212 LORD RAYLEIGH AND PROFESSOR W. RAMSAY ON ARGON, 
After all the magnesium in the tube had been converted into nitride (and this was 
easily known, because a bright glow proceeded gradually from one end of the tube to 
the other) the argon remaining in the iron tube was ‘‘ washed” out by a current of 
nitrogen; so that after a number of operations, the small gas-holder contained a 
mixture of argon with a considerable quantity of nitrogen. 
On the whole, the use of iron tubes is not to be recommended, owing to the diffi- 
culty in cleaning them, and the possible loss through their permeability to argon. 
There is no such risk of loss with glass tubes, but each operation requires a new tube, 
and the cost of the glass is considerable if much nitrogen is to be absorbed. Tubes 
of porcelain were tried ; but the glaze in the interior is destroyed by the action of the 
red-hot magnesium, and the tubes crack on cooling. 
By these processes 157 litres of “atmospheric nitrogen” were reduced in volume to 
about 2°5 litres in all of a mixture of nitrogen and argon. This mixture was after- 
wards circulated over red-hot magnesium, in order to remove the last portion of 
nitrogen. 
Fig. 5. 
To wales, pump 
To Sprengel's 
JORG 





























As the apparatus employed for this purpose proved very convenient, a full deserip- 
tion of its construction is here given. A diagram is shown in fig. 5, which sufficiently 
explains the arrangement of the apparatus. A is the circulator. It consists of a sort 
of SPRENGEL’s pump (a) to which a supply of mercury is admitted from a small 
