70 PROF. FIMUIN ..KNKIN AND MR D. R. PYK ON THE 



pn^nce of thiB small amount of air has introduced a small error into the pressure- 

 !.', ,,,,. ,urv,., hut does not appreciably affect the results of any of the other 

 experiment* 



Fig. 1. 



The general arrangement of the apparatus connected for normal working is shown 



diagrammatically in fig. 1. The gas enters the pump at pressure p 2 and is compressed 



to a higher pressure />,. It is then condensed in the condenser at the corresponding 



saturation temperature fy. From the condenser it flows as liquid through the 



weighing flasks to the throttle valve on the calorimeter. In passing the throttle 



valve the pressure falls to p. 2 , some of the liquid evaporates and the temperature falls 



to Oj. The mixture of liquid and gas then enters the calorimeter, where the rest of 



the liquid evaporates, taking up heat at the constant temperature 6 a . From the 



calorimeter the gas passes back to the pump. In order to make sure that all the 



liquid has evaporated, the gas is warmed (superheated) a few degrees above 2 before 



it leaves the calorimeter. The approximate 6<f> diagram* for this cycle is shown 



in fig. 2. 



The line AB represents the expansion of the liquid through the throttle valve from 

 j>,0, to p r AB is a line of constant total heat I. The line BE represents the 

 evaporation of the liquid at constant pressure p. t and temperature Q. 2 . The line EC 

 represents the small amount of superheating from f) 2 to 3 at constant pressure p 2 . 

 The line CD represents the adiabatic compression in the pump from p 2 to p,. The 



* Cf. EWING (4), p. 80. 



