~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 anaesthetic; _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. INDEX Acetaldehyde 405 Acetic acid 406 Acetone 411 Acetylene 203 series 399 Acids 106 binary 113 characteristics 106 definition 107 dibasic 159 familiar 106 monobasic 159 nomenclature 113 organic 405 preparation 141 strength 111 ternary 113 undissociated 107 Acker furnace, 279 Agate 260 Air 83 a mechanical mixture 89 carbon dioxide in 87 changes in composition 87 liquid 91 nitrogen in 87 oxygen in 85 poisonous effects of exhaled 88 properties 90 quantitative analysis of 85 regarded as an element 83 standard for density 229 water vapor in 87 Alabaster 308 Alchemists 9 Alchemy 9 Alcohol, common 402 denatured 404 ethyl 402 methyl 402 wood 402 Alcohols 401 Aldehydes 405 Alizarin 418 Alkali 107, 274 family 274 Alkaline-earth family 300 Alkaloids 418 Allotropic forms 22 Alloys 252