"Secondly, that the blackness of this ink does proceed from the fuliginosity or sooty part of the coal of the cork which is exceeding porous and light, and that this fuliginosity is nothing but an oil very much rarefied. "Thirdly, that the impregnation of saturn, which makes the invisible ink, is only a lead dissolved, and held up imperceptibly in an acid liquor, as I have said, when I spoke of this metal. "Fourthly, that the first of these liquors in a mixture of the alkali and igneous parts of quick-lime with the sulphureous substance of arsenick; for the orpin is a sort of arsenick, as I said before. "All this being granted, as no body can reasonably think otherwise, I now affirm, that the reason why the visible ink does disappear, when the defacing liquor is rubbed upon it, is that this liquor consisting of an alkali salt, and parts that are oily and penetrating, this mixture does make a kind of soap, which is able to dissolve any fuliginous substance, such as burnt cork, especially when it has been already rarefied and disposed for dissolution by aqua vitae, after the same manner as common soap, which is compounded of oil, and an alkali salt, is able to take away any spots made by grease. "But it may be demanded, why after the dissolution the blackness does disappear. "I answer, that the fuliginous parts have been so divided, and locked up in the sulphureous alkali of the liquor, that they are become invisible, and we see every day that very exact solutions do render the thing dissolved imperceptible, and without colour. "The little alkali salt which is in the burnt cork may also the better serve to joyn with the alkali of the quick-lime, and to help the dissolution. "As for the invisible ink, it is easy to apprehend how that appears black, when the same liquor, which serves to deface the other, is used upon it. For whereas the impregnation of saturn is only a lead suspended by the edges, of the acid liquor, this lead must needs revive, and resume its black colour, when that which held it rarefied is entirely destroyed; so the alkali of quick- lime being filled with the sulphurs of arsenick becomes very proper to break and destroy the acids, and to agglutinate together the particles of lead. It happens that the visible ink does disappear by reason that the parts which did render it black have been dissolved; and the invisible ink does also appear because the dissolved parts have been revived. "Quick-lime and, orpiment being mixed and digested together in water, do yield a smell much like that which happens when common sulphur is boiled in a lixivium, of tartar. This here is the stronger, because the sulphur of arsenick is loaded with certain salts that make a stronger impression on the smell. Quick- lime is an alkali that operates in this much like the salt of tartar in the other operation; you must not leave the matrass open, because the force of this water doth consist in a volatile.