C H E -M I S T R Y. 
nuift be ,burnt by a very flow fpontaneous combuftion 
otfer a glafs funnel leading into a cryftal phial; after a 
few days, the phofphorus is found oxygenated, and the 
phofphorus acid, in proportion as it forms, attrabls moif- 
ture from the air, and drops into the phial. Seethe lec¬ 
tion on Phcfphorus, p. 100. This acid may be formed 
alfo by decompofing phofphoric acid; anda'certainquantity 
of it is always difengaged in the operation for phofphorus. 
Phofphorous acid may be regarded as phofphoric acid 
holding a little phofphorus in dilfolution. This acid 
gives out a fetid and difagreeable odour when rubbed, 
and efpecially when heated; one part of it volatiiifes in 
white vapour very Iharp and pungent; it is therefore 
more volatile than phofphoric acid. If this experiment 
be made in a bulbous tube, or in an apothecary’s phial, 
phofphoric fparks arife from the middle, and bum in the 
air, which does not take place with the phofphoric acid 
faturated with oxygen. By thus heating the phofphorous 
acid, it becomes phofphoric acid ; it feems that the parts 
which fly off in vapour by the ablion of the fire, are more 
apt to be difengaged by caloric, and are lefs faturated 
with oxygen ; and that it is when they are difengaged in 
this manner, that the remainder is phofphoric acid ; and 
even the burnt bubbles, faturating themlelves with oxy¬ 
gen, fall down again in part into.the phofphorus acid 
Hate. This property alone would be fufticient to diftin- 
guilh this acid from phofphoric acid. 
SULPHURIC ACID. 
Sulphur, as we have already remarked, burns only in 
proportion as oxygen gas is united with it, The methods 
of obtaining fulpfiuric acid, are two : 1. By extracting it 
from fuch'fubltances as contain it. z. By manufacturing 
It. In the firft cafe, a dillillation is made from fulphat 
of iron, or vitriol of iron, copper, or zink, or even of 
alumine, or of lime ; whence this acid has been called 
s vitriolic , and, according to its degrees of concentration, 
J'pirit of ‘vitriol, oil of •vitriol , and concentrated or frozen 
oil of ‘vitriol. But, in modern times, it is procured at a 
much cheaper rate, by the combuftion of fulphur. 
In the manufaStories for making fulphuric acid in the 
large way, a mixture of nitre and fulphur is burnt in 
clofe built chambers lined with lead. Suppofe it were 
required to make 4oolbs. of this acid in a day, a chamber 
of thirty feet long, as many broad, and twenty high, 
will anfwer the purpofe of obtaining that quantity ; for 
t3olbs. of the acid, there will require about 9olbs. of 
fulphur, and 7|- of nitrat of potafli. Sulphuric acid re- 
fjilts from the combuftion of the fulphur, which, in burn¬ 
ing, combines with the bale of vital air, or oxygen, 
which is contained in the atmofplverical air, and in the 
nitre added to the fulphur ; the mixture is fet on nre, and 
the vapours are received in the chamber, which has a 
little water at the bottom for facilitating the condenfa- 
tion of the vapours. In this fecond cafe it is fulphur 
completely burned ; the acid therefore is radically formed. 
When taken out of the chamber, the fulphuric acid 
is black, impure, not concentrated, is mixed with a fu- 
perabundant quantity of water, and retains the fmell of 
fulphurous acid and fomewhat of nitrous acid ; by leav¬ 
ing it for lome time expoied to the air, the odour of ful¬ 
phurous acid is diflipated. Yet this is not fufficient; then 
it is made to evaporate by dillillation in large retorts or 
open veflels, which reftifies it from the nitrous acid. To 
have it perfectly reflified and pure, it will be neceflary, 
after having leparated the firft; portion, which is weakly 
acid, to continue the dillillation till no liquor remains in 
the retort; this is called dillillation to ficcity or drynels. 
The refiduum is a imaU quantity of alkali which proceeds 
from the nitre, and which remains combined with the 
excels of fulphurated acid ; this is acid fulphat of potalh; 
a little fulphat of lead is often found alfo. For this 
rectification choofe a retort not too high, and fix it well 
in the furnace, that the motion occafioned by tire-ebullition 
jof the acid may not break it, 
Vo Li IV, No. jgo. 
213 
It requires but a very finall quantity of animal or ve¬ 
getable fubftance to give this acid a brown colour. 
Sulphur may be converted into fulphuric acid by oxy¬ 
genated muriatic acid, as will be hereafter lhewn. By 
diitilling nitric, acid over fulphur, fulphuric acid is pro¬ 
duced alfo. For the experiment, fee on Nitric Acid. 
Properties of fulphuric acid. —It is thick, running in 
ropes like oil; it is inodorous, it burns, it carbonifes, it. 
dcltroys qll animal and vegetable fubltances; it burns, 
and corrodes the lion, therefore mult be handled with, 
caution. It is much heavier than diftilled water, and 
imparts a bright red to blue vegetable colours. It in- 
creafes in abfolute weight by being expofed to the air, be- 
caufe it ablorbs tire humidity of the atmofehere very 
quickly; but, on the other hand, it becomes weaker,, 
and loles in Jpecific weight. 
To perform the experiment, place a porcelain tube 
acrofs a furnace, and adapt thereto a couple of tubes of 
glafs; one mull communicate with a machine for obtain¬ 
ing hydrogen gasj as before deferibed ; the other with a 
retort containing pure concentrated fuphuric acid; the 
lower end is t;o be furnilhed with a bent tube, whidi goes 
under a jar with mercury, in order to obtain fulphuric 
acid gas. Then heat the porcelain tube, and firft let in 
the fulphuric acid boiling; then the hydrogen gas. The 
experiment is dangerous, as it often happens that there 
are ftrong expiofions. In the cold way, fulphuric acid, 
is not decompofed by carbon ; but by heat it is changed 
into fulphurous acid; for this purpofe, put charcoal in 
powder, v<?ry dry, into a retort; pour fulphuric acid, 
over it, and then heat it. If a tube be adapted to the 
retort, carbonic acid gas will be obtained. 
According to the experiments of Pelletier, fulphuric 
acid is not decompofed by phofphorus; neither is it de¬ 
compofed by pure fulphur. By boiling fulphuric acid 
over red oxyd. of fulphur, the fulphuric is changed to 
fulphurous acid. 
Certain metals decompofe fulphuric acid ; and fulphu¬ 
rous gas is the produbl. Others, on the contrary, mull 
be burnt before they will dilfolve in fulphuric acid ; in 
that cafe they decompofe the water; but, inilead of ful¬ 
phurous gas, hydrogen gas is difengaged ; in this man - 
net is generally wrought the dilfolution of zink and of 
iron, by the aqueous fulphuric acid. \ 
Concentrated fulphuric acid has a great affinity with, 
water, and alfo with caloric. When this acid is mixed 
with water, the heat rifes, and the node made in the 
union ariles from the air contained in the water. The 
mixture attains a heat of 120°, fo that water may_.be 
boiled in it. Four parts of fulphuric acid and one of 
water give out a very ftrong heat. At a low temperature, 
when the acid is pure, it congeals and cryftaUiftk in prifms 
of fix fides. It Ihould be left to congeal in a mixture of 
fait and ice, and be ilirred : this was called frozen ful¬ 
phuric acid. 
Sulphuric acid is decompofed by all combuftible fub- 
ftaifces. Straws turn black in this acid, becaufe hydro¬ 
gen, which is the principle of vegetation, combines with 
the oxygen, and leaves the carbon of the vegetable at li¬ 
berty ; fuCh alfo is the theory of the carbonization of all 
vegetables. 
The fulphuric acid is ufed in many of the arts, parti¬ 
cularly in hat-making, and in dying. It is one of the 
moil common and molt hecelfary loivents ufed in chemif- 
try : it is employed in medicine externally, as a power- 
ful'cauftic; and internally, when diluted with water, lb 
as to be fcarce fenfibly acid, as a refreftung, cooling, and 
antifeptic, medicine. 
SULPHUROUS ACID. 
This is produced by the fecond degree of oxygenation; 
of fulphur. There are two modes of obtaining it. 1. By 
combining the fulphur with fuch a quantity of oxygen 
only as is neceflary to change it into fulphurous acid. z„ 
By feparating from fulphuric add that portion of oxygen 
which is over and above the nature of fulphuric acid. 
3 1 > . Take 
