[23] Page 162. _Sulpho-indigotic Acid._--A mixture of one part of
indigo and fifteen parts of concentrated oil of vitriol. It is bleached
on the side at which hydrogen gas is evolved, in consequence of the
liberated hydrogen withdrawing oxygen from the indigo, thereby forming
a colourless deoxidised indigo. In making the experiment, only enough
of the sulpho-indigotic acid must be added to give the water a decided
blue colour.
[24] Page 164. _Lead Tree._--To make a lead tree, pass a bundle of
brass wires through the cork of a bottle, and fasten a plate of zinc
round them just as they issue from the cork, so that the zinc may be
in contact with every one of the wires. Make the wires to diverge so
as to form a sort of cone, and having filled the bottle quite full of
a solution of sugar of lead, insert the wires and cork, and seal it
down, so as to perfectly exclude the air. In a short time the metallic
lead will begin to crystallise around the divergent wires, and form a
beautiful object.