��DEVELOPMENT OF HEAT.
��CHAP.
��where a strong current circulating between two carbon poles, A and B (Fig. 54), is so influenced by an electromagnet, jB, fixed perpendicularly to the plane in which A and B lie, that a pointed, highly deflected arc, £, is formed. The point of this arc is directed against the substance S, which is con- tained in the fire-proof furnace U. This principle has been used by Lejeune and Ducretet in the furnace constructed by them (Fig. 55). In this furnace any gas may be introduced
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��Fig. 54.
��Fia. 55.
��through the side tube R] it is provided on two sides with mica windows, so that the process taking place inside may be observed. The crucible is filled through the opening 0, which can be closed by the plug P. The crucible U, con- taining the reaction mixture, can be moved up or down by means of the screw V, The arc formed between A and B is directed by the aid of an electromagnet placed outside.
Moissan's furnace (/-J) differs from the one just described, inasmuch as the carbon electrodes are placed horizontally, and the charge can be introduced through a slightly bent carbon tube, which is fixed on the side of the furnace, whose walls are made of lime.
Zerener's electrical blowpipe was originally constructed for soldering and welding, but in recent times it, as well as
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