1892.] Flame to Detection and Measurement of Fire-damp. 91 



lamp glass at the back, a distinct flame cap, 7 mm. in height, was 

 seen in air containing only 0*5 per cent, of methane or fire-damp. The 

 height, density, and definition of the cap over this flame were found 

 to increa se pretty regularly as the percentage of " gas " in the air was 

 augmented. The efficiency of this lamp for lighting and testing is 

 thus placed beyond doubt. 



In continuing the experiments described in the former paper, how- 

 ever, a comparison of the " caps " produced by the flame of this lamp 

 with those produced by a small alcohol flame and a small hydrogen 

 flame showed that the latter flames were more sensitive as gas indi- 

 cators than that of the benzoline lamp. Thus, when an alcohol and 

 hydrogen flame, each 10 mm. in height, were introduced, together 

 with the small blue benzoline flame, into the testing chamber, which 

 was filled with air containing 1 per cent, of coal gas, flame caps of the 

 following dimensions were obtained : — 



Hydrogen 27 mm. 



Alcohol 19 „ 



Benzoline 7*2 „ 



It is true that the benzoline flame employed in this experiment was 

 much smaller than the two other competing flames. But it must be 

 remembered that the benzoline flame is necessarily small when it is 

 employed for gas-testing, since, if its dimensions are increased, it 

 becomes luminous, and renders the pale " cap " invisible. And one 

 of the principal advantages of the alcohol and hydrogen flames con- 

 sists in their remaining non-luminous, even when they are made of 

 large dimensions ; the greater surface and higher temperature of 

 their larger flames producing, therefore, much larger and more visible 

 " caps " than is possible with a small benzoline flame. 



It will be seen from the results of the experiment just described 

 that the hydrogen flame has the advantage over the alcohol flame in 

 the dimensions of the " cap " which it yields. But by prolonging the 

 test, another advantage of the hydrogen flame over its rival was 

 ascertained. The two flames were allowed to burn side by side in the 

 chamber, charged with air containing 1 per cent, of coal gas, for over 

 thirty minutes. Throughout this protracted test both the hydrogen 

 flame and the " cap " above it remained unaltered in size and ap- 

 pearance. The alcohol flame and its " cap," however, steadily 

 diminished in size : after five minutes the height of the cap had fallen 

 from 19 mm. to 12*5 mm., and after another interval of five minutes 

 the height of the cap was reduced to 6' 5 mm. : and thirty minutes 

 after the beginning of the experiment the flame was spontaneously 

 extinguished. This result seems to indicate that the alcohol flame 

 is much more sensitive to the influence of the presence of products 

 of combustion, and to deficiency of oxygen, than the hydrogen flame 



