210 LORD RAYLEIGIL AND PROFESSOR W. RAMSAY ON ARGON, 
found in the gas when collected over water must therefore have been extracted from 
the water. 
A similar set of experiments was carried out with magnesium. The nitrogen, of 
which three litres were used, was prepared by the action of bleaching-powder on 
ammonium chloride. It was circulated in the usual apparatus over red-hot magnesium, 
until its volume bad been reduced to about 100 cub. centims. An equal volume of 
hydrogen was then added, owing to the impossibility of circulating a vacuum. The 
circulation then proceeded until all absorption had apparently stopped. The remaining 
gas was then passed over red-hot copper oxide into the SPRENGEL’s pump, and 
collected. As it appeared still to contain hydrogen, which had escaped oxidation, 
owing to its great rarefaction, it was passed over copper oxide for a second and a 
third time. As there was still a residue, measuring 12°5 cub. centims., the gas was 
left in contact with red-hot magnesium for several hours, and then pumped out ; its 
volume was then 4°5 cub. centims. Absorption was, however, still proceeding, when 
the experiment terminated, for at a low pressure, the rate is exceedingly slow. This 
gas, after being sparked with oxygen contracted to 3:0 cub. centims., and on 
examination was seen to consist mainly of argon. The amount of residue obtainable 
from three litres of atmospheric nitrogen should have amounted to a large multiple 
of this quantity. 
In another experiment, 15 litres of nitrogen prepared from a mixture of ammonium 
chloride and sodium nitrite by warming in a flask (some nitrogen having first: been 
drawn off by a vacuum-pump, in order to expel all air from the flask and from the 
contained liquid) were collected over water in a large gas-holder. The nitrogen was 
not bubbled through the water, but was admitted from above, while the water escaped 
below. This nitrogen was absorbed by red-hot magnesium, contained in tubes heated 
in a combustion-furnace. The unabsorbed gas was circulated over red-hot magnesium 
in a special small apparatus, by which its volume was reduced to 15 cub. centims. 
As it was impracticable further to reduce the volume by means of magnesium, the 
residual 15 cub. centims. were transferred to a tube, mixed with oxygen, and submitted 
to sparking over caustic soda. The residue after absorption of oxygen, which 
undoubtedly consisted of pure argon, amounted to 3°5 cub. centims. This is one-fortieth 
of the quantity which would have been obtained from atmospheric nitrogen, and its 
presence can be accounted for, we venture to think, first from the water in the 
gas-holder, which had not been freed from dissolved gas by boiling in vacuo (it has 
already been shown that a considerable gain may ensue from this source), and second, 
from leakage of air which accidentally took place, owing to the breaking of a tube. 
The leakage may have amounted to 200 cub. centims., but it could not be accurately 
ascertained. Quantitative negative experiments of this nature are exceedingly 
difficult, and require a long time to carry them to a successful conclusion. 
