NEW CHEMICAL REACTIONS. 7? 
worth testing. A solution of the yellow chromate of potash, 
the color of which may be made almost, if not altogether, 
identical with that of the liquid nitrite of arnyl, was found 
far more effective in stopping the chemical rays than 
either the red or the yellow glass. But of all substances 
the liquid nitrite itself is most potent in arresting the rays 
which act upon its vapor. A layer one-eighth of an inch 
in thickness, which scarcely perceptibly affected the lu- 
minous intensity, absorbed the entire chemical energy of 
the concentrated beam of the electric light. 
The close relation subsisting between a liquid and its 
vapor, as regards their action upon radiant heat, has been 
already amply demonstrated.* As regards the nitrite of 
amyl, this relation is more specific than in the cases hith- 
erto adduced; for here the special constituent of the beam, 
which provokes the decomposition of the vapor, is shown 
to be arrested by the liquid. 
A question of extreme importance in molecular physics 
here arises: What is the real mechanism of this absorption, 
and where is its seat?f I figure, as others do, a molecule 
as a group of atoms, held together by their mutual forces, 
but still capable of motion among themselves. The va- 
por of the nitrite of amyl is to be regarded as an assem- 
blage of such molecules. The question now before us is 
this: In the act of absorption, is it the molecules that are 
effective, or is it their constituent atoms? Is the vis viva 
of the intercepted light-waves transferred to the molecule 
as a whole, or to its constituent parts? 
The molecule, as a whole, can only vibrate in virtue of 
the forces exerted between it and its neighbor molecules. 
The intensity of these forces, and consequently the rate of 
vibration, would, in this case, be a function of the distance 
between the molecules. Now the identical absorption of the 
liquid and of the vaporous nitrite of amyl indicates an 
identical vibrating period on the part of liquid and vapor, 
and this, to my mind, amounts to an experimental proof 
that the absorption occurs in the main within the molecule. 
For it can hardly be supposed, if the absorption were the 
* " Phil. Trans." 1864 ; "Heat, a Mode of Motion," cLap. xii.; and 
p. 45 of this volume. 
f My attention was very forcibly directed to this subject some years 
ago by a conversation, with my excellent friend Professor, Cla,usiua, 
