SUL 
that the sulphurous acid is often used in 
bleaching. When the sulphurous acid is in 
the form of gas, it does not readily combine 
with oxygen. In its fluid form it unites 
more readily, and is converted into sulphu- 
ric acid. In making a mixture of sulphu- 
rous acid gas and oxygen gas pass through a 
red-hot tube, they combine together, and 
are converted into sulphuric acid. There 
seems to be no action between sulphurous 
acid and azotic gas. Water has a strong 
attraction for sulphurous acid gas. A piece 
of ice brought in contact with it, is imme- 
diately melted without any perceptible 
change of temperature. When water is 
saturated with this gas, it is known by the 
name of sulphurous acid, or liquid sulphurous 
acid. The specific gravity is 1.04. At the 
temperature 0143“ water combines with one- 
third of its weight of sulphurous acid gas ; 
biit as the temperature increases, it absorbs 
it in smaller proportion. It freezes at a 
temperature a few degrees below 32", and 
it passes' into the solid state without parting 
with any of its acid. The liquid sulphurous 
acid has the smell, taste, and other proper- 
ties of the gas, and particularly that of de- 
stroying vegetable colours. When exposed 
to the atmosphere, it gradually absorbs oxy- 
gen, and passes into the state of sulphuric 
acid. • This change goes on more rapidly 
when it is diluted with water, and agitated 
in contact with the air. The sulphuric acid 
separates the sulphurous acid in the gaseous 
form from its combinations, and even from 
wdter. Concentrated sulphuric acid ab- 
sorbs this gas, which imparts to it a yel- 
lowish brown colour and renders it pungent 
and fuming, The two acids strongly at- 
tract each other, so that when they are ex- 
posed to the action of heat, the first vapour 
which rises crystallizes in long, white, nee- 
dle-shaped prisms. This is a compound of 
the two acids. It smokes in the air; dis- 
solves with effervescence in it, and when 
thrown into water produces a hissing noise, 
like a red-hot iron, Snlphurous acid is very 
much employed in the arts, and sometimes 
in medicine. In the state of gas it is used 
for the bleaching of silk and wool, by ex- 
tracting the colouring matter. It removes 
also the stains arising from vegetable juices, 
and spots of iron from linen. According to 
Fourcroy, 100 parts of this acid are com- 
posed of 
Sulphui- 85 
Oxygen 15 
too 
SUN 
But according to the analysis of Dr. Thom- 
son, 
Sulphur. 
Oxygen, 
. 68 
32 
100 
The compound salts formed by this acid are 
denominated sulphites. 
SUM, in mathematics, signifies the 
quantity that arises from the addition of 
two or more magnitudes, numbers, or 
quantities together. The sum of an equa- 
tion is, when the absolute number being 
brought over to the other side of the equa- 
tion, with a contrary sign, the whole be- 
comes equal to 0: thus, the sum of the 
equation — 12 4:1 x — 42, is a:’ — 
12 a? -4- 41 X — 42 = 0. 
.SUMMER, in architecture, is a large 
stone, the first that is laid over columns and 
pilasters, in beginning to make a cross 
vault. 
Summer, in carpentry, is a large piece 
of timber, which being supported on two 
stone piers, or posts, serves as a lintel to a 
door, window, &c. 
SUN, in astronomy, the most conspicu- 
ous of the heavenly bodies, which occupies 
the centre of the system which comprehends 
the earth, the primary and secondary 
planets, and comets. The sun is the mag- 
nificent luminary which enlightens these 
worlds, and by its presence constitutes day. 
We have referred to this article from the 
fixed Stars, because the sun agrees with 
them in several particulars, as in the pro- 
perty of emitting tight continually, and in 
retaining constantly its relative situation 
with but little variation : they may have 
probably many other properties in common. 
The sun is, therefore, justly considered as 
a fixed star comparatively near us ; and the 
stars as suns at immense distances from 
our earth ; and we reasonably infer, from 
the same analogy, that the stars are posses- 
sed of gravitation, and of the other general 
properties of matter; they are supposed to 
emit heat as well as light ; and it has been 
conjectured that they serve to cherish the 
inhabitants of a multitude of .planetary bo- 
dies revolving round them. 
In a paper on the “ Constructions of the 
Heavens,” Dr. Herschel says, it is very pro- 
bable, that the great stratum called the 
milky way is that in which the sun is placed, 
though perhaps not in the centre of its 
thickness, but not far from the place where 
some smaller stratum branches from it. 
Such a supposition will satisfactorily, and 
