C6H5NO2 + 6H = C6H5NH2 + 2H2O.
The resulting compound is known as aniline, a liquid boiling at 182°. When first prepared it is colorless, but darkens on standing. Large quantities of it are used in the manufacture of the aniline or coal-tar dyes, which include many important compounds.
Carbolic acid (C6H5OH). This compound, sometimes known as phenol, occurs in coal tar, and is also prepared from benzene. It forms colorless crystals which are very soluble in water. It is strongly corrosive and very poisonous.
Naphthalene and anthracene. These are hydrocarbons occurring along with benzene in coal tar. They are white solids, insoluble in water. The well-known moth balls are made of naphthalene. Large quantities of naphthalene are used in the preparation of indigo, a dye formerly obtained from the indigo plant, but now largely prepared by laboratory methods. Similarly anthracene is used in the preparation of the dye alizarin, which was formerly obtained from the madder root.
THE ALKALOIDS
This term is applied to a group of compounds found in many plants and trees. They all contain nitrogen, and most of them are characterized by their power to combine with acids to form salts. This property is indicated by the name alkaloids, which signifies alkali-like. The salts are soluble in water, and on this account are more largely used than the free alkaloids, which are insoluble in water. Many of the alkaloids are used in medicine, some of the more important ones being given below.
Quinine. This alkaloid occurs along with a number of others in the bark of certain trees which grow in districts in South America and also in Java and other tropical islands. It is a white solid, and its sulphate is used in medicine in the treatment of fevers.
Morphine. When incisions are made in the unripe capsules of one of the varieties of the poppy plant, a milky juice exudes which soon thickens. This is removed and partially dried. The resulting substance is the ordinary opium which contains a number of alkaloids, the principal one being morphine. This alkaloid is a white solid and is of great service in medicine.
Among the other alkaloids may be mentioned the following: Nicotine, a very poisonous liquid, the salts of which occur in the leaves of the tobacco plant; cocaine, a crystalline solid present in coca leaves and used in medicine as a local anæsthetic; atropine, a solid present in the berry of the deadly nightshade, and used in the treatment of diseases of the eye; strychnine, a white, intensely poisonous solid present in the seeds of the members of the Strychnos family.