NIT 
tlie rapid action of the snlplnir on the nitre. 
By the application of the heat, tlie sulphur 
and potash form a sulphuret, which is com- 
bustible at a lower heat probably than even 
sulphur. Sulphurated hjdrogen gas, azotic 
gas, and perhaps also sulphurous acid gas, 
are disengaged almost instantaneously. It 
is to the sudden action of these on the sur- 
rounding air that the report is to be as- 
cribed. Its loudness evidently depends 
upon the combustion of the whole powder 
at the same instant, which is secured by 
the previous fusion that it undergoes ; 
whereas the grains of gunpowder burn in 
succession. A mixture of equal parts of 
tartar and nitre, deflagrated in a crucible, is 
known by the name of white flux. It 
is merely a mixture of carbonate of potash, 
with some pure potash., When two parts 
of tartar, and one of nitre, are defla- 
grated in this manner, the residuum is 
called black flux from its colour. It is 
merely a mixture of charcoal ajid carbonate 
cf potash. 
Nitre is much used in medicine, in fe- 
vers, as a cooling remedy, and as a diuretic, 
in urinary affections. It is employed also 
in many arts, as in dying ; and in domestic 
economy, for the preservation of animat 
substances used for food. To these sub- 
stances it imparts a red colour. See Ni- 
trous add; also Gunpowder. 
NITRIC acid. The two principal con- 
stitueiit parts of our atmosphere, when in 
pertain proportions, are capable, under 
particular circumstances, of combining 
chemically, into one of the most powerful 
acids, the nitric, which consists, according 
to Blr. Davy, of 70,5 of oxygen, apd 29.5 
of azote, or nitrogen. If these gases be 
mixed iii this proportion in p glass tube, 
about a line in diameter, over mercury, 
and a series of electric shocks be passed 
through them for some hours, they will 
form nitric acid ; or, if a solution ot potash 
l;e present with them, nitrate of potash will 
be obtained. Tim constitution of this acid 
may be further proved, analytically, by 
driving it through a red-hot porcelain tube, 
as thus it will be decomposed into oxygen 
and nitrogen gases. For all practical pur- 
poses, however, the nitric acid is obtained 
tfom nitrate of potash, from which it is ex- 
pelled by sulphuric acid. 
Four parts of pure nitrate of potash, 
coarsely powdered, are to be put into a 
glass retort, and three parts of concen- 
trated sulphuric acid cautiously added, tak- 
ing care to avoid the fumes that arise, which 
NIT 
is best done by standing in a current of air- 
to convey them up the chimney. Join to 
the < retort a tubulated receiver of large 
capacity, with an adopter ipterposed, and 
lute the junctures with a mixture of pipe- 
clay, sifted sand, and cut tow. In the tu- 
biihire fix with fat lute a glass tube termi- 
nating in another, large receiver, in w'hich 
is a small quantity of water ; and, if you 
wish to collect the gaseous products, let a 
bent glass tube from this receiver commu- 
nicate with a pneumatic trough. Apply 
heat to the receiver by means of a sand 
bath. The first product that passes into 
the receiver is generally red and fuming ; 
but the appearances gradually diminish, till 
the acid comes over pale, and even colour- 
less, if the materials used were clean. After 
this it again becomes more and more red 
and fuming, till the end of the operation ; 
and the whole mingled together will be of 
a yellow or orange colour. 
In the large wa 5 ', and for the purposes of 
the arts, extremely thick cast iron or earthen 
retorts are usually employed, to wdiich an 
earthen head is adapted, and connected 
with a range of proper condensers. The 
strength of the acid too is varied, by put- 
ting more or less water in the receivers. 
The nitric acid thus made generally con- 
tains sulphuric acid, and also muriatic from 
the impurity of the nitrate employed. If 
the former, a solution of nitrate of barytes 
will occasion a white precipitate : if the 
latter, nitrate of silver will render it milky. 
The sulphuric acid may be separated by a 
second distillation from very pure nitre, 
equal in weight to an eighth of that origi- 
nally employed ; or by precipitating with nir 
trate of barytes, decanting the clear liquid, 
and distilling it. The muriatic acid may be 
separated by proceeding in the same way 
with nitrate of silver, or with litharge, de- 
canting the clear liquor, and redistilling it, 
leaving an eighth or tenth part in the. retort. 
The acid for the last process should be con- 
densed as much as possible, and the redis- 
tillation conducted very slowly ; and if it 
be stopped when half is come over, beau- 
tiful crystals of muriate of lead will be ob- 
tained on cooling the remainder, if litharge 
be used, as M. Steinacher informs us ; who 
also adds, that the vessels should be made 
to fit tight by grinding, as any lute is liable 
to contaminate the product. 
As this acid still holds in solution more or 
less nitrous gas, it is not, in fact, nitric acid, 
but a kind of nitrous : it is therefore neces- 
sary to put if into a retort, to whicli a r§<- 
