Some notes on Carbon HPHT

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	ARTIFICIAL PRODUCTION OF DIAMOND 221 gressively increased charges were used, and even with relatively small charges the block cracked on the second round. With the 90 per cent, excess charge, the block always split on the first shot, but this probably occurred after impact, and not till the full instantaneous pressure had been exerted, which was estimated to be greater than with the plain hole, probably over 5000 tons. Only graphite was placed at the bottom of the hole in these latter experiments, and the analysis yielded nothing. Experiments on pressure in cast iron when cooled

	It has been generally assumed that iron rich in carbon expands on setting, and that this supposed property is a contributory cause in the formation of diamond.



	Several experiments were made by pouring iron saturated with carbon from the electric furnace through a narrow git into a very massive steel mould, closed at the bottom with a breech screw (Fig. 9). When cold, the breech screw was easily removed, and there was no sign of any appreciable pressure having come on the threads. Not being sure that, because of capillarity, the corners of the mould had been quite filled, a steel mandril was, immediately after pouring, forced down the git-hole by a press giving a fluid pressure in the mould of 75 atmospheres. The observed pressure on the breech screw appeared not to have exceeded this pressure. Highly carburised iron, therefore, does not expand with any considerable force on setting. The reason why a lump of cast iron thrown into a ladle of molten metal first sinks to the bottom and soon rises and floats on the surface is probably that cast iron is about seven times stronger in compression than in tension.

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