324 Mr. Donovan on the [Nov. 



riate. Hence, by trituration of black oxide of mercury with very 

 weak acid, we obtain a muriate very near the point of saturation ; 

 and by boiling very dark-coloured submuriate with dilute acid, 

 the salt becomes nearly as white as calomel. 



53. When this gray submuriate is exposed to heat in a sublim- 

 ing apparatus, a quantity of acid forsakes one part, and unites 

 with the other : hence calomel sublimes, the oxide forsaken by 

 the acid is reduced, oxygen being evolved, and a large quantity 

 of mercury volatilized ; but there is not a particle of oxymuriate 

 formed. These changes exactly correspond with the constitu- 

 tion of a subsalt. 



54. When solution of corrosive sublimate is boiled on red 

 oxide of mercury, no change takes place at first, but after some 

 time, the oxide suddenly becomes black. 



This black powder, after being well washed, will afford the 

 red oxide unaltered, when acted on by pure potash. If dilute 

 nitric acid be poured on the black powder, it instantly dissolves, 

 and the solution will be copiously precipitated by nitrate of 

 silver. From these facts, and from the union of the red oxide 

 with muriatic acid in a neutral solution of oxymuriate of mercury, 

 the black substance is evidently a sub oxymuriate. 



This salt is scarcely soluble in water. However, if boiled in 

 water, a little dissolves, which imparts a most disagreeable taste; 

 the water, on cooling, deposits a small quantity of opaque 

 crystalline grains, which are of a deep brown colour on account 

 of the water which they contain. 



55. It now remains to ascertain the constitution of the oxides 

 which constitute the bases of the muriates of mercury. The 

 decomposition of calomel has been already amply considered. 

 The following is the theoiy of some other circumstances atten- 

 dant on that process, which could not be explained without a 

 previous knowledge of the suboxymuriate. When a few drops 

 of solution of potash are let fall on calomel, a brown colour is 

 given to it. The alkali takes up part of the acid, forming a sub- 

 muriate, and reduces part of the oxide ; the oxygen passing to 

 the submuriate, forms a certain portion of brown suboxymuriate. 

 When a sufficiency of alkali is poured on, the submuriate and 

 suboxymuriate are decomposed, giving rise to black and red 

 oxide. This theory accounts for the different changes of colour 

 during the process, which are otherwise inexplicable. 



56. The power which pure alkalies possess of partially reduc- 

 ing the oxide contained in the protosalts of mercury, might, 

 perhaps, leave it doubtful what is the exact degree of oxidation 

 of the metal in calomel. I conceive it to be the black oxide, as 

 commonly supposed, on the following accounts. When nitrate 

 of mercury is decomposed by acetate or muriate of soda, there 

 is no reason to suppose any change in the oxidation of the 

 metal : hence we conclude that calomel and acetate of mercury 

 contain the same oxide. Now as the acetate is formed by 



