alkaline amalgam and a metallic salt, or by electrolysis of saline
solutions, with employment of mercury as the negative electrode,
apply _a fortiori_ to metals capable of combining directly with the
quicksilver. The latter of these methods is especially utilized for the
preparation of alkaline earthy metals by electrolytic decomposition of
the solutions of their salts or hydrated oxides with quicksilver as a
cathode.
«General Properties of Amalgams.»—Amalgams are liquid when the
quicksilver is in great excess; solid, but readily fusible, when the
alloyed metal predominates.
They have a metallic luster, and a metallic structure which renders
them brittle. They even form crystallized metallic combinations of
constant proportions, dissolved in an excess of quicksilver, when the
excess is separated by compression in a chamois skin, or by filtration
in a glass funnel of slender stem, terminating with an orifice almost
capillary.
According as the fusing heat of a metal is less or greater than
its combination heat with quicksilver, the amalgamation of this
metal produces an elevation or a lowering of temperature. Thus {86}
potassium, sodium, and cadmium, in alloy with quicksilver, disengage
heat; while zinc, antimony, tin, bismuth, lead, and silver combine
with mercury with absorption of heat. The amalgamation of 162 parts of
quicksilver with 21 parts of lead, 12 parts of tin or of antimony, and
28.5 parts of bismuth, lowers the temperature of the mixture 79° F.
Amalgams formed with disengagement of heat are electro-negative with
reference to the metals alloyed with the quicksilver. The products with
absorption of heat are electro-negative with reference to the metals
combined with the quicksilver; consequently, in a battery of elements
of pure cadmium and amalgamated cadmium, the cadmium will be the
negative pole; in case of zinc and amalgamated zinc, the zinc will be
the positive pole.
Heat decomposes all amalgams, vaporizing the mercury and leaving the
metal alloys as a residue.
Water is decomposed by the amalgams of potassium and sodium, because
the heat of formation of these amalgams, although considerable, is even
less than the heat disengaged by potassium and sodium, on decomposing
water. The alkaline amalgams may, therefore, serve as a source of
nascent hydrogen in presence of water, giving rise to an action less
energetic, and often more advantageous, than that of the alkaline
metals alone. Thus is caused the frequent employment of sodium amalgam
for hydrogenizing a large number of bodies. As a consequence of their
action on water, the alkaline amalgams are changed by moist air, with
production of free alkali or alkaline carbonate.
«Applications of Potassium Amalgams.»—I.—They furnish a process for
preparing potassium by the decomposition of potash by the electric
current, by employing quicksilver as the cathode, and vaporizing the
quicksilver of the amalgam formed by heating this in a current of dry
hydrogen.
II.—They can serve for the preparation of the amalgams of the metals,
other than those of the alkaline group, by decomposing the salts of
these metals, with formation of a salt of potash and of the amalgam of
the metal corresponding to the original salt.
III.—They can be employed as a source of nascent hydrogen in presence
of water for hydrogenizing many substances.
«Applications of Sodium Amalgams.»—These are nearly the same as those
of the potassium amalgams, but the sodium amalgams are employed almost
exclusively, because sodium is easier to handle than potassium, and is
cheaper. These employments are the following:
I.—Sodium amalgam furnishes a process for the preparation of sodium
when soda is decomposed by means of the electric current, employing
quicksilver as the cathode, and afterwards vaporizing the quicksilver
of the amalgam formed by heating this in a current of dry hydrogen.
II.—Amalgams of sodium serve for the preparation of amalgams of the
other metals, particularly alkaline earthy metals and metals of high
fusing points, by decomposing the salts of these metals, with formation
of a salt of soda and of the amalgam of the metal corresponding to the
original salt.
III.—They serve for amalgamating superficially the metals of high
fusing point, called “refractory,” such as iron and platinum, when a
well-cleaned plate of these metals is immersed in sodium amalgam in
presence of water.
IV.—An amalgam of 2 or 3 per cent of sodium is employed in the
processes of extraction of gold by amalgamation. It has the property of
rendering quicksilver more brilliant, and consequently more energetic,
by acting as a deoxidant on the pellicle of oxide formed on its surface
in presence of certain ores, which, by keeping it separated from the
particles of gold, destroy its activity. Sodium amalgam of 3 per
cent is utilized with success for the amalgamated plates employed in
crushers and other apparatus for treating the ores of gold. If a few
drops of this amalgam are spread on a plate of copper, of tin, or of
zinc, a brilliant coating of an amalgam of tin, copper, or zinc is
immediately formed.
V.—Amalgams of from 2 to 8 per cent of sodium serve frequently in
laboratories for reducing or hydrogenizing organic combinations,
without running the risk of a partial destruction of these compounds by
too intense action, as may occur by employing free sodium instead of
its amalgam.
«Applications of Barium Amalgams.»—These can, by distillation, furnish
barium. It is one of the processes for preparing this metal, which,
when thus obtained, almost always retains a little sodium.
«Applications of Strontium Amalgams.»—These amalgams, washed and dried
rapidly immediately after their preparation, and then heated to a
nascent red {87} in a current of dry hydrogen, yield a fused mass of
strontium.
«Applications of Cadmium Amalgams.»—Amalgams of cadmium, formed of
equal weights of cadmium and quicksilver, have much power of cohesion
and are quite malleable; the case is the same with an amalgam formed of
1 part of cadmium and 2 parts of quicksilver. They are used as dental
cements for plugging teeth; for the same purpose an amalgam of 2 parts
of quicksilver, 1 part of cadmium, and 2 parts of tin may be used.
«Applications of Zinc Amalgams.»—The principal employment of zinc
amalgams is their use as a cathode or negative electrode in the
batteries of Munson, Daniels, and Lechanché. This combination is
designed to render the zinc non-attackable by the exciting liquid of
the battery with open circuit. The action of the mercury is to prevent
the zinc from forming a large number of small voltaic elements when
foreign bodies are mingled with the metal; in a word, the giving to
ordinary zinc the properties of pure zinc, and consequently of causing
a great saving in expense.
For amalgamating a zinc plate it is plunged for a few seconds into
water in which there is one-sixteenth in volume of sulphuric acid,
then rubbing with a copper-wire brush which has been dipped in the
quicksilver. The mercury takes more readily on the zinc when, after the
zinc has been cleaned with water sharpened with sulphuric acid, it is
moistened with a solution of corrosive sublimate, which is reduced and
furnishes a first very thin coat of amalgam, on which the quicksilver
is immediately fixed by simple immersion without rubbing.
The zinc of a battery may be amalgamated by putting at the bottom of
the compartment containing each element, a little quicksilver in such
a way that the zinc touches the liquid. The amalgamation is effected
under the influence of the current, but this process applies only
on condition that the zinc alone touches the bottom of the vessel
containing the quicksilver.
«Applications of Manganese Amalgams.»—These may serve for the
preparation of manganese. For this purpose it is sufficient to distill
in a current of pure hydrogen. The manganese remains in the form of a
grayish powder.
«Applications of Tin Amalgams.»—I.—Tinning of glass. This operation
is accomplished in the following manner: On a cast-iron table, quite
horizontal, a sheet of tin of the dimensions of the glass is spread
out and covered with a layer of quicksilver, 5 or 6 millimeters in
thickness. The glass is made to slide on the sheet of tin in such a
way as to drive off the excess of quicksilver; when the two surfaces
are covered without interposition of air, weights are placed on the
glass. In a few days, the glass may be removed, having been covered
with an adhering pellicle of amalgam of 4 parts of tin and 1 part of
quicksilver. (See also Mirrors.)
II.—An amalgam consisting of 2 parts of zinc and 1 part tin may be
used for covering the cushions of frictional electric machines. This
amalgam is prepared by first melting the zinc and tin in a crucible and
adding the quicksilver previously heated.
III.—Mention has been made of the cadmium amalgam employed for plugging
teeth, an amalgam of 2 parts of quicksilver, 2 parts of tin, and 1 part
of cadmium. For the same purpose an amalgam of tin, silver, and gold is
employed. (See also Cements, Dental.)
«Applications of Copper Amalgams.»—I.—An amalgam of 30 per cent of
copper has been employed for filling teeth. This use has been abandoned
on account of the inconvenience occasioned by the great changeableness
of the product.
II.—The amalgam of 30 per cent of copper, designated by the name of
“metallic mastic,” is an excellent cement for repairing objects and
utensils of porcelain. For this employment, the broken surfaces are
heated to 662° F., and a little of the amalgam, previously heated to
the consistency of melted wax, is applied.
III.—Copper amalgam, of 30 to 45 per cent of copper, rendered
plastic by heating and grinding, may serve for obtaining with slight
compression copies of delicate objects, which may, after hardening of
the amalgam, be reproduced, either in wax or by galvanic process.
IV.—According to Debray, when a medal, obtained with an amalgam of
45 per cent of copper, by compression in the soft state, in molds of
gutta percha, is heated progressively to redness in an atmosphere of
hydrogen, the quicksilver is volatilized gradually, and the particles
of copper come together without fusion in such a way as to produce a
faithful reproduction, formed exclusively of metallic copper, of the
original medal.
V.—In the metallurgy of gold, the crushers are furnished with
amalgamated plates of copper for retaining the gold. The preparation
of these plates, {88} which are at least 0.128 inches in thickness, is
delicate, requiring about two weeks. They are freed from greasy matter
by rubbing with ashes, or, better, with a little sand and caustic soda,
or if more rapid action is desired, with a cloth dipped in dilute
nitric acid; they are washed with water, then with a solution of
potassium cyanide, and finally brushed with a mixture of sal ammoniac
and a little quicksilver, until the surface is completely amalgamated.
They are finally made to absorb as much quicksilver as possible. But
the plates thus treated are useful for only a few days when they are
sufficiently covered with a layer of gold amalgam; in the meantime
they occasion loss of time and of gold. So it is preferable to cover
them artificially with a little gold amalgam, which is prepared by
dissolving gold in quicksilver. Sometimes the amalgam of gold is
replaced by an amalgam of silver, which is readily poured and more
economical.
Another method giving better results consists in silvering copper slabs
by electroplating and covering them with a layer of silver. Then it
is only necessary to apply a little quicksilver, which adheres quite
rapidly, so that they are ready for use almost immediately, and are
quite active at the outset.
These amalgamation slabs ought to be cleaned before each operation.
Potassium cyanide removes fatty matter, and sal ammoniac the oxides of
the low metals.
«Applications of Lead Amalgams.»—These meet with an interesting
employment for the autogenous soldering of lead. After the surfaces
to be soldered have been well cleaned, a layer of lead amalgam is
applied. It is afterwards sufficient to pass along the line of junction
a soldering iron heated to redness, in order that the heat should cause
the volatilization of the quicksilver, and that the lead, liberated in
a state of fine division, should be melted and cause the adherence of
the two surfaces. The only precaution necessary is to avoid breathing
the mercurial vapor, which is quite poisonous.
«Applications of Bismuth Amalgams.»—The amalgam formed of 1 per cent of
bismuth and 4 parts of quicksilver will cause the strong adherence of
glass. It is employed with advantage in the tinning of glass globes.
For this operation it is poured into a dry hot receiver, and then
passed over the whole surface of the glass; it solidifies on cooling.
For the purpose of economizing the bismuth, the price of which is high,
the preceding amalgam is replaced by another composed of 2 parts of
quicksilver, 1 part of bismuth, 1 part of lead, and 1 part of tin. The
bismuth, broken into small fragments, is added to the tin and lead,
previously melted in the crucible, and when the mixture of the three
metals becomes fluid, the quicksilver is poured in, while stirring with
an iron rod. The impurities floating on the surface are removed, and
when the temperature is sufficiently lowered this amalgam is slowly
poured into the vessels to be tinned, which have been previously
well cleaned and slightly heated. M. Ditte recommends for the same
employment, as a very strong adherent to the glass, an amalgam obtained
by dissolving hot 2 parts of bismuth and 1 part of lead in a solution
of 1 part of tin in 10 parts of quicksilver. By causing a quantity of
this amalgam to move around the inside of a receiver, clean, dry, and
slightly heated, the surface will be covered with a thin, brilliant
layer, which hardens quite rapidly.
For the injection of anatomical pieces an amalgam formed of 10 parts
of quicksilver, 50 parts of bismuth, 31 parts of lead, and 18 parts
of tin, fusible at 77.5° and solidifiable at 60° C., is made use of;
or, again, an amalgam composed of 9 parts of Darcet alloy and 1 part
of quicksilver fusible at 127 1/2° F., and pasty at a still lower
temperature. This last amalgam may also be used for filling carious
teeth. The Darcet alloy, as known, contains 2 parts of bismuth, 1 part
of lead, and 1 part of tin, and melts at 199 1/2° F. The addition of
1 part of quicksilver lowers the fusing point to 104° F.
«Applications of Silver Amalgams.»—I.—In the silvering of mirrors by
the Petitjean method, which has almost universally replaced tinning,
the property of silver in readily amalgamating is taken advantage of,
by substituting the glass after silvering to the action of a dilute
solution of double cyanide of mercury and potassium in such a manner
as to form an amalgam of white and brilliant silver adhering strongly
to the glass. To facilitate the operation and utilize all the silver,
while economizing the double cyanide, M. Lenoir has recommended the
following: Sprinkle the glass at the time when it is covered with the
mercurial solution with very fine zinc powder, which precipitates the
quicksilver and regulates the amalgamation.
II.—The metallurgy of silver also takes advantage of the property
of this {89} metal in combining cold with quicksilver; this for the
treatment of poor silver ores.
In the Saxon or Freiburg process for treating silver ores, recourse is
had to quicksilver in the case of amalgam in amalgamating casks, in
which the ore, after grinding, is shaken with disks of iron, and with
mercury and water. The amalgam, collected and filtered under strong
pressure, contains from 30 to 33 per cent of silver. It is distilled
either in cylindrical retorts of cast iron, furnished with an exit
tube immersed in the water for condensing the mercurial vapors, or on
plates of iron, arranged over each other along a vertical iron stem,
supported by a tripod at the bottom of a tank filled with water, and
covered with an iron receiver, which is itself surrounded with ignited
charcoal. It should be remarked that the last portions of quicksilver
in a silver amalgam submitted to distillation are volatilized only
under the action of a high and prolonged temperature.
«Applications of Gold Amalgams.»—I.—Gilding with quicksilver. This
process of gilding, much employed formerly, is now but little used.
It can be applied only to metals slightly fusible and capable of
amalgamation, like silver, copper, bronze, and brass. Iron can also be
gilded by this method, provided it is previously covered with a coating
of copper. To perform this gilding the surface is well cleaned, and the
gold amalgam, consisting of 2 parts of gold and 1 part of quicksilver,
prepared as mentioned before, is applied. The piece is afterwards
heated to about the red, so as to volatilize the mercury. The gold
remains, superficially alloyed with the metal, and forms an extremely
solid layer of deadened gold, which can be afterwards polished. The
volatilization should be effected under a chimney having strong
draught, in order to avoid the poisonous action of the mercurial vapors.
II.—The amalgamation of gold finds its principal applications in the
treatment of auriferous ores. The extraction of small spangles of gold
scattered in gold-bearing sands is based on the ready dissolution of
gold in quicksilver, and on the formation of an amalgam of solid gold
by compression and filtering through a chamois skin, in a state more or
less liquid. The spangles of gold are shaken with about their weight
of quicksilver, collected in the cavities of sluices and mixed with a
small quantity of sand. The gold is dissolved and the sand remains.
The amalgam thus obtained is compressed in a chamois skin, so as to
separate the excess of mercury which passes through the pores of the
skin; or, yet again, it is filtered through a glass funnel having a
very slender stem, with almost capillary termination. In both cases an
amalgam of solid gold remains, which is submitted to the action of heat
in a crucible or cast-iron retort, communicating with a bent-iron tube,
of which the extremity, surrounded with a cloth immersed in water,
is arranged above a receiver half full of water. The quicksilver is
vaporized and condensed in the water. The gold remains in the retort.
The property of gold of combining readily with quicksilver is also
used in many kinds of amalgamating apparatus for extraction and in the
metallurgy of gold.
In various operations it is essential to keep the quicksilver active
by preserving its limpidity. For this purpose potassium cyanide and
ammonium chloride are especially employed; sometimes wood ashes,
carbonate of soda, hyposulphite of soda, nitrate of potash, cupric
sulphate, sea salt, and lime; the latter for precipitating the soluble
sulphates proceeding from the decomposition of pyrites.
The amalgamation of gold is favored by a temperature of 38° to 45° C.
(100° to 113° F.), and still more by the employment of quicksilver
in the nascent state. This last property is the base of the Designol
process, which consists in treating auriferous or auro-argentiferous
ores, first ground with sea salt, in revolving cylinders of cast
iron, with iron and mercury bichloride, in such a way that the
mercury precipitated collects the gold and eventually the silver more
efficaciously.
«Gold Amalgam.»—Eight parts of gold and 1 of mercury are formed into an
amalgam for plating by rendering the gold into thin plates, making it
red hot, and then putting it into the mercury while the latter is also
heated to ebullition. The gold immediately disappears in combination
with the mercury, after which the mixture may be turned into water to
cool. It is then ready for use.
«Zinc Amalgam for Electric Batteries.»—Dissolve 2 parts of mercury in
1 part of aqua regia. This accomplished, add 5 parts of hydrochloric
acid. This solution is made warm. It suffices to dip the zinc to be
amalgamated into this liquid only for a few seconds. {90}
«Amalgam for Cementing Glass, Porcelain, Etc.»—Take tin 2 parts, and
cadmium 1 part. Fuse in an iron spoon or some vessel of the same
material. When the two materials are in fusion add a little mercury,
previously heated. Place all in an iron crucible and boil, agitating
the mass with a pestle. This amalgam is soft and can be kneaded between
the fingers. It may be employed for luting glass or porcelain vessels,
as well as for filling teeth. It hardens in a short while.
«Amalgam for Silvering Glass Balls.»—Lead, 25 parts; tin, 25 parts;
bismuth, 25 parts; mercury, 25 parts; or, lead, 20 parts; tin, 20
parts; bismuth, 20 parts; mercury, 40 parts. Melt the lead and the tin,
then add the bismuth; skim several times and add the mercury, stirring
the composition vigorously.
(See also Mirror-Silvering).
«Copper Amalgam.»—Copper amalgam, or so-called Viennese metal cement,
crystallizes with the greatest readiness and acquires such hardness on
solidifying that it can be polished like gold. The amalgam may also be
worked under the hammer or between rollers; it can also be stamped,
and retains its metallic luster for a long time in the air. In air
containing hydrogen sulphide, however, it quickly tarnishes and turns
black. A very special property of copper amalgam consists in that it
becomes very soft when laid in water, and attains such pliancy that
it can be employed for modeling the most delicate objects. After a
few hours the amalgam congeals again into a very fine-grained, rather
malleable mass. An important application of copper amalgam is that for
cementing metals. All that is necessary for this purpose is to heat the
metals, which must be bright, to 80–90° C. (176–194° F.), to apply the
amalgam and to press the metal pieces together. They will cohere as
firmly as though soldered together.
Copper amalgam may be prepared in the following manner:
Place strips of zinc in a solution of blue vitriol and agitate the
solution thoroughly. The copper thus obtained in the form of a very
fine powder is washed and, while still moist, treated in a mortar with
a solution of mercury nitrate. The copper powder thereby amalgamates
more readily with the quicksilver. Next, hot water is poured over the
copper, the mortar is kept hot, and the mercury added. Knead with the
pestle of the mortar until the copper, pulverulent in the beginning,
has united with the mercury into a very plastic mass. The longer the
kneading is continued the more uniform will be the mass. As soon as the
amalgam has acquired the suitable character—for its production 3 parts
of copper and 7 parts of mercury are used—the water is poured off and
the amalgam still soft is given the shape in which it is to be kept.
For cementing purposes, the amalgam is rolled out into small cylinders,
whose diameter is about 0.16 to 0.2 inches, with a length of a few
inches. In order to produce with this amalgam impressions of castings,
which are made after woodcuts, the amalgam is rolled out hot into a
thin plate and pressed firmly onto the likewise heated plaster cast.
After the amalgam has hardened the thin plate of it may be reinforced
by pouring on molten type metal.
«Silver Amalgam.»—Silver amalgam can easily be made with the help of
finely powdered silver. The mercury need only be heated to 250° to
300° C. (482° to 572° F.); silver powder is then sprinkled on it, and
mixed with it by stirring. The vessel is heated for several minutes
and then allowed to cool, the excess of mercury being removed from the
granulated crystalline amalgam by pressing in a leather bag. Silver
amalgam can also easily be made by dissolving silver in nitric acid,
evaporating the solution till the excess of free acid is eliminated,
diluting with distilled water, and adding mercury to the fluid in
the proportion of 4 parts, by weight, of mercury to 1 of the silver
originally used. The mercury precipitates the silver in a metallic
state, and immediately forms an amalgam with it; the fluid standing
above after a time contains no more silver, but consists of a solution
of mercury nitrate mixed with whatever copper was contained in the
dissolved silver in the form of copper nitrate. The absence of a
white precipitate, if a few drops of hydrochloric acid are added to a
sample of the fluid in a test tube, shows that all the silver has been
eliminated from the solution and is present in the form of amalgam.