measured on the dial pass through it for one
analysis. The air as measured in the meter is, however, under markedly
different conditions from the air inside the respiration chamber. While
there is the same temperature, there is a material difference in the
water-vapor present, and hence the moisture content as expressed in
terms of tension of aqueous vapor must be considered. This obviously
tends to diminish the true volume of air in the meter.

Formerly we made accurate correction for the tension of aqueous vapor
based upon the barometer and the temperature of the meter at the end of
the period, but it has now been found that the reduction of the meter
readings to conditions inside of the chamber can be made with a
sufficient degree of accuracy by multiplying the volume of air passing
through the meter by a fraction, _(h-t)/h_, in which _h_ represents the
barometer and _t_ the tension of aqueous vapor at the temperature of the
laboratory, 20 deg. C. Since the tension of aqueous vapor at the
laboratory temperature is not far from 15 mm., a simple calculation will
show that there may be considerable variations in the value of _h_ without
affecting the fraction materially, and we have accordingly assumed a
value of _h_ as normally 760 mm., and the correction thus obtained is
(760 - 15)/760 = 0.98, and all readings on the meter should be
multiplied by this fraction.

On the one hand, then, there is the correction on the meter itself,
which correction is +1.4 per cent (see page 75); and on the other hand
the correction on the sample for the tension of aqueous vapor, which is
-2.0 per cent, and consequently the resultant correction is -0.6 per
cent. From the conditions under which the experiments are made, however,
it is rarely possible to read the meter closer than +-0.05 liter, as the
graduations on the meter correspond to 50 cubic centimeters. It will be
seen, then, that this final correction is really inside the limit of
error of the instrument, and consequently with this particular meter now
in use no correction whatever is necessary for the reduction of the
volume. The matter of temperature corrections has been taken up in great
detail in an earlier publication, and where there are noticeable
differences in temperature between the meter and the calorimeter chamber
the calculation is very much more complicated.

For practical purposes, therefore, we may assume that the quantity of
air passed through the meter, as now