Dissolution of Gases in Liquids. 37 



By plotting the results against percentage-composition and 

 drawing a curve through them, I have obtained the value for 

 the heat of dissolution of a gram-molecular proportion of the 

 substance in 22,400 cub. centim. (gas strength) of the solvent 

 (1244 H 2 0, 396 C 2 H 4 2 or 245 C 6 H 6 ), and also of the heat 

 of dissolution in an infinite amount of the solvent. In some 

 cases these values can be but approximately correct, for the 

 heat of dissolution often increases very quickly with the dilu- 

 tion and renders extrapolation uncertain. In three cases, 

 pyridine and carbon disulphide in acetic acid, and ether in 

 benzene, there is no sensible alteration in the value with 

 dilution; in every other it occurs in the above-named direc- 

 tion, whether the heat of dissolution is positive or negative, 

 and is particularly large in the case of alcohol in benzene ; 

 a fact which is in harmony with the rapid increase of the 

 molecular depression of the freezing-points of benzene by 

 alcohol as the dilution increases (Phil. Mag. xxxiii. p. 449, 

 AB, fig. 2, and p. 461), since both these phenomena point 

 to the existence of alcohol aggregates in comparatively strong 

 solutions, and the breaking up of these on further dilution. 

 In Table II. I have collected the values for the heat of disso- 

 lution of the liquids in infinity of solvent, and also that of the 

 corresponding gases in 22*4 litres of solvent, the heat of 

 vaporization at 18° being also given here. This latter is not 

 known very accurately in many cases, and in that of the 

 pyridine is not known at all. 



This Table shows at a glance that, whatever gaseous sub- 

 stance or solvent we take, a considerable amount of heat is 

 evolved during the dissolution, from 5000 to 10,000 cal., and, 

 therefore, that there is a disappearance of a considerable 

 amount of potential energy, so that we can but conclude that 

 combination in some form or another, whether chemical or 

 otherwise, must have occurred. 



Further, just as in the case of every known instance of 

 chemical combination, the amount of heat evolved is not con- 

 ditioned by the nature of one of the reagents only, but by 

 that of both of them, so, here, the heat evolved by dissolving 

 different gases in the same solvent is very different, showing 

 a variation of as much as 6000 cal. ; while the dissolution of 

 the same substance in different solvents gives as great a di- 

 versity of values, the variation in this case also amounting to 

 some 6000 cal. Nor does there even appear to be any relation- 

 ship in the differences ; for the differences between the values 

 for the various substances are not the same in the case of the 

 three solvents, as will be seen from the columns headed " Diff." 

 in Table II. The only general conclusion which can be 



