2 Lord Bayleigh, [Jan. 17, 



of nitrogen. Wlien the gas is withdrawn for weighing, the space left 

 vacant must be filled up with liquid, and afterwards when the gas is 

 brought back for repurification, the liquid must be removed. In 

 order to effect this the working vessel (Fig. 7*) communicates by 

 means of a siphon with a 10-litre "aspirating bottle," the ends of 

 the siphon being situated in both cases near the bottom of the liquid. 

 In this way the alkaline solution may be made to pass backwards 

 and forwards, in correspondence with the desired displacements of 

 gas. 



There is, however, one objection to this arrangement which requires 

 to be met. If the reserve alkali in the aspirating bottle were allowed 

 to come into contact with air, it would inevitably dissolve nitrogen, 

 and this nitrogen would be partially liberated again in the working 

 vessel, and so render impossible a complete elimination of that gas 

 from the mixture of argon and oxygen. By means of two more 

 aspirating bottles an atmosphere of oxygen was maintained in the 

 first bottle, and the outermost bottle, connected with the second by a 

 rubber hose, gave the necessary control over the pressure. 



Five glass tubes in all were carried through the large rubber cork 

 by which the neck of the working vessel was closed. Two of these 

 convey the electrodes : one is the siphon for the supply of alkali, 

 while the fourth and fifth are for the withdrawal and introduction of 

 the gas, the former being bent up internally, so as to allow almost 

 the whole of the gaseous contents to be removed. The fifth tube, by 

 which the gas is returned, communicates with the fall-tube of the 

 Topler pump, provision being made for the overflow of mercury. In 

 this way the gas, after weighing, could be returned to the working 

 vessel at the same time that the globe was exhausted. It would be 

 tedious to describe in detail the minor arrangements. Advantage 

 was frequently taken of the fact that oxygen could always be added 

 with impunity, its presence in the working vessel being a necessity 

 in any case. 



When the nitrogen had been so far removed that it was thought 

 desirable to execute a weighing, the gas on its way to the globe had 

 to be freed from oxygen and moisture. The purifying tubes contained 

 copjier and copj^er oxide maintained at a red heat, caustic soda, and 

 phosphoric anhydride. In all other respects the arrangements were 

 as described in the memoir on the densities of the principal gases,| 

 the weighing globe being filled at 0°, and at the pressure of the 

 manometer gauge. 



The i^rocess of purification with the means at my command proved 

 to be extremely slow. The gas contained more nitrogen than had 

 been expected, and the contraction went on from day to day until 

 I almost desj^aired of reaching a conclusion. But at last the visible 

 contraction ceased, and soon afterwards the yellow line of nitrogen 



* Phil. Trans, loc. cit. p. 218. 



t Roy. Soc. Proc. vol. 53, p. 134, 1893. 



