Page:Outlines of Physical Chemistry - 1899.djvu/226

 208 OUTLINES OF PHYSICAL CHfcMISTBY

the value of the coefficient of dissociation :

In this equation x denotes the degree of dissociation of an electrolyte at any particular dilution, n is the molecular conductivity measured at the same dilution, and ^ is the conductivity calculated for infinite dilution (the sum of u and v). The determination of the electric conductivity of a solution, therefore, offers us a method of ascertaining the degree of dissociation of the dissolved substance.

We shall have occasion later to return to the subject of dissociation in solution.

��III. THE NATURE OP SALT SOLUTIONS

��The comparative study of electric conductivities has led us to assume a certain dissociation for dissolved electro- lytes. 1 Let us now see if this hypothesis is in thorough agreement with all the characters of salt solutions, and particularly with the exceptional properties which have been referred to in the chapter on ' Osmotic Methods.'

In connection with osmotic pressure it has already been pointed out that varCt Hoff's law is only directly applicable to the majority of organic substances, and in general to substances of a not very well denned chemical character. Strong acids, strong bases, and salts develop an osmotic pressure which is too high, and which is more or less proportional to the number of ions of which the dissolved molecule is composed.

In treating of the density of gases and vapours, and of the application of Avogadro's hypothesis, we remarked on an anomaly of the same kind. Certain substances, such

1 For the present we shall consider only aqueous solutions; especially as the dissociation is most distinctly manifested in aqueous solution.

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