INFUSIONS are solutions of some of the principles of vegetables, generally in water, but occasionally in other vehicles. When water is employed it may either be hot or cold. It is customary to use warm water, but in many instances cold is preferable. Sometimes alcohol is added, after straining, to assist in keeping the infusion, or to increase its powers. Hard water should, if possible, be avoided in the preparation of infusions.
INK. The writing ink of the ancients was essentially different from that which is now employed. Its basis was finely divided char coal, mixed with some mucilaginous or adhe sive fluid : it was much less destructible than modern writing ink, and somewhat more re sembled printer's ink. Writing ink is now a chemical compound, and not a mere mechan ical mixture. Its basis is proto-gallate and proto-tannatc of iron, which by oxidisement become per-gallate and per-tfinnate ; and it is owing to the oxygen of the air effecting this change gradually that recent writing is of a comparatively light colour, and that it subse qnently becomes black. Many processes have been given for preparing writing ink. The common ingredients are galls and sulphate of iron ; in fact, while printers' ink may be con sidered as a black paint, writing ink may be regarded as a black dye. The following, which is recommended by Mr. Brande, gives, he says, an excellent ink, and it possesses the merit of greater simplicity than most others : —Aleppo galls, bruised, 6 ounces ; sulphate of iron, 4 ounces ; gum arabic, 4 ounces ; wa ter, 6 pints. Boil the galls in the water, then ' add the other ingredients, and keep the whole in a well-stopped bottle, occasionally shaking it. In two months strain and pour off the ink into glass bottles, to be well corked. To prevent mould, add one grain of corrosive sublimate, or three drops of creosote, to each pint of ink. Modern writing ink, unlike the ancient, is readily destroyed by chlorine, acids, and alkalis. Red, blue, and other coloured inks have nearly the same chemical properties as black ink, and depend for their colour on the kind of ingredients employed. A Mayic Sand has been recently introduced, to 'write without ink,' and to avoid spilling and spot ting. The magic consists probably in sand
being saturated with ink.
Indian Ink.—The cakes of this ink are made of lamp-black and size, or animal glue, with the addition of perfumes or other sub stances not essential to its quality as an ink. It is used in China with a brush, both for wri ting and for painting upon paper of Chinese manufacture. It is used in Europe for designs in black and white, in which it possesses the advantage of affording various depths of shade, according to the degree of dilution with water.
Printers' Ink is of two kinds : for letter press printing and for copper plate printing. Printers' ink is prepared by boiling linseed or nut oil in an iron pot ; and, if it does not take fire of itself, it is kindled, and suffered to burn for about half an hour ; the flame is then extinguished by closely covering the vessel, and the oil is by this operation found to have acquired the necessary drying quality, after being again boiled. It is then mixed with a proper quantity of lamp-black, when black ink is required ; if red ink be required, the colour ing matter employed is vermillion for finer works. Copper-plate printers' ink is made with oil which is less boiled, and the charcoal used is Frankfort black, made from vine twigs. Marking Ink is employed for marking linen : it is a solution of nitrate of silver, written with a pen upon the fabric to be marked after it has been moistened with an alkaline solution, as potash or soda. By this process oxide of sil ver is precipitated upon and combines with the cloth so as to be scarcely removeable by any reagent which does not also destroy its texture. There are other chemical prepara tions used for this purpose.
Sympathetic Inks are such as are invisible until heat is applied, and then, by the chemi cal change induced, the writing becomes visi ble. The most remarkable of these is that prepared from cobalt, called Iiellot's Sympa thetic Ink, which is a chloride of the metal. When the written paper is held to the fire so as to evaporate the water,the letters become green.