638 EVENING DISCOURSES. 



by the pressure in atmospheres — in each case was 5'4 per cent, of an atmosphere. 

 This holds good also down to about two-thirds' of an atmosphere in analyses 

 taken at high altitudes. At lower atmospheric pressures than this oxygen want 

 comes in, with the production of lactic acid in the tissues and blood, as a dis- 

 turbing factor. It is clear, then, that the effect of a given percentage of CO, in 

 the diver's helmet varies with the depth. If air containing 5 per cent. C0 2 pro- 

 duces great panting at 1 atmosphere, air containing — =0-68 per cent, will 



produce the same degree of panting at 35 fathoms (7'4 atmospheres). It follows 

 from this that whatever the pressure a diver is under, he requires the same volume 

 of air measured at that pressure to ensure the ventilation of his helmet. At 2 

 atmospheres the ventilation must be doubled, at 3 atmospheres trebled, at 6 

 atmospheres increased six-fold. Under the old conditions of working, often with 

 leaky pumps and tired men to pump, the ventilation has been acutally less, not six 

 times greater as it ought to be, at a depth of 165 feet. 



With a pressure of 2 per cent, of CO, in the inspired air the pulmonary 

 rentilation is increased about 50 per cent. ; with 3 per cent, about 100 per cent. ; 

 'ith 4 per cent, about 200 per cent. ; with 5 per cent, about 300 per cent, j and with 

 j per cent, about 500 per cent. If the diver is working hard the extra produc- 

 tion of C0 2 will make him pant, and this coupled with the effect of the excess in 

 the helmet" which often reaches 3 to 4 per cent., makes breathing distressing 

 and the feeling of oppression intense. Thus at a depth of 139 feet with a CO, 

 pressure of 4-28 per cent, of an atmosphere, Lieutenant Damant was unable to 

 continue for more than 8 minutes the exertion of lifting a weight of 56 lb. about 

 9 feet per minute. The Admiralty Committee found that the divers could con- 

 tinue work for long periods at depths of even 210 feet so long as the C0 2 pres- 

 sure was kept below 3 per cent, of an atmosphere- 



To keep the CO, down to this level a diver ought to have at least 1-5 cubic 

 feet of air per minute when working, and he must, have this volume of air pass 

 through the helmet at whatever pressure he be at. Each cylinder of the regu- 

 lation service pump ought to yield T x 5 cubic feet per revolution. Assuming an 

 unavoidable leakage of the pumps ot 10 per cent, at 100 feet and 24 per cent, 

 at 200 feet, the Admiralty Committee ordered for 33 feet (depth) one cylinder, 

 thirty revolutions per minute, and two men per spell, the work being estimated 

 at 4,440 foot-lb. per minute ; while for 165 feet depth four cylinders, twenty- 

 seven revolutions, and twelve men are required — the work being 34,000 foot-lb. 

 per minute; for 198 feet (depth) six cylinders, twenty-three revolutions, eighteen 

 men, the work being 43,000 foot-lb. per minute. Provision ought to be made to 

 give' a third more than this supply if the diver gets into difficulties. 



At 210 feet thirty -six men were working very hard in alternate 5-minute spells 

 of rest and work, and were scarcely able to keep up the proper air-supply. Long 

 handles were supplied to allow three men on each side of the pump. 



To avoid this excessive labour. R. H. Davis (of Siebe, Gorman & Co.) and 

 I have added to the diving dress this metal box containing trays of caustic soda. 

 A mouthpiece is placed within the helmet, and a tube leads from this through 

 the soda-box and back to -the helmet. The diver when oppressed in the slightest 

 degree can take hold of the mouthpiece with his lips, and breathe through the 

 caustic soda, and so lessen the concentration of CO,. There is no risk of his 

 suffering from want of oxygen so long as the pumps give him a moderate supply 

 of air. This device ought to save a great deal of hard pumping work. 



The Self-contained Diving Dress. 

 We have also contrived a self-contained diving dress fitted with cylinders 

 containing compressed air enriched with oxygen (to 50 per cent.), and a caustic- 

 soda chamber. The oxygen supply is delivered to the helmet by a reducing valve 

 in constant supply (5 litres per minute), and the force of the oxygen stream is 

 used, by means of an injector, to suck the air in the helmet through the 

 caustic-soda chamber. No life-line or air-pipe is carried, only a light telephone, 

 cable, and this makes the dress suitable for exploration of flooded mines, tunnels, 

 ships, &ot, through which the heavy pipes and lines cannot be dragged. Air 

 containing 50 per cent, oxygen is used in place of oxygen (Haldane), so that 

 there is no risk of oxygen poisoning if used for an hour at depths of 70 to 80 feet, 

 or even 100 feet, for half an hour. 



