When acids combine with bases or metallic oxides to form salts, they produce com pounds, the names of which are influenced by the terminations of the acids. Thus, sulphuric acid and soda form the sulphate of soda; sulphurous acid and soda, the sul phite of soda; and hyposulphurous acid and soda, the hyposulphite of soda. In the same manner, nitric acid with potash forms the nitrate of potash, whilst nitrous acid and pot ash produce the nitrite of potash.
If a symbol be employed alone, it represents one equivalent of the element. Thus, 0 signifies one equivalent, or eight parts by weight, of oxygen; C, one equivalent, or six parts by weight, of carbon; 11, one equivalent, or one part. by weight, of hydrogen. The combination of two elements is represented by placing the symbols for those elements side by side; thus, HO signifies one equivalent of hydrogen and one equivalent of oxy gen in a state of chemical combination (viz., water); and NaC1 is one equivalent of sodium (Lat. natron)united with one equivalent of chlorine (viz., common salt).
When two or more equivalents of one element unite with one or more equivalents of another element, the number of such equivalents is signified by a small figure being placed immediately after the symbol of the element so multiplied. Thus, HO, repre sents one equivalent of hydrogen in combination with two equivalents of oxygen per oxide of hydrogen); lSInO, is one equivalent of manganese with two of oxygen (black oxide of manganese); Fe20, is two equivalents of iron with three equivalents of oxygen (rust); and is three equivalents of lead with four equivalents of oxygen (red lead).
In expressing the formula of a compound substance, the symbol of the metal or its analogue is placed first in order, and is succeeded by the oxygen, chlorine, or similar element. Thus, the symbol for the chlorine of mercury is always written HgC1, never ClHg. The same order is carried out in the construction of the formula of more com plex substances; the metallic half is placed first. Thus, sulphate of iron—containing sulphuric acid and the oxide of iron—is always expressed as never In other words, the symbols are written in the order in which the substances would be named in Latin.
In the construction of the formulas of complex substances, the comma (,) and plus sign (-4-) are often introduced; the former to separate the symbols of substances which are closely united together, and the latter to form a line of demarcation where the com ponents are less intimately combined. Thus, represents the com pound of the sulphate of iron with the sulphate of potash; KC1+PtC1, is the double chloride of potassium and platinum.
Large figures placed at the left hand of a formula multiply all the symbols till a comma or plus sign appears. Thus, represents three equivalents of sulphuric acid; 3PbO,A is three equivalents of oxide of lead, and one equivalent of acetic acid; and 24110 (alum) is one equivalent of the sulphate of potash, with one equivalent of the sulphate of alumina, and 24 equivalents of water. When a com pound substance requires to be multiplied, it is inclosed within parentheses, and a large figure placed immediately before it; thus 3(K0,C,03)+ Fe,03,3C,03 +6110 represents three equivalents of oxalate of potash, one equivalent of oxalate of iron, and six equiva lents of water.
In expressing the formulas of organic compounds, the symbols are written in the following order: CHNO. Thus, turpentine is alcohol is and morphia is C341113D4 06.
Arbitrary symbols are occasionally used to represent important complex substances. Cyanogen is known as Cy; the organic acids are recognized by their initial letter with the sign (—) drawn above, as T for tartaric acid, A for acetic acid, 04H,0,; and 0 for oxalic acid, while the alkaloids are represented by their initial letter or letters with the sign (+) above; thus, tr for strychnine, l'tIo for morphia, and for quinine, C401124N,0,.
Occasionally, in treatises on mineralogical chemistry. arbitrary modes of expressing the composition of minerals are resorted to, which it is not necessary here to explain.