Prof. Tyndall's Contributions to Molecular Physics, 517 



vapours. It is also mixed with the vapour of water and carbonic 

 acid, both of which contribute their quota to the total radiation. 

 It is therefore probable that the greater accord between the 

 periods of the name and those of the vapours is due to the slower 

 periods of the substances which are unavoidably mixed with the 

 body to which the flame mainly owes its light. 



The next source of heat employed was the flame of a Bunsen's 

 burner, the temperature of which is known to be very high. 

 The flame was of a pale-blue colour, and emitted a very feeble 

 light. The following results were obtained : — 



Table XXV. — Radiation of heat through Vapours. Source, 

 pale-blue flame of Bunsen's burner. 



From Table XXIV. 



Luminous jet of gas. 

 120 

 9-8 

 19-5 

 22-0 

 30-2 

 35-7 

 34-6 

 38-7 

 1000 



The total heat radiated from the flame of Bunsen's burner is 

 greatly less than that radiated when the incandescent carbon is 

 present in the flame. The moment the air is permitted to mix with 

 the luminous flame, the radiation falls so considerably that the 

 diminution is at once detected, even by the hand or face brought 

 near the flame. Comparing Tables XXIV. and XXV., we see 

 that the radiation from the Bun sen's burner is, on the whole, 

 less powerfully absorbed than that from the luminous gas jet. 

 In some cases, as in that of formic ether, they come very close 

 to each other ; in the case of amylene and a few other substances 

 they differ more markedly. But an extremely interesting case 

 of reversal here shows itself. Bisulphide of carbon, instead of 

 being first, stands decidedly below chloroform. With the lumi- 

 nous jet, the absorption of bisulphide of carbon is to that of 

 chloroform as 100 : 122, while with the flame of Bunsen's burner 

 the ratio is 100 : 56 ; the removal of the carbon from the flame 

 more than doubles the relative transparency of the chloroform. 

 The case is of too much interest to be passed over without veri- 

 fication : here is the result obtained with a different total heat : — 



Name of vapour. 



Deflection. 



Absorption. 



Chloroform . . 



o 



. 5-0 



6-2 



Bisulphide of carbon 90 



11-1 



Iodide of ethyle 



. 11-3 



14-0 



Benzole . . . 



. 14-5 



17-9 



Amylene 



. 196 



24-2 



Sulphuric ether . 



. 25-8 



31-9 



Formic ether 



. 27-0 



33-3 



Acetic ether 



. 29-4 



3G3 



Total heat . . 



. 50-6 



1000 



