Tlll.KMAI, PROPERTIES OF GAUBONIC ACID AT LOW TEMPERATURES. 73 



111. --!'. ,r (Ms SLM'lrs tin- liorni.'il :irr:iii^<Miii-iit "f tin- ;ip|i;ir;ilus w:is 



slightly modified, as is shown in fig. 5, by inserting calorimeter II. between calori- 

 meter I. and the pump. The gas leaving calori- 

 meter I. at a temperature 6 3 was warmed to any 

 desired extent in calorimeter II. The quantities 

 measured in this series were the rate of flow of 

 CO a , the rise of temperature of the gas in calori- 

 meter II., and the electrical power supplied to 

 calorimeter II. From these data the specific 

 heat of the gas at constant pressure was calcu- 

 lated. A series of measurements was made with different values of Q r The results 

 are shown in fig. 6, where the specific heat of the gas near the limit curve* is plotted 

 against the pressure. 



CALOHIHC ren I CALO*i*e re KM 

 Fig. 5. 



0-6 



0-5 



0-4 



0-3 



0-2 



0-1 



Spec : heat of C0 jas 



at const: press. 

 Near the .saturated condition 



IOO 



zoo 



500 



400 500 



Lba/iq.incn. 

 Fig. 6. 



600 



700 



600 



900 





Combining the results of Series I., II., and III., an approximate value of the latent 

 heat may now be calculated. If we neglect the complications introduced by the 

 changes of volume of liquid CO a (or what is equivalent, if we assume, as a first 

 approximation, that the limit curve coincides with the constant-pressure curves) 

 then the difference of total "heat I 8 I, from 6 3 to 0, is represented in fig. 2, p. 71, 

 by the area RGAM. 



k The limit curve is the boundary of the area on the diagram representing saturated vapour, separating 

 it on the one side from the area representing liquid and on the other from the area representing super- 

 heated gas. The two sides of the curve re called the " liquid-limit curve " and the " gas-limit curve " ; 

 they meet at the critical point. 



VOL. CCXIII. A. L 



