第60章

SOME OBSERVATIONS ABOUT "ADDED" COLOR TO INK--INVENTION OF COAL TAR COLORS--CHRONOLOGICAL HISTORYOF THE "ANILINES" EMPLOYED AS INK--OTHER SUBSTANCES USED FOR THE SAME PURPOSE.

THE term "added color," as applied to ink, is the popular phraseology for a multitude of materials which have been more or less utilized for a period of centuries, in adulterating and coloring ink. In olden times they were introduced into ink with an honest belief that it would also improve and ensure its lasting qualities, but latterly more often to cheapen the cost of its manufacture. Reference has been made to a large variety of these substances used for this purpose and the story told of the effect of the test of time upon them as indicative of their supposed value.

Attention has also been directed to the discovery during the nineteenth century of the colors which owe their origin to by-products of coal tar.

Generically these colors are classified as "anilines."They have worked a revolution in all the arts in which colors are used. Employed without a mordant, with few exceptions, they are measurably affected by both light, heat, moisture, or other changes and as made into inks are never permanent. Hence they should not be used for records, because if obliterated from any cause whatever, there are no known means to render them again legible.

The origin and history of the "anilines" are known. Viewed from an ink standpoint they are of vast interest. So extended in number are the "anilines"(they run into the thousands) that they include every shade of black and all possible tints or hues of the colors of the rainbow.

The chronological history of such of these artificial colors which appertain to ink or its manufacture is important as locating the dates of their invention and commercial use.

The first discovery of "aniline" is credited to Helot in 1750. In 1825 Faraday in rectifying naphtha discovered benzole, which by the action of strong nitric acid be converted into nitro-benzole; and this latter, when agitated with water, acetic acid and iron filings produced aniline. Unverdorben in 1826 discovered an analogous material in products obtained by the destructive distillation of indigo. Runge in 1834 claims to have detected it in coal tar and called it kyanol, which after oxidation became an insoluble black pigment and known as aniline black. It could not, however, be used as an ink. Zinan in 1840, experimenting along the same lines, produced another compound terming it benzidam. Fritsche in the same year by the distillation of indigo with caustic potash developed a product which he also called aniline, the name being derived from the Portuguese word anil, meaning indigo. Shortly afterwards A. W. Hoffman established the identity of these substances.

Aniline when pure is a colorless liquid, possessing a rather ammoniacal odor. It soon becomes yellow and yellow-brown under the influence of light and air.

It does not affect litmus paper.

In 1856 Perkins accidentally discovered the violet dye called mauve, which acquired considerable commercial importance besides its utility for ink purposes.

Nicholson in 1862 succeeded in producing the first of the soluble blue anilines.

The discovery of induline, one of the modifications of aniline black, was made known in 1864.

Nigrosine, produced by the action of concentrated sulphuric acid on the insoluble indulines, was discovered in 1868.

The soluble indulines and nigrosines differentiate in appearance, the first a bronzy powder and the latter a black lustrous powder. When made into ink they possess about equal color values.

In 1870 the German chemists, Graebe and Liebermann, announced that they had succeeded in producing artificial alizarin,--the coloring matter of the madder root. Commercial value was not given to this discovery until it was put on the market in 1873, although it did not meet all the requirements.