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X. Saturation of Salt-solutions. — Part II. By W. W. J. 

 Nicol, M.A., D.Sc, F.R.S.E., Lecturer on Chemistry, 

 Mason College, Birmingham* 



Section I. 



IN my paper f, of which this is a continuation, I endeavoured 

 to show that the solubility of a salt in water is dependent 

 on the difference between the molecular volume of the salt in 

 dilute solution and that in the saturated solution, compared 

 with the difference between this last volume and that in the solid 

 state. Thus, the greater the cohesion of the salt the less its 

 solubility, and vice versa. The adhesion of the water to the 

 salt is also a factor in solution ; the greater the adhesion the 

 more soluble the salt. In very dilute solutions, when once the 

 salt is dissolved the cohesion of the salt is practically nil ; for 

 the molecules encounter one another so rarely that no appre- 

 ciable number are in collision at any one time. As the con- 

 centration of the solution increases the collisions of salt mole- 

 cules become more frequent, and their cohesion asserts itself 

 more and more, as shown by the gradual increase of the mean 

 molecular volume of the salt in solution. Finally, when the 

 cohesion of the salt and the adhesion of the water to the salt 

 are in equilibrium the solution is saturated. 



It is this gradual increase of the mean molecular volume %, 

 from that in the most dilute solutions to that at the point of 

 saturation, that forms the subject of the present paper. 



In the course of the work connected with the other papers 

 that I have published on solution, I had accumulated a great 

 number of data dealing with the density and molecular volume 

 of various solutions of numerous salts, and in the instances 



t Communicated by the Author. 



Phil. Mag. June (Suppl.), 1884. 

 % By mean molecular volume is meant the apparent volume of any 

 one molecule of salt present in the solution, the volume of water being 



r 



assumed constant. It is Thomsen's - ; thus 



Mol. vol. of solution = ^ — '- — — ; 



r = 1800+»(M..W.)_- 1800 , 



- = mean molecular volume ; 

 (M.W.) = molecular weight of the salt in grammes. 



