PEOFESSOE TYNDALL’S CONTEIBUTIONS TO MOLECULAE PHYSICS. 335 
The foregoing results are collected together in the folloing Table : — 
Table VIII. — Absorption of heat by Liquids. Source, platinum spiral heated to a bright 
redness by a voltaic current. 
Liquid. 
Thickness of liquid in parts of an inch. 
0 - 02 . 
004 . 
0 - 07 . 
0 - 14 . 
0 - 27 . 
Bisulphide of Carbon 
5-5 
8-4 
12-5 
15*2 
17*3 
Chloroform 
16-6 
25-0 
35-0 
40-0 
44-8 
Iodide of Methyl 
36*1 
46-5 
53'2 
65*2 
68*6 
Iodide of Ethyl 
36*2 
50-7 
59-0 
69-0 
71*5 
Benzol 
43-4 
55*7 
. 62-5 
71-5 
73-6 
Amylene 
58-3 
65-2 
73-6 
77*7 
82*3 
Sulphuric Ether 
63-3 
73-5 
76-1 
78-6 
85-2 
Acetic Ether 
74-0 
78*0 
82-0 
86-1 
Formic Ether 
65-2 
76-3 
79-0 
84-0 
87-0 
Alcohol 
67-3 
78-6 
83-6 
85-3 
89*1 
Water 
80*7 
86-1 
88-8 
91-8 
91*0 
Had it been desirable to push these measurements to the utmost limit of accuracy, I 
should have repeated each experiment, and taken the mean of the determinations. But 
considering the way in which the different thicknesses check each other, an inspection 
of the Table must produce the conviction that the results express, within small limits 
of error, the action of the bodies mentioned. 
§ 3. 
As liquids, then, those bodies are shown to possess very different capacities of inter- 
cepting the heat emitted by our radiating source ; and we have next to inquire whether 
these differences continue after the molecules have been released from the bond of 
cohesion. We must, of course, test the vapours by waves of the same period as those 
applied to the liquids ; and this our mode of experiment renders easy of accomplishment. 
The heat generated in a wire by a current of a given strength being invariable, it was 
only necessary, by means of the tangent compass and rheocord, to keep the current con- 
stant from day to day in order to obtain, both as regards quantity and quality, an 
invariable source of heat. 
The liquids from which the vapours were derived were placed in a small long flask, a 
separate flask being devoted to each. The air above the liquid, and within it, being first 
carefully removed by an air-pump, the flask was attached to the experimental tube in 
which the vapours were to be examined. This tube was of brass, 49 - 6 inches long, 
and 2 ‘4 inches in diameter, its two ends being stopped by plates of rock-salt. Its 
interior surface was polished. At the commencement of each experiment, the tube 
having been thoroughly cleansed and exhausted, the needle stood at zero*. The cock 
of the flask containing the volatile liquid was then carefully turned on, and the vapour 
allowed slowly to enter the experimental tube. The barometer attached to the tube 
was finely graduated, and the descent of the mercurial column was observed through a 
magnifying lens. When a pressure of 0-5 of an inch was obtained, the vapour was cut 
* It is hardly necessary to remark that the principle of compensation described in my former memoirs was 
employed here also. 
MDCCCLXIV. 2 Z 
