. Carnegie Institution of Washington publication. THE REGULATION OF TEMPERATURE. 67 temperature of the hydrant water and that which is to be maintained in the bath. If the hydrant water is to be cooled before entering the bath, as when a low temperature, e. g., 5°, is to be maintained in sum- mer, it is first passed through the coils of pipe seen in Figure 33, which are embedded in ice. The arrangement shown in Figure 32 C is also employed in this bath to secure a constant pressure upon the circulating Fig. 34.—Rectangular bath for general laboratory use. (1) to (8) Brass tubes for cir
. Carnegie Institution of Washington publication. THE REGULATION OF TEMPERATURE. 67 temperature of the hydrant water and that which is to be maintained in the bath. If the hydrant water is to be cooled before entering the bath, as when a low temperature, e. g., 5°, is to be maintained in sum- mer, it is first passed through the coils of pipe seen in Figure 33, which are embedded in ice. The arrangement shown in Figure 32 C is also employed in this bath to secure a constant pressure upon the circulating Fig. 34.—Rectangular bath for general laboratory use. (1) to (8) Brass tubes for circulation of hydrant water; (9) and (10) copper cylinders, opening on opposite sides of the bath, for the lamps; (11) pump; (12) and (13) pipes through which water is drawn out of the bath and over the gas stoves seen at the end; (14) large pipe through which water heated by the gas stoves is drawn and delivered at (11). A word of caution may be given regarding the valves to be used when a constant pressure on running water is to be maintained. Our first pressure arrangements were constructed in accordance with correct prin- ciples, so far as we knew, but it was found that they would not maintain constant pressures. The flow of water diminished continually, and very small streams ceased altogether after a time. After a long search, the difficulty was located in the valves. Those we were using—the so-called "gate-valves"—were found to be so constructed as to permit the accumulation of the gas which is expelled from water, when its tem- perature is raised, to such an extent as to impede the flow of the water, and to stop it altogether if only a little were passing through the valves. After replacing the "gate-valves" by others of the common lever variety, the difficulty disappeared. The "heating" surface is furnished by the two copper cylinders (9 and 10), the latter of which is broken in order to show the location of the stoves. The large wood
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