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XLII. On the Bromo-cyanide and Chloro-cyanide of Potas- 

 sium and Mercury. By R. H. Brett, Esq.* 

 HPHE iodo-cyanide of potassium and mercury has been de- 

 A scribed by Liebigf, according to whom, the mercury in 

 the cyanide is combined with twice as much cyanogen as would 

 be necessary to convert the potassium of the iodide into cy* 

 anide of potassium, from which statement it would appear 

 that the double salt is compounded of an atom of iodide of 

 potassium, and an atom of bicyanide of mercury, its symbolic 

 representation would therefore be K I + Hg 2 Cy. The salt 

 in question is deposited in crystals, when saturated solutions 

 of its component salts are mixed together, or still better when 

 an alcoholic solution of iodide of potassium is added to a sa- 

 turated solution of bicyanide of mercury in water. This salt 

 when collected on bibulous paper and dried possesses a re- 

 markable brilliancy, assuming the appearance of plates not 

 unlike cholesterine; it is heavy, speedily sinking in water, in 

 which, as well as in alcohol, it readily undergoes solution, espe- 

 cially with the assistance of heat. The acids even when di- 

 luted decompose it, causing a deposition of biniodide of mer- 

 cury and evolution of hydro-cyanic acid. The salts about to 

 be described, also compounded of two haloid salts, and which 

 I shall call the bromo-cyanide and chloro-cyanide of potas- 

 sium and mercury, may be obtained in the following manner. 



The Bromo-cyanide of Potassium and Mercury. — If to a so- 

 lution of the bicyanide of mercury in water, an aqueous solu- 

 tion of bromide of potassium be added, and the fluid set aside, 

 after some time crystalline plates of much brilliancy, and very 

 like cholesterine in appearance, begin to pervade the fluid ; if 

 cold and saturated solutions of the salts be employed, the cry- 

 stalline deposit takes place at once. The readiest mode per- 

 haps of obtaining this double salt is to mix moderately concen- 

 trated solutions of the two components, evaporating the result- 

 ing fluid to a small bulk, and then transferring the fluid to a 

 convenient glass vessel, to plunge the whole into cold water, by 

 which means the largest amount of double salt is obtained ; 

 this should be thrown on a filter and washed with a very small 

 quantity of cold water, then pressed between folds of bibulous 

 paper until all moisture is removed. By somewhat slow cry- 

 stallization from an aqueous solution, this salt may be ob- 

 tained in delicate acicular crystals; these under a microscope 

 appear to be flattened quadrangular prisms. 



The salt in question is soluble both in hot and cold water, 

 also in alcohol, especially when hot. 



* Communicated by the Author. 



f The iodo-cyanide of potassium and mercury was described by Dr. 

 Apjohn in 1831, Phil. Mag. and Annals, N.S. vol. ix. p. 401.— Edit. 



