368 Royal Society. 



When solutions of common salt and sulphate or nitrate of 

 copper are mixed together at common temperature, the solu- 

 tion remains blue; on applying heat to it, it gradually changes 

 to green, and if allowed subsequently to cool, regains its ori- 

 ginal blue colour. It has been supposed from this appear- 

 ance that common salt does not at common temperature de- 

 compose sulphate or nitrate of copper, but that at the boiling 

 temperature it is able to effect their decomposition, and that 

 the green colour of the boiling solution is evidence of the pre- 

 sence of chloride of copper. The facts above stated, however, 

 show that the green colour which the solution acquires when 

 heated is no proof of the formation of chloride of copper, as 

 a dilute solution of the chloride itself is blue when cold, and 

 becomes green when heated. When the mixed solution of 

 nitrate of copper and common salt is evaporated, it becomes 

 permanently green ; hence it was supposed that under these 

 circumstances the salts completely decomposed each other, 

 whilst, when the solutions were dilute, the affinities remained 

 so balanced, that a slight increase or decrease in the tempe- 

 rature was sufficient to determine the arrangement of the acids 

 and bases. The truth however evidently is, that the chloride 

 is formed when the cold solutions are mixed, and becomes 

 permanently green from concentration, like the blue dilute 

 solution of the chloride. That this is really the case is also 

 easily shown by taking, in place of solutions of the two salts, 

 the dry sulphate of copper and chloride of sodium in powder ; 

 mixing them and adding a small quantity of water, a deep 

 green solution of chloride of copper, together with sulphate of 

 soda, is immediately formed. When sulphate of copper is de- 

 composed by chloride of calcium or barium, a blue or green 

 solution of chloride of copper results, after separating the sul- 

 phate of lime or barytes, the colour of which depends on the 

 strength of the solutions originally employed ; if weak and 

 blue, it acquires a green colour when heated; and if concen- 

 trated, becomes permanently green. 

 October 15th, 1843. 



XLVII. Proceedings of Learned Societies. 



ROYAL SOCIETY. 

 [Continued from p. 57«] 

 March 30, HPHE following papers were read, viz.— 



1843. ■*- 1. " Researches into the Structure and Develope- 

 ment of a newly discovered parasitic Animalcule of the Human 

 Skin, the Entozoon folliculorum." By Erasmus Wilson, Esq., Lec- 

 turer on Anatomy and Physiology at the Middlesex Hospital. Com- 

 municated by R. B. Todd, M.D., F.R.S. 



