96 
but that it decreases regularly by 4° until it becomes the 
well known difference of 19°, as the following table will 
show — 
Boiling-points. 
( — 
Found (mean). 
Calculated. 
Difference 
c h 4 
... 
c 2 h 6 
... 
c 3 h 8 
c 4 H 10 
1° ... 
i° ... 
c 3 h 4j 
38 
38 
37° 
c 6 h 14 
70 
71 
33 
C 7 h 16 
99 
100 
29 
c 8 h 18 
124 
125 
25 
C 13 H a6 
202 
201 
4 x 19 
c 10 h 34 
278 
278 
4x 19 
It appeared to me of interest to compare the boiling 
points of other normal compounds, selecting of course those 
only of which the boiling points have been carefully deter- 
mined and corrected for pressure and expansion of the 
mercurial column of the thermometer above the vapour. 
The result of this investigation is that in most of the other 
series the difference between the boiling points also steadily 
decreases by about 2° ; but I am not in a position to state 
whether this decrease ceases when the difference becomes 
19°, as we do not yet know a sufficient number of compounds. 
(1) Normal Iodides. 
Boiling-points. 
Methyl C H 3 1 
Observed. 
40° 
Calculated. 
... 40° 
Difference. 
Ethyl 
CoH 6 I 
72 
... 72 
... 32° 
Propyl C 3 H 7 I 
102 
... 102 
... 30 
Butyl C 4 H 3 1 
129-G 
... 130 
... 28 
Pentyl C 5 H U I 
155-4 
... 15G 
... 26 
Hexyl C 6 H,,I 
179-5 
... 180 
... 24 
Heptyl C 7 H j3 I 
— 
... 202 
... 22 
Octyl 
c 8 h 17 i 
... 221 
... 222 
... 20 
