40 



THE ROYAL SOCIETY OF CANADA 



Fig. 1 



There is always the difficulty of adiabatic heating when com- 

 pressing, but if the compression is slow enough this is not serious. 

 But it must be excessively slow. However, the temperature being 

 slightly higher during the compression, liquid forms after the pres- 

 sure increase is discontinued due to the cooling that ensues. The 

 pressure was applied up to a value slightly lower than that at which 

 condensation was expected, closed and the mixture allowed to come 

 to equilibrium. Then the pressure was increased by very small 

 increments until a trace of liquid was seen in the tube. Then the 

 pressure reading was taken and the pressure increased until the liquid 

 nearly filled the tube, and the final filling was accomplished by small 

 increments again. If these increments are small enough, the two 

 pressures may be found accurately. The pressures are probably 

 correct to within much less than a tenth of an atmosphere. The 

 further study of the condensation curve, and the repetition of the 

 work described in this paper for several different mixtures of nitrogen 

 and oxygen is contemplated. 



At the plait-point temperature when the tube was half full of 

 liquid and pressure is applied, the meniscus fades out without change 

 of level. Also for temperatures slightly below this, the meniscus 



