NOV. 22 , I 9 I 5 
Improved Respiration Calorimeter 
3i9 
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 1 degree the temperature of 
water flowing at the rate of 1 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 effects sufficient to raise 
the temperature of the water about 1, 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 imthecoil 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 1 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 
