CONTRIBUTIONS TO MOLECULAR PHYSICS. 295 



absolutely the same. There is no known exception to this 

 law; so that, to determine the position of a vapor as an 

 absorber or a radiator, it is only necessary to determine the 

 position of its liquid. 



This result proves that the state of aggregation, as far 

 at all events as the liquid stage is concerned, is of altogether 

 subordinate moment a conclusion which will probably 

 prove to be of cardinal importance in molecular physics. 

 On one important and contested point it has a special bear- 

 ing. If the position of a liquid as an absorber and radiator 

 determine that of its vapor, the position of water fixes that 

 of aqueous vapor. Water has been compared with other 

 liquids in a multitude of experiments, and it has been 

 found, both as a radiant and as an absorbent, to transcend 

 them all. Thus, for example, a layer of bisulphide of car- 

 bon 0.02 of an inch in thickness absorbs 6 per cent., and 

 allows 94 per cent, of the radiation from the red-hot 

 platinum spiral to pass through it; benzol absorbs 43 and 

 transmits 57 per ceut. of the same radiation; alcohol absorbs 

 67 and transmits 33 per cent., and alcohol, as an absorber 

 of radiant heat, stands at the head of all liquids except 

 one. The exception is water. A layer of this substance, 

 of the thickness above given, absorbs 81 per cent., and 

 permits only 19 per cent, of the radiation to pass through 

 it. Had no single experiment ever been made upon the 

 vapor of water, its vigorous action upon radiant heat 

 might be inferred from the deportment of the liquid. 



The relation of absorption and radiation to the chemical 

 constitution of the radiating and absorbing substances was 

 next briefly considered. For the six substances in the list of 

 liquids examined, the radiant and absorbent powers aug- 

 ment as the number of atoms in the compound molecule 

 augments. Thus, bisulphide of carbon has 3 atoms, 

 chloroform 5, iodide of ethyl 8, benzol 12, and amylene 15 

 atoms in their respective molecules. The order of their 

 power as radiants and absorbents is that here indicated, 

 bisulphide of carbon being the feeblest and amylene the 

 strongest of the six. Alcohol, however, excels benzol as 

 an absorber, though it has but 9 atoms in its molecule; 

 but, on the other hand, its molecule is rendered more com- 

 plex by the introduction of a new element. Benzol con- 

 tains carbon and hydrogen, while alcohol contains carbon, 

 hydrogen and oxygen. Thus, not only does atomic multi- 



