FLAMES OF COMPOUNDS OF CARBON AND HYDROGEN. 413 



them, becomes effectually mixed with the air which enters at the bottom ; and the 

 mixture of gas and air, when lighted, burns at the top of the tube with a volu- 

 minous flame, without smoke. A thorough mingling of the gas and air is essential 

 to the success of the arrangement, which will be found to fail when a plain burner 

 is substituted for the " union jet" 



The flame of the Bunsen lamp consists of at least two distinct portions, — a 

 luminous hollow cone of a strong bluish green colour, about two inches in height, 

 and a very diffuse outer mantle, about 6 inches in height, reddish towards the 

 interior, but externally of a pale lavender tint. In this, also, as in the ordinary 

 flame of coal gas, but in much greater profusion, there is a perpetual scintillation 

 of yellow sparks, arising apparently from foreign matter suspended mechanically, 

 partly in the gas, and probably more abundantly in the air which enters the tube 

 and mingles with the gas before combustion. This matter is projected continually 

 through the walls of the flame, where it becomes for a moment incandescent.* 



The light of the exterior envelopes of flames, is, I conceive, chiefly due to the 

 presence of minute particles of solid matter, derived partly from the substance 

 undergoing combustion, and often, as in the case of the Bunsen lamp, from the 

 air which enters the flame. The outer envelope of the flame of the Bunsen lamp 

 possesses so little inherent luminosity, that it is peculiarly susceptible of having 

 its colour influenced by the accidental presence of foreign matter. As the salts 

 of sodium are well known to be remarkably energetic in producing homogeneous 

 yellow light, I made the following experiment, in order to ascertain how small a 

 portion of matter could in this way render its presence sensible. 



One-tenth of a grain of common salt, carefully weighed in a balance indicating 

 ygg of a grain, was dissolved in 5000 grains of distilled water. Two perfectly 

 similar slips of platinum foil were then carefully ignited by the Bunsen lamp, until 

 they nearly ceased to tinge the flame with yellow light ; for to obtain the total 

 absence of yellow light is apparently impossible. One of the slips was dipped into 

 the solution of salt, and the other into distilled water, the quantity of the solu- 

 tion of salt adhering to the slip, being considerably less than £o grain, and both 

 slips were held over the lamp until the water had evaporated. They were then 

 simultaneously introduced into opposite sides of the flame ; when the slip which 

 had been dipped into the solution of salt, invariably communicated to a consider- 

 able portion of the flame a bright yellow light, easily distinguishable from that 

 caused by the slip which had been dipped into pure water. It is thus proved, 

 that a portion of chloride of sodium, weighing less than 1 00 o, oo °f a grain is able 



* If the air be dusty from any cause, these scintillations become very abundant. Thus, i:' the 

 floor be swept, or a piece of charcoal be scraped with a knife at a little distance from the lamp, 

 minute particles are carried by the current of air into the tube, and cause a profusion of sparks, which 

 exhibit a very beautiful appearance, while they confirm the opinion that the ordinary sparks are oc- 

 casioned chiefly by particles of dust carried by the air. 



