Green Sympathetic Ink. — Dissolve cobalt in nitro-muriatic acid, and write with the solution. The letters will be invisible till held to the fire, when they will appear green, and will disappear completely again when removed into the cold. In this manner they may be made to appear and disappear at pleasure. A very pleasant experiment of this kind is to make a drawing representing a winter scene, in which the trees appear void of leaves, and to put the leave) on with this sympathetic ink ; then upon holding the drawing near to the fire, the leaves will begin to appear in all the verdure of spring, and will very much surprise those who are not in the secret.
Blue Sympathetic Ink. — Dissolve cobalt in nitric acid ; precipitate the cobalt by potass; dissolve this precipitated oxide of cobalt in acetic acid, and add to the solution one-eighth of common salt. This will form a sympathetic ink, that, when cold, will be invisible, but will appear blue by heat.
13. Lithographic lnk.—As the art of lithography is treated of generally under its initial letter in this work, we shall in this place simply notice the autographic ink, suitable for transferring to stone the writings or drawings which have been executed on paper prepared for the purpose. This ink ought to be and somewhat thicker than that used for drawing or writing imme diately on stone ; so that when it is dry on the paper, it may be still sufficiently viscous to cause it to adhere to the stone by simple pressure. The follow ing is the mode of preparing it : dry soap, 100 drachms ; white wax, pure, 100 ditto; mutton suet, 30; shellac, 50; mastic 50; and lamp-black, (fine, from the combustion of resin,) 30 to 35 drachms. These are to be melted over a brisk fire in a metal pot over a chafing dish ; first melt the soap and the suet, then add the shellac very gradually ; next the soda, a little at a time, and after this the mastic, taking care to stir it from time to time with a wooden spatula ; lastly the lamp-black, stirring it all the time. When these materials are well incorporated, they are poured on a plate of cast iron, made warm, and oiled, in order that the composition may be easily detached from it. Ledges of wood are put on the plate to keep the thickness of the composition uniform, which when congealed, but still warm, is cut into sticks, like Indian ink.
14. Indian Ink.—The genuine article, which is used by the Chinese for writing with a brush, as well as for painting upon their soft, flexible paper, is ascertained by experiment and information to consist of lamp-black and size, or animal glue, with the addition of perfumes or other substances not essential to its quality as an ink. The fine soot from the flame of a lamp or candle, received by holding a plate over it, mixed with clean size from shreds of parch ment of sheep and goat skins, will make an ink equal to that imported. We have been in the habit of using, during many years, both the genuine and the imitation Indian ink indifferently, not being able to discover that either merits a preference.
15. Lithographic Drawing Ink.—This composition is the same as the ink used for writing upon stone and lithographic transfer paper, already described ; the artist rubbing it down usually upon a slab, as Indian ink, for his use.
16. Letter-press Printing Ink is a very smooth and jet black oil paint. The consistence and tenacity of the oil in this composition are greatly increased, and its greasiness diminished, by means of fire. Linseed oil, or nut oil, is made choice of for this use. The nut oil is supposed to be the best, and is accordingly preferred for the black ink, though the darker colour it acquires from the fire renders it less fit for the red. It is said, that the other expressed oils cannot be sufficiently freed from their unctuous quality. Ten or twelve gallons are set over the fire in an iron pot, capable of holding at least half as much more ; for the oil swells up greatly, and its boiling over into the fire would be very dangerous. When it boils, it is kept stirring with an iron ladle; and if it do not of itself take fire, it is kindled with a piece of flaming paper or wood. It is found that, mere boiling, without setting it on fire, does not give it a sufficiency of the drying quality. The oil is suffered to burn for half an hour or more, and is then extinguished by covering the vessel close, and excluding the air. The boiling is continued with a gentle heat, till the oil has attained the proper consistency, in which state it is called varnish. It is neces sary to have two kinds of this varnish, a thicker and a thinner, (from the greater or less boiling it has received,) which are occasionally mixed together, to suit different purposes ; for that which answers well in hot weather, becomes too thick in cold, and large characters or type do not require such stiff ink as the small. The thickest varnish, when cold, may be drawn into threads, like glue • and the workmen taking out small quantities, from time to time, judge of the proper degree of boiling required, by testing its tenacity in that manner. The oil loses by the boiling about one-eighth of its weight. The varnish readily mingles with fresh oil, and it will unite with mucilages, into a mass that is after wards diffusible in water. About one-seventh part, by weight, of lamp-black is added to the varnish, to give it the depth of colour. Boiled with caustic alkali, a soapy compound is formed, and printers availing themselves of this fact, are in the habit of cleaning their types by soap-makers' lees and a brush. It is said that when very new oil is used in ,making ink, it does not readily dry without the addition of litharge, or the oil of turpentine, and these addi tions (which are not necessary in old oil) cause it to stick very hard to, and clog up the types.