from the Coal Mines near Newcastle. 387 



disappeared. The volume of carbonic acid gas sometimes fell short of half 

 the diminution 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 carbonaceous 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 per- 

 fect 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 enquiry, I 

 quote three analyses, in the first of which an error, from deposited carbon, 

 is apparent. 



/. Analysis of fire-damp from Jarroiv Colliery, which issued from a seam 

 of coal, 11 fathoms below the Bensham Seam. 



Specific gravity, as found by weighing the gas, ... = 0*6209 

 Tested by nitrous gas it was found in one experiment to contain 2*25 per 

 cent, of oxygen, and in a second 2 - l per cent., indicating as a mean 2 - 2 per 

 cent, of oxygen, equivalent to 11 percent, 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 11 measures of air. A gas so constitu- 

 ted, and assuming - 5595 as the specific gravity of marsh gas, should have 

 a specific gravity 0-6079, for 0-5595+0-89 + 011=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 

 Residual oxygen, determined by filing with hydro- 

 gen gas, = 10*5 



Deducting 10 - 5+9"4, the oxygen above accounted 

 for, from 31*3, the whole oxygen gas ori- 

 ginally present there remain as — 

 Oxygen gas, which went to the production of water, = 11*4 



