204 LORD RAYLEIGH AND PROFESSOR W. RAMSAY ON ARGON, 
tube into which the gas could be drawn from the gas-holder A. The stop-cock, as 
shown, allows gas to pass through the horizontal tubes, and does not communicate 
with A ; but a vertical groove allows it to be placed in communication either with the 
gas-holder, or with the apparatus to the right. The compartment (a) of the second 
drying-tube D contained soda-lime, and (b) phosphoric anhydride. The tube D com- 
municated with a hard-glass tube E, heated over a long-flame burner ; it was partly 
filled with metallic copper, and partly with copper oxide. This tube, as well as the 
tube F filled with magnesium turnings, was connected to the drying-tube with india- 
rubber. The gas then entered G, a graduated reservoir, and the arrangement H 
permitted the removal or introduction of gas from or into the apparatus. The gas 
was gradually transferred from the gas-holder to the tube C, and passed backwards 
and forwards over the red-hot magnesium until only about 200 cub. centims. were 
left. It was necessary to change the magnesium tube, which was made of smaller 
size than formerly, several times during the operation. This was done by turning out 
the long-flame burners and pumping off all gas in the horizontal tubes by means of 
the SPRENGEL’S pump. ‘This gas was carefully collected. The magnesium tube was 
then exchanged for a fresh one, and after air had been exhausted from the apparatus, 
nitrogen was introduced from the reservoir. Any gas evolved from the magnesium 
(and apparently there was always a trace of hydrogen, either occluded by the magne- 
sium, or produced by the action of aqueous vapour on the metal) was oxidised by the 
copper oxide. Had oxygen been present, it would have been absorbed by the metallic 
copper, but the copper preserved its red appearance without alteration, whereas a little 
copper oxide was reduced during the series of operations. The gas, which had been 
removed by pumping, was reintroduced at H, and the absorption continued. 
The volume of the gas was thus, as has been said, reduced to about 200 cub. 
centims. It would have been advisable to take exact measurements, but, unfor- 
tunately, some of the original nitrogen had been lost through leakage; and a natural 
anxiety to see if there was any unknown gas led to pushing on operations as quickly 
as possible. 
The density of the gas was next determined. The bulb or globe in which the gas 
was weighed was sealed to a two-way stop-cock, and the weight of distilled and 
air-free water filling it at 17°15° was 162°654 grms., corresponding to a capacity of 
162°843 cub. centims. The shrinkage on removing air completely was 0:0212 cub. 
centim. Its weight, when empty, should therefore be increased by the weight of 
that volume of air, which may be taken as 0°000026 grm. This correction, however, 
is perhaps hardly worth applying in the present case. 
The counterpoise was an exactly similar bulb of equal capacity, and weighing about 
02 grm. heavier than the empty globe. The balance was a very sensitive one by 
OERTLING, which easily registered one-tenth of a milligrm. By the process of 
swinging, one-hundredth of a milligrm. could be determined with fair accuracy, 
In weighing the empty globe, 0:2 grm. was placed on the same pan as that which 
