ANALYSES OF AIR FROM COAL MINES. 59 



This report gives in a tabular form, the effects on man and 

 on naked lights of varying proportions of these ingredients, from 

 which we take a few figures to shew the difference in behaviour 

 of carbonic acid and black damp. Carbonic acid in air affects the 

 breathing when it is mixed with air in the proportion of 3 5 per 

 cent, carbonic acid and 96 - 5 per cent, air, but it does not extinguish 

 flame until 15 per cent, carbonic acid is reached, at which point 

 initial loss of consciousness occurs. Black damp on the other 

 hand extinguishes flame when 16 per cent, is present, but this 

 atmosphere has no effect on the breathing which is not affected 

 until nearly twice the quantity of blac£ damp is present. If we 

 put down the exact composition of these mixtures, the reason of 

 this rather peculiar characteristic will be plain. 



A mixture of air containing 3*5% C0 2 has the composition: — 



Effects on man. Effects on light. 



Oxygen 20-17 

 (A.) Nitrogen 76-33 affects breathing no effect 



CO, 3-50 



100-00 



A mixture of air containg 16% black damp has the comprsition: 



Effects on man. Effects on light. 



Oxygen 17*56 

 (B.) Nitrogen 80-36 no effect extinguished 



C0 3 2-08 



100-00 



The breathing is affected in (A.) because of the presence of 3*5 

 per cent. C0 2 which has no influence on the light. The light is 

 extinguished in (B.) because the oxygen has diminished to 17*5. 



It is, therefore, clear that if the contamination is due only to 

 diminished oxygen or to the presence of black damp, a man can 

 breathe the air so contaminated at a point far beyond that at 

 which a candle is extinguished. 



