ORGANIC CHEMISTRY. The science of chemistry is generally studied under two distinct heads or divisions, namely, first the chemistry of inorganic or mineral matters, and the numerous substances derived from them by artificial processes ; and secondly, the chemistry of compounds obtained either directly or indirectly from organised beings, vegetable or animal. The first division constitutes inor ganic chemistry, the second organic chemistry. So long as the peculiar compounds recognised as organic could be obtained only through the iuetrumeutality of that combination of conditions sometimes termed vital force, the above division of the science was quite definite and philosophical, but as early as the year 1525, Wdhler succeeded in producing artificially the substance urea, a body which had up to that time been known only as a product of the animal organism. This discovery was followed many years later by the artificial formation of acetic acid, from exposing a mixture of protochloride of carbon, water, and chlorine to sunlight, and the reduction of the chloracetic acid thus obtained into acetic acid by an amalgam of potassium. The subsequent production of methyl from acetic acid added one of the organic radicals to the list of compounds obtainable from their elements without vital action. Although little further progress was made for several years in this department of chemical research, yet the artificial production of urea and acetic acid, together with their derivatives, completely broke down the barrier between so-called still organic and inorganic bodies; the name organic was retained for the class of bodies to which it had previously been assigned, although now obviously no longer strictly applicable.
Whilst the term organic chemistry is thus deprived of its original meaning, it would still be difficult to devise a more convenient name for that portion of the science which treats of compounds that aro ordinarily though not invariably derived from organised beings, hence the continuance of its use to the present day.
Classification of organic compounds.—Tho number of compounds included within the domain of organic chemistry has of late years become so vast, owing to the laborious researches of numerous chemists, as to render some system of classification almost absolutely necessary to enable the mind to grasp a branch of knowledge embracing such an infinite number of experimentally demonstrated facts.
Whilst on the one hand, it cannot be said that organic chemistry is not yet sufficiently developed to admit of satisfactory generalisations, on the other, it is evident that in a science which is yearly making such rapid progress, any system of classification, however satisfactory when first proposed, can scarcely be expected long to fulfil all the con ditions demanded of it. Hence it would not be difficult to advance objections against the excellent system recently submitted by M. Gerhardt—a system which, notwithstanding all drawbacks, is generally admitted to be by far the bent hitherto proposed. It has therefore been adopted as far as possible in the chemical articles of this Cycl optedia.
The essential portion of Gerhardt's system may be explained in very few words.
All organic compounds which have been sufficiently studied are arranged around a certain number of centres or pivots chosen from amongst the two homologous series of acids, beginning respectively with formic acid and benzoic acid. The two great divisions thus created are termed sections, and the families arranged about the centres are named series. Thus we get the following arrangement :— Each series is subdivided into groups : the benzoic series for instance consists of eight groups. (BENZOIC SERIES.] Under each group will generally be found described or mentioned every individual member belonging to that group, thus under BENZOIC GROUP, one of the groups of the Benzoic series, a large number of compounds more or less intimately connected with each other, and with benzoic acid, will be found described.