Page:Text-book of Electrochemistry.djvu/60

 It should be mentioDed that here also salts seem to behave anomalously. Baoult only investigated few of these. "We return later to a consideration of their hehavionr.

Vapour Pressure of Solutions in Ether. — Baoult proved that for solutions in ethyl ether the relative lowering of vapour pressure is independent of the. c a a temperature. He used the ordinary method for determining the vapour pressure, namely allowing the liquid to evaporate in a barometer vacuum. The barometric height A was read off on the barometer A (Fig. 13); into another barometer, B, ether was introduced, and the mercury meniscus sank to hi. The vapour pressure p of the ether is given by h — ki. Into a third p,n i8.

barometer, C, was introduced a solution, e.g. of 1 gram-molecule (136 grams) of turpentine in 1000 grams, that is, 1552 gram-molecules, of ether.

For this solution Eaoult found the vapour pressure p'. The calculation leads to —

��r ^?r

whilst the experiment gave 0-071.

The experiments were carried out in a room in which the temperature varied between 0° and 20°, but the same lowering,

- - - = P, was always obtained, although p varied over a

tolerably wide range (from 185 to 442 mm.).

Other substances besides turpentine were examined, in all cases 1 gram-molecule in 1000 grams of ether being ' taken. The values obtained, which are given in the follow- ing table, all agree, within the limits of experimental error, with the result found for turpentine 0071 and the theoretical value 0074.

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