202 = G. F. Becker—Solutions of Cinnabar, Gold, ete. 
above experiments show that this soluble double salt can be 
_represented only in the formula HgS, 2Na°S. The soluble mix- 
ture given by Méhu answers to HgS+2-07 Na’S and isthus, so- 
far as it goes, confirmatory of the above experiments. 
Solubility of HgS in Na’S.—The most carefully prepared so- 
lutions of sodium sulphide dissolve mercuric sulphide freely. 
This statement is directly contrary to that which some of the 
chemists referred to have made, and it would be a rash one if 
the evidence to be adduced for it depended simply upon bringing 
solutions of sodic sulphide into contact with mercuric sulphide ; 
for it is impossible to make certain that there is no trace of free 
caustic alkali or of sulphydrate in a solution of sodie sulphide, 
however closely its analysis may correspond to its theoretical 
composition. If, however, a solution of sodic sulphide contain- 
ing sodic hydrate i is treated with hydrogen sulphide, itis grad- 
ae converted into sodic sulphydrate and passes through 
a point at which the only compound present is the monosul- 
phide. If mercuric sulphide is dissolved in a mixture of sodic¢ 
sulphide and caustic soda, and the clear filtrate is treated with 
hydrogen sulphide, the mercuric sulphide begins to be precipi- 
tated when very little free caustic alkali is left, and is contin- 
uously precipitated until the entire amount of sodium present is 
converted into sulphydrate. The purest preparations of Na’S 
which we have been able to make, dissolve mercuric sulphide 
less freely than mixtures of sodic sulphide and sulphydrate. 
Different preparations, however, shown by most careful analysis 
to correspond very accurately to the formula Na’S, give some- 
what different results, possibly indicating a minute variation 
from absolute purity. It does not seem a@ priort improbable, 
that the soluble sait when the sodic sulphide is absolutely pure 
is HgS, 3Na’S; and one of our preparations gave almost exactly 
this result. It may also be that mixtures of HgS, 2Na’S, and 
- HgS, 4Na’S are formed in proportions varying with other condi- 
tions than the purity of the sodium sulphide, such as tempera- 
ture and concentration. 
Insolubility of HgS in cold NaHS.—Repeated experiments and 
analyses undertaken during this investigation have shown that 
mercuric sulphide is totally insoluble in sodium sulphydrate at 
ordinary temperatures, and that any preparation of this com- 
pound which will dissolve a trace of mercuric sulphide can be 
shown by analysis to fall short of complete saturation. A long 
time and an enormous quantity of hydrogen sulphide are 
required to completely saturate even a small amount of caustic 
soda with sulphur. As already mentioned, both Weber and Bar- 
foed were aware of the insolubility of mercuric sulphide in 
sodium sulphydrate at ordinary temperatures. It will be seen 
later that the behavior of these compounds varies with the tem- 
