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EXPERIMENTS ON CARBON AT HIGH TEMPERATURES
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tained
at from 5 to 15 tons per square inch; the initial size of the rod was
in all cases 1/4 inch, and the current from 100 to 300 amperes.
Results.
In some of these experiments a considerable quantity of gas was
generated, and the press had to be slightly slacked back during the
experiment to accommodate it and maintain the pressure constant.
In all cases there was a soft friable black deposit of considerable thickness on the carbon.
In
no case was the specific gravity of the carbon rod increased by this
process. There was no change in appearance of the fracture, excepting
when chloride of carbon had been the fluid; it was greyer in this case.
The
rate of burning of samples placed in arc lamps was not diminished by
the process. Various rates of deposition were tried, but with the same
result; and the conclusion seems to be that under very high pressures,
such as from 5 to 15 tons per square inch, the deposit of carbon by
heat from hydro-carbons, chloride of carbon, bisulphide of carbon,
treacle, etc., is of a sooty nature, and unlike the hard steel-grey
deposit from the same liquids or their vapours at atmospheric or lower
pressures.
Experiments. Class II
In
these experiments the asbestos-rubber packing was omitted, the plunger
and spigot being an easy fit in the mould. A layer of coke powder under
the plunger formed the top electrical connection with the rod.
No.
1. Silver sand or silica was run around the carbon rod, and pressures
of from 5 to 30 tons per square inch applied; the rod was usually about
1/4 inch diameter, and currents up to 300 amperes passed.
Results.
The silica was melted to the form of a small hen's egg around the rod.
When the current was increased to about 250 amperes the rod became
altered to graphite, the greater the heat apparently the softer the
graphite. There was no action between the silica and the carbon, the
surface of the carbon remained black, and there were no hard particles
in or on the carbon rod.
Other substances, such as an hydrated alumina and mixtures of alumina and silica, gave the same results.
The density of the carbon was considerably increased, in some cases from normal at 1-6 to 2-2 and 2-4;
in these cases the carbon appeared very dense, much harder than the
original carbon, and about as hard as the densest gas-retort carbon. No
crystalline structure was visible.
The
specimens were treated with solvents, and there appeared no indication
of the surrounding substance having penetrated the rod; the carbon was
undoubtedly consolidated by 30 per cent.
In some cases, when the material surrounding the rod was alumina
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