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, a small quantity of a
glass-like residue is left, which, I suppose, is melted alumina. When
compressed strongly they conduct very well, but not as well as
ordinary carbon. The powder, which is obtained from the crystals in
some way, is practically non-conducting. It affords a magnificent
polishing material for stones.
The time has been too short to make a satisfactory study of the
properties of this product, but enough experience has been gained in a
few weeks I have experimented upon it to say that it does possess some
remarkable properties in many respects. It withstands excessively high
degrees of heat, it is little deteriorated by molecular bombardment,
and it does not blacken the globe as ordinary carbon does. The only
difficulty which I have found in its use in connection with these
experiments was to find some binding material which would resist the
heat and the effect of the bombardment as successfully as carborundum
itself does.
I have here a number of bulbs which I have provided with buttons of
carborundum. To make such a button of carborundum crystals I proceed
in the following manner: I take an ordinary lamp filament and dip its
point in tar, or some other thick substance or paint which may be
readily carbonized. I next pass the point of the filament through the
crystals, and then hold it vertically over a hot plate. The tar
softens and forms a drop on the point of the filament, the crystals
adhering to the surface of the drop. By regulating the distance from
the plate the tar is slowly dried out and the button becomes solid. I
then once more dip the button in tar and hold it again over a plate
until the tar is evaporated, leaving only a hard mass which firmly
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