Nov. 1, 1864.] THE TECHNOLOGIST. 



ON CHEMISTRY APPLIED TO THE ARTS. 165 



which ia well-known as a distinguishing feature of Russia leather. As to 

 its preparation, I will merely state that it is very similar to that of Mo- 

 rocco, with these differences, that hot solutions of willow bark are used 

 instead of sumach ; that it is generally dyed with sanders wood and a 

 decoction of alum ; and, lastly, as already stated, the birch-tree oil is 

 used in currying it. 



Enamel Leather. — This class of leather is usually prepared with calf 

 and sheep skins tanned in the ordinary manner. They are dyed black 

 by rubbing them over with a decoction of logwood, and then with iron 

 liquor or acetate of iron. The leather is softened with a little oil, and is 

 ready to receive a varnish, which is applied by means of a brush. The 

 varnish is composed of bitumen of Judea,* copal, turpentine, and boiled oil. 



Tawed or Kid Leathers.— The manufacture of this class of leathers 

 differs entirely from that of those already described, as their preserva- 

 tive qualities are imparted by quite different substances from those used 

 with other leathers, the preservative action of the tannin being substi- 

 tuted by that of a mixture of alum and common salt. In the produc- 

 tion of this class of leather, one of the most interesting characteristics 

 is that of unhairing sheep, lamb, and kid skins, after they have been 

 well washed and fleshed on the beam. The old process of unhairing by 

 smearing the fleshy side with a milk of lime was improved by mixing 

 with the lime a certain amount of orpiment, or sulphuret of arsenic ; 

 but Mr. Robert Warrington having ascertained that the rapid removal 

 of hair in this case was not due to the arsenic, but to the formation of 

 sulphuret of calcium, proposed, with great foresight, the following 

 mixture as a substitute for the dangerous and poisonous substance 

 called orpiment, viz. : Three parts of polysulphuret of sodium, 10 parts 

 of slacked lime, and 10 parts of starch. The polysulphuret of sodium 

 may be advantageously replaced by the polysulphuret of calcium. 

 The skins, unhaired by any of these processes, are now ready to be 

 placed in a bran or rye bath, as with Morocco leather, or in a weak 

 solution of vitriol, to remove, as already stated, the lime. After the 

 lime has been thoroughly removed from the skins, they are dipped in 

 what is called the white bath, which is composed, for 100 skins, of 13 

 to 20lbs. of alum and 4 to 5lbs. of chloride of sodium or common salt, 

 and the skins are either worked slowly in this bath or introduced into 

 a revolving cylinder to facilitate the penetration of the preservative 

 agent, which, according to Berzelius, is chloride of aluminium resulting 

 from the action of the chloride of sodium on the alum. When the 

 manufacturer judges that the skins have been sufficiently impregnated 

 with the above mixture, he introduces them into a bath composed of 

 alum and salt in the same proportions, but to which are added 20lbs. 

 of rye flour and fifty eggs for 100 skins. After remaining a few 

 hours they are removed and allowed to dry for about fifteen days, and 



* Query Asphalte.— Editob Tech. 



