696 THE POPULAR SCIENCE MONTHLY 



riety of theories which may be formed on the slender foundation of 

 one or two facts, I am convinced that it is the business of the true 

 philosopher to avoid them altogether. It is more laborious to accu- 

 mulate facts than to reason concerning them; but one good experi- 

 ment is of more value than the ingenuity of a brain like Newton's." 

 Quarterly Journal of Science. 



THE CAUSE OF THE LIGHT OF FLAMES. 



bt w. stein. 



THE correctness of the old and well-founded conception that the 

 light of flame is caused by incandescent carbon-molecules, has 

 been disputed by Dr. Frankland, who contends and tries to prove that 

 it is derived from hydrocarbon-vapors. It is evident that the old 

 theory would have to give place to the new doctrine as soon as the 

 untenability of the former and the correctness of the latter are proved. 

 But neither the one nor the other has, I think, yet been done. Prof. 

 Frankland can, therefore, only be pleased if the present paper subjects 

 the 2^^*^^ aiitl cons of the new and old theory to an impartial exami- 

 nation. 



As proof of his ideas he mentions that the soot deposited on a cool 

 surface, when introduced into a flame, does not consist of pure carbon, 

 but that it contains also hydrogen ; that, in fact, it seems nothing else 

 than a collection of the densest light-giving hydrocarbons, whose 

 vapors condense on the cold surface. 



Against this we may mention that not only do the heavy hydro- 

 carbons, but even marsh-gas, split up at high temperatures on exclu- 

 sion of atmospheric air ; and as the hydrocarbons, whose vapors are 

 supposed to cause the luminosity of the flame, are precisely under such 

 conditions before they come into contact with the air, it cannot be 

 doubted that they suffer decomposition into carbon and hydrogen in 

 the luminous portion of the flame. It is of little importance whether 

 the eliminated carbon is chemically pure, or whether it contains still a 

 hydrogen compound ; the important question is this, Is the soot held 

 by the flame in the shape of vapor or in the solid form ? If the soot 

 was nothing but a conglomeration of the densest light-giving hydro- 

 carbons, whose vapors condense on a cool body, then, when sufiiciently 

 highly heated by exclusion of air, it ought to reassume vapor-form. 

 This is, however, not the case, as every one will find who tries the ex- 

 periment. 



Its chemical composition is just as little favorable to Frankland's 

 view. It ought, presumedly, to vary according to the lighting mate- 

 rial from which it was derived nay, even according to the place of 



