126 



REPOET 1886. 



is taken as one of the two substances, as the substance of reference, the 

 observed pressures agree with those calculated by the formula with re- 

 markable accuracy ; and doubtless equal accuracy could be got by using 

 i>ther substances of reference. 



We will give some results illustrative of the accuracy which this 

 formula shows : — 



1. The absolute temperatures of water at various pressures being- 

 known, the following are absolute temperatures of CS2 calculated from 

 the formula, and absolute temperatures of CS2 obtained by observation. 



Found c= -0006568. 



The greatest difference between the observed and the calculated tem- 

 peratures of CS2 is here only 0-4° at the pressure 5000 mm. 



2. The absolute temperatures of CS2 being known for a series of 

 vapour pressures, to find by the formula the absolute temperatures of 

 sulphur at the same pressures. 



Regnault gives ' a list of corresponding temperatures and vapour- 

 pressures for sulphur ; taking some of these and the temperatures of 

 CS2 for the same pressures, and adding 273 to the temperatures to get the 

 absolute temperatui'es, the value of c is found=: — "0006845. 



A series of absolute temperatures of sulphur can now be constructed 

 for various pressures by calculation by the formula from the absolute 

 temperatures of CS2 at the same pressures ; and these can then be com- 

 pared with the data obtained by interpolation from the temperatures and 

 vapour-pressures given by Regnault. 



The following are among the results for sulphur : — 



Besides the substances mentioned, the formula was applied to methyl 

 alcohol, ethyl chloride, ethyl bromide, chlorobenzene, bromobenzene, 

 aniline, methyl salicylate, bromonaphthalene, ethylene, oxygen, acetic acid, 

 nitric peroxide, chloral-alcoholate, chloral-methylalcoholate, ammonium 

 chloride, ammonium carbonate ; and^ to carbon tetrachloride, ethyl oxide, 

 chloroform, and mercury (which has been already mentioned). 



The results in such a variety of cases being extremely accurate for 

 elements such as oxygen and sulphur, and compounds of such different 

 types, there can be no doubt that the relation E,':.=R + c {f — t) very 

 accurately rejDresents an actual relationship between temperature and 

 vapour-pressure such that the different substances taken are in this way 



' Mem. t. xxvi. p. 527. 



■ Phil. Mag. February 1886. 



