Page:The American Cyclopædia (1879) Volume IX.djvu/296

 284: INK ous solution of carbonate of soda to vhich gum arable was added. The best marking inks are now made by combining the two preparations at once, and bringing out the col- or after the application to the cloth by expo- sure to heat. A good ink is made by dissolv- ing 7 parts of carbonate of soda in 12 of water, and adding 5 parts of gum arabic, then mixing with this 5 parts of nitrate of silver liquefied in 10 of ammonia; the mixture is to be grad- ually heated to ebullition in a flask, when it becomes very dark and of the proper consis- tence. Tartaric acid is sometimes advanta- geously employed to produce tartrate of silver, as by the following process : nitrate of silver is triturated in a mortar with an equivalent of desiccated tartaric acid; water added causes crystals of tartrate of silver to separate with liberation of nitric acid ; this is neutralized by careful addition of ammonia, which also dis- solves the tartrate of silver ; the preparation is then thickened with gum, and coloring mat- ter is added at pleasure. The Italian marking ink is terchloride of gold applied to cloth mois- tened with solution of chloride of tin. The subject of indelible inks will be further treated under NITRATES. Sympathetic inks are prepa- rations which when used for writing leave no visible, or at least only colorless, marks upon the paper. These are afterward brought out in colors by exposure to heat or to moisture, or by application of other substances. By the ancients it was known that new milk or the milky sap of plants might be so used, the wri- ting with it being made visible by dusting over it a black jjowder. The property of writing made with the solution of acetate of lead to turn black by application of gaseous or liquid sulphuretted hydrogen was known in the 17th century, and ascribed to magnetic influences. The action was afterward styled sympathetic, and the name has continued to be applied to the various preparations of this nature. The materials of the common ferro-gallic inks may be used separately for a sympathetic ink, the writing being done with the sulphate of iron solution and washed over with that of the galls, as the writing of some old manuscripts is now occasionally restored. A dilute solution of chloride of copper used for writing is invisi- ble until the paper is heated, when the letters are seen of a beautiful yellow, disappearing with the heat that developed them. The salts of cobalt, as the acetate, sulphate, nitrate, and chloride, possess a similar property, the letters appearing blue. The addition of a salt of nick- el renders them green. The magic or chemical landscapes are made by the use of these me- tallic salts. The sky being painted with salt of cobalt alone, and foliage with the same mixed with nickel, the application of heat brings them out in their appropriate colors. A winter landscape, with the bare trees and ground covered with snow, may thus by acces- sion of warmth be clothed with the green hues of summer. Lithographers employ an ink for tracing designs on paper, which are to be trans- ferred to stone, composed of shell lac 1-J oz., soap 2 oz., white wax 3 oz., tallow 1 oz., a strong solution of gum sandarach 3 tablespoon- fuls, and lampblack ; also an ink for taking im- pressions from engraved plates, which are to be transferred to stone, composed of tallow, wax, and soap, each 4 oz., shell lac 3 oz., gum mastic 2$- oz., black pitch 1-J- oz., and lamp- black. Printing ink is a preparation very dif- ferent from any of the inks used for other purposes ; and its manufacture demands no lit- tle skill and experience. It should be of a soft adhesive character, readily attaching itself to the surface of the types, and as easily trans- ferred to the paper pressed upon them, con- veying in a clear tint the exact stamp. Thus spread in a thin film and pressed into the pa- per, it should quickly dry, and at the same time be so incorporated with the paper as not to be removable by mechanical means, while its composition insures for it durability and a power to resist the action of chemical agents as well as atmospheric influences. While dis- posed to dry readily on being applied to paper, it should retain its softness in the mass and while excluded from the air, and in this condi- tion undergo no change. Its ingredients must not be of a corrosive nature to injure the roll- ers employed in spreading it. The appearance of good ink is glossy and somewhat oily ; its texture smooth without grains ; and its te- nacity such as to cause it to adhere to the finger pressed against it, and yet leave but a short thread suspended from a portion taken out. The usual materials employed in its manu- facture are linseed oil, rosin, and coloring mat- ters. Eosin oil is largely used for some of the cheaper inks. For the best inks the linseed oil is selected of the purest quality, and this is clarified by digesting it for some hours with dilute sulphuric acid at a temperature of 212, and then washing it with hot water ; it will then dry much more quickly. The oil is then boiled, and the inflammable vapors that rise are ignited, and when they have burned a few minutes a cover is placed over the vessel, extin- guishing the flame. The boiling is not stopped until a drop taken out and placed on a cold sur- face is covered with a film as it cools. A portion of rosin is then dissolved in the oil, the quan- tity depending on the degree of stiffness the ink may require; that for books and strong, stiff paper bearing more rosin, and receiving in consequence more gloss, than the ink for newspapers. The degree of viscidity given to the oil should also have reference to the use required of the ink. For letterpress printing soap should be added to the materials to enable the ink to be taken up clearly from the types without smearing. The best kind is yellow rosin soap, cut up into slices, dried, reduced to powder, and incorporated with the oil and rosin, or varnish, and before mixing placed again over the fire to expel any remaining moisture. Lampblack is almost universally