ADDENDUM TO GUAPTER VII. 

 SOLUBILITY OF CINNABAR IN AMMOXIACAL SOLUTIONS. 



As appears in part tVoiu the ibregoiug chapter, repeated efforts were made to 

 detect mercury in tlie waters of Sulpliur Bauk, but without success. Consequently, 

 althougli the deposit is of such a character as to suggest very strongly that cinnabar 

 is still being formed, such a deposition could not be definitely asserted at the time when 

 (his memoir was transmitted. The absence of mercury from these w^aters was not a 

 little perplexing, for, as will be described in Chapter XV, I had found cinnabar soluble 

 to a very considerable extent in artificial solutions not dissimilar to the waters of Sul- 

 phur Bank, and everything pointed to the conclusion that the ore of this locality must 

 have been deposited from waters like those which now flow from it. These waters, 

 however, are ammoniacal, and experiments in my laboratory had proved that, under 

 ordinary conditions, ammonium salts completely precipitate cinnabar from artificial 

 solutions. 



Consideration of all the circumstances showed it very improbable that the waters 

 had recently become ammoniacal, and I therefore inferred, as was mentioned on page 

 2G0, that cinnabar was probably soluble at high temperatures and pressures in am- 

 moniacal waters, seeing, also, in this hypothesis an explanation of the remarkable 

 fact that cinnabar nowhere appeared at the original surface of the bank. 



To test the matter I devised certain simple experiments, which were carried out 

 after the transmission of this volume. A solution of mercuric sulphide was first made 

 in a manner which will be described in detail in Chapter XV. The solvent is prepared 

 by dividing a solution of sodic carbonate into two portions, saturating one of them 

 with hydrogen sulphide and mixing the fluids. This liquid dissolves mei curie sulphide 

 as a double sulphide of mercury and sodium. The solvent was charged with mercuric 

 sulphide and filtered. Ammonium carbonate was then added till a large precii)itate 

 formed, and portions of the mixture were sealed in glass tubes, which were about half 

 filled. These tubes were then heated to various temperatures above 100° C. At 120° 

 the solutions still showed the dark tint due to the presence of undissolved sulphide, 

 but at 145° and at ITJo the mercuric sulphide was entirely dissolved in less than an 

 hour. On cooling, the black color again appeared, and it was found by appropriate 

 tests that this coloration was due to reprecipitated mercuric sulphide. 



Ammonia in the presence of hydrosulphuricand carbonic acids thus does not com- 

 pletely precipitate mercuric sulphide at high temperatures and pressures, and waters 



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