( 179 ) 



The gas was obtained from the monazite (see $ 1) by means of 

 heating, it was exploded with oxygen, cooled with liquid air, and, 

 compressed, led over charcoal at the temperature of liquid air. Then 

 it was burned over CuO. Then it was compressed over charcoal at 

 the temperature of liquid air, after which it was under pressure 

 led over charcoal at the temperature of liquid hydrogen several 

 times till the gas which had been absorbed in the charcoal and then 

 separately collected no longer contained any appreciable admixtures. 



This way of preparation (to be treated in a following Comm.) 

 was also applied in Comm. N°. 105. 



§ 4. Tlie experiment. After on July 9 th the available quantity of 

 liquid air had been increased l ) to 75 liters, all apparatus examined as 

 to their closures, exhausted, and tilled with pure gas, we began the 

 preparation of liquid hydrogen on the 10 th of July, 5.45 a.m., 

 20 liters of w T hich was ready for use in silvered vacuum glasses 

 (cf. Comm. N°. 94/ PI. Ill) at 1.30 p.m. In the meantime the helium 

 apparatus had been exhausted while the tube with charcoal belonging 

 to it was heated, and this tube being shut off, the gas contained in 

 the rest of the helium circulation was freed from the last vestiges 

 of air by conduction over charcoal in liquid air through the side- 

 conduit. The hydrogen circulation of the helium apparatus was con- 

 nected with the hydrogen gasholder and the air-pump, which had 

 served as methyl chloride pump in the preparation of air the day 

 before, and this whole circulation was exhausted for so far as this 

 had not yet been done, and filled with pure hydrogen. Moreover 

 the space between the vacuum glasses (E a and Eb) which was 

 to be filled with liquid hydrogen as a protection against access 

 of heat, was exhausted and filled with pure hydrogen, and the 

 thermometers and thermoelements were adjusted. 



At 1.30 p.m. the cooling and filling of the glasses which, filled 

 with liquid air, were to protect the glasses which were to be filled 

 with liquid hydrogen, began with such precautions that everything 

 remained clear when they were put in their places. At 2.30 a 

 commencement was made with the cooling of the graduated vacuum 

 glass and of the hydrogen refrigerator of the helium liquefactor by 

 the aid of hydrogen led through a refrigerating tube, which was 

 immerged in liquid air. At 3 o'clock the temperature of the refri- 

 gerator had fallen to — 180° according to one of the thermo-elements. 

 Then the protecting glass {Eb) was filled with liquid hydrogen, and after 



l ) [With the help of the regenerative cascade Gomp. Coram. N°. 94, f. XIII and 

 Supplem. N°. 18]. 



