On the Maximum Pressure and Latent Heat of Vapours. 531 



Formulae of three terms were also found to represent the 

 results of Dr. lire's experiments on tlie vapours of alcohol and 

 aether, and formulae of two terms, those of his experiments on 

 the vapours of turpentine and petroleum, as closely as could be 

 expected from the degree of precision of the experiments. A 

 formula of two terms was found to represent accurately the 

 results of M. Regnault's experiments on the vapour of mercury. 



4. These formulae, with a comparison between their results 

 and those of the experiments referred to, were published in the 

 Edinburgh New Philosophical Journal for July 1849, in a paper 

 the substance of which is summed up at its conclusion in the 

 following proposition : — 



If the maximum elasticity of any vapour in contact with its 

 liquid be ascertained for three points on the scale of the air^ther- 

 mometer, then the constants of an equation of the form 



may he determined, which equation will give, for that vapour j with 

 an accuracy limited only by the errors of observation, the relation 

 between the temperature (t), measured from the absolute zero, and 

 the maximum elasticity (P), at all temperatures between those three 

 points, and for a considerable range beyond them, 



5. In the case of water and mercury, the precision of the expe- 

 rimental data left nothing to be desired. I have, however, in 

 the table of constants at the end of this paper, so far modified 

 the coefficients for water and mercury as to adapt them to a 

 position of the absolute zero (274° Centigrade, or 493° -3 Fahr- 

 enheit below the temperature of melting ice), which is probably 

 nearer the truth than that employed in the original paper, which 

 was six-tenths of a Centigrade degree lower. This modification, 

 however, produces no practically appreciable alteration in the 

 numerical results of the formulae. 



6. It was otherwise with respect to the other fluids mentioned, 

 for which the experimental data were deficient in precision, so that 

 the values of the constants could only be regarded as provisional. 



7. A summary, published in the Comptes Rendus for the 14th 

 of August 1854*, of the extensive and accurate experiments of 

 M. Regnault on the elasticities of the vapours of aether, sulphuret 

 of carbon, alcohc', chloroform, and essence of turpentine, has 

 now supplied the means of obtaining formulae, founded on data 

 as precise as it is at present practicable to obtain, for the maxi-^ 

 mum pressures of these vapours. 



A synopsis of these formulae, and of the constants contained 

 in them, is annexed to this paper. The constants, as given in 

 * See p. 269 of the present volume of this Journal. 



