THE BOOK OP THE LANTERN-.
31
adopted on a commercial scale, depends upon the action of
cobalt on bleaching powder (Calcic hypochlorite). The
lime must be in the form of a concentrated solution, and
this is best brought about by mixing, say, one pound of
bleaching powder, which is commonly called chloride of
lime, with a quart of water. Stir this mixture and allow
it to remain for an hour. Now decant the clear liquid,
and pour it upon a fresh pound of lime—stir as before,
and strain the product through a calico or flannel bag.
Place the liquid in a large bottle, to the cork of which
a tube is fitted. Now drop into the liquid, taking the
cork out for the time being, a small quantity (say 2 ounces)
of a strong solution of cobaltic peroxide, when oxygen gas
will be quickly evolved, and will come off through the
replaced tube. The evolution of gas is increased by
warmth. The same cobalt can be used again and again, as
it does not undergo any permanent change. It seems to
act merely as a conveyer of oxygen, taking it from the
lime, passing it to a higher state of oxidation, and then
giving it up again ; any solution of cobalt will answer the
purpose. When the gas ceases to come, the residue in the
bottle should be diluted with water, and, after having been
allowed to rest for some time, the cobalt will settle at the
bottom of the vessel. This can then be washed, kept in a
moist state, and used over again as often as required.
But the more general method of preparing the gas is by
means of the decomposition of potassic chlorate, and
that method I shall now, therefore, describe in detail.
The lime-light has, in certain quarters, earned the cha¬
racter of being dangerous, not so much from accidents