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Experiments on Carbon HPHT

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From the Philosophical Magazine for September, 1893*
The primary object of these experiments was to obtain a dense form of carbon which should be more durable than the ordinary carbon when used in arc lamps, and at the same time to obtain a material better suited for the formation of the burners of incandescent lamps.
There were a considerable number of experiments made in which the conditions were somewhat alike, and many were almost repetitions with slightly varying pressures and temperatures. They may, however, be divided into two distinct classes: the first, in which a carbon rod surrounded by a fluid under great pressure is electrically heated by passing a large current through it; the second, in which the liquid is replaced by various substances such as alumina, silica, lime, etc.
The arrangement of the experiment was as follows: A massive cylindrical steel mould of about 3 inches internal diameter and 6 inches high was placed under an hydraulic press; the bottom of the mould was closed by a spigot and asbestos-rubber packing similar to the gas check in guns; the top was closed by a plunger similarly packed; this packing was perfectly tight at all pressures. In the spigot was a centrally bored hole into which the bottom end of the carbon rod to be treated fitted; the top end of the carbon rod was connected electrically to the mould by a copper cap which also helped to support the carbon rod in a central position. The bottom block and spigot were insulated electrically from the mould by asbestos, and the leading wires from the dynamo being connected to the block and mould respectively, the current passed along the carbon rod in the interior of the mould.
The fluid was run in so as to cover the rod completely. The plunger was then free to exert its pressure on the liquid without injuring the carbon. The pressure in the mould was indicated by the gauge on the press.
Experiments. Class I
Among the liquids tested were benzene, paraffin, treacle, chloride and bisulphide of carbon.
The pressures in the mould during the several experiments were main-
* From the Proceedings of the Royal Society, Vol. xliv. Communicated, with an additional note on Diamond Manufacture, by the Author.
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