480 Metals. MINERALOGY. Metals. 
and are now much ufed in chemical manipulations. This 
metal may now be purchafedin bars at the rate of 15s. an- 
oun'ce; whilft a few years ago, its price was between two 
and three times as great. The price of platinum, in 
grains, fluctuates between 3s. and 4s. an-ounce. 
Fulminating Platinum. —Mr. Edmond Davy, profeflor 
of chemiftry to the Cork Inftitution, has recently difco- 
vered a fulminating compound of platinum, which has 
fome curious properties. He is at prefent engaged in 
examining this fubftance, and will fhortly make known 
the refults of his inveftigation. This peculiar compound 
explodes at a moderate heat. This eft eft is accompanied 
by a Hath of light. The fubftance is completely decom- 
poled, and relolved into metallic platinum and gafeous 
produfts. When the fulminating platinum is put into 
liquid ammonia, it is partially decompoled, and a quan¬ 
tity of gas is evolved. In ammoniacai gas, this fubftance 
becomes ignited. When it is moiftened with alcohol a 
flight crackling noife is produced. The fubftance lcin- 
tillates, and burns with a red flame. Annals of PMlofophij, 
June 1 is 16. 
Aurum, Gold.—Of a reddifh-yellow colour, not tar- 
niflied by the air; foftifh and very tenacious, not fono- 
rous, exceedingly malleable and duftile; fpecific gravity, 
19-3 : burning in a red heat with a fea-green light, and 
melting at a white heat. Soluble only in nitro-muriatic 
acid and giving the folution a yellow' colour: when, 
■melted with borax, producing a ruby-coloured glafs. 
There are twelve fpecies. 
1. Aurum nativuiji. or native gold: not combined with 
•other minerals, very ponderous, duftile, vifible in its ma¬ 
trix. Found in the fand of a llream flowing from mount 
Croghan near Arklow, in the county of Wicklow, in 
Ireland ; in Cornwall and Scotland ; in the mines of Peru 
and Chili, New Spain, Java, Siberia, Tranfylvaniy, Spain, 
Hungary, France, and moft countries, of Europe ; gene¬ 
rally near the furface, or mixed with fand in the beds of 
rivers. It is rarely found quite pure, but alinoft always 
mixed with filver, copper, or other fubftances, giving 
more or lefs variation to its appearance or colour. Its 
form is generally common, or imbedded in its matrix in 
various lhapes ; fometimes it has decuflating grooves on 
its furface, or is cellular or piumofe, orrefembling teeth, 
branches, briftles, or hairs. In its cryftallized ftate, it is 
ufually in fmall aggregate fix-fided tables, with a right- 
angled four-fided prilin ending in a point, or terminated 
at each end by an imperfeft four-fided prilin ; in cubes, or 
■Ample three-lided or double four-fided pyramids. It has 
no perceptible tafte or fmell, and does not alter or lofe its 
luftre by any expofure to the air or water: its malleabi¬ 
lity is fuch, that one grain of gold may be beaten fo thin 
as to cover 565 fquare inches ; an ounce of gold upon 
filver wire is capable of being extended more than 1300 
miles; and fo great is its tenacity, that a gold wire 0-078 
inch in diameter is able to lupport a weight of ijlbs. 
avoirdupoile without breaking. The largeft lump of na¬ 
tive gold known was brought from Wicklow in the year 
1795; it weighed 22 ounces. See the article Ireland, 
vol. xi. p. 361. 
The author of Lord Anfon’s Voyage fays, that gold 
was firft difcovered in Brafil about the year 1710, in the 
mountains which lie adjacent to the city of Rio Janeiro. 
The moft common account of its dilcovery is, that the 
Indians at the back of the Portuguefe fettlements were 
obferved, by fome loldiers there ftationed, to make ule of 
this metal for fiftiing-hooks ; and by inquiry it was found 
to be feparateu from the fand and gravel depofited in the 
valleys by torrents from the neighbouring mountains. 
The author of the Voyage law a large fragment of thefe 
rocks, in which a conliderable lump of gold was entan¬ 
gled. He fays that the Haves, who were employed to col¬ 
lect the gold, were bound to iupply their mailers with 
fifty grains a-day, the value of which was equal to about 
nine Ihillings. What they coliefted above fifty grains 
they had the right of retaining for themlelves. 
Gold is commonly, recovered from the fand containing 
it by the procefs of walhing : by which, in confequence 
of the difference in the fpecific gravity of the two fub¬ 
ftances, a feparation is eafily effected.: the gold almoft im¬ 
mediately fubfiding, while the find is poured off together 
with the water, that for a time is capable of holding it in 
fulpenfion. The land of any river is worth working for 
the gold it contains, provided it will yield twenty-four 
grains in a hundred weight: but the fand of the African 
rivers often yields fixty-three grains in not more than 
five pounds weight; -which is in the proportion of more 
than fifty times as much. See Gold, vol. viii. 
In fome inftances the gold contained in the fand of 
rivers has been brought down from the mountains where 
thofe rivers originate; but this is not always the cafe; 
fo that thofe who have traced the current of a river to¬ 
wards its fource, with the hope of finding a more abun¬ 
dant fupply of gold in that quarter, have often been de¬ 
ceived. In fome rivers, indeed, the fand of thofe parts, 
which are farther removed from the fource, is richer in 
the gold than the fand of thofe parts which are nearer; 
which of itfelf is almoft futficient to prove, that the gold 
has not in thefe inftances been brought from the moun¬ 
tains. in the cafe of the Tefino, which flow's through 
one of the lakes in the north of Italy, the quantity of 
gold in that part of the river which is below the lake is 
in much greater abundance than in that part of the river 
which is above the lake; where indeed a very fmall quan¬ 
tity, if any, is found: but, luppoling the gold to have 
been detached from the mountains near the fource, it 
would hardly have been conveyed through the lake, 
where the current of the river muft neceflariiy have been 
much thickened, to be depofited in a more diftant part, 
where the current was much ftronger. But there are 
ftrong pofitive grounds for luppoling that the gold found 
in the fand of many rivers has been derived from the foil 
lurrounding that part of their courfe where it is met 
with; for it is found in very circumfcribed fituations; 
and the quantity is always greater after violent Ihowers 
have fallen upon the open country immediately adjoin¬ 
ing ; and the foil of this adjoining country, if walhed, 
itfelf affords gold. 
Moft of the gold of commerce comes from Africa and 
from South America; and, from various accounts, it ap¬ 
pears that alluvial diftrifts afford by far the greateft pro¬ 
portion of this ; and that the alluvion in which it is con¬ 
tained is principally a ferruginous fand. The only con- 
fiderable gold-mines in Europe are thofe of Hungary. 
The gold-mines of Bambouk, in Africa, are a national 
property, over which the kings, or tarims, have no other 
perlonal authority than that of watching over and pro- 
tefting them : the inhabitants work thole which are fitu- 
ated within their own territory. The country of Bam¬ 
bouk is, ftriftly fpeaking, “ auriferous earth,” fays Gol- 
berry; but the four principal mines are thofe of Natakon, 
Semayla, Nambia, and Kombadyrie. The working of the 
mines is carried on during the eight months of dry wea¬ 
ther, and ceafes when the rainy feafon commences. As 
all the gold is obtained by ablution, thofe blacks who 
belt underftand the working it obtain the greateft quan¬ 
tity of gold. They obtain it by digging pits about fix 
feet in diameter, and varying in depth from thirty to forty 
feet; the earth is brought up by baficets, taken to a rivu¬ 
let, and undergoes a thorough ablution : when they have 
dug about four feet deep, they meet with a flat argilla¬ 
ceous earth, intermingled with fmall grains of iron ore, 
of loadftone, and emery, all of which are covered with 
little particles and fpangles of gold. Ail the rivulets of 
the valley of Natakon convey gold with their water; the 
lands and mud which form the bed of them are alfo full 
of the lame metal; the foil compofmg the bed of the 
Colez-Rio-d’Oro produces a conliderable quantity of 
gold, and the whole plain of Natakon. From all thefe 
circumftances Mr. Golberry is induced to believe, that 
the mountains lurrounding Natakon contain in their 
1 beds 
