11)19] on Liquid Oxygen in Warfare 503 



tliiii stream. When this was moved slowly across the gap it was at 

 first bent out of the vertical, and finally was all attracted to one pole 

 of the magnet, to which it adhered in a bul)bling' mass."' 



8. The spheroidal state of the liquid was shown by the mobility 

 of drops of liquid air falling on the surface of some tetrachloride of 

 carbon. These darted about, enveloped in their cushions of va])our 

 — comet-like clouds of condensed tetrachloride. This was in striking 

 contrast to their behaviour when scattered on sulphuric acid, on 

 which they scarcely moved, but left small frozen areas floating about 

 as the drops rapidly evaporated. Another example was provided by 

 a faintly glowing piece of charcoal thrown on the surface of some 

 liquid oxygen. The slow combustion of the charcoal at once increased 

 to brilliant incandescence as it rushed al)out on the continuously 

 renewed cushion of oxygen gas. 



4. The application of liquid oxygen for explosive purposes was 

 illustrated by soaking a wad of cotton in liquid air and applying a 

 light to it. It instantly burnt with a brilliant flash like guncotton. 

 Finely divided organic matter mixed with liquid oxygen can be 

 used for blasting, when packed into a rock boring, and detonated 

 by an electric discharge. It has the advantage of retaining its 

 explosive properties only for a short time, with consequent absence of 

 danger from any unexploded charge. 



.5. The high vacuum produced by charcoal in liquid air was 

 exemplified in the mercury- vapour-radiometer first shown in lOOT.f 

 The radiometer was provided with a drop of mercury in a side tube 

 and with a gram of charcoal in the bulb below. With the charcoal 

 and mercury both cooled in liquid air, no activity could be induced, 

 even with a condensed arc beam focussed on tlie vanes, showing that 

 the pressure had been reduced to below 5^^Jth of a millionth of an 

 atmosphere. AVhen the vapour pressure of the mercury was increased 

 to this value by allowing its temperature to rise to - 20° C.,the vanes 

 started rotating. 



APPLICATION FOR PURPOSES OF RESPIRATIOX. 



An important war-time application of liquid oxygen was to supply 

 oxygen gas for airmen at high altitudes and also for treatment of 

 " gassed " cases in trench or hospital. For this purpose the liquid 

 was volatilised from some form of vacuum container by regulated 

 influx of heat, whence the gas was conveyed by tubes to mouth-pieces 

 for breathing. Apparatus of this kind was found in German aero- 

 planes brought down when raiding London. This method has the 

 advantage over that of carrying the necessary oxygen compressed in 



* Proc. Roy. Inst., xiii. 698. 

 t Proc. Roy. Inst., xviii. 755. 



