( 175 ) 



continued, with which it is connected by six strengthened supporting 

 ribs Ba^. At the top it is strengthened by a brass rim Ba^ with a 

 protruding part, against which presses the upper rim Ua of the 

 case U. On Ba^ rests the cover ^Vm in which a stopper is placed 

 carrying the measuring apparatus. The india rubber band effects 

 the closure (comp. also Comm. Nos. 83, 94'" and 9-4<0. 



c. In the case U the vacuumglass B\, of which the inner wall 

 B\^ is protected by the thin new-silver cup Bb, is suspended by 

 bands L\ and supported by the wooden block L\. The card-board 

 cover B\ forces the evaporated hydrogen, which escapes between 

 the interstices of the supporting ridges, over the paste-board screen 

 B\^^ with notches B\^^ along the way indicated by arrows, to escape 

 at 2\^. The case is lined with felt, covered with nickel paper (comp. 

 Comm. W. 14, Dec. '94, and Comm. W. 51, Sept. '99). 



d. The keeping of liquid hydrogen within an enclosed space, oi 

 which the walls have for a great part a much higher temperature 

 than the critical temperature of hydrogen, involves special safety 

 arrangements. That this was no needless precaution appeared when 

 the vacuum glass cracked unexpectedly (comp. X § 1) and of a quantity 

 of more than 1,5 liter of liquid hydrogen nothing was to be seen 

 after a few seconds. Now this disappearance is equivalent with the 

 sudden formation of some hundreds of liters of gas, which would explode 

 the case if no ample opportunity of escape were offered to the gas 

 as soon as the pressure rises a little above the atmospheric. 



In the new cryostat I have avoided this danger in the same way 

 as at the time Avhen I first poured off a bath of liquid oxygen within 

 a closed apparatus (comp. Comm. N". 14, Dec. '94). 



The bottom of the case U is made a safety valve of very 

 large dimensions; as cover W^ of pei'forated copper with strengthened 

 ridges it fits into the cylindrical case Ub, which is strengthened 

 with the rim W. Over the external side of this co^•er (as in the 

 safety tubes for the hydrogen liquefactor) a thin india rubber sheet 

 IFj — separated from the copper by a sheet of paper — is stretched, 

 which at the least excess of pressure swells and bursts, while moreover 

 the entire vacuum glass or pieces of it, if they should be forced out 

 of the case, push the cover W^ in front of them without resistance. 

 As the airtight fit of the sheet of india rubber W^ on the ring W 

 is not trustworthy and diffusion through contact of the india-rubber 

 with the air must be prevented, it is surrounded with hydrogen; 

 this is done by filling the india rubber cylinder \Va, drawn over 

 the supporting ring Ub^ and the auxiliary cover Wb, with hydrogen 

 along Wc. 



