. Manual of physico-chemical measurements. can be put in throughthe condensing tube at K^; evenif it does not fall completely intothe boiling vessel it is soon washeddown by the condensing solvent. The solution in the boilingtube is more concentrated thanis given by the weighing, as a portion of the solvent during ebullitionis removed, partly as vapour, and partly as liquid in the correction of 02 g., in the case of water 035 g., must therefore bededucted from the weight of the solvent. Glass vapour jackets are very liable to crack, and it is there-fore advisable to use one of copp
. Manual of physico-chemical measurements. can be put in throughthe condensing tube at K^; evenif it does not fall completely intothe boiling vessel it is soon washeddown by the condensing solvent. The solution in the boilingtube is more concentrated thanis given by the weighing, as a portion of the solvent during ebullitionis removed, partly as vapour, and partly as liquid in the correction of 02 g., in the case of water 035 g., must therefore bededucted from the weight of the solvent. Glass vapour jackets are very liable to crack, and it is there-fore advisable to use one of copper for high boiling liquids. Theopacity is no drawback, as the movements of the thermometerafford a sufficient indication of what is going on inside thevessel. For another form of boiling point apparatus see J. Sakurai ( Soc, 1892, p. 989). I have as yet had no opportunity oftesting it personally. The calculation is done by a formula quite analogous to that forthe freezing point. If A is the elevation of the boiling point, s the. 188 PHYSICO-CHEMICAL MEASUREMENTS CHAP. weight of substance, L the weight of solvent, and M the molecularweight of the substance, we have The constant h has the following values :— Ethyl ether 2110 Benzene . 2670 Chloroform . .3660 Carbori bisulphide. .2370 Acetic acid . 2530 Ethyl alcohol 1150 Ethyl acetate . 2610 Acetone 1670 Water . .520 Ethylene dibromide . 6320 Aniline . 3220 Phenol . 3040 These values change somewhat with the pressure, and are validfor the mean barometric pressure. For several special purposes we can use a method worked out atmy suggestion by J. AValker ^ for aqueous solutions, and applied laterin a somewhat altered form by Will and Bredig ^ to alcoholic solu-tions. It depends on the measurement of the ratio of the vapourpressures of solution and pure solvent by vaporisation in an aircurrent. Two Liebigs potash bulbs containing the solution, and one con-taining water, are connected with each other. The last is weighed
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