304 Mr. W. 0. Unwin on the Relations of Pressure, 



b *" 





tt+1 



= 2-3025n ^-'°fy ) -- • • (3«) 



= 2"3025n(a-log d p) (4a) 



For the latent heat, besides the ordinary formula, 



ra 



L = w r (5) 



(a — logj?)» 

 And consequently if v is the volume in cubic metres of the 

 vapour and s that of the liquid, 



JL 



dt 



13-497L 

 pn(a— logjj)' ^ ' 



In all these equations the quantity required is expressed 

 simply in terms of the pressure or the temperature, a result 

 not obtainable with the formulae previously used. 



Formula} for Steam. 



To test the value of these equations, the author has calcu- 

 lated the constants for steam most suitable for the complete 

 range of Regnault's experiments, from —30° C. to 230° C, 

 and from 0*4 millim. pressure to 20,000 millim. pressure. 

 The proposal of a new empirical formula, and one not so 

 accurate as Bankings or Regnault's, for the relation of p and 

 t in the case of steam, will probably appear the reverse of 

 commendable. Still the fact that it gives a series of expres- 

 sions, all directly derived from it, simple enough for ordinary 

 use in engine calculations and accurate enough for practical 

 purposes, is a strong reason in its favour. Its applicability 

 can only be determined by testing its accuracy in a suffi- 

 cient number of cases. In all the following calculations the 

 calculated values are compared with the most accurate values 

 thus far computed, over a range of pressure and temperature 

 greater than would occur in practical cases. 



The primary equation, derived from Regnault's data, for 

 millimetres of mercury, Centigrade degrees reckoned from 



