46*3 Earths. MINERALOGY. Earths.' 
As this earth was not noticed under Chemistry, we 
fhall here give the mode of procuring it, by feparating it 
from the different fubftances it is combined with,’ as em¬ 
ployed by M. Vauquelin in the year 1800. M. Vauquelin 
found the new earth united in the gadolinite with filex, 
oxydated iron, oxyd of manganefe, and lime. He fepa- 
rated it in two different ways ; of which it will be fuffi- 
cient for us to report one. One hundred parts of gadoli¬ 
nite being dilfolved in diluted nitrous acid, he then eva¬ 
porated ; applying a brifk heat at laft to effebt the com¬ 
plete decompofition of the nitrat of iron. On re-diffolu- 
tion in water, he obtained the peculiar earth diffolved, the 
filex and iron being detached. To feparate the latter of 
thefe from the former, the mixture was boiled in rather 
ftrong marine acid ; and the iron difunited by filtration. 
Ammonia was then added to the nitrous folution ; this 
left the lime, and feparated the new earth with the man¬ 
ganefe. Thefe latter were then diffolved a third time ; 
and a folution of hydro-fulphuret of potafli was gradually 
added, to feparate only the metallic parts. 
This earth differs from alumine and glucine in not 
being foluble in cauftic fixed alkali. It combines rapidly, 
and with heat, with fulphuric acid. The fait has an 
afiringent tade at fil'd:, and afterward a fweet flavour like 
a fait of lead ; which is diflinguifhable from that of fait of 
glucine. Yttria forms deliquefcent falts with nitrous and 
muriatic acids. Prufiiat of potafli, cryftallized, and re- 
diflolved in water, caufes a white grainy depolition in fo- 
lutions of this earth in acids ; which is not the cafe with 
folutions of glucine. 
Feldspatum, Felfpar.—Confiding of the greater part 
filex, fome alumine and potafh, and a very lmall quan¬ 
tity of lime and oxyd of iron ; hard, lightiih, fhining, la¬ 
mellar, breaking into fragments which prefent four faces ; 
mouldering into argil, parafitical; not effervefcing with 
nitric acid ; eafily melting, without ebullition, into a pel¬ 
lucid glafs. 
Felfpar fignifies rock-fpar, from the German word fels, 
a rock.' By fome it is called feldfpar or field-fpar, from 
the German word felcl, a field; crydals of it being often 
found difperfed over open traits of country. It is fufli- 
cientlv hard to fcratch glafs, and ftrike fire with fteel. 
Phofphorefcent, and eleitric (though not eafily) by fric¬ 
tion. It has a double refrabting power. Specific gravity 
Varies from 2 - 4 to 2-7. Primitive form, an irregular 
obliquely-angled parallelopiped. It occurs both cryftal¬ 
lized and amorphous. Sometimes uninterrupted maffes 
of felfpar are met with in the form of rocks or mountains; 
but molt commonly it is a condiment part of other rocks, 
particularly granite and porphyry. 
Felfpar is often remarkably difpofed to undergo a fpon- 
taneous difintegration ; which there is reafon to fuppofe, 
in fome indances at lead, depends on a previous alteration 
in the nature of proportions of its component principles. 
This alteration is thought by Werner to have been ef¬ 
fected by the lofs, either partial or entire, of the potafli 
naturally contained in it. And this opinion is fupported 
by the obfervation that felfpar is, often, lei's fufible in 
proportion to its date of difintegration ; and that thofe 
felfpars in which a confiderable proportion of potafli is pre- 
dent are very fufible. Some have thought that the difin¬ 
tegration depends on expofure to the atmofphere; but 
Mr. Jamefon obferved, at great depths in the mines of 
Freyberg, beds of gneifs completely iheltered from the 
action of the weather, in which the felfpar was entirely 
difintegrated. Perhaps this altered date of felfpar may 
be referred, as Dr. Davy has l'uggeded with refpebt to the 
fpontaneous alteration of mineral fubdances in general, 
to the agency of elebfricity. 
The felfpar of the white granite in many parts of Corn¬ 
wall occurs in a completely-difintegrated date. Here and 
there indeed the procefs has not advanced fufficiently far 
to dedroy the cohefion of the particles of the felfpar, 
though its fubdance is fo far foftened as eafily to yield to 
the knife, like iteatite j but upon the whole it is in a loofe 
earthy,date. In the neighbourhood of St. Audle there 
is a tin-mine, or rather quarry, in which the different 
dages of this procefs may be traced very fatisfabtorily. 
The altered date of the felfpar renders the granite of this 
quarry fo friable, that it is very eafily removed ; and hence 
the veins of tin-ore by which it is interfered are not fol¬ 
lowed in the ufual manner by means of fliafts and levels ; 
but the granite is quarried like free-done, and the ore is 
feparated by the procefs of damping and wafhing. In 
fome parts of the quarry the difintegrated felfpar occurs 
in didinbt patches, and may be eafily detached without 
any particles of the quartz, with which it is in general in¬ 
timately mixed ; but at all times it may be feparated by 
fimply damping the granite, and diffufing it through 
water. The particles of tin-ore and of quartz very foon 
fubfide, in conlequence of their greater bulk or l'pecific 
gravity 5 and the fupernatant water, together with the 
felfpar ful'pended in it, is drawn od' and conveyed to pits, 
&c. excavated for the purpofe. By degrees the felfpar 
fubfides ; and, the water being again drawn od', a white 
fediment is left of the confidence of pade; if this be dried, 
it contrabls into a foft earthy mafs of a very white colour, 
and in appearance and general charablers clofely refembles 
a very pure natural clay. This procefs is analogous to 
that by which whitening is prepared from chalk. The 
felfpar thus feparated is extenfively employed in the ma- 
nufabture of porcelain. There are fix fpecies. 
1. Feldl'patum cubicum, cubic felfpar, or petrilite : 
reddilh-brown, of a glafi'y ludre, and fomewhat fplintery 
frabture, breaking into cubic fragments which are not 
fpecular, falling fpontaneoufly into crudole fragments. 
Found, though rarely, in Saxony, of a common form, 
diaphanous or fomewhat opake ; fragments cubic or in¬ 
clining to that form, the faces of which are not polilhed : 
is very brittle, and at 160 0 of heat whitens and concretes 
without any farther fign of fufion. 
a. Felfpatum vulgare, or common felfpar : of a glaffy 
ludre and foliated texture, breaking into rhomboidal 
fragments with four fpecular faces. There are many va¬ 
rieties, differing chiefiy in the form of the crydals. Com¬ 
mon felfpar is found every-where in primitive mountains, 
forming a part of granite, porphyry, and gneifs, rocks ; 
compabl, folid, and incorporated with other fubdances j 
and generally moulders into a kind of porcelain-clay. 
Commonly dedi-colour, bluilh-grey, yellowifh-white,milk- 
white, or brownifh-yellow, rarely blue or olive-green, 
very rarely black 5 texture in draight filming foliations, 
crofs-frabture uneven ; when heated, the crydallized kind 
often decrepidates : it is lefs hard than quartz, but drikes 
fire with deel. Contains filex 62V83, alumine 17-02, po¬ 
tafli 16, lime 3, oxyd of iron 1. 
3. Felfpatum variabile, or Labrador felfpar: of a vi¬ 
vacious ludre, reflebling various colours in certain pofi- 
tions of light, of a foliated texture, breaking into rliom- 
boidal fragments with four fpecular faces. Found on the 
Labrador coad, the Ifl&nd St. Paul, and in various parts 
of America and Europe, in round mafles and detached, 
and often containing fliorl, mica, and pyrites. It is called 
opaline felfpar from a remarkable play of colours, vilible, 
as it were in its interior, when held in particular direc¬ 
tions : the mod conlpicuous colours are blue, green, pur¬ 
ple, and orange-red; the intenfity of thefe altering ac¬ 
cording to the direbtion in which the done is held. 
4. Felfpatum lunare, pure felfpar, or moondone : pellu¬ 
cid, white, of a high ludre, and draight lamellar texture, 
breaking into rhomboidal fragments. Found in Ceylon, 
and Swiflerland, Bohemia, and Saxony, in folid mafles 
and alio crydallized ; the crydals rhomboidal, of irregu¬ 
lar angular broad lix-fided columns terminating in pyra¬ 
mids and in rebtangular four-fided plates. Colour white, 
with fometimes a fliade of yellow, green, or red ; the fur- 
face often reflebling iridefcent colours; the fragments 
often appear driated. This fpecies is fometimes called 
Adularia, from Adula, an old name of one of the heights 
of St. Gothard j where it was dilcovered in the fiffures of 
rocks 
