Of the bases of the CnH2n—11N series, obtained from coal-tar and from the “acid-tar” from the distillation of shale, only three are known, viz., Leucoline, C9H7N; Iridoline, C10H9N; and Cryptidine, C11H11N. These are isomeric with the bases obtained by the distillation of cinchonine with caustic potash, and are described by their discoverer, Greville Williams, in “ Trans. Royal Society, Edinburgh,” vol. xxi. The leucoline series of bases, at first thought to be identical with the cinchonine series, Williams has shown to be isomeric, but otherwise having important differences, these differences chiefly being apparent in their boiling points, their slight tendency to form crystallisable salts, and their reaction with iodide of amyl.
The source of the leucoline bases of Greville Williams was “coal-oil of a very high boiling point, and a density greater than that of water;” his process of separation was to treat the oil with sulphuric acid, and distil the acid liquid with lime; that portion of the distillate which sinks in water is treated with nitrite of potash and hydrochloric acid to destroy phenols; the acid liquid is placed in an iron retort and a current of steam passed through it; the residue remaining in the retort, after being treated with caustic potash, is distilled, and the distillate, consisting of the mixed bases, purified by fractional distillation; the bases were then identified by converting the fractions into platinum and other salts. Proceeding in this manner, Greville Williams separated the three bases—leucoline, iridoline, and cryptidine; the last, cryptidine, C11H11N, being found in his highest fraction, that boiling 270°–275° C, and from what I can learn from other authorities, the isolation of the higher members of this series has not been attempted.