302 Mr. W. C. Unwin on the Relations of Pressure, 



Values of - -~- for different vapours. 



p dt L 



















r _« 





• rH CD 



g s 

 B £ 



^Carbon 

 bisulphide, 



CS . 



,-1 .2 H 



w £d 



© rH 



So 



a 



Is 



few 



1° 



o 







.20 



o . 



Carbonic 



anhydride, 



C0 2 . 



100 



12-80 



1364 



13-04 









1607 



16-42 





500 



10-83 



11-31 



11-22 



11-66 



13-20 



12-12 



13-81 



14-39 





1000 



10-10 



10-37 



1051 



10-85 



11-89 



11-20 



12-95 



13-83 





3000 



8-68 



8-96 



9-24 



9-27 



11-23 



9-67 



11-58 



11-99 





5000 



8-22 



8-26 



8-66 



8-46 



9-73 





10-89 



11-29 





10,000 















1003 



10-39 



7-62 



15,000 















9-50 



9-89 



7-63 



20,000 















9-13 



9-54 



7-57 



50,000 



















6-77 



But now it may be pointed out that - -4-r is not a mere 



arbitrary expression for 



t dp _ r 

 p dt Apu 



(Hirn, torn. i. p. 319). That is, it is the ratio between the 

 total heat of evaporation and the heat expended in external 

 work. What we have found, therefore, is that this ratio 

 approaches constancy for widely different substances and 

 under considerable differences of pressure. This approxima- 

 tion to constancy appears to me to lie at the basis of all the 

 relations Messrs. Young and Ramsay have found. 



The constancy of this ratio of internal and external work, 

 for different vapours at one pressure, has been investigated 

 by Messrs. Young and Ramsay from other data, but it does 

 not seem to have occurred to them that it would be obtained 

 in the simple way given above. 



The author noticed that another relation, namely, 



dp 



gave values for each vapour, far more constant at different 

 pressures than 



t dp 



p dt' 



The following table gives some of these values :- 



