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," chap, xii.; and 

 p. 45 of this volume. 



f My attention was very forcibly directed to this subject some years 

 ago by a conversation with uiy excellent friend Professor Clausius, 



