I58 the art of projecting.
To water made slightly acid, add enough litmus
solution to turn it red and project it ; then drop a lump
of carbonate of aihmonia into it. It will dissolve
rapidly with effervescence, and the solution will be
made blue about the crystal, and if there is enough of
it the whole solution will ultimately become blue.
The gradual solution of substances in water may be
nicely shown by filling the tank with pure water and
dropping a crystal of alum or sulphate of zinc or sul¬
phate of copper into it. Where the substance is dis¬
solved the solution will be denser, and its refractive
powers changed, which will be manifest by gently stir¬
ring it with a glass rod.
A dilute solution of copper sulphate may be placed
in the tank. With a pipette, force into the solution
some ammonia water : A dense precipitate will at first
be formed, which will afterwards be dissolved if am¬
monia enough has been added, leaving the solution a
beautiful blue color. A few drops of sulphuric acid
will reproduce the precipitate and destroy the color;
and when the solution again becomes clear, a few drops
of ferrocyanide of potassium added will produce a
brownish-red bulky precipitate, which will present a
fine appearance upon the screen.
In like manner all of the characteristic reactions of
inorganic chemistry may be projected, and often with
much less expenditure of materials than would be used
if large vessels were employed to demonstrate the
same things. One who has projected a number of
these phenomena will find no difficulty in projecting
any reaction that may be observed in a test-tube.
Pictures of chemical apparatus, of processes, etc.,
will be very convenient for projection when instruction
is given in chemistry.