Decomposition of Perchloride of Mercury . 133 



detach the required quantity of muriatic acid : the precipitates 

 obtained in both cases were reddish-brown, not at all crystal- 

 line, much less dense than the dipermuriate, and contained 

 scarcely 6'5 per cent of muriatic acid. From all these circum- 

 stances I have no doubt that both products were mixtures of 

 dipermuriate and peroxide of mercury. 



The colour, density and crystalline appearance of the diper- 

 muriate of mercury depend on the mode in which it is pre- 

 pared. When hard carbonate of lime, such as Iceland spar, 

 is put into a solution of corrosive sublimate, months are re- 

 quired to obtain even a few crystals of the salt ; these are 

 nearly blaok, and adhere strongly to the carbonate : powdered 

 marble acts more readily, and without the application of heat. 

 By this method I have produced the most regular crystals, 

 and they may be separated by elutriation from all admixture 

 of the undissolved carbonate : some which I procured were 

 sufficiently large to exhibit distinct rhombic planes. Preci- 

 pitated carbonate of lime acts more rapidly than powdered 

 marble, but still the effect is slowly produced unless the mix- 

 ture be heated : it is difficult, however, to procure the diper- 

 muriate without some admixture of carbonate of lime; and its 

 colour is much lighter, and the crystals are smaller than those 

 obtained by slower action. 



By the following process I obtained the dipermuriate per- 

 fectly ,free from all admixture : — Dissolve 1 atom = 272 grains 

 of perchloride of mercury in water, heat the solution ; and add 

 to it e^S grains = 3 atoms of peroxide of mercury, obtained 

 either by decomposing the pernitrate with heat, or corrosive 

 sublimate with potash; I prefer the latter on account of its 

 state of minute division. When the mixture is boiled, a dark 

 precipitate soon begins to form, and eventually nearly the 

 whole is converted into the dipermuriate ; a small portion of 

 corrosive sublimate, yielding about 6 grains of peroxide of 

 mercurj', remains undecomposed, and of course an equiva- 

 lent quantity of peroxide is diffiised through the dipermuriate 

 formed; this is easily separated by boiling the precipitate 

 with about 100 grains of muriatic acid diluted with water. 



The dipermuriate thus procured is perfectly black, dense, 

 crystalline, and frequently very brilliant. Tlie salt may also 

 be procured )K)ssessing similar apjieaiance, by heating per- 

 oxide of mercury in a quantity of muriatic acid, less than that 

 required for converting it into corrosive sublimate. 



While the foregoing paper was printing, I observed that 

 in M. Gny-Lussac's Lectures (vol. i. lecture 17), he mentions 

 tlic formation of subchloride of mercury, by mixing the per- 

 chloride 



