Metals. 
478 Metals. MINER 
but, if both be rubbed on a piece of -white porcelain, it 
will be feen that the ftreak made by the plumbago is ot 
the fame colour with the lubltance by which it was made ; 
while that made by the molybdenum has a diftinftly green 
fiiade. It may be diltinguillied from black crayon by the 
difference of the ftreaks made by the two fubftances on 
paper; the colour of that made by black crayon is a deep 
dull black ; that of plumbago has fomewhat of a metallic 
luftre. 
This very-ufeful mineral has more recently undergone 
an elaborate analyfis by M. Schrader, a German chemift. 
Beiides the places we have quoted above, he informs us 
that it exifts alio in Germany and Spain, and in a fmall 
quantity in France. The celebrated Scheele firft Ihowed 
that it confifted principally of iron and charcoal; but it 
was referved for M. Schrader to point out the prefence of 
other l'ubftances alfo generally contained in it. Thefe 
are lilex, alumine, and the oxydes of titanium and cop¬ 
per. In Spanilh graphite fome flight appearances of chro¬ 
mium were difcoverable; and there is alfo a very confi¬ 
dence proportion of fulphur united with the iron and 
copper, under the form of iron and copper pyrites. We 
have good reafon to believe, moreover, from Mr. Schra¬ 
der’s experiments, that the charcoal is not chemically 
combined with the iron or the other conftituents, as com¬ 
monly fuppofed, and hope that they may lead to the ac- 
complilhment of a method of rendering the l'ofter black 
lead of a harder texture, a delideratum which has been 
long looked forward to by the black-lead pencil manu¬ 
factures. 
Graphites carbo : of a conchoidal ftruCture, break¬ 
ing into indeterminate fragments. Found in Hungary 
near Schemnitz, imbedded in thin ftrata or veins of black 
indurated alumine, near Tfcherweniza running through 
a matrix of opal like a vein ; alfo in France and Norway. 
When expofed to a white heat, lofes all its carbon, which 
is 90 per cent, leaving a refiduum of nearly equal parts of 
alumine and oxyd of iron. 
3. Graphites fuligo: deep black internally, making a 
very black mark. Found near Duttweiler in Naflau, al¬ 
ternating in thin ftrata with coal. 
CLASS IV. METALS. 
Metallic fubftances occur in a variety of forms ; the 
inoft remarkable of which are the following: native me¬ 
tals ; metallic oxyds; metallic fulphurets; and metallic 
l'alts. 
In what is called their native ftate, they poflefs thofe 
properties on account of which they are principally valu¬ 
able ; as malleability, hardnefs, and fplendour. It fre¬ 
quently happens that two or more are intimately blended 
in the fame mafs : and wdien this is the cafe, the combi¬ 
nation is called a native metallic alloy. 
Metallic oxyds are a combination of the pure metallic 
fubftance with oxygen, or that part of atmofpherical air 
Which fupports the procefs of combuftion and of refpira- 
tion. A metallic oxyd was formerly called a metallic calx. 
Metallic o^yds are in general of an earthy texture; or, 
if they ftoiiefs the fplendour and appearance of metals, 
they are klnioll always dellitute of their tenacity ; and 
are reduced to powder upon the application of a mode¬ 
rate degree of force, as the blow of a hammer for inftance. 
Their l'pecific gravity is greater than that of earthy fub¬ 
ftances : but lei's than that of the metals from whence they 
are derived. 
Metallic fulphurets are chemical combinations of a me¬ 
tal, but moYe commonly of a metallicoxyd, with fulphur. 
They frequently have a remarkable degree of fplendour, 
and many of the external charafters of a metal; but they 
are readily reduced to powder. In many inftances arfenic 
is contained as w’ell as fulphur; and the prefence of ei¬ 
ther fubftance is eafily afcertained by means of the blow¬ 
pipe : the fulphur manifefting itfelf by its pungent odour 
and the well-known colour of its flame ; the arfenic by a 
white fimoke, and a fmell refembling garlic. 
A L O G Y. 
A metallic fait is a chemical combination of a metallic 
oxyd with an acid. 
The term metallic ore is by fome applied to thofe na¬ 
tural forms only which require fome chemical procefs in 
order to bring them back to their fuppofed original ftate; 
and by this procefs they are confequently laid to be re¬ 
duced-, by others it is indilcriminately applied to all the 
natural forms; and includes therefore native metallic 
l'ubftances. In early publications the word is fpelt ewer. 
Platinum. —Of a filvery colour not tarnillied by the 
air, very hard and tenacious, lonorous, exceedingly mal¬ 
leable and duftile ; l'pecific gravity, 22 : not fulible in any 
degree of heat, but detonating with nitre ; foluble only 
by boiling it in fixteen times its weight of nitro-muriatic 
acid, and giving the folution firft a yellow and then a red- 
brown colour; its oxyd precipitated from this folution, 
by the addition of muriat of ammonia, in the form of an 
orange powder. 
Platinum granulatum, the only fpecies. This new 
metal is often called aurum album, or white gold, from its 
great l'pecific gravity, and white colour; but its fyftematic 
name is derived from its refemblance, in its native ftate, 
to fmall grains of lilver ; the word platinum being a dimi¬ 
nutive of plata, which in Spanilh fignifies filver. 
Platinum, not being liable to oxydation by the agencies 
of heat, air, or moifture, is ufually clafled with gold and 
filver, which poflefs the fame property; and thefe three 
metals were formerly, and are ftill fometimes, called the 
noble metals, in oppofition to the baj'e metals, or thofe 
which are oxydable by air and moifture. 
The exiftence of platinum was fcarcely known in Eu¬ 
rope before the year 1740. In its native ftate it occurs in 
fmall apparently-flattened grains of a dull filvery luftre, 
and in general about the fize of a fmall pin’s head ; mixed 
with minute particles of magnetic iron, gold, and quartz. 
It is, beiides, alloyed wuth feveral metallic fubftances ; 
fome of which poifefs charadters that diftinguilh theim 
from all other metallic fubftances hitherto known. 
Vauquelin has lately difcovered the exiftence of pla¬ 
tinum in a filver-ore from Spain ; into the compofition of 
which it enters in the proportion of one tenth. With the 
exception of this Angle inftance, platinum has only yet 
been found in the gold-mines of America; near Choco 
in Peru, and at Santa-Fe near Carthagena. The particu.- 
lar places of Choco where it is found are Novita and 
Citara. The miners, difeovering at an early period that 
it was a metal, had begun to employ it in adulterating 
their gold ; and the court of Spain, it is laid, dreading 
the confequences, took meafures not only to prevent its 
exportation, but partly to conceal the knowledge of it 
from the world, for it is reported in the Annales de 
Chimie for 1792, that the gold, wdien brought from Choco 
to be coined at Santa Fe, undergoes a new examination, 
the plantinum that remains is carefully leparated, and, 
being given to officers appointed by the king, they, as 
foon as a certain quantity is collected, carry it away, and, 
before witneffes, throw it into the river Bogota, at two 
leagues diftance from Santa Fe. 
The colour of platinum, when properly refined, is 
fomething between that of iron and filver. It has no 
fmell; and is the heavieft body yet known in nature, its 
fpecific gravity being to that of water as 22 to 1, whereas 
gold is only as 193 to 1. It may likewife be faid to be 
the moll durable of all metals; it is harder than iron ; it 
undergoes no alteration in the air, and fire alone does not 
appear to poflefs the power of changing it; for which rea¬ 
fon it forms the very beft material for crucibles that has 
ever been tried. It refills the aflion of acids, alkalies, and 
fulphurs : it may be rolled wdth plates as fine as the gold- 
leaf ufed in gilding. It is likewife extremely duftile ; 
and Dr. Withering tells us, that a v'ire of platinum is 
ftronger than one of gold or filver of the fame thicknefs 5 
a wire of o - 078 of an inch in diameter fupported 27|lbs. 
avoirdupois. It is preferable to gold by the property it 
has of loldering or welding without mixture; and it 
unites. 
