SOLUTION or ClNNAl'.AH. 421 



mixtures containing free hydrate. A prol)a!)le explanation of tliis apparent 

 neglect of careful investigations will a|)i)('ar a little further on. In 187G 

 Mr. M.C. Mehu^ examined the soluble, crvstalline mercury-sodium salt cor- 

 responding to ]5runner's ixitiissium comp(unid. I le found mercuric sulidiide 

 insoluble in sodic hy<Irate or in the simple sulphide of sodium, Ijut highl\- 

 solnble in mixtures. One part of mercuric sulphide with two parts of the 

 crystallized sulphide of sodium and two parts of a solution of sodic hydrate 

 of specific gravity l.oS form, he found, a perfect fluid, which absorbs car- 

 bonic acid and gradually precipitates at first sodium carlwnate containing 

 mercuric sulphide and later crystals of cinnabar. 



Alkaline pentasulphides convert amorphous quicksilver sulphide di- 

 gested with them into cinnabar,- and this process implies a certain degree 

 of solubility. Mr. Barfoed, however, found mercuric sulphide insoluble at 

 ordinary pressures in sodium sulphydrate to which sulphur had been added, 

 and the solubility in the pentasulphide is probably slight. The conversion 

 of the l)lack into the red sulphide does not appear to imply more than a 

 mere trace of solubility, for Messrs. II. Sainte-Claire Deville and Debray 

 produced rhombohedral crystals of cinnabar by heating precipitated sulphide 

 with chlorhydric acid to 100"" C. in a closed tube.^ No statement is made in 

 the account of this experiment of any means being employed to produce 

 any great pressure. Mr. S. B. Christy^ found that at pressures of from 

 150 to oOO pounds per square inch and temperatures of from 180^ to 200° 

 various liquids heated with precipitated mercuric sulphide convert it into 

 vermilion. He experimented with polysulphides of potassium, potassic 

 sulphydrate, acid sodic carbonate charged with sulphydric acid, and a 

 spring water containing acid sodic carbonate which he charged with sulphy- 

 dric acid. He reached no conclusions as to the state of combination of 

 the mercury in solution. The fact that glass is greatly attacked at high 

 pressures and temperatures by alkaline solutions of course leaves many 

 possibilities open. Prof R. Wagner'^ has shown that mercuric sulphide is 



I Russian Jour, of Pharm., reported in Jabresbericbt der CUeuiie, 187(i, p. 282. 



^Gmelin-lCraut: Handbnch der Chemic, Anorganiscbe Cbemio, vol. 3, p. -r,.''., «bore many refer- 

 I'Mces may be found. 



'Fomiud and Micbel-L<<vy : Syntbesc des miu. et des roches, p. 313. 

 <Am. Jour. Soi., 3d series, vol. 17, 1879, p. 4.-)3. 

 6 Jour. praUt. Cbouiic, vol. 9^, ISlJG, p. 23. 



