1893.] A New Portable Miner's Safety-lamp. 489 



When " gas " is being tested for in the mine, the examination 

 would first be made in the usual way by carefully and gradually 

 drawing down the wick, watching continuously meanwhile through 

 the well- cleaned glass, with the dead-black smoked background 

 already described, whether at any stage a cap appears over the 

 flame. If a distinct cap within the limits of the glass should be 

 seen, the percentage of gas will be between 3 and 6 ; by noting the 

 height of the cap as judged against the standard 10-mm. wire, the 

 percentage of gas can be ascertained with very fair accuracy, as is 

 proved below. 



If no satisfactory cap can be seen over the reduced oil flame, and 

 small percentages of gas have to be looked for, the hydrogen cylinder 

 is attached to the lamp, the standard hydrogen flame is produced 

 within the lamp, and a cap is looked for over the flame. This standard 

 flame will readily indicate and measure percentages varying from 

 0*25 to 3: the caps being easily seen and readily measured by com- 

 paring their heights with that of the hydrogen flame or of the 

 standard wire. The cap corresponding to 0*25 of gas is very pale, 

 and is somewhat hazy and ill-defined at its edge ; the cap with 0'5 

 per cent, is somewhat more dense and well-defined ; but both these 

 caps are easily seen even by an inexperienced eye. 



The dimensions of the caps given by less than 1 per cent, of gas can 

 be much increased by turning up the hydrogen flame to 15 mm. (see 

 Hj HI, figs. 5, 6). Similarly, the cap indications of the standard 

 hydrogen flame, which exceed the height of the lamp-glass when 

 more than 3 per cent, of gas is present, can be brought within the 

 visible limits by reducing the flame, while in the presence of the gas, 

 to 5 mm. (see H 2 H 2 , figs. 5, 6). These higher percentages of gas 

 may in this way be estimated by means of the hydrogen flame, 

 instead of by the reduced oil flame. 



It has been occasionally noticed that, when the hydrogen flame is 

 allowed to burn for a long time within the lamp, the lower part of 

 the lamp-glass becomes cool, owing to the feeble radiative power of 

 the flame ; drops of water then condense upon the glass and interfere 

 with the accurate observation of the flame and of the cap. If this 

 should occur, it is only necessary to turn on the oil flame for a short 

 time; and this, by its superior lateral radiation, rapidly dissipates 

 the water. 



It will be readily understood that the main advantages resulting 

 from the use of the hydrogen flame are the following : 



1. The flame is non-luminous, whatever its dimensions may be, 



and therefore does not interfere with the perception of the 

 cap, and does not require to be screened from the eye. 



2. The flame can always be adjusted at once to standard height, and 



