THE REGULATION OF TEMPERATURE. 65 



tain fairly distinct types, though differing much among themselves in 

 respect to details. An example of each type will be given. 



Type I. 



This bath (Figures 32 and 33), which was designed for general but 

 intermittent use in connection with the work, consists of a cylindrical 

 tank of galvanized iron, which holds from 60 to 80 liters. It is sur- 

 rounded by a thick covering of hair felt (c, Figure 32), and rests upon a 

 wooden base (a, a), which is raised above the table or floor by the blocks 

 and rubber pieces (b, b). Inverted over the hole in the center, and 

 riveted and soldered to the bottom of the bath, is the cylinder (d, d, d), 

 which serves as a receptacle for the lamp (e), or any other suitable kind 

 of electrical heating device. The lamp is mounted, in the manner 

 indicated in the figure, upon the removable block (/), which is held in its 

 place by buttons screwed to the base (a, a). Resting upon the frame- 

 work i, i (Figure 32) and i, i, i (Figure 32 B) is the continuous block-tin 

 pipe (j, j, j, j), through which the hydrant water circulates. The cyl- 

 inder (d, d, d) constitutes the "heating" surface, and the pipe (j,j,j,j) 

 the "cooling" surface. The running water enters the bath at k and 

 leaves at I (Figures 32 and 32 B) . The course of the water in the pipe, 

 after entering the bath, is continuously horizontal or upward — never 

 downward. This arrangement is necessary in order to prevent the 

 lodgment of air in any part of the pipe. The successive coils of pipe 

 (six in number) are separated by the pegs seen in Figures 32 and 32 B, 

 and on these rests the galvanized iron disk (m, m). The hood (n, n), of 

 the same material, shuts down tightly over a flange on the disk (m, m) 

 and is adjusted and secured in its place by set screws directed towards 

 d, d. The form of the hood will be clear from the figure, and it is neces- 

 sary only to call attention to the small holes for the escape of air at o, o, 

 and to the larger holes at p, p, through which much of the water raised 

 by the propeller (r) escapes into the outer bath. 



The purpose of the various parts which go with the propeller— the 

 adjustable cross-bar (w, w), which is clamped to the sides of the bath, 

 the oil cup (t), the pulley (s), etc. — is sufficiently obvious. 



It is quite essential that the hydrant water which flows through the 

 pipe shall be under constant pressure, otherwise much water and heat 

 are necessarily wasted. The arrangement by which the constant pres- 

 sure is secured is shown in Figure 32 C. It consists of a large standpipe 

 (ad) with an overflow (bd) near the top. The water from the tap enters 

 at the bottom (dd) and passes to the bath through cd, where the flow is 

 controlled by a stopcock. The circulating water is thus brought under 

 an invariable pressure, and it is possible to regulate the quantity pass- 

 ing through the bath with considerable nicety and for any length of 

 time. At the highest point in the waste pipe (z, Figure 32) is placed a 

 vent through which any air carried along by the water may escape. 



