GEMS, NATURAL AND ARTIFICIAL 



" pinked." By the same process the purple amethyst 

 can be changed to a mahogany-brown stone of great 

 beauty; and brown zircons and brown quartz can be 

 made colorless. There is great danger of ruining the 

 gem during the transformation process, which consists 

 in burying it in sand and heating to the desired tem- 

 perature, afterward allowing it to cool very gradually. 



ARTIFICIAL GEMS 



The production of artificial diamonds has long been 

 the dream of the experimenter. The conditions 

 under which diamonds are produced in nature are 

 pretty well understood ; and on a small scale they have 

 for some time been duplicated in the laboratory, and 

 even though here quite unwittingly in the workshop. 

 Nothing more is necessary than to reduce carbon 

 a bit of coal or graphite or lampblack to a liquid 

 .condition, and maintain it under great pressure until 

 it cools, when crystals of carbon will separate from the 

 liquid just as crystals of quartz or sugar or salt separate 

 from their respective solutions under like conditions; 

 and these crystals of carbon constitute true diamonds. 

 But the difficulty lies in the extreme reluctance with 

 which carbon assumes the liquid state. Unlike most 

 other substances, it volatilizes directly from the solid 

 state under ordinary conditions of pressure the tem- 

 perature at which the change occurs being about 3600 

 degrees Fahrenheit. Under pressure, to be sure, it 

 will liquefy; but the pressure required, according to 

 Professor Dewar's experiments, is about fifteen tons 



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