90 PROF. C. FREWKN JENKIN AND MR. D. R. PYE ON THE 



I'M; i III -DETAILED DESCRIPTION OF THE APPARATUS AND METHOD OF 



CARRYING OUT THE EXPERIMENTS SERIES IV. AND V. 



In Series IV. the apparatus was arranged as shown in fig. 8, p. 75, the object 

 being to measure the Joule-Thomson effect, i.e., the change of temperature 0,-0 4 

 (fig. 7), corresponding to a change of pressure from p, to the pressure on the limit 

 curve p,. Iii the actual tests the pressure could not be allowed to fall quite down to 

 the limit curve for fear of introducing errors due to the commencement of evaporation. 

 To get the total 3 -6 4 , the observed difference of temperature was increased in the 

 proportion of the observed drop to the total drop of pressure. In fig. 8 the pressure 

 drop is measured by the gauges a and b and the temperature change by the thermo- 

 juuctions A and B. The liquid C0 a from the weighing flask first passes through the 

 inner coil of the calorimeter and is there cooled to any desired temperature. It then 

 flows in order past : 



Gauge a and thermo-junction A. 



Throttle valve Vj. 



Thermo-junction B and gauge b. 



Throttle valve V r 



Outer coil in the calorimeter and gauge c. 



The C0 a is liquid up to the second valve, Vj. 



The pressure of the liquid up to the valve V t is p v The valve V t is adjusted so as 

 to allow it to drop to a pressure p t a few pounds above p 2 . 



The valve V, is adjusted so as to allow it to drop from p x to p 2 , which is the 

 saturation pressure corresponding to the temperature of the liquid. The difference 

 of temperature A 9 B between A and B is the Joule-Thomson effect corresponding to 

 the drop of pressure Pip^ Therefore 



In the first series of experiments the valve V t was a large bronze hydraulic valve, 

 and the thenno-junctions were inserted in the gunmetal fittings shown in fig. 15, 

 which were connected to the valve by pipes about 6 inches long. The whole 

 apparatus was well lagged, but the amount of heat which leaked in when the 

 temperature was low was sufficient to raise the temperature of the C0 2 to an extent 

 which was large compared with the small temperature change which had to be 

 determined ; this leakage was allowed for by observing the temperature change due 

 to the leakage only, when the valve V, was full open, and subtracting this from the 

 temperature change when V, was throttled, the rate of flow being kept the same in 

 the two experiments. Conduction along the pipe between A and B has no effect. 

 Each observation was repeated a number of times and the means taken. It was not 



