g 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
are very brilliant; the latter is of nearly the same color as ordinary
diamond powder, but very much finer. When viewed under a microscope
the samples of crystals given to me did not appear to have any
definite form, but rather resembled pieces of broken up egg coal of
fine quality. The majority were opaque, but there were some which were
transparent and colored. The crystals are a kind of carbon containing
some impurities; they are extremely hard, and withstand for a long
time even an oxygen blast. When the blast is directed against them
they at first form a cake of some compactness, probably in consequence
of the fusion of impurities they contain. The mass withstands for a
very long time the blast without further fusion; but a slow carrying
off, or burning, occurs, and, finally,