1892.] On the Detection of Benzoline Vapour, fyc. 



95 



cent, of coal gas respectively : the height of the cap being noted in 

 each mixture when the hydrogen flame was first 10 mm., and then 

 15 mm., in height. 



Flame 10 mm. Flame 15 mm. 



1 per cent, gas .... 27 mm. cap 50 mm, cap. 



„ .... 23 ,, 38 „ 



Attention is directed in the above statement to the height of the 

 cap alone, but, as a matter of fact, its change in general appearance is 

 also very noticeable as the proportion of gas is increased. Yery care- 

 ful observation of the hydrogen flame in air free from gas serves to 

 detect a slender and very pale cap. When the gas in the air reaches 

 0*25 per cent, the cap becomes broader and pale grey in colour, but 

 is still indefinite in outline, especially at its summit, and is seen only 

 above the hydrogen flame. As the proportion of gas increases, the 

 flame becomes strikingly sharp and pointed in outline, distinctly 

 bluish-grey in colour, and gradually broadens and extends down the 

 sides of the hydrogen flame, finally enclosing it altogether and en- 

 circling the jet. At the same time, the hydrogen flame itself is con- 

 stantly growing in every dimension, gaining in luminosity and ac- 

 quiring a rose-red tip. It is well to have watched the above changes 

 in the test-chamber, and to have become familiar with the appearance 

 of the hydrogen flame in different percentages of gas before the flame 

 is used for gas- testing. 



The use of the hydrogen flame for gas-testing has the advantage of 

 rendering possible the employment of a non-luminous flame which 

 can be immediately adjusted to any convenient size : not only may the 

 size of the cap be thus increased at will by enlarging the flame, but 

 it is possible to avoid the risk of losing the flame in the lamp, which 

 is incurred by drawing down the wick very low when an oil flame is 

 made use of for gas-testing. 



III. " On the Application of the Safety-lamp to the Detection 

 of Benzoline Vapour and other Inflammable Vapours in 

 the Air." By Frank Clowes, D.Sc. (Lond.), Professor of 

 Chemistry, University College, Nottingham. Communicated 

 by Professor Armstrong, F.K.S. Received March 24, 

 1892. 



Since the vapour of benzoline and of petroleum spirit, when mixed 

 with air, may become dangerously explosive and inflammable, it is 

 found necessary to employ safety-lamps instead of naked lights to 

 illuminate spaces which may contain such a mixture. The safety- 

 lamp should accordingly be used in the neighbourhood of the oil 



