C H E M I 
fh'ewn, by leaving a mafs of gold for fome time in the 
Jfalt, which becomes mahifeftly whitened. This fait, 
formed by fpontaneous evaporation, is ufually called 
bay fait. The fait which is obtained by flow evapora¬ 
tion, is alfo purer than that which is formed by quick 
boiling. The Dutch fait, in fogreat repute for the fak¬ 
ing of fifh, is prepared with a very gentle fire. They 
add a quantity of four whey to their brine before evapo¬ 
ration. The adlion of this fubftance does not feem to 
be well underftood, though it is faid to conduce to the 
purity of the fait, and to favour the production of large 
cryftals. The fait obtained by quick evaporation always 
contains more or lefs of the muriat of lime and fulphat 
of foda. In the falterns of France, common fait is ob¬ 
tained by artificial evaporation, effedted by means of 
heat. In Arranchin they take the quickfands on which 
the fea-water has depofited its faline cryftals 5 thefe are 
waftied with the fmallelt quantity of water fufficient to 
difl'olve the fait, and the water is then evaporated to 
drynefs in leaden boilers. « 
There are many fait fprings, the waters of which are 
charged with different quantities of muriat of foda. At 
Montmorot, in France, a neutral fait is prepared, which 
is known by the name of Epfom fait of Lorrain, but it 
is nothing more than fulphat of foda, or Glauber's fait, 
whole cryftallization has been difturbed : it may be dif- 
tinguifhed from the fulphat of magnefia, by its effloref- 
cing in the air; whereas the Epfom fait is deliquefcent. 
Here the fpontaneous evaporation is united to evapora¬ 
tion by heat: the water of the fpring is pumped up into 
a large refervoir, at the top of a building, or Ihed, be¬ 
neath which are fufpended boards covered with little 
bundles of thorns or brufh-wood ; on thefe the water falls' 
through fmall cocks, and becomes divided into minute 
drops. The large furface of water thus expofed to the 
air, which circulates quickly through thefe Iheds, caufes 
an evaporation of nearly two thirds. Selenite is depo¬ 
fited on the brufh-wood; and when the liquid, upon trial 
with a kind of hydrometer, is found charged with fait 
to a certain degree, it is conveyed into large iron boilers, 
fupported by bars of the fame metal; thefe boilers are 
very large and (hallow, and contain a large quantity of 
fait water. A brilk heat is applied ; and, as loon as the 
water boils ftrongly, it becomes troubled, and an oche- 
rous earth is feparated, in the form of fcurn; another 
fait, of difficult folubility, is next feparated, which is 
found to be fulphat of lime, the workmen call it fch/ot, 
the fchlat, mixed with a fmall quantity of muriat of fo¬ 
da, fulphat of loda, and earthy muriats. The fcum is 
received in little troughs of cloth, placed round the fides 
of the boiler, into which it is thrown by the circulation of 
the boiling liquor. Thefe troughs are taken out and 
cleared, from time to time, and repeatedly put in again, 
till a large quantity of fmall cubical cryftals, called by 
the workmen pieds de mouches, appear on the furface of 
the liquor. At this period, the troughs are taken away 
entirely; the fire is diminifhed, and the muriat of foda 
is taken out with ladles, in proportion as it cryftallizes 
in fufficient quantity ; the evaporation is continued till 
no more cubical cryftals are afforded. The cryftals are 
larger, the flower the evaporation; and the remaining 
fluid, called mother-water, contains earthy muriats. 
Wallerius mentions a fourth procefs to obtain fait 
from fea-water. This water is expofed in trenches on 
the fea ffiore, Where it forms fo thin a ftratum, that the 
cold of the atmofphere foon freezes it; but, as the ice 
Oonfifts of mere water, the unfrozen part, after the ice 
is taken out, is of courfe more concentrated, and may 
be duly evaporated with a lefs degree of heat. It is con¬ 
veyed into leaden boilers, and evaporated by fire. Sclieele 
had obferved, that by expofing a mixture of two' parts 
of the folution of fulphat of magnefia, and one of the 
muriat of foda, to the temperature of freezing, fulphat 
©f foda was formed. More lately, Gren remarked, that 
a fimilar effedt is produced in fea water expofed to a low 
•Vox. IV, No, x93, 
S T R Y. 245 
temperature, fulphat of foda being formed in it by the 
double decompofition of its muriat of foda and fulphat 
of magnefia. It is remarkable, however, that an increafe 
of temperature will not reproduce the muriat of foda, 
nor reftore the falts to their former ftate. From thefe 
fadls, all muft perceive the diladvantage which will 
arife from concentrating fea-water by freezing, and the 
propriety of Gren’s important plan of feparating the de¬ 
liquefcent falts before evaporation, in the art of lalt mak¬ 
ing, by chemical affinity. With this view he diredfs 
the addition of fulphat of foda to waters containing only 
the muriats of lime and foda, and of lime tothofe which 
contain the muriat of magnefia and fulphat of foda. In the 
latter inftance, muriat of lime is firft formed, which after¬ 
wards decompofes the fulphat of foda by double affi¬ 
nity. Where muriat and fulphat of magnefia are pre- 
fent without the fulphat of foda, or where the waters 
contain only the muriats of lime and magnefia, lime and 
fulphat of foda fliould be added at the lame time. But 
if the water contains the fulphat and muriat of magnefia, 
together with the fulphat of foda, lime alone will be ne¬ 
ceffary, unlefs the quantity of fulphat of foda be infuffi- 
cient, in which cafe fome of it muft alfo be added. 
Many advantages are thus gained. The bitter tafte of 
common fait, occafionecl by the prefence of the fulphats 
of foda, and magnefia, is prevented; no mother water is 
formed, and pure muriat of foda alone is obtained on 
evaporating the fluid. Much expenditure of time and 
fuel is faved in the procefles of evaporation, and trying 
the falts, and a pure, not deliquefcent, fait is obtained, 
capable of refilling the impreffion of the air, and of being 
tranfported without lofs. The principal objedfion to 
thefe procefles may arife from the neceflity of purchafing 
the fulphat of foda; but the fea-water will itfelf in gene¬ 
ral produce it when brought to a temperature below 
zero; and for this purpofe it will only be neceffary to 
colledt a quantity in the bafons, to be expofed to the 
cold during the winter. We might from this water alfo 
obtain the fulphats of foda and magnefia by adding the 
fulphat of iron. It will even be found advantageous 
to purify waters by thefe means, which do not contain 
fulphat of magnefia, as the moft unprodudtive waters 
w'ill not require more than from fifty to .feventy-five 
pounds of fulphat of foda to produce thirty quintals of 
muriat of foda. In following this method it will only 
be neceffary to afcertain the component parts of the fluid 
employed previous to afcertaining what fubftances fhould 
be added. Diredt experiment will eafily point out the 
quantities which may enfure the moft perfect fuccefs. 
When mines of fal gem are found in the bofom of the 
earth, they are eafily wrought, and at a fmall expence. It is - 
fufficient to fink wells, and make galleries, and to loofen 
the fait with pickaxes, bars, levers, &c. Sal gem, befides 
partaking of different colours, as white, yellow, green, 
blue, red. &c. is either hard, foft;‘ pleafant to the tafte, 
or bitter. Its varieties of colour proceed from the oxyd 
of iron being more or lefs charged with oxygen; its hard- 
nefs depends on thequicknefs with which it was formed; 
and its difference of tafte arifes from fome other faline 
fubftances, particularly muriat of lime, commonly mix¬ 
ed with it. 
We have now given, from Fourcroy, Chaptal, &c. the 
various methods in ufe for extradfing muriat of foda from 
the waters in which it is held in folution, the objedl of 
all which is to feparate the water from it. But to redfify 
it, or to obtain it in the pure ftate which is requifite. for 
chemical experiments, difl'olve it in four parts of cold 
water ; ftrain it; the matters which do not unite with 
the water, as the clay, fait, chalk, oxyd of iron, &c. re¬ 
main behind, but the muriat of lime is diffolved alfo: 
it is decompofed by putting into the folution a few drops 
of carbonat of foda ; its bale combines with the muriatic 
acid, and the carbonic acid with the lime, and forms 
carbonat of lime, which, being infoluble, falls to the 
bottom. Care muft be taken not to add.more of the car- 
3 R bonat 
