180 
MISCELLANY. 
of a beautiful red, being ciianged into the bi-iodide of mercury; while in 
concentrated niinc acid, (spec. grav. 1.4 to 1.5,) the scale instantly becomes 
almost black, from the liberation of iodine. A scale of the salt introduced 
into a drop of the acid no larger than a pin's head will show the effect 
distinctly. 
The acids in which I have found the salt to redden are, sulphuric, hy- 
drochloric, hydrofluoric, chromic, phosphoric, (if slightly diluted,) and 
the common vegetable acids, such as oxalic, tartaric, citric and acetic 
acids. 
I have found it to blacken with chlorine gas, solution of chloride, 
(recently prepared,) bromine, sulphuretted hydrogen, nitrous acid vapours, 
and nitric acid. 
It is highly probable, that it would be blackened by bromic acid and 
chloric acid, and possibly by iodic acid, but I have not at present these 
acids in a free state to determine their action ; the method, however, in 
which I use the test will prevent any fallacy from the presence of chloric, 
bromic, iodic or chromic acids, and of sulphuretted hydrogen. It is to 
evaporate the supposed nitrate to dryness, and introduce into a tube retort 
a small portion of the salt, on which a few" drops of sulphuric acid are 
to be poured ; then on applying moderate heat, by means of a spirit lamp 
d Donionof the volatile products are to be driven over into the receiver, in 
"wnl^ha few scales of the salt are previously placed. If these are blacken- 
ed, the salt is to be considered as a nitrate, provided the presence of those 
few substances which might cause the same result has been guarded 
against. Now by the very method proposed, viz., evaporating to dryness 
and adding sulphuric acid, the presence or absence of chromic, chloric 
or iodic acid'! and sulphuretted hydrogen, will be determined ; for the 
colour of a chromate, the evolution of per-oxide of chlorine from a chlorate, 
the liberation of iodine from an iodate, and the odour from a sulphuret, 
will at once decide with regard to each. As iodic and bromic acids, even 
if they are found to blacken the salt, are not sufficiently volatile to be 
driven over by the heat to be employed, no error could arise from their 
presence. 
I have observed, that if the salt used above, or the bi-iodide of mercury 
itself, be introduced into a test tube, with strong sulphuric acid, on adding 
a concentrated solution of any nitrate, (except those of silver and mercury,) 
the red colour of the scale or bi-iodide will speedily disappear, and will 
be followed by the dark hue of iodine. Even when the sulphuric acid 
forms an insoluble precipitate, the action may be seen, by stirring up the 
precipitate with a glass rod, when the dark spots will be easily observed. 
This method of testing may sometimes be used, but is liable to the 
objection that a chromate, chlorate, and probably some other salts, would 
give the same result. It is greatly inferior to the method by distillation, 
as given above. The American Journal of Science and dris. 
