the Theory of Luminous Flames. 3()7 



capable of producing the former action ; and experiment shows 

 that they can also produce the latter*. 



Coal-gas issuing from a rather narrow horizontal tube was 

 ignited ; the flame was separated by a space of 1 or 2 centims. 

 from the orifice of the tube. A tube from which chlorine 

 issued was introduced between the burner and the flame : the 

 luminosity of the latter was at once increased ; and the flame at 

 the same time extended itself backwards to the point at which 

 the chlorine entered. The volume of the flame-mantle was 

 thus increased at the expense of the blue zone of the flame. 



If bromine be employed in place of chlorine, a sooty flame 

 is produced ; this is to be traced to the formation of a gaseous 

 compound of bromine and carbon, and consequent partial cut- 

 ting off of the supply of oxygen. 



Before deducing a wide generalization, it seemed to me ne- 

 cessary to inquire whether in every case introduction of chlo- 

 rine brought about the result theoretically foretold. 



The flame of a hydrocarbon may become feebly luminous 

 (1) when the flame-mantle contains a small number of solid 

 carbon particles. This condition is fulfilled in the flame of all 

 substances relatively poor in carbon — for instance, in the flame 

 of ordinary coal-gas. Such flames are rendered more lumi- 

 nous by addition of chlorine or bromine either before or after 

 the gas is ignited. If chlorine be added before ignition, a 

 partial combustion takes place in the innermost portions of 

 the flame ; part of the hydrogen unites with the chlorine, wdiile 

 carbon is set free in solid form and renders luminous the hy- 

 drochloric-acid flame within the main flame. Combustion of 

 carbon, and of the hydrogen which is uncombined with chlo- 

 rine proceeds at the outer part of the flame ; inasmuch, how- 

 ever, as the outer portions are comparatively poor in hydrogen 

 but rich in carbon, it follows that an increase in luminosity 

 must take place at these points also. 



If chlorine be conducted into the centre of a somewhat large 

 coal-gas flame, tw r o flames are easily distinguishable. If chlo- 

 rine be mixed with the outer atmosphere in which combustion 

 is taking place, it partially replaces not only the inert nitrogen, 

 but also the oxygen, combining at the same time with hydro- 

 gen, but not at all, or only to a very limited extent, with 

 carbon. The latter is therefore partially deposited as soot. 



Gases containing little carbon may therefore be caused to 

 burn with a feebly luminous flame by mixing with them sub- 

 stances w^hich at a high temperature partially or completely 



* Berzelius showed that the flame of alcohol is rendered luminous by 

 the introduction of chlorine. See Gmelin-Kraut's ' Handbook/ i. pt. '2, 

 p. 13 ; 6th ed. 



