CONTRIBUTIONS TO MOLECULAR PHYSICS 409 



the radiation from tlie red-hot platinum spiral to pass 

 through it; benzol absorbs 43 and transmits 57 per cent 

 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 excep- 

 tion 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 chemi- 

 cal constitution of the radiating and absorbing substances 

 was next briefly considered. For the first six substances 

 in the list of liquids examined, the radiant and absorbent 

 powers augment 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 complex by the introduction of a new ele- 

 ment. Benzol contains carbon and hydrogen, while alco- 

 hol contains carbon, hydrogen and oxygen. Thus, not 

 only does atomic multitude come into play in absorption 

 and radiation — atomic complexity must also be taken into 

 account. I would recommend to the particular attention 

 of chemists the molecule of water; the deportment of this 



substance toward radiant heat being perfectly anomalous, 



Science— V— 18 



