It is chiefly used as an oxidizing agent in volumetric work,
being sharp in its reactions and easily detected in minute quantities.
It cannot be used in alkaline solutions, since it reacts with the
hydrates, and even with the carbonates, to form iodides and iodates.
Iodine is soluble in alcohol.
~Nitric Acid, HNO_{3}.~ (Sp. gr. 1.42; boiling point 121° C.; contains
70 per cent. by weight of hydrogen nitrate).--It is convenient to
remember that one c.c. of this contains 1 gram of real acid. It combines
the properties of an acid and of an oxidising agent. One c.c. contains
0.76 gram of oxygen, most of which is very loosely held, and easily
given up to metals and other oxidisable substances. Consequently it will
dissolve many metals, &c., upon which hydrochloric acid has no action.
All sulphides (that of mercury excepted) are attacked by it, and for the
most part rendered soluble. It has no action on gold or platinum, and
very little on aluminium. The strong acid at the ordinary temperature
does not act on iron or tin; and in most cases it acts better when
diluted. Some nitrates being insoluble in nitric acid, form a protecting
coat to the metal which hinders further action. Where the strong acid
does act the action is very violent, so that generally it is better to
use the dilute acid. When iron has been immersed in strong nitric acid
it not only remains unacted on, but assumes a _passive_ state; so that
if, after being wiped, it is then placed in the dilute acid, it will not
dissolve.
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