Dissolve zaffre, in powder, in aqua regia, for twenty-four hours. Pour the liquor off, and the same quantity of common water, and keep it in a bottle well corked. This ink will not be visible till exposed to the fire or the sun; and will again be invisible when it becomes cold. _Invisible Violet Ink._ Express the juice of lemons, and keep it in a bottle well corked. Use the violet infusion to make the writing visible. _Invisible Grey Ink._ Mix alum with lemon-juice. The letters written with this ink will be invisible till dipped in water. * * * * * We now present our readers with a variety of amusing experiments, which may be performed by the foregoing inks; and they will, probably, suggest others equally amusing and useful. _A Secret Correspondence by means of Invisible Ink._ A person wishing to carry on a correspondence with another, and who is fearful of having his letter opened, or intercepted, can adopt the following plan: Write any unimportant matter with common ink, and let the lines be very wide apart: then between these lines write the communication you wish to make, with any of the above invisible inks you can most readily procure. Your correspondent is to be previously apprized of the method of making the characters visible: and writing in common ink will serve to lull the suspicions of those who might intercept the letter, and who, not finding any thing important in it, will either forward or keep it. In either case there can be no danger, as the writing will not be visible without the proper application. _The Mysterious Writing._ Write on a piece of paper with common ink any question; then underneath it write the answer either in invisible silver ink, or the invisible green ink, made with zaffre and aqua regia, described in pages 24 and 25. You give this paper to your friend, and tell him to place it against the wall, or on his dressing-table, keeping the door locked, that he may be sure no person has entered his room: he will next day find the answer written on it. _The Restored Flowers._ Make a bouquet of artificial flowers; the leaves should be formed of parchment. Dip the roses in the red invisible ink, the jonquilles in the yellow, the pinks in the violet, and the leaves in the green ink. They will all appear white; and you show them to the company, observing, that you will restore them to their natural colours, and desiring any person to fix any private mark on them he pleases, that he may be sure there is no deception. You then, unperceived by the company, dip them in the revivifying liquor, used to make the yellow ink visible, described in page 24, and, drawing them gently out, that the liquor may drop, and the flowers have time to acquire their colours, you present them to the company, who will see, with surprise, that they each appear in their natural colours. _Winter changed to Spring._