1. _Native silver_, possesses the greater part of the above properties;
yet, on account of its being more or less alloyed with other metals, it
differs a little in malleability, lustre, density, &c. It sometimes
occurs crystallized in wedge-form octahedrons, in cubes, and
cubo-octahedrons. At other times it is found in dendritic shapes, or
arborescences, resulting from minute crystals implanted upon each other.
But more usually it presents itself in small grains without determinable
form, or in amorphous masses of various magnitude.
The _gangues_ (mineral matrices) of native silver are so numerous, that
it may be said to occur in all kinds of rocks. At one time it appears as
if filtered into their fissures, at another as having vegetated on their
surface, and at a third, as if impasted in their substance. Such
varieties are met with principally in the mines of Peru.
The native metal is found in almost all the silver mines now worked; but
especially in that of Kongsberg in Norway, in carbonate and fluate of
lime, &c.; at Schlangenberg in Siberia, in a sulphate of barytes; at
Allémont, in a ferruginous clay, &c. In the article MINES, I have
mentioned several large masses of native silver that have been
discovered in various localities.
The metals most usually associated with silver in the native alloy, are
gold, copper, arsenic, and iron. At Andreasberg and Guadalcanal it is
alloyed with about 5 per cent. of arsenic. The auriferous native silver
is the rarest; it has a brass-yellow colour.
2. _Antimonial silver._--This rare ore is yellowish-blue; destitute of
malleability; even very brittle; spec. grav. 9·5. It melts before the
blowpipe, and affords white fumes of oxide of antimony; being readily
distinguished from arsenical iron, and arsenical cobalt, by its lamellar
fracture. It consists of from 76 to 84 of silver, and from 24 to 16 of
antimony.
3. _Mixed antimonial silver._--At the blowpipe it emits a strong garlic
smell. Its constituents are, silver 16, iron 44, arsenic 35, antimony 4.
It occurs at Andreasberg.
4. _Sulphuret of silver._--This is an opaque substance, of a dark-gray
or leaden hue; slightly malleable, and easily cut with a knife, when it
betrays a metallic lustre. The silver is easily separated by the
blowpipe. It consist of, 13 of sulphur to 89 of silver, by experiment;
13 to 87 are the theoretic proportions. Its spec. grav. is 6·9. It
occurs crystallized in most silver mines, but especially in those of
Freyberg, Joachimsthal in Bohemia, Schemnitz in Hungary, and Mexico.
5. _Red sulphuret of silver; silver glance._--Its spec. grav. is 5·7. It
contains from 84 to 86 of silver.
6. _Sulphuretted silver, with bismuth._--Its constituents are, lead 35,
bismuth 27, silver 15, sulphur 16, with a little iron and copper. It is
rare.
7. _Antimoniated sulphuret of silver_, the red silver of many
mineralogists, is an ore remarkable for its lustre, colour, and the
variety of its forms. It is friable, easily scraped by the knife, and
affords a powder of a lively crimson red. Its colour in mass, is
brilliant red, dark red, or even metallic reddish-black. It crystallizes
in a variety of forms. Its constituents are,--silver from 56 to 62;
antimony from 16 to 20; sulphur from 11 to 14; and oxygen from 8 to 10.
The antimony being in the state of a purple oxide in this ore, is
reckoned to be its colouring principle. It is found in almost all silver
mines; but principally in those of Freyberg, Sainte-Marie-aux-Mines, and
Guadalcanal.
8. _Black sulphuret of silver_; is blackish, brittle, cellular,
affording globules of silver at the blowpipe. It is found only in
certain mines, at Allémont, Freyberg; more abundantly in the silver
mines of Peru and Mexico. The Spaniards call it _negrillo_.
9. _Chloride of silver, or horn silver._--In consequence of its
semi-transparent aspect, its yellowish or greenish colour, and such
softness that it may be cut with the nail, this ore has been compared to
horn, and may be easily recognised. It melts at the flame of a candle,
and may be reduced when heated along with iron or black flux, which are
distinctive characters. It is seldom crystallized; but occurs chiefly in
irregular forms, sometimes covering the native silver as with a thick
crust, as in Peru and Mexico. Its density is only 4·74.
Chloride of silver sometimes contains 60 or 70 per cent. of clay; and is
then called butter-milk ore, by the German miners. The blowpipe causes
globules of silver to sweat out of it. This ore is rather rare. It
occurs in the mines of Potosi, of Annaberg, Freyberg, Allémont,
Schlangenberg, in Siberia, &c.
10. _Carbonate of silver_, a species little known, has been found
hitherto only in the mine of S. Wenceslas, near Wolfache.
TABLE of the Quantities of SILVER brought into the Market every year, on
an average, from 1790 to 1802.
+----------------+------------+---------------+------------+
| Old Continent. |Lbs. Avoird.| New Continent.|Lbs. Avoird.|
+----------------+------------+---------------+------------+
| ASIA. | | | |
|Siberia | 38,500 |Central America| 1,320,000 |
| EUROPE. | | | |
|Hungary | 44,000 |South America | 605,000 |
|Austrian States | 11,000 | | |
|Hartz and Hessia| 11,000 | | |
|Saxony | 22,000 | | |
|Norway | 22,000 | | |
|Sweden }| | | |
|France }| 11,000 | | |
|Spain }| | | |
| | --------| | ----------|
|Total of the | |Total of the | |
|Old Continent | 159,500 |New Continent | 1,925,000 |
+----------------+------------+---------------+------------+
Thus the New Continent furnished twelve times more silver than the Old.
For more detailed statistics of silver, see the end of the article.
The following is Mr. Ward’s description of the treatment of silver ores
in Mexico:--
“After returning from San Augustin,” says he, “I passed the whole of the
afternoon at the _hacienda_ (metallurgic works) of Salgado, in which the
ores of the Valenciana mine are reduced. The _hacienda_, of which a
representation is given below, _fig._ 1001. contains forty-two
crushing-mills, called _arrastres_, and thirty-six stampers. The ore, on
being extracted from the mine, is placed in the hands of the
_pepenadores_, men and women, who break all the larger pieces with
hammers, and after rejecting those in which no metallic particles are
contained, divide the rest into three classes” (inferior, middling, and
rich). “These are submitted to the action of the _morteros_ (stamps),
one of which, of eight stampers, is capable of reducing to powder ten
cargas of ore (each of 350 lbs.) in twenty-four hours. This powder not
being thought sufficiently fine for the quicksilver to act upon with
proper effect, it is transferred from the _morteros_ to the _arrastres_
(crushing-mills, see wood-cut), in which water is used. Each of these
reduces to a fine impalpable metalliferous mud, six quintals (600 lbs.)
of powder in 24 hours. At Guanajuato, where water-power cannot be
obtained, the _arrastres_ are worked by mules (see _fig._ 1001.), which
are kept constantly in motion at a slow pace, and are changed every 6
hours. The grinding-stones, as well as the sides and bottom of the mill
itself, are composed of granite; four blocks of which revolve in each
crushing-mill, attached to cross-bars of wood. This part of the
operation is thought of great importance, for it is upon the perfection
of the grinding that the saving of the quicksilver is supposed in a
great measure to depend, in the subsequent amalgamation. The grinding is
performed usually in a covered shed or gallery which in a large
_hacienda_, like Salgado, from the number of _arrastres_ at work at the
same time, is necessarily of considerable extent.”
[Illustration: 1001 _The Gallera of the Hacienda of Salgado_]
_Fig._ 1002. represents the rude grinding apparatus used at the
_lavaderos_, or gold washings, in Chile. The streamlet of water conveyed
to the hut of the gold washer, is received upon a large rude stone,
whose flat surface has been hollowed out into a shallow basin, and in
the same manner into 3 or 4 others in succession; the auriferous
particles are thus allowed to deposit themselves in these receptacles,
while the lighter earthy atoms, still suspended, are carried off by the
running water. The gold thus collected is mixed with a quantity of
ferruginous black sand and stony matter, which requires the process of
trituration, effected by the very rude and simple _trapiche_ shown in
the figure; consisting of two stones, the under one being about three
feet in diameter, and slightly concave. The upper stone is a large
spherical boulder of syenitic granite, about two feet in diameter,
having on its upper part two iron plugs fixed oppositely, to which is
secured, by lashings of hide, a transverse horizontal pole of _canela_
(cinnamon) _wood_, about 10 feet long; two men seated on the extremities
of this lever, work it up and down alternately, so as to give to the
stone a rolling motion, which is sufficient to crush and grind the
materials placed beneath it. The washings thus ground, are subjected to
the action of running water, upon inclined planes formed of skins, by
which process the siliceous particles are carried off, while a portion
of the ferruginous matter, mixed with the heavier grains of gold, is
extracted by a loadstone; it is again washed, till nothing but pure
gold-dust remain. The whole process is managed with much dexterity; and
if there were much gold to be separated, it would afford very
profitable employment; but generally the small quantity collected is
sufficient only to afford subsistence to a few miserable families.
[Illustration: 1002]
The _trapiche_, _ingenio_, or mill, for grinding the ores of silver, is
a very simple piece of mechanism. A place is chosen where a small
current of water, whose section will present a surface of six inches
diameter, can be brought to a spot where it can fall perpendicularly ten
or twelve feet; at this place a well is built of this depth, about 6
feet in diameter; in its centre is fixed an upright shaft, upon a
central brass pin; it is confined above by a wooden collar. A little
above its foot, the shaft has a small wheel affixed to it, round which
are fixed a number of radiating spokes, shaped at the end somewhat like
cups, and forming altogether a horizontal wheel, four feet in diameter.
Upon the slanting edges of the cups, the water is made to strike with
the force it has acquired in falling down a nearly perpendicular trough,
scooped out of the solid trunk of a tree. This impression makes the
wheel turn with a quick rotatory motion. The upright axis rises about 6
feet above the top of the well, at about half which height is inserted a
small horizontal arm, four feet long, which serves as an axle to a
ponderous mill-stone of granite, of from four to six feet diameter,
which is made to roll on its edge in a circular trough, sometimes made
of the same material, and sometimes of hard wood.
The weight of this quickly rolling stone effects the pulverization of
the ore. In some cases, it is taken out in the dry state, and sifted;
but more generally the separation of the finely ground particles is
accomplished by the action of running water. For this purpose a small
stream is made to trickle into the circular trough, by which the pounded
ore is worked up into a muddy consistence, and the finer particles flow
off with the excess of water, through a notch cut in the margin of the
trough. This fine matter is received in little pools, where the pounded
ore is left to settle; and the clear water being run off, the powder is
removed from the bottom, and carried to the place of amalgamation.
[Illustration: 1003]
The _ingenios_, or stamping-mills, are driven by a small breast
water-wheel, of five feet diameter, and one foot broad. _Fig._ 1003.
will give a sufficient idea of their construction. The long horizontal
shaft, fixed on the axis of the wheel, is furnished with 5 or 6 cams
placed at different situations round the shaft, so as to act in
succession on the projecting teeth of the upright rods or pestles. Each
of these weighs 200 pounds, and works in a corresponding oblong mortar
of stone or wood.
[Illustration: 1004]
The _patio_, or amalgamation floor, _fig._ 1004., is a large flat space,
open to the sky, 312 feet in length, by 236 in breadth, and securely
surrounded by strong walls. It is paved with large unhewn blocks of
porphyry, and is capable of containing 24 _tortas_, or flat circular
collections of _lama_, of about 50 feet diameter, and 7 inches deep,
when the patio is not filled, (but of somewhat smaller dimensions when
nearly so,) ranged in 4 rows, and numbered from the left-hand corner. At
one end a small space is generally set apart for the assays, which are
made each on one monton.
The following description of Mexican amalgamation is given by Captain
Lyon.
A torta of Zacatecas contains 60 montons of 20 quintals each, and is
thus formed:--In the first instance, a square space, of the requisite
size for a torta, is marked out, and enclosed by a number of rough
planks, which are propped in their places on the patio floor by large
stones, and dried horse-dung and dust are piled round their edges to
prevent the escape of the lama. A heap of saltierra (salt mixed with
earthy impurities) is then piled in the centre, in the proportion of 2
fanegas (each = 1·6 English bushels) and a half to the monton, = 150 for
the torta. After this, the lama, or ore ground into a fine paste, is
poured in. When the last or 60th monton is delivered, the saltierra is
shovelled down and well mixed with the lama, by treading it with horses,
and turning it with shovels; after which the preparation is left at rest
for the remainder of the day. On the following day comes the _el
incorporo_. After about one hour’s treading by horses, the magistral or
roasted and pulverized copper ore is mixed with the lama, (the _repaso_
or treading-mill still continuing,) in summer in the proportion of 15
cargas of 12 arrobas (25 lbs. each) to the torta, if the ore be of 6
marcs to the monton, and in winter in only half the quantity. For it is
a singular fact, that in summer the mixture cools, and requires more
warmth; while in winter it acquires of itself additional heat. With
poorer ores, as for instance those of 4 marcs to the monton, 12 cargas
are applied in summer, and 6 in winter. From November to February, lime
is also occasionally used to cool the lama, in the proportion of about a
peck per monton.
The _repaso_, or treading out, is continued by six horses, which are
guided by one man, who stands in the lama, and directs them all by
holding all their long halters. This operation is much more effectual in
a morning than an evening, and occupies about five or six hours. When
the magistral is well mixed, the quicksilver is applied, by being
sprinkled through pieces of coarse cloth doubled up like a bag, so that
it spurts out in very minute particles. The second treading of the
horses then follows; after which the whole mixture is turned over by six
men with wooden shovels, who perform the operation in an hour. The torta
is then smoothed and left at rest for one entire day, to allow the
incorporation to take place. It undergoes the turning by shovels and
treading by horses every other day, until the amalgamator ascertains
that the first admixture of quicksilver is found to be all taken up by
the silver; and this he does by vanning or washing a small quantity of
the torta in a little bowl. A new supply is then added, and when this
has done its duty, another is applied to catch any stray particles of
silver. On the same day, after a good repaso, the torta is removed on
hand-barrows by the labourers, to the _lavaderos_, in order that it may
receive its final cleansing. The general method of proportioning the
quicksilver to the tortas, is by allowing that every marco of silver
which is promised by trial of the ores as the probable produce of a
monton, will require in the whole process 4 lbs.
In metals of five to six marcs and a half per monton (of the average
richness of Zacatecas), 16 lbs. of quicksilver were incorporated for
every monton, = 900 lbs. for the torta. On the day of the second
addition, the proportion is 5 lbs. the monton; and when the torta is
ready to receive the last dose of quicksilver, it is applied at the rate
of 7 lbs. the monton, = 420 lbs.; making a total of 1620 lbs. of
quicksilver. With poorer ores, less quicksilver and less magistral are
required.
The usual time for the completion of the process of amalgamation, is
from 12 to 15 days in the summer, and 20 to 25 in the winter. This is
less than a third of the time taken at some other mines in Mexico. This
rapidity is owing to the tortas being spread very flat, and receiving
thereby the stronger influence of the sun. In the Mexican mines, only
one monton is commonly mixed at a time; and the lama is then piled in a
small conical heap or monton.
_Lavadero, or washing vat._--Here the prepared tortas are washed, in
order to carry off the earthy matters, and favour the deposition of the
amalgam at the bottom. Each vat is about 8 feet deep, and 9 in diameter;
and solidly built in masonry.
A large horizontal wheel, worked by mules, drives a vertical one, which
turns a horizontal wheel fitted round a perpendicular wooden shaft,
revolving upon an iron pivot at the bottom of the vat. To the lower end
of this shaft, four cross-beams are fitted, from which long wooden teeth
rise to the height of 5 feet. Their motion through the water being
rapid, keeps all the lighter particles afloat, while the heavier sink to
the bottom. The large wheel is worked by four mules, two at each
extremity of the cross-beam. Water is supplied from an elevated tank. It
requires 12 hours’ work of one tub to wash a torta. Eight porters are
employed in carrying the prepared _lama_ of the torta in hand-barrows to
the vats. The earthy matter receives a second washing.
[Illustration: 1005]
The amalgam is carried in bowls into the _azogueria_, where it is
subjected to straining through the strong canvas bottom of a leather
bag. The hard mass left in the bag is moulded into wedge-shaped masses
of 30 lbs., which are arranged in the burning-house, (_fig._ 1005.), to
the number of 11, upon a solid copper stand, called _baso_, having a
round hole in its centre. Over this row of wedges several others are
built; and the whole pile is called _pina_. Each circular range is
firmly bound round with a rope. The base is placed over a pipe which
leads to a small tank of water for condensing the quicksilver; a
cylindrical space being left in the middle of the _pina_, to give free
egress to the mercurial vapours.
A large bell-shaped cover, called _capellina_, is now hoisted up, and
carefully lowered over the _pina_, by means of pulleys. A strong lute of
ashes, saltierra, and lama is applied to its lower edge, and made to fit
very closely to the plate on which the base stands. A wall of
fire-bricks is then built loosely round the capellina, and this space is
filled with burning charcoal, which is thrice replenished, to keep it
burning all night. After the heat has been applied 20 hours, the bricks
and ashes are removed, the luting broken, and the capellina hoisted up.
The burned silver is then found in a hard mass, which is broken up,
weighed, and carried to the casting-house, to be formed into bars of
about 1080 ounces each. The loss of silver in burning, is about 5 ounces
to each bar (_barra_), and the loss of quicksilver, from 2-1/2 upon the
good metals, to 9 upon the coarse.
Molina told Mr. Miers, that the produce of the galena ores of Uspaltata
did not average more than 2 marcs per _caxon_ of 5000 lbs., which is an
excessively poor ore. The argentiferous galena ores of Cumberland afford
11 marcs per caxon; while the average produce of the Potosi silver ores
is only 5 or 6 marcs in the same quantity. These comparisons afford the
clearest evidence that the English mode of smelting can never be brought
into competition with the process of amalgamation as practised in
America.
Humboldt, Gay Lussac, Boussingault, Karsten, and several other chemists
of note, have offered solutions of the amalgamation enigma of Mexico and
Peru. The following seems to be the most probable _rationale_ of the
successive steps of the process:--
The addition of the _magistral_ (powder of the roasted copper pyrites),
is not for the purpose of disengaging muriatic acid from the sea salt
(_saltierra_), as has been supposed, since nothing of the kind actually
takes place; but, by reciprocal or compound affinity, it serves to form
chloride of copper, and chloride of iron, upon the one hand, and
sulphate of soda, upon the other. Were sulphuric acid to be used instead
of the magistral, as certain novices have prescribed, it would certainly
prove injurious, by causing muriatic acid to exhale. Since the ores
contain only at times oxide of silver, but always a great abundance of
oxide of iron, the acid would carry off both partly, but leave the
chloride of silver in a freer state. A magistral, such as sulphate of
iron, which is not in a condition to generate the chlorides, will not
suit the present purpose; only such metallic sulphates are useful as are
ready to be transformed into chlorides by the _saltierra_. This is
peculiarly the case with sulphate of copper. Its deuto-chloride gives up
chlorine to the silver, becomes in consequence a protochloride, while
the chloride of silver, thus formed, is revived, and amalgamated with
the quicksilver present, by electro-chemical agency which is excited by
the saline menstruum; just as the voltaic pile of copper and silver is
rendered active by a solution of sea salt. A portion of chloride of
mercury will be simultaneously formed, to be decomposed in its turn by
the sulphate of silver resulting from the mutual action of the acidified
pyrites, and the silver or its oxide in the ore. An addition of
quicklime counteracts the injurious effect of too much magistral, by
decomposing the resulting sulphate of copper. Quicksilver being an
excellent conductor of heat, when introduced in too great quantities, is
apt to cool the mass too much, and thereby enfeebles the operation of
the deuto-chloride of copper upon the silver.
There is a method of extracting silver from its ores by what is called
_imbibition_. This is exceedingly simple, consisting in depriving, as
far as possible, the silver of its gangue, then melting it with about
its own weight of lead. The alloy thus procured, contains from 30 to 35
_per cent._ of silver, which is separated by cupellation on the great
scale, as described under ores of LEAD. In this way the silver is
obtained at Kongsberg in Norway.
The amalgamation works at Halsbrücke, near Freyberg, for the treatment
of silver ores by mercury, have been justly admired as a model of
arrangement, convenience, and regularity; and I shall conclude this
subject with a sketch of their general distribution.
[Illustration: 1006]
_Fig._ 1006. presents a vertical section of this great _usine_ or
_hüttenwerk_, subdivided into four main departments. The first, A, B, is
devoted to the preparation and roasting of the matters intended for
amalgamation. The second, B, C, is occupied with two successive
siftings and the milling. The third, C, D, includes the amalgamation
apartment above, and the wash-house of the residuums below. And in the
fourth, D, E, the distilling apparatus is placed, where the amalgam is
finally delivered.
Thus, from one extremity of this building to the other, the workshops
follow in the order of the processes; and the whole, over a length of
180 feet, seems to be a natural laboratory, through which the materials
pass, as it were of themselves, from their crude to their refined
condition; so skilfully economized and methodical are the labours of the
workmen; such are the regularity, precision, concert, and facility,
which pervade this long series of combinations, carriages, movements,
and metamorphoses of matter.