some Thermodynamical Relations. 521 



Carbon bisulphide 

 Alcohol . . . 

 Chlorobenzene . 

 Bromobenzene . 

 Aniline . . . 

 Methyl salicylate 

 Bromonaphthalene 

 Mercury . , 



4436 1*000 



5873 1-324 



4724 1-065 



4703 1-060 



5124 1-155 



4959 1-112 



4930 1-111 



4812 1-085 



This may be better seen by making one of these values 

 equal to unity, and reducing the others in the same ratio. 

 The second column is thus calculated. 



Repeating this operation at another pressure, a second series 

 of values was obtained; and these were reduced in the same 

 way. - It was at once noticed that the reduced numbers at the 

 new pressure were identical within the limits of error of expe- 

 riment and calculation with those at the first pressure. 



The calculations were therefore continued so as to include 

 the widest attainable ranges of pressure, and at every pres- 

 sure the value of -j- . t for one substance was made equal to 

 unity; and the others reduced in the same ratio. The values 

 of -~- . t for water were made = 1, because the vapour-pres- 

 sures of this substance have been determined by Regnault 

 between wide limits of temperature with very great care; but 

 it was noticed that the values for both water and alcohol were 

 very much higher than for the other substances examined ; 

 and a similar comparison was therefore made by taking the 

 values for carbon bisulphide as equal to unity. 



It was then found that for pressures ranging between 1 50 

 and 1500 or 2000 millim. the reduced values for each substance, 

 with the exception of mercury, were very nearly constant 

 for all pressures. 



In the case of alcohol and water, employing the vapour- 

 pressures of water as determined by Regnault (Memoires de 

 VAcademie, vol. xxv.), and of alcohol as determined by Ramsay 



and Young, the ratio of the values -~ . t was seen to be the 



*=>' dt 



same at pressures between 150 and 20,000 millim. 



Two methods of calculation were adopted. In the first and 

 more accurate method the vapour-pressures for each degree 

 were calculated by the method of differences; and from these 



