326 Mr. Donovan on thz [Nov. 



64. Th* oxacetate and suboxaeetate are salts well known ; 

 and from Lie manner that these salts, as well as the two already 

 mentioned, are formed, it is sufficiently evident that they contain 

 no other oxides than the black and red. 



General Observations, 

 Having now endeavoured to ascertain the composition of the 

 two oxides of mercury, to enumerate the combination of the 

 chief acids with the oxides, and to prove the identity of these 

 oxides with those the composition of which had been previously 

 discovered, it appears to me that there are no grounds for even 

 supposing the existence of any other oxides than the black and 

 red, or, what is the same thing, the yellow. In the progress of 

 the inquiry, I have endeavoured to show, that in all the salts, 

 the metal unites to the acid so as to produce a neutral and a 

 subsalt with each oxide, the catalogue being completed by the 

 subsulphate, submuriate, subacetate, and suboxymuriate. As 

 to the supersalts of mercury, their existence has not been 

 proved ; in no case does the excess of acid enter into the salt 

 as an essential ingredient constituting part of a definite com- 

 pound, and retained by an affinity of any considerable force. 

 And beside this, the analogy of the definite salts, as the muriate, 

 the oxymuiiate, and the acetate, manifest no tendency to unite 

 with an excess of acid. Fourcroy found that the excess of acid 

 was easily washed away from supersulphate of mercury ; and the 

 same might be applied to all the rest; for they may all be 

 reduced to the state of subsalts by mere washing. The super- 

 salts can only exist in solution, and they should rather be consi- 

 dered as solutions of the neutral salts in an excess of their own 

 acid, which will again deposit these salts in a state of neutrality. 

 Thus sulphate of soda crystallizes neutral in an excess of its own 

 acid ; but sulphate of potash in an excess of acid, will crystallize 

 with this excess as often as we think proper, because that excess 

 is retained by real affinity. The nitrate, sulphate, and acetate, 

 will not dissolve in water of any temperature, unless there be 

 an excess of acid : and if there be no such excess, one part of 

 the salt supplies it, while a subsalt is deposited. This decompo- 

 sition originates in the affinity of the water to acid, rather than 

 of the salt to an excess of acid ; for if the affinity of the water 

 be previously satisfied by any other acid, the salt parts with 

 very little of its own. Thus a solution of nitrate of mercury may 

 be poured into a large quantity of water without decomposition, 

 if the latter be acidulated with distilled vinegar, although there 

 is no decomposition effected by the vinegar on the nitrate in the 

 cold. If we attempt to saturate the excess of acid in a solution 

 of nitrate of mercury, by an alkali, we fail ; for every addition 

 precipitates a subsalt, and yet a considerable excess of free acid 

 is found in the solution to the last. It is, therefore, impossible 

 to obtain a neutral mercurial salt while water is present ; and it 



