Chemical Nomenclature is still in an unfinished state. The chemists of all countries are, with one notable exception, agreed as to the names and symbols which should represent the different elements. The French chemists persist in designating nitrogeit by the name of azote, and of using Az instead of N for its symbol; and in Italy the term azoto is still employed, but as it is often coupled with the symbol N, it will probably soon be exchanged for the more general term nitrogen. When the elementary bodies unite together, they form a binary compound. The nomenclature of the binary compounds is. in a transitional state. The compounds of sulphur with metals used to form sulphurets, latterly they have been termed sulphides, and now they are denominated after a third fashion; sulphuret of potassium (for example), after having been for some years sul phide of potassium, now being termed potassic sulphide. In order to obtain uniformity, the following rule is adopted by the representatives of the modern school. The names of binary compounds are formed from those of their constituents, the English or Latin name of the positive constituent with the terminal ic preceding that of the negative constituent, which is made to end in ide. Thus: potassium and sulphur form potassic sulphide; sodium and oxygen form sodic oxide (formerly soda or oxide of sodium); silver and chlorine form argentic chloride (formerly chloride of silver); lead and iodide form plumbic iodide (formerly iodide of lead); calcium and chlorine form calcic• chloride (formerly chloride of calcium), etc. When the same elements form two coin pounds, the one which contains the smallest proportion of the negative element is dis tinguished by changing the terminal syllable of the name of its positive constituent into aus, while the terminal le is retained for the compound containing the larger pro portion of the negative element. Thus, 1 atom of iron and 1 atom of oxygen form ferrous oxide (the old protoxide of iron); 2 atoms of iron and 3 atoms of oxygen form ferric oxide (the old peroxide of iron). Sometimes the same elements form more than two compounds with one another, and then the prefixes hypo and per are employed. When' a binary compound contains oxygen, and becomes an acid when made to unite with water, or becomes a salt when united to a base, it is termed an anhydride (q.v.) or anhydrous acid. Thus 1 atom of carbon and 2 atoms of oxygen form carbonic anhydrid e, formerly known as carbonic acid gas; 1 atom of sulphur and 3 atoms of hydrogen form sulphuric anhydride, etc. In a considerable number of cases, the trivial or common. name has not been displaced by the new systematic name; thus water, ammonia, hydro chloric acid, phosphureted hydrogen, sulphureted hydrogen, etc., are not as yet replaced by hydric oxide, hydric nitride, hydric chloride, hydric phosphide, hydric sulphide. etc. ; and soda and potash are still preferred by some chemists to sodic and potassic hydrates.
The term acid was originally applied only to substances which, like vinegar, pos sessed an acid taste; it is now made to include a large number of compounds which do not possess this property. The most general definition of acids is that of Gerhardt, which is adopted in Watts' Dictionary of Chemistry—namely, that " acids are salts of hydrogen." A more intelligible definition to ordinary readers is that which is adopted by Frankland, in which an acid is described " as a compound containing one or more i atoms of hydrogen, which become displaced by a metal when the latter is presented to the compound in the form of a hydrate." Thus, using the new nomenclature and atomic weights, nitric acid and sodic hydrate, yield sodic nitrate and water— Nitric acid. Sodic hydrate. Sodic nitrate. Water.
or, NO,II NaOH = NO2Na in which reaction the hydrogen of the nitric acid is displaced by the sodium of the sodic hydrate (or soda), and as only one atom of hydrogen is displaced, nitric acid is said to be monobaeic. When an acid admits of the displacement of two atoms of hydrogen, it is termed dibasic—as tartaric, oxalic, and, according to recent views, sulphuric acid; and when three atoms can be replaced—as in the case of common phosphoric acid, in which H, may be displaced by K, or the acid is termed tribasic. The nomenclature of the compounds of acids with bases is, still unfixed. The names of the alkali-metals (potassium, sodium, and lithium) and alkaline-earth metals (barium, cal cium, etc.) are now commonly substituted for those of their oxides in the nomenclature of the corresponding oxygen salts—as, for example, carbonate of sodium and sulphate of calcium for carbonate of soda and sulphate of lime. The names of these bodies are thus brought into uniformity with those of the salts of iron, copper, etc. In Watts' Dictionary and Frankland's Lecture Notes such compounds are denominated sodic car bonate, calcic sulphate, sodic nitrate, etc.; and these terms will doubtless soon be generally
adopted for the metallic salts of the oxygen-acids generally. The nomenclature of com plex inorganic bodies is founded, for the most part, on the theory of types, the names of particular compounds being obtained from the name of the type by prefixing to it adjectives which express the nature of the element by which the hydrogen of the type is replaced and the number of atoms of it contained in one molecule of the compound. By way of illustration, we give a simple and a complicated example: Cl H Bi = bismuthic oxychloride, while = tetramercuro-tetrahydric dioxi ( 4 dichloro-dinitride. The nomenclature of organiC compounds is founded on the same principles as that of inorganic bodies; but our limited space prevents our entering into this subject.
Chemical notation has been considerably altered by certain members of the recent chemical school; but on the whole, the modifications, since the time when the system of Berzelius was introduced into England in the third edition of Turner's Elements of Chemistry, are not numerous. The most important are the introduction of "general formulx" by Gerhardt, in which letters of variable value are used as coefficients instead of numbers, and Odling's method of denoting the atomicity of polyatomic elements and radicals by means of accents placed above the symbols, which are then called dashed symbols. See TRIADS. Chemists are still at variance as to whether, when two or more atoms are represented in a compound, the figure indicating the repetition should be above or below the symbol; whether, for example, water should be represented by or and alcohol by or The ordinary or dualistic system, according to which the elements combine in couples to form compounds, which similarly unite by twos, led to the division of salts into two classes—viz., into salts composed of an oxygen acid and an oxygen base, which were hence called oxygen salts, as NaO,S0,, and which in the old notation represent sulphate of soda and nitrate of potash; and binary or haloid salts, of which chloride of sodium, NaCI, is the type, which are formed by the union of the radical in hydrogen acids with some metal. Davy consid ered that the former class might be made similar to the latter by regarding them as com posed of a metal and a compound radical having the same electronegative chemical relations as the radicals in the hydrogen acids. According to this view, a radical. not yet isolated, combines with hydrogen to form sulphuric acid, and with a metal to form sulphates, sulphuric acid being represented by and sulphate of lime by Ca,S06. In like manner, nitric acid and the nitrates were supposed to contain a radical, Against this view Gerhardt urges that we know nothing of the proximate con stitution, but are merely acquainted with the ultimate composition of compounds. Hence we now no longer use a formula for sulphuric acid indicating its supposed con stitution but regarding it as a dibasic acid, express it, either as Miller does, by 11250-2. or by (where S = 32 and 0 = 16), or by H2 SO2 t if we adopt thetype-notation; and we must not omit that Frankland, who may be regarded as the lead ing representative of the English school of modern chemistry, represents it by the formula when Ho is the abbreviated formula for HO, and represents a com pound radical, to which he gives the name of hydroxyle, and which is commonly known as binoxide of hydrogen, being expressed, according to the old system, by 1102. The following examples may enable the reader to pass from one system to another: The Ko, Zno", and Nao in Frankland's notation represent compound radicals, to which he has given the names potassoxyl, zincoxyl, and sodoxyl, and which are repre sented in the ordinary new notation by KO, and NaO. These new names will probably soon get into general use in consequence of Frankland's great influence as the teacher of chemistry in the government school of mines, and at the royal institution.* We must refer to the article TRIADS for a description of what is meant by atomicity, or, as Hofmann terms it, quantivalence, and the reader do well to study lectures 10 and 11 of his Modern Chemistry. In the article just mentioned, we have stated that the degree of atomicity of an element is indicated by the number of dashes with which it is furnished. In the so-called graphic notation, which, in the hands of Kekule, Crum Brown, Naquet, Frankland, and others, has proved a most valuable aid in explanation of the constitution of chemical compounds, the degree of atomicity of an atom is thus expressed• H' by Q_, Zn" by e , B"' (boron) by , 01. by 4_ , N* by , and V by *.