of Superheated Vapours. 425 



(equivalent to the above) 



<j>\dt) v ~ (1 + a/) (273+0' 

 putting a = 0*0038, we should obtain 



l(f)=0-00008, 



or, corresponding to the values of the Tables, 



100.1^=0.08. 

 <j> At 



Accordingly sulphide of carbon shows in this case only about 

 five times the variableness of vapour- density shown by carbonic 

 acid gas. 



Similarly, for the temperature of 50°, using the mean values 

 of the Tables for this temperature 



100 10A4>„ 2 



T .~5T ' 



with sulphide of carbon 



«= 0-00395. 



We see that in all there are perfectly comparable deviations 

 from the gaseous law r s to which, in this direction, sulphide of 

 carbon and carbonic acid are subject. 



On the second coefficient to be mentioned in connexion with 

 vapours, viz. the coefficient of space-expansion with constant 

 pressure, after the present results at least something general 

 must be said. For it the general formula holds :— 



Ul 



»-<: 



which, when 

 becomes 



dv 



dt/p 



) 



pv=cf>{27S + t) 



+ \dt) p 



When, now, from a determined initial point, <f> is traced for 

 heating in constant volume, we arrive at a higher final expres- 

 sion with the final temperature than when we reach the same 

 temperature, after starting from the same point, under constant 



