304 MINERALOGY. 



an earthy odour that exhales from the substance 

 when breathed upon. 



Artificial Diamonds and other Gems. 



The base of all artificial stones is a paste composed 

 of silex, potash, borax, oxide of lead, and sometimes 

 arsenic. The best silex is obtained from rock crystal, 

 and the next best from white sand or flint. The fol- 

 lowing are two receipts for making a good paste : 



No. 1. 



Grains. 



Rock crystal 4056 



Minium (red lead) 6300 



Pure potash 2154 



Borax 276 



Arsenic 12 



No. 2. 



Sand S600 



Ceruse (white lead) 8508 



Potash . 1260 



Borax 360 



Arsenic 12 



The Pearl. 



The pearl is a morbid secretion of the avicula 

 marantifera, and, like shells, is composed of car- 

 bonate of lime, united with a small portion of ani- 

 mal matter. 



