[Illustration: Fig. 21.]
Can we get it from the air? Well, there are some very complicated and
difficult processes by which we can get it from the air; but we have
better processes. There is a substance called the black oxide of
manganese: it is a very black-looking mineral, but very useful, and when
made red-hot it gives out oxygen. Here is an iron bottle which has had
some of this substance put into it, and there is a tube fixed to it, and a
fire ready made, and Mr. Anderson will put that retort into the fire, for
it is made of iron, and can stand the heat. Here is a salt called chlorate
of potassa, which is now made in large quantities for bleaching, and
chemical and medical uses, and for pyrotechnic and other purposes. I will
take some and mix it with some of the oxide of manganese (oxide of copper,
or oxide of iron would do as well); and if I put these together in a
retort, far less than a red heat is sufficient to evolve this oxygen from
the mixture. I am not preparing to make much, because we only want
sufficient for our experiments; only, as you will see immediately, if I
use too small a charge, the first portion of the gas will be mixed with
the air already in the retort, and I should be obliged to sacrifice the
first portion of the gas, because it would be so much diluted with air;
the first portion must therefore be thrown away.
Pages:
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92