SUL 
ments of Lavoisier, in which he measured 
the quantity of oxygen absorbed, by a given 
weight of sulphur during combustion, the 
proportions are. 
Sulphur 
71 
Oxygen 
100 
But other methods have been adopted. 
These are, by decomposing other substances 
which contain oxygen, by means of sulphur. 
According to the experiments of M. Chen- 
evix, conducted in this way, the sulphuric 
acid consist of. 
Sulphur 61. 5 
Oxygen 38. 5 
100. 0 
Sulphuric acid does not combine with 
oxygen, nor has it any action with azotic 
gas. It appears that hydrogen has a greater 
affinity for oxygen, than the sulphur has, 
and therefore the sulphuric acid is decom- 
posed by means of hydrogen gas. In the 
cold there is no action between hydrogen 
gas and sulphuric acid; but if they are 
made to pass through a red hot porcelain 
tube, the acid is decomposed, water is 
formed, and sulphur is precipitated. When 
hydrogen gas is employed in a greater pro- 
portion than the half of the acid, the super- 
abundant gas dissolves the sulphur, and is 
disengaged in the form of sulphurated hy- 
drogen gas. Charcoal has no action on sul- 
phuric acid in the cold ; but at the boiling 
temperature, it decomposes it, and converts 
it into sulphurous acid. If a piece of red- 
hot charcoal be immersed in a quantity of 
concentrated sulphuric acid, part of the 
acid is suddenly disengaged under the form 
of thick white fumes, accompanied with 
sulphurous acid gas. The sulphuric acid is 
decomposed; part of its oxygen is attracted 
by the charcoal, forming carbonic acid, and 
thus it is reduced to the lowest proportion 
of oitygen, in the state of sulphurous acid. 
A similar effect is produced by phosphorus, 
phosphorus, with the assistance pf heat, 
partially decomposes the sulphuric acid, by 
abstracting part of its oxygen. Phosphoric 
acid is formed, and sulphurous acid driven 
off. Ip the cold, sulphur has no action on 
sulphuric acid ; but, when they are boiled 
together, the sulphur is partly dissolved in 
the acid, and converts it into sulphurous 
acid. The sulphur which has been added 
combines with the oxygen, which is neces- 
SUL 
sary for tlie constitution of sulphuric acid, 
and thus the whole is converted into sul- 
phurous acid. Sulphuric acid combines 
with alkalies, the earths and the metals 
forming salts; which in the present lan- 
guage of chemi.stry are denominated sul- 
phates. This acid is employed in great 
quantity in many arts and manufactures. 
It is employed also in medicine and phar- 
macy; the preparation of it, therefore, has 
long been an object of considerable impor- 
tance. 
SULPHUROUS acid, was formerly call- 
ed spirit of sulphur, and volatile sulphurous 
acid. It was not till the year 1774 that its 
nature and composition were discovered by 
the labours of Priestley and Lavoisier. 
Berthollet afterwards investigated the for- 
mation, decomposition, combinations, and 
uses of this aciff Fourcroy and Vauquelin 
also have examined many of its properties, 
especially the saline compounds which it 
forms, so that now its properties are well 
known. The sulphurous acid exists in na- 
ture in great abundance, and particularly 
in the neighbourhood of volcanoes. It is 
disengaged from some lavas in a stale of fu- 
sion, and from the soil which is impregnated 
with sulphur, when a sufficient degree of 
heat is applied. It was by the vapours of 
sulphurous acid that Pliny the naturalist 
was suffocated in the eruption of Mount 
Vesusius, which destroyed Herculaneum, in 
the 79th year before the Christian sera. 
When sulphur is burnt in the open air, the 
fumes that are generated by this slow com- 
bustion, are sulphurous acid. It was in 
this way tliat this acid was formerly obtain- 
ed. The method of procuring it, which is 
now followed, is to decompose the sulphu- 
ric acid by means of any substance which 
deprives it of part of its oxygen. If one 
part of mercury and two parts of concen- 
trated sulphuric acid be exposed to heat in 
a glass retort, the mixture effervesces, and 
a gas is disengaged, which may be collected 
in jars over mercury. In this process the 
mercury attracts part of the oxygen of the 
sulphuric acid, and leaves behind that por- 
tion which constitutes the sulphurous acid. 
Sulphurous acid thus obtained is in the 
state of gas, and it is an elastic, invisible 
and colourless fluid, like common air. It.is 
rather more than double the weight of at- 
mospheric air. It reddens vegetable blues, 
and then destroys the greater number of 
tliem. It is on account of this property 
tliat the fumes of sulphur arc employed to 
remove the stains of fruit from linen, anc| 
