6'8 PROCEEDINGS OF THE AMERICAN ACADEMY 



found that ether mixed with one tenth of its weight of bi-sulphide 

 of carbon, not only had a constant boiling-point, but that this was 

 the same as that of pure ether. He also made similar observations 

 on mixtures of bi-sulphide of carbon and alcohol, and alcohol and 

 water.* 



In the case of a mixture of two liquid bodies whose physical 

 properties differ so little as those of the hydrides and iso-hydrides 

 under consideration, probably a larger proportion of the lesser 

 constituent of the mixture may be present without affecting the 

 boiling-point of the larger one, than was shown in the experiments 

 of Berthelot and Alluard; and, in such a case, it may be found 

 impossible to purify a body sufficiently for some of the require- 

 ments of an investigation. But the fact that the constituents of 

 such a mixture may be brought into such proportions by fractional 

 condensation as to give the true boiling-point of the larger con- 

 stituent, must nevertheless be regarded as of great importance in 

 many cases, since the boiling-point is frequently an invaluable 

 means of controlling the formulae in homologous series; and espe- 

 cially so when the body under examination contains so large an 

 admixture of foreign substance that the vapor density and ultimate 

 analysis cannot be relied upon, which might often occur. Evi- 

 dently these are considerations to be taken into account in passing 

 judgment upon the value of results of an investigation of a mix- 

 ture of liquids based on a proximate analysis by any method of 

 fractional distillation; and it cannot be too strongly maintained, 

 that constancy of boiling-point, even if considered only as an ap- 

 proximative indication of the degree of purity, should nevertheless 

 be regarded as of the highest importance, and scarcely less so that 

 the separations should be made under the most favorable condi- 

 tions for the removal of the largest possible amount of impurity, — 

 conditions which certainly cannot be claimed for the old process of 

 fractional distillation. 



* I propose to make a series of experiments on mixtures of pure liquid sub- 

 stances in definite proportions, with the view to determine whether, or to what 

 extent, the observations of Berthelot and Alluard will hold true when a mix- 

 ture, of constant boiling-point, and inseparable by the old method, is distilled 

 through my regulated condenser; and at the same time to determine also, ap- 

 proximately, the degree of purity attainable by my method, as a test of the 

 capability of the process. 



