8 Vie late Dr. Turner's Chemical Examination of the 



trous gas indicated the presence of 9 per cent, of air ; whereas 

 philinuin detected only 5 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 freely mixed 

 with air, then after the hydrogen gas platinum acted freely ; 

 and I have found under such circumstances the indications 

 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 indicated 

 O-'t per cent, of oxygen, equivalent to 46*5 of air; and in two 

 experiments with nitrous gas precisely the same result was ob- 

 tained. A ball of platinum may hence be applied to deter- 

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

 first diluting the gas with a known quantity of air, or enliven- 

 ing the action of the platinum by adding some explosive mix- 

 ture. 



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, sulphuretted hydrogen, and si- 

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

 To myself they do not leave the shadow of a doubt on the 

 (luestion. Those who are not familiar with such researches, 

 may be warned that, in repeating my experiments, they will 

 certainly fail of witnessing the same phgenomena, unless they 

 are very scrupulous in having pure gases, and in employ- 

 ing platinum balls with their full energy. The influence of 

 platinum on gases is modified by such very slight circum- 

 stances, that a small matter will cause a ball to be wholly inert 

 which would otherwise have acted with effect. 



In applying nitrous gas to determine the quantity of oxygen 

 in fire-damp, I employed the method of Dr. Dalton, as de- 

 scribed in Dr. Henry's Elements of Chemistry. A measured 

 quantity of fire-damp was added to the nitrous gas contained 

 in a graduated tube half an inch wide, and the gases were al- 

 lowed to act on each other over water, without agitation. The 

 diminution of volume had attained its maximum in five or six 

 minutes, and in general much sooner. Of the total loss, ^yths 

 were taken as oxygen. This method is not in all cases rigidly 

 correct, but its indications were sufficiently exact for my pur- 

 pose, controlled as they were by the action of platinum, by the 

 analysis of the gas by detonation with oxygen, and by the 

 specific gravity of the gases. Before relying at all on this 

 method, however, I ajiplied it in the analysis of gaseous mix- 

 lures containing known quantities of oxygen gas. On ap- 



