ARTIFICIAL PRODUCTION OF DIAMOND	227
	preliminary experiment as the container. The crucible was turned out of a l-1/2-inch carbon rod, and so formed on a stem that the electric current heated the bottom and sides equally. The cover was similarly formed and its holder was electrically connected with the container, but free to move vertically and to rest its weight on the crucible, electrical connection to the container being made by a layer of brass or iron turnings resting on the holder. A current of 1000 amperes at 16 volts sufficed, and the tempera­ture was observed through a glass window at the side of the container. The crucible was charged with reduced iron and lampblack. The Geryk pump evacuated the container to f inch mercury absolute; current was turned on for 15 seconds, the vacuum fell to 3 inches, when it had risen
	again to | inch current was again turned on. This was repeated three or four times, finally current was applied for 30 seconds and the vacuum again fell to 3 inches. The gas was drawn off and collected, it amounted to a total of 1/2 gallon at atmospheric pressure and consisted of 95 per cent, carbon monoxide, 1 per cent, hydrogen, 2 per cent, hydrocarbon, 2 per cent, nitrogen. The carbon which formed the crucible and cover contained a large per­centage of sihca, but the carbon monoxide was produced chiefly by the action of sand (of which there was a thick layer on the bottom of the container to protect the insulating joint from iron spilled from the crucible) on the carbon of the stem of the crucible. About one half of the iron had been evaporated, and there remained an ingot about the size and shape of a broad bean. It contained rather large graphite crystals and was easily broken. The analysis gave the largest residue of diamond in proportion
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