SKIN. 297 



process, that sole leather contains a greater proportion of tannin 

 than soft leather. While drying, it is smoothed with a rolling- 

 pin, and beat with a mallet, which must add considerably to its 

 density. * 



The process of tawing is analogous to that of tanning. By it 

 the skins are converted into white leather, for gloves and other 

 similar uses. The skins are cleaned in the usual way, steeped in 

 lime-water, well scraped and beat with wooden pestles. They 

 are then steeped in water containing bran, which undergoing the 

 acetous fermentation, causes the skins to swell up and rise to the 

 surface. They are pushed down again, and the operation is re- 

 peated till the skins cease to rise. They are then washed, well 

 scraped, and for every hundred large sheep- skins, eight pounds 

 of alum and three pounds of common salt are put into water. 

 These two salts decompose each other. Sulphate of soda is 

 formed, and chloride of aluminum ; the last of which is imbibed 

 by the skins, and combines with them. Along with the alum 

 and salt is mixed with the water, while luke-warm, twenty 

 pounds of the finest wheat-flour, with the yolks of eight dozen 

 of eggs, all of which is formed into a paste a little thicker than 

 children's pap. A quantity of hot water is put into a trough, 

 and two spoonfuls of the paste with it, to do which they use a 

 wooden spoon, containing just as much as is required for a dozen 

 of skins, and when the whole is well mixed with the water, two 

 dozen of skins are plunged into it. Care must be taken that the 

 water be not too hot ; otherwise the skins are spoiled. 



After the skins have lain some time in the trough, they are 

 taken out one by one with the hand, stretched out and well beaten 

 with wooden pestles. They are then left five or six days in a 

 vat, and hung out to dry on cords or racks, and the sooner they 

 are dried the better. Such are the most material parts of the 

 process of tawing, which consists essentially in combining the 

 skins with alumina, or more probably with dichloride of alumi- 

 num. Leather thus made is soft, pliable, and white. 



* See Davy on the preparation of Skin for Tanning. Royal Instit Jour, ii, 

 30. 



