Salts. 
474 
verts nitric acid into nitro-muriatic acid, and is foluble in 
alcohol ; its folution becomes lafitefcent by dropping vi¬ 
triolic acid into it. 
4. Amarum nitrofum : deliquefcing in the atmofphere, 
emitting red vapours when hot concentrated vitriolic acid 
is poured on it, its watery folution not made turbid by 
the vitriolic acid. Found mixed with foil and on old 
walls, and fometimes efflorefces with the Nitrum humo- 
fum ; in the fire it fwells with crackling noife, but does 
not detonate when thrown on hot coals ; it is foluble in 
alcohol; after evaporation from its watery folution, it 
cryftallizes into four-fided oblique truncate prifms. 
5. Amarum murale : deliquefcing in the atmofphere, 
emitting red vapours when concentrated cold fulphuric 
acid is poured on it, its watery folution made turbid by 
the vitriolic acid. Found generally with the Nitrum hu- 
mofum, and is likewife foluble in alcohol. 
6. Amarum animale: not deliquefcing in the atmo¬ 
fphere, not eafily melting in the fire, but emitting red 
vapours by the force of fire only. Found with the Ni¬ 
trum humofum ; and is compofed of phofphoric acid and 
nitre. 
Alumen. See Alum, vol. i.—Of a fweetifh and very 
aftringent tafle; its watery folution made turbid by foda, 
but not by prufliat of lime ; tumefying and lofing its tranf- 
parency when expofed to heat, and becoming a fpongy 
mafs after lofing its water of cryftallization. There are 
ten fpecies. 
1. Alumen phofphoreum, or phofphat of alumine : 
flying to pieces when expofed to a violent heat; confin¬ 
ing of phofphoric acid and alumine. Found in Valentia ; 
a taftelefs powder, not foluble in water; yields a gritty 
powder when dilfolved in phofphoric acid, and a gummy 
folution which is converted by heat into a tranl'parent 
glafs. It does not feem to belong to this genus. 
2. Alumen muriaticum, or muriat of alumine : ex¬ 
pofed to a violent heat, or moiltened with ftrong ful¬ 
phuric acid, emitting acrid grey vapours of a difagreeable 
odour. Found inTufcany, efflorefcing on the furface of 
aluminous foils like powder, in dry feafons ; alfo in the 
mouths of caves and Allures of rocks with the appearance 
of wool or a white cruft 5 its tafte is rather bitter than 
aftringent. 
3. Alumen nativum, or native alum t pure, dry, not 
emitting vapours when fulphuric acid is poured on it. 
There are five varieties. Found in Egypt, the illands of 
the Archipelago, Malta, Sicily, in the craters of volcanoes, 
the Alps of Swifferland, and the lakes of Tufcany, and 
in various parts of Europe, in aluminous fchift. It is dif- 
lblved in thirty-four times its weight of cold water, and 
eafily forms cryftals which efflorefce a little in the air. 
Expofed to a ftrong heat, it fublimes, fwells, foams, lofes 
its tranfparency, and at laft lofes 44 per cent, of its weight. 
Its folution always turns vegetable blues red. Specific 
gravity, ryi. Contains fulphat of alumine 49, fulphat of 
potalh 7, water 44. Vauquelin. 
4. Alumen folutum, or dilfolved alum: in. a ftate of 
folution ; not emitting vapours when fulphuric acid is 
poured on it. Found in many parts of Siberia and Italy. 
5. Alumen halotrichum, capillary alum, or hair-fait: 
dry, fibrous, of a filky luftre, not deliquefcing in the at¬ 
mofphere, nor emitting vapours when fulphuric acid is 
poured on it. Found in the quickfilver-mines of Idria, 
the lakes of Tufcany, in Italy, Sicily, Hungary, and the 
coal-mines near Whitehaven. The cryftals are tender, ca¬ 
pillary, filvery-white, filaments, generally parallel and in¬ 
curved, rarely difpol'ed in-a ftellate manner, which fre¬ 
quently adhere together, and form compact pieces; thefe, 
after expofure to the air, lole their tranfparency, and be¬ 
come more or lefs of a yellowilh or greenifh hue. Pliny 
1'eems to defcribe this fpecies in the following palfage : 
“ Concreti aluminis unum genus fchifton appellant Grseci, 
in capillamenta qutedam canelcentia dehilcens. Unde 
quidam trichitin potius appellavere.” Nat. Hift. vol. vi. 
This may by the eye be eafily miftaken for a variety of 
Salts. 
fulphat of iron, which clofely refembles it in colour as 
well as form ; but the fulphat of iron has a much more 
aftringent tafte, and produces a black colour when added 
to the infufion of oak-bark, or gall-nut. It may alfo by 
the eye be miftaken for fibrous gypfum, or for amianthus $ 
but may at once be diftinguilhed from thefe by its tafte 
and folubility. 
6. Alumen butyraceum, ftone or mountain butter: 
of a yellow colour in its native foil ; foft and fat to the 
touch ; hardening in the air, and becoming white ; of a 
waxy luftre, lamellar. Found in Siberia and Upper Lu- 
face, oozing from the furface of aluminous fchift: it is a 
little femitranfparent, foft and friable, but becomes brittle 
by expofure to the air, and contains decompofed fulphat 
of iron as well as alum. 
7. Alumen terreum, or earthy alum : combined with 
foft alumine, not emitting vapours when fulphuric acid 
is poured on it. Found in the vicinity of volcanic moun¬ 
tains, and in various parts of the continent. Colour 
rarely white ; brown or black when the earth with which 
it is combined is mixed with bitumen, in which cafe it 
flames in the fire and gives out a difagreeable odour like 
burnt peat; fometimes it fpontaneoufly hardens in the 
atmofphere, and exhibits its alum in a ftate of effiorefcence. 
8. Alumen Romanum, roche or rock or Roman alum : 
adhering to the tongue, foiling the fingers, not emitting 
vapours when fulphuric acid is poured on it, combined 
with indurated purer alumine. According to Walleyius, 
who refers to Leibnitz, this term is derived from Roeca in 
Syria ; from whence the method of artificially preparing 
alum was introduced into Europe about 350 years fince. 
According to Kircher, the diftrift of Tolfa, fituated about 
ten miles from the Tyrrhene Sea, is full of rocks, which, 
when roafted for twelve or fourteen hours, afford alum by 
evaporation ; and hence the term rock-alum. The fpecies 
is found in Britain near Whitby, in SwilTerland, and Tuf¬ 
cany, as well as at La Tolfa near Rome, forming ftrata or 
vaft mafles, with frequently fmall lumps of pyrites or ful¬ 
phat of iron interfperled, and having fometimes veins of 
white quartz running through it. It does not effervefce 
with acids; is of a white, grey, perlaceous, or rofy, colour; 
and produces alum upon combuftion, or after long expo¬ 
fure to the air. Kircher, in defcribing the artificial pre¬ 
parations of alum, fays, that the fragments of the alumi¬ 
nous rock are firft roafted ; and then heaped up in a co¬ 
nical ftiape, and expofed to the fun ; afterwards, for the 
fpace of a month, they are affufed four times a-day with 
cold water, which difintegrates and reduces them to a kind 
of argillaceous pafte. This is thrown into cauldrons and 
boiled ; and the liquor is afterwards withdrawn, and made 
to cryftallize by the procefs known to the manufacturer. 
As iron is always prelent in greater or lefs proportion 
in aluminous Ihale, and as the fulphuric acid combines 
with that metal very readily, all the natural forms of alum 
contain fome portion of iron ; the combination of the 
acid with the iron produces the metallic fait commonly 
called green vitriol; and from the prefence of this fait 
arifes the occafional light-green colour of natural alum. 
It happens that the fpecies properly called Roman alum is 
derived from an aluminous earth, which fcarcely contains 
any iron, and owes its purity to the abfence of that me¬ 
tal. By degrees the term has been extended to any pure 
form of alum. Wallerius lays that Roman alum is ob¬ 
tained by lixiviating a white aluminous earth met with at 
Tolfa, in the territory of Civita Vecchia, in Italy. 
9. Alumen commune, or common alum : not emitting 
vapours when fulphuric acid is poured upon it, mixed 
with bituminous fchift. There are three varieties : a. Very 
foft to the touch, meagre, breaking into trapezoid frag¬ 
ments. ( 2 . Hardilh, ihining internally, undulately flaty, 
a little greafy to the touch, breaking into indeterminate 
fragments, y. Slightly effervelcing with acids. They all 
occur in the neighbourhood of coal-mines in many parts 
of England, Scotland, and Wales; in Siberia, Norway, 
Sweden, many parts of Germany, See. forming vaft moun- 
3 tains, 
MINERALOGY. 
