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tainable, can be esteemed suitable for this kind of measurements : the 

 small traces of humidity already, which even the best chemicals always 

 contain, are sufficient to make the results unreliable. Most of the orga- 

 nical liquids of commerce however seem to contain several admixtures, 

 in small quantities or even larger quantities of water. We often 

 obtained a first purification by distilling a small fraction from it, 

 whose boiling point remained constant between 1° or 2° C. In 

 several cases even this appeared not to be possible: in such case the 

 preparation was dried during some days by means of anhydrous 

 sodiumsulphate ; then, if the special character of the substance did 

 not forbid this, it was dried again during a long time by means 

 of freshly sublimed phosphorpentoxide, after which the fractional 

 distillation was tried again. Commonly it appeared to be possible, 

 to separate from it a fraction, whose boiling point remained constant 

 between 1° or 2° C. With some preparations we succeeded in drying 

 them by means of metallic sodium. After very dry fractions, boiling 

 within a few degrees, had been obtained in this way, they were once 

 more distilled with a small flame only, or on the water-bath, under 

 atmospheric or reduced (12 — 20 mm.) pressure; in this operation 

 only the fraction, boiling ivithin an interval of 1 C°., was used 

 for further treatment. The liquid was then cooled during several 

 hours in a closed vessel, by means of a mixture of salt and ice, 

 or by a bath of solid carbondioxide and alcohol. If it crystal- 

 lized, a further purification was often possible by repeated 

 freezing and decanting. Often a very thin layer of a solid substance 

 (eventually of ice) was deposed at the walls of the vessel, the rest 

 remaining liquid and transparent; the liquid portion was poured 

 into a dry, clean vessel then, and the said operation repeated, 

 till no solid layer any more appeared, ff however the phenomenon 

 continued to appear, the liquid was treated again at least during a 

 week with fresh phosphorpentoxide, and the freezing repeated again 

 and again. Finally the purified liquid was distilled once more undei' 

 atmospheric or reduced pressure; only the fraction, boiling loithin 

 half a degree was collected then for the measurements. It is hardly 

 necessary to mention, that hygroscopical liquids were preserved and 

 treated in a suitable manner. The thus obtained liquid was commonly 

 only a [very small fraction (lOVo O'" 207o) of the original commer- 

 cial preparation ; it must be remarked, that the observed boiling- 

 temperatures often differed appreciably from the data, given in the 

 literature, and in several cases appeared to be lower than those; 

 — which perhaps can be explained by the fact, that in the distil- 

 lations, described in the literature, the liquid was heated too rapidly. 



