74 PRINCIPLE.- 



of heat (negative, heat), whilst their chemical combination with water 

 is accompanied by an evolution of heat ( 4- heat) ; consequently, their 

 sum may either be a cooling effect, when the positive (chemical) portion 

 of heat is less than the negative (physical), or it may be, on the 

 contrary, a heating effect. This is actually the case. 124 grams of 

 sodium thiosulphate (employed in photography) Na,S s O 3 ,5H 2 in 

 melting (at 48) absorbs 9,700 units of heat, but in dissolving in a large 

 quantity of water at the ordinary temperature it absorbs 5,700 units of 

 heat, which shows the evolution of heat (about + 4,000 units), not- 

 withstanding the cooling effect observed in the process of solution, in 

 the act of the chemical combination of the salt with water.-' But in 



25 The latent heat of fusion is determined at the temperature of fusion, whilst solution 

 takes place at the ordinary temperature, and one must think that at this temperature 

 the latent heat would be different, just as the latent heat of evaporation varies with the 

 temperature (see note 11, p. 52). Besides which, in solution there occurs a disunion (dis- 

 integration) of the particles of both the solvent and the substance dissolved, which in its- 

 mechanical aspect resembles evaporation, and which therefore must consume much 

 heat. The heat emitted during the solution of a solid must be therefore considered 

 (Personne) as composed of three factors (1) positive, the effect of combination; (2). 

 negative, the effect of transference into a liquid state ; and (3) negative, the effect of dis- 

 integration. In the solution of a liquid by a liquid the second factor is removed ; and 

 therefore if the heat evolved in combination is greater than that absorbed in disintegra- 

 tion a heating effect is observed, and in the reverse case a cooling effect ; and, indeed, 

 sulphuric acid, alcohol, and many liquids evolve heat in dissolving in each other. But the 

 solution of chloroform in carbon bisulphide (Bussy and Binget), or of phenol (or aniline) 

 in water (Alexeeff), produces cold. In the solution of a small quantity of water in acetic 

 acid (Abasheff), or hydrocyanic acid (Bussy and Binget), or amyl alcohol (Alexeeff), cold 

 is produced, whilst in the solution of these substances in an excess of water heat is 

 evolved. 



The fullest information concerning the solution of liquids in liquids has been 

 gathered by W. T. Alexe'eff (1883-1885), still these data are far from being sufficient to 

 resolve the mass of problems respecting this subject. He showed that two liquids which 

 dissolve in each other, intermix together in all proportions at a certain temperature. 

 Thus the solubility of phenol, C 6 H 6 O, in water, and the converse, is limited up to 

 70, whilst above this temperature they intermix in all proportions. This is seen 

 from the following figures, where p is the percentage amount of phenol and t the 

 temperature at which the solution becomes cloudy that is, that at which it is satu- 

 rated : 



j? = 7'12 10"20 15-31 26-15 28'55 36'70 48'K<> (51-15 71'97 

 t = l 45 60 67 D 67 67 (55 53 20 



It is exactly the same in the solution of benzene, aniline, and other substances in 

 molten sulphur. Alexeeff discovered a similar complete intermixture for solutions of 

 secondary butyl alcohol in water at about 107 ; at lower temperatures the solubility is 

 not only limited, but between 50 and 70 it is at its minimum, both for solutions of the 

 alcohpl in water and for water in the alcohol ; and at a temperature of 5 both solutions 

 exhibit a fresh change in their scale of solubility, so that a solution of the alcohol in 

 water which is saturated between 5 and 40 will become cloudy when heated to 60. 

 In the solution of liquids in liquids, Alexeeff observed a lowering in temperature (an 

 absorption of heat) and an absence of change in specific heat (calculated for the mixture) 

 much more frequently than had been done by previous observers. As regards his affir- 



