Nov. 23. igis Improved Respiration Calorimeter 317 



The coil passes once around the chamber and back again, the two 

 pipes lying not quite 5 cm. apart, with the disks on one slightly over- 

 lapping those on the other. The purpose of this arrangement is to 

 establish as much uniformity as possible in the absorption of heat from 

 the air enveloping the absorber. Incidentally this would result in cor- 

 responding uniformity in the density of the air affected by the absorber. 



Regulating and Measuring the Water Flow 



Water for the heat absorber is drawn from a small tank several feet 

 above the ceiling of the chamber, which is filled by water flowing from the 

 city main. An overflow pipe in the tank keeps the water supply at a 

 constant level ; and since the level at which the water leaves the absorber 

 is also fixed, the pressure in the system is constant. Under favorable 

 conditions the rate of flow through the absorber is quite regular. At 

 times, however, in cold weather, when a considerable amount of air is 

 dissolved in the water, some of the air that is liberated when the tempera- 

 ture of the water is raised gradually accumulates in the absorber and 

 reduces the rate of flow in an irregular manner. Under these conditions 

 the faster the rate, the more constant it is. For this reason a specially 

 devised rate valve is of only limited service in regulation of the rate of 

 flow, though it has some advantages over the common stopcock. 



The water leaving the heat absorber flows into a copper cylinder 

 holding about 3 liters and through a stopcock in the bottom of this into a 

 tank holding about 100 liters. This tank will catch all the water that 

 w^ould leave the heat absorber during a period of at least three hours, in 

 experiments in which the dissipation of heat in the chamber is about 100 

 Calories per hour, a rate of flow of 350 to 450 c. c. of water per minute, 

 with the temperature of the ingoing water about 16°, having been found 

 quite satisfactory in such circumstances. The large tank rests upon a 

 sensitive platform balance (PI. XXX) by which the weight of the water 

 is determined to o.oi kgm. The small cylinder catches the water that 

 flows while the tank is being weighed and emptied. 



Regulating the Temperature op Water Entering the Heat Absorber 



The temperature of the water entering the heat absorber is so com- 

 pletely under control that it may be kept indefinitely at any desired 

 point within narrow limits, or may be changed rapidly, if necessary, 

 from one point to another. To accomplish this, the water is first cooled 

 to a temperature below that at which it will be used and then brought to 

 the required temperature by electric heating. In these circumstances, 

 when any change in temperature is desired, it is necessary to vary only the 

 heating. The chilled water passes into a device called the preheater, 

 which does the greater part of the heating necessary to warm the water to 

 the desired temperature. The heating effect of this device is adjusted by 

 hand. From the preheater the water flows into the bottom of a large 



