Rea t 
1878. } Diamonds. ey 
acteristic of the diamond we may regard the curving of the 
crystalline faces. This occurs to so great a degree, that not 
unfrequently the specimens are nearly spherical. 
Physically, we may distinguish three varieties of diamond: the 
crystal, the carbon and the anthracitic diamond. As seen above, 
the specific gravity of diamond is 3.52, while that of carbon is 
3.01 to 3.40, and that of anthracitic diamond only 1.66. They 
show slight impurities, as compared with the crystals, but are 
chemically diamonds as also in their hardness. The: carbon is 
put to practical uses, on account of its comparatively low price and 
great hardness. Instead of being colorless it is black, or gray, 
translucent only in very thin slabs. / 
Chemically, the diamond is carbon. Ata high temperature it 
will burn, and be completely consumed, giving off carbonic acid 
gas. In an atmosphere. of pure oxygen it will burn on, if once 
ignited. Between carbon points of a heavy battery, the diamond 
will become spongy, and turn to coals. In 1694 the first experi- 
ments of burning it were made. This was accomplished by means 
of a very powerful lens, concentrating the sun’s rays. Much 
speculation became rife as to the behavior of diamonds under the 
action of great heat. Emperor Francis I, of Austria, conceived 
the brilliant idea of converting or melting a number of small 
_ diamonds together into one large one. In 1750 he placed a 
quantity of them, and some rubies, into a crucible, and subjected 
them to intense heat for twenty-four hours. After cooling, the 
rubies were found to be intact, but of the diamonds not a trace 
remained. Shortly before the French Revolution a Parisian 
jeweller asserted the possibility of exposing diamonds to a 
very high degree of heat without injuring them. He made 
his experiments before the famous chemist, Lavoisier. Maillard, 
the jeweller, had carefully surrounded his diamonds in the cruci- 
ble with pulverized charcoal, and they withstood the fire perfectly. 
So long as the oxygen of the atmosphere can be excluded, the 
diamond cannot burn, and the only harm that might befall it would 
be a cracking from the heat. This, however, occurs compara- 
tively rarely. Lavoisier, fully convinced by the demonstration, 
first offered a correct explanation of the phenomenon. 
Impurities in diamonds are partly of a physical, partly of a 
chemical nature. Among the former must be classed cracks and _ 
cavities. The latter generally manifest themselves in discoloration _ 
