ARGON, A NEW CONSTITUENT OF THE ATMOSPHERE. 25 



apparatus works (jiiite automatically. Tins foi-in of apparatus was first suo-cested 

 by Dr. Collie. 



The gas is di'awii tVoiu the gas-holdei' H, and passes tlnoiii^di a tube C, which 

 is heated to I'edness by a loug-fiaine burner, and wliicli contains in one half metallic 

 copper, and in the oflier half copper oxide. This precaution is taken in order to 

 ivmove any oxygen which may possibly be present, and also any hydrorjen oi- 

 hydrocarbon. In practice, it was never found that the co[iper becanie oxidized, or 

 the oxide reduced. It is, however, useful to guard against any jjossible contamina- 

 tion. The gas next traversed a drying-tube D, the anterior portion containing 

 ignited sodadirae, and the posterior poi'tion phosphoric anhydride. 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 l)uiner to redness. After regis- 

 tering the rate of circulation by passing a small U-tube with bulbs, filled with 

 water, it again entered the gas-holder B. 



After the magnesium-tube E had done its woi-k, the stopcocks 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 i-eintroduced into the 

 gas-holder B thi'ough the side-tube G, which requires no description. The 

 magnesium-tube was then replaced bj' a fresh one ; the system of tubes was 

 exhausted of air ; ai'gon 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 absoi-ption ceased. It was easy to decide when this point had 

 been i-eached, by making use of the graduated cylindei- H, fiom which water 

 entered the gas-holder B. It was fountl advisable to keep all the water employed 

 in these operations, for it had become saturated with argon. If gas was withdi'awu 

 from the gas-holdei', its place was taken I)}- this saturated water. 



The absorption of nitrogen proceeds very slowly towards the end of the oper- 

 ation, and the diminution in volume of the gas is not greater than four or five cubic 

 centimetres 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 therefoi'e 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 por- 

 tion of gas collected from the system of tubes was not readmitted to the gas-holder 

 B, but was separately stored. 



