( 165 ) 



copper exhaust tube are surrounded by a second India rubber tube 

 filled with glycerine. From the cock onward the conduction can be 

 exhausted; to prevent the tube from collapsing during the exhaust 

 a steel spiral has been placed in it. A float with valve Kph [Kpi) 

 prevents the oil from being drawn over into the apparatus. 



Besides these gasometers we dispose of two other gasometers holding 

 5 M' each to collect hydrogen of a less degree of purity. They 

 are built following the same system as the zinced gasometers for the 

 economizing of liquid, carefully riveted and caulked and float on 

 a solution of calcium chloride. The oil-gasholders serve only for the 

 storage of very pure hydrogen and this only while the apparatus is 

 working. 



During the rest of the time the pure hydrogen is kept in the 

 known steel bottles shown • on PI. II at "^Iha. When we wish to 

 lique'fy hydrogen, this is blown off into the gasometer through /{^ (/iTA^, 

 Kpe and Kpb for instance to Gaz b), after this gasometer, which has 

 been left standing filled with hydrogen, is washed out on purpose with 

 pure hydrogen. When we stop working the hydrogen by means of 

 © and Sp is repumped along Kpf and Kpc through Ka and Kf 

 into the reservoirs ^Xha. 



The gasometers may be connected with the pumps or the liquefactor 

 either separately or together. The former is especially required when 

 the cryostat is worked (comp. XII) and for the purification of 

 hydrogen (comp. XIV). 



§ 4. The cooling by means of liquid air. 



a. The liquid air is sucked into the refrigerator vessel F (PI. I), 

 which by A"^ (PI. II) is coupled to the vacuumpump 5, along the 

 tube Pb connected with the siphon of a vacuum bottle 21a con- 

 taining liquid air. 



This has been filled by catching the jet of liquid air from the 

 apparatus (PI. IV, fig. 2) in which it is prepared (comp. XIII), into 

 the open glass (see the annexed fig. 1) and is kept, covered with 

 a loose felt stopper m (fig. 1). To siphon the liquid air into the 

 apparatus, where it is to be used, the stopper is replaced by a cap 

 k (fig. 1) with 3 tubes; one of these d is designed to raise the 

 pressure in the bottle with a small handpump, the other c is connected 

 to a small mercury manometer, and the third b reaches down 

 to the bottom, so that the liquid gas can be let out. (When 

 the bottle is used for other liquid gases, d is used for the outlet 

 of the vapours and c for the admission of the liquid gas). One of 

 the first two tubes reaches as far as the neck. It may also be used 



12 



Proceedings Royal Acad. Amslerdam. Vol. IX. 



