Dr. H. T. Brown deduces from the following considerations that with very dilute mixtures of alcohol and water there is an expansion of volume instead of a contraction.3

The apparent specific volume, i.e., the volume occupied by unit weight of alcohol, may be expressed by the formula where D is the specific gravity of the mixture at 15.6°/15.6°, and W the weight of alcohol, expressed in grams, in 1 c.c. of the mixture. The values of the specific volume for mixtures of comparatively low alcoholic concentration are given in the following table: -

1 - (D - W)IW,

1 Graham, Phil. Trans., 1861, 151, 373.

2 Trans. Chem. Soc, 1906, 89, 1775. 3 Analyst, 1915, 40, 379.

Sp. gr. of mixture.

Sp. vol. of alcohol in mixture.

0.988

1.1713

9

1.1732

0.990

1.1750

1

1.1770

2

1.1788

3

1.1807

4

1.1818

5

1.1834

6

1.1850

7

1.1862

8

1.1874

0.999

1.1890

These values represent the volume in c.c. occupied by 1 gram of alcohol at the different concentrations when the volume-changes are all thrown on the alcohol.

The apparent specific volume of the contained alcohol increases steadily with the dilution. It follows that on progressive dilution within these limits the volume of the mixture must exceed the sum of the initial volumes of the constituents, so that an actual increase of volume must occur instead of the contraction which is observed at higher concentrations of alcohol. The critical point at which dilution ceases to produce contraction and begins to give rise to expansion occurs at a concentration corresponding very nearly with the specific gravity 09652. This point would seem to mark the completed formation of a definite alcohol hydrate, during the formation of which continuous contraction takes place; and the expansion which occurs on still further dilution may be regarded as an expression of progressive dissociation of this hydrate.

A hydrate having the composition C2H5.OH,8H10, would contain 2421 per cent, of alcohol, and dilute alcohol of specific gravity 09652 contains 24.82 per cent, (by weight).

Surface Tension

At 20°, and for alcohol of 9954 per cent. strength, the surface tension is 20.90 dynes per centimetre.