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 then the salts will re-crystallize, each kind preserving its own proper form and color.  Some occur in groups, some as single crystals.  If carefully protected from dust, these form extremely pretty ornaments for the parlor.

Alum Baskets.

These may be prepared by dissolving alum in water in such quantity that at last the water can take up no more, and the undissolved alum lies at the bottom of the vessel.  The solution thus obtained is called a saturated one.  Then procure a common ornamental wire basket, and suspend it in the solution, so as to be well covered in every part.  There should be twice as much solution as will cover the basket.  The wires of the basket should be wound with worsted, so that the surface may be rough.  Leave it undisturbed in the solution, and gradually the crystals will form all over the surface.  Before putting in the basket, it is best to further strengthen the solution by boiling it down to one half, after which it should be strained.

The Lead-Tree.

Dissolve half an ounce of acetate of lead in six ounces of water.  The solution will be turbid, so clarify it with a few drops of acetic acid.  Now put the solution into a clean phial, nearly filling the phial.  Suspend in the solution, by means of a thread attached to the cork, a piece of clean zinc wire.  By degrees, the wire will become covered with beautiful metallic spangles, like the foliage of a tree.