1 of hydrogen, with 14 of nitrogen, with 6 of carbon, with 16 of sulphur, 39 of potassium, 28 of iron, and 32 of phosphorus. 1 equivalent of hydrogen goes as far in saturating 8 of oxygen, as 108 of silver, 39 of potassum, 6 of carbon, 32 of phosphorus, and 28 of iron. 16 of sulphur combines with 28 of iron, 35.5 of chlorine. This law is never departed from in any case. It is very common to speak of such a number of equivalents of one body united to one or more equivalents of another. Sulphuric acid contains one equivalent of sulphur to three equivalents of oxygen, SO3. Potash, KO, one of potassium to one of oxygen. Phosphoric acid, PO5, one of phosphorus to five of oxygen. The combining equivalent of a compound is always the sum of the combining equivalents of its constituents. The combining equivalent of sulphuric acid is 40, 16 of sulphur, and 3 times 8 of oxygen. S 16+8+8+8=40. The combining equivalent of potash, KO, is 47, 39 the equivalent of potassium, and 8 the equivalent of oxygen, 39 +8=47. 40 parts of sulphuric acid neutralise 47 parts of potash, forming the sulphate of potash, which has a combining equivalent of 47 +40= 87. Nitric acid, NO5, has a combining equivalent of 14 + 8 +8 +8 +8 +854; the proportion of nitric acid necessary to neutralise and combine with 47 parts of potash. From this it will be evident that when neutral salts decompose each other, the resulting compound will be neutral. It will be understood that these proportions are by weight. COMBINATION BY VOLUME. It is often more convenient to measure a certain volume of gas than to weigh it. Gases and volatile vapours combine by volume according to a definite and simple law. Equivalent weights of hydrogen and chlorine occupy at the same temperature and pressure equal volumes. Oxygen occupies only half the volume. If the specific gravity of a gas or vapour, and its combining equivalent, be known, its combining volume may be determined by dividing the chemical equivalent, of the substance by its specific gravity. The combining equivalent of oxygen is 8 divided 8.000 by its specific gravity, 1·106 = =7.23, its com 1.106 bining volume. Chlorine equivalent 35.5 divided by which is 2.470= 35.50 = 14.33, its com 16.000 its sp. gr. bining volume. Sulphur vapour, sp. gr. =2.40. 6.654 From this it appears that the combining volume of chlorine is double that of oxygen; and sulphur one-sixth of chlorine. Hydrogen, nitrogen, chlorine, bromine, iodine, carbon, and mercury, in a gaseous state, have the same combining volume; oxygen, phosphorus, and arsenic, one-half; sulphur, one-sixth. Compound bodies in a state of vapour yield the same results. WEIGHT. By the term weight is meant the whole amount of matter a body contains, and this is generally expressed in grains. Specific weight, or specific gravity, is the number which expresses the ratio which the weight of a cubic inch of the body bears to the weight of a cubic inch of distilled water at a temperature of 60°. The specific gravity of So that in the same bulk we have three times more matter in platina than iron, and iron is seven times heavier than its own bulk of water. In gases, air is taken as 1000; and the specific gravity of gases are referred to that standard. Great skill is required in determining the specific gravity of gases or vapours, and nothing short of practice can give accuracy in the results. Atomic weight, or equivalent weight, is a term used to express the proportion in which bodies combine chemically. The atomic theory was first promulgated by Dr. Dalton. It assumes the existence of indivisible particles, molecules, or atoms; that compounds are formed by the union of these atoms, one to one, one to two, one to three, and so on. The compound atom thus formed unites itself to the compound atom of another kind, and combination of the second order results. If it be allowed that the relative weights of these atoms are in the proportion of their equivalent numbers, the hypothesis renders satisfactory reasons for the laws of combining proportion. Chemical compounds must be definite in their composition, always The law of containing the same number of atoms. multiple proportion is also easily explained. An amto of nitrogen unites with one, two, three, four, and five of oxygen. If the black circle represent the nitrogen atom, and the open circles the oxygen, we may help our understanding by the following diagram: In early days, fanciful names were given to chemical compounds; many of these names have been retained in common use, such as oil of vitriol, aqua fortis, spirits of hartshorn, spirit of salt, cream of tartar, sugar of lead, blue stone, flower of zinc. Lavoisier introduced a new nomenclature, which satisfied for some time all the requirements of science. In organic chemistry, which is a new department of science, the defects of this nomenclature is sometimes felt. Some of the elementary substances have names referring to some peculiarity of the body: such as barium,. antimony, chromium, chlorine, &c. When any of the non-metallic elements combine with a metal, the compound ends in ide. So we have oxides, bromides, chlorides, iodides, carbides, phosphides, and C sulphides. Carburet, sulphuret, and phosphoret are sometimes used. A compound of oxygen and iron, FeO, is the oxide of iron; by replacing the oxygen with chlorine, sulphur, or iodine, we get the chloride, sulphide, and iodide of iron. If the non-metallic bodies combine with each other, they are similarly named; as, sulphide of carbon, chloride of sulphur, phosphide of hydrogen. The oxides are generally divided into three classes. The oxides which resemble potash, soda, and lime, are called basic oxides. The oxides of the second class are the very opposite in chemical relationship to the first, and are called acids. Phosphoric, sulphuric, chloric, and nitric acid may represent this class of oxides. There is a third class called neutral oxides, of which water and the binoxide of manganese are good illustrations. It frequently happens that a metal unites with oxygen in several proportions: in such cases, one oxide has generally a strongly marked basic character; to this the term protoxide is given. The compounds next are called binoxide or deutoxide, teroxide or tritoxide; the highest oxide, not having acid properties, is called the peroxide. Any compound containing less oxygen than the protoxide is called a suboxide. If an oxide should occur between the protoxide and binoxide, it is called the sesquioxide. If the letter M represent a metal, and if oxygen unite with it in several proportions, we shall have · M2O suboxide, 3 M2O, sesquioxide, MO protoxide, 4 By substituting chlorine, or any of the other me |