276 Lord Rayleigh and Prof. Ramsay. [Jan. 31, 



was collected in a similar manner and subsequently absorbed by 

 potash, it was found to have acquired a contamination consistent 

 with this explanation. 



Negative experiments were also carried out, absorbing nitrogen by 

 means of magnesium. In one instance 3 litres of nitrogen prepared 

 from ammonium chloride and bleaching-powder was reduced in 

 volume to 4'5 c.c., and on sparking with oxygen its volume was 

 further reduced to about 3 c.c. The residue appeared to consist of 

 argon. Another experiment, in which 15 litres of nitrogen from 

 ammonium nitrite was absorbed, gave a final residue of 3' 5 c.c. 

 Atmospheric nitrogen, in the latter case, would have yielded 150 c.c., 

 hence less than -^th of the normal quantity was obtained. It 

 should be mentioned that leakage occurred at one stage, by which 

 perhaps 200 c.c. of air entered the apparatus ; and, besides, the nitro- 

 gen was collected over water from which it doubtless acquired some 

 argon. Quantitative negative experiments of this nature are exceed- 

 ingly difficult, and require a long time to carry them to a successful 

 conclusion. 



VIII. Separation of Argon on a Large Scale. 



To prepare argon on a large scale, air is freed from oxygen by means 

 of red-hot copper. The residue is then passed from a gas-holder 

 through a combustion-tube, heated in a furnace, and containing 

 copper, in order to remove all traces of oxygen; the issuing gas is 

 then dried by passage over soda-lime and phosphorus pentoxide, 

 after passage through a small (J tube containing sulphuric acid, to 

 indicate the rate of flow. It then enters a combustion-tube packed 

 tightly with magnesium turnings, and heated to redness in a second 

 furnace. From this tube it passes through a second index-tube, and 

 enters a small gas-holder capable of containing 3 or 4 litres. A single 

 tube of magnesium will absorb from 7 to 8 litres of nitrogen. The 

 temperature must be nearly that of the fusion of the glass, and the 

 current of gas must be carefully regulated, else the heat developed 

 by the union of the magnesium with nitrogen will fuse the tube. 



Having collected the residue from 100 or 150 litres of atmospheric 

 nitrogen, which may amount to 4 or 5 litres, it is transferred to a 

 small gas-holder connected with an apparatus, whereby, by means of 

 a species of a self-acting Sprengel's pump, the gas is caused to circu- 

 late through a tube half filled with copper and half with copper 

 oxide ; it then traverses a tube half filled with soda-lime and half 

 with phosphorus pentoxide; it then passes a reservoir of about 

 300 c.c. capacity, from which, by raising a mercury reservoir, it can 

 be expelled into a small gas-holder. Next it passes through a tube 

 containing magnesium turnings heated to bright redness. The gas 



