WORK UNDER PRESSURE AND IN GREAT HEAT 381 



was at surface ; and at whatever depth he may be his minimum 

 air supply must be increased in proportion to the increase in 

 the absolute air pressure. In other words, the minimum volume 

 of air supplied to him, measured at the pressure he is under, 

 must always remain the same. 



To cut a long story short, we found that as soon as this 

 condition was realised, as proved by numerous analyses of air 

 from the helmet, the discomfort and loss of working power 

 in deep water disappeared. Lieutenant Damant and Gunner 

 Catto, the two officers who carried out most of the experiments 

 in deep water, and who reached the greatest depth hitherto 

 definitely recorded, were as free from respiratory distress at 

 64 metres (210 ft.) as at 1 metre. They could also reach this 

 depth easily within two minutes, which showed the extra- 

 ordinary fallacy in the time-honoured tradition that a diver 

 should always descend slowly, so as to accustom himself by 

 degrees to the change of pressure. 



By guarding against excessive increase of C0 2 pressure in 

 the air breathed by a diver, we not only increase greatly his 

 working efficiency and comfort, but also obviate a serious 

 danger. It not infrequently happens that a diver, particularly if 

 he is somewhat unskilled, becomes unconscious or stupefied by 

 the effects of C0 2 . The consequences of this may easily be 

 fatal, as it is very dangerous to draw a man up rapidly from 

 a great depth if he has been down for any time ; and also 

 dangerous to leave an unconscious man on the bottom. 



In connection with the effects of C0 2 in a diver's helmet, I 

 should like to say something as to the presence of C0 2 and 

 other impurities in the air of mines. It is well known that 

 an excess of C0 2 and corresponding deficiency of oxygen is 

 commonly met with in the air of mines, and that certain kinds 

 of mining work are very unhealthy — particularly the mining of 

 some of the more valuable metals, such as gold, tin, silver, 

 copper, and lead. On account of the high death-rate and large 

 amount of illness among the tin-miners of Cornwall in England, 

 I was asked in 1902 by the British Government to investigate the 

 ventilation of the mines there. It was known from the results 

 of an earlier inquiry, 1 confirmed by my own analyses, that it is 

 easy enough to find many working places in these mines where 

 the proportion of C0 2 rises to as much as 50 volumes per 

 1 Report of the Royal Commission on Metalliferous Mines, 1864. 



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