1893.] 



A New Portable Miner s Safety-lamp. 



493 



however, were adjusted in the presence of the "gas" which was 

 being estimated. 



Results of Flame-cap Measurements in Air containing Methane 

 (Firedamp) . 



The gas used for these experiments was prepared by the usual 

 chemical method, which consists in strongly heating an intimate 

 mixture of dried sodium acetate with caustic soda and slaked lime. 

 This product cannot claim to consist of pure methane, but, judging 

 by the constant results which it yielded in the test- chamber, the gas 

 must at least have been of fairly constant composition. 



The lamp-flames used were of the following dimensions, some of 

 which are approximate only. They are drawn to size in fig. 4, the 

 dimensions being shown in millimetres and in inches : 



The 10-mm. hydrogen flame was adjusted to its height in gas-free 

 air; it remained unaltered in height until 3 per cent, of gas was 

 reached, when its height increased by from 2 to 3 mm. 



The 15-mm. and 5-mm. hydrogen flames were adjusted to height in 

 the presence of the gas. 



The Pieler, the benzoline, and the blue oil- flame were each of them 

 adjusted in gas-free air. The faintly luminous oil-flame was adjusted 

 in the air containing gas, the bright flame being gradually reduced 

 until the cap was seen to be of the largest possible dimensions. 



The following are the corrected cap-measurements expressed in 

 millimetres, obtained with the flames of the specified heights ; the 

 caps are graphically represented in millimetres and in inches in figs. 

 5, 6, 7, 8. In these drawings the increase in dimensions of the testing 

 flames, as the percentage of gas rises, is not shown. All the flames, 

 with the exception of the Pieler alcohol flame, were tested in the 

 Ashworth lamp. 



