( 176 ) 



The cords Wd serve to press the auxiliary cover Wb with a certain 

 force against the safety sheet, namely by so much as the excess 

 of pressure amounts to, which for one reason or other we want 

 to admit into the case. To prevent the india rubber from cooling 

 down, for then the arrangement would no longer satisfy the requi- 

 rements, the lower end of the case is lengthened by the cylindrical 

 piece Ub, which between the rim Ub^ and the principal body of 

 the case is made of new-silver to prevent the cooling of the lower 

 rim. The entire lower part is stutfed with layers of felt and w^ool 

 while also a copper flange Ub^ by conduction of heat from outside 

 protects the lower wall from cooling. 



e. The hydrogen is admitted through the new-silver tube a, on 

 which the siphon tube of a vacuumglass (X § 7) is connected with 

 a piece of india rubber tubing a^ (which otherwise is closed with 

 a stopper a^, comp. X § 4 a). The new-silver tube is put into the 

 new-silver side piece Ud, which is soldered on the case and, being 

 stuffed with capoc held back by a paper tube Ue, carries at the 

 end a piece of cork Uf for support. When the vacuum glass B^ 

 with the case U are placed round tlie beaker Ba, the tube a^ is 

 pulled back a little. When subsequently the case is fastened in its 

 position the tube is pushed forward until a ridge on a^ is checked 

 by a notch in Ud, so that its end projects into the beaker Ba 

 and the hydrogen can flow* into it. The india rubber tube a^ forms 

 the closure on a^ and Ud. 



§ 3. Remai'ks on the measurements ivith the cryostat. 

 In chapter X § 7 I have communicated how the preliminary cooling 

 is obtained. In one of the experiments, for instance, 3 liters of liquid 

 air were used for it and the temperature was diminished to — 110\ 

 Then hydrogen was very carefully siphoned into the cryostat under 

 constant stirring ; a quantity of 5 liters was sufficient to obtain a bath 

 of 1.5 liter. About 0.2 liter per hour evaporated after this. During the 

 reduction of the pressure to about 60 m.m. d= 0.2 liter evaporated, 

 and then the evaporation remained about the same. The temperature 

 could be kept constant to within 0.01° in the way described in the 

 former papers. The temperature curves obtained were no less regular 

 than those of PI. Ill in Comm. N°. 83 (Febr. and March '03). 



If the pressure is reduced down to 54 m.m. the tapping noise of 

 the valves of the stirring apparatus becomes duller. This is a warning 

 that solid hydrogen begins to deposit. 



