Royal Society. 299 



theory of isomorphism for doubting the correctness of the received 

 atomic weights of silver, sodium, &c., but that the difficulty, or 

 anomaly, if it may be so called, should be considered as attaching 

 itself to the di- compounds of copper; and that Faraday's proposi- 

 tions on this subject remain unimpeached. 



4. " Second series of Approximate Deductions made from about 

 50,000 observations taken during the years 1836, 1837, and 1838, 

 at the Port Louis Observatory, Mauritius, four times each day ; 

 namely, at 8 A.M., at noon, and at 4 and 8 P.M." By J. A. Lloyd, 

 Esq., F.R.S. 



5. " On the Solubility of Silica by Steam ; with an account of 

 an experiment on the subject, conducted in the East Indies by 

 Julius Jeffreys, late of the Hon. East India Company's Medical 

 Establishment." 



The inner surfaces of a flue built of siliceous bricks appeared to be 

 deeply eroded by the passage over it of steam at a very high tem- 

 perature, and fragments of siliceous materials laid in the course of 

 the current were partially consumed. A siliceous crust was de- 

 posited on several vessels of stone ware, coated with a micaceous 

 glaze, placed in the upper part of the furnace, and this crust was 

 re-dissolved when the vessels were removed to a hotter situation in 

 the same furnace. The author notices the experiments of Dr. 

 Turner* and others, which failed in showing the solubility of silica 

 by steam, in consequence, as he conceives, of the heat having not 

 been sufficiently great to effect the solution. 



June 4. A paper was read, entitled, " Contributions to the Che- 

 mical History of Archil and of Litmus." By Robert Kane, M.D., 

 M.R.I.A. Communicated by Francis Baily, Esq., V.P.R.S, 



After a preliminary sketch of the labours of Heeren and of Robi- 

 quet in investigating the origin of the beautiful colouring materials 

 termed Archil and Litmus, obtained from different kinds of colourless 

 lichens, and their detection of the two proximate principles termed 

 erythrine and orceine, the author states the object of the inquiries de- 

 tailed in the present paper to be threefold ; viz. 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 co- 

 loured substance is developed ; secondly, to determine the nature of 

 the various colouring substances which exist in the archil of com- 

 merce ; 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 pro- 

 cesses 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 che- 

 mical formulae given, which are deducible from their respective ana- 

 lyses. The author finds the archil of commerce to consist essen- 

 tially of three ingredients, namely, orceine, erythroleic acid, and 



[* See L. & E. Phil. Mag. vol. v. p. 297. EDIT.] 



