THE CALORIMETER SYSTEM AND MEASUREMENT OF HEAT. 123 



The ingoing air is caused to pass over a 32-candlepower 2 20- volt 

 lamp, which is placed in an enlargement of the air-pipe made of a gal- 

 vanized-iron T and a short section of pipe, with a cap. The position 

 of the lamp is shown in figure 32. The connections between this lamp 

 and the electrical circuits are shown in figure 37, in which it is seen 

 that the lamp-cord is connected with two binding posts on the wall of 

 the calorimeter. These binding posts are connected in turn by two 

 wires leading to the rheostat on the observer's table. As with the 

 heating circuits for the air-spaces about the calorimeter, here also the 

 amount of heat developed in the electric lamp, and consequently the 

 degree of warming the air current, can be regulated with great exact- 

 ness by means of the variable resistance (see p. 1 18) connected with the 

 rheostat. 



When, as is occasionally the case, the temperature of the air in the 

 calorimeter laboratory is greater than that of the interior of the cham- 

 ber, it is necessary to cool the air current. This is accomplished by 

 causing a current of cold water to flow through a lead pipe which is 

 closely coiled about the ingoing air-pipe. The lead pipe is connected 

 at one end with the water supply and at the other end with the drain. 

 By opening a small wheel valve at the extreme left of the lower row of 

 valves at the observer's table (see fig. 37) water can be caused to pass 

 through this pipe and effect the cooling of the air. To prevent sudden 

 changes caused by variations in the room temperature, the lead pipe is 

 covered with cotton felt and canvas, as is seen in figures 3 and 37. 



MEASUREMENT OF HEAT. 



It has been stated that most of the heat generated within the chamber 

 is carried away by a current of cold water. The quantity thus brought 

 out is determined from the amount of water, its rise in temperature, 

 and the specific heat of water at different temperatures. The devices 

 for absorbing the heat and the method of determining the quantity 

 generated are here described. For illustration of this description refer- 

 ence is continually made to the view of the interior of the chamber 

 shown in figure 33. 



THE HEAT-ABSORBING SYSTEM. 



The device for absorbing heat is shown at H, H, H, in figure 33. 

 Copper pipe, of about 10 mm. outside diameter, bent to conform to 

 the shape of the chamber, is suspended from the ceiling at about 13 

 cm. from each wall. A large number of sheet copper disks, about 

 5 cm. in diameter, are soldered along the pipe at intervals of about i 

 cm., their purpose being to increase the area of surface exposed to 



