Aniline Colors. Aniline is a liquid of a color varying from yellow to dark brown. The commercial article is never chemically pure, being a mixture of pure aniline, toluidine, and odorine. Its boiling point ranges from 356° to 482° Fahr. If aniline boils at a lower temperature than 356°, it contains too much odorine, and is, therefore, of poor quality. It is obtained by conversion from nitro-benzole, a preparation of the benzole obtained from coal tar (not from petroleum). In preparing nitro-benzole on a large scale, 12 parts benzole are mixed with 13 parts fuming nitric acid, and 8 parts oil of vitriol, in a cast iron apparatus. The character of the product depends greatly on the purity of the benzole, and also on the management of the reaction. The conversion of nitro-benzole into aniline is, by B'echamps' process, performed in iron tanks, heated by steam, and provided with stirrers, and a still-head to collect the distillates. The tank or still is charged with 100 parts nitro-benzole, 150 clean wrought iron filings, 100 water, and 150 acetic acid; when these are mixed spontaneous heat is evolved, which causes some of the liquid to pass into the condensers, whence it is returned to the tank. As the heat is not sufficient for the complete conversion of the nitro-benzole, steam is introduced after a time, and the stirring and steaming is continued until no more nitro-benzole appears in the distilled vapor. At this point the temperature is increased, and, if necessary, aided by direct fire, to cause complete distillation of the aniline which has formed, and which passes off with water, and separates from it on standing, as the heavier stratum. The aniline used for the various colors is taken of different composition and boiling-point. A. W. Hof-mann has shown that a mixture of an equivalent of aniline and two of toluidine produces the largest yield of rosaniline (fuchsine). The substance used for this manufacture begins to boil at about 347°, and as the heat increases to 390° 80 per cent, will have distilled over. Aniline blue and purple require an oil which begins to boil at 374°, and at 392° has lost only 60 per cent. Evidently with these properties it contains less aniline than the preceding one. The changes which these bases undergo when converted into dyes or compounds of rosaniline, are brought about by the partial destruction of a portion of them.

2553. Rosaniline, or Fuchsine

2553.    Rosaniline, or Fuchsine. The principal methods for the manufacture of fuchsine employ arsenic acid, the reaction being brought about in a cast iron still with movable head, connected with a condenser, and provided with a manhole, and also a place for a thermometer. This still sits in a jacket containing a hot bath of palm-oil, which keeps it at a temperature of from 320° to 356° Fahr. A charge consists of 100 parts aniline and 200 parts arsenic acid, and the reaction is ordinarily completed in about 6 hours, sometimes in 5, but at others only in 12 hours, during which time the temperature is carefully regulated. Assays are taken from time to time, and the completion of the process is known by the pure bronze color of the sample. The fused mass is transferred to a tank, in which, after cooling, it is broken up, and at once treated with water and steam. The base fuchsine (rosaniline) dissolves, leaving behind the resinous products of the reaction; the arsenic acid is separated by the addition of milk of lime. The filtered solution, after proper concentration, deposits, on cooling, fine crystals of fuchsine, as do also the first mother liquors. An inferior quality of fuchsine is obtained by adding a portion of salt, varying in quantity.