ACCESSORY APPARATUS. 6 1 



made, and, as it need be read only to the nearest half degree, no 

 corrections are made. Consequently to facilitate in the calculations, 

 reference is made to tables giving the true correction to be deducted in 

 every case from the actual reading of the barometer and for every 

 half inch difference in the height of the barometer and for every half 

 degree difference in the temperature. The correction as recorded 

 on this table is the standard temperature correction for reducing the 

 mercury column minus the scale error and capillarity correction of this 

 special barometer (0.002 inch), as mentioned above. To facilitate the 

 calculations, the corrected reading of the barometer is converted by 

 means of a table to the metric reading in one-hundred ths of a millimeter. 



OBSERVATION OF TEMPERATURE. 



The total air in the closed circuit may be considered as being made 

 up of two portions. The larger portion, amounting to about 5,000 

 liters, is that in the respiration chamber proper ; the remaining portion, 

 of about 62 liters, is that contained in the air-pipe, absorbing system, 

 pump, and pans. (See p. 70.) 



The air in the chamber is maintained at a fairly constant temperature 

 as a result of the heat-regulation devices described elsewhere (p. 124). 

 The temperature is recorded quite accurately by means of the electrical 

 resistance thermometers (p. I35). 1 These thermometers are assumed to 

 give the temperature of the air within 0.01. In addition, a mercury 

 thermometer, graduated to tenths of degrees, is suspended in the cham- 

 ber near the window as a guide to the actual temperature expressed in 

 degrees centigrade. 



The air outside the chamber is subject to a number of temperature 

 fluctuations. As has been described, the calorimeter laboratory is 

 heated by steam-pipes suspended near the top of the room. Conse- 

 quently a very great difference in temperature exists between the air at 

 the level of the absorbing system and that of the pipes conducting the 

 air to and from the chamber. To obtain the temperature of these 

 portions of the system, we rely upon other mercurial thermometers. 

 One is attached to the outside of the chamber, so as to hang just in 

 front of the window. A second thermometer k is suspended near the 

 pans, so that the bulb is on a level with the horizontal air-tube. A 

 third thermometer, the bulb of which is immersed in the water in the 

 Elster meter, gives the temperature of the air sample. These ther- 

 mometers are designated respectively as T, T 1; and T m . The first two 



1 For a discussion of the significance of the' temperature measurements by these 

 thermometers, see page 91. 



