1895.] Nature and Physiological Action of Black-damp. 255 



The undiluted black- damp had thus the following composition and 

 specific gravity : 



No. 1. No. 2. 



Nitrogen 87'87 86'48 



Carbonic acid.. 12'13 13'52 



Total., 100-00 100-00 



Specific gravity T0390 T0468 



This composition supports the view that black-damp is the 

 residual gas left on slow oxidation of the carbon and hydrogen 

 of coal by air. Supposing that the black-damp were produced by 

 the oxidation of the carbon and hydrogen which would, under 

 other conditions, be given off as methane, it would consist of 88*30 

 per cent, of nitrogen and 11'70 per cent, of carbonic acid. This com- 

 position very closely approximates to that actually found in the first 

 specimen. The second specimen shows a larger proportion of 

 carbonic acid, and corresponds to the oxidation of material contain- 

 ing about 3 atoms of hydrogen to one of carbon. It must be borne 

 in mind, however, that the coal may itself supply part of the oxygen 

 required for the formation of carbonic acid and water in the oxida- 

 tion process. 



The physiological action of black- damp such as that examined is 

 due partly to its deficiency in oxygen, and partly to its carbonic acid. 

 When mixed in increasing proportions with air, its action, as shown 

 above, first becomes sensible when the oxygen is diminished to about 

 15 per cent, and the carbonic acid increased to about 3'5 per cent. 

 From the observations previously made by Hermans, and by Lorrain 

 Smith and myself,* it follows that the hyperpncea which began to 

 be produced at this point was due to excess of carbonic acid, and not to 

 deficiency of oxygen. Until the carbonic acid is increased to about 

 7 per cent, the same inference holds good ; the effect on the respiration 

 is almost the same as that of air or oxygen containing 7 per cent, of 

 carbonic acid ; and the breathing of such air for some time is 

 attended with no immediate risks to normal persons. When, how- 

 ever, the air is still further vitiated the deficiency in oxygen begins 

 to tell dangerously ; and when the oxygen is reduced to about 7 per 

 cent, there is imminent risk of loss of sensation and power over the 

 limbs. The danger-point from deficiency of oxygen (about 7 per 

 cent.) is sooner reached in the case of a mixture of black-damp and 

 air than the danger-point from excess of carbonic acid. The presence 

 of the carbonic acid in black-damp would seem in reality to diminish 

 the risk, since, by causing panting, it gives some warning of the 



* " The physiological effects of Air vitiated by Kespiration," ' Journal of Patho- 

 logy and Bacteriology,' Oct., 1892. 



