CHAPTER XL
Conclusions from the Dissociation Theory. Additive
Properties of Solutions.
General Remarks. — The properties of a solution may be regarded as the sum of the properties of the substances present in the solution. A solution of cane sugar contains two substances ; that which is present in excess is generally termed the solvent, and the other the dissolved substance ; the physical, chemical, physiological, and other properties of the solution can be regarded as approximately the sum of the corresponding properties of the two substances mixed (water and sugar).
Now, since salts are highly dissociated in aqueous solution, the properties of the solution will be equal to the sum of the properties of the solvent (water), of the ions, and of the undissociated substance. For dilute solutions the undis- sociated part is comparatively small, and it appears in many cases that its properties, when they diflFer appreciably from those of the two ions {e.g, with reference to reactivity and occasionally with reference to colour, etc.), ai*e not striking. For such cases it is usual to say that the properties of the salt solution are equal to the sum of the properties of the two ions, and leave the properties of the solvent out of account. This rule enables us to review the pi'operties of the numerous salts in solutions (dilute), because the number of ions obtained from these salts is comparatively small. The experimental confirmation of this rule may be regarded as a strong support of the view that the salts are electrolytically dissociated.
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