130 Detection and Measurement of Inflammable Gas in Mines. 



considered, cannot fail to be of assistance in laying out and 

 regulating the ventilation of extensive collieries. There is, 

 however, another and perhaps more urgent requirement which 

 I hope a slight modification of this instrument may also be 

 able to meet. 



There exist many gassy collieries where safety lamps are 

 aloi?e employed, and yet where the hardness of the coal 

 necessitates the use of powder in order that it may be worked 

 at a profit. Now in such workings, before each shot is fired, 

 it is necessary for the sake of safety (and enforced by the 

 Coal-Mines Regulation Act) that the working-place and its 

 neighbourhood should be carefully tested for gas. This is of 

 course done at present by aid of the lamp, and, it is to be 

 feared, too often without that degree of care and deliberation 

 by which alone the test can be considered efficacious. Be this 

 as it may, all are agreed that some more striking and definite 

 test would be of great value for this purpose, if it could be 

 practically introduced. 



For this object I propose a slight modification of the in- 

 strument described, in which the screen is fixed at some definite 

 percentage, such as 2 per cent., the one side being marked G, 

 the other A ; the directions for use being that so long as the 

 side A of the screen is the brightest the shot may be fired, but 

 if G- become equal to or brighter than A the shot should not 

 be fired. 



For this purpose the instrument and machine would be best 

 made in one piece, and would have to be constructed as strongly, 

 simply, and cheaply as possible, with an easy means of re- 

 placing the platinum spirals, should they be melted through 

 carelessness. 



I may add that the chief difficulty about the introduction 

 of the instrument is to find a sufficiently compact and portable 

 source of the necessary electrical current that can be made at 

 a moderate price. 



There is yet one other possible application of the instrument 

 — namely, for the examination of the heating-value of the waste 

 gases from blast-furnaces, where it is of importance to regu- 

 late the conditions of burning so as to reduce the carbonic 

 oxide in the waste gases to a minimum. Of course the sample 

 of waste gas would have to be mixed with some definite quan- 

 tity of air, to supply oxygen, before examination. 



Explanation of Plate II. 



R and S are two strong brass plates that form the terminals of the elec- 

 trical machine and at the same time act as supports for the instrument. 

 D and E are wooden plugs with copper wires carrying the platinum 



