Mr JOHNSTON on the Combination of Chlorine. 211 



the precipitates which they give with the metallic oxides, and 

 which have led some to doubt the accuracy of their indications. 

 The grounds of this opinion will appear in the sequel of the 

 present paper. 



In BREWSTER'S Journal (vol. v. p. 247.), Dr TURNER has 

 shown, that, by previously digesting the Prussian blue in dilute 

 muriatic acid, all loss in the preparation of the cyanide of mercury 

 may be avoided ; but as he found the acid to have taken up only 

 iron and alumina, he leaves it to be inferred that one or both of 

 these is the cause of the impurity above referred to. What is 

 its true nature, I proceed to show. 



To obtain it in a separate state, let the common Prussian 

 blue of the shops be digested in boiling water, a bright greenish- 

 yellow solution will be formed, perfectly neutral, and having the 

 following properties : 



With Caustic Alkalies, Sulphate of Soda, Benzoate of Ammonia, Lime- 

 water, and Salts of Lead, it gives no precipitate. 

 Nitrate of Silver,... it gives a bright brick-red. 



Sulphate of Copper, a brown or dirty brownish-yellow. 



Sulphate of Zinc, light yellow, sometimes brownish. 



Bichloride of Mercury, slight, yellowish, becoming blue. 



Sulphate of Nickel, yellow. 



Cobalt, blood-red. 



Nitrate of Bismuth, chrome-yellow. 



Muriate of Gold, slight, yellowish. 



Sulphate of Cadmium, chrome-yellow. 



Muriates of Tin, beautiful white. 



Sulphates of Iron, deep blue. 



Pernitrate of 'Uranium, slight greenish-yellow. 



Sulphate of Manganese, dirty brown. 



Sulphate of Cerium, none. 



Muriate of Platinum, yellow, soluble in hot water. 



Hydrosulphuret of Potash, . . . white powder. 

 Tincture of Galls, brown. 



If several ounces of Prussian blue be digested in this way 

 with repeated affusions of hot water, and the several solutions be 



