728 EKPOBT— 1893. 



in the long limb, starting in each case from the level of the horizontal tuhe. This 

 tube is filled with mercury up to the zero points, and indicates the rate of exhaus- 

 tion of the apparatus, and is also a test of leakage. 



The second tube a little further on points downwards for attachment to a 

 Geissler's water-pump. Still further on a stopcock is let into the main horizontal 

 tube, which then bends downwards for communication with a Sprengel pump. 



The apparatus is put into connection with both mercurial and water-pumps, 

 and the stopcock at the base of the cup is closed. By means of the water-pump the 

 apparatus is exhausted in a great measure of air ; five minutes' pumping with high- 

 pressure water produces a vacuum of 730 mm., when the barometer stands at 75.3. 

 The water-pump stopcock is then closed, and exhaustion is completed by the 

 Sprengel in about thirty minutes more. 



The liquid to be examined for gases is then, after measurement, introduced by 

 the cup into the upper flask, whence it flows into the lower one. 



The liquid is allowed to stand for an hour, so that gases disengaged at ordinary 

 temperatures may come oil'. These are collected by the Sprengel and analysed in 

 the usual way. 



The vacuum having been restored, heat is cautiously applied to the lower flask 

 by means of a Bunseii burner. If carefully done there is no bumping. The effect 

 of heat is, by disengaging gas, to increase tension, and to enable the water to 

 become hotter. The mercury in the mercurial tube and that in the thermometer 

 rise. AVhen the mercury in both places remains constant the Bunsen burner is 

 removed. 



The gas given off by boiling is then collected and analysed. 



A Discussion on Explosions in Coal Mines, with special reference to the 

 Bust Theory, was opened by Professor H. B. DixON, F.B.S. 



6. The A]jplication of the Hydrogen Flame in an Ordinary Miner's Safety 

 Lamp to Accurate and Delicate Gas Testing. By Professor Feank 

 Clowes, D.Sc. Land. 



The 'flame cap' or halo seen in the dark above a pale flame in air containing 

 combustible gas serves as the most rapid and practical means of detecting the 

 presence of inflammable gas or vapour in the air. The method has been in common 

 use by the miner, but the oil flame which he uses for the purpose is wanting, not 

 only in delicacy, but also in accuracy. It will not readily detect the presence of less 

 than 3 per cent, of fire-damp in the air, whereas for modern purposes it should detect 

 less than 0'5 per cent. ; and, owing to the variation in the size and adjustment of 

 this flame when applied to testing, its indications are very variable, and are not of 

 a standard character. Many objections exist to the employment of a separate 

 alcohol lamp carried for testing purposes. None of these applies to the use of the 

 hydrogen flame, especially when it is applied in an ordinary safety lamp burning 

 oil from a wick in the usual way. The hj'drogen flame is the most delicate indi- 

 cator known, and it is applied of uniform size, giving standard and invariable 

 indications. 



The author's early work consisted in measunng with accuracy the height and 

 noting the appearance of the flame cap appearing over the standard 10 mm. 

 ( = 0'4 inch) hydrogen flame. The flame was exposed for this purpose to air containing 

 known percentages of gas in the ' test chamber ' specially devised for the purpose. 

 The statement, previously made, that the hydrogen flame is the most delicate gas- 

 testing flame known was fully confirmed by comparing its indications with those 

 yielded by a small alcohol flame and by a reduced oil flame. The small alcohol 

 flame could not detect less than 1 per cent, of fire-damp, even under the most 

 favourable conditions ; the reduced oil flame could not detect with certainty less 

 than 3 per cent. 



The author then directed his attention to applying the hydrogen flame in a 



