MODERN INK, on the contrary, leaves its marks upon paper, parchment, &c., by penetrating the material to such a depth that it cannot be erased (mechanically) without the removal or destruction of the surface which it has _tinged_. Chemical agency, as of various acids, chlorine and its compounds, is generally employed, therefore, to discharge the color from modern writing-ink-marks. CARBON, in all its common forms, (charcoal, bituminous coal, anthracite, jet, plumbago, lignite, ivory-black, lamp-black and soot,) is wholly unalterable in color by any of these chemical means. PRINTING INK (which is composed of carbon suspended in a drying oil) is, in essential characteristics, identical with the writing-inks of the ancient Romans and Greeks. It is impressed upon the surface of paper, (that which is _unsized_ or bibulous being commonly preferred,) and is retained unchanged by the action of moisture, on account of the insolubility of the carbon and the repulsion between oil and water. These two forms of ink are therefore the exact opposites of each other, in the qualities on which their use and permanence depend. The most important peculiarity of the modern writing-ink, as contrasted with the ancient, naturally suggested the two names which it bore in the Latin and Greek of the middle ages, or (to speak more definitely,) the time of its invention and first employment. It was a _Tincta_, a DYE, or STAIN, which _tinged_ and _tinctured_ the material on which it was placed, entering among its fibres as coloring fluids do into cloth in the ordinary processes of manufacture. It penetrated the substance of the paper (as caustics or powerful chemical solvents and corrosives act on the organic fibre): it _bit in_, or _burned in_,—and was therefore well named ENCAUSTON and _Incaustum_. CHEMISTRY or COMPOSITION of INK. We do not propose to furnish recipes, prescriptions, directions or instructions for the manufacture of this article. No mere statement in words can enable any one to arrive at perfection, or excellence, or practical success in the production of this article, or any articles whatsoever. A skill and carefulness, which can be acquired only by long and laborious experience, are indispensable to the management of the various processes. Time is an essential element of success in this peculiar art; and that makes absolutely requisite also, two other conditions,—_patience_ and _capital_. We shall therefore be brief on this point,—referring those who wish for minute details, to the cyclopaedias, dictionaries of the arts and sciences, and the larger works on practical chemistry. The following we venture to present as the most correct account of this subject, derived from the latest scientific and practical authorities. The composition of ink varies according to its colors, and the purposes to which it is to be applied.