228 DIAMONDS. 



straight, as it were, from the inventor's laboratory. I am also indebted 

 to the directors of the iNotting Hill Electric Lighting Company and to 

 the general manager, Mr. Scliultz, for enabling me to perform several 

 operations at their central station, where currents of 500 amperes and 

 100 volts were placed at my disposal. 



The first necessity is to select pure iron — free from sulphur, silicon, 

 phosphorus, etc. — and to pack it in a carbon crucible with pure charcoal 

 from sugar. Half a pound of this iron is then put into the body of the 

 electric furnace, and a powerful arc formed close above it between car- 

 bon poles, utilizing a current of 800 amperes at 40 volts pressure. The 

 iron rapidly melts and saturates itself with carbon. After a few min- 

 utes' heating to a temperature above 4,000° C. — a temperature at which 

 the lime of the furnace melts like wax and volatilizes in clouds — the 

 current is stopped, and the dazzling fiery crucible is plunged beneath 

 the surface of cold water, where it is held till it sinks below a red heat. 

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

 from the liquid to the solid state. The sudden cooling 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 pressuie the dissolved carbon 

 separates out in a transparent, dense, crystalline form — in fact, as 

 diamond. 



Now commences the tedious part of the process. The metallic ingot 

 is attacked with hot nitro-hydrochloric acid until no more iron is dis- 

 solved. The bulky residue, consisting chiefly of .graphite, together 

 with translucent iiakes of a chestnut- colored carbon, black opaque car- 

 bon of a density of from 3 to 3.5, and hard as diamonds — black dia- 

 monds or carbonado, in fact, and a small portion of transparent colorless 

 diamonds showing crystalline structure. Besides these, there may be 

 carbide of silicon and corundum, arising from imijurities in the mate- 

 rials employed. 



The residue is first heated for some hours with strong sulphuric acid 

 at the boiling point, with the cautious addition of powdered niter. It 

 is then well washed and allowed for two days to soak in strong hydro- 

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

 soft graphite will disappear, and most, if not all, of the silicon com- 

 pounds will be destroyed. Hot sulphuric acid is again applied to 

 destroy the fluorides, and the residue, well washed, is repeatedly 

 attacked with a mixture of the strongest nitric acid and powdered 

 potassium chlorate, kept warm, but, to avoid explosions, not above 

 60*° 0. This ceremony must be repeated six or eight times, when all 

 the hard graphite will gradually be dissolved, and little else left but 

 graphitic oxide, diamond, and the harder carbonado and bort. The 

 residue is fused for an hour in fluorhydrate of fluoride of potassium, 

 then boiled out in water, and again heated in sulphuric acid. The 

 well-washed grains which resist this energetic treatment are dried, 



