The expenses of the new method altogether, including 3_s._ per fodder of
patent dues are about one-third of the old; being 17_l._ 13_s._ and
54_l._ 16_s._ respectively, upon 84 cwts. of lead, at 29 oz. per fodder.
In the conditions above stated, the treatment of argentiferous lead
occasions the following expenses:--
FOR ONE FODDER. _£_ _s._ _d._
By the new process 0 13 7
old process 2 2 2
Admitting that the treatment of silver holding lead is economically
possible only when the profit is equal to one-tenth of the gross
expenses of the process, we may easily calculate, with the preceding
data, that it is sufficient for the lead to have the following contents
in silver:--
With the new process, 3 ounces per fodder; or, 0·000078
With the old process, 8-4/10 ounces per fodder; or, 0·000218
To conclude, the refining by crystallization reduces the cost of the
parting of lead and silver, in the proportion of 3 to 1; and allows of
extracting silver from a lead which contains only about 3 oz. per ton.
In England, the new method produces at present very advantageous
results, especially in reference to the great masses to which it may be
applied. In 1828, the quantity of lead annually extracted from the mines
in the United Kingdom had been progressively raised to 47,000 tons.
Reduced almost to one-half of this amount in 1832, by the competition of
the mines of la Sierra de Gador, the English production began again to
increase in 1833. In 1835, 35,000 tons of lead were obtained, one-half
of which only having a mean content of 8-1/2 oz. of silver per ton, was
subjected to cupellation, and produced 14,000 oz. of that precious
metal. The details of this production are--
Silver extracted from 17,500 tons of lead, } 140,000 oz.
holding upon the average 8-1/2 oz. per ton. }
Silver extracted from silver ores,
properly so called, in Cornwall 36,000
-------
176,000
In 1837, the production of lead amounted probably to 40,000 tons; upon
which the introduction of the new method would have the effect not only
of reducing considerably the cost of parting the 20,000 tons of lead
containing 8 oz. of silver per ton, but of permitting the extraction of
4 or 5 oz. of silver, which may be supposed to exist upon an average in
the greater portion of the remaining 20,000 tons. Otherwise, this mass
of the precious metal would have had no value, or have been
unproductive.
There are two oxides of silver; called argentic oxide, and suroxide, by
Berzelius. 1. The first is obtained by adding solution of caustic
potassa, or lime-water, to a solution of nitrate of silver. The
precipitate has a brownish-gray colour, which darkens when dried, and
contains no combined water. Its specific gravity is 7·143. On exposure
to the sun, it gives out a certain quantity of oxygen, and becomes a
black powder. This oxide is an energetic base; being slightly soluble in
pure water, reacting like the alkalis upon reddened litmus paper, and
displacing, from their combinations with the alkalis, a portion of the
acids, with which it forms insoluble compounds. It is insoluble in the
caustic lyes of potassa or soda. By combination with caustic ammonia, it
forms _fulminating silver_. This formidable substance may be prepared by
precipitating the nitrate of silver with lime-water, washing the oxide
upon a filter, and spreading it upon gray paper, to make it nearly dry.
Upon the oxide, still moist, water of ammonia is to be poured, and
allowed to remain for several hours. The powder which becomes black, is
to be freed from the supernatant liquor by decantation, divided into
small portions while moist, and set aside to dry upon bits of porous
paper. Fulminating silver may be made more expeditiously by dissolving
the nitrate in water of pure ammonia, and precipitating by the addition
of caustic potassa lye in slight excess. If fulminating silver be
pressed with a hard body in its moist state, it detonates with
unparalleled violence; nay, when touched even with a feather, in its dry
state, it frequently explodes. As many persons have been seriously
wounded, and some have been killed, by these explosions, the utmost
precautions should be taken, especially by young chemists, in its
preparation. This violent phenomenon is caused by the sudden production
of water and nitrogen, at the instant when the metallic oxide is
reduced. The quiescent and divellent affinities seem to be so nicely
balanced in this curious compound, that the slightest disturbance is
sufficient to incite the hydrogen of the ammonia to snatch the oxygen
from the silver. The oxide of silver dissolves in glassy fluxes, and
renders them yellow. It consists, according to Berzelius, of 93·11 parts
of silver, and 6·89 of oxygen. 2. The suroxide of silver is obtained by
passing a voltaic current through a weak solution of the nitrate; it
being deposited, of course, at the positive or oxygenating pole. It is
said to crystallize in needles of a metallic lustre, interlacing one
another, which are one-third of an inch long. When thrown into muriatic
acid, it causes the disengagement of chlorine, and the formation of
chloride of silver; into water of ammonia, it occasions such a rapid
production of nitrogen gas, with a hissing sound, as to convert the
whole liquid into froth. If a little of it, mixed with phosphorus, be
struck with a hammer, a loud detonation ensues. With heat it
decrepitates, and becomes metallic silver.
Sulphuret of silver, which exists native, may be readily prepared by
fusing the constituents together; and it forms spontaneously upon the
surface of silver exposed to the air of inhabited places, or plunged
into eggs, especially rotten ones. The tarnish may be easily removed, by
rubbing the metal with a solution of _cameleon mineral_, prepared by
calcining peroxide of manganese with nitre. Sulphuret of silver is a
powerful sulpho-base; since though it be heated to redness in close
vessels, it retains the volatile sulphides, whose combinations with the
alkalis are decomposed at that temperature. It consists of 87·04 of
silver, and 12·96 of oxygen.
A small quantity of tin, alloyed with silver, destroys its ductility.
The best method of separating these two metals, is to laminate the alloy
into thin plates, and distil them along with corrosive sublimate. The
bichloride of tin comes over in vapours, and condenses in the receiver.
Silver and lead, when combined, are separated by heat alone in the
process of cupellation, as described in the article ASSAY, and in the
reduction of silver ores. See _suprà_.
An alloy, containing from one-twelfth to one-tenth of copper,
constitutes the silver coin of most nations; being a harder and more
durable metal under friction than pure silver. When this alloy is boiled
with a solution of cream of tartar and sea-salt, or scrubbed with water
of ammonia, the superficial particles of copper are removed, and a
surface of fine silver is left.
Chloride of silver is obtained by adding muriatic acid, or any soluble
muriate, to a solution of nitrate of silver. A curdy precipitate falls,
quite insoluble in water, which being dried and heated to dull redness,
fuses into a semi-transparent gray mass, called, from its appearance,
_horn-silver_. Chloride of silver dissolves readily in water of ammonia,
and crystallizes in proportion as the ammonia evaporates. It is not
decomposed by a red heat, even when mixed with calcined charcoal; but
when hydrogen or steam is passed over the fused chloride, muriatic acid
exhales, and silver remains. When fused along with potassa (or its
carbonate), the silver is also revived; while oxygen (or also carbonic
acid) gas is liberated, and chloride of potassium is formed. Alkaline
solutions do not decompose chloride of silver. When this compound is
exposed to light, it suffers a partial decomposition, muriatic acid
being disengaged. See ASSAY by the _humid method_.
The best way of reducing the chloride of silver, says Mohr, is to mix it
with one-third of its weight of colophony (black rosin), and to heat the
mixture moderately in a crucible till the flame ceases to have a
greenish-blue colour; then suddenly to increase the fire, so as to melt
the metal into an ingot.
The subchloride may be directly formed, by pouring a solution of
deuto-chloride of copper or iron upon silver leaf. The metal is speedily
changed into black spangles, which, being immediately washed and dried,
constitute subchloride of silver. If the contact of the solutions be
prolonged, chloride would be formed.
The bromide, cyanide, fluoride, and iodide of silver, have not been
applied to any use in the arts. Sulphate of silver may be prepared by
boiling sulphuric acid upon the metal. See REFINING OF GOLD AND SILVER.
It dissolves in 88 parts of boiling water, but the greater part of the
salt crystallizes in small needles, as the solution cools. It consists
of 118 parts of oxide, combined with 40 parts of dry acid. Solutions of
the hyposulphite of potassa, soda, and lime, which are bitter salts,
dissolve chloride of silver, a tasteless substance, into liquids
possessed of the most palling sweetness, but not at all of any metallic
taste.
The iodide of silver is remarkable, like some other metallic compounds,
for changing its colour alternately with heat and cold. If a sheet of
white paper be washed over with a solution of nitrate of silver, and
afterwards with a somewhat dilute solution of hydriodate of potash, it
will immediately assume the pale yellow tint of the cold silver iodide.
On placing the paper before the fire, it will change colour from a pale
primrose to a gaudy brilliant yellow, like the sun-flower; and on being
cooled, it will again resume the primrose hue. These alternations may be
repeated indefinitely, like those with the salts of cobalt, provided
too great a heat be not applied. The pressure of a finger upon the hot
yellow paper makes a white spot, by cooling it quickly.
Fulminate of silver is prepared in the same way as FULMINATE _of
Mercury_, which see.
On the 10th of February, 1798, the Lords of the Privy Council appointed
the Hon. Charles Cavendish, F. R. S., and Charles Hatchett, Esq., F. R.
S., to make investigations upon the wear of gold coin by friction. Their
admirable experiments were begun in the latter end of 1798, and
completed in April 1801, having been instituted and conducted with every
mechanical aid, as devised by these most eminent chemical philosophers,
and provided, at no small expense, by the government. The following are
the important conclusions of their official report:--[54]
[54] It is inserted in the Philosophical Transactions for 1803.
“Gold made standard by a mixture of equal parts of silver and copper, is
not so soft as gold alloyed only with silver; neither is it so pale; for
it appears to be less removed from the colour of fine gold, than either
the former or the following metal.
“Gold, when alloyed with silver and copper, when annealed, does not
become black, but brown; and this colour is more easily removed by the
blanching liquor, or solution of alum, than when the whole of the alloy
consists of copper. It may also be rolled and stamped with great
facility; and, under many circumstances, it appears to suffer less by
friction than gold alloyed by silver or copper alone.
“If copper alone forms the alloy, it must be dissolved and separated
from the surface of each piece of coin, in the process of annealing and
blanching.
“Upon a comparison of the different qualities of the three kinds of
standard gold, it appears (strictly speaking) that gold made standard by
silver and copper is rather to be preferred for coin.”
It will, undoubtedly, seem not a little strange to the uninitiated, that
this report, and its important deductions, should have been of late
years entirely set at nought, without any scientific reason or research,
apparently for the purpose of giving a certain official in our Mint a
good job, in sweating out all the silver from our sovereigns, and
replacing it, in the new coinage, with copper, taking on an average
3_d._ worth of silver out of each ounce of our excellent gold coin, and
charging the country 6-1/2_d._ for its extraction, besides the very
considerable expense in providing fine copper to replace the silver. The
pretence set up for this extraordinary degradation of the gold, was,
that our coin might peradventure be exported, in order to be de-silvered
abroad, a danger which could have been most readily averted, by leaving
out as much gold in every sovereign as was equivalent to the silver
introduced, and thus preserving its intrinsic value in precious metal.
When the film of fine gold which covers each of our present pieces has
been rubbed off from the prominent parts, these must appear of a very
different and deeper colour than the flat part or ground of the coin.
“The reason, therefore, is sufficiently apparent, says Mr. Hatchett, why
gold which is alloyed with silver only, cannot be liable to this
blemish;” and with one-half of silver alloy, it must be much less liable
to it, than with copper alone. Why did the political economists in the
recent Committee of the House of Commons on the Mint, blink this
question, of public economy and expediency?
Gold, as imported from America, Asia, and Africa, contains on an average
nearly the right proportion of silver for making the best coin; and were
it alloyed to our national standard, of 22 parts of gold, 1 of silver,
and 1 of copper, as defined by Messrs. Cavendish and Hatchett, then by
simply adding the deficient quantities of one or two of these metals, by
the rule of alligation, the very considerable expense would be saved to
the nation, and sulphureous nuisance to the Tower Hamlets, now foolishly
incurred in de-silvering and cuprifying sovereigns at the Royal Mint.
It was long imagined in Europe, that the average metallic contents of
the silver ores of Mexico and Peru, were considerably greater than those
of Saxony and Hungary. Much poorer ores, however, are worked among the
Cordilleras than in any part of Europe. The mean product of the whole
silver ores that are annually reduced in Mexico, amounts only to from
0·18 to 0·25 of a per cent.; that is, from 3 to 4 ounces in 100 lbs.;
the true average being, perhaps, not more than 2-1/2. It is by their
greater profusion of ores, not their superior richness, that the mines
of South America surpass those of Europe.
GOLD and SILVER produced in Forty Years, from 1790 to 1830.
+------------+------------+--------------+
| | Gold. | Silver. |
| +------------+--------------+
|Mexico |_£_6,436,453|_£_139,818,032|
|Chile | 2,768,488| 1,822,924|
|Buenos Ayres| 4,024,895| 27,182,673|
|Russia | 3,703,743| 1,502,981|
+------------+------------+--------------+
RETURNS of the DOLLARS coined at the different Mints in MEXICO.
+-----------+----------+----------+----------+----------+
| | 1829. | 1830. | 1831. | 1834. |
| +----------+----------+----------+----------+
|Mexico | 1,280,000| 1,090,000| 1,386,000| 952,000|
|Guanajuato | 2,406,000| 2,560,000| 2,603,000| 2,703,000|
|Zacatecas | 4,505,000| 5,190,000| 4,965,000| 5,527,000|
|Guadalaxara| 596,000| 592,000| 590,000| 715,000|
|Durango | 659,000| 453,000| 358,000| 1,215,000|
|San Luis | 1,613,000| 1,320,000| 1,497,000| 928,000|
|Ilalpan | 728,000| 90,000| 323,000| |
| +----------+----------+----------+----------+
| Total |11,787,000|11,295,000|11,722,000|12,040,000|
+-----------+----------+----------+----------+----------+
The returns for 1832 and 1833 are wanting.
PERU.--RETURNS of GOLD and SILVER coined at the Mints of Lima and Casco.
+-----+-------+---------+------------------+
| | Gold. | Silver. |Total, in Dollars.|
| +-------+---------+------------------+
|1830 |180,000|2,015,000| 2,195,000 |
|1831 | 92,000|2,384,000| 2,476,000 |
|1832 | 94,000|3,210,000| 3,284,000 |
|1833 |150,000|2,990,000| 3,140,000 |
|1834 |110,000|3,150,000| 3,260,000 |
+-----+-------+---------+------------------+
RETURNS of SILVER in BARS produced at the different Smelting-works in
PERU.
+----+-------+-------+---------+-------+-------+-------+---------+
| |Lima. |Truxil-|Pasco. |Aya- |Puno. |Are- |Total, in|
| | |lo. | |cucho. | |quipa. |Dollars. |
| +-------+-------+---------+-------+-------+-------+---------+
|1830|270,000|190,000| 780,000|120,000|250,000|150,000|1,760,000|
|1831|270,000| 60,000|1,110,000| 70,000|310,000|110,000|1,930,000|
|1832|290,000|100,000|1,800,000| 70,000|345,000| 25,000|2,640,000|
|1833|222,000| 70,000|2,130,000| 50,000| 25,000| 65,000|2,562,000|
+----+-------+-------+---------+-------+-------+-------+---------+
+----+---------+-------+----------+
| |Coquimbo.|Huasco.| Copiano. |
| +---------+-------+----------+
|1831| 785,000|115,000| 670,000 |
|1832| 316,000| | 36,000 |
|1833| 490,000|100,000| 585,000 |
| +---------+-------+----------+
| |1,591,000|215,000|1,291,000 |
+----+---------+-------+----------+
SANTIAGO--Mint Coinage.
Gold. Silver. Total.
1832, 174,000; 1833, 392,500 1832, 42,000; 1833, 92,000 700,500