SULPHURIC ACID. 
life. If sulphuretted hydrogen gas be kin- 
dled in contact with the atmospheric air, it 
burns with a blue lambent flame. When 
mixed with atmospheric air it does not de- 
tonate, and the combustion of its elements 
is not complete, part of the sulphur being 
deposited on the sides of the vessel. With 
oxygen gas it detonates. Sulphuretted hy- 
drogen has a peculiar action on metals, by 
tarnishing them, and communicating to 
them shades of yellow, purple, &c. It is 
possessed of the properties of an acid, and 
enters into combination with the alkalies, 
and forms compoimds, some of which are 
crystallizable. It changes vegetable blues 
to red. It decomposes .soap; combines 
with the metallic oxides, and precipitates 
sulphur from its combinations with potash 
or lime. 
SULPHURIC acid, in chemistry. The 
name of sulphuric acid is given to the com- 
bination of sulphur and of oxygen, with the 
greatest proportion of the latter. It was 
formerly called vitriolic acid, because it 
was obtained from vitriol by distillation, 
which is a compound of sulphuric acid and 
an oxide of iron. When it is strongly con- 
centrated, it is called oil of vitriol. If a 
quantity of flowers of sulphur be exposed 
To a degree of heat sufficient to inflame it, 
and if, when it is in a state of ignition, it be 
introduced into a jar filled with oxygen gas, 
it burns with great splendour, and emits a 
great quantity of white fumes. These 
fiimes may be condensed, by pouring a 
small quantity of water into the jar, and 
when this is examined, it is found to possess 
acid properties. This is the sulphuric acid. 
It is procured, as appears by this experi- 
ment, by burning sulphur in oxygen gas. 
The process for obtaining sulphuric acid 
in the large way is the following. A mix- 
ture of sulphur and nitre is burnt in leaden 
chambers. The use of the nitre is to sup- 
ply a quantity of oxygen for the combus- 
tion of the sulphur. There is a little water 
in the bottom of the vessel, which serves to 
condense the vapours given out during the 
combustion. 
The acid which is obtained in this way is 
very weak, for it is diluted with the water 
in which it was condensed, which water 
may be' separated by distillation. Even af- 
ter this it is usually contaminated with a 
little lead from the vessels, some potash, 
and sometimes nitric .and sulphurous acids. 
To obtain it perfectly pure, the sulphuric 
acid of commerce must be distilled. This 
process is conducted by putting a quantity 
of the acid into a retort, and exposing it to 
a degree of heat sufficient to make it boil. 
The beak of the retort is put into a re- 
ceiver, in which the acid, as it comes over, 
is condensed. The acid thus purified, is a 
transparent colourless liquid, of aii oily con- 
sistence. It has no smell, but a strong acid 
taste. It destroys all animal and vegetable 
substances. It reddens all vegetable blues. 
It always contains water. When this is 
driven ofi^ by a moderate heat, the acid is 
said to be concentrated. When as much 
concentrated as possible, the specific gra- 
vity is 2, or double that of water ; but it 
can rarely be obtained of greater density 
than 1.8. The sulphuric acid suffers no 
change from being exposed to the light. It 
boils at the temperature of 546°, or, ac- 
cording to Bergman, 540°. When this acid 
is deprived of its caloric, it is susceptible 
of congelation, and even of crystallization, 
in flat, six-sided prisms, terminating in a 
six-sided pyramid. It crystallizes most 
readily, when it is neither too much con- 
centrated, nor diluted with water. Of the 
specific gravity of 1.6 it crystallizes at the 
temperature of a few degrees below the 
freezing point of water. Of the specific 
gravity of 1.8, it resists the greatest degree 
of cold. Chaptal observed it crystallize at 
the temperature of 48°, and Mr. Keir found 
that it froze at 45° of the specific gravity 
of l.^s. Sulphuric acid has a strong at- 
traction for water. 
In some experiments that have been 
made, sulphuric acid, when exposed to the 
atmosphere, attracted above six times its 
weight of water. When four parts of con- 
centrated sulphuric acid, and one part of 
ice at the temperature of 32°, are mixed 
together, the moment they come in contact 
the ice melts, and the temperature rises to 
212°. A greater quantity of caloric is given 
out when the two bodies are mixed to- 
gether in the liquid state. If four parts of 
the acid and one of water are suddenly 
mixed together, the temperature of the 
mixture rises to about 300°. This extrica- 
tion of caloric, it is obvious, arises from the 
sudden condensation of the two liquids, the 
medium bulk of which is considerably less 
than the two taken together. So great is 
the attraction of this acid for water, that 
the strongest that can be prepared can 
scarcely be supposed to be entirely free 
from it. Attempts have been made to de- 
termine the proportion of oxygen and sul- 
phur, which enter into the composition of 
sulphuric acid. According to the experi- 
