and _camphor_, which Dumas first showed to have the composition C10H16O, should be closely allied in constitution, and that it ought to be readily possible to effect their mutual transformation. The constitution of camphor was long one of the standing problems of organic chemistry, and dozens of formulæ have been suggested at various times during the last twenty years in explanation of its structure. That it contained a benzene nucleus seemed to be proved by the ease with which it yielded toluene, cymene, and other benzene homologues. The first real insight into its structure was gained when Bredt ascertained the constitution of _camphoronic acid_, C6H11 (CO2H)4—a product, together with _camphoric acid_, of the oxidation of camphor—which he found broke up into trimethylsuccinic acid and _iso_butyric acid, and the structure of which was established by Perkin and J. F. Thorpe. The result of the Japanese monopoly has been to greatly enhance the price of natural camphor; during the last ten years it has practically trebled. This has naturally stimulated endeavours to prepare this substance by synthetical means. _Artificial camphor_ is now made from _pinene_ by transforming the hydrocarbon into bornyl chloride by the action of hydrochloric acid. From this _camphene_ is prepared; by treatment with glacial acetic acid it forms _isobornyl acetate_. On hydrolysis this is transformed into _isoborneol_, which by oxidation yields _camphor_, differing from the naturally occurring variety only in the fact that it is optically inactive. All so-called aromatic compounds are not necessarily cyclic systems, for it has been recognised within the past few years that some of the most valuable natural perfumes, such as that of the rose, lavender, and orange blossom, lemon-grass, geranium, ylang-ylang, neroli, etc., owe their characteristic aroma to the presence of terpenes and camphors, which are not strictly benzenoid or cyclic compounds, but “ruptured rings” behaving like open-chain or aliphatic substances. To judge from past experience, it may confidently be stated that, now the constitution of these substances is understood, their synthetical preparation on an industrial scale is practicable. The discovery by Cahours in 1844 that _oil of wintergreen_ is substantially methyl salicylate led to its artificial production from synthetically prepared salicylic acid. Sir William Perkin in 1868 effected the synthesis of _coumarin_, the aromatic principle in woodruff and hay. Fittig and Mielck in 1869 synthesised _heliotropin_, and in 1871 Tiemann and Haarmann obtained _vanillin_, the characteristic aromatic body in the vanilla pod, by synthetic means, and established its manufacture on a commercial scale. The chemical nature of the characteristic odoriferous substances in oil of cumin, anise, rue, cinnamon, heliotrope, jasmine, violet, parsley, etc., has now been established and some of them are made industrially.