52 
SELECTED ARTICLES. 
nitric acid contained in the solution was dissipated and de- 
stroyed by ebullition and repeated additions of hydrochloric 
acid. The liquid thus obtained was perfectly clear and co- 
lorless; evaporated to a small residuum, and chloride of tin being 
added, it gave a grayish-black cloud, which was condensed by 
heat and the addition of a little alcohol into globules of me- 
tallic mercury, so easy of recognition, that doubt no longer 
remained with respect to the presence of mercury in solution 
in this decoction. But the quantity was too small to be able 
to appreciate it correctly. M. Wiggers estimates it approxi- 
mative^ at one-half a millogramme to the four pounds of 
decoction. The quantity of mercurial combinations which are 
active, when this decoction is employed, is certainly greater, 
not, however, in a state of solution, but in that of simple sus- 
pension, as it is directed not to filter it, but to simply pour it 
off; in fact, the little bag, in which the calomel and cinnabar 
ought to be suspended in the liquid during ebullition, allows 
a large quantity of these bodies to escape, which finally 
pass through the linen serving as a filter. 
The small quantity of mercury in solution does not permit 
of determining exactly under what form it exists. The 
cinnabar, a body completely insoluble in water, and which 
does not undergo any decomposition under the circumstances 
which attend the preparation of this decoction, appears not to 
be the cause of the solution of the mercury; but we may sup- 
pose, according to M. Wiggers, that the calomel is decom- 
posed by a catalytic action into metallic mercury and corro- 
sive sublimate, a decomposition which is brought about in it, 
as is known, by many bodies. In this case the mercury may 
be found dissolved in the decoction, partly in the state of sub- 
limate, and partly in the metallic state, under the form of gas; 
and M. Wiggers believes this proposition more likely than 
the opinion of Catel, who thinks that the mercury becomes 
oxydised, and is dissolved under the form of the acid sulphate 
of the deutoxide of mercury, by means of the sulphuric acid 
of the alum which is added. 
After having thus proved, beyond doubt, the actual solu- 
