l8o Inquiry into the Laws of Jffinity. 



The folutions and precipitates of mercury have appeared to me to be particularly worthy 

 of attention, becaufe chemifts have obferved them with more care, and it is more eafy to 

 determine the conditions. 



2. Fourcroy has defcribed in the Memoirs of the Academy of Sciences, 1790, a fulphatc 

 of mercury, which he proves to be analogous to calomel, that is to fay, formed by mercury 

 little oxigenated. He has (hewn that the fulphate of mercury, particularly when fuch a 

 degree of heat only was employed as not to produce complete deficcation of the fulphuric 

 acid and mercury, was divided by the a£lion of the water into two fulphates, one of which 

 may be called oxigenated fulphate, and the other mild fulphate. A fimple method of 

 obtaining this laft combination, is to dilute by a nearly equal volume of water, the 

 fulphuric acid which is treated with mercury, and to caufe the mixture to boil ; little ful- 

 phureous acid is formed, and inftead of oxigenated fulphate of mercury, that fulphate is 

 obtained of which the properties have been fo well inveftigated by Fourcroy. 



In the determination which Fourcroy has given of the conflituent parts of the mild ful- 

 phate of mercury, he fixes at 0,05 the proportion of oxigen which is combined with the 

 mercury ; but for this determination, he fuppofes that on decompofing this fait by pot-alh, 

 it is the pure oxide of mercury which is precipitated. But the metallic precipitates 

 retain a portion of acid vhich he has neglefted; I therefore believe, that according to his 

 experiment, the proportion of oxigen ought to be rather greater than that which he cfta- 

 blifhes. I obferve, that in many determinations made by chemifts in modern times, this 

 confideration has been neglected, which renders them in feme meafure uncertain. 



The mild fulphate of mercury forms a permanent combination, which is not decom- 

 pofed by water^ as the oxigenated fulphate; of mercury is, upoij which I ftiall proceed ta 

 make fome obfervations. 



If the procefs indicated by Fourcroy be' employed, that is to fay, if the concentrated 

 fulphuric acid be made to boil with the mercury, without letting it arrive at a ftate of 

 deficcation, a white mafs is obtained, compofed of fweet fulphate and oxigenated fulphate. 

 By the careful method of wafliing which he points out, the excefs of acid that maintains 

 the folution may be feparated, from the oxigenated fulphate, and a portiorrof the mild 

 fulphate. 



When the operation is carried farther, or when a fufiicient degree of heat is applied' to 

 . the mild fulphate, a greater quantity of fulphureous acid is difengaged ; the mercury be- 

 conies too much oxided to form the mild fulphate, and the combination is found inrirely 

 in the ftate of oxigenated fulphate, which varies in the quantity of fulphuric acid it retains. 

 Let us examine it in the ftate it poflefles when the operation has been carried to drynefs, in 

 which confequently it may be confidered as not poffeffing an excefs of acid. 



In this ftate water produces a feparation ; the mafs which was before white, turns yel- 

 low } the liquid becomes very acid, and holds a part of the fulphate in folution ; there is 

 formed what has been called, fince the time of Rouelle, a fait with excefs of acid, and a 

 (^t with the leaft jortion of acid ;_ but the proportions of thefe two combinations vary, i. 



according. 



