Page:Proceedings of the Royal Society of London Vol 4.djvu/363

Rh The Council have awarded one of the Royal Medals for this year, which had been proposed for the subject of Chemistry, to Robert Kane, M.D., M.R.I.A., Professor to the Royal Dublin Society, for his paper " On the Chemical History of Archil and Litmus," pub- lished in the Philosophical Transactions for 1840.

It has been found that various lichens, which communicate no colour to pure water, strike a fine blue with solution of ammonia. The valuable colouring matters archil, litmus and cudbear, are com- mercial preparations of these lichens. Some progress had already been made in the investigation of their colouring principles by the labours of Robiquet, Heeren, and Dumas ; of which the most im- portant step was the discovery of Orcine, and also of Orceine, into which the former is converted by ammonia ; but the observations were isolated, and the whole subject was in the greatest obscurity. The present memoir by Dr. Kane records the first attempt to sketch a general history of the class : and, considering the great and pecu- liar difficulties attending inquiries into organic colouring matters, the attempt may be esteemed eminently successful. It proved an investigation of considerable intricacy and great extent, involving several hundred organic analyses ; and it has been conducted in a manner highly creditable to the author's skill as an analyst. The paper contains an account of the discovery of a large number of new compounds, not less than twelve, derived from archil and litmus, together with the more exact discrimination of several others, already known, but imperfectly described. The distinction made of two Orceines, which have hitherto been confounded as one, is a striking result contained in the paper : while the observations on the action of chlorine and of nascent hydrogen upon several of the bodies described, open new branches of inquiry.

The objects which the author had in view in these inquiries were the three following : namely, first, to ascertain the primitive form of the colour-making substance in a given species of lichen, and trace the stages through which it passes before the coloured sub- stance is developed ; secondly, to determine the nature of the various colouring substances which exist in the archil of commerce ; and thirdly, to examine the colouring materials of ordinary litmus. He finds in the lichen Roccella tinctoria the following bodies, either pre- existing in the plant, or formed during the processes employed for its analysis: 1. Erythryline; 2. Erythrine (the Pseudo-erythrine of Heeren) ; 3. Erythrine bitter ; 4. Telerythrine ; and 5, Roccelline (the Roccellic acid of Heeren). The properties and constitution of these substances are then described, and the chemical formulse given, which are deducible from' their respective analyses. The author finds the archil of commerce to consist essentially of three ingre- dients, namely, orceine, erythroleic acid, and azoerythrine ; of each of the two former there exist two modifications, and there is, in ad- dition, a yellow matter. After comparing his results with those ob- tained by Heeren, by an examination of the products evolved by his erythrine in contact with air and with ammonia, and stating rea- sons for some changes in nomenclature, the author gives the chemi-