fixation must be due to another factor, very probably the increased number of acidic protein groups. In experiments with the extremely basic liquors of colloidal character and possessing a considerable amount of chrome anions, the increase in specific surface by the deaggregation process comes in play, and the enormous increase on the 0 rr m ,J k I .A A ,i, 20 amount of fixed Crz03 noted for the hide powder treated a t Concentration of solution in grams CrrO; per liter pH of 12.2 in its reaction with the 37 per cent acid liquor is Figure &Fixation of Chromium f r o m a 37 Per Cent Acid Chromic in part due to the colloidal phase besides the above discussed Sulfate Liquor by Hide Powder Proper and Hide Powder Formaldehyde-Tanned a t pH 8.0 a n d 12.2 as a Function of the factor. The value of 50 per cent Crz03 on collagen basis Concentration of Chromic Solution found in this case is the greatest amount of chromium incorporated with hide protein as yet recorded. The maximum means of neutral salts, thus indicating reactions in part of chrome fixation is for this liquor shifted toward higher governed by specific surface conditions. concentration of solution in case of the formaldehyde-treated The anionic oxalato compounds give, as all other chromium stocks compared to regular hide powder. The curves show compounds, lower chrome fixation in reactions with formalthat chromic sulfates of high per cent acidity and low concen- dehyde collagen formed in the optimal pH range. Notetrations give practically the same chrome fixation by regular worthy is the fact that the values of combined CrzOs found hide powder and the two kinds of formaldehyde-treated for formaldehyde-treated hide powder of pH 12.2 are of about stocks. With decrease in per cent acidity the differences in the same magnitude as that found for the formaldehydechrome fixation are more pronounced. The data in Table I collagen compound formed a t the optimal pH. This finding and the curves in Figure 1 demonstrate the heavy drop in offers further evidence in support of the correctness of the chrome fixation caused by formaldehyde treatment of hide view previouslf advanced that the formation of molecular powder a t pH = 8 from solutions of the extremely basic compounds by means of basic protein groups is the principal chrome liquor. This contained considerable amounts of reaction in this instance. If the acidic protein groups were
i l
25
Gustavson, J . Am. Leather Chem. Assoc., 31, 366 (1926).
21
Stiasny and Szegoe, Collegium, 1936, 41.
INDUSTRIAL A N D ENGINEERISG CHEMISTRY
248
involved, the amount of fixed Cr203would be expected to be greater than with regular hide powder, as found for chromic salts. The reverse is true. I n the solutions employed, this compound existed principally as a crystalloid. The extent of colloidal reaction may therefore be expected t o be insignificant. For comparison, data are given from experiments with basic aluminum sulfate and hemlock bark extract. Evidently these agents show a close parallelism to the behavior of chromium compounds with colloidal characteristics. This investigation shows that the experimental conditions under which the formaldehyde treatment of hide powder is carried out, particularly the H-ion concentration of pretanning solution, radically iduences the behavior of the treated stock toward chromium compounds. Inconsistent findings in the literature are in part to be traced t o omission of pH control in first hand. 1
I
I
I
I
I
14
20
40
*1
60
I
I
60
20
80
Concentration of solution in grams cTzo3 per liter Fibure &Fixation of Chromium from a 44.5 Per Cent Acid Chromic Chloride by Hide Powder Proper and Hide Powder Formaldehyde-Tanned a t pH 8.0 and 12.2 as a Function of the Concentration of Chromic Solution
The data,obtained in regard to the effect of alkali treatment of proteins as influencing the fixations of tanning agents have received striking verification by investigations of hide powder treated at different pH values and then brought back to isoelectric state in its behavior to these compounds. In the comparison of data from the cationic chrome fixation by regular hydrated hide powder with those from the hide powder formaldehyde-tanned in buffer solutions, or a t high pH values, it must be borne in mind that in the latter process two opposing reactions take place. The fixation of formaldehyde tends to inactivate the basic groups of the protein, where, on the other hand, chemical and colloidal changes are due to the action of buffers. For a true evaluation of the influence of the formaldehyde treatment in the problem in question, hide powder blanks treated with the same buffer solutions as employed in this tannage should be used. Under these conditions, pretannage with formaldehyde a t high pH values leads also to a diminished chrome fixation as compared to similarly peptized hide powder. In the optimal pH range of the fixation of formaldehyde the buffer action tends to give slightly higher values for amounts of chromium fixed by the hide powder hydrated with buffer solutions. The differences between regular and formaldehyde-tanned hide powder are therefore actually greater. Summary
Data showing the fixation of the constituents of various chromium compounds, employed as tanning agents, by hide powder treated with formaldehyde and by regular hide powder are presented in detail. The pH value a t which the formaldehyde treatment occurs greatly affects the behavior of the formaldehyde-collagen toward chromium salts. The
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formaldehyde-collagen formed a t pH values in the vicinity of the true neutrality (pH 6-8) has, as a rule, less capacity than the regular hide powder of combining with chromium and the acidic constituent in cationic chromic chlorides and sulfates. Diminished chrome fixation results also from anionic sulfito and oxalato compounds in the case of formaldehyde-collagen. The formaldehyde tanning taking place a t high pH (in this case about 12) leads to the formation of a product which shows greater capacity of chrome fixation than the regular hide powder from solutions of cationic chromium compounds. This increase in combining capacity of the formaldehyde-collagen is accentuated by decrease in per cent acidity of the chrome liquor. A 37 per cent acid sulfate liquor shows, for example, the values of 50.1 and 24.6 per cent Crz03on a hide substance basis after a 48-hour interaction with formaldehyde-collagen (formed at pH = 12.2) and collagen proper, respectively. The anionic sulfito compound exhibits also an increased rate of tanning power in this case but anionic oxalato compounds give also here diminished fixation. The per cent acidity of the resulting chromeformaldehyde-collagen compound is in all instances lower than the corresponding chrome compound with collagen proper. This investigation clears up the numerous contradictions in the literature in regard to the influence of formaldehyde treatment of hide substance upon the fixation of tanning agents. The diminished fixation of cationic chromium is probably caused by the decrease in acid fixative capacity of the formaldehyde-hide protein with inactivated basic groups. The presence of the latter explains the decrease in anionic chrome fixation. The increased capacity of chrome fixation by formaldehyde-collagen of high pH history is probably due to an “activation” of carboxyl groups or the breaking-up of the internal protein structure occurring in the salt formation with alkali. For sulfito complexes, and related compounds of colloidal nature, the increase in fixed CrzOa by the formaldehyde stock formed a t high pH values is probably connected with changes which the hide powder undergoes in the alkali treatment, tending to deaggregate the structure. This investigation offers ample evidence of the great importance to be attached to the previous history of the hide substance, as influencing its behavior toward tanning agents.
Sales of National Forest Timber The two largest timber sales ever offered by the Forest Service, United States Department of Agriculture, are being advertised for competitive bids. These are sales of pulpwood in Alaska, each for five billion board feet. One sale is in the northern part of the Tongass National Forest not far from Juneau, and the other is in the southern part of the Forest near Ketchikan. The establishment of a t least a 200-ton paper mill in Alaska is required as a condition of each sale, with opportunity to expand to 500 tons. The advertisements are in response to applications for timber and water-power permits filed by a number of companies or groups of responsible individuals. According to Secretary Jardine, the purposes of the department in offering these sales are first of all t o aid in the economic development of the Territory by establishing large units of il new industry, using National Forest wood as its raw material; and secondly, to make t h a t industry permanent by insuring a perpetual supply of timber. We invite and will protect the investment of capital necessary t o establish large units of paper manufacture. At the same time, we must fully protect the public interest by getting fair compensation for the government timber. The sales are offered with all these purposes in mind.
Mr. Jardine said that southeastern Alaska has the timber, the water power, and transportation facilities necessary for the development of a large paper-manufacturing industry. I n the eastern United States scarcity of available timber close to cheaply developed water power has prevented the growth of papermaking. The offerings of Alaska timber will result in mills on American soil, using American timber, and supplying American paper users with a native instead of a n imported product. Two big paper mills will mean much to Alaska, the Secretary said. The territory needs new and permanent industries.
