fire, and afterwards filter it while hot. Put it again over the fire, and dissolve in it, first, half an ounce of gum arabic, and afterwards of alum and white sugar, each half an ounce.

Printing Ink.

Printers' ink is a black paint composed of lampblack and linseed or suet oil boiled, so as to acquire considerable consistence and tenacity. The art of preparing it is kept a secret; but the obtaining good lamp-black appears to be the chief difficulty in making it.

The ink used by copper-plate printers, differs from the last only in the oil not being so much boiled, and the black which is used being Frankfort black.

Sympathetic Inks.

Sympathetic inks are such as do not appear immediately after they are written with, but which may be made to appear at pleasure, by certain means. A variety of substances have been used for this purpose. We shall describe the best

of them.

1. Dissolve some sugar of lead in water, and write with the solution. When dry, no writing will be visible. When you want to make it appear, wet the paper with a solution of alcaline sulphuret (liver of sulphur), and the letters will immediately appear of a brown colour. Even exposing the writing to the vapours of these solutions will render it apparent.

2. Write with a solution of gold in aqua regia, and let the paper dry gently in the shade. Nothing

will be seen; but draw a sponge over it, wetted with a solution of tin in aqua regia; the writing will immediately appear of a purple colour.

3. Write with an infusion of galls, and when you wish the writing to appear, dip it into a solution of green vitriol; the letters will be black.

4. Write with diluted sulphuric acid, and nothing will be visible. To render it so, hold it to the fire, and the letters will instantly appear black.

5. Juice of lemons, or onions, a solution of sal ammoniac, green vitriol, &c. will answer the same purpose, though not so easily, or with so little heat.

6. Green sympathetic ink. Dissolve cobalt in nitro muriatic acid, and write with the solution. The letters will be invisible till held to the fire, when they will appear green, and will disappear completely again when removed into the cold. In this manner they may be made to appear and disappear at pleasure.

A very pleasant experiment of this kind is to make a drawing representing a winter scene, in which the trees appear void of leaves, and to put the leaves on with this sympathetic ink; then, upon holding the drawing near to the fire, the leaves will begin to appear in all the verdure of spring, and will very much surprise those who are not in the secret.

7. Blue sympathetic ink. Dissolve cobalt in nitric acid; precipitate the cobalt by potash; dissolve this precipitated oxyd of cobalt in acetic acid, and add to the solution one-eighth of common salt.

This will form a sympathetic ink, that, when cold, will be invisible, but will appear blue by heat.

REMOVING STAINS.

To remove Ink Stains.

The stains of ink on cloth, paper, or wood, may be removed by almost all acids; but those acids are to be preferred which are least likely to injure the texture of the stained substance. The muriatic acid, diluted with five or six times its weight of water, may be applied to the spot, and, after a minute or two, may be washed off, repeating the application as often as may be found necessary. But the vegetable acids are attended with less risk, and are equally effectual. A solution of the oxalic, citric (acid of lemons), or tartareous acids, in water, may be applied to the most delicate fabrics without any danger of injuring them; and the same solutions will discharge writing, but not printing ink. Hence they may be employed in cleaning books which have been defaced by writing on the margin, without impairing the text. Lemon-juice, and the juice of sorrels, will also remove ink stains, but not so easily as the concrete acid of lemons, or citric acid.

To remove Iron Stains.

These may be occasioned either by ink stains, which, on the application of the soap, are changed ́into iron stains, or by the direct contact of rusted iron. They may be removed by diluted muriatic acid, or by one of the vegetable acids, already mentioned. When suffered to remain long on cloth, they become extremely difficult to take out, because the iron, by repeated moistening with water, and exposure to the air, acquires such an addition of oxygen, as renders it insoluble in acids. It has

been found, however, that even these spots may be discharged, by applying first a solution of an alcaline sulphuret, which must be well washed from the cloth, and afterwards a liquid acid. The sulphuret, in this case, extracts part of the oxygen from the iron, and renders it soluble in diluted acids.

To remove the Stains of Fruit and Wine.

These are best removed by a watery solution of the oxygenated muriatic acid, or by that of oxygenated muriate of potash or lime, to which a little sulphuric acid has been added. The stained spots may be steeped in one of these solutions till it is discharged; but the solution can only be applied with safety to white goods, because the uncombined oxygenated acid discharges all printed and dyed colours. A convenient mode of applying the oxygenated acid, easily practicable by persons who have not the apparatus for saturating water with the gas, is as follows: Put about a table-spoonful of muriatic acid (spirit of salt) into a tea-cup, and add to it about a tea-spoonful of powdered manganese; then set this cup in a larger one filled with hot water; moisten the stained spot with water, and expose it to the fumes that arise from the tea-cup. If the exposure be continued a sufficient length of time, the stain will disappear.

To remove Spots of Grease from Cloth.

Spots of grease may be removed by a diluted solution of potash; but this must be cautiously applied, to prevent injury to the cloth. Stains of white wax, which sometimes fall upon the

clothes from wax candles, are removable by spirits of turpentine, or sulphuric ether. The marks of white paint may also be discharged by the lastmentioned agents.

To take Spots of Grease out of Books, Prints, or Paper.

After having gently warmed the paper that is stained with grease, wax, oil, or any other fat body, take out as much as possible of it by means of blotting paper; then dip a small brush in the essential oil of turpentine, heated almost to ebullition (for when cold it acts only very weakly), and draw it gently over both sides of the paper, which must be carefully kept warm. This operation must be repeated as many times as the quantity of the fat body imbibed by the paper, or the thickness of the paper, may render necessary. When the greasy substance is entirely removed, recourse may be had to the following method to restore the paper to its former whiteness, which is not completely restored by the first process. Dip another brush in highly rectified spirit of wine, and draw it in like manner over the place which was stained, and particularly round the edges, to remove the border that would still present a stain. By employing these means with proper caution, the spot will totally disappear, the paper will resume its original whiteness, and if the process has been employed on a part written on with common ink, or printed with printer's ink, it will experience no alteration.