512 



then flows tln-ougli the small stop-cock E„k\ into the vacuum-vessel 

 aSj of the ci'yostat; for the description of tlie cryostat and its pump- 

 stirrer we may refer to Coram. 123l'^ wiiere the lettering is identical. 

 The ditference between the valve used at present (for details see 

 separate drawing in fig. 1) and that of Coram. 123i is of minor 

 importance and consists in the valve not having a turning movement, 

 but moving vertically up and down, being guided by the two rods 

 EnH and carried by the german-silver strip Eaki ■ The small stop- 

 cock is connected to the orifice E„i;r^ by means of two german-silver 

 rings Eaku and E„ks) ■ 



Fig. 1 represents the condition, in which the cryostat contains a 

 helium-thermometer ?7i,"' with capillary Tk^" (as in the Plate of 

 Coram. 123/>, this time however the thermometer used in Coram. 147), 

 a resistance SiAu, as in the same Plate, and moreover a piece of 

 apparatus for the measurement of the vapour-pressure of hydrogen 

 above its boiling point (vessel P^ , which contains the liquid hydrogen, 

 besides tube and capillary P^, P., I\ for connection with the further 

 apparatus): the measurements with this arrangement will be dealt 

 with in a coramunication to be made conjointly with Mr. P. G. Cath. 



Two tubes are attached to the cover of the cryostat, S\ (comp. 

 figure of Plate in Coram. 24, where however the corresi)onding 

 letter is wanting) and S' , leading to a manometer and the apparatus 

 (conip. § 3) for regulating the temperature in the cryostat. 



The temperature in the cooling-spiral «j a, in the liquefactor, a, 

 being protected from supply of heat by a covering of wool, may 

 be regulated by the aid of the thermometer ƒ, /,ƒ,ƒ, /s, exactly as 

 in the apparatus for the purification of hydrogen, for the desci'iption 

 of which we may again refer to Corara. 109. 



Care has to be taken, that only liquid neon can enter the draw- 

 off tube. For this purpose a small vessel /i is contrived, which fits 

 in the vacunui-vessel willi a thin layer of flannel; it is open at the 

 bottom and just above the o|iening li^ carries a filter ^i,, which can 

 be warmed by means of hydrogen of ordinary temperature which 

 can be blown through the tube rt^ and the small spiral «„; by which 

 means the temperature of the draw-off tube can be permanently 

 kept above that of the melting-point of neon. Solid and less volatile 

 substance, say nitrogen, which might fall down, is retained on the 

 filter and if the nitrogen which has collected there happened to 

 melt by the temperature rising it flows on the small tray y, where 

 it remains while only liquid neon can flow down'). 



') 111 orrjer to make the arrangement completely adequate — solid nitrogen is 

 lighter than liquid neon — this tray should be provided with a standing-up rim 

 of gauze, which was not yet the case. 



