(85 ) 



it. The liquid-space ^i is contained between the needle points of 

 a double cock; the chamber of cock Ai is connected with the reser- 

 voir by a brass overpipe r/, which is provided with two nuts, and 

 in which a narrow steel capillary tube has been soldered which is 

 so long that the lower end of it reaches as far as the chamber of 

 Jj and the upper end not only goes through the plug but emerges 

 nearly 5 m.m. beyond it. 



Thus has been obtained that the communication of B with A 

 has as little volume as possible; 'while at the same time at the 

 lower end of the reservoir an annular space has been formed, in 

 which may settle particles from the walls or from the packings 

 which during the distilling of the gas might get into the reservoir. 



A rim on the plug protects the capillary tube from being damaged 

 by the stirring-rod. 



In the plug at the upper end of the reservoir three copper ca- 

 pillary tubes have been soldered. 



One of these, />, leads to the cock Z?i ; the vapour-space Z? consists 

 in a spiral made of a copper capillary tube (long 80 cM.) of the 

 same diameter. Care has been taken that the channel through which 

 the vapour streams out has the same diameter over its whole length 

 in order to prevent as much as possible the condensing of the vapour 

 by adiabatic expansion. 



A second tube c leads to the cock C2 and serves to connect the 

 purifying apparatus with the reservoir. The third tube d connects 

 this reservoir with the apparatus for the measuring of the pressure. 



§ 4. The measuring of the pressure. 



Special care is required for this. By filling the tube which leads 

 to the closed air-manometer with mercury, we may prevent conden- 

 sation or evaporation in that tube caused by differences of tempe- 

 rature between that tube and the water-bath of the apparatus. But 

 then the mercury-meniscus on which the vapour presses must be 

 within the water-bath and moreover it must be visible in order to 

 enable us to read the difference in height with the meniscus of the 

 closed manometer. 



Therefore the tube d has been connected through the cock Cj 

 with the copper capillary tube e, which ends in the upper part of 

 the glass reservoir D, which is again connected with the mercury 

 in the air-manometer through the steel capillary tubes f, g and the 

 steel cock Dx. With a view to greater accuracy two air-manometers 

 are used, the one for pressures from 4 to 20, the other for 

 pressures from 18 to 90 atmospheres, so that their indications may 

 be compared together. 



6* 



