C H £ M ] 
converted or decompofed into nitrous gas. Nitric acid 
may be deconipofed alfo by being made to pats through 
a heated porcelain tube, about two feetand a half long: 
if the tube be,very hot, oxygen patfes over, and the re- 
fidue is azot; but, if not hot enough, much of the ni¬ 
tric acid will not be decompofed; frequently indeed this 
nitric acid will attraft azot, and fo form nitrous acid. 
By this decompofition a fort of aimofpheric air is pro¬ 
duced ; but nitrous acid cannot be decompofed in this 
way. 
Nitric acid may be made, by paffing ammoniacal gas 
over oxyd of manganefe. This experiment, and the 
preceding, may be performed with the fame apparatus 
as exhibited in the Chemiltry Plate IV. fig. 2; and the 
following defeription may lerve for both. A is a retort 
containing eight parts of liquid ammoniac; B, a porce¬ 
lain tube fixed to the retort, and going acrofs a furnace, 
and containing three parts of oxyd of manganefe in pow¬ 
der; at the other extremity is a bent tube C, which 
runs into a two-necked bottle D, one fourth part filled 
•with diftilled water. It is neceffary, to prevent ablorp- 
tion, not to plunge the tube into the water; it need only 
touch the furface. From the fecond neck goes out a 
tube of fafety E, which runs under, an inverted jar F, in 
the pneumatic apparatus. Make the tube red-hot, and 
then heat the ammoniac; red vapour will pafs over, 
then a wdiite fmoke, which is azot and water in vapours ; 
afterwards nitrat of ammoniac is formed : if the tube be 
not fufficiently heated, a little oxygen gas is difengaged 
at the beginning of the operation. By evaporating the 
water contained in the bottle, nitrat of ammoniac is ob¬ 
tained, whence the nitric acid may be re-drawn by 
means of fulphuric acid. Under the jar will be found, 
,3. Oxygen which comes from the manganefe, which is 
decompofed quicker by the caloric than the ammoniac. 
2. Hydrogen gas, which arifes from the decompofition 
of the ammoniac. 
This acid fets charcoal in a flame ; but it mud be very 
dry and warm, and the nitric acid much concentrated! 
It difengages nitrous acid and carbonic acid; the red 
fmoke arifes from the nitrous gas. To perform this ex¬ 
periment, put the charcoal into a glafed earthern pan. 
Take a Hick a yard long; i'plit it at one end, and between 
the cleft introduce the neck of an apothecary’s phial; 
tie it fait; the operator is by this means free from dan¬ 
ger. When you want to fet' fire to the charcoal, pour 
the nitric acid into the phial, and with it fprinkle the 
charcoal, it takes fire immediately.—Phofphorus catches 
flame in the fame manner, and the fmoke that flies off is 
phofphoric acid ; which proves, not only that nitric acid 
contains oxygen, but likewife that the oxygen is in a 
ftate ready for difengagement. 
Sulphur alfo decompofes nitric acid, and reduces it to 
nitrous gas; for only thus far has the fulphur more affi¬ 
nity with the oxygen than the nitric acid, or rather than 
the azot; for tl\e fulphur does not attack the nitric acid: 
fulphuric acid and nitrous acid are therefore formed. 
Put fix parts of nitric acid, of 30 0 to one of fulphur: by 
diltillation the nitric acid will -be decompofed, nitrous 
gas will be difengaged, and fulphuric acid will be form¬ 
ed.—If you would operate with phofphorus, take a tubu¬ 
lated retort with a ftopperof cryftal; put in nitric acid of 
30°; then through the tube introduce iome little bits of 
phofphorus, about one part of phofphorus to fix of the. 
acid. Place the retort over a fand-bath, adapt a receiver, 
and heat the retort gently. The phofphorus is diffolved 
with effervefcence; the nitrous gas efcapes at the fame 
time in vapours : then increafe the fire fo as to drive away 
the lafl: portions of the nitric acid; and phofphoric acid is 
found in the retort, partly in a concrete form, and part¬ 
ly liquid. 
Water combines with nitric acid in all proportions, and 
caloric is dilengaged during the combination : with two 
parts of concents ated nitric acid and one of water, the 
mercury in Reaumur’s thermometer will rife to 35 0 , By 
S T R Y. 215 
ufing fnow inftead of water, contrary effects are pro¬ 
duced, that is to'fay, there is an abforption of caloric^ 
and the thermometer may be made to fall from o to 22 0 
below, by mixing four parts of fnow with one of nitric 
acid; by cooling in this firft mixture fome freffi acid.and 
freffi ice, and then ftirring them together in the midft of 
this bath, the temperature may be brought down to 32 or 
3 3° below o. This property in the nitric acid to produce 
fuch extreme cold with ice, arifes from the great affinity 
it has to unite with water; and in fome degree forces 
the bale, with which in that ftate it cannot unite, to 
take from the neighbouring bodies the caloric of which 
it Hands in need to become liquid. It furniffies to clie- 
mifts fome ufeful -hints, of which perhaps they do not 
take fufficient advantage, for examining the properties 
of bodies at a low temperature ; it was this which de- 
monftrated that mercury became a folid body at 31 or 
32 0 below o. 
What we call aqua fortis, is nothing but nitric acid 
diluted with water. When we come to fpeak of nitrat 
of" potafh, we fliall give the method of obtaining it by 
means of potter’s clay. 
Molt metals ad upon nitric acid, and occafion a change 
therein, which, has of late greatly affifted chemifts in 
their enquiries into the nature of its principles. Metals 
ad upon nitric acid in two different ways: 1. Some are 
completely oxydated, as tin, antimony, &c. and decom- 
pole the nitric acid entirely. 2. Some are oxyded, and 
decompofe the acid but in part, as copper, &c. Nitrous 
gas is produced both ways. 
The nitric acid cf commerce-often contains muriatic 
acid and fulphuric acid, which are very troublefome in 
all operations. The method of purifying it is as follows: 
Put lome femi-vitreous oxyd of lead, or litharge, into a 
glafs retort; pour the nitric acid over it: diltil to dry- 
nefs There will remaih in the retort, a muriat and a 
fulphat of lead, if the nitric acid contained fulphuric 
acid. Another way is to ufe nitrat of lead or filver: a 
precipitate is immediately formed, which is muriat of 
lead or of filver : then draw off the acid, or rather diftil 
to drynefs. This laft is a very good method when mu¬ 
riatic acid only is mixed with the nitric acid ; but, when 
there is fulphuric acid, the firft method is to be preferred, 
feeing that a fuiphat and a muriat of lead are formed at 
the fame time. 
Of NITROUS GAS. 
Nitrous gas is the appellation of that aeriform fluid which 
is difengaged during th? aftion of iron, copper, filver, or 
mercury, upon nitric acid. To get this fubftance pure, 
free from azotic gas, as required for eudiometrical ex¬ 
periments, it is not a matter of indifference what com- 
buftible is ufed ; for there are fome which aft fo ftrongly 
upon oxygen, that they draw it entirely from fome parts 
of the azot, and then the nitrous gas will be mixed with 
azotic gas. Silver and copper are the bell metals for the 
purpole ; and the denfity of the nitric, acid fhould not 
exceed 20 or 25° of Baume’s aerometer; otherwife its 
aftion would be too brilk, the nitrous gas would be dif¬ 
engaged too rapidly, and might burft the apparatus ; be-$ 
fides, it is not lo pure in that cafe. • Humboldt has (hewn, 
by careful experiments, that, by pouring nitric acid up¬ 
on copper wii e, a part of the acid was decompofed en¬ 
tirely, and thereby the nitrous gas was mixed wfith 
azot; but, that, by employing a folution of fulphat of 
iron, the nitrous gas was totally abforbed, and the quan¬ 
tity of azot might be meafured, amounting to from 0-07 
to 0-67, and even beyond. 
To obtain this gas, take clean copper-filings ; put them 
into a phial or fmall matrals ; pour in nitric acid of 20 
or 25 0 , llop the phial with a cork, to which a glafs tube 
is adapted, whole bent extremity is plunged into the wa¬ 
ter-trough of the pneumatic apparatus.; on the fnelf of 
the trough is *a bell-glafs filled with water, which corre- 
Iponds to the orifice of the bent tube. Things thus pre¬ 
pared-, 
