( 174 ) 



also at reduced pressure and to prevent any admixtures of air from 

 entering into the pure hydrogen used, the whole bath has been placed 

 in a stout cylindrical copper case Ub, which can be exhausted. 



This cryostat is especially fit for hydrogen, yet may protitably 

 replace those described till now, at least when it is not necessary 

 that we should see what takes place inside the bath. A modified pattern, 

 where this has become possible, in the same way as in the cryostat 

 with liquid oxygen of Comm. N". 14, Dec. '94, I hope to describe 

 erelong. 



In the cryostat now to be described, as in the former, the meas- 

 uring apparatus, without our changing anything in the mounting 

 of them, will go through the whole range of temperatures from 

 — 23° to — 90^ with methyl chloride, from — 103° to — 160° with 

 ethylene, from — 183° to — 217° with oxygen and from — 252° 

 to — 259° with hydrogen (only for the temperatures between — 160° 

 and — 180° we still require methane). 



^ 2. Description. 



a. The new cryostat is represented on PL V. The letters, in so 

 far as the parts have the same signification, are the same as for the 

 descriptions of the olher cryostats; modified parts are designated by 

 new accents and new parts by analogous letters, so that the expla- 

 nations of Comms. N". 83, N°. 94^ and N°. 94^' on the attainment 

 of uniform and constant temperatures, to which I shall refer for 

 the rest, can serve also here. PI. II shows how the cryostat is 

 inserted into the hydrogen cycle. In chapter X § 7 is described how 

 the liquid hydrogen is led into the cryostat. Especially for the regu- 

 lation of the temperature this plate should be compared with PI. VI 

 of Comm. N". 83, March '03. Instead of Bu Vac on the latter plate, 

 the compressor © serves as vacuumpump here (see PI. II of the 

 present paper). 



b. The measuring apparatus (as on the plate of Comm. N°. 94'' 

 VIII I have represented here the comparison of a thermoelement 

 with a resistance thei-mometer) are placed \vithin the protecting 

 cylinder §„ of the stirring apparatus. This is held in its place by 4 

 glass tubes l^^ fitted with caps of copper tubing ^^^ and %^^ at the 

 ends of the rods. 



The beaker Ba, containing the bath of liquid hydrogen, is supported 

 by a new-silver cylinder Ba^, in the cylindrical rim Ba^ of which 

 the glass fits exactly ; the beaker is held in its place by 4 flat, thin, 

 new-silver suspension bands running downwards from Ba^ and 

 uniting below the bottom of Ba. The ring Ba^ is the cylinder Ba, 



