THE GENESIS OF THE DIAMOND. 195 



^^Hiile (Tocoite is the only mineral that exceeds the dispersive power 

 of diamond to dissolve white light into rainbow tints, in its powers 

 of reflection, refraction, and dispersion taken together the diamond 

 is unmatched." It is highly phosphorescent, and even the blackest 

 diamond is transparent to the X ray. The diamond glows under the 

 influence of the B rays from radium. Diamonds when subjected to 

 the action of radium for several months assume a green color, but 

 cut stones when treated in this manner seem to lose part of their 

 brilliancy. It is insoluble in all acids, and can easil}'^ be burned and 

 converted into carbon dioxide. It volatilizes at a temperature of 

 about 3,600° C. and passes from the solid to the gaseous state without 

 liquefying. 



Sir William Crookes went through the process of producing dia- 

 monds before the eyes of his audience, but was only able to show them 

 the result of this experiment by reproducing a lantern slide of 

 microscopical diamonds which he had made in the same way pre- 

 viously, for it takes a fortnight to separate them from the iron and 

 other substances in which they are embedded. The scientific prin- 

 ciple upon which this experiment rests, according to Sir William 

 Crookes, is that molten iron absorbs carbon, and as iron increases in 

 volume as it j)asses from the liquid to the solid state, if the outer 

 crust of the iron is suddenly cooled and the center remains in a liquid 

 state, the enormous pressure caused by its expanding while cooling 

 affords the tAvo factors necessary for the crystallization of a dia- 

 mond — heat and pressure. 



Authorities differ somewhat as to the exact moment when molten 

 iron expands on cooling, but it is the generally accepted theory that 

 expansion takes place at the moment of solidification. It is also a 

 well-known fact that shrinkage or contraction takes place as the 

 solidified metal cools. It is therefore possible to obtain enormous 

 pressure in the molten center of a casting by the contraction of the 

 outer shell which has been rapidly cooled and the expansion of the 

 inner mass just as it begins to solidify.^ 



It is noteworthy that the diamond is a nonconductor of electricity, 

 while graphite and amorphous carbon, substances so closely allied to 

 it in chemical composition, are good electrical conductors. By the 

 application of friction the diamond can be positively electrified, but 

 it very soon loses its electricity. The diamond is easily cleaved in 

 planes parallel to the octahedral faces. Pieces may be easily broken 

 from the facets of a cut stone by striking it with a hard substance. 



o Fenchtw anger's Ti'eatise on Gems. 



6 American Society Mechanical Engineers, Vol. XVIII, pp. 419 and 4.31; Vol. 

 XVII, pp. 12G and 1015. 



