CH-EMISTR Y. 
260 
of marine plants: fuch is the carbonat of foda met with 
in commerce. But it is found ready formed in the earth, 
and in ieveral mineral waters, as the acidulated alkaline 
waters j the overflowings of the Nile leave it abundantly 
on the iiirface of the earth. Native carbonat of foda 
feems to come from marine fait, decompofed by vege¬ 
table and animal fubftances, and efpecially by lime; 
lienee we fee efflorefcences of carbonat of foda on walls 
built with lome peculiar kinds of earth, under the arches 
of bridges, and particularly in caverns near the fea; this 
is muriat of foda decompofed by a terreftrial agent. 
But foda, with us, is molt ufually obtained from ma¬ 
rine plants by combuftion; Spanifh barilla furniflies the 
belt. Colledt a heap of thefe faline plants, and dig a 
round pit near them, growing larger towards the bottom, 
and about a yard deep ; by means of this the vegetables 
are to be burned, and the combuftion is to be continued 
without interruption for feveral days; when the com¬ 
buftion is finilhed, a mafs of alkaline fait is found, which 
is'divided in pieces for fale or exportation ; this is called 
■foda-Jlone, or foda. This is to be pounded, and expofed 
in a fubterraneous place, where it may attradl carbonic 
acid; it is then walhed as for falt-petre j the fea-falt is 
feparated, • then drawn off; and, finally, you have pure 
carbonat of foda. The foda exifts in the cauftic (late in 
.the plant; for, if fulphuric or muriatic acid be poured 
over the pulverized plant, a muriat, or fulphat, will be 
obtained without effervefcence; but, by combuftion, the 
carbon of the plant itfelf furniflies the carbonic acid, and 
the carbonat is formed. 
To obtain this fait quite pure and well cryftallized, 
proceed as for carbonat of potafh. It may likewife be 
prepared by pouring carbonic acid into a veffel, the tides 
of which have been moiftened with a folution of foda. 
The veffel is covered with a wet bladder, and, at the end 
of a few hours, the combination is effe&ed. The blad¬ 
der finks in the veffel, on account of the vacuum which 
is formed in it, while the fait is depoftted in regular cryf- 
tals on its fides. 
The carbonat of foda has an alkaline tafte, and ren¬ 
ders the fyrup of violets green, though this does not alter 
its colour fo much as the cauftic foda does; its tafte is 
urinous, but neither fo burning nor fo cauftic as that of 
the fame alkali in a ftate of purity. This neutral fait 
haftily cryftallized, appears to be formed of rhomboidal 
laminae, obliquely applied on each other, after the man¬ 
ner of tiles. When it is (lowly cryftallized, it takes the 
form of rhombic o&ahedrons, whole pyramids are trun¬ 
cated very near their bafe, or decahedral folids, with two 
acute and two obtule angles. By the aftion of heat it 
Jofes 0 64 of its weight. If the fire be kept up, it lofes 
its carbonic acid, and becomes cauftic; for, in propor¬ 
tion as part of the acid is difengaged, what remains is 
more concentrated, and more ftraitly liolden by the fo¬ 
da, which makes a ftrong heat neceffary at the end of 
the operation. This fait efflorefees in the air, and its 
cryftals fall to powder, becaufe this carbonat has lefs 
affinity with water than air. The warm dry air of fum- 
mer ails brilkly upon it; yet air takes away only one 
half of the weight of the water it contains; to feparate 
a greater quantity, there requires more than the aftion 
of dry air, namely, that of caloric. 
Carbonat of foda produces cold by its folution in w'a- 
ter* it is more foluble than carbonat of potafh, as it re¬ 
quires only twice its weight of cold water, or half that 
quantity of boiling water, to hold it in folution. It cryl- 
tallizes by cooling; but Spontaneous evaporation affords 
more regular cryftals. 
This fait, well faturated and dried, is decompofed by 
phofphorus. See the procefs in tlie account we have 
given of Carbonic Acid. This carbonat favours the fu- 
iion of vitrifiable earths much more than potalh ; and 
the glafs it forms is more durable. If a folution of ba¬ 
rytes, ftrontian, or lime, be poured into a folution of 
carbonat of foda, a precipitation takes place immediate¬ 
ly : the carbonic acid feizes on the earths, and forms an 
infoluble fait; the foda remains in folution in the liquor. 
Potafh decompofes this fait alfo. All the acids feparate 
its carbonic acid with effervefcence. Nothing is more 
eafy than to decompofe the alkaline carbonats; which; 
no doubt, arifes from the carbonic acid having a great 
affinity for caloric; and this affinity a6ts in molt of the 
experiments. 
Carbonat of foda decompofes the calcareous, magne- 
fian, and aluminous, falts. When a calcareous fait is to 
be decompofed by carbonat of foda, the liquor mull be 
heated ; otherwife there will remain in the lolution 
enough of carbonat of foda to hold the carbonat of lime 
in folution; this excefs of acid is diffipated by heat. It 
is the fame with the magnefian falts. This carbonat may 
be employed for the fame ufes as the carbonat of potafh, 
and is much more valuable in the manufactories of glafs, 
foap, &c. 
Carbonat of Ammoniac. —Pure ammoniac and 
carbonat of ammoniac w'ere formerly fuppofed to be the 
fame thing. It was formerly concrete volatile alkali, and 
volatile fait of ammoniac , and a great affinity for lime is 
given to it in the ancient tables : this was an error; it 
is known now, that this affinity arofe from the prefence 
of the carbonic acid, which was not then underftood or 
even fufpedted; and the effects it produced were attri¬ 
buted to the ammoniac. 
Befides the methods pointed out in fpeaking of carbo¬ 
nat of lime, carbonat of ammoniac may be obtained fe¬ 
veral different ways ; as, 1. By agitating the alkali in the 
upper part of a vat of fermenting liquor: 2. By palling 
the carbonic acid into volatile alkaline fpirit: or, 3. By 
pouring the acid into a veffel, on the (ides of which a 
few drops of ammoniac diffolved in water are fpread; 
4.. By combining direCtly over mercury carbonic acid gas 
and ammoniac. Thefe two gafes immediately unite; 
much heat is extricated, and a concrete fait is formed 
on the fides of the veffel in which the mixture is made. 
In all thefe cafes, cryftals of ammoniacal carbonat are 
formed. It is likewife obtained by decompofing ammo¬ 
niacal muriat, by the addition of carbonic neutral falts, 
with bafe of potalh or foda. Its tafte is urinous, but 
much lefs fo than that of pure and cauftic ammoniac; 
its fmell, though fimilar, is much fainter: it converts fy¬ 
rup of violets to a green. It is very volatile, and the 
fmalleft heat fublimes it entirely, if it be well cryftal¬ 
lized. The firft effect of heat is that of liquefaction, by 
means of its water of cryftallization, or the aqueous fu- 
fion. It flowly attradls moillure from the air, efpecially 
•when it is not entirely faturated with carbonic acid. It 
is very foluble in water, and, like all other neutral falts, 
produces cold; a property fo contrary to that of pure 
ammoniac, as to afford an additional argument for rank¬ 
ing it among the neutral falts. Two parts of cold water 
diffolve more than one of carbonat of ammoniac; hot 
water dilfolves more than its own weight. Its cryftals 
are many-fided prifms. But it is very difficult to obtain 
this fait well cryftallized; for, being more volatile than 
water, if the liquor be left to evaporate, it will volati¬ 
lize : the carbonat of ammoniac mult therefore be dif¬ 
folved in water of 30 0 heat; (train the liquor with a 
covered funnel; then, being lefs foluble cold than hot, 
it cryftallizes as it cools. Carbonat of ammoniac will 
not decompofe phofphorus ; becaufe the double affinity, 
which favours this decompofition with alkalis, does not 
take place here. 
The fulphuric, nitric, muriatic, and fluoric, acids, 
have a ftronger affinity than the carbonic acid to ammo¬ 
niac : when one of thefe acids is poured on the carbonat 
of ammoniac, a ftrong effervefcence arifes from the dif- 
engagement of the carbonic acid. If this decompofition 
be made in a tall (lender veffel, the prefence of the car¬ 
bonic acid gas may be obferved by the extinction of a 
lighted candle, the reddening of the tinfture of tumfole, 
or the precipitation of lime-water immerfed in a (mall 
