368 M. H. Sainte-Claire Deville on Affinity and Heat, 



would have been a change of condition, owing to the mixture of 

 the two gases ; and the beautiful verification of Lavoisier would 

 have been invalidated in an irrefutable manner. The argument 

 drawn from the proportions of the two gases, oxygen and nitro- 

 gen, which are not in atomic proportion in the air, is without 

 value. One of the two elements might simply have been in ex- 

 cess over a combination of the two others. There would have 

 been mixture and combination, and therefore change of state for 

 one portion of the air alone, which is not the case. 



Combination being thus characterized by change of state, and 

 therefore well defined; what is the particular form of com- 

 bination which merits more especially the name of solution ? I 

 say especially; for it would be impossible to say now whether 

 water and sulphuric acid, acetic acid, chloride of calcium, and 

 many other bodies are combined with or merely dissolved in one 

 another. But there is a fundamental difference between the 

 effects produced when potash is thrown into sulphuric acid, and 

 the effects observed when common salt is placed in water. 



In both cases the change of state is manifest; but When 

 sulphate of potash has been obtained after the combination of sul- 

 phuric acid and of potash, new chemical properties have become 

 strikingly evident. It is in fact by these chemical properties 

 that change of state is most clearly manifested at the time of 

 energetic combination. In the second place, when the solution 

 of common salt in water is effected, the chemical properties of 

 the elements in presence remain virtually unchanged. First a 

 true fusion of the salt is noticed, which assumes the liquid state — 

 a change of physical condition accompanied most frequently by 

 an absorption and disappearance of heat, — then variation in the 

 density, or phenomena of contraction*, alteration in the volume 

 of the elements, which, again, is a change of physical properties 

 which essentially characterizes true solution. 



Yet an exclusive value must not be given to these differences, 

 in the chemical properties to designate a combination, in the phy- 

 sical properties to designate a solution. We all know, from the 

 beautiful experiments of Henry Rose, that very weak solutions 

 of the alkaline carbonates of borax have reactions differing essen- 

 tially from those which their concentrated solutions present. This 

 remark is sufficient once more to show that the phenomena due 

 to changes of state cannot be ranged in two distinct categories, 

 combination and solution. I shall recur to this once more, in refer- 

 ence to diffusion, or the indefinite extension of matter in menstrua. 



What I have said enables me to use the two words, combina- 

 tion and solution, in a perfectly definite sense, without the risk 

 of considering them to express an unknown cause, and cha- 

 * Contraction is here a generic term ; if it be negative, it is an expansion. 



