1893.] A New Portable Miners Safety-lamp. 485 



have been introduced with the object of enabling percentages of gas 

 as low as 0'5, and even as 0'25, to be determined. The lower propor- 

 tion, 0'25 per cent., is considered to be low enough for all practical 

 purposes. 



Of these apparatus, the following are considered to effect their 

 purpose satisfactorily: E. H. Liveing's electrical indicator ('Physical 

 Soc. Proc.,' June, 1880) : Fr. Pieler's alcohol-lamp, described in a 

 pamphlet ('Ueber einfachen Methoden zur Uiitersuchung der Gru- 

 benwetter,' Aachen, 1883) : and an apparatus brought forward by 

 Coquillon and by others, which depends upon measuring the reduc- 

 tion of pressure produced in a confined volume of the mine-air when 

 the firedamp is burnt out of it, this being effected by maintaining 

 the air in contact with a metallic wire rendered incandescent by an 

 electric current. 



Apart from general considerations of convenience and of safety 

 when these apparatus are in use in the mine, a serious objection to 

 each of them is that it is by no means small or light, and that it 

 must be carried together with an ordinary safety-lamp, since it does 

 not itself serve for illuminating the darkness of the mine. 



The Liveing apparatus has recently been proved by James Grundy, 

 working with my test- chamber, to give very accurate readings of 

 "gas" varying in percentage from Oil to 2*2; but he found the 

 platinum wire exposed to the gas to be subject to changes when in 

 use, which make the apparatus difficult to maintain in working order 

 and which sometimes render it useless. 



There seems to be a general disposition amongst all classes in- 

 terested in mining to improve, if possible, the flame-cap test, rather 

 than to resort to other methods for securing accuracy and delicacy in 

 gas-testing. This object was in some measure attained by MM. Mal- 

 lard and Le Chatelier in 1881 (' Annales des Mines,' 7th Ser., vol. 19, 

 p. 186), by suitably screening the reduced oil flame of the safety- 

 lamp, and then viewing its tip against a black background of cloth 

 or of blackened metal sheet. It is stated that a slight indication was 

 obtained by this means when the percentage of gas present was as 

 low as 0*5. The lamp, however, suffered a loss of illuminating power 

 when its flame was turned up, owing to the obstruction of the screens. 

 The indications of the lower percentages were also confessedly ex- 

 tremely slight and feeble ; they are further rendered uncertain by the 

 fact that an oil-flame itself gives a feeble cap-like mantle. Still the 

 improved lamp has the advantage of being at once an illuminator 

 and also a gas-tester of greater delicacy than the lamps in ordinary 

 use. 



The inventors of this improved oil-lamp state that they consider 

 the hydrogen flame to be superior to any other for gas-testing. They 

 ascertained that this flame would detect 0*25 per cent, of gas ; but 



2 K 2 



