[ 314 ] 

 XL. Proceedings of Learned Societies, 



ROYAL SOCIETY. 

 [Continued from p. 84.] 



June 19, 1873. — "William Spottiswoode, M.A., Treasurer and 

 Yice-President, in the Chair. 



r llHE following communication was read : — 

 4* "Researches on Emeralds and Beryls. — Parti. On the Co- 

 louring-matter of the Emerald." By Greville Williams, E.E.S. 



A considerable amount of discussion has taken place at various 

 times regarding the cause of the colour of the emerald. Klaproth 

 concluded from his earlier analyses that it was due to iron*; but 

 the results of his later experiments f, made after he became aware 

 of Vauquelin's discovery of the presence of chromium in emeralds J, 

 confirmed the observations of that chemist. 



Erom the time of Vauquelin's analyses, the colour of the emerald 

 was always regarded as due to the presence of oxide of chromium, 

 until the publication of the memoir of Lewy§, who, having burnt 

 emeralds in oxygen in a similar apparatus to that employed by M. 

 Dumas in his researches on the atomic weight of carbon, ascertained 

 that they contained that element, and concluded that the colour was 

 due to the presence of some organic substance. Lewy also affirmed 

 that the deepest-tinted emeralds contained the most carbon. The 

 small quantity of chromium contained in emeralds he considered 

 to be insufficient to account for the colour. Wohler and Bose||, 

 on the other hand, having exposed emeralds to a temperature equal 

 to the fusing-point of copper for one hour without their losing 

 colour, and also having fused colourless glass with minute quanti- 

 ties of oxide of chromium and obtained a fine green glass, consi- 

 dered chromium and not organic matter to be the cause of the 

 colour. 



Boussingault^T, in the course of an investigation of the "moral- 

 Ions " **, arrived at the same conclusion as Wohler and Eose ; and 

 although admitting them to contain carbon, denied that it was the 

 cause of their colour, inasmuch as they endured heating to redness 

 for one hour without loss of colour. This result has been confirmed 

 by Hofmeistertt, who found that an emerald endured a red heat 

 for hours without destruction of the colour, except at the edges, 



* Klaproth, Chem. Essays, vol. i. p. 325 (London, 1801). 



t Klaproth, loc. cit. vol. ii. p. 172 et seq. (1804). 



\ Yauquelin, Ann. de Chim. vol. xxvi. [1] p. 262 (1798). 



§ Comptes Eendus, vol. xlv. p. 877 (1857). 



|| Chem. News, vol. x. p. 22. 



f Comptes Eendus, vol. lxix. p. 1249 (1869). 



** The emeralds from the mines of New Granada arc divided, according to 

 Boussingau.lt, into classes, two of the most important being the " canutillos," 

 or finely crystallized, and the " morallons," or amorphous emeralds. 



ft Journ. fur prakt. Chem. vol. lxxvi. p. 1 (1859). 



