Therefore in place of the term "equivalent" or "combining proportion," it is more usual to employ that of "atomic weight." Thus the atomic weight of Oxygen is 8, represented by the symbol O; that of Sulphur is 16; hence the atomic weight of the compound atom of Sulphuric Acid, or SO{3}, is necessarily equal to the combined weights of the four simple atoms; _id est_, 16 + 24 = 40. ON THE CHEMISTRY OF ORGANIC SUBSTANCES. By "organic" substances are meant those which have possessed _life_, with definite organs and tissues, in contra-distinction to the various forms of dead inorganic matter, in which no structural organization of that kind is found. The term organic however is also applied to substances which are obtained by chemical processes from the vegetable and animal kingdoms, although they cannot themselves be said to be living bodies; thus Acetic Acid, procured by the distillation of woody fibre, and Alcohol, by fermentation from sugar, are strictly organic substances. The class of organic bodies embraces a great variety of products; which, like inorganic Oxides, may be divided into neutral, acid, and basic. The organic _acids_ are numerous, including Acetic Acid, Tartaric, Citric, and a variety of others. The _neutral substances_ cannot easily be assimilated to any class of inorganic compounds; as examples, take Starch, Sugar, Lignine, etc. The _bases_ are also a large class. They are mostly rare substances, not familiarly known: Morphia, obtained from Opium; Quinia, from Quinine; Nicotine, from Tobacco, are illustrations. _Composition of organic and inorganic bodies contrasted._--There are more than fifty elementary substances found in the inorganic kingdom, but only _four_, commonly speaking, in the organic: these four are Carbon, Hydrogen, Nitrogen, and Oxygen. Some organic bodies,--oil of turpentine, naphtha, etc., contain only Carbon and Hydrogen; many others, such as sugar, gum, alcohol, fats, vegetable acids--Carbon, Hydrogen, and Oxygen. The _Nitrogenous bodies_, so called, containing Nitrogen in addition to the other elements, are principally substances derived from animal and vegetable tissues, such as Albumen, Caseine, Gelatine, etc.; Sulphur and Phosphorus are also present in many of the Nitrogenous bodies, but only to a small extent. Organic substances, although simple as regards the _number_ of elements involved in their formation, are often highly complex in the arrangement of the atoms; this may be illustrated by the following formulæ:-- Starch C{24}H{20}O{20} Lignine C{24}H{20}O{20} Cane Sugar C{24}H{22}O{22} Grape Sugar C{24}H{28}O{28}