[dawks] specific heat OF A GAS AT CONSTANT PRESSURE 2^93 



A preliminary experiment showed that the fall of pressure of the 

 gas m passing through the calorimeter was less than one fifth the pres- 

 sure indicated hy the manometer C. 



C. Method of Experiment. 



In making a determination the following procedure was adopted. 

 When the water in E had been raised to the boiling point the valve a 

 was opened, and the gas allowed to pass through the apparatus, 

 leadings were taken on the calorimeter scale, and on the gauge 

 and on the thermocouple scale respectively once a minute. B 

 was adjusted as required to keep the gas flowing uniformly. 

 The water manometer C was maintained at a ditt'erence of level of eight 

 inillimeters, so that the fall in pressure of the gas as it passed through 

 the calorimeter was less than 8/5 millimeters of water. The galvano- 

 meter in a few minutes assumed a constant deflection, showing that the 

 temperature of the {/ junction had become steady. From the calorimeter 

 readings the average number of divisions per minute was determined by 

 finding, first, the average number per twenty minutes from, a number 

 of sets of readings, and then taking one twentieth of that number. The 

 rate of fall of pressure was found in a similar manner from the read- 

 ings of the gauge. 



After the gas had been flowing for a sufficient time, the valve h 

 was opened and a closed, so that the gas passed out without going through 

 the coil. The rate of flow was adjusted so that the thermocouple d 

 was kept at a temperature used in the previous observations. Readings 

 of the calorimeter and of the thermocouple scales were taken once a 

 minute as before, and the average number of divisions per minute on the 

 calorimeter scale was found in the way explained above. 



From these readings the following deductions were made : — 



(1) The temperature in degrees centigrade corresponding to the 

 thermocouple deflection was found from the curve of Fig. 4. 



(2) The number of grams of gas per minute was found from the 

 rate of fall of the pressure by means of curve 5. 



(3) By the aid of curve 6 the number of calories communicated per 

 minute to the calorimeter was deduced from the number of divisions 

 moved over per minute by the mercury thread. 



D. Theory. 



It will be seen that with the exception of the air which passed 

 through the coil (e) during the first set of observations the sources of 



Sec. III., 1906. 13. 



