THE ARTIFICIAL PRODUCTION OF DIAMOND. 79 



percentages of aluminium, magnesium, calcium, one or all are important ; sulphur, 

 manganese, and cobalt increase the yield, nickel appeared to be a disadvantage. An 

 alloy of iron and 10 per cent, manganese, 10 per cent, cobalt, and 5 per cent, silicon 

 gave out much gas when cooled slowly, and on quick cooling in water and mercury 

 most of the spherules were burst and shredded. 



Finally about 1 to 3 per cent, of the other elements added to iron appeared to give 

 the best results and the spherules were not then burst. 



An experiment was made by letting the ingot remain in the bed till it had quite 

 set, hard enough to handle with the iron spoon, and then, cooled in water and 

 mercury, it gave a fair diamond residue. 



Experiments on the Conversion of Diamond to Graphite. 



A clear octahedral diamond was placed in a small carbon crucible and packed 

 loosely with Acheson graphite and heated for 10 minutes to about 1400" C. The 

 diamond was coated with a firm layer of graphite. 



After two prolonged treatments with fuming nitric acid and potassium chlorate, 

 alternating with boiling sulphuric acid and nitre, the opaque coating was removed 

 and there remained a blackish translucent skin. When fractured the interior was 

 unaltered and perfectly transparent. 



A piece of bort somewhat laminated, after the same treatment, showed the 

 laminations separated by cracks starting from the outside. Upon breaking, the 

 interior surface of the fissures showed an incipient change to graphite, but less rapid 

 than on the outside surface. There was a sinuous pitting, deepest near the outside 

 and diminishing inwards. The substance of the bort between the fissures was 

 unaltered. 



The change of diamond to graphite under the conditions described is gradual, th<^ 

 surrounding gases, carbon monoxide, carbon dioxide, nitrogen, hydrogen, and also 

 vapour of iron (as an impurity in the graphite) singly, or collectively, probably play a 

 part, and further investigation as to this seems to be desirable. 



Sir JAMES DEWAR, in 1880, heated a diamond in a carbon tube to a temperature of 

 2000 C., while a flow of pure hydrogen was maintained through the tube. The 

 diamond soon became covered with a coating of graphite (' Proceedings of the Royal 

 Institution '). 



A clear diamond plunged into molten iron saturated with carbon at about 1400 C. 

 for 5 minutes was deeply pitted. When removed from the iron small globules of iron 

 adhered to the surface and the pits appeared to occur at these spots. 



A clear diamond was disintegrated by cathode rays, the temperature by pyrometer 

 being 1890 C., the splinters were quite black and opaque, but after several prolonged 

 treatments with fuming nitric acid and potassium chlorate, alternating with boiling 

 sulphuric acid and nitre, the coating that remained was a dusky grey, but 



