SECTION III. 73 



And afterwards it is to be bruflied with 

 a brufh charged with emery, putty, or 

 tripoli, till it becomes polifhed, or glofly ; 

 but if, inftead of a thick Epidermis, it 

 is a meer pellicle, it is fufficient to fteep 

 it in hot water, and then pick it, or 

 {lightly file it off. Vinegar, or a w^^ 

 acid, is alfo good, and, indeed, much 

 better than aqua fortis. 



When the Epidermis is fo very crafs, 



or grofs, that acids diluted, and even pure 



aqua fortis, does not do ; ftrong emery, 



with ftrong brufhes, feals Ikin, or pumice- 



ftone, is fometimes employed : if that 



does not do, the only way left, is to fteep 



it in a cup of pure aqua fortis, in the 



following manner. Firft ftop or cover the 



mouth or opening of the Shell vvith wax, 



that the acid may not penetrate to, or 



touch, the infide of it. And care muft be 



taken, from minute to minute, or from 



time to time, to plunge it in clean cold 



water, and every time to examine what 



efredls 



