498 



Prof. F. Clowes. 



[Feb. 2, 



(water- white) produces an apparent cap, which, though some- 

 what more intense than the natural mantle seen in gas-free 

 air, is only equal to this mantle in dimensions, and might 

 easily be mistaken for it. 



The oil flame, when it is reduced until it just loses its 

 luminous tip, however, gives distinct indications from 3 to 

 6 per cent. 



The largest indications are produced by drawing down the 

 flame in the presence of the gas, until a cap of maximum size is 

 obtained. 



A carefully regulated oil flame may, therefore, conveniently supple- 

 ment the hydrogen flame for the indication of gas varying from 3 to 

 6 per cent., and in the new hydrogen lamp this will be found to be a 

 convenient method to adopt. 



The use of colza alone in the oil-lamp is very inconvenient for gas- 

 testing : the wick quickly chars and hardens on the top, and the flame 

 cannot then be reduced without danger of extinction ; the flame can 

 never be obtained satisfactorily in a non-luminous condition. The 

 admixture with petroleum obviates these difficulties. 



Results of Flame-cap Measurements in Air containing Coal-gas. 



The miner's safety-lamp is frequently employed for purposes of 

 illumination in gas-works, and in other places in which the air may 

 be contaminated with coal-gas. It seems, therefore, only reasonable 

 to make the lamp also serve the purpose of detecting the percentage 

 of coal-gas present. The amount of gas thus found indicates whether 

 the air is in a dangerous condition. Careful measurements were 

 accordingly made of the flame-cap heights seen over the hydrogen 

 and oil flames of the safety-lamp, when it was placed in the test- 

 chamber with air containing a known admixture of Nottingham 

 coal-gas. 



The following measurements in millimetres were obtained. They 

 are represented graphically in millimetres and in inches in fig. 9, but 

 no attempt is made in these drawings to show the marked increase in 

 dimensions which the test-flame undergoes in the presence of the 

 higher percentages of gas : 



