Examples of acids are: HCl. Hydrochloric acid or chlorhydric acid. It is also called muriatic acid, and is the chloride of hydrogen. HS. Hydrosulphuric acid or sulphydric acid. It is also called sulphuretted hydrogen, and is the sulphide of hydrogen. HNO,. Nitric acid; also called aquafortis. H.SO. Sulphuric acid; also called oil of vitriol. HO+CO2. Carbonic acid and water. The hydrogen of each of these bodies may be replaced by a metal, as potassium, zinc, silver. Thus I. II. $58. When the hydrogen of an acid has been thus replaced by a metal or similar body, a salt is obtained. Thus all the bodies in II. are salts. A salt may therefore be defined as an acid whose hydrogen has been replaced by a metal. It is clear that if the metal of a salt be replaced by a second metal, the same salt is got as if the hydrogen of the corresponding acid had been replaced by the second metal. A salt may be easily, difficultly, or not at all soluble in water. Of the above examples the following are insoluble: ZnS, ZnCO„, AgCl, Ag„S, Ag,CO,. Sparingly soluble is Ag2SO; all the rest are readily soluble in water. Soluble salts have a peculiar taste called saline, and resembling that of tablesalt, but modified both by the nature of the metal and of the nonmetallic part. They are generally solid bodies, and frequently consist of crystals having a very distinct shape, called the "crystalline form." § 59. The physical properties of salts, such as their crystalline form, colour, degree of solubility in water, &c. are often so characteristic as to be used in determining what metal is present, or, if this be known, in finding the non-metallic or acid part. § 60. Salts, even when soluble in water, often take no effect upon vegetable colours, and are then said to be physically neutral. Sometimes only half or other fraction of the hydrogen of an acid is replaced by a metal. When this is the case a chemically acid salt results. Such a salt, if soluble in water, generally, but by no means invariably, is also physically acid. § 61. It is clear that if any of the above acids which contain water have that water replaced by a metallic oxide, the same salt is got as when the hydrogen is replaced by the simple metal. Thus, KNO, may be got from 2(HNO、) by replacing H2O by KO, Ag2SO H2SO1 Ag2O, and so on. If, in fact, oxide of potassium be added to nitric acid, water is liberated and the above salt is formed; or if oxide of silver is added to sulphuric acid, it replaces the water. This is shown in the following equations: § 62. In such a reaction, therefore, from an acid, by the addition of a metallic oxide, we get a salt. The metallic oxide neutralizes the acid. A body, very often an oxide, which thus takes the place of water in an acid, liberating and replacing the water and neutralizing the acid, is called a Base. The oxides of all metals are bases. § 63. When such a body as HS or HCl is acted on by a metallic oxide, the sulphide, chloride, &c. of the metal is generally formed, and water is also produced. On account of their forming salts (Ag2S, NaCl, &c.) with metallic oxides, such bodies as HCl and HS are called acids, although, unless in the presence of water, they are physically neutral. § 64. When more than one equivalent of a base combines with one equivalent of an acid, displacing one equivalent of water, the salt formed is called a basic, or sometimes a subsalt. § 65. It is evident that the more soluble a metallic oxide is in water, the more readily will it neutralize an acid. Those metallic oxides which are the most soluble in water are called alkalies, and their solutions are called alkaline. The metals which such alkalies contain are called alkaline metals. The chief of these are potassium and sodium. An alkali, therefore, is a very soluble base. § 66. Several acids, especially volatile ones, are readily expelled from their bases. It follows that salts of those acids, especially such as are soluble in water, neutralize acids just as free bases do. Thus = H,SO, Na,CO, H2O + CO2+ Na,SO. 4 2 Such salts (as Na,CO1) are called alkaline salts because, like free alkalies, they turn blue vegetable colours reddened by acids. § 67. The names given to the various acids are formed somewhat in the same manner as those composed of two elements, or binary compounds. If, as frequently happens, two non-metallic elements unite in various proportions, more than one of the combinations, in presence of water, has acid properties. Thus P and O unite in two proportions, P,O, and P,O,; each of these combines with water and forms an acid. 5 Phosphorous 2(H ̧PO1). Phosphoric acid. The name of the first ends in ous, that of the second in ic. And in all cases the termination ous implies a less quantity of oxygen than is contained in the corresponding acid whose name ends in ic. Thus 2 § 68. Frequently more than two combinations of two elements are acids. Thus the body P2O has acid properties. A name is given to it expressing that it contains less oxygen than phosphorous acid does; it is called hypophosphorous acid. So four of the oxides of chlorine in combination with hydrogen are acids. § 69. When water is taken from an acid, or metallic oxide from a salt, neither the one nor the other being replaced, or if in any other way a body is got which would form an acid if it combined with water, or would form a salt if it combined with a base, that body is called an anhydrous acid, or simply an anhydride; thus SO, is anhydrous sulphurous acid or sulphurous anhydride. SO, 2 2 sulphuric acid or sulphuric anhydride. carbonic acid or carbonic anhydride. § 70. The nomenclature of salts stands in a very simple relation to that of acids. An acid containing oxygen whose name ends in ic forms salts whose names end in ate. An acid containing oxygen whose name ends in ous forms salts whose names end in ite. Thus ZnSO,, sulphate of zinc. HCIO, hypochlorous acid,,, Hg2(CIO), hypochlorite of mercury. § 71. It is evident therefore that acids are salts of hydrogen —that sulphuric acid is, for instance, the sulphate of hydrogen, nitric acid is nitrate of hydrogen, &c. Acids are hydrogen salts. Anhydrous acids or anhydrides may either combine with water, F and so form true acids, or with metallic oxides, and so form metallic salts. § 72. Acids which do not contain water, such as hydrochloric acid, HCl, hydrosulphuric acid, HS, when they combine with bases, form of course chloride and sulphide, &c., of the metal (§ 63). §73. Many metals, such as magnesium, calcium, potassium, sodium, &c., rarely occur in the uncombined state. They were long known as oxides, and names were given to the salts which those oxides formed with acids. Such names are often retained. Thus K,SO, is frequently called sulphate of potash. 4 Such names are not quite systematic; these salts should be, and often are, called sulphate of potassium, sulphate of calcium, carbonate of magnesium. § 74. Many compound bodies, besides their chemical names, have familiar ones which are sometimes conveniently used for brevity. Such are water (oxide of hydrogen), saltpetre or nitre (nitrate of potassium), litharge (oxide of lead), lime (oxide of calcium), &c. The method of symbolization and nomenclature will become familiar as the following chapters are studied. $75. Oxygen is the most abundant of all the elements, and |