124 Prof. F. Clowes, An Apparatus for [June 18, 



sectior? of the chamber, and suspended by an axis from t-he upper 

 corner of the chamber. The mixer was moved rapidly backwards and 

 forwards from the side to the top of the interior of the chamber, by 

 grasping a handle projecting through the front of the chamber. 



When a mixture of air with a certain definite percentage of fire- 

 damp was required, the methane, prepared and purified by ordinary 

 chemical methods, was introduced into the chamber in the requisite 

 quantity by the top inlet. It displaced an equal volume of air, which 

 escaped through the lower outlet, the exit end of 'which was sealed by 

 being' immersed just beneath a water surface. A vigorous use of the 

 mixer secured a uniform mixture of gas and air throughout the interior 

 of the chamber in the course of a few seconds. The lamp was then 

 introduced into the chamber, and placed in position behind the glass 

 window. The simplicity of arrangement of the water-seal rendered 

 the necessary opening of the chamber very brief, and the introductioa 

 and removal of the lamp many times in succession was not found to 

 produce any appreciable effect upon the composition of the atmosphere 

 inside the chamber. The appearance and dimensions of the " cap " 

 over the flame were noted as soon as the cap underwent no further 

 change. A lamp was left burning in the chamber for a considerable 

 length of time, and its indications underwent no change, owing to the 

 large capacity of the chamber and the very limited amount of air 

 required to support the combustion of the small tiame always used in 

 gas-testing. The whole interior of the chamber and mixer were 

 painted dead-black, so as to render visible pale and small caps against 

 a black ground. 



The methane was introduced from an ordinary gas-holder. A 

 volume of water, equal to that of the methane to be displaced, was 

 poured into the top of the gas-holder. The gas-tap of the holder was 

 then momentarily opened, so as to produce equilibrium of pressure 

 between the methane and the atmosphere. The gas-tap having then 

 been placed in connexion with the upper inlet of the chamber, the 

 water-tap was opened, and the measured volume of water was allowed 

 to flow down and drive the methane into the chamber. As soon as 

 bubbles of air ceased to appear through the water at the outlet, the 

 chamber was closed ; the mixer was then vigorously worked for a few 

 seconds, and the mixture of gas and air was ready for the introduction 

 of the lamp. Before introducing the methane for a fresh mixture, the 

 atmosphere of the chamber was replaced by fresh air by removing the 

 water- tray from beneath the opening at the bottom of the chamber, 

 and blowing in a powerful stream of air from a bellows to the top of 

 the chamber. 



The chamber was supported on legs, which were arranged so as to 

 place it at a convenient height for observations through the window, 

 and also for the introduction and removal of the safety-lamp. 



