SALT 
most simple is merely to procure the salt 
by a slow artilicial evaporation. It then 
crystallizes with scarcely any mixture of 
the others. This is the cause of the supe- 
rior purity of the bay-salt. Hence, also, the 
larger the crystals of sea-salt are, they may 
be justly supposed to be the purer, as the 
largeness of the crystals is owing to the 
slowness of the evaporation bj' which they 
are formed. 
For chemical purposes, muriate of soda 
is most easily purified, by dissolving it in 
water, and adding to its solution a solution 
of carbonate of soda, drop by drop, till no 
cloudiness is produced by the addition. 
Every foreign salt is thus decomposed and 
precipitated, and the strained solution will 
contain the pure mmiate of soda, which may 
be crystallized. Muriate of soda has a salt, 
rather agreeable taste, being, when pure, 
free from all bitterness ; it is soluble in ra- 
. ther less than three parts of water, at the 
temperature of 60°. The crystals neither 
deliquesce, nor effloresce, on exposure to 
the air ; the common sea-salt, indeed, is de- 
liquescent; but this is owing to the muriates 
of magnesia and lime, which adhere to it. 
Exposed to heat, the crystals of muriate of 
soda decrepitate from the sudden conver- 
sion of their water of crystallization into va- 
pour. If the temperature is raised to a red 
heat, the salt melts ; in an intense heat, it 
is volatilized in white vapours, without hav- 
ing undergone any decomposition. 
Crystallized muriate of soda contains S3 
of soda, and 47 of acid, containing, how- 
ever, some water of composition, so that of 
real acid, the quantity is 38.83. Its speci- 
fic gravity is 2.12. Tlus salt is decomposed 
by the sulphuric and nitric acids, in the 
same manner as the muriate of potash is. 
It is from its decomposition by the sulphu- 
ric acid, that "the muriatic acid is best ob- 
tained, as has already been observed. When 
decomposed by the nitric acid, part of the 
latter is decomposed, a quantity of its oxy- 
gen being transferred to the muriatic. One 
of the most important practical problems in 
chemistry is to decompose this salt, so as to 
obtain its alkali. It abounds so much in 
nature, that if such a process, capable of 
being carried on to advantage, could be dis- 
covered, a vast supply of soda would be ob- 
tained ; and as this alkali can be employed 
for every purpose that potash can, and is 
even much superior to it for some uses, such 
a discovery would be of much importance to 
the chemical arts. Salt is decomposed in 
the usual mode by sulphuric acid ; and to 
defray the expense, the muriatic acid is 
collected and employed in the manufacture 
of sal ammoniac, in the preparation of oxy- 
muriatic acid for bleaching, or for any other 
useful purpose to which it can be applied. 
The sulphate of soda is calcined in a rever- 
beratory furnace, to free it from any super- 
fluous acid. It is then to be decorqposed. 
It is of very extensive use. Its applica- 
tion to preserve animal substances from 
putrefaction is well known ; the theory 
of its antiseptic quality has never yet been 
properly explained. It is also taken uni- 
versally as a seasoning to food, and seems 
to be very necessary to promote digestion, 
as even the lower animals, it has been 
proved, languish when altogether deprived 
of it. It is employed in a variety of arts. 
In the manufacture of pottery of the 
coarser kind, when it is thrown into the 
oven in which the ware is baked, it is con- 
verted into vapour, and, being applied in 
this state to the surface of the vessels, glazes 
them, an effect probably owing to the com- 
bination of its alkali with the siliceous earth 
of the pottery. It is employed in the ma- 
nufacture of glass, which it is said to render 
whiter and clearer ; in that of soap, which 
it makes harder ; as a flux, in the melting 
of metals from their ores ; and in a variety 
of chemical and pharmaceutical processes. 
Salt, in a chemical sense, is a chrystal- 
lizable substance, considerably soluble in 
water, and highly sapid. The term is ap- 
plied likewise by modern chemists to all 
the crystallizable acids, or alkalies, or earths, 
or combinations of acids with alkalies, 
earths, or metallic oxides ; hence salts in 
chemistry are distinguished into alkaline, 
earthy, and metallic, and they take their 
names from the acid, and alkali, &c. of 
which they are combined : thus the sul- 
phate of soda is a combination of sulphuric 
acid and soda; the sulphite of soda is a com- 
bination of sulphurous acid and soda. The 
termination ate denotes that the salt is 
formed of the acid containing the greater 
quantity of oxygen, and the termination ite 
of the acid, containing the smaller quan- 
tity of oxygen. There are also salts oftriple 
combinations, as alum, tartarized antimony, 
&c. Salts are either also neutral, that is 
where the ingredients are in perfect satura- 
tion, (see NEUTRALtzATroN,) or with the 
acid in excess, of which tartar is an exam- 
ple, or with an excess of the, base, as in 
borax. These circumstances have been 
distinguished by the prefix super in the first 
case, and sub in the latter : hence tartar is 
