134 ON A PROCESS OF FRACTIONAL CONDENSATION. 
But in my investigations, I have undertaken to prove the negative as well as the 
positive. I have attempted to carry the process of separation so far, that I might 
assert the absence of other bodies, as well as the presence of those obtained; and this 
clearing up of the intermediate fractions has generally been the most tedious part of the 
work. I have continued to operate upon these by themselves, until they also have 
become distributed in regular course — no new bodies appearing — among the frac- 
tions of constant boiling-point, or to such an extent that the intermediate quantities 
have become too small to admit of further continuance of the process. 
This process has been in constant use in my laboratory during the last three years. 
In this time it has been applied in the study of petroleums, coal oils, the more volatile 
parts of coal- and wood-tars, the essential oil of cumin, commercial fusel oil, from corn 
whiskey, and even to mixtures more complex than either of these. As the result of 
this long experience, I can say that as regards bodies not decomposed by heat in dis- 
tillation, I have not yet found a mixture so complex that it may not be resolved by 
this process into its proximate constituents so completely, that these shall have almost 
absolutely constant boiling-points. In repeated instances, even from petroleums, I 
have obtained these constituents so pure, that the contents of an ordinary tubulated 
retort charged with one of them has been completely distilled off without any essen- 
’ tial change of temperature; i. e., not to the amount of }° C., the thermometer fre- 
quently remaining absolutely constant for more than half an hour, a constancy of 
boiling-point not exceeded by that of distilled water. This state of purity, I think I 
may safely assert, has never before been attained from such mixtures by any system 
of fractional distillation. 
As I shall soon be prepared to present to the Academy detailed results of the inves- 
tigations above referred to, I may omit further allusion to them on this occasion. 
I would remark, in conclusion, that it seems to me not improbable that this process 
may ultimately prove to be of great value in the arts. It is not too much to anticipate 
that, whenever the various constituents of the mixtures referred to shall have been 
separately and thoroughly studied in a pure state, some of them may be found to pos- 
sess properties which will give to them great commercial value, sufficient to justify the 
expenditure necessary to separate them in large quantities. 
