holds good: the button withstands the bombardment better with currents
of very high frequency. But this is due to the fact that a high
frequency discharge passes through a rarefied gas with much greater
freedom than a steady or low frequency discharge, and this will say
that with the former we can work with a lower potential or with a less
violent impact. As long, then, as the gas is of no consequence, a
steady or low frequency current is better; but as soon as the action
of the gas is desired and important, high frequencies are preferable.
In the course of these experiments a great many trials were made with
all kinds of carbon buttons. Electrodes made of ordinary carbon
buttons were decidedly more durable when the buttons were obtained by
the application of enormous pressure. Electrodes prepared by
depositing carbon in well known ways did not show up well; they
blackened the globe very quickly. From many experiences I conclude
that lamp filaments obtained in this manner can be advantageously used
only with low potentials and low frequency currents. Some kinds of
carbon withstand so well that, in order to bring them to the point of
fusion, it is necessary to employ very small buttons. In this case the
observation is rendered very difficult on account of the intense heat
produced. Nevertheless there can be no doubt that all kinds of carbon
are fused under the molecular bombardment, but the liquid state must
be one of great instability. Of all the bodies tried there were two
which withstood best--diamond and carborundum. These two showed up
about equally, but the latter was preferable, for many reasons. As it
is more than likely that this body is not yet generally known, I will
venture to call your attention to it.
It has been recently produced by Mr. E.G. Acheson, of Monongahela
City, Pa., U.S.A. It is intended to replace ordinary diamond powder
for polishing precious stones, etc., and I have been informed that it
accomplishes this object quite successfully. I do not know why the
name "carborundum" has been given to it, unless there is something in
the process of its manufacture which justifies this selection. Through
the kindness of the inventor, I obtained a short while ago some
samples which I desired to test in regard to their qualities of
phosphorescence and capability of withstanding high degrees of heat.
Carborundum can be obtained in two forms--in the form of "crystals"
and of powder. The former appear to the naked eye dark colored, but
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