1879.] On the Vapour Densities of Potassium and Sodium. 207 



After the apparatus had "been placed in the furnace and had risen to 

 a dull red heat, the tube B was inserted into it and made airtight at 

 C by the india-rubber tubing F, the point of the tube reaching almost 

 to the bottom of A. Hydrogen was now passed into the apparatus by 

 D, and a current kept up until the apparatus was thoroughly reduced : 

 by this time the temperature had risen sufficiently for the experiments 



to be proceeded with. The apparatus was now filled with nitrogen, 

 which was likewise passed in at D, the tube E withdrawn, and an 

 india-rubber stopper inserted into C, and the end of D immersed in 

 water or mercury. The weighed substance was then dropped in at 

 C, and the gas expelled, collected in a graduated jar in the usual 

 manner. 



The substances whose vapour densities are to be determined, were 

 placed, after weighing, in small iron capsules and kept in them by a 

 plug of wire gauze. This was done in order to ensure their reaching 

 the bottom of the apparatus, and the wire gauze plug also had the 

 advantage of moderating the rate at which the gas came off. The 

 potassium and sodium were placed in tared iron capsules and weighed 

 in dry carbonic acid, and then the ping of wire gauze inserted. 



To test the apparatus cadmium was tried and gave very good 



