Schluttig and Neumann in 1890 issued their Edition Dresden on the subject of "Iron and Gall inks." In this valuable work is to be found the formula which has been generally adopted as the standard where one is used for tanno-gallate of iron ink. The investigations of other scientific men like Lepowitz, Booth, Desormeaux, Chevreuse, Irvine, Traille, Bottger, Riffault, Precht, Nicholes, Runge, Gobert, Penny, Arnold, Thomson (Lord Kelvin), Davids, Kindt, Ure, Wislar and many more who have dealt with the chemistry of inks, present to us some testimony during a considerable portion of the nineteenth century of the efforts made to secure a good ink. CHAPTER XIV. CLASSIFICATIONS OF INK. INK USED BY US HAS NOTHING IN COMMON WITH THAT OF THE ANCIENTS--MANUFACTURERS OF THE PRESENT TIME HAVE LARGELY UTILIZED FORMULAS EMPLOYED IN PAST CENTURIES--THE COMMON ACCEPTATION OF THE TERM INK--SEVEN DIFFERENT CLASSES OF INKS AND THEIR COMPOSITION BRIEFLY TOLD--FAILURE OF EFFORTS TO SECURE A REAL SAFETY INK. THE inks used by us have nothing in common with those of the ancients except the color and gum, and mighty little of that. Those of the "gall" class employed in the fourteenth, fifteenth, sixteenth, seventeenth and eighteenth centuries, some formulas of which are utilized by the manufacturers of ink in our own time, consisted generally in combination; infusions of nut-galls, sulphate of copper or iron, or both, and fish-glue or gum, slightly acidulated. The frequent introduction of the so-called "added" color into these inks, time has shown to have been a grave mistake. The common acceptation of the term "ink" may be said to characterize an immense number of fluid compounds, the function of which in connection with a marking instrument is to delineate conventional signs, characters and letters as put together and commonly called writing, on paper or like substances. To classify them would be impossible; but black writing ink, chemical writing fluid, colored writing ink, copying ink, India ink, secret or sympathetic ink, and indelible ink make seven classes; the others may be denominated under the head of miscellaneous inks, and of them all, there is no single ink answering every requirement and few answer at all times the same requirements. Ink may be either a clear solution of any coloring matter or of coloring matter held in suspension. It is a remarkable fact that although most inks are chemical compositions and many times made after the same formula, identical results cannot always be calculated or obtained. This is more particularly to be noted in the case of black writing inks otherwise known as the tanno-gallate of iron inks [gallic and gallotanic acid obtained from nut-galls, sulphate of iron, (green copperas) and some gummy vehicle].