Madder dyes are sometimes slow in being turned to a violet by potassa, and this shade when produced is often brownish. They might thus be confounded with the dyes of the fourth group, i.e., rosolic acid, coralline, eosine, and coccine. None of these colors gives the characteristic reaction with milk of lime and boiling soap-lye. If plunged in milk of lime, they resume their rose or orange shades, while the madder colors become violet. Murexide is turned, by potassa, gray in its light shades and violet in its dark ones. It might, then, be confounded with orchil, but it is decolorized by hydrochloric acid, which leaves orchil a red. Moreover, it is turned greenish by stannous chloride. A special character of this dye (murexide) is the presence of mercury, the salts of which serve as mordants for fixing it, and may be detected by the ordinary reagents. The second group comprises merely sandal wood or sanders red, which turns to a brown. On boiling it with copperas it becomes violet, while on boiling with potassium dichromate it changes to a yellowish brown. The third group includes safflower, magenta, and murexide (light shades). If the action of the potassa is prolonged the (soft) red woods enter into this group. Safflower turns yellow by the action of potassa, and the original rose shade is not restored by washing with water. Hydrochloric acid turns it immediately yellow. Citric acid has no action. Magenta is completely decolorized by potassa, but a prolonged washing in water reproduces the original shade. This reaction is common to many aniline colors. These decolorations and recolorations are easily produced in dark shades, while in very light shades they are less easily observed, because there is always a certain loss of color. Stannous chloride turns magenta reds to a violet. Hydrochloric acid renders them yellowish brown (afterward greenish?). Water restores the purple red shade. The fourth group comprises saffranine, azo-dinaphthyldiamine, rosolic acid, coralline, pure eosine and cosine modified by a salt of lead, coccina, artificial ponceau, and red-wood.