large coils for the cooling of the
air in the calorimeter laboratory. As the brine passes through this
coil, which is not shown in the figure, it cools the water in which it
is immersed and the water in turn cools the coil through which the
water-supply to the calorimeter passes. The brass coil only is shown in
the figure. The system is very efficient and we have no difficulty in
cooling the water as low as 2 deg. C. As a matter of fact our chief
difficulty is in regulating the supply of brine so as not to freeze the
water-supply.

_Water-mixer._--If the valve _b_ is opened, water flows through this
short length of pipe much more rapidly than through the long coil, owing
to the greater resistance of the cooling coil. In conducting these
experiments the valve c is opened wide and by varying the amount to
which the valve _b_ is opened, the water is evenly and readily mixed.
The thermometer C is in practice immersed in the water-mixer constructed
somewhat after the principle of the mixer inside the chamber described
on page 21. All the piping, including that under the floor, and the
reheater D, are covered with hair-felt and well insulated.

_Rate-valves._--It has been found extremely difficult to secure any form
of valve which, even with a constant pressure of water, will give a
constant rate of flow. In this type of calorimeter it is highly
desirable that the rate of flow be as nearly constant as possible hour
after hour, as this constant rate of flow aids materially in maintaining
the calorimeter at an even temperature. Obviously, fluctuations in the
rate of flow will produce fluctuations in the temperature of the ingoing
water and in the amount of heat brought away. This disturbs greatly the
temperature equilibrium, which is ordinarily maintained fairly constant.
Just before the water enters the reheater D it is caused to pass through
a rate-valve, which at present consists of an ordinary plug-cock. At
present we are experimenting with other types of valves to secure even
greater constancy, if possible.

_Electric reheater._--In order to control absolutely the temperature of
the water entering at E, it is planned to cool the water leaving the
water-mixer at C somewhat below the desired temperature, so that it is
necessary to reheat it to the desired point. This is done by passing a
current of electricity through a coil inserted in the system at the
point D. This electric reheater consists of a standard "Simplex" coi