"Take an ounce of quick-lime, and half an ounce of orpin, powder and mix them, put your mixture into a matrass, and pour upon it five or six ounces of water, that the water may be three fingers breadth above the powder, stop your matrass with cork, wax, and a bladder; set it in digestion in a mild sand heat ten or twelve hours, shaking the matrass from time to time, then let it settle, the liquid becomes clear like common water. "Burn cork, and quench it in aqua vitae, then dissolve it in a sufficient quantity of water, wherein you shall have melted a little gumm arabick, in order to make an ink as black as common ink. You must separate the cork that can't dissolve, and if the ink be not black enough, add more cork as before. "Get the impregnation of saturn made with vinegar, distilled as I have shewn before, or else dissolve so much salt of saturn as a quantity of water is able to receive: write on paper with a new pen dipt in this liquor, take notice of the place where you writ, and let it dry, nothing at all will appear. "Write upon the invisible writing with the ink made of burnt cork, and let it dry, that which you have writ will appear as if it had been done with common ink. "Dip a little cotton in the first liquor made of lime and orpin, but the liquor must be first settled and clear; rub the place you writ upon with this cotton and that which appeared will presently disappear, and that which was not seen will appear. ANOTHER EXPERIMENT. Take a book four fingers breadth in bigness, or bigger if you will: write on the first leaf with your impregnation of saturn, or else put a paper that you have writ upon between the leaves; turn to t' other side of the Book, and having observed as near as may be the opposite place to your writing, rub the last leaf of the book with cotton dipt in liquor made of quick- lime and orpin, nay and leave the cotton on the place clap a folded paper presently upon it, and shutting the book quickly, strike upon it with your hand four or five good strokes; then turn the book, and clap it into a press for half a quarter of an hour; take it out and open it, you'll find the place appear black, where you had writ with the invisible ink. The same thing might be done through a wall, if you could provide something to lay on both sides, that might hinder the evaporation of the spirits. REMARKS. "These operations are indeed of no use, but because they are somewhat surprizing, I hope the curious will not take it ill, that I make this small digression. "It is a hard matter to explicate well the effects I have now related, nevertheless I shall endeavour to illustrate them a little, without having recourse to sympathy and antipathy, which are general terms, and do not explicate nothing at all; but before I begin, we must remark several things. "The first is, that it is an essential point to quench the coal of cork in aqua vitae, that the visible ink may become black with it.