Dr. Lewis and others have recommended vinegar as the menstruum in preference to water; on which, as well as the sulphate of copper of Mr. Ribaucourt, Dr. Ure acutely observes, "l have found an inconvenience in the use of either, which, though it does not relate to the goodness of the ink, is sufficiently great, in their practical exhibition, to forbid their use. The acid of the vinegar acts so strongly upon the pen, that it very frequently requires mending; and the sulphate of copper has a still more unpleasant effect upon the pen-knife. It seldom happens that when a pen requires mending, that the ink is wiped very perfectly from it; and often, when the nib is only to be taken off, it is done without wiping at all. Whenever this is the case, the ink immediately deposits a film of copper upon the knife, and by superior electric attraction of the sulphuric acid, a correspondent portion of the edge of the knife is dissolved, and is by this means rendered incapable of cutting until it has been again set upon the hone.

4. Copying Ink, - for transferring writings to thin unsized paper is prepared by the simple addition of a little sugar to common writing ink. The powerful affinity of water to sugar, causes the damp paper to immediately absord the ink by the powerful aid of the copying-machine. See Copying Press.

5. Indelible Ink. - It is well known that common writing ink may be easily obliterated by the application of oxymuriatic acid, or aqueous chlorine; it therefore becomes an important object to employ those substances which shall be indestructible by the application of any process that will not at the same time destroy the material upon which it shall be used. For this purpose Mr. Close has recommended twenty-five grains of copal in powder, dissolved in two hundred grains of oil of lavender, by the assistance of a gentle heat, and then mixed with two and a half grains of lamp-black, and half a grain of indigo. A little oil of lavender, or of turpentine, may be added if the ink be too thick. Mr. Sheldrake suggests that a mixture of genuine asphaltum, dissolved in oil of turpentine, amber varnish, and lamp-black, would be superior to the foregoing. For many common purposes the introduction of a little lampblack into the composition of common ink will answer sufficiently. In the Journal of the Royal Institution the following process of making an indelible ink has been recommended: - Let a saturated solution of indigo and madder in boiling water be made in such proportion as to give a purple tint; add to it from one-sixth to one-eighth of its weight of sulphuric acid, according to the thickness and strength of the paper to be used.

This makes an ink which flows pretty freely from the pen; and when writing which has been executed with it is exposed to a considerable but gradual heat from the fire, it becomes completely black, the letters being thoroughly burnt in, and charred by the action of the sulphuric acid. If the acid has not been used in sufficient quantity to destroy the texture of the paper, and reduce it to the state of tinder, the colour may be discharged by the oxymuriatic and oxalic acids, and their compounds, though not without great difficulty. When the full proportion of acid has been employed, a little crumpling and rubbing of the paper reduces the carbonaceous matter to powder; but by putting a black ground behind them they may be preserved; and thus a species of indelible writing ink is procured, (for the letters are in a manner stamped out of the paper) which might be useful for some purposes, perhaps for the signature of bank notes. (See the inks for marking linen.) When writing with common ink has been effaced by means of aqueous chlorine, the vapour of sulphuret of ammonia, or immersion in water impregnated with this sulphuret, will render it again legible.

Or if the paper that contained the writing be put into a weak solution of prussiate of potash, and when it is thoroughly wet, a little suphuric acid be added to the liquor, so as to render it slightly acidulous, the same purpose will be answered.

6. Red Inks. - Steep one pound of powdered Brazil wood, and one ounce of powdered cochineal, in two gallons of vinegar. Let them macerate for twelve hours. Then put the whole on to a slow fire, with four ounces of alum, and one ounce of lump-sugar, in a pewter vessel, until a good red colour is obtained. When the ink is settled it may be decanted, pouring it through a piece of cloth into bottles, and preserved for use. Cochineal is a very expensive article, and although it is usual to recommend its introduction into red ink, on account of the richness of its colouring matter, we know from experience that it is by no means a necessary ingredient, and that a beautiful and very permanent red may be obtained without it. We have before us a recipe, written fifteen years ago in the identical red ink it is descriptive of the process of making; the colour is extremely beautiful, nor in the least deteriorated by the lapse of time. The process differs only from the above recipe in using no cochineal, but it contained as much alum as the liquid would dissolve in its cold state; the Brazil wood was macerated during a night, and was very gently boiled in an unglazed earthen pot on the next day, for half an hour; afterwards one pound of Senegal gum, and a quarter of a pound of lump-sugar, were added.

With so large a proportion of mucilage as just mentioned, and so much alum, it is probable that vinegar may be dispensed with, and that water alone, which is a good menstruum for the colouring matter of Brazil wood, will answer very well, and materially cheapen the ink. Care should be taken to discontinue the boiling after the full bright red is obtained, as by continuing it the colour darkens; also, that copper or iron vessels should not be used, unless they are perfectly coated with tin in every part. A solution of tin heightens the red colour, and tends to restore it, if it has acquired a purple tint