( 171 ) 



into which the hydrogen is siphoned. To this end tlie tube b'\ of Pi. Ill 

 is connected (again by a piece of india rubber tubing, enveloped in 

 flannel and wool) to the inflow tube a^ of the eryostat and the 

 tube d^ to an inflow tube of pure hydi'ogen under pressure, which is 

 admitted from üvAc, PI. II, along Kwa. With all these connections and 

 disconnections care must be taken that there should always be an 

 excess of pressure in the tubes that are to be connected, that the 

 disconnected tubes should be immediately closed with stoppers 

 but that ürst the apparatus after having been exhausted should prelimi- 

 narily be filled with pure hydrogen. The liquid hydrogen is not 

 admitted into the eryostat ^r until the latter has been cooled — 

 coupled in another way (see the dotted line on PI. II) — by means 

 of pure hydrogen which has been led from d\hc through a cooling 

 tube immersed in liquid air. This refrigerator is of a similar construc- 

 tion as the nitrogen condenser PI. VII of Comm. N". 83 (March '03). 

 Instead of Nliq should be read H^ and instead of Ox liq, Aër liq, 

 which is siphoned from the vacuum flask 21c. (comp, § 6). 



During the siphoning of the liquid hydrogen into ^r the rapidity 

 of the influx is regulated after a mercury manometer, which is con- 

 nected with the tube c on the cap h, PI, III (comp. fig. 2 of ^ 4). 



b. From the eryostat the evaporated hydrogen escapes along 3%^ 

 into the compressor (^), PI. II, which can also ser^•e as vacuumpump 

 and which precautiously through .p and Kfixi the dotted connection Kf 

 stores the gas, which might contain minute impurities, in the separate 

 reservoir ^ilid; or it escapes along Y^^ and Kpe or /i^x/ into the gas- 

 holders Gaz a or Gaz b. 



XI. The purification of hydrogen for the cycle. 



a. This subject has been treated in Comm. W. 94(/ IX. To be 

 able always to obtain pure hydrogen, to make up for inevitable 

 losses, and lastly to be freed from the fear of losing pure hydrogen, 

 which perhaps might deter us from undertaking some experiments, a 

 permanent arrangement for the purification has been made after the 

 principle laid down in IX. The apparatus for the purification is 

 represented on PI. IV and is also to be found on PL II at 3- 



The impure hydrogen from :)\hb is admitted through Kn and along 

 a drying tube into a regenerator tube (see PI. IV) consisting of two 

 tubes enclosing each other concentrically, of which the outer a serves 

 for the inflow, the inner b for the outlet. Outside the apparatus 

 a and b are separated as a^ and b^, within the apparatus from the 

 point c downwards a is continued as «i and subsequently as the spiral 



