In light the inverted gas burner is very little superior to oil, but it is whiter, slightly more concentrated, and freer from smell, and therefore to be regarded as preferable if a supply of gas is available.
Methylated Spirit Burners.—Incandescent mantles heated by methylated spirit are also largely used, and provide a light decidedly superior to gas and nearly equal to acetylene. Some arrangement must be made for volatilising the spirit and driving the vapour out under pressure, and the most usual contrivance is somewhat as illustrated in Fig. 3.
In this apparatus the spirit is contained in a metal reservoir at the rear and air pressure is provided by a pair of rubber balls and valves after the manner of a medical spray. Sufficient
pressure having been obtained, the liquid spirit is forced into a vaporising chamber immediately behind the mantle, and a kind of miniature pitchfork, with its prongs wrapped in asbestos wool, is soaked in spirit, and pushed over the brass fitting of the burner in such a way that when lighted the flame heats the chamber and volatilises the spirit. The burner can now be lit, and although the fork burns out in the course of a minute or so, the heat from the mantle itself is thereafter sufficient to vaporise the spirit as rapidly as required. This lamp works exceedingly well in practice, but has one drawback, viz. that it is possible to obtain too much pressure and squirt liquid spirit through the burner, when it naturally catches fire and may even run on to the floor.
An accident of this sort is rare and usually harmless even if it does occur, but an audience is easily frightened, and hence this burner should only be used by an operator with experience. An altogether better arrangement is that made by Messrs. Hughes of Kingsland and known as the 'Luna' Lamp (Fig. 4).
In this burner there is no pump and no volatilising chamber;
the spirit is contained as before in a metal reservoir and a separate burner underneath is used to keep this sufficiently hot to both vaporise the spirit and provide the necessary pressure. The heat can be regulated by means of an adjustable sheath to the burner, and a simple safety valve provides against an excess of vapour.
I do not say that an accident of the sort previously referred to is impossible even with this burner, but I have never heard of it happening, and the lamp is certainly the best apparatus of its kind that I am acquainted with.