GAS. 
the plate, and unite with it so as not to be 
separable without detaching the glaze, 
though it lias passed through perhaps two 
inches of water. 
As oxygen gas appears to be a very 
powerful stimulus to the animal ceconomy, 
it has been applied medicinally; and is 
reported to have been of great service in 
many cases of debility, palsy, nervous af- 
fections, scrofula, rickets, and even hydro- 
cephalus. 
Gas, sulphurous acid. When sulphur is 
burnt slowly, a gas arises, of a suffocating 
pungent smell, consisting of sulphur com- 
bined with oxygen in less proportion than is 
requisite to form sulphuric acid. This was 
known to the earlier modern chemists, and 
Stahl examined some of its combinations ; 
Priestley showed it was permanently elastic ; 
Berthollet pointed out its difference from 
the sulphuric acid ; and Fourcroy and Vau- 
quelin completed its examination. 
In the mode above mentioned, it is very 
difficult so to regulate the combustion, as 
to obtain it free from sulphuric acid, which 
is formed when the sulphur burns with a 
certain degree of rapidity; so that it is 
commonly made by subtracting oxygen 
from sulphuric acid, by some other inflam- 
mable substance. The metals answer the 
purpose, but such as do not decompose 
water should be employed, otherwise more 
or less hydrogen will be evolved. Tin or 
quicksilver answers best ; one part of which 
may be put into a retort, with two of con- 
centrated sulphuric acid, and heat applied. 
It should be received over mercury, as 
water aborbs it, taking up thirty-three 
times its bulk. 
This gqs is above twice as heavy as at- 
mospheric air: it kills animals very speedily, 
and extinguishes burning bodies. From 
this latter property it has been recommend- 
ed, when a chimney is on fire, to throw a 
spoonful or two of flowers of sulphur into 
the grate. It whitens and gives lustre to 
silk, and is useful in bleaching woollens. 
Fresh prepared muriate of tin decomposes 
it, sulphur being deposited, and the muriate 
oxygenized. Mr. Northmore has con- 
densed it by pressure : and Monge did the 
same, with the addition of artificial cold. 
According to Dr. Thomson, it consists of 
sulphur sixty-eigbt parts, oxygen thirty-two. 
One hundred grains of water take up 5 
grains of this gas, or 25 parts by measure ; 
or, according to Dr. Thomson, 8.2 grains, 
equal to 33 times its volume. The solution 
has a pungent disagreeable odour, and an 
acid taste. It reddens some of the vege- 
VOL. III. 
table colours, such as that of litmus, or red 
cabbage ; there are others, however, the 
colour of which it destroys, as that of the 
red-rose. The effect of the gas upon these 
colours is similar. 
The saturated solution allows the gas to 
escape at a very moderate heat, and by 
boiling, the greater part is expelled, though 
the liquor remains acid, apparently from the 
presence of sulphuric acid. It is singular 
that it is not expelled by freezing ; but still 
remains combined with the ice, and ren- 
ders it so heavy that it sinks in water. This 
fact shews that this gas has, comparatively 
with others, little tendency to pass into the 
aeriform state. The freezing of the solu- 
tion takes place at a few degrees below 32. 
When two parts of the gas are mixed with 
one part of oxygen gas, if the mixture is 
kept over mercury, they do not act on each 
other. But if a small portion of w'ater is 
introduced, they gradually combine and 
form sulphuric acid, a fact explained by 
Mr. Murray, on the supposition that the 
water exerts a strong disposing affinity to 
this acid, or to speak more intelligibly, ac- 
cording to the explanation of disposing af- 
finity given under our article Chemistry, 
the water attracks the sulphureous gas, and 
by depriving it of its state of elastic fluiditj', 
renders it capable of more readily uniting 
Vith the oxygen, which is also effected by 
a like action of the water; and as these 
combine into sulphuric acid, which is more 
soluble than the sulphureous, the process is 
still more facilitated, and goes on progres- 
sively until the effect is completed. By 
passing a mixture of oxygen gas, and Sul- 
phureous acid gas, through a tube heated 
to redness, they instantly combine, and sul- 
phuric acid is formed. 
This acid combines with facility with the 
alkalies, fornringsalts denominated sulphites, 
which differ considerably from the salts 
formed by the sulphuric acid. Their taste is 
sulphureous; they are decomposed by a 
high temperature, their acid being either 
expelled, or a portion of sulphur being 
driven off, in which case they become sul- 
phates ; they are also decomposed by the 
greater part of the acids, and then the sul- 
phureous acid is disengaged with effer- 
vescence. The alkaline sulphites are more 
soluble than the sulphates in water, the earthy 
sulphites less so. AH these salts are convert- 
ed into sulphates by exposure to the atmos- 
pheric air, or by the action of any substance 
capable, of affording them oxygen. They suf- 
fer this change, for example, by deflagration 
with nitre. See Sulphureous Acid. 
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