Page:Outlines of Physical Chemistry - 1899.djvu/281

 been studied. For the lowest members of these series G, Carrara and P. Dutoit 1 have discovered the following facts :

a. If we consider only the data obtained from the boiling point 8, the dissociation is very small in methyl alcohol solution

b. From the electro-chemical point of view, the opposite is the case — methyl alcohol, acetone, and acetonitrile have a fairly powerful dissociating action. For, in very dilute solution, it frequently happens that the conductivity /^ or /z °° of the dis- solved substance is as great in the organic solution as in aqueous solution, or even greater. 3 It is true that at moderate dilution water has by far the greater dissociating power, and that a methyl alcohol or acetone solution is generally a much poorer conductor than an aqueous solution of the same concen- tration. 4 Yet the fact remains that organic liquids may give solutions which are good conductors, that is to say, highly dis- sociated solutions, and consequently the two methods of investi- gation a and b seem- to contradict each other.

To show that this contradiction is only apparent, we shall go a little deeper into the matter and consider the following :

1. As far as the disintegration of a dissolved substance is concerned, it is necessary to distinguish between the decompose tion of the molecular aggregates and the dissociation proper.

1 O. Carrara, 'Gazz. Chim. Ital.' 26, i. 119, and 27, i. 207; P. Dutoit and Aston, 'Comptes Rendus,' 125, 240; Dutoit and Friderich, 'Bull, de la Soc. Chim./ 19, 321.

2 In acetone solution Dutoit and Friderich have found the normal molecular weight by the boiling-point method for the salts : NCSNH 4 , Nal, LiCl, HgCl,, Cdly

8 This high conductivity has been found by Carrara in methyl alcohol solution for certain neutral salts, such as N(CH S ) 4 I, and 8(0^5)51, and in acetone solution for the salts: EI, Nal, NH 4 I, N(CH,) 4 I, S(C2H 5 ) S I. According to Dutoit and Friderich, the con- ductivity /a 00 of AgNO s and Nal in acetonitrile solution is much greater than in aqueous solution.

For HC1 and CClg-CO^H, as also for the free alkalis KOH, N(CH 3 ) 4 OH, Ac, the conductivity /a <» is much lower in methyl alcohol than in water. In acetone solution the conductivity of the acids mentioned has been found to be very low (Carraray.

The tertiary electrolytes HgClg and Cdl 2 nave, in acetonitrile solution, a very low conductivity (Dutoit).

4 At moderate dilution, in order that the dissolved substance attain a certain degree of dissociation, the methyl alcohol or acetone solution must be more dilute than the aqueous solution (Carrara),

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