A method of using the
tables, by which a closer approximation to the true temperature may be
reached, will be pointed out in a subsequent article.
[Illustration: Fig. 2.]
DETERMINATION OF THE CALORIFIC CAPACITY OF THE METALS OF THE PYROMETER,
in terms of water, i.e., in British thermal units.
First. Weigh the cup, or cell, the lower plate of the cover and the
metallic portion of the agitator, and compute their heat-capacity by the
specific heat of the respective metals. Compute also the heat capacity
of the thermometer; or, if it be long, of so much of it as is found to
share nearly the temperature of the immersed portion. The result will
be a minimum--indeed, in so small a vessel the inevitable loss by
conduction and radiation will amount to more than one-third as much as
the simple heat capacity of the metals.[1] The total must be ascertained
by an application of the method of mixture. Ascertain the temperature of
the interior of the instrument simply; pour in quickly but carefully a
known quantity of water, say about two pounds, of known temperature, say
about 100 deg. F., and ascertain the temperature as soon after pouring as
mixing can be properly performed.
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