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LXL Saturation of Salt-Solutions. By W. W. J. Nicol, 

 M.A., B.Sc, F.R.S.E., Sfc, Lecturer on Chemistry, Mason 

 College, Birmingham* . 



ACCORDING to the theory of solution brought forward 

 in my paper on the Nature of Solution")*, saturation of a 

 solution of a salt results when the sum of the attractions of 

 the salt-molecules present in the solution for any individual 

 salt-molecule is equal to the sum of the attractions of the 

 water-molecules for that particular salt-molecule — the attrac- 

 tion of the water-molecules for one another being disregarded, 

 as a probably constant quantity. At that time I endeavoured 

 to prove that the attraction of the dissimilar molecules of water 

 and salt is one cause of the contraction attending the solution 

 of a salt, while the attraction of the similar molecules of the 

 salt has an opposite effect, and tends to produce an increase in 

 the volume. 



I wished at the time of publication of the above to show a 

 connexion between the molecular volume of a salt in the solid 

 state and its solubility. That such a connexion does exist, my 

 early experiments soon convinced me. But as yet I am in a 

 position only to indicate the nature of this relation: sufficient 

 evidence is still wanting to give my conclusions a quantitative 

 value- 



The results J obtained by comparisons of the molecular 

 volumes of dilute solutions of various salts, show that in such 

 solutions the intermolecular spaces are practically coextensive 

 whatever may be the salt, while this is clearly not the case in 

 the solid state, except with isotomous salts. In solution the 

 molecules of salt are so far apart that they are out of the sphere 

 of one another's attraction ; in the solid state, on the other 

 hand, they are packed more or less closely together, according 

 to the temperature § of crystallization and the attraction they 

 have for one another. If, now, the above theory of saturation 

 be the correct one, it is evident that, since loose packing of 

 the molecules — that is, large molecular volume in the solid 

 state — is due to weak attraction between the molecules of the 

 salt, such a salt should be more easily dissolved than one which 

 differs from it only in the attraction between its molecules 

 being so great as to cause a smaller molecular volume. I hope 

 to be able to show that this is the case. 



As already shown by Gerlach and others, the rate of increase 



* Communicated "by the Author. 



t Phil. Mag. 1883, xv. p. 91. 



j Phil. Mag. 1883, xv. p. 121, and Ber. d. deut. chem. Ges. 



§ Phil. Mag. Feb. 1883, p. 94. 



