UTILIZATION OF THE SKINS OF AQUATIC ANIMALS. 331 



cementing substance of the filior must bo 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 by tlie "bran drench," either 

 alone or supplemented by dung ])ates. Hot water is poured upon ])ran, 

 and the mixture set with a few pailsful of a fermenting drench li<(uor. 

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

 of 70° F., fermentation soon ensues, Uoating the skins up to the surface. 

 The}^ are again forced mechanical]}^ down into the liquid, l)ut soon rise 

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

 hours, the action is generally sufficient. Large hides, especially 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 OO"^ F., and in this 

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

 previousl}^ plump skins become extremely soft and flaccid, and may be 

 stretched in an}^ 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 artiticial heat and th(^. process 

 requires four or Ave daj^s. 



The hide is now a simple network of liber, all the intcrtibrous sub- 

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

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

 viz, dehvdrating 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 acjuatic leathers are prepared 

 by 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 days, 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 arc finished. This operation differs 

 so much, according to the variet}- and quality of the skins, that accounts 

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

 for appropriate subchapters. 



