From experiences of this kind I am led to infer that, in order to be
most durable, the refractory button in the bulb should be in the form
of a sphere with a highly polished surface. Such a small sphere could
be manufactured from a diamond or some other crystal, but a better way
would be to fuse, by the employment of extreme degrees of temperature,
some oxide--as, for instance, zirconia--into a small drop, and then
keep it in the bulb at a temperature somewhat below its point of
fusion.
Interesting and useful results can no doubt be reached in the
direction of extreme degrees of heat. How can such high temperatures
be arrived at? How are the highest degrees of heat reached in nature?
By the impact of stars, by high speeds and collisions. In a collision
any rate of heat generation may be attained. In a chemical process we
are limited. When oxygen and hydrogen combine, they fall,
metaphorically speaking, from a definite height. We cannot go very far
with a blast, nor by confining heat in a furnace, but in an exhausted
bulb we can concentrate any amount of energy upon a minute button.
Leaving practicability out of consideration, this, then, would be the
means which, in my opinion, would enable us to reach the highest
temperature. But a great difficulty when proceeding in this way is
encountered, namely, in most cases the body is carried off before it
can fuse and form a drop. This difficulty exists principally with an
oxide such as zirconia, because it cannot be compressed in so hard a
cake that it would not be carried off quickly. I endeavored repeatedly
to fuse zirconia, placing it in a cup or arc light carbon as indicated
in Fig. 23. It glowed with a most intense light, and the stream of the
particles projected out of the carbon cup was of a vivid white: but
whether it was compressed in a cake or made into a paste with carbon,
it was carried off before it could be fused. The carbon cup containing
the zirconia had to be mounted very low in the neck of a large bulb,
as the heating of the glass by the projected particles of the oxide
was so rapid that in the first trial the bulb was cracked almost in an
instant when the current was turned on. The heating of the glass by
the projected particles was found to be always greater when the carbon
cup contained a body which was rapidly carried off--I presume because
in such cases, with the same potential, higher speeds were reached,
and also because, per unit of time, more matter was projected--that
is, more particles would strike the glass.
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