New forms of instruments for showing the presence and amount of combustible gas in the air . ular gas. Again referring the results to hydrogen, therelative deflections caused by the explosive mixtures were asfollows: Relative de-flectioncaused byexplosivemixture Hydrogen 100 Gasoline 139 Ether .146 Benzene 132 Acetone 133 Carbon monoxide 100 These results, while not of great accuracy, show that the indica-tion given by the explosive mixture of a gas in air is of the same orderof magnitude whatever the gas may be. Weaver!Weibel J Combustible Gas Detectors3. GLOWING-WIRE INDICATOR 77 The tempera
New forms of instruments for showing the presence and amount of combustible gas in the air . ular gas. Again referring the results to hydrogen, therelative deflections caused by the explosive mixtures were asfollows: Relative de-flectioncaused byexplosivemixture Hydrogen 100 Gasoline 139 Ether .146 Benzene 132 Acetone 133 Carbon monoxide 100 These results, while not of great accuracy, show that the indica-tion given by the explosive mixture of a gas in air is of the same orderof magnitude whatever the gas may be. Weaver!Weibel J Combustible Gas Detectors3. GLOWING-WIRE INDICATOR 77 The temperature at which a platinum wire shows a visible glow,while depending somewhat upon the conditions of observation,can be judged quite accurately under any ordinary conditions ofillumination. Six observations were made upon a 31 cm lengthof wire C by the following method: The wire was stretched hori-zontally in an ordinarily well-lighted room, but in a position inwhich the light from the windows did not fall directly upon was then heated by a current which was slowly increased until *t. 1 < Z UJO zoo /* /S /f. 3 4 S 6 7 8 7 /O // 72 73 RESISTANCE R SHUNTING ACTIVE WIRE (OHMS) Fig. 15.—Diagram of connections and curve showing performance of glowing-wire indi-cator the reflected light was no longer noticed in comparison with theradiated light. The resistance was then measured and the tem-perature calculated, with the following results for the six obser-vations: 6750, 6840, 6840, 68o°, 688°, 6900 C. The precisionwith which the temperature at the first visible glow can be deter-mined is thus evident. It has been shown by Lummer and Kurlbaum6 that, at this tem-perature a change of 1 per cent in the absolute temperaturecauses a change of about 30 per cent in the light emitted. Takingdata from Figs. 4, 7, and 10, it is found that at this temperature1 per cent change in current causes a change of about per cent 6 Verh. d. Deutsch, Phy s. Ges., II, p. 89; 1900. 78 Bulletin
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