THE SCIENTIFIC ASPECTS OF TANNING. 93 



ment of calf skins, kips, and horse hides, the main difference 

 in the process being in the preparation of the skin for the tanning. 

 The endeavour of the light leather tanner is to make his leather 

 solid, yet supple and flexible. To attain this, all the lime has to 

 be removed before the tanning process commences ; the skin must 

 also be brought lower in condition. The skins are therefore allowed 

 to remain a certain time in pits containing an admixture of 

 pigeon's dung and water. The carbonate of ammonia neutralizes 

 the caustic properties of the lime, which is eventually removed in 

 the form of chalk. Charcoal and glucose are also employed for 

 this purpose. 



The tanning proper of light leather is essentially the same as 

 the other, but the liquors are weaker and the process more gradual. 

 For the majority of skins and hides intended for shoe and harness 

 purposes, oak bark is employed, producing leather of the best 

 quality : in proof of which, it is known that tanned English calf 

 skins are exported to France, there curried, and returned to us as 

 French calf. 



In thus hastily looking at the tanning process we have not gone 

 aside to criticize the various patents which a few years ago were 

 brought forward, such as those of Chaplin, Spilsbury, and in Bristol, 

 Cox and Herapath, — all of which were but short lived, and of no 

 practical value. We shall lengthen our paper with a few remarks 

 on the different tests which are employed in the Tannic Acid j and 

 in doing so. would advance cautiously any opinions of our own. 

 The most natural process would be to place a piece of prepared 

 pelt into the solution of the material desired to be tested. Having 

 abstracted all the tannin, the difference between the previous 

 weight and the weight after the operation should give the per- 

 centage. But the difficulty is found to be great in obtaining the 

 same conditions of dryness in both cases. Gelatine, or more 

 properly, a warm standard solution of gelatine, has been generally 

 employed with satisfactory results. Some have tried it volu- 

 metically, but the best results are given with the use of Schuster's 

 Alkalimeter, which enables the experiment to be performed with 



