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(showing how coniine, piperine, atropine, nicotine, caffeine, theobromine, and others, have been synthesised; and that quinine, strychnine, morphine, and codeine await conquest).

Liebig, Gerhardt, and other chemists had been progressing towards this attainment by studying the structural constitution of various alkaloids. In 1842 Gerhardt separated a base which he called quinoline from quinine, cinchonine, and strychnine. This base was subsequently identified by Hofmann with the leucol which Runge had obtained from coal-tar in 1834. In 1846 Runge also produced a substance which he called pyridine from bone oil. Hofmann showed that this was the base of certain other alkaloids, coniine, piperine, nicotine, and atropine among these. Now it will be necessary to illustrate progress by means of a few formulæ diagrams.

Benzene is C6H6; aniline is a derivative of benzene in which one atom of hydrogen has been replaced by the amino-group, NH2. Its formula is C6H5NH2, and it is represented thus:

Aniline is basic; that is, it combines with acids to form salts. Together with aniline in coal-tar there occur other basic nitrogenous substances; of these pyridine and quinoline have already been mentioned, and to them must be added isoquinoline, which is also the parent substance of a series of alkaloids.