C H E M I 
cup below its orifice. Thefe decompofitions of the car- 
bonat of ammoniac by lime and fixed alkalis, which ieize 
its acid and fepprate the ammoniac, and by acids which 
ieize the alkali, and dilengage the carbonic acid, clearly 
ills tv the nature of this felt. Bergman has found, by ac¬ 
curate experiments, that a cententary of this fait, con¬ 
tains forty-three parts of ammoniac, forty-five parts of 
carbonic acid, and twelve of water. Fromtfteconf.de- 
ration that this fait contains a larger proportion of acid 
than carbonat of foda, and this laft a larger quantity 
than carbonat of potalh, he concluded, that the weaker 
the alkaline bafe, the more carbonic acid will be required 
for its feturation. The acid of borax does not decom¬ 
pofe the carbonat of ammoniac in the cold; but when 
the latter is poured on a hot folution of boracic acid, a 
very lenfible effervefcence is produced, and the difen- 
gagement of carbonic acid is fhown by the ufual me¬ 
thods ; a true borat of ammoniac being alio found at 
the bottom of the veiled. This experiment, proves, that 
heat modifies or changes the laws of affinity, or eleftive 
■attraftion, as Bergman long ago obferved. 
This carbonat is decompoied by barytes, ftrontian, 
and lime. If powdered lime be mingled with carbonat 
■of ammoniac, an ammoniacal odour arifes immediately; 
this will be facilitated by adding a few drops of water. 
But the experiment may be made at once with lime-wa¬ 
ter. If lime-water be poured into a folution of carbonat 
of ammoniac, a precipitate is immediately formed, and 
a ftrong fin ell of volatile alkali is perceived. The lime 
feizes the carbonic acid, and forms chalk, or calcareous 
carbonat, which falls down, and the ammoniac is difen- 
gaged and volatilizes. With magneiia, there is but a 
flight precipitate, becaule the mixture, while cold, re¬ 
tains a fufficient excefs of carbonic acid to hold the car¬ 
bonat of magnefia in folution; but, if the liquor be 
heated, this excefs of acid is difiipated, and a precipitate is 
formed. Potalh and foda decompofe this felt, as well as 
lime, barytes, and ftrontian, by feparating the pure am¬ 
moniac, and uniting with its acid. 
The carbonat of ammoniac is employed in medicine 
as a fudorific, anti-hyfteric, &c. It is mixed with certain 
aromatic matters ; and thus is prepared what we in Eng¬ 
land call fal 'volatile. It has been confidered as a fpecific 
againft the bite of vipers ; but the Abbe Fontana, with 
great reafon, combats this opinion. Many have advifed 
the ufe of the carbonat of ammoniac, or concrete volatile 
alkali, as a remedy in venereal dilorders; experience, 
however, has not yet decided on this head. All the know¬ 
ledge the art of medicine poffeffes with regard to this lalt 
is, that it is purgative, opening, diuretic, diaphoretic, 
difeuffive, and that it has a good e if eft in luch dilorders 
as depend on the denfity of the lymph 5 as certain vene¬ 
real cafes, coagulations of milk, fcrophulous dilorders, 
-&c. It is adminiftered in dofes of a few grains, in a pro¬ 
per vehicle, or compounded with opium. 
Carbonat of Magnesia. —This is faid to be found 
in.quarries in Savoy ; feveral mineral waters hold it in fo¬ 
lution; they waih it away in their courie, then it preci¬ 
pitates and cryftalliz.es. It is more foluble than lime in 
acidulated waters which have an excefs of carbonic acid. 
This felt has borne different names, it was ufed in me¬ 
dicine under the name of mica, or zvhite magnefia ; it was 
•formerly made with the mother-water of nitre evaporat¬ 
ed to drynefs, or precipitated by fixed alkali; it was firft 
known by the name of Count Palma's povjder, fovuder of 
Sentinelli. It has likevrife been called laxative polycbrejl 
povjder by Valentini, white magnefia of nitre, magnefia of 
■cdmtnon fait, becaufe it was like wife obtained from the 
mother-water of this laft felt. But the medicine, fo pre¬ 
pared, always contains calcareous earth, and other foreign 
fubltances. The magnefia at prelent uled is commonly 
precipitated from lulphat of magnefia by the fixed vege¬ 
table alkali or carbonat of potalh. Mr. B.utini lias del- 
■cribed a procefs for obtaining very fine magnefia in the 
greateft poffible quantity, A certain quantity of potalh 
Vol. IV* No. 194. 
S T R Y. 26 ! 
is diftblved in double- its weight of cold water, and ex- 
pofed to the air for fome months, if time permits, that 
it may abforb carbonic acid from the atmofphere and pre¬ 
cipitate itsearth. Thisbeingfiltered,afolution ofanequ.al 
weight of lulphat of magnefia in four or five times its 
weight of water is made ; the dilution is filtered, and frefh 
water added in about fifteen times the weight of the fait. 
This liquor is heated, and, when it boils, the alkaline di¬ 
lution is poured in. A precipitate of magnefia being 
formed, the mixture"fnuft be agitated and poured on a 
filter of paper. The precipitate mult be walhed on the 
filter with boiling water, to carry off the fulphat of pot- 
alh it may contain. It is then taken from the filter, and 
thinly fpread on papers, to dry by the heat of a ftove ; 
when dry, it is in white pieces, eafily broken into a very 
fine p’owder, which adheres to the Akin. This fait may 
be obtained in the cryftallized form ; fometimes in final! 
cubes ; at others in very fine brilliant needles, which 
through a magnifier exhibit prifms of fix or eight fides. 
To obtain very light carbonat of magnefia, the depo- 
fits Ihould be dried very (lowly, in firiall pieces, and in 
the fliade: this flow drying favours the fufpenfion of the 
molecules, or elementary particles, and occafions thole 
finail lump6 to preferve their lightnefs. Its talle is fweet- 
ilh, almoft infipid; but its effeft is more fenfible on the 
inteftines, as appears by its afting as a purgative. Ex- 
pofed to the fire in a crucible, its lofes its acid and water, 
and the magnefia remains pure : it is then called cauftic 
tnagnefia ; but it is not fo, for La Grange afferts that half 
a pound of it may be eaten without danger. When per- 
feftly calcined, it no longer eifervelces with acids. 
Calcined magnefia is ul'ed with good effedl to abforb aci¬ 
dity on the ftomach. If carbonat of magnefia be calcin¬ 
ed in dole veffels by the aid of the pneumatic apparatus, 
the water and acid may be preferved. 
Carbonat of magneiia is not leniibly altered by expo- 
fure to air; yet, as it gathers into lumps when kept in 
a moift place, it feems to be (lightly deliquefcent. Wa¬ 
ter diffolves but an exceedingly fmall quantity of this 
felt; and this lolubility varies accordingly as the quan¬ 
tity of carbonic acid is greater or lefs. The lulphuric, 
nitric, and muriatic, acids, decompofe carbonat of mag¬ 
neiia. They unite to the magneiia, with which they have 
a ftronger affinity than the carbonic acid, and difengage 
the latter in the galeous form, which conftitutes effer¬ 
vefcence. 
Barytes, ftrontian, and lime, decompofe this felt: By 
pouring a folution of thefe earths into carbonat of mag¬ 
nefia, a confiderabie precipitate is produced, how final! 
foever be the quantity of this neutral felt holden in fo¬ 
lution by the water. Fixed alkalis and ammoniac work 
the feme effeft. The neutral calcareous (alts are decom- 
pofed by magnefia with effervefcence, by the aftion of 
double affinity. 
Carbonat of Glucinc. —The carbonic acid unites 
alfo with glucine, by direft combination ; for, if a pre¬ 
cipitate ol this earth by cauftic alkali be dried in the air, 
it will produce an effervefcence by folution in other acids. 
This carbonat is white, infipid, ii> foluble, and very light; 
however dry it may be, it is never inclined to fall to pow¬ 
der ; it is always clammy, lumpy, fat, and loft to the 
touch. It contains about one fourth of its weight of car¬ 
bonic acid, which it eafily lofes by heat. It appears 
fcarcely foluble in carbonic acid; yet it is decompofed 
by all the acids and alkalis. 
Carbonat of Alumine.- —Though the union of the 
carbonic acid with alumine has been hitherto fcarcely 
examined, yet it is certain that a portion of this acid 
combines with aluminous earth; becaule, 1. According 
to the remark of Bergman, when a folution of alum is 
precipitated by the alkaline carbonats, the filtered liquor 
depofits, at the end of a certain time, a finail quantity of 
earth, which was held in folution by the carbonic acid, 
and is feparated in proportion as that acid flies oft. 
z. This precipitation, when made in the cold, is not at- 
3 X tended 
