e nitric acid, the fluid will
again become as clear as pure water.

_To Make a Splendid Scarlet._

Again take some solution of sulphate of copper. Add to it a little
solution of bichromate of potash. Then add a little solution of nitrate
of silver, and there is produced a splendid scarlet color.

_To Make a Deep Blue._

Now, take a nearly colorless solution of sulphate of iron, and drop into
it, slowly, a small quantity of solution of yellow prussiate of potash.
This will induce a beautiful deep blue, quite different from the blues
that are produced from copper salts.

_To Make a Yellow Color._

Take a solution of acetate of lead, and add a few drops of solution of
iodide of potassium, and a most lovely canary-yellow color is produced.

_Invisible Inks._

Nearly all those experiments which result in the production of color may
be performed in another way, and be then applied to the purposes of
secret writing. Thus:

Write with dilute solution of sulphate of copper. The writing will be
quite invisible, but become blue when held over the vapor of liquid
ammonia.

Write with the same solution, and wash the paper with solution of yellow
prussiate of potash, and the writing, previously invisible, will become
brown. If you choose you may reverse this method, writing with solution
of the prussiate of potash, and washing the paper with solution of the
copper salt.

Write with solution of sulphate of iron, and the writing will again be
invisible. Wash it over with tincture of galls, and it becomes black.

Write with sulphate of iron, and use a wash of yellow prussiate of
potash, and the writing will come out blue. This experiment may likewise
be reversed, and with similar result.

_How to Copper a Knife-Blade._

Make a rather strong solution of sulphate of copper. Let a clean and
polished piece of steel or iron, such as the blade of a knife, stand in
it for a few minutes, and the iron will become covered or encrusted with
a deposit of pure copper.

_To Make Beautiful Crystals._

Dissolve, in different vessels, half an ounce each of the sulphates of
iron, zinc, copper, soda, alumina, magnesia, and potash. The solutions
can be made more rapidly by using warm water. When the salts are all
completely dissolved, pour the whole seven solutions into a large dish,
stir the mixture with a glass rod, then place it in a warm place, where
it will not be disturbed. By degrees, the water will evaporate, and th