CHEMISTRY.
Continued from No. 11.
ACIDS.
Acids are a most important class of chemical compounds, and have the following characteristic properties:裕he greater number of them have a sour taste, and are very corrosive. With few exceptions, they change vegetable blues to red, they are mostly soluble in water, and they unite with the alkalies, earths, and metallic oxides, forming what are called salts預n order of bodies of the highest importance in the arts, manufactures, &c. Some acids are destitute of a sour taste, but their affinity for the three classes of bodies above named is a universal characteristic. Acids are all compound bodies, and some of them have more than one basis or radical. There are a number of acidifying principles, but oxygen (which shall be immediately described) is the most extensive one. The acid is distinguished by the name of its base, and its degree of oxidation, that is the quantity of oxygen it contains, by the termination of that name in ous, or ic, or the prefix hype (under.) The highest degree of oxygenation is marked by the termination ic, as nitric acid, and salt that is formed from it, is made to terminate in ate; the next by that of ous, as nitrous acid, and the salt that is formed from it is made to terminate in ite; and the lowest by hypo, as the hyponitrous acid. Sometimes oxygen combines in a greater quantity with the acidifiable radicals, in which case the product is said to be superoxygenated. All acids are not susceptible of these various degrees of oxygenation, some being limited to only one. There are a considerable number of acids, and the number is continually increasing by the discovery of new ones; but of the most important there are few, and these we shall notice as we come to treat of their bases.
This term has been usually employed to denote a compound, in definite proportions, of acid matter with an alkali, earth, or metallic oxide. When the proportions of the constituents are so adjusted that the resulting substance does not affect the color of infusion of limus or red cabbage, it is then called a neutral salt, because the peculiar powers of both bodies are suspended and concealed; they are rendered neutral and inactive. When bodies combine in such a way as to satisfy their mutual affinities, they are said to saturate each other. When the predominance of acid is evinced by the red of these infusions, the salt is said to be acidulous, and the prefix super or bi, is used to indicate the excess of acid. If, on the contrary, the acid matter is deficient, or short of the quality necessary for neutralizing the alkalinity of the base, the salt is then said to be with excess of base, and the prefix sub is attached to its name. These must be understood however, only as general rules. There are exceptions to be found in the case of some salts, as the compounds formed by an acid and an alkali, an earth, or a metallic oxide, are denominated.
Specific Gravity is the relative gravity or weight of any body or substance, compared with that of some other body which has been fixed upon as a standard. By universal consent, pure distilled water has been assumed as a standard; and it fortunately happens that a cubic foot of pure water weighs exactly 1000 ounces avoirdupois. Water is indicated by unity葉hus 1. When, therefore, it is expressed that any body has a specific gravity of 2, then, bulk for bulk, it is just twice the weight of water. If there be more figures than one, and there be a dot or point between them葉hus, 2.5葉he unit is here divided into ten parts, and the body is twice and five-tenth times, or two and a half times heavier than water. If two figures occur葉hus, 10.40葉he unit is supposed to be divided into a hundred parts, and the body is ten and forty hundredth part times heavier than water. If there are three figures, the unit is supposed to be divided into a thousand parts; if four, into ten thousand parts, and so on; the number and value of the figures always indicating the exact specific gravity of the body according to the above principle. Common air is sometimes taken as a standard with which to compare gases, but all the solids and fluids are estimated with regard to water.