THE ROMANCE OP THE DIAMOND 9 



As is well known, iron increases in volume at the moment 

 of passing from the liquid to the solid state. The sudden 

 cool ing solidifies the outer layer of iron and holds the inner 

 molten mass in a tight grip. The expansion of the inner 

 liquid on solidifying produces an enormous pressure, and 

 under the stress of this pressure the dissolved carbon 

 separates out in transparent forms minutely microscopic, 

 it is true but all the same veritable diamonds, with crystal- 

 line form and appearance, color, hardness and action on 

 light the same as the natural gem. 



Now commences the tedious part of the process. The 

 metallic ingot is attacked with hot nitro-hydrochloric acid 

 until no more iron is dissolved. The bulky residue con- 

 sists chiefly of graphite, together with translucent chest- 

 nut-colored flakes of carbon, black opaque carbon as 

 hard as diamonds black diamonds, in fact and a small 

 portion of transparent colorless diamonds showing crystal- 

 line structure. 



The residue is first heated for some hours with strong 

 sulphuric acid at the boiling-point, with the cautious addi- 

 tion of powdered nitre. It is then well washed, and for 

 two days allowed to soak in strong hydrofluoric acid in 

 cold, then in boiling, acid. After this treatment the soft 

 graphite disappears, and most, if not all, the silicon com- 

 pounds have been destroyed. 



Hot sulphuric acid is again applied to destroy the flu- 

 orides; and the residue, well washed, is attacked with a 

 mixture of the strongest nitric acid and powdered potas- 

 sium chlorate, kept warm but not above 60 C., to avoid 

 explosions. This treatment must be repeated six or eight 

 times, when all the hard graphite will gradually be dis- 

 solved, and little else left but graphitic oxid, diamond and 

 the harder carbonado or black diamond and boart. The 

 residue is fused for an hour in fluorhydrate of fluorid of 

 potassium, then boiled out in water, and again heated in 

 sulphuric acid. 



The well-washed grains which resist this energetic treat- 



