﻿and Expansions of some Liquids. 153 



containing three molecules of water, which changes its appa- 

 rent specific heat. 



Pursuing the same hypothesis, he has more recently* pro- 

 posed the study of the specific heats of solutions and their ele- 

 ments as a means of determining the degree of dissociation 

 produced in them by heat. I cannot, however, share his 

 opinion of the results to be expected from this study ; for his 

 calculations rest upon a principle the accuracy of which is not 

 demonstrated — namely, that the heat disengaged by the total 

 combination of the two bodies would be the same at all tem- 

 peratures. 



It must be acknowledged that this hypothesis of a change in 

 the chemical constitution of solutions according to the tempera- 

 ture removes a great difficulty. It very easily accounts for what 

 takes place in a mixture of water and alcohol. The combination 

 of these two bodies disengages heat; it seems very natural to 

 admit that the rise of temperature of the mixture determines a 

 dissociation, which must necessarily absorb heat and conse- 

 quently increase the apparent specific heat. On the contrary, it 

 is difficult to conceive that the rise of temperature of a mixture 

 of water and sulphuric acid determines a chemical action that 

 disengages heat — that is to say, a more intimate combination. 



Yet I do not think that this difficulty ought to cause the re- 

 jection before-hand of this hypothesis as baseless ; and it appears 

 to me useful to enunciate or recall these theoretic ideas at a time 

 when several able investigators are directing their researches to 

 these questions. 



I will add another consideration which seems to me to de- 

 monstrate well the existence of this internal chemical work, deter- 

 mined by the change of temperature, in certain solutions. Let 

 us compare water and a saline solution, that of chloride of sodium 

 for example. This is less compressible than water ; therefore 

 more work must be consumed to produce an equal change of 

 volume without alteration of temperature. But, on the other 

 hand, its coefficient of dilatation is much higher than that of 

 water, and its specific heat less. For these two reasons a much 

 less quantity of heat is necessary to produce the same change of 

 volume accompanied by a rise of temperature. These two facts, 

 apparently contradictory, can only be explained by admitting 

 that an internal chemical work, determined by the rise of tem- 

 perature, has furnished a part of the heat necessitated by the 

 dilatation. 



In a subsequent article I will exhibit the results of my study 

 of the densities and dilatations of the aqueous solutions the spe- 

 cific heats of which have been determined in this memoir. 

 * Zeitsch.fur Chemie, year xiii. p. 66. 



