420 Prof. E. Frankland on the Combustion of Hydrogen [June 1 1, 



the presence of solid particles. Tn reference to gas- and candle-flames, it is 

 now well known that the fuliginous matter produced when a piece of wire- 

 gauze is depressed upon such flames, and the sooty deposit which coats a 

 piece of white porcelain placed in a similar position, are not pure carbon, 

 but contain hydrogen, which is only completely got rid of by prolonged 

 exposure to a white heat in an atmosphere of chlorine. On pursuing the 

 subject further, I found that there are many flames possessing a high 

 degree of luminosity which cannot possibly contain solid particles. Thus 

 the flame of metallic arsenic burning in oxygen emits a remarkably intense 

 white light; and as metallic arsenic volatilizes at 180° C, and its pro- 

 duct of combustion (arsenious anhydride) at 218° C, whilst the tempe- 

 rature of incandescence of solids is at least 500° C, it is obviously im- 

 possible here to assume the presence of ignited solid particles in the flame. 

 Again, if carbonic disulphide vapour be made to burn in oxygen, or oxygen 

 in carbonic disulphide vapour, an almost insupportably brilliant light is 

 the result. Now fuliginous matter is never present in any part of this 

 flame, and the boiling-point of sulphur (440° C.) is below the temperature 

 of incandescence, so that the assumption of solid particles in the flame is 

 here also inadmissible. If the last experiment be varied by the substitu- 

 tion of nitric oxide gas for oxygen, the result is still the same ; and the 

 dazzling light produced by the combustion of these compounds is also so 

 rich in the more refrangible rays, that it has been employed in taking instan- 

 taneous photographs, and for exhibiting the phenomena of fluorescence. 



Many other similar cases of the production of brilliant light from incan- 

 descent, gaseous, or vaporous matter might be cited ; but I will mention 

 only one other. Amongst the chemical reactions celebrated for the pro- 

 duction of dazzling light, there are few which surpass the active combustion 

 of phosphorus in oxygen. Now phosphoric anhydride, the product of 

 this combustion, is volatile at a red heat ; and it is therefore manifestly im- 

 possible that this substance should exist in the solid form at the tempera- 

 ture of the phosphorus-flame, which far transcends the melting-point of 

 platinum. For these reasons, and for others stated in the lectures above 

 quoted, I consider that incandescent particles of carbon are not the source 

 of light in gas- and candle-flames, but that the luminosity of these flames is 

 due to radiations from dense but transparent hydrocarbon vapours. As a 

 further generalization from the experiment above mentioned, I was led to 

 the conclusion that dense gases and vapours become luminous at much 

 lower temperatures than aeriform fluids of comparatively low specific 

 gravity, and that this result is to a great extent, if not altogether, inde- 

 pendent of the nature of the gas or vapour, inasmuch as I found that 

 gases of low density, which are not luminous at a given temperature when 

 burnt under common atmospheric pressure, become so when they are 

 simultaneously compressed. Thus mixtures of hydrogen and carbonic 

 oxide with oxygen emit but little light when they are burnt or exploded 

 in free air, but exhibit intense luminosity when exploded in closed glass 

 vessels, so as to prevent their expansion at the moment of combustion. 



