THE JOURNAL OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
414
.
of sodium sulfide. Procter’s suggestion that the addition of calcium chloride would permit the use of sodium sulfide for unhairing skins even for this delicate work is thus seen t o have a sound theoretical basis. Guisiana has suggested a similar procedure. It will be noticed by reference to Table I that an increase of alkalinity from 0.05 N (which is approximately the strength of saturated lime water) to 0.1 N (or a rise of pH from 12.70 to 13.0) does not produce any increase in swelling but, rather the reverfie. In practice, however, if a lime liquor be strengthened with sodium sulfide or sodium carbonate, the hides or skins will be found to be much more plumped or swollen. This increased swelling was formerly thought to be due to the increased alkalinity, but it would seem more in accordance with the true facts of the case to ascribe it to the increased swelling due to sodium collagenate. Here, again, some calcium hydroxide would be forced out of solution by the increased alkalinity. The present writer and his collaborators* have proposed two methods for the determination of the caustic alkalinity of lime liquors, but in view of these results the simplest control of lime-yard liquors would be to carry out smelling experiments on hide porder exactly as described in this paper. The swellings could be plotted against pH values and in this way successive liquors could be checked and a graphical record preserved. WASHIKG OF HIDEs-It has been the custom of many sole leather tanners to wash out practically all the salt in the hides before they are limed. Reference to Table I1 will show that, the presence of sodium chloride causes more swelling of barium collagenate than when barium hydroxide alone is used. The same effect will be shown with calcium collagenate. The sole leather tanner can use as ;sharpening agent to promote swelling and plumping, the salt that is already present in the hides and need not wash it out before liming. This method of working has been used with success in a large sole leather yard in England. The reason why such care has been taken by tanners to remove salt from the hide appears to be the fear that salt may be carried forward to the tan pits and produce a flat empty leather. The employment of the three-pit system of liming and subsequent deliming would remove practically all the salt before the hides went forward to the tan liquors. AMMONIUM HYDROXIDE-An interesting confirmation of the results given in this paper was described by Stiasny. Calf skin with the hair on was soaked in 200 cc. of liquor consisting of 0 . 5 N ammonium hydroxide to which equivalent quantities of various chlorides had been added: 0 84 g. NaC1, 0.8 g. CaC12,or 1.76 g. BaCl2 (Table 111). TABLE 111-WEIGHT
ABSORPTION(PER CENT) ”4OH NHaOH 4- NaCl After 1 day 37.4 58.6 After 2 days 65.5 45.8
CHLORIDES “4OH
WITH VARIOUS
NHiOH CaClz
4- BaClz
16.5
14.1 19 8
+
14.9
The pickling effect of the salts was apparent in each case but the repression of swelling was much greater with barium and calcium chlorides. In the chse of ammonia and ammonia plus sodium chloride the hair was quite loose after 4 days, but not in the cases where calcium or barium chloride was used. Stiasny suggested that the explanation might be due to the formation of complex ammonia compounds of the type Ca(KH3)&12, but it has been shown by J . Atkin and the writerg that the hydroxyl-ion concentration of ammonia solutions is not altered by the addition of sodium chloride or calcium chloride. The explanation of the differences in swelling is of course exactly the same as for the results given in Table 11, but the differences in unhairing capacity seem to require further investigation. 8 9
J . SOC.Leather Trades’ Chem., 4 (1920), 111, 236, 248, 268 Ibid.. 4 (1920), 236.
Vol. 14, No. 5
EFFECTOF CONCENTRATION OF SALTS The influence of salt solutions of various concentrations on gelatin has been investigated by H. R. Procter, who found that increasing concentrations of salt caused an increased swelling; this, however, attained a maximum and afterwards fell on increasing the concentration of the salt solution. Commercial gelatin appears t o be almost always on the alkaline side of the isoelectric point and really contains some calcium collagenate, as the ash always contains calcium. By treatment with sodium chloride the following equilibrium is set up: Ca(Col1)z
+ 2NaC1 * PNaColl + CaC12.
the sodium collagenate chusing an increase of swelling. Higher concentrations of salt then cause a depression of swelling. MeunieP found that potassium carbonate solutions of high concentration completely dehydrate pelt and yield a leather which is wet back into pelt on treatment with water. The action may be explained on similar grounds to the above: the production of potassium collagenate and the pirliling effect of the excess potassium carbonate. hfeunier, however, showed that a permanent leather could be obtained by using potassium carbonate together with formaldehyde in 0 . 3 per cent solution: AlcI,augh!inll has published two papers dealing with the swelling of pelt in acids, one using limed pelt and the other with fresh pelt. The results are vitiated, however, by the facts that in the first paper no allowance was made for the lime in the pelt and the consequent buffer action of the calcium salts dissolved out by the acids and also that the concentrations of the acids are given only in terms of normality by titration and the normality so stated is that before equilibrium has been set up. It is well known that hide, like gelatin, takes up a certain amount of acid and therefore the concentration of the residual acid after equilibrium should be determined. Further, Loeb’s work has shown that comparisons of swelling are only valid if made a t the same hydrogen-ion concentration, but McLaughlin makes no determinations of this; furthermore, it is not possible to calculate it from the dissociation constants of the acids for the reasons given above. It is very much to be regretted that so much painstaking work has been to a large extent nullified by these omissions. 10 11
Collegium, 1912, 11, 54, 420. J. Am. Leather Chem Assoc , 18 (1920), 228; 16 (1921), 295.
The International Chemical Conference The general program of the Third International Chemical Confeience, to be held a t Lyons, France, June 27 to July 2, inclusive, includes meetings of the Council, reports of committees and visits to factories in the vicinity. On July 2, the delegates will go down the RhBne by boat to the neighborhood of Marseilles, where they will have an opportunity to attend the second congress of industrial chemistry, which has been arranged by the SocietC de Chimie Industrielle. This congress will be held July 2 to 7. Among the general questions which will be considered are the animal, vegetable, and mineral resources of the French colonies. In addition to this, fats, soaps, etc., will be discussed.
Professor Moody Succeeds Professor Baskerville On March 27, Prof. Herbert R. Moody, for seventeen years connected with the Department of Chemistry of the College of the City of New York as Professor of Industrial Chemistry and Chemical Engineering, was unanimously appointed to the Directorship of the Department to fill the vacancy caused by the death of Prof. Charles Baskerville
