But a correction is necessary for
loss of heat in the act of pouring. To ascertain the amount of this
correction prepare a bath of tepid water, and bring all parts of the
instrument--outside, inside, and interior portions, together with the
vessel to pour from--exactly to one common, carefully ascertained
temperature. Now take two pounds of the water and pour it into the
cell in the same manner as before. Exposure of so thin a stream on
two surfaces to the air of the room will produce a certain degree of
refrigeration in the water, which is supposed to be warmer than the air,
say at about 160 deg. F. This effect will be due to conduction, by contact
with the air, to radiation, and to evaporation; and by so much the
refrigeration observed in mixing is to be diminished.
[Footnote 1: In our case the heat-capacity, thermometer included, was
0.0757; total, 0.1053; radiation, etc., 0.0296. Respectively, 71.9 per
cent, and 28.1 per cent. of the total.]
Four experiments, carefully conducted, gave the following results:
Loss of temperature by pouring at 170 deg. F., 0.81 deg., 0.86 deg., 1.00 deg., and
1.07 deg. F.; mean, 0.935 deg. F.
The following are values of the calorific capacity of my pyrometers,
that is, of those parts of each which share directly the temperature
of the inclosed water, including the thermometer to be used with the
instrument, and the heat communicated to the eider-down and otherwise
lost during an observation, expressed in decimals of a British thermal
unit, or in decimals of a pound of cold water:
0.
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