MANUFACTURE OF LEATHER FROM MARINE SOURCES 539 



This consists in treating the skins in a paddle vat with water containing 10 

 per cent by weight of the hides of slaked lime and 2 per cent by weight of the 

 hides of sodium sulfide. The action of the solution is to swell the fiber bundles, 

 remove the cementing material, and loosen the hair and epidermis. In addition 

 to this the lime has a certain action upon the fat, partly saponifying it and causing 

 it to be more easily eliminated. A solution of arsenic sulfide and sodium hydroxide 

 is sometimes used as an accelerating agent. 



The time consumed in depilating depends somewhat upon the nature of the 

 skin, but more especially upon the product to be manufactured. Skins to be used 

 for oil tannage, where softness is desired, are given a fairly long liming. The pro- 

 duction of fancy leather, used in making handbags, suitcases, and brief cases, 

 requires a shorter liming period. The usual method of procedure consists in placing 

 the skins in a vat containing a mixture of lime and sodium sulfide. The skins are 

 passed to stronger solutions from day to day, and, finally into very strong lime 

 solutions to which no sodium sulfide has has been added. This gradual increase 

 in the strength of the solution prevents "case hardening" of the hide. 



When the hair has become sufficiently loosened to rub off with the hand and 

 the skins are in a properly plumped condition, they are placed over a beam and 

 the hair and epidermis are removed with a blunt knife. In place of the hand 

 operation dehairing machines are now commonly used for this purpose. After 

 dehairing, the stock is washed in drums with running water until perfectly clean. 



Bating. To remove the lime which has been absorbed during depilation and 

 to bring the skins to a soft and flaccid condition again they must be bated. This 

 operation formerly consisted in running the skins in a warm fermenting infusion 

 of pigeon or hen manure. In recent years, however, this objectionable procedure 

 has been entirely superseded by more scientific methods, in which a combination 

 of chemical and enzyme action is utilized to secure the desired results. Bating 

 consists essentially of immersing the hides in a solution of ammonium chloride 

 or sulphate as the deliming agent. The solution also contains pancreatin, an 

 enzyme for the removal of certain proteins, chiefly elastin, and improves the color 

 of the grain. The ammonium salt adjusts the pH and activates the enzyme. This 

 solution reduces the swelling of the hide produced by the previous treatment. 

 The time of bating depends upon the product to be manufactured, but it may 

 be said that the longer the bating the softer the resulting leather. 



Vegetable Tanning. Most hair sealskin leather is prepared by the chrome 

 method, which is generally used for light-weight leathers. One method, which 

 requires vegetable tannin and gives very good results, consists in milling the skins 

 for one hour in a 10° barkometer solution of quebracho extract. This serves to set 

 the grain. The skins are then transferred to a vat containing a 12° liquor, the 

 strength of which is gradually increased to 30°. They remain there about a week, 

 or until tanned. When tanned the skins are milled for 2 hours with a strong 

 sumac liquor and, after being set out, are hung up to dry. The dried skins are 

 dampened in water, set out again, sometimes shaved, and, while yet moist, are 

 colored as desired. The colored skins are then usually tacked out on boards to 

 dry again. 



Chrome Tanning. This method is used where it is desired to produce a light- 

 weight soft, flexible leather. The chemical and physical mechanism of chrome 

 tanning is not well understood. In its operation a chromium salt is used to replace 



