296 report — 1859. 



homogeneous. Some experiments of Bisehoffand Debus led to the conclusion 

 that gravity acted upon a solution of a salt and caused an accumulation of 

 the salt molecules in the lower portion of a column of the solution. Lieben 

 has, however, found that the solution of a single salt is perfectly homogene- 

 ous. It yet remains to be proved whether saline solutions, containing a 

 number of salts in solution, are homogeneous. 



But if we admit the homogeneity of saline solutions, it appears to me that 

 we must of necessity assume that in the solution the salt is combined with n 

 molecules of water — n being variable according as the. conditions of equili- 

 brium are modified, or we shall be forced to admit the infinite divisibility of 

 matter. 



There is an evident relationship between solution and fusion. When a 

 salt is fused, a quantity of heat is absorbed ; when dissolved in water, a still 

 larger quantity of heat is in most cases absorbed. Thus, according to 

 Person*, 1 gramme of KO, N0 5 absorbs 49 heat-units of latent fusion 

 heat ; but if dissolved in 5 grms. of water, 69 heat-units are absorbed and 80 

 when it is dissolved in 20 grms. Whenever the same body is fused under 

 the same pressure, the quantity of heat absorbed is always the same ; but 

 when a soluble substance is dissolved, the absorption of heat increases with 

 the amount of water employed though not in a direct ratio. Even the 

 dilution of a solution causes an absorption of heat ; and with every success- 

 ive dilution an additional quantity disappears, the only apparent limit being 

 our means of detecting it. It is difficult to reconcile this phenomenon with 

 that of homogeneity, unless we admit solution to be combination ; and even 

 then there must be a limit somewhere, unless we consider matter infinitely 

 divisible. 



The solution heat of a salt appears from the experiments of Person t to 

 diminish as the temperature increases, a result which was pointed out by 

 Graham, and which we might indeed have anticipated from the diminution 

 of the specific heat according as the temperature rises, and from, as Person 

 suggests, the specific heat of the saline solution being less than that of the 

 separate constituents. On dissolving 1 grm. of chloride of sodium in 7*28 

 grms. of water at 70°, no absorption of heat was observed. Fusion, solution, 

 and dilution are evidently but varieties of the same phenomena, and should 

 be included together in any hypothesis framed to account for latent heat. 

 MM. Favre and Silbermann proposed a very ingenious hypothesis to account 

 for the latent heat of fusion : they considered it as the result of chemical 

 combination or decomposition. They looked upon ice as isomeric water, 

 n (HO), where n is any simple number ; when HO becomes n (HO), heat is 

 evolved ; when, on the other hand, ice melts, that is n (HO) splits into HO, 

 heat is absorbed. In the same way they looked upon a crystallized salt as 

 an isomeric form of the same salt when in solution, e. g. S0 4 K, and S 2 O s K 2 . 

 This hypothesis would account for latent solution heat, which it would assi- 

 milate to latent fusion heat; by a slight modification it may be made also to 

 account for the latent dilution heat, — by supposing crystallized salts to be 

 higher multiples than that above assumed in the case of sulphate of potash, 

 which may be considered to be n (S0 4 K) ; and that when it is dissolved in 

 a small quantity of water, it splits into two or more molecules of a lower 

 isomeric body, and this again into others on further dilution. 



The modification here proposed seems to receive support from the 

 discovery of a number of isomeric salts. For instance, LowelJ has obtained 

 two salts with the empiric formula NaO, C0 2 + 7HO, of different solubilities, 



* Compt. Rend. vol. xxxi. p. 566. t Ann. de Cbim. et de Phys. (3) vol. xxxiii. p. 448. 



X Ibid. vol. xxxiii. p. 334. 



