204 Chemical Examination of the Fire-Damp. 



The analysis of fire-damp was performed by detonation with 

 oxygen gas over mercury. In successful analysis with all the 

 gases, the diminution in volume subsequent on detonation with 

 the electric spark, and due to gaseous matter condensed as water, 

 was precisely twice the volume of carbonic acid gas which was 

 generated, and equal to the oxygen gas which disappeared. The 

 volume of carbonic acid gas sometimes fell short of half the dim- 

 inution due to production of water, but this only took place when 

 the combustion was incomplete. Sometimes the gaseous mixture, 

 after detonation, was more or less obscured by a deposit of carbon- 

 aceous matter, and in such instances, as already remarked by Dr. 

 Henry, there is always a deficiency of carbonic acid gas, which 

 deficiency is less considerable the more completely the mixture 

 at the moment of detonation approximates to perfect transparency. 



I have occasionally observed this cloud, even when ample oxygen 

 for complete combustion was present ; but with a decided excess 

 of oxygen it generally does not occur at all, or at most in so slight 

 a degree as not to be appreciable. To show the course of the 

 inquiry, I quote three analyses, in the first of which an error, from 

 deposited carbon, is apparent. 



I. Analysis of fire-damp from Jarroiv Colliej^y, which issued 

 from a seam of coal eleven fathoms below the Bensham seam. 



Specific gravity as found by weighing the gas = 0-6209. Tes- 

 ted by nitrous gas it was found in one experiment to contain 2-25 

 per cent, of oxygen, and in a second 2;1 per cent., indicating as a 

 mean 2-2 per cent, of oxygen, equivalent to 11 per cent, of air. 

 This gas, which was quite free from carbonic acid gas, may be 

 considered as a mixture of 89 measures of real marsh gas with 



II measures of air. A gas so constituted, and assuming 0-5595 

 as the specific gravity of marsh gas, should have a specific gravi- 

 ty 0-6079; for 0-5595-f 0-89+0-ll = 0-6079. Of this gas 12-3 

 measures, containing 0-3 of oxygen and 11 of real marsh gas, 

 were fired with 32-7 measures of a sample of oxygen gas, which 

 contained 31 of real oxygen gas: — 



Loss due to condensed water .... =22.3 



Carbonic acid gas generated and absorbed by potassa =9-4 

 Risidual oxygen, determined by firing with hydrogen 



gas . .' =10-5 



Deducting 10 -5 -|- 9. 4, the oxygen above accounted 



for, from 31-3, the whole oxygen gas originally 



