TANNING. 207 



with the liquor in which they are immersed. The 

 strength of the hquor will by this means be consi- 

 derably diminished, and must, therefore, be renew- 

 ed. When the hides are by this means completely 

 saturated, that is to say, perfectly tanned, they 

 are to be removed, and slowly dried in the shade. 



It has been proposed to use the residuum of the 

 tanning lixivium, or the exhausted ooze (which 

 contains a portion of Gallic acid, this forming a 

 constituent part of astringent vegetables), for the 

 purpose of taking off the hair ; but tliis liquor 

 seems to contain no substances capable of acting 

 upon the epidermis, or of loosening the hair ; and 

 when skin is taken off by being exposed to it, the 

 effect must really be owing to incipient putre- 

 faction. 



The length of time necessary to tan leather 

 completely, according to the old process, is cer- 

 tainly a very great inconvenience ; and there is no 

 doubt but that it may be much shortened by fol- 

 lowing the new method. It has been found, how- 

 ever, that the leather so tanned has not been so 

 durable as that which has been formed by a slower 

 process. 



The public is much indebted to Sir Humphry 

 Davy, for the attention which he has paid to this 

 subject. From his excellent paper " On the Con- 

 stituent Parts of Astringent Vegetables,'* in the 

 Philosophical Transactions, we present the reader 

 with the following extract. 



" In considering the relation of the different 

 facts that have been detailed, to the processes of 

 tanning and of leather-making, it will appear suf- 

 ficiently evident, that when skin is tanned in as- 

 tringent infusions that contain, as well as tannin, 

 extractive matters, portions of these matters enter, 



