$2$ "kef Marches refpcBing 



combination, which is not decomposed by water as the <stj-> 

 genated fulphate of mercury is, upon which I (hall proceed 

 to make fome obfervations. 



If the proccfs indicated by Fourcroy be employed, a white 

 mals is obtained, compofed of fweet fulphate and oxygenated 

 fulphate. By the careful method of wafhing which he points 

 out, the excefs of acid that maintains the folution may be 

 fens rated from the oxygenated fulphate and a portion of the 

 mild fulphate. When the operation is carried further, or 

 when a fufticicnt degree of heat is applied to the mild ful- 

 phate, a greater quantity of fulphureons acid is difen gaged, 

 the mercury becomes too much oxided to form the mild ful- 

 phate, and "the combination is found entirely in the Hate of 

 oxygenated fulphate, which varies in the quantity of fulphuric 

 acid which it retains. Let us examine it in the (late it pof- 

 lWFcs when the operation has been carried to drynefs, in 

 which, confequcntly, it may be confidered as not pofleiling 

 an excels of acid. 



In this (late water caufes a feparatlon ; the mafs which was 

 before white, turns vellow ; the liquid becomes verv acid, 

 and holds a part of the fulphate in folution; there is formed 

 what has been called, iince the time of Rouelle, a fait \vith 

 excels of acid, and a fait with the leaft portion of acid : but 

 the proportions of thefe two combinations vary, I, According 

 to the quantity of acid the firft combination had retained; 

 2. According to the quantity of water employed : 3. Accord- 

 ing to the temperature; for the heat concurs with the a£tion 

 of the water. 



If for fimple water an alkaline folution be employed, which 

 exerts a more powerful action upon the acid than pure water, 

 two combinations are formed, one of which is found to be 

 almoft entirely the oxide, and the other in which the acid is 

 for the moft part engaged : the precipitate obtained differs 

 principally from that which water alone would have produced, 

 bv the fmaller proportion ofac'id which it retains, and which 

 depends on the degree of concentration of the alkaline liquor 

 which a£ts upon it. 



When the oxygenated fulphate of mercury retains a more 

 confiderable excels of acid, the aclion of the latter mar 

 be fo weakened by the water, that no reparation will take 

 place. 



3. I have hitherto fuppofed btrt two fulphates of mercury 

 to exift, one with the fmalleft poffibie proportion of oxygen, 

 and the other with the greateft ; but it is manifeft that two 

 extremes only are thus fixed, fo that they may contain within 

 their limits alf the other degrees of oxydation: the properties 



of 



