SCIOPTIOON MANUAL.
85
of copper, and mix it well with the water of the tank,
then with the pipette run in, with more or less force,
some diluted ammonia, pausing from time to time to
observe the progress of the effect. On the screen will
be observed the gathering of a tempest of black storm-
clouds, which twirl around in violent commotion, as if
urged by a tornado of wind, but as the action continues,
these clouds will melt away, and leave the entire field
of a serene and beautiful sky-blue.
By now throwing in some diluted sulphuric acid, the
same changes can be reproduced, and so on alternately
for a number of times. Then when the tank is clear,
with an excess of acid, let fall a few drops of a solution
of ferrocyanide of potassium from a small pipette, and
rich red curdled clouds of ferrocyanide of copper will
form with a beautiful appearance.
Experiment 2d. Having rinsed the tank, or taken a
fresh one with water in it as before, add to this some
solution of litmus, until the whole acquires a purplish-
blue tint. How throw in very gently a little very dilute
acid, and allow it to diffuse. On the screen will appear
the image of a beautiful sunset sky, with its changing
tints of drifting clouds.
When all has changed to red, add ammonia, and so
reverse the change, which may then be repeated.
Experiment 3d. Proceed exactly as in the last case,
but with a solution of cochineal in place of litmus. The
red color will then be changed by the acid to a brilliant
yellow, and by ammonia to a rich purple.
Experiment 4th. Into a tank of water drop slowly a
strong solution of the acid perchloride of tin. This
on the screen will resemble the eruption of a submarine
volcano.
When a pretty strong solution has thus been made in