A NEW CONSTITUENT OF THE ATMOSPHERE. 213 
reservoir (b). This mercury is delivered into a gas-separator (c), and the mercury 
overflows into the reservoir (d). When its level rises, so that it blocks the tube (/), 
it ascends in pellets or pistons into (e), a reservoir which is connected through (9) 
with a water-pump. The mercury falls into (>), and again passes down the SPRENGEL 
tube (a). No attention is, therefore, required, for the apparatus works quite auto- 
matically. This form of apparatus was employed several years ago by Dr. CoLtts. 
The gas is drawn from the gas-holder B, and passes through a tube C, which is 
heated to redness by a long-flame burner, and which contains in one half metallic 
copper, and in the other half copper oxide. This precaution is taken in order to remove 
any oxygen which may possibly be present, and also any hydrogen or hydrocarbon. 
In practice, it was never found that the copper became oxidised, or the oxide reduced. 
It is, however, useful to guard against any possible contamination. The gas next 
traversed a drying-tube D, the anterior portion containing ignited soda-lime, and the 
posterior portion phosphoric anhydride. From this it passed a reservoir, D’, from 
which it could be transferred, when all absorption had ceased, into the small gas- 
holder. It then passed through E, a piece of combustion-tube, drawn out at both 
ends, filled with magnesium turnings, and heated by a long-flame burner to redness. 
Passing through a small bulb, provided with electrodes, it again entered the fall 
tube. . 
After the magnesium tube E had done its work, the stop-cocks were all closed, and 
the gas was turned down, so that the burners might cool. The mixture of argon and 
nitrogen remaining in the system of tubes was pumped out by a SPRENGEL’S pump 
through F, collected in a large test-tube, and reintroduced into the gas-holder B 
through the side-tube G, which requires no description. The magnesium tube was 
then replaced by a fresh one; the system of tubes was exhausted of air; argon and 
nitrogen were admitted from the gas-holder B; the copper-oxide tube and the 
magnesium tube were again heated ; and the operation was repeated until absorption 
ceased. It was easy to decide when this point had been reached, by making use of 
the graduated cylinder H, from which water entered the gas-holder B. It was found 
advisable to keep all the water employed in these operations, for it had become 
saturated with argon. If gas was withdrawn from the gas-holder, its place was taken 
by this saturated water. 
The absorption of nitrogen proceeds very slowly towards the end of the operation, 
and the diminution in volume of the gas is not greater than 4 or 5 cub. centims. per 
hour. It is, therefore, somewhat difficult to judge of the end-point, as will be seen 
when experiments on the density of this gas are described. The magnesium tube, 
towards the end of the operations, was made so hot that the metal was melted in the 
lower part of the tube, and sublimed in the upper part. The argon and residual 
nitrogen had, therefore, been thoroughly mixed with gaseous magnesium during its 
passage through the tube E. 
To avoid possible contamination with air in the SPRENGEL’s pump, the last portion 
