Page:Outlines of Physical Chemistry - 1899.djvu/280

 262 OUTLINES OF PHYSICAL CHEMISTEY

also very energetically dissociates electrolytes. Some other solvents are, to a certain degree, possessed of the same proper- ties as water, inasmuch as they have the power of isolating the molecules of dissolved substances ; but they exercise only a very weak dissociating action, or none at all, 1 on electrolytes. To this category belong the lower members of the series of organic alcohols and acids, and also some substances which contain no hydroxyl, such as ketones, nitroethanes, and nitriles. The hydrocarbons, nitrobenzene, ethylene bromide, chloroform, car- bon disulphide, and some other organic liquids employed in boiling and freezing point determinations, have only a very weak disintegrating action, and in some cases they even allow the dissolved substance 2 to remain in the state of double or multi- molecules.

Such are the results furnished by the indirect osmotic methods. But we must notice that a certain number of the liquids mentioned are able to dissolve some electrolytes and thus form solutions which conduct fairly well ; hence it would be desirable to submit these first results to an electro- chemical investigation.

For aqueous solutions the factor x, which denotes the degree of dissociation of the dissolved substance, is, as we have already seen, independent of the method by which it is arrived at ; s and, indeed, we have taken this agreement as the principal confirma- tion of our theories on the constitution of salt solutions.

But in the case of solutions in an organic solvent^ it very often happens that this agreement no longer exists and that the value found for x by the boiling-point method is lower than its electro-chemical value. And in face of this disagreement between the two &'s, our theoretical conceptions seem to be rather compromised.

Amongst organic solvents of a more or less dissociating power, a certain number of alcohols, ketones, and nitriles have

��1 N.B. — We confine ourselves here to indications given by osmotio methods. We shall find later that a correction must be introduced.

2 Namely, alcohols, phenols, certain organic acids, &c.

1 By boiling or freezing point method x = — ; electro-chemi-

cally x = -^£-*

f* 00 .,. .

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