412 MR 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 Humpury 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.+ The bright white light of the upper portions of the flame was proved by 
Sir Humpury 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” gas burner, which, when 
used in the ordinary manner, would produce a flat, fan shaped flame. The 
burner is surrounded by a brass tube, 0:4 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. 
£ By Dr Rozerr Fercuson, whose interesting account of ine lamp will, I believe, appear in the 
Hifansdetions of the Royal Scottish Society of Arts. 
