Mr. Duncan on Tivo Neiv Salts of Chromic Acid. 7 



seem to have no idea of its relation to the Piacaba palm. [A reduced 

 coloured figure of this Palm has been published in Hooker's Journal of 

 Botany and Kew Miscellany, for April, 1849.] 



ISth December, 1848. — The President in the Chair. 



On the motion of Mr. Cockey, it was agreed to print a supplementary 

 catalogue of the Library. 



The following gentlemen were admitted members of the Society : — Hon. 

 James Anderson, Lord Provost, Messrs. John M. Rowan, John FuUerton 

 Sloane, Gavin Rae, Jun., Robert Readman, and George M'Leod, M.D. 



The following paper was communicated by Dr. R. D. Thomson : — 



I. — On Two Neio Salts of Chromic Acid. By Archibald Duncan, 

 JuN., Esq. 



In 1827, Dr. Thomson described in his paper on the compounds of 

 chromium, (PhU. Trans. 1827, p. 223,) the double salt — Potash chromate 

 of magiiesicc — (KO CrOg MgO CrOg 2 HO) obtained by digesting a 

 solution of bi-chromate of potash over carbonate of magnesia. I obtained 

 a corresponding lime salt about two years ago by the following process. — 

 A boiling solution of bi-chromate of potash was poured over newly slaked 

 lime in a tall vessel. The undissolved lime having subsided, the super- 

 natant fluid, which was of a lemon yellow colour, was drawn off by a syphon, 

 and slowly evaporated in a hot air stove at 80°. During the first two 

 days of the evaporation, crystalline crusts of an orange salt were formed 

 on the surface of the liquor, and required to be frequently removed. 

 After this time, however, these crusts ceased to be produced, and crystals 

 of a ydlov) salt began to make their appearance at the bottom of the 

 evaporating bason, and in two or three days more a mass of beautiful 

 crystals was obtained. The proportion of the orange to the yellow salt 

 depends a good deal on the temperature employed in the evaporation. 

 Li one experiment the heat was raised to boiling, and no yellow crystals 

 were obtained at all, — orange crusts continuing to separate as fast as they 

 could be removed. 



YcUov) PotOAih Chromale of Lime. — This salt crystallises in lemon yellow 

 four-sided oblique prisms. It is soluble in water, but insoluble in cold 

 alcohol, and is formed in the latter part of the process described. 



The salt, when ignited, fu.se.s, and on cooling, tlic mass has a crystalline 

 aspect, and is quite soluble in water. ^ 



The mean of several analyses gave the following result : — 



