ON SOLUBILITY. 459 



existence was recognised of a chemical attraction between the molecules 



of solute and the molecules of solvent. 



iqqq Gay-Lussac held the opinion that dissolution was a physical 



process,* being dependent upon the molecular state, and show- 

 ing a great resemblance to the phenomena of fusion and vaporisation, 

 iftzin ^^ e researcnes °f Karston 11 upon the influence of one salt 



on the solubility of another, as, for example, the influence of 

 other soluble nitrates on the solubility of sodium nitrate, did not indi- 

 cate the existence of any law governing the change of solubility ; how- 

 ever, it was concluded that aqueous solutions of salts must be regarded 

 as chemical compounds. 



1856 These conclusions were further emphasised by Pfaff. 2i Some 



1866 y ears ^ a * er Mulder 40 supported the view that solubility was to be 



regarded as a chemical process, and published his work upon 

 the saturation of water with two salts. Evidence was found therein 

 indicating the formation of some chemical compound (double salt) in 

 solution, the composition of which varied with the temperature, and 

 also with the quantity of the components present. 



Dossios 43 advanced a theory to explain the difference in 

 ■ solubility of substances, which was based upon the conception of 

 an attraction between the particles of solvent and the particles of solute 

 being greater than the attraction between the solute particles them- 

 selves. Unfortunately, no experimental justification for this assump- 



tion was given. Handl 50 expressed the opinion that the solu- 



bility of a substance is not conditioned by any property of the 

 solvent, but by the establishment of a state of equilibrium between 

 the number of particles leaving the solid body and the number return- 

 ing. Further work bearing on the nature or theory of solubility was 

 1Qrt - published by Pfaundler, 56 who studied the phenomenon of a 



crystal changing shape and not weight when kept in its saturated 

 solution ; the explanation put forward being that the energy of vibration 

 was unequal on different crystal surfaces. These views were, how- 

 ever, adversely criticised by Lecoq de Boisbaudran. 60 



In the following year Isidor Walz M published ' a contribu- 



tion to the theory of solubility ' in which he adopted an extended 

 view of solution, embracing themolecular intermixture of solids. The 

 size of the molecules and the intermolecular spaces were regarded as 

 having an important bearing upon the solubility of substances. 



From an entirely different source — namely, the study of suspension 



of clay in water and in saline solutions, Durham 70 came to the 



conclusion that chemical combination, solution, and suspension 

 are all manifestations of the same force, differing only in degree. 



Hannay and Hogarth 80 observed the solubility of solids in 



gases, and from their results concluded that the dissolution of a 

 solid substance was a function of all fluids ; the requisite condition being 

 molecular closeness and thermal activity. 



The behaviour of anhydrous copper sulphate towards anhydrous 



* Further observations by this author relative to ' solubility ' will be found, 

 Ann. Ch. Ph., 1819 (2), 11, 296 ; ibid., 1832 (2), 49, 393 ; ibid., 1839 (2), 70, 423 ; 

 Campt. rend., 1839, 8, 1000 ; and Ann. Ch. Ph., 1845 (3), 13, 567. 



