Identifier: philtrans08812111 (find matches)
Title: On Vapour-Pressure and Osmotic Pressure of Strong Solutions
Year: 1908 (1900s)
Authors: Callendar, H.
Subjects: Proceedings of the Royal Society of London Philosophical Transactions of the Royal Society
Publisher: Royal Society of London

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this assumption differs widely from the assumption of a cryoscopicconstant for volume-normal solutions (gramme-molecules per litre) which isoften made in reducing freezing-point observations according to the gas- iC- ( Roy. Soc. Proc., JunCj 1900. The vapour-pressures of water below the freezing-point are often calculated from Regnaults formula for the latent heat,, which appears(loc. cit.) to be inaccurate. 1908.) Osmotic Pressure of Strong Solutions, 489 pressure theory. The curve so obtained depends on the density of the solution^and is different for different substances. If the depression of the freezing-point for solutions of cane-sugar were proportional to the number of gramme-molecules per litre, we should obtain the curve marked I in Hg. 7, whichillustrates the danger of pushing an attractive analogy too far. The depressioncalculated on the gas-pressure theory would be 3°*72 for a solution containing2 gramme-molecules of sugar per litre, as against 6°-6 if the depression is
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To ?? Iz n u TT Fig. 7.—Depression of the Freezing-point in Aqueous Solutions. 76 IT proportional to n/N. Experiment gives 9°*15, according to Jones and Getman.The gas-pressure theory is inconvenient, because it involves considerations ofdensity, and it fails to represent the observations satisfactorily, even forweak solutions, because it gives in many cases so bad an approximation tothe vapour-pressure curve. The crosses marked S, representing the observations on the depression ofthe freezing-point for cane-sugar, agree very well with the curve markedVOL. LXXX.—A. 2 M a 490 Prof. H. L. Callendar. On Vapour-pressure and (Mar. 10, a = 5, as in the case of the osmotic pressure. Thus the observed depressions,t n = 6-41 is ?^ = —9^-15. The calculated value for a = 5 is t = — 9*^-30.Yant Hoffs rule gives t = — 6°-60. For a = 0 the depression wou.ld bet = — 6^42. The depressions recorded in Landolt and Bornsteins tables formethyl and ethyl alcohols, marked A in fig. 7a, agree

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