T’V'^ *.fwY % 't 
SALT. 
ways of a cubical form. The colours have 
been supposed to depend on the oxide or 
muriate of iron. In general it is pure, and 
hence its taste is purely saline ; but some- 
times it is bitter from the presence of fo- 
reign salts. There are immense mines of 
it in ditferent countries. Those of Cracow, 
in Gallicia, have been long celebrated. It 
abounds in the east and south of Germany, 
is found in large quantities in Spain, and 
likewise in Cheshire, in England. In Afri- 
ca, Asia, and America, it is not less exten- 
sively distributed, forming hills above the 
surface, or very extensive beds. It is al- 
ways connected with rocks of secondary 
formation, and generally with gypsum or 
sulphate of lime. 
Dr. Watson, in the second volume of his 
“ Essays,” speaking of the salt mines, says, 
“ There are several mines of rock-salt near 
Nortliwich in Cheshire, the first of which 
was discovered aS they were boring for coal 
in the year 1670. The springs which are 
met with both above and below the level 
of the Nortliwich bed of rock-salt, are 
strongly impregnated with salt. This is, 
easily accounted for: the rain-water, in 
sinking through the ground which lies over 
the rock-salt, at last arrives at the salt ; its 
further descent is in a great measure ob- 
structed by the solid body of salt ; it rests 
upon it, and, in resting upon it, dissolves it, 
and thus constitutes a brine-spring above 
the level of the bed of rock-salt. The brine- 
springs, which are found below that level, 
probably arise from the water, which has 
dissolved a portion of rock-salt, in sinking 
^o that depth in the earth. I have,” conti- 
;iues the Doctor, “ had the curiosity to go 
to the bottom of some of the most famous 
mines in England, but I never thought my 
labour, in these subterraneous expeditions, 
so well rewarded as in the sight of the 
rock-salt mines at Northwich. These are 
superior to the mines at Cracow, in Poland, 
which have, for many centuries, been the 
subject of general admiration.” A single 
pit, at Northwich, yields, at a medium, 
4,000 tons of salt in a year. 
In different countries, the process of ob- 
taining salt is differept. In very cold cli- 
mates, the water being received into shal- 
low ditches during the winter, is frozen, by 
which a great part of the superfluous water 
is removed, and the remaining liquor af- 
fords salt, by artificial evaporation. In 
warm climates, it is obtained by sponta- 
neous evaporation. The water is received 
into broad, shallow trenches at the sea-side, 
without the reach of the tide. The bottom 
of these is made of clay, well beaten, and 
tliey are divided into several departments. 
The fluid being thus spread out on an exten- 
sive surface, quickly evaporates, and by 
sluices it is removed from one department 
to another, so that when it arrives at the 
last, it is a strong brine, and the salt is soon 
deposited. It is necessarily mixed with 
the clay of the ground, and with several of 
the neutral salts, and other impurities, 
which sea-water contains. Salt, prepared 
in this manner, is known by the name of 
bay-salt. In colder climates, recourse must 
be had to artificial evaporation. The wa- 
ter is heated in .shallow iron pans. Muriate 
of soda possesses the singular property, 
that it is as soluble in cold as in hot water; 
after due evaporation, therefore, it begins 
to crystallize on the surface of the hot li- 
quor ; the crystals, as they increase, fall to 
the bottom of the vessel, are raked out, and 
set to drain. This is the process by which 
it is obtained in this country. Sometimes 
this method is conjoined with natural eva- 
poration. The sea water, before it is re- 
ceived into the boiler, is pumped into a 
large reservoir, under which faggots of 
thorns, &c. are suspended. It is allowed 
to drop over these, and a large surface be- 
ing thus presented to the atmosphere, while 
the air is also rapidly renewed, a consider- 
ably part of the water is evaporated. It is 
then conveyed to the boiler, and evaporated 
in the usual manner. Or, in some of the 
northern departments of France, the sea- 
water is made to flow over a bottom of clay 
covered with sand, which favours both the 
evapojation of the water, and the concre- 
tion of the salt ; the saline deposit, which is 
at length formed, is lixiviated with sea-wa- 
ter, which, becoming thus more impreg- 
nated with salt, is concentrated by boiling, 
so as to afford it by hasty ciystailization. 
Sea-salt, obtained by any of these pro- 
cesses, is never perfectly pure. Sea-water, 
by its analysis, is found to contain, besides 
muriate of soda, several other neutral salts, 
particularly muriate of magnesia, muriate 
of lime, and sulphate of soda. These being 
much more soluble in hot, than in cold wa- 
ter, remain dissolved in the hot liquor, from 
which the salt crystallizes. A small quan- 
tity of them, however, still adheres to the 
muriate of soda, they render it deliquescent, 
give it a bitter taste, and considerably im- 
pair its antiseptic power. Different pro- 
cesses have therefore been contrived to ob- 
tain the salt free from these mixtures. The 
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