CHEMISTRY. 
246 
bonat of foda than is neceflary, as in that cafe there will 
be as much inconvenience another way : when there is a 
fufficiency, the drops no longer caule any matron in the 
liquor: then let the folution evaporate, collefit the fait as 
it feparates, and it will be very pure. To have it in re-, 
gular cryftals, the fpontaneous evaporation mult be em¬ 
ployed ; then the faline molecules or elementary particles 
ea'fily re-unite, and form cubic cryftals. Lord Dundo- 
nald propofes, in the purification of muriat of foda, to 
take advantage of the fait, that water, faturated with one 
fait, will yet diliblve a portion of another fait. The pro- 
cefs which he recommends is as follows : Take a conical 
vefiel, having a hole in the fmallend, which is to be un¬ 
dermoll, and place it, filled with common fait, in a mo- 
do ate heat; laturate a portion of water with this fait, 
and pour the folution, boiling hot, on the fait in the co¬ 
nical vefiel. The boiling water will not diflblve any of 
the common fait, but will diflblve the bitter earthy fait 
which it contains. When the folution ceafes to drop 
out of the hole at the bottom of the vefiel, the fame pro- 
cels is to be repeated by means of frefli portions of the 
fame parcel of fait, already partly purified, till it be 
brought to the degree of purity required. Lord Dundo- 
nald reckons that three fuch waffiings make the common 
fait of this country purer than any foreign fait; that 
each wafhing makes it 44 times purer than before ; fo 
that (difregarding fractions) after the fecond wafhing it 
"will be twenty times, after the third ninety-one times, 
after the fourth 410 times, and, after the fifth, 1845 times, 
purer than at firft. 
The tafte of this fait is well known, as it is daily ufed. 
When expofed to a brifk heat, it burfts,and flies in pieces. 
This phenomenon is called decrepitation, and is produced, 
ns we have already obfervedi by the rarefaction of tiie 
water of cryftallizatipn. When all the water is evapo¬ 
rated in this manner, the decrepitation ceafes, and the 
fait is reduced to a pul verulent form : if the heat be con¬ 
tinued, it melts after ignition, and being poured on a 
fmooth ftone, becomes a kind of mineral cryftal ; 
but it is not at all altered, for its original form may be 
again reflored by folution in water. Fire does not, there¬ 
fore, decompofe it; a very itrong heat volatilizes it with¬ 
out alteration. 
Muriat of foda, when pure, is not fenfibly changed 
by expofure to the air; it rather becomes dry than moift, 
and attra£!s humidity only in fuch cafes as it contains 
rpuriats with earthy bafes. It is very folubie in -water; 
no more titan three parts of this fluid being required to 
diifolve one of the fait. Three ounces and a half of wa¬ 
ter difiolve one ounce of fait very completely; and it is 
not more folubie in bailing than in cold water. Heat 
caufes the folution to be made form what more quickly. 
The cryftals of this fait are obtained by a very flow eva¬ 
poration. 
As muriat of foda combines very quickly with water, 
it produces a great degree of cold, that is to fay, much 
caloric is absorbed in .a fliort time. We are not to fup- 
pofe, however, that it requires more heat than any other 
fait for its folution ; there are fome faCts which ieem to 
prove, that it rather requires lels than many others. It 
feems to have more affinity with water than mofc other 
lalts ; for, except thofe that are deliquefeent, it precipi¬ 
tates moll of them from their folutions; and during thefe 
precipitations a certain quantity of caloric is always 
difengaged. 
Sulphuric acid decompofes muriat of foda; muriatic 
acid is thereby difengaged, which is difpoied to combine 
with all the fubftances -preferited-to it, except filex. The 
refidue of this'operation is the/a/ admirabile of Glauber, 
which may be ufed in medicine or in the -manufacture 
of foda. 
To extraft muriatic acid, an apparatus is ufed, as re- 
preieiited on theChemiftry Plate V. fig. 3. Take eight 
parts of purified foda in powdey; put this into a re¬ 
tort A, or into a matrafs ; add five parts of fulphuric 
acid at 66° by means of a doubly-CUrvated tube E ; fome’ 
water may be put in, to prevent the effervefcence from 
being too ftrong. Adapt a matrafs, C, to the neck of 
the retort, to receive thofe portions of fulphuric and mu¬ 
riatic acids which pafs over, particularly towards the end 
of the operation, by means of the heat. D, E, F, are 
collateral bottles, containing water equal in weight to 
the fait; thefe bottles are united by tubes, widen have 
tubes of fafety G G. The joinings mult be carefully lut¬ 
ed. When things are thus prepared, make fome fire un¬ 
der the retort, and increafe the heat by degrees till no¬ 
thing comes over. If, inltead of a retort, a matrafs he 
ufed, the firft receiver muft be a two-necked bottle, as 
reprefented in the Plate ; a little water ihould be put in 
this bottle alfo, and a tube of fafety inferted, in order 
to retain the fulphuric acid, and the oxyd of iron, which 
rife towards the end of the experiment. When the gas 
combines with the water, there is heat; and, when the 
temperature is lowered., the water becomes fufeeptibie 
of abiorbing more. To make this experiment anfwer, 
the bottles ihould be furrounded with ice; but care mult 
be taken they do not burft at the time when, by the rail¬ 
ing of the temperature, the water can no longer retain 
the acid ; for it muft not be forgotten, that warm water 
reftrains the muriatic acid much lei's than cold. 
Nitric,acid decompofes muriat of foda in the cold; but 
the muriatic acid hereby obtained is not pure; it is proper¬ 
ly nitrous acid mingled with oxygenated muriatic acid: Put 
muriat of foda reduced to powder into a retort; add ni¬ 
tric acid in the fame proportion as for the decoinpofition. 
of this fait with fulphuric acid: adapt to the retort a tu¬ 
bulated balloon, whence runs a tube of fafety, which 
goes into a Woulfe’s bottle, containing water equal in 
weight to the fait in the retort. Heat the apparatus by 
degrees. The nitric acid begins by uniting with the 
foda,- forming nit vat of foda; and very-concentrated mu¬ 
riatic acid is difengaged. This acid attacks the nitric acid 
not yet combined, takes a portion of its oxygen, and 
forms oxygenated muriatic acid. In the mean time ni¬ 
trous acid is formed, proceeding from that part of the 
nitric acid which could not combine with the ioda, even 
before it could have formed that combination ; and the 
oxygenated muriatic acid, combined with the nitrous 
acid, -converts this into nitric acid : by giving it its oxy¬ 
gen, it is.reduced to the ftate of fimple muriatic acid. 
The other acids have noeft'eCt, when cold, upon muriat 
of foda.; but feme will decompoie it by the aid of calo¬ 
ric, or heat; fuch are the phofphoric and boracic acids. 
The reafon of this difference is, that muriatic acid is 
inclined to combine with -caloric, when accumulated and 
concerned in this manner in the muriat of fodw, which 
confequently weakens the,affinity between the principles; 
now the jphol'phoric and boracic acids not having the 
fame attraction for caloric, and tlreir tendency to com¬ 
bine with the foda not being fpread or divided, it happens 
at a certain time that the affinity of the caloric for the 
muriatic.acid, and of the fixed acids for the bafe of the 
marine fait, muft prevail; and then the decoinpofition 
takes place. In one cafe, phofphat of foda is the relult; 
in the other, borat of foda. 
Of all earthy fubftances, barytes only decompofes this 
fait in the cold: it feizes on the muriatic acid, and ieaves 
the foda in the cauitic-ftate. Though 1'oda has common¬ 
ly more affinity with muriatic acid than alumine has, 
yet, by raffing the temperature, a certain quantity of 
muriatic acid may be difengaged by alumine; and this 
is the procefs ufed in manufactories of aqua fortis to make 
what is called fpirit of fait. It is probable that this de- 
compofiiiion -is chiefly owing to-the pyrites, .which are al- 
moft always contained in the filiceous clays .uied in this 
operation. 
Lime decompofes this fait alfo. Boil muriat of foda 
and lime together; the foda riles to the furiace, becomes 
•carbonat oi loda by abiorbing the carbonic acid.contain¬ 
ed in the atmofphere. It mult be fuppoled, tiiat there is 
a com- 
