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XVII. On an Electric-light Fire-damp Indicator. 

 By Walter Emmott and William Ackroyd. * 



THE Royal Commission on Accidents in Mines point out, 

 in their recently issued Report, a serious objection to 

 the use of the electric light in mines, notwithstanding its 

 many other great advantages, in that the light of an incan- 

 descent lamp being produced within a vacuum cannot admit 

 of any device for the indication of fire-damp such as is 

 employed in the Davy for example. This difficulty was 



Fig. 1. 



experienced by one of us in the course of an installation of 

 the electric light in the Lofthouse pit, Wyke, Yorks, in the 

 summer of 1885 ; and we have since made a series of experi- 

 ments with the object of devising a method of making the 

 electric light an indicator of fire-damp. The apparatus 

 placed before the Physical Society is the outcome of our 

 work. It consists of two incandescent lamps, one with 

 white glass and the other with red, and other necessary 

 adjuncts, such that in an ordinary atmosphere the white 

 incandescent lamp alone shines, but in fire-damp the white 

 lamp goes out and the red one begins to emit its light. 

 This is effected as follows : — A porous pot of unglazed hard- 

 baked porcelain is joined by air-tight connections to a tube 

 a portion of which is represented by TT 1 , fig. 2. This tube is 

 of such an internal diameter that it will readily admit of 

 being sealed with a small quantity of mercury, H<7. A 

 platinum wire runs the whole length of the tube and is 

 * Communicated by the Physical Society : read June 12, 1886. 

 Phil. Mag. S. 5. Vol. 22. No. 135. August 1886. L 



