G. F. Becker—Solutions of Cinnabar, Gold, ete. 205 
of the alkaline sulphydrates at ordinary pressures has, so far as 
I know, never been explicitly stated, I have no doubt that 
chemists have observed it and that, in consequence of this 
observation, the general statement of the solubility of mercuric 
sulphide in alkaline sulphydrates has remained in chemical 
literature in spite of the observation of Weber and Barfoed. 
The preparation in which I originally observed this important 
reaction was one from which mercury had already been removed 
by precipitation with hydrosulphuric acid. The experiment 
was afterwards repeated by Dr. Melville with several prepara- 
tions of sulphydrate which had been accurately analyzed and had 
been tested in numerous ways. Now in a mixture of the car- 
bonates and sulphides of sodium at the temperature of the water- 
bath, either sodic sulphide or sodic sulphydrate is present, or, 
more probably, both coexist. If, then, mercuric sulphide is 
added to such a solution, either sodic sulphide combines directly 
with mercuric sulphide, or sodic sulphydrate is decomposed by ~ 
mercuric sulphide setting free hydrogen sulphide, which must 
be immediately absorbed by neutral sodic carbonate. Hence in 
any case the salt dissolved in the mixture must be of the form 
HgS, nNa’S. 
Effects of dilutvon—Laboratory experiments are usually made 
with solutions which are much more concentrated than those 
found in nature. Hence the effect of dilution on solutions of 
HegS, nNa’S are important. Whether mercuric sulphide is dis- 
solved in a mixture of sodium monosulphide and sodium 
hydrate, or of the former and sulphydrate, dilution with cold 
water precipitates mercuric sulphide. 
The cause of this precipitation. which is attended by some 
curious phenomena to be described hereafter, is clear. It is 
known through the investigations of Messrs. Kolbe, Thomsen . 
and others, that while in moderately concentrated solutions 
NaHS +NaHO=Na’S + H’O, 
this reaction is partially reversed on dilution ; or that, in the 
presence of much water, sodic sulphide is decomposed by water, 
the proportion of the sulphide undergoing this decomposition 
increasing gradually with the dilution. It is evident that the 
decomposition of HgS, nNa,S is effected in the same way, more 
and more of the monosulphide being converted into the sulphy- 
drate as the dilution increases, probably without any limit. 
Since mercuric sulphide decomposes hot sodic sulphydrate, the 
effect of dilution in hot solvents will evidently be less than in 
cold ones. 
Brunner* found that dilution of solutions of his salt pre- 
cipitated a black mass in which, on examination with the 
* Loe, cit. 
