INCANDESCENT GAS.
The incandescent gas light may be suc cessfully employed for portraiture, for which purpose a" sufficient number of burners are fixed in rows within a large white reflector. Suitable fittings are ob tainable, or can readily be made with a certain amount of contrivance. The light ing is satisfactory as regards softness and modelling, but a considerable amount renders it well adapted for photographic purposes. It is generally employed in the form of powder, either forced rapidly through a stationary flame by means of a sudden and strong artificial draught, or incorporated with certain rapidly igniting chemicals, such as chlorite of potassium, so that the mixture will burn instantane ously on the application of a light. Such compounds are, however, hardly suitable for use in a lamp, on account of the risk of explosion, hut should be burned in the open. Spreading the magnesium powder on gun-cotton is a satisfactory method of ignition, but requires extreme caution it is better in such a case to fire it by means of electricity, and to keep it at a safe distance. Magnesium produces a certain
amount of dense white smoke during com bustion, and this has sometimes been found inconvenient. The objection may, however, be overcome by means of ade quate ventilation, or by trapping the lens of large aperture should he used, and focussing may be clone by the aid of a paraffin lamp or gas burner held near the face, or even by means of a candle held level with the latter. Care should be taken to shade the lens from the direct light of the magnesium by means of a screen or a cloth thrown over parallel rods attached to the sides of the camera. The most rapid plates should be ern- ' ployed, preferably backed. The "War wick-Brookes " flashlight apparatus has an electric ignition, and gives an instan taneous flash the moment the switch is .
smoke in a box immediately after each exposure. There are several patterns of lamps in the market which make provision for removing the smoke difficulty, and there are also various patent flash mix tures which are guaranteed smokeless.