}^^ Mn Berzelim on Hydracids, J83 



of mercury be placed in contact with prussic acid gas, the latter 

 is absorbed and water disengaged, while the product is cyanuret 

 qf mercury. TJiis water proceeds from the hydrogen of the 

 prussic acid and the oxygen of the oxide of mercury, neither of 

 ' which enter into the new pombination ; but this compound, for^ 

 merJy called prussiate of oxide of mercury, possesses so plose a 

 resemblance to the salts of that oxide, in appearance, taste, and 

 all its other properties, that the most positive evidence to the 

 contrary would be requisite in order to convince one that it is 

 not a salt of the oxide of mercury, I have myself ascertained, 

 that if the ferroprussiate of potash, that is, a combination of 

 prussic acid with potash and oxidule of iron, be crystallized, 

 there results a compound, containing precisely the quantity of 

 oxygen and hydrogen which would be necessary to convert it 

 into a double salt of prussic acid with oxidated bases ; but that 

 these crystals lose the whole of their water like an efflorescent 

 salt, either when confined in vacuo in the ordinary temperature 

 of the atmosphere, or when exposed to dry air in a temperature 

 between 77° and 86° ; and it is certainly a far simpler view of 

 the phaenomena to re2;ard this water as existing in the state of 

 mere water of crystaUization, than to assume that efflorescence, 

 which can result only from the expansive force of water already 

 formed, should have occasioned the mutual decomposition of 

 the base and acid. Besides, we have never been able to disco^ 

 ver any other difference between the compounds which are 

 regarded as salts of hydracids, and those which indisputably 

 contain no other ingredient except the radicals of the acids and 

 bases, than that which subsists between salts with and without 

 water of crystallization. 



We adopt, therefore, in preference, the theory that salts con^ 

 tainirig a liydracid do not exist, but that when a hydracid is 

 brought into contact with an oxidated base, the hydrogen of the 

 acid combines with the oxygen of the base and forms water, 

 while, at the same instant, the radicals of both unite mutually 

 in their reduced condition, and the product is a substance which 

 resembles so closely the salts of the oxidated radical of the base, 

 that it cannot be distinguished from them in any of its physical 

 characters. Hence, when sulphoprussic acid, which, although 

 wholly destitute of oxygen, possesses a strong and pure acidity, 

 is mixed with carbonate of potash, and when carbonic acid is 

 thereby expelled with the same degree of effervescence which 

 would be occasioned by the addition of an oxygen acid,, the 

 potash is decomposed by the hydrogen of the acid, and a com- 

 bination ensues between sulphuretted cyanogen and potassium. 

 If the mixture was sufficiently concentrated, it crystallizes, and 

 the crystals contain neither hydrogen nor oxygen, but only 

 potassium, sulphur, carbon, and azote ; nevertheless they resem- 

 ble a sahne cQmpo^uftd^ particiil9,rly nitre, so perfectly ;tth^at they 



