1897.] on Diamonds. 493 



and the lowest that of hydrogen, about 20 atmospheres. In other 

 words, the critical pressure of water is ten times that of hydrogen, 

 and the critical pressure of carbon is ten times that of water. 



Now 15 tons on the square inch is not a difficult pressure to 

 obtain in a closed vessel. In their researches on the gases from 

 fired gunpowder and cordite, Sir Frederick Abel and Sir Andrew 

 Noble obtained in closed steel cylinders pressures as great as 95 tons 

 to the square inch, and temperatures as high as 4000° C. Here, then, 

 if the observations are correct, we have sufficient temperature and 

 enough pressure to liquefy carbon; and if the temperature could only 

 be allowed to act for a sufficient time on the carbon there is little 

 doubt that the artificial formation of diamonds would soon pass from 

 the microscopic stage to a scale more likely to satisfy the require- 

 ments of science, industry and personal decoration. 



I now proceed to manufacture a diamond before your eyes — don't 

 think I yet have a talisman that will make me rich beyond the 

 dreams of avarice ! Hitherto the results have been very microscopic 

 and are chiefly of scientific interest in showing us Nature's workshop, 

 and how we may ultimately hope to vie with her in the manufacture 

 of diamonds. Unfortunately the operations of separating the diamond 

 from the iron and other bodies with which it is associated are some- 

 what proloniicd — nearly a fortnight being required to detach it from 

 the iron, graphite and other matters in which it is embedded. I can, 

 however, show the dilferent stages of the operations, and project on 

 the screen diamonds made in this manner. 



In Paris recently I saw the operation carried out by M. Moissan, 

 the discoverer of this method of making carbon separate out in the 

 transparent crystalline form, and I can show you the operations 

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

 indebted to the Directors of the Notting Hill Electric Lighting 

 Co., and to the general manager, Mr. Schultz, 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 lirst necessity is to select pure iron — free from sulphur, 

 silicon, phosphorus, &c. — 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 carbon poles, utilising a current of 700 amperes 

 at 40 volts pressure. The iron rapidly melts and saturates itself 

 with carbon. After a few minutes' heating to a temperature above 

 4000° C. — a temperature at which the lime of the furnace melts like 

 wax and volatilises 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, 



