<)8 DENSITIES OF OXYGEN AND HYDROGEN 



l)le. The sole use of these stoiicocks was, to 2>reveiit the adiiiissinn of any loii- 

 siderable (luaiitity of airdiiring the ].reparation of the tube for fUliii-jr it again witli 

 hydrogen. 



To the tube of infusil^le glass a,a, therefore, was fitted by a gi-ound joint the 

 stopcock <', ending in another ground joint. When the tube was to be filled w itli 

 hvdiogen, a connecting tube with a ground joint wjus fitted to the second joint. <l. 

 with parattin, ami connected by fusion to the source of hydrogen. The connect- 

 ing tubes were then freed from air by repeated exhaustion. Tlie stopcock •■ was 

 then o[)ened, the palladium was heated, and the exhaustion continued. After cool- 

 ing the ])alladiuni, hydrogen wjjs admitted to saturation. In tlie.se two experiments, 



any nitrogen which might possibly have ac- 



__^^__^jjrhi_i< I corapanied the hydiogeu was removed, or, 



' rather, an attempt was made to remove it. 



Fir.. 34.— Palladium lube proteclcd against leakage l^y repeated exluUlStionS of the tubc at the 

 through stopcock. 



end of the admission of hydrogen. 



When the tube was charged with hydrogen, the pressure in the tube was a 

 little gi'eater than that of the atmosphei-e. No leakage was therefore to be fearetl 

 during tlie moment required to remove the ground joint which connected the 

 palladium tube with the source of hydrogen, its stopcock being closed, ami to re- 

 place it with tbe joint /, I, Fig. .'54, which had been prepared beforehand. The 

 tube g w\<is then connected with the air pump, and the space between the stop- 

 cock and tlie plug of fusible metal h was lepeatedly exhausted and filled with 

 hydiogen. AVlien it was exhausted foi- the last time, the connection with the 

 pump was closed by fusion at g. 



The space between the fusible metal plug //. and the point /, had been ex- 

 hausted before the point I was sealed. Tiic apparatus, therefore, contained no gas 

 but hydrogen. 



The volume of the two tiil)cs was now detei-mined by a hydrostatic weigh- 

 ing of both at once. A counter[)oise was made of the same two kinds of glass, and 

 of nearly the same volume and weight. 



When the hard glass tubes containing the palladium were used, they w-ere 

 heated so gentl)^ that it was obvious that 

 no chansre of volume was to be feared ; it ' \ ^ "^ j 



= "■ V • I - — L if— ''^-^ 



was therefore unnecessary to determine ® T 



,1 - 1 I'l. il 1 * J! 4-1 Fic. ii — T'all:i(lliiin tiihf. second form. 



their volume atter the expulsion ot tlie 

 gas by a second hydrostatic weighing. 



Procuriu"- .some tubes larffe enouirh to contain the whole of the iialladium. 

 it was concluded to use them, although they were of soft glas.s. 



