VI. 



On a Process of Fractional Condensation ; applicable to the Sepat 



small Differences between their Boiling-Points 



Bodies h 



By C. M. WARREN. 



Communicated May 10th, 1864. 



It is well known that the process in general use for the proximate analysis of 



tures of 



liquids, — viz., that of simple fractional distill 



fr 



tubulated retort or from a flask with bulbs, as proposed by Wurtz,* — affords but 

 very imperfect and unsatisfactory results, and not unfrequently leads to gross errors 

 and misconceptions, except in those cases in which the boiling-points of the constitu- 

 ents are widely different, or in which some auxiliary method can be advantageously 

 employed. 



The want of a more efficient process for effecting such separations has long been 

 recognized. There are numerous natural and artificial products, of the highest 

 scientific interest, — such as petroleums, essential oils, tars, and other mixtures of 

 oils obtained by the distillation, under varied circumstances, of bituminous, vegetable, 

 and animal substances, — of which it may at least be said that we have but very imper- 

 fect knowledge, — I might almost say no knowledge, except such as could be derived 

 irom the study of very impure materials, — still mixtures of different bodies, — with 

 winch, instead of the pure substances sought for, chemists have felt compelled to 

 content themselves, as the best results which they were able to obtain by the means 

 at their command. 



in repeated instances, apparently after persevering and protracted efforts, investiga- 

 tors have been forced to assert either the impossibility, or their inability, to obtain, 

 from such mixtures, bodies of constant boiling-point, — a property which is generally 

 received as a test of purity for liquid bodies. 



I 



may here specify a few recent instances of this kind 



vol. ix. 



* Annates de Chimie et de Physique, 3 e Serie, XLII. 132 



20 



