Decreased Pressure 991 



To be completely safe it is necessary only to breathe an air 

 whose oxygen content rises proportionately as the pressure falls; 

 so that the oxygen tension may always remain the same, or at 

 least always be equal to, if not higher than, that which exists in 

 the air at normal pressure. In balloon ascensions, nothing is 

 simpler to carry out, since space is not wanting. 



Therefore there should be fastened to the ring of the balloon 

 two bags of goldbeater's skin, one of which, filled with a mixture 

 containing 70% of oxygen, will serve for heights from 5000 to 7000 



35 

 meters: oxygen tension at 6000 meters = 70 x — = about 32. The 



76 



other, as pure as possible (95% in practice), will serve for the 

 greater heights: at 9000 meters, the oxygen tension of the mixture 



24 

 will be about 95 x — = 30, that is, it will be double that of ordinary 

 76 



air at 2700 meters. The size of the bags should be calculated to 

 provide 10 liters per man and per minute of stay in dangerous 

 regions; so, in the fatal and glorious voyage of the Zenith, to avoid 

 all danger and gain advantage from the whole ascent, they should 

 have taken 1300 liters of the first mixture and 1800 liters of the 

 second, 23 that is, about 3 cubic meters in bags of a 9 meter capacity, 

 because of the extreme expansion of the gas at these heights. But 

 this quantity, I must say, would have been absolutely the maximum. 

 1 cannot recommend too strongly that at 5000 or 6000 meters a 

 direct and compulsory connection be made between the oxygen 

 bags and the mouths of the aeronauts, by means of a mouthpiece 

 like those of the Galibert or Denayrouze apparatuses. If such a 

 precaution had been taken for the Zenith, there would have been 

 no disaster to deplore; simply recall the touching account of M. G. 

 Tissandier: "I wanted to seize the oxygen tube, but I could not 

 raise my arm." If he had had the tube in his mouth, they would 

 all have been saved! 



2. Mountain travellers. 



The conditions in which mountain travellers are placed differ 

 from those of aeronauts in two important points: A. the muscular 

 efforts required by the act of ascent; B. the relative slowness of 

 the ascent and the duration of the stay in lofty places. 



