1825.] peculiar Class of Comhinalions, 133 



cyanuret of mercury was ascertained by dissolving 0'67 gramme 

 of the crystals in hot water, and precipitating the silver by cyanic 

 acid. The filtered liquid was then evaporated to dryness, in 

 order to expel the excess of cyanic acid, and the disengaged 

 nitric acid. 0"36 gramme of pure cyanuret of mercury remained 

 = 53'74 per cent. 

 Hence 100 parts of this compound consist of 



Nitrate of oxide of silver 37'96 1 atom 



Cyanuret of mercury 53*74 2 



Water 7-60 8* 



99-30 



Here therefore we have a compound destitute of oxygen, and 

 analogous to the metallic sulphurets and chlorides, associated in 

 determinate proportions with another compound, which belongs 

 in the strictest sense of the word to the class of salts. As we 

 knovv that many bodies exert sometimes an electro-positive and 

 at other times an electro-negative action, and that many com- 

 pounds, which, by themselves, appear of an indifferent nature, 

 may assume either of these characters with reference to certaiu 

 other substances, it follows, that the compound here examined 

 must, in this point of view, be regarded as a saline combination, 

 in wliich the nitrate of oxide of silver acts as the acid, and the 

 cyanuret of mercury as the base. The existence of water of 

 crystallization in the compound, which neither of its ingredients 

 in a separate state possesses, affords an additional argument for 

 ranking it in the class of salts. Berzelius, when he formed the 

 white crystalline compound of prussian blue and sulphuric acid, 

 was the first person who discovered the existence of this class of 

 combinations. 



I now attempted to form other compounds, in which the 

 nitrate of oxide of silver would act as an acid when united with 

 metallic cyanurets. 



Newly precipitated and washed cyanuret of silver was boiled 

 in a solution of nitrate of silver : it dissolved slowly, but com- 

 pletely. As soon as the temperature fell a few degrees below 

 the boiling-point, there was deposited a large quantity of long 

 white shining needles, so that the liquid became converted 

 almost into a magma. They were transferred upon blotting- 

 paper and dried. This compound cannot be washed, for the 

 affinities by which it is maintained are so feeble, that when 

 placed in contact with water, it is instantly resolved into pulve- 

 rulent cyanuret of silver, and the soluble nitrate. Hence in its 

 preparation it is necessary to employ a pretty concentrated 



• Or 4 atoms of water, adopting Dr. Thomson's numbers.— Ed. 



