Page:Text-book of Electrochemistry.djvu/176

 X. OSMOTIC AND ELECTRICAL DETERMINATIONS. i6i

part to errors of experiment with which the methods are infected. Thus, Jones (J) found for a 0*75 per cent, solu- tion of cane sugar a molecular depression of the freezing point which was too great by 27 per cent., and all the older observations on dilute solutions are subject to similar deviations. Nemst and Abegg (4) have shown that this want of agreement is partly attributable to the fact that the freezing out of the solid solvent does not take place instantaneously, and in consequence the observed temperature is to a certain extent influenced by the tempemture of the surrounding freezing mixture. The ideal method would therefore be to work with a freezing mixture the temperature of which is only infinitessimally lower than the freezing point to be determined. Interesting observations in this respect have been made by Jones, Loomis, Baoult, and others. The salt which has been most thoroughly investigated cryoscopically is potassium chloride, which possesses the great advantage that the internal friction of the solution differs but slightly from that of pure water, so that a cor- rection for the influence of this friction on the conductivity, within the limits of concentration employed, can safely be neglected. Loomis (5) found the following freezing points for solutions of this salt : —

��Conoentration,

��FreesiDg point,

��0-0360°

��(i + a)l'8«. DIff. iu per cent.

��For concentrations up to 0*2-normal the agi-eement is perfect (within the experimental error). The data obtained by Loomis have been fully confirmed by Jones, Abegg, Barnes,

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