Hydrogen, although a gas, is recognized by chemists as a metal, and when
combined with any solid metal--as in the case known to electricians as
the polarization of a negative element,--the compound may correctly be
termed an alloy; while any compound of hydrogen with the fluid metal
mercury may with equal correctness be termed an amalgam of hydrogen, or
"hydrogen amalgam." The efforts of many chemists and mining engineers
have for many years been devoted to a search for some effective and
economical means for preventing the "sickening" of mercury and its
consequent "flouring" and loss. Some sixteen or more years ago,
Professor Crookes, F.R.S., discovered and, after a series of
experiments, patented the use of an amalgam of the metal sodium for this
purpose. He made the amalgam in a concentrated form, and it was added
in various proportions to the mercury used for gold amalgamation. Water
becoming present, it will readily be understood that the sodium, in
being converted into the hydrate (KHO) of that metal, caused a rapid
evolution of hydrogen. The hydrogen thus evolved was the excess over a
certain proportion which enters into combination with the mercury. While
the mercury retained the charge of hydrogen, the "quickness" of the
fluid metal was preserved; but upon the loss of the hydrogen the
"quickness" ceased, and the mercury was acted upon by the injurious
components contained in the ore.
Since the introduction of the sodium amalgam, many attempts have been
made, more especially in America, to overcome the tendency of mercury to
"sicken" and lose its "quickness." The greater number of these efforts
have been made by the use of electricity as the active agent in
attaining this end; but such efforts have been generally of a crude and
unscientific character. Latterly Mr. Barker, of the Electro-amalgamator
Company, Limited, has introduced a system--already detailed in these
pages--by which the mercury is "quickened." In his method the running
water passing over the tables, or other apparatus of a similar
character, is used as the electrolyte. In this arrangement, the mercury
being the cathode, plates or wires of copper constituting anodes are
brought into contact with the water passing over the mercury in each
"riffle." Both the cathode and the anodes are, of course, maintained in
contact with the poles of a suitable source of electrical supply. The
current then passes from the copper anode through the running water
to the mercury cathode, and so on to the negative pole of the
electro-motor. As a consequence of this arrangement, hydrogen is evolved
from the water, and has the effect of reducing any oxide or other
detrimental compound of the metal; in other words, it "quickens" and
prevents "sickening" of the fluid metal, and consequent "flouring" and
loss. While the hydrogen is evolved at the cathode, oxygen enters into
combination with the copper constituting the anodes. This to some extent
impairs the conductivity of the circuit.
The latest process, however, is that of Mr. Bernard C. Molloy, M.P.,
which we have already characterized as highly scientific and effective,
the production of a suitable amalgam being obtained under the most
economical and simple conditions. This process has the advantage of
producing not only a hydrogen amalgam, but also at will an amalgam of
hydrogen combined with any metal electro-positive to this latter. Thus
hydrogen potassium or hydrogen sodium can be obtained, as will be seen
by the following description.
Mr. Molloy's effort appears to have been, in the first place, directed
to a system which could be adapted to any existing apparatus, and in
certain cases where water was scarce, to avoid altogether the use of
that, in some districts, rare commodity. For the purpose of explanation
we select an ordinary amalgamating table fitted with mercury riffles.
The surface of the table is in no way interfered with or disturbed. The
bed of the riffle, however, is constructed of some porous material, such
as leather, non-resinous wood, or cement, which serves as the diaphragm
upon which the mercury rests, and separates the fluid metal from the
electrolyte beneath. Running the full length of the table is a thin
layer of sand, supported and pressing against the diaphragm, and lying
in this sand is the anode, formed preferably of lead. A peroxide of
that metal is formed by the action of the currents, and may be readily
reduced for use over and over again after working for from one to three
months. The peroxide of lead, as is well known, is a conductor of
electricity, and this fact constitutes an important advantage in the
working of the process. The thin layer of sand is saturated with an
electrolyte, such as dilute sulphuric acid (H_{2}SO_{4} + 20H_{2}O)
to give a simple hydrogen amalgam; (Na_{2}SO_{4} + xH_{2}O) to give a
hydrogen sodium amalgam; or (K_{2}SO_{4} + xH_{2}O) to give a hydrogen
potassium amalgam. Numerous other electrolytes constituted by acids,
alkalies, and salts can be used to form an amalgam permanently
maintained in a condition of "quickness" and freed from all liability
to "sicken," whatever the components of the ore may be. The mercury
is connected with the negative pole of the voltaic battery or other
electro-motor, and the lead made with the positive pole of the same
source. When the current passes there is formed according to the nature
of the electrolyte, a hydrogen amalgam, or an amalgam of hydrogen with a
metal electro-positive to hydrogen. The electrolyte, which, it will be
understood, is distinct and apart from the body of water passing over
the table, will last almost indefinitely, there being no consumption of
any of its constituents, excepting hydrogen and oxygen from the water
of solution. The quantity of acid or saline material contained in the
electrolyte is so very small that there can be no difficulty in finding
a supply in any district. The question of the supply of electricity is
one which in many mining districts involves considerations of practical
importance, since a large supply would necessitate water or steam power.
It has been found that two cells having an electromotive force of about
two volts each will in this process suffice; if preferred, however,
a very small dynamo machine can be used. In connection with the
electro-motive force it is requisite to use, it may be observed that an
amalgam of sodium containing only a small quantity of this metal would,
when constituting a positive element in conjunction with a lead negative
and on an aqueous electrolyte, give an opposing electro-motive force of
less than three volts. Such an amalgam could therefore be obtained under
an electro-motive force of about four volts. The electrical resistance
in the circuit constituted by the apparatus being very small, no
electrical power is wasted. When water constitutes the electrolyte, as
in Barker's system, then the electro-motive force required to obtain a
given current would be very much greater than that above specified.
The conditions assured under this process appear to be all that can
be required, while the amalgams obtained are those most calculated to
preserve the "quickness" and prevent the "sickening" of the mercury.
Mr. Molloy has designed a special form of amalgamating machine to be
used in conjunction with the above process, and with or without the aid
of water. By the employment of this machine, each particle of the ore
is slowly rolled in the quickened mercury for from fifteen to thirty or
more seconds.
When the extent of the gold and silver mining industries is considered,
and when it is borne in mind that a considerable percentage of the
precious metal present in the ore is, in the ordinary process of
extraction, lost through defective amalgamation--due to insufficient
contact with the mercury or to a total absence of contact, as in the
case of float gold--it is obvious that the introduction of any system
obviating such loss is a matter of very great importance to those who
are interested in the above mentioned industries. We expect shortly to
hear of the practical introduction on a large scale of Mr. Molloy's
process, and we look forward with interest to the results which may be
obtained from it.--_The Engineer_.
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