UTILIZATIOlSr OF THE SKINR OP AQUATIC AKIMALS. 331 



cementing substance of the fiber must be dissolved. Removal of the 

 lime is sometimes accomplished by neutralizing it with an acid, as sul- 

 phuric or boracic, and then washing out the neutral salt. 



A more common method, however, is b}^ the "bran drench," either 

 alone or supplemented by dung bates. Hot water is poured upon bran, 

 and the mixture set with a few pailsf ul of a fermenting drench liquor. 

 When the skins are placed in this liquid, maintained at a temperature 

 of 70^ F., fermentation soon ensues, floating the skins up to the surface. 

 They are again forced mechanicall}^ down into the liquid, but soon rise 

 as before. When this has occurred three or four times, in 12 to 16 

 hours, the action is generally sufficient. Large hides, especiall}^ those 

 of alligators, are sometimes submitted to the action of paddle wheels to 

 hasten the removal of the lime and make that removal more uniform. 



This process is often preceded by treating the skin in a fermenting 

 infusion of excrement of dogs in the preparation of lighter skins, and 

 of pigeon or hen dung in case of heavy leathers. This not only acts 

 on the lime so as to make it possible for it to be easily washed out, 

 but it also renders the leather soft and pliable. The dog dung, called 

 puer, is dissolved in water at a temperature of 90'^ F. , and in this 

 liquor the skins are kept in gentle motion for an hour or more. The 

 previously plump skins become extremely soft and flaccid, and may be 

 stretched in any direction without springing back. This operation is 

 known as puering. The treatment with hen or pigeon bate is similar, 

 except that it usually takes place without artiiicial heat and the process 

 requires four or five days. 



The hide is now a simple network of fiber, all the iutertibrous sub- 

 stance, or filler, having been removed in the various processes above 

 noted. Next comes the principal operation in the process of tanning, 

 viz, dehydrating* the skin and combining with it certain agencies which 

 change the fiber network into leather. These agencies are (1) mineral 

 salts, when the product is known as "tawed leather''; (2) oils and fats, 

 making "chamois leather''; and (3) tannin or tannic acid, resulting in 

 "tanned leather." Mineral salts are rarely used in tanning aquatic 

 skins, being employed mostly in preparing laces for belts; and the 

 chief use of the oils and fats for aquatic leathers is in preparing por- 

 poise hides for shoelaces. Most of the aquatic leathers are prepared 

 b}^ the third process, the use of tannin or tannic acid. 



After liming and bating, the hides are submitted to the action of 

 infusions of tanning material. They are first worked by wheels in the 

 tanning liquors for one to three da3\s, according to the result desired, 

 and then placed in tanks or pits, where, for several weeks, they are 

 subjected to fresh tanning liquor, with frequent renewals of the liquor. 

 On removal therefrom the skins are finished. This operation difi'ers 

 so nuich, according to the variety and qualit}^ of the skins, that accounts 

 of the special treatment of the diflerent kinds of skins are reserved 

 for appropriate subchapters. 



