r 257 ] 
XVI. On the delation betimen Boiling-foint and Composition in Organic Compounds. 
By HEEMAjiTiir Kopp, M.B., Ph.D., Professor of Theoretical Chemistry in the 
University of Giessen. Communicated hy Br. A. W. Hofmann. 
Eeceived Marcli 20, — Bead May 3, 1860. 
The researches which I beg, in the following pages, to submit to the Royal Society, 
embody the results obtained in the further development of an observation which I made 
a considerable number of years ago, and which, since that time, I had to defend against 
the objections of others, both by experimental inquiries of my own, and by the collection 
and discussion of facts elicited in the investigations of other observers. As far back as 
1841* * * § I pointed out that in analogous compounds the same ditference of composition 
frequently involves the same difference in boiling-points. The assertion of the existence 
of this law-like relation between the chemical composition of substances and one of 
their most important physical properties, when first enunciated, met rather with the 
opposition than with the assent of chemists. In Germany especially it was contested 
by ScHEODEE in his memoh' “On the Molecular Volume of Chemical Compounds f.” 
These objections led me to collect additional evidence J in favour of my views, and to 
show more particularly that in very extensive series of compounds (alcohols C^ Og ; 
acids Cn H„ O 4 ; compound ethers C„ O 4 , &c.) an elementary difference xC^ Hg is 
attended by a difference of xX 19° C. in the boiling-points, and how this fact is intimately 
connected with other regularities exhibited by the boiling-points of organic compounds. 
Almost at the same period Scheodee § convinced himself that the relation I had pointed 
out obtains in most cases. He collected himself a considerable number of illustrations 
of the regularities 1 had traced, and showed that the relation in question is rendered 
more especially conspicuous if the compounds be expressed by formulae representing 
equal vapour-volumes of the several substances. Some of the views, however, which 
were peculiar to Scheodee have not gained the approbation of chemists. This physicist 
was inclined to consider the boiling-point of a substance as the most essential criterion 
of its proximate constituents, as the most trustworthy indicator of its molecular consti- 
tution. His ■views "were chiefly based upon the assumption that the elementary difference 
CgHg, when occurring in alcohols C^Hn+gOg, involved a difference of boiling-points 
other than that occasioned by the same elementary difference obtaining in acids H„ O 4 , 
* Ann. der Chem. und Pharm. vol. xlix. pp. 71 and 169. 
t Ueber die Molecular- Volume der Chemisclien Verbindungen, 1843. 
% Ann. der Chem. und Pharm. vol. 1. p. 128. 
§ TJeber die Siedbitze der Chemischen Verbindungen, 1844. 
2 M 
MDCCCLX. 
