134 A RESPIRATION CALORIMETER. 



It was found with both thermometers that the maximum corrections 

 occurred near the beginning of the graduation, and that along toward 

 the top of the scale the correction became smaller. This would be 

 expected from the increase in length of the column of mercury pressing 

 on the thermometer bulb. The thermometer readings are corrected 

 accordingly, and only the corrected readings used in determining the 

 differences in temperatures. 



CORRECTION FOR PRESSURE OF WATER ON THE MERCURY BULB. 



As pointed out by Armsby, 1 the pressure of the water current on the 

 bulb of the thermometer may introduce an appreciable error in measure- 

 ment. Since differences in temperature are what is desired, this error 

 would of course be negligible were the pressure the same on both 

 thermometers. This, however, is not the case. The pressure on the 

 thermometer bulb in the water entering the chamber is greater than that 

 on the bulb of the second thermometer, as the latter is much nearer the 

 water exit. It was found by actual trial that when the water was pass- 

 ing through the system at the rate of 10 kg. in 7 minutes, which is the 

 maximum rate in experiments, suddenly shutting off the current caused 

 a fall of 0.07 in the column of mercury in the thermometer in the 

 ingoing water, and of 0.015 in that of the thermometer in the outgoing 

 water. For this rate of flow, therefore, the mercury in the ingoing water 

 thermometer reads 0.07 too high, and that of the outgoing water ther- 

 mometer 0.015 too high. Unless these corrections are applied, the 

 difference in temperature is obviously 0.055 too low; consequently this 

 amount is added to the difference as observed. The necessary correc- 

 tions for all rates of flow occurring in actual experiments have been 

 determined and are always applied to the readings, though in many of 

 the experiments the rate of flow is so slow that the effect of pressure 

 on the bulb is inappreciable. 



MEASUREMENT OF TEMPERATURE OF THE CALORIMETER. 



It has been stated that the rate at which heat is absorbed and carried 

 out of the chamber is regulated in accordance with that at which it is 

 generated within it, so that the temperature of the chamber may be 

 kept constant. To this end it is necessary to be able to determine 

 fluctuations in the temperature of the chamber. 



While mercury thermometers have been used to indicate the temper- 

 ature of the water current in the heat-absorbing system, their use in 

 measuring the temperature of the air in the calorimeter, or of the metal 

 walls of the chamber, has not been successful, and we rely on the 

 measurement of changes in resistance of coils of pure copper wire which 

 are distributed at several points on the walls of the chamber. 



1 U. S. Dept. of Agr., Bureau of Animal Industry Bull. 51, p. 34. 



