NITRIC 
ceiver is added, the two vessels not being 
luted, but merely joined by paper ; and to 
apply a very gentle heat for several hours, 
changing the receiver as soon as it is filled 
with red vapours. The nitrous gas will thus 
be expelled, and the nitric acid will remain 
in the retort, as limpid and colourless as 
water. It should be kept in a bottle se- 
cluded from the light, otherwise it will lose 
part of its oxygen. 
The strongest acid that Mr. Kirwan 
could procure at 60“ was 1.5.943, which by 
his calculation contained .7354 of real acid ; 
but Rouehe professes to have obtained it 
of 1.583. It is observable, that, on com- 
paring the tables of Kirwan and Davy, the 
aeriform acid appears to contain a consider- 
able portion of water more than that which 
is combined with soda to form the nitrate. 
Nitric acid should be of the specific 
gravity of 1,5, or a little more, and colour- . 
less. It boils at 248“, and may be distilled 
without any essential alteration. Exposed 
to the air it absorbs moisture. If two parts 
be suddenly diluted with one of water, the 
temperature will rise to about 112“ ; but 
the addition of more water to this diluted 
aci4 w'ill lower its temperature. It retains 
its oxygen with little force, so that it is 
decomposed by all combustible bodies. 
Brought into contact with hydrogen gas at 
a high temperature, a violent detonation 
ensues, so that this must not be done with- 
out great caution. It inflames volatile oils, 
such as those of turpentine and cloves, when 
suddenly poured on them ; but, to perform 
this experiment with safety, the acid must 
be poured out of a bottle tied to the end of 
a long stick, otliervrise the operator's face 
and eyes will be greatly endangered. If it 
be poured on perfectly dry charcoal pow- 
der, it excites combustion, with the emis- 
sion of copious fumes, By boiling it with 
sulphur it is decomposed, and its oxygen, 
uniting with the sulphur, forms sulphuric 
acid. Chemists in general agree, that it 
acts very powerfully on almost all the me- 
tals : but Baume has asserted, that it will 
not dissolve tin ; and Dr. Woodhouse of 
Pennsylvania afiirms, that in a highly con- 
centrated and pure state it acts not at all 
pn silver, copper, or tin, though with the 
addition of a little water its action on them 
is very powerful. He does not mention 
the specific gravity of this acid: he only 
says, that it was prepared by first expelling 
the water of ci 7 stallization from nitre by 
heat, and then decomposing this nitre by 
means of strong sulphuric acid. 
ACID. 
The nitric acid is of considerable use 
in the arts. It is employed for etching 
on copper; as a solvent of tin to form with 
that metal a mordant for some of the finest 
dyes ; in metallurgy and assaying ; in va- 
rious chemical processes, on account of 
the facility with which it parts with oxygen 
and dissolves metals ; in medicine as a to- 
nic, and as a substitute for mercurial pre- 
parations in siphylis and aifections of the li- 
ver ; as also in the form of vapour to de- 
stroy contagion. For the purposes of the 
arts it is commonly used in a diluted state, 
and contaminated with the sulphuric and 
muriatic acids, by the name of aqua fbrtis. 
This is generally prepared by mixing com- 
mon nitre with an equal weight of sulphate 
of iron, and half its weight of the same sul- 
phate calcined, and distilling the mixture : 
or by mixing nitre with twice its weight of 
dry powdered clay, and distilling in a rever- 
beratory furnace. Two kinds are found in 
the shops, one called double aqua fortis, 
which is about half the strength of nitric 
acid ; the other simply aqua fortis, which is 
half the strength of the double. 
A compound made by mixing two parts 
of the nitric acid w'ith one of muriatic, 
known formerly by the name of aqua regia, 
and now by that of nitro-muriatic acid, has 
the property of dissolving gold and platina. 
On mixing the two acids, heat is given out, 
an effervescence takes place, oxygenated 
muriatic acid gas is evolved, and tlie mix- 
ture acquires an orange colour. This is 
likewise made by adding gradually to an 
ounce of powdered muriate of ammonia, 
four ounces of double aqua fortis, and keep- 
ing the mixture in a sand-heat till the salt is 
dissolved ; taking care to avoid the fumes, 
as the vessel must be left open : or by dis- 
tilling nitric acid with an equal weight, or 
rather more, of common salt. 
With the different bases the nitric acid 
forms nitrates. 
The nitrate of barytes, when perfectly 
pure, is in regular octaedral crystals, though 
it is sometimes obtained in small shining 
scales. It may be prepared by uniting 
barytes directly with nitric acid, or by 
decomposing the carbonate of sulphuret 
of barytes with this acid. Exposed to heat 
it decrepitates, and at length gives out its 
acid, which is decomposed ; but if the heat 
be urged too far, the barytes is apt to vitrify 
with the earth of the crucible. It is so- 
luble in 12 parts of cold, and 3 or 4 of boil- 
ing water. It is said to exist in some mine- 
ral waters. 
