bi) Chemical Action. 101 



the light emitted by flames is due to electric discharges; 

 others, regarding h'ght and heat as material bodies, which can 

 be incorporated or united with ponderable substances, suppose 

 that they are disengaged as chemical changes go on. In this 

 confusion of opinions, a niultitude of interesting and hitherto 

 unanswered questions present themselves. It is known that 

 different substances when burning emit lights of different co- 

 lours : thus sulphur and carbonic oxide burn blue, wax yellow, 

 and cyanogen HIac. What are the chemical conditions that 

 determine these singular differences? How is it that, by 

 changing the circumstances of combustion, we can vary the 

 nature of the light? We turn aside the flame of a candle by 

 means of a blowpipe, and a neat blue cone appears; why does 

 it shine with a blue light? 



Such inquiries might be multiplied without end ; but a little 

 consideration shows that their various answers depend on the 

 determination of a much more general problem ; viz. can any 

 connexion be traced bel-iSoeen the chemical conditions imder which 

 a body burns, and the nature of the light it emits? It is to the 

 discussion of that problem that this memoir is devoted. 



Sir H. Davy has already furnished us with two important 

 circumstances in relation to the nature of flame : — 1st. All 

 common flames are incandescent shells, the interior of which 

 is dark ; 2nd, the relative quantity of light emitted depends 

 on the temporary disengagement of solid particles. 



It is only by a very general examination of the light arising 

 from various solids, vapours and gases, when burning, that 

 we can expect to obtain d^ta for a true theory of combustion. 

 This is what I shall endeavour to furnish on the present oc- 

 casion. 



As was foreseen by all the older chemists, the true theory 

 of combustion, whatever it may prove to be, must necessarily 

 be one of the fundamental theories of chemistry. It must in- 

 clude the nature of all chemical changes whatsoever. The sub- 

 ject is therefore not alone interesting in a popular sense, but 

 of great importance in its scientific connexions. 



I. Prismatic analysis of the jlames of various vapours and 

 gases ; jJfovifig that they yield all the colours of the spectrum, 



I commenced this investigation of the nature of flame, and 

 of combustion generally, by an optical examination of various 

 bodies in the act of burning. Some authors have asserted 

 that certain flan<cs yield monochromatic lights. It is necessary 

 to verily this assertion if true, or set it aside if false. 



The instrumental arrangement which I have employed is as 

 follows : — Tlie rays of the flame, of which the examination is to 



