206 =G. Fl. Becker—Solutions of Cinnabar, Gold, ete. 
lens, minute globules of mercury were visible. The quantity 
of mercury was extremely small, so that the precipitate on 
analysis corresponded very closely indeed to the composition 
expressed by the formula HgS. Gmelin-Kraut* appear to 
have some independent confirmatory evidence on this point. If 
metallic mercury is precipitated in diluted solutions, of course 
sulphur is liberated ; and, as shown above, sodium hydrate must 
also be present. Now when these two substances are brought 
in contact, sodic hyposulphite forms. Accordingly Brunner 
found hyposulphite in the solution forty years before the 
decomposition of sodic sulphide in dilute solution had been 
elucidated. 
As Brunner experimented with HgS, Na’S, I thought it best 
to compare the action of HgS, 4Na’*S. A very concentrated 
perfectly clear solution of freshly prepared mercuric sulphide in 
a mixture of sodic sulphydrate and caustic soda, containing 
very little of the latter, was suddenly diluted with cold water to 
200 times its volume and rapidly filtered. Minute globules of 
mercury could be seen with the black sulphide on the filter. 
On digestion (after thorough washing) with very dilute nitric 
acid, a solution was obtained from which sulphydrie acid pre- 
cipitated black sulphide. The decomposition thus appears to 
be the same in each of the compounds, HgS, Na’S and Hg§s, 
4Na'S. 
Influence of foreign substances.—The fact that sodium carbon- ° 
ates do not prevent the solution of HgS in Na’S is evident both 
from Méhu’s result and from ourown. Experiments show that 
borax solutions precipitate a portion of the mercury from solu- 
tion, but not the whole. The precipitation does not appear to be 
progressive, like that accompanying dilution, but to reach a 
sharp limit beyond which further additions produce no effect. 
A large amount of borax added to a concentrated solution of 
Na’S and NaHS does not rob it of the power to dissolve Hgs. 
It is easy to imagine reactions by which borax may precipitate 
a portion of the mercuric sulphide. But the behavior of solu- 
tions of borax to sulphydric acid and to alkaline sulphides is 
very peculiar and, so faras I am aware, has not been thoroughly 
investigated.t Very concentrated solutions of sodium chloride 
do not precipitate mercuric sulphide from strong solutions in 
mixtures of sodic sulphydrate, and they even appear to delay 
but not to prevent, precipitation by dilution 
Solubility of Fe*S —The sulphide which is most frequently 
associated with that of mercury is pyrite or marcasite, indeed 
these minerals in greater or smaller quantities are to be found 
in nearly every hand specimen of ore, and occur very abund- 
antly in most quicksilver mines. On making the experiment 
* L.c¢., vol. iii, p. 851. + Gmelin-Kraut, 1. ¢., vol. ii, p. 160. 
