684 On the Maximum Pressure and Latent Heat of Vapours, 



and thus to solve many problems connected with engines driven 

 by vapours of different kinds. 



12. It is somewhat remarkable, that the coefficients of the reci- 

 procal of the temperature (B) in the formulae for aether, sulphuret 

 of carbon and alcohol, are nearly equal ; as also those of the 

 square of the reciprocal of the temperature (C) for sether and 

 sulphuret of carbon. 



In consequence of this, the pressure of the vapour of sether, 

 and its latent heat for unity of space as above defined, at a given 

 temperature, exceed the corresponding quantities for sulphui'et 

 of carbon at the same temperature, in a ratio which is nearly, 

 though not exactly constant, and whose average value is some- 

 what less than 1*5. 



Synopsis of the Formula, ^c. 



Notation, 



T ^ absolute temperature = temp. Centig. +274° C. 



= temp. Fahr. +461°-2 F. 

 P = maximum pressure of vapour at the absolute temperature r, 

 V = volume of unity of weight of the liquid. 

 V= volume of unity of weight of saturated vapour. 

 L = latent heat of evaporation of unity of weight of the fluid 



expressed in units of work. 

 A, B, C constants. 



Formula. 



1. To find the maximum pressure from the temperature, 



com. los:r=A s. 



2. To find the temperature from the maximum pressure, 



1_ / f A-com.logP B^ \ B 

 t""V [_ C "^40^/ 2C* 



3. To find the latent heat of evaporation (expressed in units 

 of work) of so much of the fluid that its bulk when evaporated 

 exceeds its bulk in the liquid state by an unit of space, that is 



to say, of the weight ^__ of fluid. In this formula the press- 

 ure must be expressed in units of weight per square unit. 



L dV T3/B 2C\ , , .^ 



V3i^=T^=P(-+^jxhyp.loglO. 



(Hvp. log 10=2-30258509, 

 the common logarithm of which is 0*3622157.) 



Units of work are reduced to units of heat (degrees in unity 



