( 172 ) 



a, to terminate at the top of the separating cylinder d, from which 

 the gas escapes through h^, and the impurities separated from the 

 hydrogen as liquid escape along e and Km (comp. PI. II). The liquid 

 air, with which the cooling tube and the separating cylinder are cooled, 

 is admitted along / and the cock ?« (and drawn from the vacuum glass 

 215, PI. II) ; a float dr indicates the level of the liquid air. The eva- 

 porating air is drawn oiï by the vacuumpump S (PI. II) along Kt. 

 The refrigerator vessel p is protected against heat from outside by 

 a double wall q of new-silver with capoc v packed between, of 

 which the lower end is immersed in a vacuum glass i\ while the 

 whole is surrounded with a layer of capoc enclosed in a varnished 

 cover of card-board pasted together in the same way as for the 

 hydrogen liquefactor. The glass tube Y, opening below mercury, 

 serves among others to read the pressure under which the evaporation 

 takes place. 



The cock Km is turned so that some more bottles of known 

 capacity are collected of the blown- oiF gas than, according to the 

 analysis, would be formed by the impurities present in the gas. In 

 this way the purity of the hydrogen is brought to V20 Vo- ^^ i'' ^^d 

 along Kl to the gasholders, and compressed by v^ and S^ in dJid. 



h. A second purification is effected in the following manner. When 

 we have operated with the liquefactor with pure hydrogen we 

 always, after the experiments are finished, admit a portion of this 

 not yet quite pure gas into the apparatus. After some time, usually 

 after 4 liters of liquid hydrogen are formed, the cock is blocked. As 

 soon as it becomes necessary to move this repeatedly to and fro 

 — Travers and Olszewski say that this is constantly necessary but 

 I consider it as a sign that the apparatus is about to get more and 

 more disordered — the work is suspended and the cock M (PL I) 

 closed, after which 2)^ and 2)^ (PI. II) are blown off to the gas- 

 holders along Ka and Kg, and Kc is shut. The liquid hydrogen, 

 after being siphoned, is allowed to evaporate and to pass over into 

 the gasholder for pure hydrogen. The impurities are found when, 

 with M and Kc closed, we return to the ordinary temperature and 

 analyze the gas, which in 2) has come to high pressure. 



If necessary, the purified hydrogen is once more subjected to this 

 process. 



When, after the liquefactor with pure hydrogen has been worked, 

 we go on admitting a quantity of preliminarily purified hydrogen of 

 Vjo Vo ^nd take care that the impurities are removed, we gradually 

 obtain and maintain without trouble a sufficient quantity of pure 

 hydrogen. 



