1893.] 



on Liquid Atmospheric Air. 



11 



As the nitrogen boils 10° C. lower than oxygen, after a time the 

 liquid alters its composition and boiling point, finally becoming 

 pure oxygen. During the evaporation the liquid air changes very 

 remarkably in colour, passing from a very faint blue to a much 

 deeper shade. The changes can be traced best by the marked 

 increase in the width of the absorption bands of liquid oxygen. If 

 air, collected in the above manner in a vacuum vessel, is isolated 

 from a rapid heat supply by immersing the vessel in liquid oxygen, 

 and then a powerful air-pump brought to act upon it, after a time it 

 passes into the condition of a clear, transparent, solid ice. Nitrogen 

 solidifies, under such conditions, into a white mass of crystals, 

 but all attempts to solidify oxygen by its own evaporation have 

 failed. Such liquids as air and oxygen, we should anticipate, 

 would be especially transparent to heat radiation, seeing they are 

 very diathermic substances in their gaseous state. The thermal 

 transparency of liquid oxygen can be shown by passing the radiation 

 from the electric arc, as shown in the diagram, through a spherical 



Fig. 9. 



vacuum vessel filled with clear filtered liquid, thereby concentrating 

 the rays at a focus and igniting a piece of black paper held there. 



In this experiment the oxygen lens has a temperature of — 180° C, 

 yet it does not prevent the concentrated radiation reaching a red heat 

 at the focus. At such low temperatures as boiling oxygen and air 

 all chemical action ceases. If some liquid oxygen is cooled to 

 — 200° C, and a glowing piece of wood inserted into the vessel 

 above the liquid, it refuses to burst into flame, because of the 

 low pressure of the vapour. An interesting experiment may be made 

 by immersing an electric pile, composed of carbon and sodium, into 

 liquid oxygen, when almost immediately the electric current ceases. 

 The gaseous oxygen coming from the liquid must be exceedingly 

 pure and dry, and as it has been alleged two chemical substances 

 require the presence of a third one in order that they may combine, 

 it was interesting to ascertain if a substance like sulphur would 

 continue to burn after ignition in such an atmosphere. Sulphur 

 placed in a small platinum vessel that had just been heated to 

 redness, was raised to the boiling point, and in the act of combustion 

 lowered into a vacuum vessel containing liquid oxygen. The com- 



