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48 THE ADVANCE OF PHOTOGRAPHY
surpassed by the effect of the lime, the magnesium, the incandescent gas and electric lights. The magnesium light is very simply produced by the burning of magnesium wire.
Magnesium is a metal which forms the chief component part of magnesia. Magnesia is nothing but magnesium rust — that is, a combination of magnesium with oxygen.
If magnesium wire or ribbon is burned, it combines with the oxygen of the air, producing a brilliant light and forming the oxide of magnesium. This light is very convenient in its application.
Magnesium in some form or other, very often as a powder, is so often used now for flash-light scenes that a large number of simple appliances are on the market by means of which the risk and dirt caused by the use of this substance as an illuminator are reduced to a minimum.
When the ribbon is used, it is often burnt by a lamp supplied with a clockwork arrangement, by means of which a continuous supply of ribbon is forthcoming at a constant rate. The powder form is much more effective as a light producer, since combustion takes place with much greater rapidity. When used in this form it is a very common practice to blow a certain definite quantity of the powder into a flame. Various kinds of lamps have been devised for this purpose, in some of which gas, and in others methylated spirit, is used. The powder is, of course, blown into the flame by means of some form of bellows, such, for example, as a pneumatic bulb.
Great care should be taken that the whole of the powder used is ignited. To ensure this the force of the air blast must be such that it carries the whole of the powder into the flame, but none of the powder should be projected beyond the flame.
In the early days of photography Dr Vogel repeatedly employed magnesium wire with success in taking photographs of the sculptures in the sepulchral monuments of