In cases where pencil writing has been removed with a soft rubber or fresh bread, the parts thus erased will assume, when subjected to iodine fumes, a brown color trending towards violet and much darker than the undisturbed portions of the paper. Lines impressed upon paper with a "stylus," a glass or ordinary dry pen, can be made visible by the fumes of iodine, the lines showing with a stronger coloration than the surrounding paper. CHAPTER XX. FUGITIVE INK. SOME OBSERVATIONS ABOUT "ADDED" COLOR TO INK-- INVENTION OF COAL TAR COLORS--CHRONOLOGICAL HISTORY OF 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.