On the Relation between Boiling-point andComposition. 229 
belonging to the same type, and exhibiting the same chemical cha- 
racter, boil at the same temperature, and that there is no reason why, 
for the class of bodies mentioned, this coincidence should not obtain 
generally. On the other hand, different boiling-points are observed 
in isomeric compounds possessing a different chemical character, 
although belonging to the same type (e. g. acids and compound ethers, 
C,,H,O,; alcohols and ethers, C,,H,,,:02), and im isomeric com- 
pounds belonging to different types (e. g. allylic alcohol and acetone). 
The author shows that the determination of the boiling-point of a 
substance, together with an inquiry into the compounds serially 
allied with it by their boiling-points, constitutes a valuable means of 
fixmg the character of the substance, the type to which it belongs, 
and the series of homologous bodies of which it is a term. He 
quotes as an illustration eugenic acid. The boiling-point of this 
acid, C,,H,,0,,is 150°; and on comparing this boiling-point with the 
boiling-points of benzoic acid, C,,H,O, (boiling-point 253°), and of 
hydride of salicyl, C,,H,O, (boilmg-point 196°), it is obvious that 
eugenic acid cannot be homologous to benzoic acid, whilst, on the 
other hand, it becomes extremely probable that it is homologous to 
hydride of salicyl, and consequently that it belongs rather to the 
aldehydes than to the acids proper. 
The author, in conclusion, calls attention to the importance of 
considering the chemical character in comparing the boiling-points 
of the volatile organic bases, and shows the necessity of distinguish- 
ing between the primary, secondary, and tertiary monamines in order 
to exhibit constant differences of boiling-point for this class of sub- 
stances. He discusses the boiling-points of the several bases, 
C,Hn»_sN and CrHn+3N, and points out how in many cases the 
particular class to which a base belongs may be ascertained by the 
determination of the boiling-point. 
The comprehensive recognition of definite relations between com- 
position and boiling-point is for the present chiefly limited to organic 
compounds. But for the majority of these compounds, and indeed 
for the most important ones, this relation assumes the form of a 
simple law, which, more especially for the monatomic alcohols, 
C,,H,,O2, for the monobasic acids, C,,H,,O4, and for the compound 
ethers generated by the union of the two previous classes, is proved 
in the most general manner ; so much so, indeed, that in many cases 
the determination of the boiling-poiat furnishes most material assist- 
ance in fixing the true position and character of a compound. 
The author points out more especially that the simplest and most 
comprehensive relations have been recognized for those classes of 
organic compounds which have been longest known and most accu- 
rately investigated, and that even for those classes the generality and 
simplicity of the relation, on account of numerous boiling-poits in- 
correctly observed at an earlier date, appeared in the commencement 
doubtful, and could be more fully acknowledged only after a consi- 
derable number of new determinations. Thus he considers himself 
justified in hoping that also in other classes of compounds, in which 
simple and comprehensive relations have not hitherto been traced, 
these relations will become perceptible as soon as the verification of 
