412 ME WILLIAM SWAN ON THE PRISMATIC SPECTRA OF THE 



On the Nature of Flame. 



We owe to Hooke, probably the first careful inquiry into the constitution of 

 flame. More recently, the subject has been studied by Sir Humphry Davy and 

 Professor Draper.* 



The flame of coal gas or of a common candle, as is well known, consists of 

 several portions, readily distinguishable by the eye, and in which the matter 

 composing the flame exists in very different conditions. There is, first, the inte- 

 rior non-luminous portion, composed of gases not yet ignited ; secondly, a blue 

 conoidal shell, near the wick or burner, which, as it extends upwards, seems gra- 

 dually to change its colour to a brilliant yellowish white ; and, thirdly, an outer 

 mantle or envelope of faintly luminous matter. On a careful examination, it 

 will be found that the blue cone envelopes the white one ; the blue, gradually 

 thinning out towards the top, and the white, towards the bottom of the flame. 



It has been supposed that, in the blue portion of the flame, the supply of oxy- 

 gen is sufficient to insure the complete combustion of the gases, so that, in a 

 carbohydrogen flame, there is the immediate production of water and carbonic 

 acid, j The bright white light of the upper portions of the flame was proved by 

 Sir Humphry Davy to proceed from the separation of solid carbon, which becomes 

 brilliantly incandescent at the high temperature to which it is exposed, and 

 which, when not converted into carbonic acid, escapes in the form of smoke. 



The external mantle of the flame, according to Professor Draper, derives its 

 light chiefly from incandescent carbonic acid and aqueous vapour. 



While in the ordinary flames of coal gas and oil, solid carbon is separated, it 

 is well known that by burning a mixture of gas and air, the separation of carbon 

 may be entirely prevented, and a smokeless flame obtained. My attention was at 

 first accidentally directed to the subject of this paper while using a species of 

 gas lamp in which this object is effected in a very simple manner. As this 

 lamp — the invention of Professor Bunsen of Heidelberg— has only lately been 

 introduced! into this country, and as I have made extensive use of it in my ex- 

 periments, it may be proper to explain its construction. 



It consists of a common "union" or "bat-wing 1 ' gas burner, which, when 

 used in the ordinary manner, would produce a flat, fan shaped flame. The 

 burner is surrounded by a brass tube, - 4 inch in diameter, and about 3 inches in 

 height, having apertures immediately below the burner, which can be opened or 

 closed, so as to admit a regulated supply of air. The gas issuing from the burner 

 in a fan shape strikes obliquely the walls of the tube, and being reflected from 



* Works of Sir H. Davy, vol. vi., Lond. 1840. Draper on the Production of Light by Chemical 

 Action, Lond. Phil. Mag., 1848, vol. xxxii., p. 100. 



\ Kane's Chemistry, p. 289. . 



J By Dr Robert Ferguson, whose interesting account of the lamp will, I believe, appear in the 

 Transactions of the Roval Scottish Societv of Aits. 



