Chemical Symbols, abbreviations of the chemical names of the elements, which are combined into formulas, with or without quantitative signs, to represent the composition of compound bodies. The idea of representing the names of chemical substances by conventional signs or abbreviations appears to be a very old one. The alchemists were in possession of a set of hieroglyphics by which the metals and the four so-called elements, fire, air, earth, and water, and indeed many other substances, were designated. At a later period, as chemical knowledge became more consolidated, various modifications of the alchemistical notation were from time to time proposed, and adopted to a greater or less extent. Among these should be specially mentioned the system of notation offered in 1787 by Hassen-fratz and Adet, as an appendix to Guyton de Morveau's revised system of nomenclature, since its failure enables us the better to appreciate the peculiar excellence of the system which now prevails. Here was a system of symbols by no means devoid of ingenuity, and much more complete than any previous 'method, published in connection with a new system of nomenclature, which was soon universally adopted, and recommended by the committee of the French academy by whom this nomenclature had been prepared; yet it met with little or no favor among chemists, and was soon forgotten.
This last remark applies as well to the symbols proposed by Dalton in 1808, in connection with his writings upon the atomic theory. None of these systems ever came into general use, nor does it appear that they were of much value as instruments of study even in the special cases in which they were employed. It is to Berzelius that chemical science is chiefly indebted for the simple and rational system of notation now in use, which has done so much to advance knowledge and to lighten the labors of chemical investigators. This system, in its first outlines at least, appears not to have been the result of any premeditated plan or special study, but to have followed incidentally as a natural result from the investigation of the combining proportions of bodies with which its author was occupied. Thus in 1814 he first mentions his symbols in a foot note to a memoir upon nitrous acid (Gilbert's Annalen der Physik, xlvi., 154), as convenient abbreviations for expressing the composition of bodies, which he has himself frequently employed in his private memoranda.
Subsequently a more complete exposition of the plan appeared in his Lehrbuch, and in Poggen-dorff's Annalen, 182G, viii., 7. As a sign to express the name and combining equivalent of an element, Berzelius chose the initial letter of its Latin name; and in those cases where the names of several elements commence with the same letter, he annexed to the common initial the first of the following letters in the Latin name of the element which is peculiar to it; thus, the symbol C indicates an equivalent of Carbon, CI an equivalent of chlorine, and Cr an equivalent of chromium. (For a complete list of these symbols, see Equivalent, Chemical.) There are various other symbols used in chemistry, some to express qualities as well as the atoms or molecules of substances, as, for instance, the signs which express the quantivalence of bodies. (See Atomic Theory, vol. ii., p. 88.) The signs +, - , and = are also used in chemical writing for the purpose of joining the symbols of the elements together in formulas, as K2O + H2S04=K2S04 + 2H, or C6H1206- H20 =C6H10O5. When united by the sign = the formulas are called equations.
Thus the latter formula is an equation which represents starch as being formed from the elements of glucose or grape sugar, by the abstraction of a molecule of water or of the elements of such molecule. The quantity of any substance is usually expressed by placing a numeral before it, whether the substance is an element or a compound, unless where the numeral is used to express the number of separate elements or substances which enter into the composition of a compound. Thus 3H signifies three atoms of hydrogen, and 3H20 three molecules of water, one molecule of water being composed of two atoms of hydrogen and one of oxygen. The prefixed numeral however only includes those symbols which are not separated by a + sign or a comma, or which are included in parentheses; as 2KCl,PtCl4, which is the formula of potassic-platinic chloride, and which contains two molecules of chloride of potassium united to one molecule of tetrachloride of platinum. Two molecules of potassic-platinic chloride would be written 2(2KCl,PtC]4). A numeral placed at the right of a symbol and a little below (or sometimes above) multiplies that symbol only. Thus, the formula of sulphuric acid, H2SO4, signifies that it contains two atoms of hydrogen, four of oxygen, and one of sulphur.
A numeral placed in the same position with regard to any number of symbols placed in parentheses has the same function. Thus (H4N)2CO3, which is the formula of normal amnionic carbonate, indicates that two molecules of the compound basyle ammonium, H4 N, are united to one molecule of the oxion C03, or carbion. A capital letter with a dash above it is often used to stand for a compound instead of an element, as a for acetic acid, C2H4O2; 0 for oxalic acid, C2H2O4. Other symbols and abbreviations are also given in the article Atomic Theory.