( 161 ) 



towards the delivery cock JSf^i. Here, as at the ethylene cock 

 (description of Mathias 1. c. fig. 2), the packing iVj and the screw- 

 thread are in the portion that is not cooled. The pin ^'^j, made of a new- 

 silver tube, passes through the cock-carrying tube iV^. Both the outlet 

 tube iVo and the delivery cock jV^ are surrounded by a portion of 

 the cold hydrogen vapours, which to this end are forced to escape 

 between the double wall of the tube through iYgj^ and along Kha 

 {Kd on PL II). The outer wall jVjoi, ^^503 of the double-walled tube is 

 insulated from the side tube T^ji at the case F30 by means of wool. 



The glass L is covered with a felt cover Zg, fitted at the bottom 

 with a sheet of nickel-paper to prevent radiation towards the liquid 

 hydrogen. This cover fits tightly on the lower end E^ of E and 

 rests on the tube ,^501 ^"d the pulley-case L^^. 



f. We still have to describe the various safety arrangements to 

 prevent the apparatus from bursting when the cock M should sud- 

 denly admit too much gas, as might occur when the opening has 

 been blocked by frozen impurities in the gas, which suddenly let 

 loose or when one of the tubes breaks down owing to the same 

 blocking or an other cause. 



For this purpose serves in the first place the wide glass tube 

 TFi, which ends below mercury. The quantity of gas which of a sudden 

 escapes, and the great force with which the mercury is sometimes 

 flung away rendered it necessary to make a case TF30 with several 

 screens W^^ all of varnished card-board to collect the mercury and 

 to reconduct it into the glass IF, (where a sufficient quantity of it must 

 be present for filling the tube during the exhaustion). 



If the pressure in the reservoir rises higher than that for which the 

 safety tube is designed, the thin-walled india rubber tube V^^, which is 

 drawn over the perforated brass cylinder wall V^-^ (separated from 

 it by a thin sheet of tissue-paper), breaks. The safety apparatus is 

 connected with the case V^ by a wide new-silver tube F^^. 



In order to avoid impurities in the hydrogen in the liquefactor 

 through diffusion of air the india rubber cylinder V^^^ that is drawn 

 over the rings F431 and V^^^ after being exhausted is filled through 

 the cock V^^ with hydrogen under excess of pressure; during the 

 exhaust the india rubber cylinder F^,, is pressed against the india 

 rubber wall F^,. 



An arrangement of an entirely identical construction protects the 

 case C/j, which encloses the principal regenerator, and the case U^ 

 which encloses the forecooling regenerator C. 



As to the protection against pressure which may occur in conse- 

 quence of evaporation of air, it was suflicient to protect the refri- 



