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XX. On a new Instrument for the Detection and Measurement 

 of Inflammable Gas in Mines. By E. H. Liveing, Assoc. 

 R.S.M* 



[Plate II.] 



THE instruments hitherto contrived for the detection of gas 

 in mines may be divided under two heads: — 1st, those which 

 depend for their action on the Physical properties of the gaseous 

 mixture ; 2nd, those dependent on its Chemical or com- 

 bustible properties. 



Under the former head we have the instruments of Mr. 

 Ansell and Prof. Forbes — the one depending on the diffusion 

 of gases, and the other on the velocity of sound ; while under 

 the latter head we have the ordinary flame test, the instrument of 

 M. Coquillion, and, lastly, my own instrument. Strong argu- 

 ments can be urged to show the superiority of the latter class 

 of tests over those of the former type ; for it is the heating- 

 value of the gaseous mixture, or its approach towards the ex- 

 plosive proportion, that we really want to know. 



It is quite possible to alter the physical properties of a 

 gaseous mixture to a very large extent while its combustible 

 properties remain scarcely changed. Thus the presence of 6 per 

 cent, of marsh-gas in atmospheric air is sufficient to render it 

 explosive in an upward direction, and there may be present in 

 the mixture amounts of C0 2 from 1 up to 15 per cent, without 

 preventing the mixture being explosive. 



Atmospheric air containing 8 per cent. CH 4 + 8 per cent. 

 C0 2 is highly explosive ; and yet both the instruments above 

 mentioned as dependent on the physical properties would in- 

 dicate such a mixture as perfectly harmless, indeed would fail 

 to detect the presence of any combustible gas whatever. 



There are other drawbacks to these instruments, but I will 

 not occupy your time by detailing them. On turning to 

 the other class we have, first, the flame test. This has, of course, 

 been the practical every-day test employed in collieries for a 

 century or more past, and was applied at a considerable risk 

 before the introduction of the safety lamp, and since that time 

 with comparative security. 



The tail or cap observable upon a flame when brought into 

 an atmosphere contaminated with combustible gas is nothing 

 more than a region where the weak mixture of gas and air 

 receives sufficient auxilliary heat to sustain its ignition-tem- 

 perature, or, in other words, to burn. It is then a direct 

 combustion test, and therefore on the right principle. There 



* Communicated by the Physical Society, having been read June 26th, 

 1880. 



