228 Royal Society :— 
The author demonstrates in the next place that in many series of 
compounds other than those hitherto considered, the elementary 
difference, eC, H,, likewise involves a difference of x x 19° in the boil- 
ing-point. He further shows that on comparing the boiling-points 
of the corresponding terms in the several series of homologous sub- 
stances hitherto considered, many other constant differences in boiling- 
point are found to correspond to certain differences in composition. 
Thus a monobasic acid is found to boil 44° higher than its ethyl 
compound, and 63° higher than its methyl compound ; and this con- 
stant relation holds eood even for acids other than those previously 
examined, e. g. for the substitution-products of acetic acid. Also in 
eabitanecs sat are not acids, the substitution of C,H, or C,H, 
for H, occasionally involves a depression of the boiling-points re- 
spectively of 44° and 63°; the relation, however, is by no means 
generally observed. 
The author, in addition to the examples previously quoted, shows 
that compounds containing benzoyl (C,,H,O,) and benzyl (C,, H.) 
boil 78° (=4 x 14°°5+4 x “50) higher than the corresponding terms 
containing valeryl (C,,H,O,) and amyl (C,,H,,), a relation, however, 
which is ieee ise not generally met with. He discusses, moreover, 
other coincidences and differences of boiling-points of compounds 
differing in a like manner in composition. Not in all homologous 
series does the elementary difference «C,H, involve a difference of 
2xX19° in boiling-point. The author shows that this difference is 
greater for the hydrocarbons, C, H»-6 and CxHn+2; for the acetones 
and aldehydes, C,H, Oz; for the so-called simple and mixed ethers, 
C,H»+202; for the chlorides, bromides, and iodides of the alcohol 
radicals, Cy, H»+1, and for several other groups; that it is, on the con- 
trary, smaller for the anhydrides of monobasic acids, Cp Hn—20¢; for 
the ethers, C, H»-2Og (which may be formed either by the action of 
one molecule of a dibasic acid, C, H,-20s, upon two molecules of a 
monatomic alcohol, C,,H,+4202, or by the action of two molecules of 
a monobasic acid, C,,H,,0,, upon one molecule of a diatomic alcohol, 
C,,Hn+204), and several other series. 
The author thinks that the unequal differences in boiling-points 
corresponding in different homplogaug series to the elementary differ- 
ence wC, H,, are probably regulated by a more general law, which will 
be found when the boiling-points of many substances shall have been 
determined under pressures differing from those of the atmosphere. 
“From the observations at present at our disposal it may be 
affirmed as a general rule, that in homologous compounds belonging 
to the same series, the differences in boiling-points are proportional 
to the differences in the formule. Exceptions obtain only in cases 
when terms of a particular group are rather difficult to prepare, or 
when the substances boil at a very high temperature, at which the 
observations now at our command are for the most part uncertain. 
Again, it may be affirmed that the difference in boiling-points, 
corresponding to the elementary difference C,H,, is in a great many 
series =19° ; in some series greater, in some series less.” 
The author proceeds to discuss the boiling-points of isomeric com- 
pounds. Ie shows that in a great many cases isomeric compounds 
