C H £ M I 
dunged in confequence of its union with alkalis; they 
imagine that it refembles aluminous earth, and is capa¬ 
ble of uniting with acids, and forming aluminous falts: 
this was the opinion of Pott and Bauniej but Schecle 
has fliown, that this foluble portion of the earth preci¬ 
pitated from the liquor of flints, is obtained from the 
veffel of alumine in which the filiceous earth and alkali 
are fufed. The fame experiments may be made with alu- 
mine and potafli. 
The exigence of potafn in the mineral kingdom has 
of late been proved by accurate experiments. Klaproth, 
in the analyiis of the fubftance which he terms leucit, 
found that it formed about i-5th of that ftone. In the 
lepidolite he obtained only 4-iooths. Vauquelin has^ 
fince fhown that potafli is contained in a large proportion 
in the white Vefuvian garnet, and in the lava which 
ferves as its matrix. He found alfo a fmall proportion of 
this fubftance in zeolite from the Ferro Iflands; and Dr. 
Kennedy of Edinburgh has lately difcovered potafn in 
an analyiis of the pumice-ftone. 
Potafh has the property of feparating filex and alumine 
from lime, when the fubftances happen to be found to¬ 
gether. The true- nature of potafli, however, ftill re¬ 
mains unknown. Only a few imp erf eft experiments have 
as yet been made to decompoie it; and thefe in vain. 
Analogy, however, would incline us to believe that it is 
a compound body. Vegetable phyfiologifts are not 
agreed whether this alkali be derived-from the foil in 
which plants grow, whether it exifts uncombined with 
anj' acid in plants, whether it be a produft of vegetation, 
or whether it be not rather generated during the procefs 
of combuftion. Thefe are queries highly neceflary to 
fclve, and well deferring the attention of chemifts. 
Pure Soda.— This alkali poffefles the ferae general 
charafters as potafh ; and it is impoflible to diftinguifh 
them when in a ftate of purity. It appears, however, 
that cauftic l'oda attrafts the moifture of the air lei's pow¬ 
erfully, and is not fo quickly diffolved in water. It is 
only by its efiefts in chemical combinations, and efpeci- 
ally with 3cids, that potafh andfodacan be known apart. 
Soda is produced from feveral fea plants by combuftion. 
Solid cauftic foda, or cauterifing-ftone, is always found 
mingled with other faline and terreftrial fubftances, from 
which it muft be feparated ; fordoing which, the procel's 
is the fame as already direfted for potafli. When pure, 
its tafte is as ftrong as potafli; it turns f'yrup of violets 
green. It melts on the fire, and volatilizes in a violent 
heat. It attrafts humidity from the air; is foluble in 
water with caloric; combines well with fulpliur whence 
refuits a fulphure. Hydro-fulphure of foda is produc¬ 
ed in the fame manner as that of potafli ; it combines in 
the dry way with filex, and forms a kind of glafs. Glals- 
malters have obierved that this fait produces a more fu- 
fible and folid glafs than potafh; for which reafon they 
prefer it in the manufaftute of that commodity : fo that 
what we have faid relative to this art under the article 
potafli, may be equally applied to foda. Like the potafn, 
it combines with acids, and with a great number of bo¬ 
dies hereafter to be treated of. From thefe obfervations 
it is evident, that the difference between the two fixed 
alkalis, in a ftate of purity, is not very confiderable, an d 
that their refpeftive properties can only be known with 
certainty from th eir combinations. When united with 
the fame acid, they produce neutral falts exceedingly 
different in all their properties; a circumftance which 
feems the more lingular, as it is abfolutely impoflible to 
point out any difference between them in their pure and 
cauftic ftate. Bergman adds, as a diliinguifhing proper¬ 
ty of thefe two falts, that their affinity with acids is not 
the fame, that of the potafli being the ftronger; fo that 
it is capable of decompofing falts, whole bale is foda.. 
The intimate nature or compoiition of the foda, is not 
more known than, that of the potafh. This fubftance, 
however, in combination with carbonic acid, exifts in 
confiderable quantity in various parts of the earth. In 
VOL. IV. No. 131. 
S T R Y. 225 
this ftate it has been termed native mineral alkali. In 
l'ome fituations it is depofited in beds under the furface 
of the earth, as in China; in others, at the bottom of 
lakes, as in Hungary and Egypt. Efflorefcent cryftals of 
mineral alkali, are often found on the infide of the wails 
of houfes, in fulpterranean caverns, and on foils occa- 
fionally overflowed by waters holding this fait in lolution. 
The exiftence of this fubftance in mineral fprings has 
been known for feveral years. Dr. Black found it un- 
combined, as he conceived, in water brought to him 
from the hot fprings in Iceland; but Klaproth, in an 
analyfis which he has lately publifhed, affects that this mi¬ 
neral alkali is not free, but exifts in thefe waters in com¬ 
bination with carbonic acid. The fame ch^milt found 
carbonat of foda in ccnfiderable quantity in tjie,mineral’ 
waters of Carlfbad. The fea and fait mines are, however, 
the grand ref’ervoir in which this aikaii, united to the 
muriatic acid, is contained. The variety of plants em¬ 
ployed for the purpofe of obtaining; foda, is very con¬ 
fiderable. In Spam this fubftance is procured from the 
different lpecies of the falfo la falicortiia and bat is mariti- 
ma. The xojlera r/iaritima is burnt in l'ome places on the- 
borders of the Baltic, as is the anabafis aphjlla on thofe 
of the Cafpian. In this country we burn the various 
fpecies of fufi. Along with the falicortiia they burn alfo 
the chenopodium maritimum in the fouth of P'rance. It is 
deferving of notice, that fome plants, which in their na¬ 
tive foil yield only vegetable alkali, afford alfo the mine¬ 
ral, when they happen to grow in the neigbourhood of 
the fea, or in lands occafionally wafhed with fea-water. 
The native mineral alkali found in Egypt and Barbary, 
is faid to be about fifty per cent, ftronger than common 
foda. Mr. Kirwan confiders the cryftals of l'oda as a very 
fit ftandard by which to try the ftrength of the other 
kinds of mineral alkali, as the quantity of alkali in thefe 
cryftals continues at all times very nearly the lame. See 
Irijb Tranf. for 1790. A ready way to diftinguifh the 
mineral from the vegetable alkali, is to drop a l'mall 
quantity of the acid of fugar into a lolution of thefe fub¬ 
ftances in water. With the vegetable this acid will form 
a very foluble fait; with the mineralone difficultly foluble. 
The gradual decompofition of the muriat of foda by 
lime, is one of thofe anomalous fails in chemiftry which 
it is difficult' to explain. It forms an apparent deviation 
from the laws of chemical affinity, for the muriat of lime 
is decompcfed by the mineral alkali, either in its mild 
or cauftic State. This experiment is the more valuable, 
as it enables us to account for the prefence of mineral 
alkali in many of thofe fituations in which it is now* 
known to exiff. 
In this country, various methods of obtaining mineral- 
alkali are followed by different chemifts. Some of thefe 
methods are carefully concealed, while others of them 
are but very imperfeftly explained in the letters patent 
which thofe who praftife them have obtained. In pre¬ 
paring this mineral alkali, on a large fcale, vre muft often 
be direfted in the choice of our means by local circum- 
ftances, by the nature and price of the materials that are 
within our reach, and by the value and demand, not only 
for the alkali itfelf, but alfo for the other ufeful fub* 
fiances that may be procured in this interefting procefs; 
for in this, as well as in every other mercantile concern, 
calculations with regard to the expence, and the profits, 
muft neceffarily form the bafis of every rational enterprife. 
Ammoniac. —The name of ammoniac is given to the 
fait known by the term volatile alkali. It is diftinguifh - 
ed from the two foregoing by its ftrong and fuffocating 
lhu 11 , and its lingular volatility. Like the fixed alkalis, 
this lalt was not known in its ftate of purity before the 
ingenious-experiments of Black and Prieftiey: that which 
was confidered as luch, is a fpecies of imperfect neutral 
, fait, in a folid and cryftaliized form, pofleffingfome of 
the properties of volatile alkali, but really compofed of 
two faline fubftances, viz. carbonic acid, and ammoniac: 
the charafteror property of effervefcing with acids, which 
3 M was 
