96 Prof. F. Clowes. Application of Safety-lamp [Mar. 31, 



tanks in petrolenm-canying steamers, in petroleum stores, and in 

 chambers in which processes are carried on which involve the use of 

 light petroleum oil. 



The suggestion naturally occurs, that the safety-lamps used in these 

 places should be applied to ascertain whether the amount of inflam- 

 mable vapour present in the air is sufficient to give rise to danger if 

 it should come into contact with a naked flame ; in other words, to 

 ascertain if the space is efficiently ventilated. Experiments were 

 accordingly undertaken to discover whether benzoline vapour would 

 give rise to a " cap " over the flame of the safety-lamp, and if a " cap " 

 appeared, to discover how small a proportion of the vapour could be 

 detected in air by this flame-cap test. Since the hydrogen flame in 

 the safety-lamp, and the benzoline flame in Ashworth's modified 

 lamp, had been found to be most convenient for the formation of 

 visible " caps," these lamps were employed in the experiments; and 

 the test-chamber above described was employed for exposing the 

 lamps to mixtures in varying proportions of benzoline vapour with 

 air. 



Since benzoline is a mixture of liquids, and is therefore not of 

 invariable chemical composition, no attempt was made to ascertain 

 the actual percentage of the vapour present in the air. The per- 

 centages of vapour, even if known and identical in amount, would 

 probably have different effects when derived from different samples 

 of benzoline, or even when derived from the same samples under 

 different conditions. Accordingly an approximate determination only 

 was made of the amount of further dilution with air, which an ex- 

 plosive or inflammable mixture might undergo, before the " cap " it 

 produced over the safety-lamp flame ceased to be easily visible. 



A large gas-holder was filled with air which had bubbled through 

 benzoline, and was thus charged with the vapour at the ordinary tem- 

 perature, in the same way as air w r ould be charged with the vapour from 

 the evaporation of stored benzoline. This mixture was inflammable 

 when kindled in the open air. Varying proportions of this mixture 

 with additional air were then prepared, and the effect was ascertained 

 of introducing a flame into them. It was found that a mixture of 1 

 volume of the benzolised air with 4 volumes of air was violently 

 explosive. When the proportion of air was increased from 4 to 7 

 volumes' the mixture was still inflammable, and when the air was 

 increased to 9 volumes the mixture ceased to be inflammable. 

 Mixtures of the same benzolised air were then made in the test- 

 chamber (pp. 87 — 90) with still larger proportions of air, and the 

 appearance of the safety-lamp flames was examined in these mix- 

 tures, with the following results : — - 



