208 Chemical Exatninaiioii of the Fire- Damp. 



The action was equally rapid with the other gases ; nearly the 

 whole explosive mixture disappearing within the first or second 

 minute after the introduction of the platinum ball, whether 



In no instance did barytic water, subsequently 



warm 



admitted, detect in the residue a trace of carbonic acid gas. 



When to any specimen of fire-damp hydrogen was added, the 

 action of platinum always revealed the presence of air. When 

 the quantity of air was small, the action of platinum was of course 

 slow ; nor did it in that case indicate with fidelity the quantity of 

 air present, a portion of oxygen not uniting with hydrogen. 



om 



nitrous gas, indicated the presence of 6-2 per cent, of air, and pla- 

 tinum only 3-3 per cent. In the gas from the Bensham Seam, 

 Wallsend Colliery, nitrous gas indicated the presence of 9 per 

 cent, of air ; whereas platinum detected only five per cent, in one 

 trial, 8-5 per cent, in a second, and 6 per cent, in a third. A 

 certain degree of impediment to the action of platinum by marsh 

 gas is thus rendered apparent. But when the fire-damp was free- 

 ly mixed with air, then after the hydrogen gas platinum acted 

 fi'eely ; and I have found under such circumstances the indica- 

 tions from platinum to coincide with those from nitrous gas. 

 Thus in fire-damp from the low main coal seam, Killingworth 

 Colliery, of specific gravity 0-8226, platinum and hydrogen indi- 

 cated 9-4 per cent, of oxygen, equivalent to 46-5 of air; and in 

 two experimems with nitrous gas precisely the same result was 

 obtained. A ball of platinum may hence be applied to determine 

 the air in fire-damp, even when its quantity is small, by first dilu- 

 ting the gas with a known quantity of air, or enlivening the ac- 

 tion of the platinum by adding some explosive mixture. 



To those chemists who chance to be practically conversant 

 with the action of platinum on gaseous mixtures, the evidence 

 above adduced as to the freedom of fire-damp from hydrogen, 

 carbonic oxide, olefiant gas, sulpheretted hydrogen, and similar 

 inflammable gases, will, I doubt not, be quite satisfactory. To 

 myself they do not leave the shadow of a doubt on the question. 

 Those who are not familiar with such researches, may be warned 

 that, in repeating my experiments, they will certainly fail of wit- 

 nessing the same phenomena, unless they are very scrupulous in 

 having pure gases, and in employing platinum balls with their 



full energy. The influence of platinum on gases is modified by 



