MET 
adit, the water is extracted by pumps, which 
are moved either by a stream, or by a pond, 
or by vapour of water introduced, and con- 
densed in cylinders. 1 hese last machines, 
called steam-engines, are at present in rich 
more common than formerly. (See Steam 
Engine.) It is an object of great difficulty 
sometimes to defend the works against enor- 
mous masses of water which rush forth when, 
in digging, a vast subterranean reservoir is 
opened. I hese cases happily are very rai e ; 
but they are in some measure provided 
against by a kind of moveable strong door, 
or barricado, which the workmen place at the 
moment when they iind by the particular 
sound of the rock, that the waters are com- 
in<r in upon them, which barricado, by sepa- 
rating them from the liquid, gives them time 
to save themselves. 
Idle destructive clastic fluids, which so 
frequently are disengaged in the cavities ot 
mines, and particularly the carbonic acid gas, 
and different species of mixed hydrogen 
gases, more or less pernicious, are also 
among the most formidable enemies of 
miners. Galleries, tires, ventilators, inflam- 
mations by means of torches held at a great 
distance in those parts of the mines which 
are mephitized by the inflammable gases, 
and particularly * the various methods of 
causing fresh air to enter, are the only reme- 
dies which can be opposed to these subterra- 
neous evils. 
Few metals are found in a pure state; gold, 
silver, and sometimes copper, are excep- 
tions. The other metals are generally found 
in the state of ores, in which they are mixed 
and blended with other substances, so as not 
to have the ductil ty or other qualities of me- 
tals: often, indeed, they have not the metallic 
lustre. Sometimes the ore is only a pure 
oxide, which requires no more than that the 
oxygen should be drawn from it by heating 
it with an inflammable substance. Such are 
all the ferruginous ochres, which are oxides of 
iron. 
The ores of metals are generally found in 
the veins of mountains or rocky strata, and 
are always separated from the rocks on each 
side by "a quantity of spar, quartz, or some- 
times softer clay or earth. T he spar is ge- 
nerally of the gypseous kind. These form 
the matrix of the" ore ; in English, called the 
rider. In different veins it is of different 
thicknesses; the quantity of the ore increas- 
ing as that of the matter which surrounds it 
diminishes. Often the ore is in branching 
masses wandering irregularly through it, and 
is often rudely mixed with the matrix in veins 
of different thicknesses. These are called 
brangled ores. 
The veins or fissures of the rocky strata 
are sometimes only a few inches wide, -and 
sometimes many yards. In rich mines there 
are immense masses of ore many feet broad. 
Where the veins happen not to be filled up, 
we find the ores crystallized round the cavity. 
The ore, when separated from the matrix, 
generally contains some other matter; as sul- 
phur, arsenic, or both: and sometimes an 
earthy substance, the whole being united into 
a compound which at first appears homoge- 
neous. 
The first operation on metals is to separate 
the ore from the matrix. W hen the ore is 
found in large masses, most oi it may be dug 
M E T 
up free from the matrix, and those pieces to 
which it adheres may be freed by a hammer. 
But as the ore is often intimately mixed with 
the matrix, it is necessary to try otliei me- 
thods. 
Sometimes the whole is reduced to pow- 
der and thrown into water; the water is then 
put in motion, and the earthy matter floats 
above the ore, on account of their ditferc nt 
specific gravity. It is still better to place t lie 
powder on a board, over w hich water may be 
made to run ; being stirred while the watei 
runs over it, the earthy parts float and aic 
carried off, whilst the metallic parts remain 
behind. This operation is called washing 
the ore. 
M E T 
lG5 
When. the matrix is not divisible by wa- 
ter, a stamping-mill is employed, w hich con- 
sists of an axis turned by a w ater-wheel. On 
the axis there are a number of cogs, which, 
lift up a perpendicular p ilar oi wood plated 
at bottom with iron; tins falling down bruises 
the matrix to powder. It often happens that 
the matrix is harder than the ore, and in this 
case the ore will be reduced to a much finer 
powder than it. Here the ore is a much 
heavier substance; yet its surface may be so 
much increased, that it may be carried ofl by 
the, water before the matrix. This may be 
obviated by subjecting the mass to a brisk 
heat, and throwing water upon it when red- 
hot, w hich renders the matrix more easy to 
be powdered. There are many ores of tjiis 
kind which undergo a fusion by heat; hence 
the small particles of the matrix, which are 
angular and irregular, contract themselves 
into little spheres, by which means losing 
part of their surface, they become specifi- 
cally heavier, and fall more readily to the 
bottom -of the water: the ore too generally 
loses part of the sulphur it. contains, and on 
this account becomes specifically heavier: 
the stone becomes softer, and is sometimes 
disposed to fall into powder merely by the 
application of water, especially if composed 
of gypseous spar. Quartz is not indeed so 
easily heated in this way, but it becomes 
softer by these means ; cracks and flaws are 
produced in it, and of consequence it is more 
easily divided. 
After all there will in washing be some loss 
of the metal : hence it is found more expedi- 
ent to bring the whole mass into fusion, as is 
practised in Germany. The fusion is per- 
formed in some of the ordinary furnaces, 
and commonly with the addition of particu- 
lar stones, or the scoriae ot former fusions, 
which greatly promote the fusion of the new 
matter. Thus the metallic matter settles to 
the bottom still in the state of an ore, whence 
the process is called crude separation. \v lien 
the ore is thus freed from its matrix, the 
next operations are, to separate the sulphur, 
arsenic, &c. which the metals may contain; 
and this must be done by a mild heat, be- 
cause of their strong adhesion to the metals, 
which the metallurgists call their rapacity. 
If exposed to a violent heat, tlie arsenic will 
hardly separate when forced 41^' intensely, 
'sometimes carrying oil part of the metal 
along with it. "This treating the ore in a 
gentle heat, is called roasting- it. 1 he work- 
men commonly build the ore into heaps with 
fuel, so that the whole may become red-hot, 
and the air have free passage through it. 
Some ores,, as those oi copper, require many 
repetitions of the process, the sulphur and 
arsenic adhering so closely. 
In consequence ot this operation, the me- 
tal remains more or less in the form oi an 
oxide.; the operation of reduction becomes 
therefore necessary It is often necessary to- 
add earths to the ores, as they often contain 
earths not so easily fusible, but which by mix- 
ture with others "become so. i he fires being 
kept up for some time the ore melts ; and as 
it passes through the fuel, which is generally, 
charcoal of wood, the oxygen, which toe ox- 
ide contained, is drawn oil by the cliaicoal 
forming fixed air, and the metal falls into 
the bason constructed lor that purpose in tne 
furnace. 
Thus the metal is obtained free from earthy 
and stony matter, and generally Irom arsenic 
and sulphur, but it contains other metals i 
thus copper has always with it more or less of 
iron, silver a quantity of copper, &c. 
Some, as lead ores when rich, are heated* 
by immediate fusion, without previous roast- 
ing; for though iji would give a greater 
quantity of the metal, it would be too ex- 
pensive, There are many ores in whic h tire 
metal exists in the state ot an oxide. Here 
previous roasting would be ot no advantage.. 
The ores of silver and gold require certain 
additions to them to attract the sulphur and 
arsenic, and to melt the other matter which, 
is mixed with them, so as to dispose them lo- 
separate. See Assaying, &c. 
METAPHOR, in rhetoric, a trope, byr 
which we put a strange word for a proper 
word. See Rhetoric. 
M ETAPHYSICS. 1 1 is remarkable that 
scarcely any two writers are agreed with re- 
spect to the meaning ot the word metaphy- 
sics. One lexicographer tells us, somewhat 
obscurely, that it is the doctrine ot the ge- 
neral affections of substances existing. * 
Another that “ it is a science which treats of 
being as such in the abstract.” While a 
third most gravely assures us, it means “ that 
part of philosophy which considers the nature 
and properties of thinking beings.” This* 
last definition must evidently be unfounded, 
since “ the nature and properties of thinking, 
beings” are either a branch of natural philo- 
sophy or of logic. See Logic . 
The word seems to have originated with: 
Aristotle, who has termed a treatise which is 
placed after his Physics, /**?<* la tpvont*. So 
that it may mean either something “ beyond 
Physics,” or merely “ an appendix to Ins 
physics” or natural history. This treatise 
chiefly relates to -the intellectual world. 
The mode in which authors have treated 
of metaphysics is as various as their defini- 
tions of the term. One author, under the 
form of a treatise of metaphysics, presents us 
with a discussion on abstract words, their 
meaning and application; another with an 
enquiry into the faculties and operations of 
the human mind; a third with a volume of 
theologv, a dissertation on the being and at- 
tributes of God, And the nature of spiritual 
and celestial intelligences ; and a fourth with 
a treatise of ethics or moral philosophy. 
A science so subtle,, so indefinite, so eva- 
sive, which, under so- many 1 lotous toiins^ 
eludes our grasp, is scarcely a proper subject, 
for a practical work like this. vV hat aie- 
metaphysics? Every thing! Nothing ! Yet. 
there are some " subjects width the teamed! 
