509 



when phenomena have to be followed by the eye, the oryostat with 

 liquid neon is very mnch to preferred. 



It was gratefnllj mentioned before, when the attempts to arrange 

 a neon-cryostat were discussed for the first time (Comm. 112 June 

 1909), that the gas was very kindly put at our disposal by Mr. G. 

 Claude and the "Soeiété d'Air Liquide" in Paris. This gas was 

 I'ich in neon and from it the large quantity of pure neon which is 

 now in circnialion in (he laboratory has been separated (Comp. 

 Leiden Oomm. Suppl. 21A p. 40 — 41). It is there described, how 

 by a prelin)iiiary pui'ification of the crude gas hy mean.s of freezing 

 in liquid hydrogen, pnnqiiug off the helium and se|)aration of the 

 large quantity of nilrogen present, a gas was obtained almost totally 

 free from hydrogen and helium and piincipally only containing some 

 nitrogen. Continued fractionation further diminished the (piantity of 

 the admixtures and the ultimate pui'ification was conducted by 

 means of the neon cycle itself and the removal of the last traces of 

 oxygen and nitrogen by the aid of carbon cooled in Jiipiid air. 



2. Thi' ncon-liqv.efnctor and neon-cryostat. These are combined 

 into one i)iece of apparatus (see fig. 1 below). The liquefactor 

 somewhat resembles in its construction the apparatus for the |)uri- 

 fication of hydrogen fComm. Wdh March 1909). The cryostat is 

 constructed exactly as the heliiun-cryostal in its most recent form 

 (Comm. 123, June J 911). The connection between li(piefactor and 

 cryostat is essentially the same as that between the helium-liqne- 

 factor and the helium-cryostat of Leiden. Comm. Sup|)l. 21 fig. 5 

 (Oct. 1910). To facilitate a comparison with the helium-cryostat, 

 the parts of the neon-liquefactor in fig. 1 are marked with the same 

 letters as the conesponding parts of the helium-cryostat in the 

 Plate of Comm. 123. For parts of modified construction, but of 

 analogous purpose accented letteis have been used. 



The principle of the apparatus (comp. fig. 1) consists in this, that 

 in the licpiefactor the neon is made to condense on a spiral a^ a, r/, 

 (comp. n^a.^ni in Plate of Comm. 1096), which is cooled below the 

 boiling point of neon by means of liquid hydrogen. From the coils 

 of this spiral the liquefied neon flows down into the ciyostat. If 

 locally the tenqjcralure of the cooling-spiral descends below the 

 melting-point of neon, the substance will there be deposited as a 

 solid crust on the spiral. The external surface of the spiral, where 

 this happens, and the lemaining free passages between the spiral 

 and the vessel, ijisiile which the spiral is suspended are so large, 

 that a considerable quantity of solid neon can be deposited in this 



33* 



