Take one part of mercury, an.d two of fulphuric acid; 
put tliefe into a long-necked mattrafs, to which adapt a 
bent tube which goes to the bottom of the water contain¬ 
ed in a VVoulfe’s bottle. The fulphuric acid, which is 
dilengaged at the lame time with the fulphurous acid 
gas, is arretted and diffolved in the water of this firft 
bottle : from this goes a fecond tube, to conduct the 
fulphurous acid into jars inverted over mercury, or into 
bottles filled with water, if it be required to have it liquid. 
The fecond method is by the flow combulrion of ful- 
phur. Put fu’olimed fulphur into a fmall veffel of earth 
or porcelain; heat them (lightly, and fet'fire to the lul- 
phur with a coal; when it is well inflamed, cover the 
fulphur with a jar ftlfed with air: place in a diih, and 
pour water round it. A white fmoke rifes, which is dif- 
folved in the water; this W'ater becomes acid: this is ful¬ 
phurous acid. The fulphurous gas is in form of (moke 
or cloud under the jar, becaule it is combined with the 
water contained in the air in the jar : in a dry air, it is 
very traniparent. This acid was formerly called J'pint 
of fulphur. 
Sulphurous acidgasisinvifibleand elaltic, with a briflc 
penetrating fmell; it is neither proper for combuftion 
nor refpiration ; \ its tafte is lively, warm, and pungent. 
It reddens and difcolours molt of the blue vegetable tints ; 
it has the property of cleaning and whitening filk, and 
giving it a glofs. It is employed in dying; and is ufed 
to take out ipots occafioned by vegetable juices, &c. It 
is'twice as heavy as atmofpherical air. In a high tempe¬ 
rature, it is faid by Prieftley, Bergman, and Bertholet, 
to produce fulphur; but Fourcroy and Vauquelin, after 
new and careful experiments, deny the faft. It combines 
flowly with oxygen ; but at length fulphuric acid is the 
refult. There is no aftion between hydrogen gas and 
fulphuric acid gas when cold; but, by putting into a 
red-hot porcelain tube, a mixture of three parts in vo¬ 
lume of hydrogen gas, and one part of fulphurous acid 
gas, the laft is decompofed ; a little fulphurated hydrogen 
gas is formed ; and at the extremity of the tube oppoflte 
to that through which the gafes palled, a quantity of cry- 
ltals of fulphur will be found. 
With the following apparatus, as delineated in the 
Chemiifry Plat.e IV. fig. i. may be exhibited two fets of 
experiments proper to fhew the nature of fulphurous 
acid : the one with oxygen gas, the other with hydrogen 
gas. A is the furnace ; B, a retort, containing one part 
of mercury, and two of fulphuric acid : the fulphuric 
acid is decompofed, and fome fulphurous acid gas is dif- 
engaged : this laft paffes through a bent tube C, into the 
common refervoir G; into which comes alfo the tube D, 
to which is faltened a bladder F, pierced by a copper 
cock E, fixed to the end of the tube D, that, by fqueef- 
ing the bladder, its contents, whether oxygen or hydro¬ 
gen, may be injected upon the fulphurous acid gas, which 
paffes into G. In the refervoir G fhould be put alfo a 
little mercury, which in oxydating purines the fulphuric 
acid gas. H is a tube to continue the communication: 
II, is a pipe of luted glafs or porcelain, capable of lup- 
porting a itrong heat, and placed acrofs the furnace K. 
L is a bent tube adapted thereto, whofe other extremity 
is plunged into a two-necked bottle M, which contains 
a little water; from the other aperture of this bottle 
goes out a bent tube of fafety, which goes under the 
jar at N, inverted over mercury, or in a trough of w r a- 
ter, to gather the remainder of the gales. If you prefs 
the bladder which contains the hydrogen over the ful¬ 
phurous acid gas, and make them run together in a por¬ 
celain tube made red-hot, at that temperature the hydro¬ 
gen feizes on the oxygen of the fulphurous acid, and 
fulphur is precipitated on the tubes and fides of the bot¬ 
tles. The hydrogen combines with the oxygen forming 
water ; and the excels of the uneombined hydrogen gas 
is fet at liberty, and paffes under the jar N. If the blad¬ 
der be filled with oxygen gas, inftead of hydrogen, this 
gas pafips with the fulphurous acid gas, combines with 
S T R Y. 
the acid gas, and reftores to it the oxygen it had loft by 
oxyding the metal in the retort. Sulphuric acid is form¬ 
ed, which is diffolved in the water of the bottle or re- 
fervoir G. This experiment, which will fucceed only 
at a high temperature, (hews that at that time the hydro¬ 
gen has more affinity with the oxygeg than with the ful¬ 
phur, which is not the cafe when cold. Thus fulphu¬ 
rous acid is changed into fulphuric acid by means of 
oxygen at a high temperature ; and, by means of hydro¬ 
gen, fulphurous acid is decompofed ; then, taking from 
that the portion of oxygen which kept it acid, the ful¬ 
phur remains. 
Pholphorus has no adlion with fulphurous acid. By 
heating fulphurous acid with carbon, fulphur is obtain- 
. ed ; and a little fulphurated hydrogen gas is difengaged. 
In water cooled by ice, the combination is fo rapid, that 
not a bubble rifes to the furface ; ice from a cellar melts 
very quickly, which (hews a confiderable dilengagement 
of heat; the w’ater at this temperature increaies 0-15 of 
its weight, or nearly a feventh part. The fpecific gra¬ 
vity of liquid fulphurous acid faturated, is to that of 
diftilled water as 1020 to 1000. 
Expofed to the temperature of 15-I-0, this faturated 
water throws up a vaft quantity of little bubbles; this 
is fulphuric acid gas, which dt that temperature can no 
longer remain combined with the water. If a veffel filled 
with liquid fulphurous acid be plunged into water, it 
boils with aftonifhing rapidity, and the liquor loles a 
great part of its lmell and its acidity. Water faturated 
with fulphurous acid freezes at fome degrees below o j 
but not an atom of gas is dilengaged, as happens with 
carbonic acid; the lulphurous acid therefore has more 
attraction for the water. 
If fulphurous acid gas be put into concentrated ful¬ 
phuric acid, a concrete acid is obtained, which is Cub- 
limed in the neck of the retort. 
O? NITRIC ACID. 
Nitric acid is one of the mod important in nature, on 
account of its frequent ufe and great utilityin chemiftry. 
It gives out its oxygen fo eafily to combultible bodies,.. 
that.it has been the,* inftrument of many difcoveries. 
The ancient chemifts knew no fuch thing as white nitric 
acid; they defcribed it as very red, giving out yellow 
vapours, &c. 
Nitric acid is extracted from a fait known in the arts, 
by the name of faltpetre, the method of producing it we 
(ball hereafter delcribe in (peaking of the nitrat of potafh. 
This acid, pure and concentrated, is heavy, with a white 
fmoke. When diftilled in a glafs retort with the pneu¬ 
matic apparatus, in a heat futficient to make it boil, a 
red vapour is exhaled, which condenfes in the receiver 
into a liquid of the fame colour; and a little oxygen gas 
paffes under the jar. 
Put coloured nitric acid into a retort; adapt thereto a 
balloon with a little water in it. Place the retort in a 
fand-bath, and diftil : a red vapour is thrown off, and 
the acid becomes white. If nitric acid, very much con¬ 
centrated, be left in contaft with atmofpherical air, it 
attracts the humidity of the atmofphere, and is thereby 
weakened. 
If very pure nitric acidbe expofed to therays of light, it 
may thereby be decompofed. For this purpofe put ni¬ 
tric acid, very pure, into a bottle; fix in a bent tube 
which is to go under an inverted jar in the pneumatic 
apparatus; be careful that the tube does not touch the 
acid :. in a certain time the acid changes colour, becom¬ 
ing yellow, green, and then red; and fome oxygen gas 
is difengaged. It is not the affinity of the light tor the 
oxygen which decompofes the nitric acid; it is becaufe 
there is at the fame time a great affinity between nitric 
acid and the nitrous gas which is formed. The action of 
light will not proceed fo far as to take away all the oxy¬ 
gen from the nitric acid, fo as to reduce it to an azot 5 
but, by continuing the experiment, nitric acid may be 
^ con- 
