1891.] testing the Sensitiveness of Safety-law ps. 125 



The accuracy of this method was tested by introducing the Pieler 

 lamp into the chamber, which was charged successively with a series 

 of mixtures containing proportions of methane varying from 0'5 to 

 4 per cent. The height and appearance of the cap over the flame 

 absolutely corresponded with a series of standard tests already pub- 

 lished, and made by a different method, in which firedamp was used 

 instead of methane. 



The observations were usually made in a darkened room, but the 

 flame-caps were easily seen in a lighted room, provided direct light 

 falling on the eye or chamber was avoided. 



The capacity of the chamber was 95,220 c.c. ; accordingly the follow- 

 ing volumes of methane were introduced : for ^ per cent, mixture 

 476 c.c., for 1 per cent. 952 c.c., for 2 per cent. 1904 c.c., for 3 per- 

 cent. 2856 c.c., for 4 per cent. 3808 c.c., and for 5 per cent. 4760 c.c. 

 It will be seen that a series of tests, in which the above-mentioned 

 percentage mixtures were employed, involves an expenditure of only 

 15 litres of methane, a quantity far smaller than that required by any 

 other method of testing as yet described. 



Of many forms of safety-lamp tested in the above apparatus, the 

 one which most satisfactorily fulfilled the two purposes of efficient 

 illumination and delicacy in gas-testing was Ashworth's improved 

 Hepplewhite-Gray lamp. This lamp is of special construction, burns 

 benzoline from a sponge reservoir, and its flame is surrounded with a 

 glass cylinder, which is ground rough at the hinder part ; this latter 

 device prevents the numerous reflected images of the flame, and the 

 generally diffused reflections which are seen from a smooth glass 

 surface, and which render the observation of a small pale flame-cap 

 very difficult, if not impossible. 



The wick of this lamp, when at a normal height, furnishes a 

 flame of great illuminating power. When lowered by a fine screw 

 adjustment the flame becomes blue and non-luminous, and does 

 not interfere therefore" with the easy observation of a pale cap. 

 The following heights of flame-cap were observed, which fully bear 

 out the unusual sensitiveness of this flame. With 0'5 per cent, 

 of methane 7 mm. ; with 1 per cent. 10 mm. ; with 2 per cent. 

 14 mm. ; with 3 per cent. 20 mm. ; with 4 per cent. 25 mm. ; and 

 with 5 per cent. 30 mm. The cap, which with the lower proportions 

 was somewhat ill-defined, became remarkably sharp and definite 

 when 3 per cent, and upwards of methane was present. But even 

 the lowest percentage gave a cap easily seen by an inexperienced 

 observer. 



It appears from the above record of tests that the problem of pro- 

 ducing a lamp which shall serve both for efficient illuminating and 

 for delicate gas-testing purposes has been solved. The solution is in 

 some measure due to the substitution of benzoline for oil, since the 



