386 THE POPULAR SCIENCE MONTHLY 



explosions in coal mines is that proposed by J. Harger, viz., to ven- 

 tilate them with air containing 17 per cent, of oxygen. 2 There is little 

 doubt that all the great mine-explosions have been caused by the en- 

 forcement of a high degree of chemical purity of the air. In the old 

 days when ventilation was bad there were no great dust explosions. 

 Mr. W. H. Chambers, general manager of the Cadeby mine, where the 

 recent disastrous explosion occurred, with the authority of his great 

 and long practical experience of fiery mines, told me that the spon- 

 taneous combustion of coal and the danger of explosion can be wholly 

 met by adequate diminution in ventilation. The fires can be choked 

 out while the miners can still breathe and work. The Coal Mines 

 Eegulation Act enforces that a place shall not be in a fit state for 

 working or passing therein, if the air contains either less than 19 per 

 cent, of oxygen, or more than 1^ per cent, of carbon dioxide. A mine 

 liable to spontaneous combustion of coal may be exempted from this 

 regulation by order of the Secretary of State. 



The regulations impel the provision of such a ventilation current 

 that the percentage of oxygen is sufficient for the spread of dust 

 explosions along the intake airways, with the disastrous results so 

 frequently recorded. If the mine were ventilated with air containing 

 17 per cent, of oxygen in sufficient volume to keep the miners cool 

 and fresh, not only would explosions be prevented, but the mines could 

 be safely worked and illuminated with electricity, and miners' nystag- 

 mus prevented, for this is due to the dim light of the safety lamp. 

 The problem possibly may be solved by purifying and cooling the 

 return air, and mixing and circulating this with a sufficiency of 

 fresh air. 



Owing to the fact that the percentage of C0 2 is the usual test of 

 ventilation and that only a very few parts per 10,000 in excess of fresh 

 air are permitted by the English Factory Acts, it is generally supposed 

 that C0 2 is a poison and that any considerable excess has a deleterious 

 effect on the human body. No supposition could be further from 

 the truth. 



The percentage of C0 2 in the worst ventilated room does not rise 

 above 0.5 per cent., or at the outside 1 per cent. It is impossible that 

 any excess of C0 2 should enter into our bodies when we breathe such 

 air, for whatever the percentage of C0 2 in the atmosphere may be, 

 that in the pulmonary air is kept constant at about 5 to 6 per cent, of 

 an atmosphere — by the action of the respiratory center. It is the con- 

 centration of C0 2 which rules the respiratory center, and to such pur- 

 pose as to keep the concentration both in the lungs and in the blood 

 uniform (Haldane) ; the only result from breathing air containing 

 0.5 to 1 per cent, of C0 2 is an inappreciable increase in the ventila- 



2 Trans. Inst, of Mining Engineers, 1912. 



