THE SCIENTIl'IC ASPECTS OF TANNING. 8t 



We will now, first, look at the raw materials employed in the 

 trade : secondly, the process of Tanning itself : lastly, one or 

 two questions bearing on the testing of Tanning materials. 

 The Raw materials. 

 The Natural History of the Hide. 



Skins vary m texture and substance, as much as the character 

 of the animals they cover. 



The sheep, though valuable for its wool, gives but a spongy, 

 porous skin, only available for common work. The pig with a 

 skin of a closer texture, is yet of so mferior a description as to be 

 principally confined to saddlers' work, for which it is well adapted. 

 The horse is the possessor of a remarkably thin skin, almost 

 transparent, the naturalist would do well to notice one peculiarity 

 about It, that is, that whilst three-fourths of the hide make the 

 best curried leather, the remaining portion, from the hip bones, 

 covering the rump, has under the true skin a layer of horny 

 substance, giving to it an inflexibility very foreign to the rest of 

 he hide 



The hide of the ox is that to which our attention may be 

 chiefly directed. 



The calf and younger cattle give us skins which are mainly 

 used for the uppers of boots. The ox at maturity furnishes the 

 stouter hide, which the tanner transforms into sole leather. 



A transverse section of fresh skin shows it to be a gelatinous 

 mass, the substance of which is full of fibres interlacing each other 

 in every direction. The microscope reveals to us the true skin, and 

 cuticle or epidermis, between the two lies the Rete Mucosum. 

 The cuticle in which the hair is embedded, being of a horny 

 nature, is removed during the process with the hair : leaving the 

 true skin to be made into leather. The Rete Mucosum, the 

 intermediate layer or rather semi-fluid, in some cases is scarcely 

 discernible, some breeds of sheep show it plainly. Returning to 

 the corium or true skin j this placed in boiling water, dissolves, 

 which on evaporation, yields gelatine or glue. Whether the 

 substance of the pelt is identical before and after it has been 



