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30. The Art of holding a secret Correspondence by the Means of Sympathetic Ink. The secret of the ink of sympathy consists in two waters of different virtues which, though very clear separately, become opaque and of a deep brown colour, after being mixed together. They are thus composed: a gallon of distilled vinegar, in which has been put an ounce of litharge of silver, is made to boil during half a quarter of an hour. This is the first composition. The second is made with a piece of quick lime, and a little orpiment, infused for four and twenty hours in a sufficient quantity of water: Now very clean and well-varnished earthen pots must be used for this purpose. These two liquors must be filtrated separately, and they are found perfectly transparent. Their use is in this manner: You write, with the first water, what you would not have seen, and the writing disappears, the moment it is dry; but he who receives the Letter, by running over the paper a spunge tho' ever so little humected with the second water, the writing will begin to appear in the colour of a red bordering upon black. When those waters are newly made, & care has been taken to cover the pot close, in which the quick-lime was infused, it is not necessary that the humected spunge should touch the writing to make it appear; it will be sufficient to hold it over ^ [[at]] a little distance. It has been frequently seen, that lime-water is so efficacious, that, after [[strikethrough]] lying [[/strikethrough]] laying upon a table the letter written with the first water, and covering it over with a ream of paper, by pouring some of the second water on the upper leaf, the only that is made wet, its virtue will penetrate through the thickness of the intire ream, and the writing will grow black. The ink of sympathy acts and obtains its effect through a book, and even a wall. Cheats have sometimes made use of those secrets, in order to pretend to a more than ordinary profound knowledge & sagacity, by finding [[strikethrough]] ? [[/strikethrough]] answers to questions proposed by simple & ignorant persons, on blank papers & sealed up with Care. The physical cause of these phenomena proceeds from the force of the lime-water, and this force consists in volatile spirits, which pass through bodies with an astonishing subtility, and even extend to a considerable distance Universal Mag. for Apr. 1764. p. 184. Immerge two capillary Tubes into clear water, observe the height of the water in both, then take out one and break it off where the water stood within, and immerge it again in the water to the same depth with the other, in which situation, [[strikethrough]] or if they are both suspended[[/strikethrough]] ^[[as well as in[[strikethrough]]of [[/strikethrough]] that of being]] perpendicularly suspended out of the water, the Liquor will stand highest in the longest Tube, (*) which seems to show, that the pressure of the Air at Top has some effect in this pheno [[strikethrough]] no [[/strikethrough]]menon. [[strikethrough]] under which[[/strikethrough]] in the latter case, there always hangs a quantity of the Liquor at the bottom of both Tubes to counterballance the ascended Column within. If there be take^[[n]] in the Tube a shorter column of the Liquor than will keep suspended, it may be made to rest anywhere therein by inclining the Tube, whereas by the [[underlined]] Newtonian Attraction [[/underlined]] it ought to remain at rest and fixed to the bottom, because the Tube (*) and will never rise to the Top of any one be it ever so short being