by Chemical Action. 105 



exterioi* stratum oxygen is in excess, at the interior the com- 

 bustible vapour, and between these limits there must be an 

 admixture of the two, which differs at different depths. Ad- 

 mitting the results of the foregoing experiments with anthra- 

 cite coal and charcoal to be true, viz. that as combustion is 

 more active rays of a higher degree of refrangibility are 

 evolved, it follows that each point of the supetjicies of eve7\y 

 Jlame, no matter what the combustible may be, must yield all the 

 colours of the spectrum, the violet coming from the outer strata, 

 the yellow from the intermediate, and the red from those 

 within. If we could isolate an elementary horizontal section 

 of a flame, it should exhibit the appearance of a rainbow-ring ; 

 and when those compound rays are received on the face of a 

 prism, the constituent colours are parted out, by reason of 

 their different refrangibility, and the eye thus made sensible 

 of their actual existence. 



When thus, by the aid of a prism, we analyse the light that 

 comes from any portion of the superficies of a flame, we in 

 effect dissect out in a convenient manner, and arrange together 

 side by side, rays that have come from different strata of the 

 burning shell. These, without the prism, would have pursued 

 the same normal path, and produced a commixed effect on 

 the eye, but with it are separated transversely, and each be- 

 comes perceptible. 



It might be supposed that, in the familiar instance of an 

 oil-lamp, if we put any check on the supply of the air and 

 thereby check the intensity of combustion, we ought to have 

 the flame emitting rays of light, the refrangibility of which 

 becomes less anil less, and which, from their being quite white, 

 should pass through different shades of orange, and end in a 

 dull red. But the compound nature of the burning vapour 

 interferes with that result ; for when a certain point is gained, 

 the hydrogen for the most part alone burns, the carbon being 

 set free as smoke, and such a flame cannot support itself in 

 strict accordance with the principle given. 



We must then search for other conditions under which car- 

 bon is found which are free from this difficulty. Two at once 

 present themselves; they are carbonic oxide and cyanogen 

 gas. In the former the carbon is already united with half the 

 quantity of oxygen recjuired for maximum oxidation, its com- 

 plete combustion can therefore be carried on with a limited 

 supply of atmospheric air; in the latter the carbon is united 

 witli nitrogen, whicii during combustion is set free, and inter- 

 feres with the process by cutting off' the more complete access 

 ol" the atmosphere. 



In place of the burning coal of tlie former experiments I 



