( 178 ) 



Liquid air has striking advantages above liquid oxygen when 

 we have to store large quantities or when with the gas liquefied in 

 the cryogenic laboratory we must cool instruments in other rooms. 

 Only where constant temperatures are aimed at pure oxygen or 

 nitrogen will be preferred for refrigerating purposes, and even then 

 the liquid air can be the intermediate agent, for we need only lead 

 the gases mentioned through a cooling tube immersed in liquid air in 

 order to liquefy nearly as much of it as the quantity of air evaporated 

 amounts to. And so the permanent stock of liquid air maintained 

 in the Physical Laboratory has gradually increased, so that for several 

 years liquid air has been immediately sent off on application both 

 at home and abroad. 



§ 2. The airliquef actor . The apparatus for the preparation of liquid 

 air by means of liquid oxygen is in principle identical with that 

 serving for nitrogen, but of larger dimensions (see PI. VI). 



Identical letters designate corresponding parts of the apparatus 

 represented (Comm. N°. 83, PL VII) for the liquefaction of nitrogen. 

 To liquefy air the ordinary atmospheric air, after being freed by a 

 solution of sodium hydroxide from carbon dioxide, is compressed to 10 

 atmospheres in the spiral RgRf, PI- VI tig. 1. This spiral branches 

 off from the tube Rq^^ in the soldered piece Rg^^ and carries four 

 branches Rg^, Rg^, Rg^ and Rg^. Each of these tubes has an internal 

 diameter of 3.5 mm., an external diameter of 5.8 mm., and is 22 M. 

 long. The spiral is wound in 63 layers in the same way as the regenerator 

 spiral of the hydrogen liquefactor (comp. X )and, lined with flannel, it fits 

 the new-silver tube p^, round which it is drawn in the new silver case p. 

 The four windings are united below to one soldered piece to the 

 spiral Rf, 8 M. long, w^hich is immersed in a bath of liquid oxygen 

 and whence the liquid air flows through Rf\ into the collecting 

 apparatus (see fig. 2). This is placed by the side of the principal 

 apparatus (see fig. 2) and contains the collecting vessel ?•„, where 

 the liquid air is separated and whence it is drawn through the 

 siphon. The collecting glass is fitted with a float dr. During work 

 we can see it rising regularly at a fairly rapid rate. 



§ 3. Further improvements. The regenerative cascade might still 

 be modified in many points before the principle is fully realized and 

 before one improvement or other, made for one of the cycles, has been 

 introduced also in the others and the efficiency is grown to a maximum ; 

 but this problem is rather of a technical nature. We prefer (o spend 

 the time at our disposal on other problems, as enough liquid air is 



