THE ARTIFICIAL PRODUCTION OF DIAMOND. 
89 
it was noticed that in the water-cooled areas of the quartz tube a lustrous black rino- 
had formed. On being strongly heated, some of this, evidently carbon, burnt off, 
leaving a white film, presumably silica. This seems to show that a volatile silico- 
organic compound, containing carbon, hydrogen, and silicon, was evolved from the 
iron on heating.” 
It would appear from our experiments that probably a ferro-silicon carbonyl is 
given off from the iron, for, as has been said, we observed a corrosive action on 
carborundum by tlie gas evolved from iron borings at red heat under a liigh vacuum, 
and the same action was produced by gaseous ferro-carbonyl, and also by carbon 
monoxide, previously passed over molten iron sulpliide at atmospheric pressure. 
Let us consider what happens in an ingot or spherule when rapidly cooled 
simultaneously on all sides. It is first surrounded by a thin coat of solidified metal 
which, below 600° C., is impervious to gases. As the coat thickens layer within 
layer, more and more gas is ejected by the solidifying metal, and its semi-solidified 
centre, still pervious to gas, receives the charge. As this process progresses the 
pressure may rise higher and higher, though there may be a limit to the pressure 
against which the metal is able to eject gas when setting. All we, however, know is, 
that the mechanical strength of the ingot or spherule places a limit of about 7000 
atmospheres on the gaseous pressure, and, as we have already mentioned in the case 
of some iron alloys, most of the spherules are split or shredded, with an appearance 
consistent with this view. 
Crookes’ microscopical examination of diamonds with polarized light supports this 
view. In his lecture at Kimberley, in 1905, he states: “I have examined many 
hundred diamond crystals under polarized light, and with few exceptions all show 
the presence of internal tension. 
“ On rotating the polarizer, the black cross most frequently seen revolves round a 
particular point in the inside of the crystal; on examining this point with a high 
power we sometimes see a slight flaw, more rarely a minute cavity. The cavity is 
ffilecl with gas at enormous pressure, and the strain is set up in the stone by the 
effort of the gas to escape.” 
It seems therefore probable, or indeed almost certain, from the accumulated 
evidence, that the chief function, of quick cooling in the production of diamond in an 
ingot or spherule is to bottle up and concentrate into local spots the gases occluded 
in the metal which, under slow cooling, would partially escape and the remainder 
become evenly distributed throughout the mass. 
As to the condition in which the gases exist within the iron at temperatures above 
500° C. little is known, though at 200° C. and at 180 atmospheres Mond has shown 
that iron penta-carbonyl is formed. The intimate contact betAs^een the occluded 
gases and other elements, metals or carbides, must favour complex interactions as 
cooling takes place. Such actions might be concentrated by the heat flow across the 
metal on quick cooling. 
