_Peroxide of hydrogen_ bleaches organic substances, dark or red hair being thereby changed to reddish-yellow or pale blonde. The coloration, or rather bleaching, does not appear at once, but is complete only after some time. The peroxide of hydrogen only exists in aqueous solution, which should be quite concentrated (15 to 20 per cent.). Owing to the mode of preparation, the solution always contains some nitric acid and readily decomposes, when exposed to light and air, whereby it becomes useless. In the following, a number of formulæ for hair-dyes are given. According to their constitution, they may be divided into two groups, viz: A. Dyes which contain the coloring matter in a finished state; and, B. Dyes which are formed upon the hair by a chemical process. The dye should first be applied in a dilute state, and the application repeated in case the desired shade is not produced, since by the use of the dye in a concentrated form a shade not resembling any natural color might be obtained, hair which is to be colored black acquiring, for instance, a metallic blue-black lustre. A. SINGLE HAIR DYES. _Teinture Orientale (Karsi)._--Ambergris 2¾ drachms, gall-nuts 4 lbs., pulverized iron 1¾ ozs., pulverized copper 1 drachm, musk 1 drachm. Convert the gall-nuts to a fine powder, and roast the powder in an iron pan, stirring constantly until it is dark brown to blackish. Rub the powder together with the metallic powders, and the perfume substances and keep the mixture in a damp place. For use moisten some of the powder upon the hand and apply to the hair, rubbing it in vigorously. In a few days the hair acquires a deep black, quite natural color. In roasting, the tannin-substances contained in the gall-nuts are converted into gallic and pyrogallic acids, which yield with the metals combinations of a deep black color, and are even readily converted into black-brown bodies (humin bodies). _Teinture Chinoise (Kohol)._--Gum-arabic 1 oz., Chinese ink 1¾ ozs., rose-water 1 quart. Reduce the gum-arabic and Chinese ink to fine powder, and triturate the powder in small quantities with rose water until a homogeneous black fluid free from grains is formed. Collect this fluid in a bottle and mix it with the remaining rose water. Kohol is only suitable for persons with black hair and is especially used for dyeing the eyebrows. The coloring matter of this preparation consisting only of carbon in a very finely divided state, it is perfectly harmless.