Page:Popular Science Monthly Volume 25.djvu/217

Rh Not a fixation of oxygen, but a departure of hydrogen, takes place. Then a phenomenon of condensation is exhibited; a number of the molecules unite to form a molecule of rosaniline. This wonderful colorant may be constituted by the action of almost any of the oxidizing agents known in chemistry upon aniline. Curiously, rosaniline would not be formed if the aniline were absolutely pure. Theoretically, its molecule is formed by the union of a molecule of aniline and two molecules of toluidine, with a loss between the two of six atoms of hydrogen. It can not be obtained by oxidizing either of these bases separately. Rosaniline is solid at ordinary temperatures, and crystallizes readily in lozenges or in fine needles, which are white when protected from the air, but become rose and then red when brought in contact with it. The nature of the change it undergoes is unknown. It is not apparent in the composition. Rosaniline is soluble in water, and more soluble in alcohol, and has basic qualities so strong as to displace ammonia from its salts; and it is most frequently employed as a salt. It furnishes not red only, but all colors, according as it is treated in the combinations into which it is made to enter. Violet was first discovered by Mr. Perkins, in 1856, while trying to make artificial quinine by the action of bichromate of potash on sulphate of aniline. He gave up the search for quinine, and turned his attention to manufacturing the color. Three years afterward MM. Renard and Verguin produced fuchsine, a purple salt of rosaniline, by treating commercial aniline with a dehydrogenizing agent, bichloride of tin. It is a mixture of hydrochlorate of rosaniline and salts of tin, and is used by dyers and wine-merchants. Aniline is now oxidized by the action of arsenic into crude red (rouge brut), a violet mixture, composed principally of arsenite and arseniate of rosaniline, which is converted into fuchsine by bringing about a substitution of hydrochloric for arsenious or arsenic acid. This is done by boiling crude red with hydrochloric acid, or, more usually, with sea-salt. A double decomposition takes place, and, when the liquor is cooled, crystals of fuchsine are found in the bottom of the vessel, while the arsenites and arseniates of soda are retained in the mother-water. Not all the coloring-matter, however, is deposited in the crystals, and a good operator loses nothing. Treated with carbonate of soda, the mother-water gives a precipitate, from which is extracted a color known as aniline garnet or yellow fuchsine. Nor is this all. The crude red has left a violet deposit in the bottom of the boats in which it was cooled; this is washed in boiling water; the water is colored red, and a blue dye-stuff is collected from it. More is left still. The crude red has passed through filters, and they have retained some insoluble substances. These are carefully gathered up; they form a paste which is boiled with diluted hydrochloric acid and filtered over again to extract what fuchsine is left. The insoluble residue furnishes aniline maroon, a beautiful color readily applicable to wool. Thus a single