The second, of those which do not appear so long as they are kept close, but soon become visible on being exposed to

the air.

The third, of such as become apparent by strewing or sifting some very fine powder over them.

The fourth, of those which do not become visible till they are exposed to the fire, or heated.

The fifth, like the fourth, of such as appear by heat, but disappear again when the paper becomes cold, or has had a sufficient time to imbibe the moisture of the air.

Sympathetic Inks of the First Class.-Put some litharge into strong distilled vinegar, and let it stand for twenty-four hours; then strain it off, and, after it is quite settled, put it into a bottle closely corked, and preserve it for use. Having done this, put into a pint bottle two ounces of quicklime, one ounce of orpiment in powder, and as much water as will rise two or three fingers' breadth above them; and when the solution is made, pour the liquid gently off, and let it stand in the sun for two or three days, observing to turn it five or six times each day.

When these liquors are ready for use, any letters written by the first, being exposed to the vapours of the second, will quickly become visible; and if you would have them disappear again, you must draw a sponge, or pencil, dipt in aquafortis, or spirit of nitre, over them: and if, after this, you would have them appear again, stay till the paper is quite dry, and then pass the vivifying liquor, made of the solution of orpiment, over them, as before.

Another Ink of this Class.-Dissolve bismuth in the nitrous acid, and any letters written with this ink will become quite black, by being exposed to the vapour of liver of sulphur, which is of so penetrating a nature, that it will act upon the ink through a quire of paper, or even the slight partition of a room.

A Sympathetic Gold Ink of the Second Class.-Put as much gold into a small quantity of aqua-regia as will dissolve it, and then dilute it with two or three times as much distilled water.

Also dissolve, in a separate vessel, fine pewter in aquaregia; and when it is well saturated, add to it an equal quantity of distilled water.

Then, if any characters be written with the solution of gold, put them in the shade till they become quite dry, and they will not appear for the first seven or eight hours, but if you dip a pencil, or small fine sponge, in the solution of pewter, and draw it lightly over the invisible characters, they will presently appear of a purple colour.

The purple colour of these letters may be effaced again, by

wetting them with aqua-regia, and may be produced a second time, by passing the solution of pewter over them as before.

A Sympathetic Ink of the Second Class.-Dissolve fine silver in aqua-fortis, and add some distilled water to the solution, in the same manner as in the gold ink; then, whatever is written with this ink, will remain invisible for three or four months, if it be kept close from the air; but if it be exposed to the sun, it will appear in about an hour, of a gray colour, like that of a slate.

Sympathetic Inks of the Third Class,-or such as become visible by having any fine powder strewed over them,--may be composed of the glutinous and colourless juice of any vegetable, the milk of animals, and several other sub

stances.

Sympathetic Inks of the Fourth Class,-are made by diluting acid of vitriol with about three times its weight of common water, or as much as will prevent it from corroding the paper. The juice of lemons, or onions, will answer the same purpose; but either of them requires more heat than the first, and will not keep so long.

A Green Ink of the Fifth Class.-Take zaffre in powder, and let it remain dissolved in aqua-regia for twenty-four hours; after which pour the liquor off clear, and, adding to it as much common water, keep it in a bottle well corked. Then, if any characters be written with this ink, and exposed to the fire, or strong rays of the sun, they will appear of a lively green.

It is the peculiar property of this ink, that as soon as the paper becomes cold again, the letters will disappear; and this alternate appearance and disappearance may be repeated a great number of times, provided the heat be not too great.

Other Sympathetic Inks.

A Yellow Ink of this kind may be made, by steeping the flowers of marigolds seven or eight days in clear distilled vinegar, and then pressing them out, and keeping the liquor well corked in a bottle for use.

For a Red invisible Ink,--take the pure spirit of vitriol, or that of nitre, and add to it eight or ten times as much water, according as you would have it more or less red.

For a Green Ink of this sort,-dissolve salt of tartar, the clearest and driest you can procure, in a sufficient quantity of river water; and for a Violet sympathetic Ink, express the juice of lemons, and keep it in a bottle well corked.

Then, if any characters be written with one of these inks, they will appear in their proper colours, the paper having been dipped in the following liquor.

Take a sufficient quantity of the flowers of pansies, or

common violets, and after adding some water to them, strain the liquor through a cloth, and keep it in a bottle for use.

A Sympathetic Ink which appears by being wetted with Water.

Mix alum with a sufficient quantity of lemon juice; then, if any letters or characters be written with this mixture, they will be invisible till they are wetted with water, which will make them appear of a grayish colour, and quite transparent.

Or, you may write with a strong solution of roch-alum only, and when the writing is dry, pour a small quantity of water over it, and it will appear of a white colour, like that of the paper before it was wetted.

Also all saline liquors, such as vitriolic, nitrous, and marine acids, diluted with water, the liquor of fixed vegetable alkalis, and even vinegar, will produce the same effect.

If a little aqua-fortis be mixed with the water, the writing will dry well, and not run out of its form when the paper is wetted.

A curious Recreation with Sympathetic Ink, called the Book of Fate.

Make a book, consisting of seventy or eighty leaves, and in the cover at the end of it, let there be a case which opens next to the back, that it may not be perceived. At the top of each right-hand page, write any question you please; and at the beginning of the book, let there be a table of those questions, with the number of the pages in which each is to be found. Then write with common ink on separate papers, each about half the size of the pages, the same questions that are in the book; and under each of them, write the answer with the ink made with the litharge of lead, or the solution. of bismuth.

Soak a double paper in the vivifying ink, made of quicklime and orpiment, or the liver of sulphur; and just before you make the experiment, place it in the case that is in the cover of the book.

Having done this, deliver some of the papers on which the questions are written, to the company; and after they have chosen such as they wish to have answered, let them put them into those leaves where the same questions are contained; then shutting the book for a few minutes, the sulphureous spirit, with which the paper in the cover of the book is impregnated, will penetrate the leaves, and make the answer visible, which will be of a brown colour, and more or less deep, in proportion to the time the book has been closed.

A curious Recreation, called the Transcolorated Writing. Write on a paper, with a violet-coloured liquor, as many letters or words as you please, and ask any person which he will choose to have the writing,-yellow, green, or red. When he has made his choice, have a sponge ready with three sides, which you can easily distinguish, and dip each of its sides in one of the three sympathetic inks; then draw the side of the sponge which corresponds to the colour the person has chosen, over the writing, once only, and it will directly change to the colour required.

An Experiment with Sympathetic Ink, called the Oracular Letters. Write on several slips of paper different questions, and such as may be answered by the name of some person: for example, Who is the merriest man in company?-Answer, Mr. ***. To whom will Miss *** be married?-Answer, To Mr. ***. These questions are to be written in the sympathetic ink of the fourth class, and exposed to the fire, and the answers written in the same ink, and left invisible. The papers are then to be folded in the form of letters, and in such a manner, that the part where the name is written shall be directly under the seal; in which case, the heat of the wax will make it visible. Then, if the letter be given to the person who requires the answer, he will find it plainly

written.

An Experiment with Sympathetic Ink, called Winter changed to Spring.

Take a print which represents winter, and trace over the trees, plants, and ground, with the green sympathetic ink; observing to make some parts deeper than others, according to their distance. When those parts are dry, paint the other objects in their natural colours; then put the print into a glazed frame, and cover the back of it with a paper, pasted over its border only. When this print is exposed to the heat of a moderate fire, or to the warm rays of the sun, all the grass and foliage will turn to a pleasing green; and if a yellow tint be given to some parts of the print, before the sympathetic ink be drawn over it, the green will be of different shades, and the scene, that a minute before represented Winter, will now be changed into Spring. When this print is placed in the cold, Winter will appear again, and be again driven away by the warm rays of the sun; and this alternate change of seasons may be repeated as often as you please, provided the print be not made too hot.

A remarkable Experiment, called the Revivified Rose.

Take a rose that is quite faded, and throw in some common sulphur in a chafing dish of hot coal. Hold the rose over the fumes, and it will become quite white; then dip it into a basin of water, and giving it to any one, tell him to put it into his box or drawer, and after locking it, to give you the key. About five or six hours afterwards, return him the key, and when he unlocks his drawer, instead of the white rose he put into it, he will find one perfectly red.

How to Write on Glass by means of the Rays of the Sun.

Dissolve chalk in aqua-fortis, to the consistence of milk, and add to it a strong solution of silver; keep this liquor in a glass decanter, well stopped, and cutting out from a paper the letters you wish to appear, paste it on the decanter, and place it in the sun, in such a manner, that its rays may pass through the spaces cut out of the paper, and fall on the surface of the liquor; then will that part of the glass through which the rays pass be turned black, while that under the paper will remain white; but particular care must be taken that the bottle be not moved during the time of the opera

tion.

To produce different Colours, by pouring a colourless Liquor into a clean Glass.

Take a strong solution of quicksilver, made with spirit of nitre; dilute it with water, and pour it into a hot glass, rinsed in strong spirit of sea-salt, and it will instantly become coloured. Or, if a solution of silver, made with spirit of nitre, considerably diluted, be poured into a glass, prepared in the manner above-mentioned, it will produce the same effect. And if you pour hot water upon new-made crocus metallorum, and put it into a clean glass, rinsed with any acid, it will produce an orange colour.

To produce a Colour which appears and disappears by the Influence of the Air.

Put into a decanter some volatile spirit, in which you have dissolved copper filings, and you will have a fine blue tincture; and if the bottle be stopped, the colour will soon return again; and this experiment may be repeated a considerable number of times.