Nov. 22, I9I5 Improved Respiration Calorimeter 319 



There are seven resistance coils in the heater, of which four have a 

 resistance of about 340 ohms each. There would be a little less than 

 0.65 ampere of current flowing in such a coil at 220 volts, which would 

 give approximately 140 watts. To raise i degree the temperature of 

 water flowing at the rate of i liter per minute requires approximately 

 70 watts; hence, each of these four coils would increase the temperature 

 about 2 degrees. The resistances of the three other coils are, respectively, 

 about 680, 1,360, and 2,720 ohms, and their output, respectively, about 

 70, 35, and 18 watts, with corresponding heating efi'ects sufficient to raise 

 the temperature of the water about i, 0.5, and 0.25 degree. 



If these coils were all wound in one tube, the heater would be incon- 

 veniently long. Two similar tubes, each 30 mm. long, are used, with 

 the five coils of smaller resistance in one and the two coils of larger 

 resistance in the other. The cold water flows first through the former 

 and then through the latter. The two tubes mounted side by side on 

 the same base may be seen in Plate XXXVI, figure 2, on a board attached 

 to the side of the calorimeter. 



WATER HEATER OPERATED AUTOMATICALLY 



The final regulation of the temperature of the water for the heat 

 absorber is done in a short tube inclosing a water channel, called the 

 "final heater," which is shown in Plate XXXVI, figure 2, beside the 

 preheater, on the board attached to the side of the calorimeter. In the 

 upper end of the channel is an electric resistance thermometer coil that 

 is connected with an indicator on which may be set the temperature at 

 which it is desired to keep the water entering the heat absorber. In the 

 lower end of the channel is an electric heating coil, in series with which is 

 a rheostat for varying the current in the coil. The slider of the rheostat 

 is adjusted by a screw shaft that is driven by a small electric motor. 

 The water passing through the channel flows directly from the heater to 

 the thermometer. If the temperature of the water flowing over the 

 thermometer differs as much as 0.05 degree from that set on the indicator, 

 the armature of the small motor turns in one direction or the other, de- 

 pending on whether the water is too cold or too warm, and adjusts the 

 rheostat until the current in the coil is just enough to heat the water to 

 the desired temperature. 



The water tube in this device, which is 28 cm. long, has a narrow 

 channel, the cross section being 12 mm. in length and 4 mm. in width 

 and having round ends. It was made by flattening thin- walled copper 

 tubing of an external diameter of i cm. At each end the tubing is 

 left circular in cross section and is soldered into a short nipple, which is 

 screwed into one end of a special brass fitting with side outlets. Thin- 

 walled brass tubing 2.5 cm. in external diameter, extending from one 

 nipple to the other, forms a case around the channel, protecting it from 



