f vacuum-jacketed glass tube, which gives the
most satisfactory insulation. However, this system of insulation is
impracticable when electric-resistance thermometers are used for
recording the water-temperature differences and can be used only when
mercurial thermometers exclusively are employed. The electric-resistance
thermometers are constructed in such a way, however, as to make
negligible any inequalities in the passage of heat through the
hard-rubber casing. This will be seen in the discussion of these
thermometers.

_Measuring the water._--As the water leaves the respiration chamber it
passes through a valve which allows it to be deflected either into the
drain during the preliminary period, or into a small can where the
measurements of the rate of flow can readily be made, or into a large
tank (G, fig. 14) where the water is weighed. The measurement of the
water is made by weight rather than by volume, as it has been found that
the weighing may be carried out with great accuracy. The tank, a
galvanized-iron ash-can, is provided with a conical top, through an
opening in which a funnel is placed. The diagram shows the water leaving
the calorimeter and entering the meter through this funnel, but in
practice it is adjusted to enter through an opening on the side of the
meter. After the valve _f_ is tightly closed the empty can is weighed.

When the experiment proper begins the water-current is deflected so as
to run into this can and at the end of an hour the water is deflected
into a small can used for measuring the rate of flow. While it is
running into this can, the large can G is weighed on platform scales to
within 10 grams. After weighing, the water is again deflected into the
large can and that collected in the small measuring can is poured into G
through the funnel. The can holds about 100 liters of water and
consequently from 3 to 8 one-hour periods, depending upon the rate of
flow, can be continued without emptying the meter. When it is desired to
empty the meter at the end of the period, the water is allowed to flow
into the small can, and after weighing G, the valve _f_ is opened. About
4 minutes are required to empty the large can. After this the valve is
again closed, the empty can weighed, and the water in the small
measuring-can poured into the large can G through the funnel. The scales
used are the so-called silk scales and are listed by the manufacturers
to weigh 150 kilograms. This form of scales