88 PROF. C. FKKWKN .IKNKIN AND MR. D. H. PYE ON THE 



In Series III. the apparatus was connected as shown in fig. 5, p. 73, the object being 

 to measure the specific heat of the gas at various temperatures near the saturation 

 points. Tin- .iil.jiistiiHMits of the pump, throttle valve, and electrical power for the 

 large calorimeter were made exactly as in Series I. The electrical power put into 

 the small calorimeter was adjusted so as to keep it at a steady temperature, a 

 moderate amount above 6* It was not possible to start heating the gas exactly 

 at 0,, but 0, was kept as close to 0., as possible, so that the range through which the 

 gas was heated began only a few degrees above the saturation temperature. The 

 actual ranges are shown in lines 4 and 5, Table IV. The last line gives the mean 

 specific heat for this range of temperature. 



During the test the following observations were made : 



Times when weighing bell rang ; 



E.M.F. on each heating coil in calorimeter II., observed every minute ; 



Temperature 9 3 of gas entering calorimeter II., every three minutes ; 



,, ,, leaving ,, ,, ,, ,, , 



bath, calorimeter II., every three minutes ; 



cold junction, several times during test ; 



atmosphere, ,, ,, ,, . 



As an example, the complete records for one experiment are given in Tables XV. 

 and XVI. The times when the weighing bell rang were plotted as a check on the 

 uniformity of the rate of flow of CO., during the experiment. 



Corrections. 



Before making use of the data obtained in the tests, it is necessary to consider the 

 effects of differences between the actual and theoretical cycles and also the corrections 

 for radiation, conduction, and change of temperature of the calorimeter during 

 the test. 



Differences betiveen the Actual and the Ideal Cycle. 



(i.) Friction in the evaporation coil produces a small difference of pressure between 

 the two ends. The evaporation, therefore, should not be represented by the constant- 

 pressure line BE (fig. 7), but by a curved line starting a little above B and falling 

 to E. It is easy to show that this has no effect on the heat absorbed, which is 

 always I B -I A , and is accurately represented by the rectangle NBEP. 



(ii.) The vapour is moving in the pipe with some velocity and consequently 

 possesses kinetic energy. A simple calculation shows that the kinetic energy is 

 always small enough to be neglected. 



(lii.) The compression in the pump is not adiabatic and there are other deviations 

 in the condenser, but as this part of the cycle is not included in the measurements 

 they have no effect. 



