134 



Physical Properties 



[CH. vi 



pressure measured in atmospheres, the isothermals only being shewn for 

 pressures above 47 atmospheres. The figures on the right-hand denote the 

 temperatures Centigrade of the corresponding isothermals. 



The isothermal corresponding to the temperature 311 is of great interest, 

 as being very near to the critical isothermal, the value of the critical tem- 

 perature being given by Andrews as 30'92. On this isothermal, as on all 

 those above it, the substance remains gaseous, no matter how great the 

 pressure. 



no 



100- 



90- 



ao- 



70- 



60- 



50- 



Fio. 11. 



On the next lower isothermal, corresponding to temperature 21'5C., we 

 notice a horizontal range at a pressure of about 60 atmospheres. As the 

 representative point moves over this range, boiling or condensation is taking 

 place. Thus at a pressure of about 60 atmospheres the boiling point of 

 carbon dioxide is about 21'5C. The ratio of volumes in the liquid and 

 vapour states is equal to the ratio of the two values of v at the extremities of 

 the horizontal range a ratio of about one to three. 



The lowest isothermal of all corresponds to a temperature of 13'1C. 

 Here the inequality between the volumes of the liquid and the gas is greater 

 than before. In fact an examination of the general theoretical diagram 

 given in fig. 10 shews that as the temperature decreases the inequality 



