THE LIBRARY

THE UNIVERSITY

OF CALIFORNIA

DAVIS

CALIKORXIA STATE NIINING BUREAU.

J. J. CRA'WFORD, State Mineralogist.

BULLETIN NO. 5.

San Francisco, October, 1894.

THE

CYANIDE PKOCESS

ITS

PRACTICAL APPLICATION AND ECONOMICAL RESULTS.

By dr. a. SCHEIDEL, E.M.

SACRAMENTO:

STATE OFFICE, : : : A. J. JOHNSTON, SUPT. STATE PRINTING.

1894.
LIBRARY

UNIVERSITY or CALIFORNIA
DAVIS

San Fkancisco, October 1, 1894.

Hon. J. J. Crawford, State Mineralogist, San Francisco, Calif.:

Dear Sir: In accordance with your letter of December 8, 1893, I
herewith submit my report on the cyanide process. I have endeavored
to describe that process in its practical application and economical
results. The information it conveys includes my own experience, and
is supplemented from articles which appeared in technical periodicals;
also from the records of patents granted by the Patent Offices of the
United States and Great Britain, and from the Blue Books issued by
the Mining Departments of the British Colonies of Australasia. I am
largely indebted for special communications received from metallurgists
in charge of prominent companies and important works, and from the
officers of the government mining departments of the Australian Colo-
nies. It has seemed advisable with some " improvements," and generally
with the patents, to simply place them on record without any special
comment.

Respectfully yours,

A. SCHEIDEL, Ph.D., E.M.

THE CYANIDE PROCESS

ITS

PRACTICAL APPLICATION AND ECONOMICAL RESULTS.

By A. ScHEiDEL, Ph.D., E.M.

The "cyanide process" for extracting gold and silver from ores is
based on the fact that a diluted solution of potassium cyanide dissolves
these metals, forming, respectively, auro-potassic cyanide and argento-
potassic cyanide, from many ores, without dissolving to any material
extent the other components thereof. The process consists of treating
suitable ores, when finely divided, with a weak solution of potassium
cyanide, either by allowing the solution to percolate through the ore or
by agitating a mixture of the ore and solution. This part of the opera-
tion being completed, the solution is separated from the solid material
and the gold and silver are precipitated in metallic form. This process
for the extraction of gold and silver is comparatively old in its principle,
but modern in its technical application. During the last four years it
has been introduced into almost every gold field, and upwards of
$14,000,000 in gold and silver have been recovered by the process, which
demonstrates beyond doubt that it is one of the most important additions
to the wet methods of gold and silver metallurgy. The aim of this
paper is to present the history of the process and to describe the ores for
which it is adapted, together with their preparation and manipulation
during treatment. The economical features of the cyanide process are
also dwelt on at some length. The text is illustrated by plans and
diagrams.

The State Mining Bureau of California was among the first in the
United States to investigate the merits of the cyanide process, as set forth
in a paper by Dr. W. D. Johnston, in the Xth Report of the Bureau. The
process has since found extensive application, and other valuable and
interesting papers have been published, but an exact account of the
methods employed in all parts of the world is still wanting. This writing
is undertaken at the request of Hon. J. J. Crawford, State Mineralogist of
California. The facts herein recorded are obtained from the practical
experience of the writer in New Zealand and the United States, and of
others who have been very successful in the application of the cyanide
process. I take great pleasure in expressing my sincere appreciation of
and gratitude for the assistance my contributors have extended. I desire
especially to acknowledge my obligation to Mr. John S. MacArthur, of
Glasgow, Scotland, and to Mr. J. M. Buckland, the general manager of
the African Gold Recovery Company, Lim., in Johannesburg, South
African Republic. In order to allow a comparatively full description of
methods and appliances, in the following pages, theoretical matter is
limited to the main chemical reactions incidental to the* process, and an
explanation of some of the difficulties most frequently met. To facili-
tate the consultation of the paper, I prefix the following synopsis:

6 THE CYANIDE PROCESS.

I. History of process: Solubility of gold and silver in cyanide as
known to Hagen, Bagration, Eisner, Faraday; its technical
application by Wright and Elkington; its metallurgical appli-
cation by Rae, Simpson, Endlich and Miihlenberger, Louis
Janin, Jr., Dixon, MacArthur and Forrest, Molloy, A. Janin and
Merrill, W. D. Johnston.
II. Scope of process.

III. Chemistry of process.

IV. Demonstration of the process. Methods of operation:

A. The agitation process.

B. The percolation process.

(o) Percolation of ores.

(6) Percolation of tailings.

(c ) Percolation of concentrates.

C. Cyanide and cyanide solutions.

D. Treatment of the gold solutions. Recovery of the gold and silver.

(a) Precipitation by zinc.

(b) The Molloy process.

(d) The Pielsticker process.

(e) The Moldenhauer process.
(/) The Johnston process.

V. Percentage of extraction.

VI. Working costs of process.

VII. Cost of cyanide plants.

VIII. Machinery and appliances.

IX. Laboratory work.

X. Danger in working the process.

XL Exemplification of the process. The process in various countries:

A. Africa.

B. Australasia. ,

(a) New Zealand.
(&) Tasmania.

(c ) Western Australia.

(d) South Australia,
(c) Queensland.

(/) New South Wales.
ig) Victoria.

C. United States of America.

(a) Utah.
(6) Montana.

(d) Nevada.

(e) Arizona.

If) New Mexico.

\g) South Dakota. ^

{h) California.

D. Mexico, Colombia, Straits Settlements, Russia, Borneo.

XII. Summary and conclusions.
XIII. Patents:

Julio IT. Rae. Improved mode of treating auriferous and argentiferous
ores. U. S. patent 61,866, dated February 5, 1S67.

Thomas C. Clark. Extracting precious metals from ores. U. S. patent
229,586, dated July 6, 1880.

Hiram W. Faucett. Process of treating ore. U. S. patent 236,424, dated
January 11, 1881.

John F. Sanders. Composition for dissolving the coating of gold in ore.
U. S. patent 244,080, dated July 12, 1881.

Jerome W. Simpson. Process of extracting gold, silver, and copper from
their ores. U. S. patent 323,222, dated July 28, 1885.
^ John Stewart MacArthur, Robert Wardrop Forrest, M.D., and William
Forrest, M.B. Improvements in obtaining gold and silver from ores and other
compounds. English patent 14,174; 1887.

THE CYANIDE PROCESS. •

XIII. Patents (continued):

John Stewart Mac Arthur, Robert Wardrop Forrest, and William Forrest
Process of obtaining gold and silver from ores. U. S. patent 403,202, dated
May 14, 1889.

John Stewart MacArthur. Metallurgical filter. U. S. patent 418,138, dated
December 24, 1889.

John Stewart MacArthur, Robert Wardrop Forrest, and William Forrest.
Process of separating gold and silver from ores. U. S. patent 418,137, dated
December 24, 1889.

Edward D. Kendall. Composition of matter for the extraction of gold and
silver from ores. U. S. patent, dated September 13, 1892.

Bernard Charles Molloy. Improvements in precipitating and collecting
metals from solutions containing them. English patent 3,024; 1892.

John Cunninghame Montgomerie. Improvements in the extraction of
gold and silver from ores or compounds containing the same, and in appa-
ratus applicable for use in the treatment of such materials by means of
solvents. English patent 12,641; 1892.

John Stewart MacArthur and Charles James Ellis. Improvements in ex-
tracting gold and silver from ores and the like. New Zealand paten t-speciti-
cation, June 29, 1893.

Carl Moldenhauer. Improvements in recovering gold and other precious
metals from their ores. ISIew Zealand patent-specihcation, August 31, 1893.

Carl Pielsticker. Improvements in the extraction of gold and silver from
ores. New Zealand patent-specification, December 14, 1893.

Alexis Janin and Charles W. Merrill. Process of leaching ores with solu-
tions of alkaline cyanides. U. S. patent 515,148, dated February 20, 1894.

William David Johnston. Method of abstracting gold and silver from their
solutions in potassium cyanides. U. S. patent 522,260, dated July 3, 1894.

XIV. List of plans, diagrams, and tables:

Details of the false bottoms of the percolation vats. (W. R. Feldtmann.)
Plant to treat a minimum of 2,000 tons per month. (MacArthur.)
'Table giving sizes and material of percolation vats. (A. Scheidel.)
Zinc box. (MacArthur.)
Zinc filter. (A. Scheidel.)
Porcelain filter. (A. B. Paul.)

Table giving extraction results on various ores. (A. Scheidel.)
Discharging tailings-vats at the Langlaagte Estate Company's plant.

(W. R. Feldtmann.)

Square filter vats at the works of the Crown Company, with doors for the

discharging trucks. (Irvine.)
Variation No. 1 in designs of cyanide plants. (W. R. Feldtmann.)
Variation No. 2 in designs of cyanide plants. (W. R. Feldtmann.)
Variation No. 3 in designs of cyanide plants. (W. R. Feldtmann.)
Side discharge at percolation vats. (W. R. Feldtmann.)
Bottom discharge at percolation vats. (Chas. Butters.)
Bottom discharge at percolation vats. (W. E. Irvine.)
The cyanide works of the Robinson Company. (Chas. Butters.)
The cyanide plant of the Crown Company. (John MacConnell.)
The Sylvia Company's Cyanide Works, Tararu, Thames, New Zealand. (A.

Scheidel.)

Melting room for cyanide bullion in the Sylvia Company's Works, Tararu,

New Zealand. (A. Scheidel.)
The tailings cyanide works at Waihi. (A. James.)
The concentrating and cyanide extraction works of the Sylvia Gold and

Silver Mining Company. (A. Scheidel.)
The cyanide plant of the Sylvia Company (plan and longitudinal section).

(A. Scheidel.)
Table showing the concentrating and cyanide process in the works of the

Sylvia Company. (A. Scheidel.)
Bullion furnace. (A. Scheidel.)

Wet-mill cyanide plant, Revenue. (F. B. & R. B.Turner.)
Dry-mill cyanide plant. Revenue. (F. B. & R. B. Turner.)
U tica Company cyanide plant (plan and longitudinal section). (A. Scheidel.)
The vacuum filter, Utica cyanide plant. (A. Scheidel.)
The bullion filter, Utica cyanide plant. (A. Scheidel.)
Agitator. (J. H. Rac.)
Metallurgical filter. (J. S. MacArthur.)

Apparatus for treatment of ores, etc., by means of solvents. (J. C. Mont-
gomerie.)

Improved apparatus for the extraction of gold and silver from ores. (C. M.

Pielsticker.)
Table giving analysis of gold production in the Witwatersrand District for

April, 1894. (Witwatersrand Chamber of Mines.)

; THE CYANIDE PROCESS.

XV. List of abbreviations of literature:

E. & M. J. — Engineering and Mining Journal, New York.

M. I. — Mineral Industry.

M. S. P. — Mining and Scientific Press.

Tr. A. I. M. E. — Transactions of the American Institute of Mining Engineers.

J. S. Chem. I.— Journal of .Society of Chemical Industry, England.

J. fr. Chem. — Journal fiir practische Chemie.

J. Ch. S. — Journal Chemical Society.

Tr. Phil. Soc. — Transactions of the Philosophical Society.

M. Sc. — Moniteur Scientifique.

A. Ch. Ph.— Annales de Chimie et de Physique.
Ch. N. — Chemical News.

B. A. I. Sc. — Bulletin de I'Acad^mie Imperiale des Sciences de St. Peters-
bourg.

B. S. Ch. — Bulletin de la Society Chimique de Paris.

HISTORY.

I. HISTORY.

The fact of gold being soluble in cyanide of potassium solution has
been known for a considerable time. Hagen is reported to have men-
tioned it in 1806. Dr. Wright, of Birmingham, England, used gold-
cyanide solution for electroplating in 1840j he made this application in
consequence of his studies of Scheele's report on the solubility of gold-
cyanide in a cyanide of potassium solution. J. R. & H. Elkington
patented Wright's invention; they speak in tbeir patent-specification of
a boiling solution of gold or cyanide of gold in prussiate of potash.
The first record in scientific literature of experiments in which metallic
gold was dissolved in a cyanide of potassium solution consists in Prince
Pierre Bagration's paper in the Bulletin de I'Academie Imperiale des
Sciences de St. Petersbourg, 1843, t. 11, p. 136. Bagration, who alludes
to Elkington's process, preserved cyanide of potassium solution in a
dish, gilded on the inside. He noticed that after eight days the whole
gold surface had been attacked. He experimented then with finely
divided gold under the influence of the galvanic current; the latter he
soon recognized as not of any benefit in the dissolving process. He pre-
cipitated the gold out of the cyanide solution by means of the electric
current on a cathode of copper. Continued experiments proved the
advantage of higher temperature during the dissolving process, and
taught the precipitation of gold from its still warm solution by means
of silver or copper plates, without the electric current. The higher tem-
perature had, however, the disadvantage of the silver and copper being
strongly attacked by the cyanide solution during the precipitation process.
Bagration extended his experiments to solutions of ferroeyanide, which he
found to act like cyanide, but in a much less degree. He further studied
the solubility of gold in the form of plates, in cyanide, and found it to be
dissolved in such form at a considerable rate at a temperature of 30° to
40° C. He noticed the influence of the air on the reaction. Bagration
believes that hydrocyanic acid in a state of generation is a gold solvent,
and he concludes his paper with the remark that in the future, cyanide
of potassium must be enumerated among the solvents of gold. L. Eisner
published in J. fr. Chem., 1844, p. 441, his observations on the reactions
of "reguline metals" in an aqueous solution of cyanide. He found that
gold and silver were dissolved in potassium cyanide without decomposi-
tion of water. "The dissolution of the metals is, however, the conse-
quence of the action of oxygen, which, absorbed from the air, decomposes
part of the cyanide." His reaction has been expressed by others in the
following equation:

2 Au + 4 KCy + -f H2O =

2 AuKCya -f 2 KOH

(Gold.) (Cyanide (Oxygen.) (Water.)
of potassium.)

(Auro-potassic (Potassic
cyanide.) hydrate.)

It is generally called Eisner's equation. Some years after, Faraday
made use of the solubility of gold in cyanide solution for reducing the
thickness of gold films (Exp. relations of gold and other metals to light,
Tr. Phil. Soc, 1857, p. 147). The basis of the most modern process
for the extraction of gold was thus provided. It took many years,
however, before the enumerated facts* were made use of for the extrac-
tion of gold from ores. In 1867, Julio H. Rae took out United States
patent No. 61,866, dated February 5th, for an "improved method of

JO THE CYANIDE PROCESS.

treating auriferous and argentiferous ores " with a current of electricity
in connection with suitable liquids — such, for instance, as cyanide of
potassium. Rae's process is an agitation process; he proposed to " expose
the auriferous or argentiferous rock to the combined action of a current
of electricity and of suitable solvents, and to separate the gold or silver
from the rocks containing the same by the action or aid of electricity."
The principle of Rae's process, as stated by him, distinguishes his
method from the modern cyanide process. His method does not appear
to have advanced beyond the laboratory stage or to have found exten-
sive and successful practical application, and it sank into oblivion.
Since then, cyanide of potassium in connection with gold and silver
metallurgy has repeatedly been made a patent claim; in many cases,
however, the application recommended is in its principle different from
the application which characterizes the modern cyanide process. Thomas
C. Clark, of Oakland, Cal. (United States patent No. 229,586, July 6,
1880), roasted his ore to a red heat, and placed it in that condition in a
cold bath composed of a solution of salt, prussiate of potash, and caustic
soda. H. W. Faucett, of St. Louis, Mo. ( United States patent No. 236,424,
January 11, 1881), subjects hot crushed ores to the action of disintegrat-
ing chemicals, cyanide of sodium among others, in solution under
pressure, the pressure being effected by the steam generated by the con-
tact of the hot ores with the chemical solution in a closed vessel. This
treatment, like that proposed by Clark, was intended as preliminary to
amalgamation. John F. Sanders, of Ogden, obtained United States
patent No. 244,080, dated July 12, 1881, for "composition for dissolving
the coating of gold in ore." This composition is made of cyanide of
potassium and glacial phosphoric acid. He stated that by using this
mixture he could dissolve " the impure coatings of gold, leaving the gold
free and exposed, and permitting it to be amalgamated." It is evident,
therefore, that these processes bear no similarity or relation to the
modern cyanide process. For a considerable time, cyanide of potassium
has been used in the gold fields of California and Australasia for remov-
ing film-coating from gold in ores; its application in the pan-amalga-
mation process may have been a source of loss of gold.

The application of a cyanide of potassium solution for the extraction
of gold and silver direct from their ores, which application had
been neglected since Rae, was taken up again by Jerome W.
Simpson, of Newark, N. J., who obtained United States patent No.
323,222, dated July 28, 1885, for a process of extracting gold, silver,
and copper from their ores. Simpson reduced his ore to a powder and
agitated it with a solution of certain salts, which combine chemically
with the metal in the ore and form therewith a soluble salt. The
salt solution was composed of one pound of cyanide of potassium, one
ounce of carbonate of ammonia, one half ounce of chloride of sodium,
and sixteen quarts of water. This solution is described as particularly
adapted to ores containing gold, silver, and copper in the form of sul-
phurets. In the absence of silver no chloride of sodium is used; for
ores rich in silver a proportionately larger quantity of chloride of
sodium is employed. The metals dissolved in the salt solution were
precipitated by means of zinc, suspended therein in form of pieces or
plates. Simpson was aware that^ cyanide of potassium, in connection
with an electric current, had been used for dissolving metal, and also
that zinc had been employed as a precipitant. What he claims as new

HISTORY. 1 1

is: (1) The process of separating gold and silver from their ores, which
consists in subjecting the ore to the action of the solution of cyanide of
potassium and carbonate of ammonia, and subsequently precipitating
the dissolved metal by means of zinc. (2) The process of separating
metals from their ores, to wit, "subjecting the ore to the action of a
solution of cyanide of potassium, carbonate of ammonia, and chloride of
sodium, and subsequently precipitating the dissolved metals."

My own experiments have proved that the addition of sodium chlo-
ride is of no benefit for the extraction of silver. The addition of ammonium
carbonate is not beneficial to the extraction of either gold or silver,
except under certain conditions, when it may be substituted advanta-
geously by an alkali or an alkaline earth; in the presence of base metals
it is of disadvantage. Simpson's patent description appears to indi-
cate that he had not discovered the most important property of
dilute cyanide solutions, namely, that of dissolving, without the addi-
tion of other chemicals, the noble (in preference to the base) metals.
His patent-claim consists eminently in adding to the cyanide solution
the chemicals mentioned above. His process, like that of Rae, is an
agitation process. The zinc for precipitating the bullion he used in the
form of plates or pieces. There is no record in the technical literature
in reference to the application of Simpson's process before the issue of
the MacArthur and Forrest patents in 1889. After Rae and Simpson,
others have made experiments with cyanide solutions for the purpose of
gold and silver extraction from ores. F. M. Endlich and N. H. Miihlen-
berger are reported to have filed a caveat in 1885, without, however,
securing a patent, the former having apparently become doubtful as to
the applicability of cyanide as an economical process (E. & M. J.,
1891, p. 86). Louis Janin, Jr., made interesting experiments in the
same direction in Park City, Utah, of which he published the results
in 1888 (E. & M. J., 1888, p. 548). These experiments refer chiefly
to silver extraction, but he mentions as well the results on gold ores;
his results appear to have been encouraging, and led to his filing a caveat
on May 1, 1886, but this was not pushed on to the taking out of a patent.

In the southern hemisphere, W. A. Dixon has made experiments with
cyanide on Australian ores as early as 1887. He recorded his results,
which are at least of historical interest, in a paper read before the Royal
Society of New South Wales. Dixon describes therein the experiments
made by him at the instigation of the Government Inspector of Mines,
who suggested that the extraction of gold from complex minerals was a
subject worthy of investigation. Dixon tried on such ores amalgama-
tion and a number of solvents. He found "the aurocyanides of the
alkaline metals of sufficient stability to render their use possible for the
extraction of the gold." He mentions Bagration's and Eisner's publi-
cations and alludes to Rae's patent, of which, however, he possessed no
particulars. Dixon feared that "the high price of cyanide, its insta-
bility when exposed to the air, and its extremely poisonous qualities,"
would prove such obstacles as to preclude its use for metallurgical pur-
poses. He found the reaction between gold and cyanide slow if " the
gold was at all dense"; in presence of alkaline oxidizing agents, how-
ever, he found the dissolving process suflliciently rapid. Dixon experi-
mented also with the ferrocyanide of potassium. His results generally,
did not, as far as known, lead to the metallurgical application of
cyanide as a gold and silver solvent.

12 THE CYANIDE PROCESS.

T have thus described the history of cyanide of potassium .as a gold
dissolving agent from the early laboratory experiments up to its metal-
lurgical application for ore extraction; this latter, however, did not gain
any practical importance until John S. MacArthur and W. Forrest, of
Glasgow, Scotland, took out their patents for the use of cyanide as a
gold and silver solvent from ores, and gave thereby the cyanide process
a start all over the world. Their patents mark an epoch in gold
metallurgy. The results of the application of cyanide, as suggested by
them, have been very satisfactory; the $14,000,000 of bullion pro-
duced by it during the five short years of its working represents what,
by the ordinary methods, would have been irrecoverably lost; hence its
value and importance from the standpoint of metallurgy and political
economy. The experiments of MacArthur and Forrest with gold dissolv-
ing reagents occupied some years before their English cyanide patents
were applied for (J. S. MacArthur, J. S. Chem. I., March 31, 1890, No. 3,
vol. 9). They drew out a list of possible solvents having a stronger
affinity for gold than for sulphides, which included the cyanides, and
which they found to solve the problem. Their experiments, conducted
first on a small scale and with ores of many kinds and of different
sources, were so satisfactory that they gradually worked on a larger scale,
and their results formed the basis for the introduction of the cyanide
process into most gold-producing fields. Their English patent was
applied for October 19, 1887. Since then they applied for and obtained
patents in many gold-producing countries. Their United States patents
are dated as follows: 403,202, May 14, 1889; 418,137, December 24, 1889;
418,138, December 24, 1889. Their invention is described "as having
principally for its object the obtaining of gold from ores, but it is also
applicable for obtaining silver from ores containing it whether with or
without gold, and it comprises an improved process, which, while appli-
cable to auriferous and argentiferous ores generally, is advantageously
and economically effective with refractory ores, or ores from which gold
and silver have not been satisfactorily or profitably obtainable by the
amalgamating or other processes hitherto employed; such as ores con-
taining sulphides, arsenides, tellurides, and compounds of base metals
generally, and ores from which the gold has not been easily or completely
separable on account of its existing in the ores in a state of extremely
j&ne division." The patentees describe their invention (I am following
United States patent 403,202) as consisting in subjecting the ores to the
action of a solution containing a small quantity of cyanide, without any
other chemically active agent. In dealing with ores containing per ton
twenty ounces or less of gold or silver, or gold and silver, they find it
most advantageous to use a quantity of cyanide, the cyanogen of which
is equal in weight to from one to four parts for every thousand parts of
the ore dissolved in a quantity of water of about half the weight of the ore ;
they generally use a solution containing two parts of cyanogen for every
thousand parts of the ore. In the case of richer ores, while increasing the
quantity of cyanide to suit the greater quantity of gold or silver, they also
increase the quantity of water so as to keep the solution dilute; in other
words, the cyanide solution should contain from two to eight parts, by
weight, of cyanogen to one thousand parts of water, and the quantity
of the solution used should be determined by the richness of the ore.
The patentees state: "By treating the ores with the dilute and simple
solution of a cyanide, the gold or silver is, or the gold and silver are,

HISTORY. 13

obtained in solution, while ahy base metals in the ores are left undis-
solved except to a practically inappreciable extent; -whereas, when the
cyanide is used in combination with an electric current, or in conjunc-
tion with another chemically active agent, such as carbonate of ammo-
nia, or chloride of sodium, or phosphoric acid, or when the solution
contains too much cyanide, not only is there a greater expenditure of
chemicals in the first instance, but the base metals are dissolved to a
large extent along with the gold or silver, and their subsequent separation
involves extra expense, which is saved by their process." Later on
MacArthur and Forrest obtained patents covering the use of zinc in a
fine state of division for the purpose of precipitating gold and silver
from cyanide, chloride, bromide, thiosulphide, sulphate, or other similar
solutions; they further protected the use of an alkali or alkaline earth
for neutralizing ores preparatory to subjecting the same to the action of
cyanogen or of a C3'anide. The MacArthur-Forrest patent-claims con-
sist, therefore, in three points: (1) The application of diluted solutions
of cyanide (not exceeding eight parts of cyanogen to one thousand parts
of water); (2) the use of zinc in a fine state of division; (3) the pre-
paratory treatment of the ore, which has become partially oxidized by
exposure to the weather, with an alkali or alkaline earth, for the purpose
of neutralizing the salts of iron or other objectionable ingredients formed
by partial oxidation.

It is not the purpose of this paper, which is intended to describe the
historical development of the cyanide process and its present forms of
application, to enter into a judicial discussion of patent-claims and
patent-rights. It is the duty of the historian to date the cyanide
process as a commercial success from 1890, when it was introduced as
"the MacArthur-Forrest process" on the Witwatersrand gold fields, in
the South African Republic. Its success as a metallurgical experiment
may be dated from the tests made on a large scale with ore from the New
Zealand Crown Mine in June and July, 1888. The practicability of
the cyanide process once established, others endeavored to introduce
improvements in its application, which they protected by letters patent.
A patent which once promised to become of practical importance is that
of B. C. MoUoy, of Johannesburg, whose "improvement" consists in the
abolition of zinc as a precipitant of gold, and in the revivification of the
cyanide of potassium in the solution. In this process the ore is treated
with cyanide of potassium as usual; the resulting liquors are passed
through a "patent Molloy separator," which consists of an amalgama-
tor, the mercury of which is constantly being charged electrolytically
with potassium. The potassium on coming into contact with the water
of the solution decomposes it with the evolution of hydrogen and the
formation of the oxide of the alkaline metal. The nascent hydrogen
decomposes the solution of the cyanide of gold, and sets the gold free,
which is precipitated upon and collected by the mercury; the metal of
the alkaline oxide reacts upon the cyanogen compound, and so repro-
duces the cyanide of potassium. The original solution, thus regenerated,
is then ready for use again. (In reference to further details see under
precipitation of gold and silver, p. 38.)

Among other cyanide patent-specifications may be mentioned the fol-
lowing: John C. Montgomerie, of Scotland, obtained English patent No.
12,641,1892, "for improvements in the extraction of gold and silver
from ores and in apparatus applicable for use in the treatment of such

14 THE CYANIDE PROCESS.

by means of solvents." His process is the well-known agitation process
of finely divided ore with cyanide solution and the addition of an alka-
line oxide " for the purpose of economizing the solvent and expediting
its action." The patent-specification does not contain any claims which
might be termed either an invention or an improvement, either chemic-
ally or mechanically. One of the latest additions to the cyanide patent
literature is United States patent 515,148, dated February 20, 1894, of
Alexis Janin and Charles W. Merrill, for a process of leaching ores with
solutions of alkaline cyanides. (For patent-specification, see Appendix.)
They claim as new " the art of leaching ores with solution of alkaline
cyanides, which consists in first leaching the- ore with such solutions,
then adding to the solution an agent which will precipitate the silver
present as a sulphide, and then precipitating the gold in the solution
with metallic zinc." The practical advantages of this complication will
have to be proved.

A patent description of interest, although not a " cyanide process "
strictly speaking, is that of E. D. Kendall, of Brooklyn, N. Y., dated
September 13, 1892, who claims the use of potassium ferrocyanide com-
bined with cyanide of potassium, for extracting gold and silver from
ores, etc., as his invention. (For patent-specification, see Appendix.)

A further addition to the patent literature is the specification of Mac-
Arthur and Ellis, who propose to increase the efficiency and economy of
the process in cases in which from the nature of the ores treated or other
circumstances, soluble sulphides are formed, which retard and objec-
tionally affect the action of the cyanide on the precious metals by adding
to the ore or the cyanide solution suitable salts or compounds of metals
which will form with the sulphur of the soluble sulphides an insoluble
or inert sulphide. For this purpose preference is being given to the
metallic salts or compounds in the following order: Salts or compounds
of lead — such as plumbates. carbonates, acetate or sulphate of lead —
sulphate or chloride of manganese, zincates, oxides, or chloride of
mercury, ferric hydrate or oxide. The proportion to Idc used is easily
to be ascertained by trials of a few samples in each case. (See patent-
specification of John Stewart MacArthur and Charles T. Ellis, in Ap-
pendix.)

C. Moldenhauer proposes to render the cyanide process more expedi-
tious and considerably cheaper by, firstly, adding to the cyanide solution
an artificial oxidizing agent, by preference ferricyanide of potassium in
alkaline solution, and, secondly, in precipitating the extracted precious
metal out of its cyanide solution by means of aluminium, or alloys, or
amalgam thereof. (See patent-specification in Appendix.)

C. M. Pielsticker reverts to the application of the electric current, in
conjunction with the cyanide solution. He proposes to continuously
circulate the solvent, to continuously precipitate the dissolved precious
metals by electrolysis, and continuously regenerate thereby the reagent.
(See patent specification in Appendix.)

The latest patent in connection with cyanide treatment of ores is that
of Dr. W. D. Johnston, "for abstracting gold and silver from their
cyanide solutions by means of pulverized carbon" (for further details,
see page 40).

To make this report as complete as circumstances permit, I append
the specifications of the patents which have been mentioned in the body

SCOPE OP PROCESS. 15

of this paper, that the mining public may know the exact wording of
descriptions and claims.

Such is the history of the cyanide process, rapidly sketched by tracing
its development through the phases of its evolution and the intricacies
of its patent literature. The modern cyanide process consists in the
treatment of ores by means of dilute cyanide of potassium solutions, as
a rule without the addition of other chemical substances, and in the
subsequent precipitation of the gold and silver from the solution by
means of zinc in form of shavings. It is commonly known as the Mac-
Arthur- Forrest process. I now propose to enter into a description of the
process itself. I embody in it the information given me by Mr. John S.
MacArthur, of Glasgow, Scotland.

II. SCOPE OF PROCESS.

The process can be advantageously applied to many gold ores and
many silver ores, and is often suitable for ores which are generally con-
sidered as rebellious or refractory. The word " ore '' is here meant to
include ores, tailings, concentrates, ajid all similar products from ore.
The term "refractory" is used to signify any ore which cannot be satis-
factorily amalgamated. The refractory character of such ores can be
caused by the presence of base metals in combination with sulphur or
arsenic, or otherwise by their physical structure, which prevents the gold
from coming in contact with the mercury during the amalgamation
process. To the latter class belong the ores in which the gold is "coated"
with substances which prevent metallic contact ("rusty gold"). (An
excellent instance of such coated ore is that found in the Mount Morgan
Mine, in Queensland, where the finely divided gold is coated with a film
of what has been termed hydrous peroxide of iron, which makes the
gold absolutely refractory to amalgamation.) To the same class of
refractory ores belong those in which the gold is so finely divided that
the film of air surrounding the auriferous particles prevents amalgama-
tion even under the most favorable conditions. The base metals which
most frequently accompany refractory ores are iron, zinc, lead, copper,
and antimony — usually as sulphides, sometimes as arsenides. When
ores containing gold, silver, copper, zinc, iron, etc., are treated with solu-
tions of cyanide of potassium, these metals are dissolved more or less,
forming soluble cyanides. The solvent action on the base metals can
be reduced to a minimum by reducing the strength of the solutions, the
readily soluble gold and silver being easily dissolved out with only traces
of copper, zinc, etc. The action of these weak cyanide solutions on iron,
lead, arsenic, etc., is practically nil, and the solvent action on copper or
zinc depends much upon the state of chemical combination in which
they exist.

The cyanide process is adapted to treat most of such refractory ores
as are described above. The principal exce])tions are the ores which
contain hydrated copper oxides and copper carbonates, and thdse which
contain an appreciable quantity of antimony. "When copper com-
pounds exist in a state physically hard, the cyanide solution does not
readily act on them; but when the copper compounds are soft, porous,
and spongy, the action of the cyanide is so decided as to interfere mate-
rially with its action on gold" (MacArthur). In reference to copper

16 THE CYANIDE PROCESS.

sulphide I found it no impediment to the process; carbonate of copper,
however, was so readily attacked by cyanide that its presence proved
absolutely prohibitive to the extraction of silver and interfered seri-
ously with the extraction of gold. This most refractory ore, that I am
speaking of, came from old workings in the Sylvia Mine, Tararu, New
Zealand, where part of the ledge containing a large percentage of copper
pyrites had been exposed for many years to the influence of moisture
and the atmosphere; the resulting carbonate was hard, but notwith-
standing this its reaction on cyanide solutions w^as very marked. One
and a fourth ounce of such copper ore, finely divided and shaken for less
than fifteen minutes with a 2.73 per cent cyanide of potassium solution,
reduced the strength of the solution to 0.05 per cent of cyanide. The
treatment of the ore in question proved that the affinity of cyanide to
gold is at least equal to that of cyanide to copper, and very much greater
than to silver, as, notwithstanding the rapid consumption of cyanide
by the copper compound, upwards of 70 per cent of the gold assay-
value was extracted by cyanide solution of the usual strength, whereas
at the same time absolutely no silver had gone into solution. A pre-
liminary treatment of such ore by sulphuric acid had a beneficial eftect
on the consumption of cyanide and thereby on the extraction of silver.
"In the case of antimonial ores, there is little or no interaction
between the antimony and the cyanide, consequently the latter is not
taken up; but as gold seems to be very firmly held by antimony, and
as the compound is very impervious, the cyanide is unable to penetrate
the mass, and to dissolve and separate the precious from the base metals.
In the case of both copper and antimon}' the cyanide solution will act,
but in the case of copper, if there is much present and acted upon, the
consumption of cyanide is so great that the operation is not profitable,
and in the case of the antimonial ores, though the cyanide will act with
fine grinding and long contact, the expense involved often overbalances
the value of the gold contents" (MacArthur). The physical state in
which obnoxious compounds are found, is of the greatest importance.
Hard-surfaced crystals are, even if finely divided, naturally less acted
upon by cyanide than soft, spongy masses of the same size. For tech-
nical purposes, cyanide treatment of any ore will be called unsuccessful
if the large consumption of cyanide precludes a commercial success,
although finally a satisfactory extraction in percentage may be achieved.

ni. THE CHEMISTRY OF THE PROCESS.

The chemical reaction on which the cyanide process of gold extraction
rests is that of the formation of the double cyanide of gold and potassium:

2 Au -f 4 KCy + + HgO = 2 AuKCyj -f 2 KOH

(Gold.) (Cyanide (Oxygen.) fWater.) (Auro-potassic (Potassic

of potassium.) cyanide.) hydrate.)

That of silver extraction produces the double cyanide of silver and
potassium:

2Ag -I- 4 KCy -f + H2O = 2 AgKCys + 2 KOH

/Silver.) (Cyanide of (Oxygen.) (Water.) (Argento-potassic (Potassic

potassium.) cyanide) hydrate.)

THE CHEMISTRY OF THE PROCESS. 17

Silver in the metallic state is, however, rarely met with in ores which
are subjected to cyanide treatment. The part taken by oxygen in these
reactions, first noticed by Prince Bagration and later confirmed by
Eisner, has of late been disputed, but again confirmed by McLaurin,
who published his experiments (J. Ch. S., 1893, May, p. 724) in refer-
ence to the question, and came to the following conclusions: (1) That
oxygen is necessary for the solution of gold in cyanide of potassium, and
that it combines with the potassium of the potassium cyanide in the
proportions required by Eisner's equation; (2) That the rate of solu-
tion of gold in a solution of potassium cyanide passes through a maxi-
mum in passing from dilute to concentrated solution, and this remark-
able variation is capable of explanation by the fact that the solubility
of oxygen in a cyanide solution decreases with the concentration. The
double compounds of cyanide of potassium and gold and silver, respect-
ively, have been described in the Annales de Chimie et de Physique, 53,
p. 462, 1858, and in Bull, de la Societe Chimique de Paris, 29, 1878, p.
460. Both compounds are easily soluble in water.

The cyanide process, as illustrated by the before-mentioned equations,
appears very simple indeed. Its adoption in many places has been very
rapid, and its success, particularly on the tailings of the Johannesburg
mills, has been great. The practical working and technically success-
ful carrying out of cyanide treatment of any ore, even under the most
favorable circumstances, is beset with complications, which require a
■careful study of all the circumstances connected with the case. All
operations offer occasions for loss and opportunities for improvement.
The reaction between cyanide and the metals, so simple in theory, is in
practice more or less complicated by the reaction of other ore com-
pounds on the cyanide and by other causes which it will be useful to
investigate. That such reactions take place is put in strong evidence by
the amount of cyanide consumed in treating ores, which is always con-
siderably larger than the quantity theoretically necessary to dissolve
the gold. In accordance with Eisner's equation, 10 parts of cyanide
should dissolve 15.12 parts of gold. In the works at Johannesburg,
however, in treating free-milling ore, 40 parts of cyanide are required to
dissolve one part of gold; that is to say, 40 parts of cyanide are con-
sumed for each part of gold obtained. The main reason for this fact
must be looked for in secondary reactions, which as yet have only been
partly studied. The great loss of cyanide takes place during the
extraction process, and particularly during the first part of it, as proved
by the rapid diminution in the strength of the solution. The loss of
cyanide in the zinc boxes has often been exaggerated (see page 34).
A loss of cyanide occurs by absorption in vats and tanks, which is
given as high as one pound per ton of ore in Johannesburg (Butters
and Clennell). Some loss will always result from the action of carbonic
acid gas, which is always present in the atmosphere, and displaces
cyanogen from the alkali, setting prussic acid free, which escapes into
the air; if caustic alkali is present the freed prussic acid will be neu-
tralized. The extent of loss by hydrolysis requires further investiga-
tion. The presence of free sulphuric acid or other products of more
or less advanced decomposition of pyritic matter will naturally consid-
erably interfere with the simple reaction by increasing the consumption
of cyanide, and may, under the most unfavorable circumstances, com-
pletely prevent successful treatment. " In many cases tailings which
2cp

18 THE CYANIDE PROCESS.

have been exposed to the weather contain oxidized compounds, such as
sulphate of iron, and similar sulphates of alumina and magnesia,
formed by the action of the metallic sulphates on the earthy constitu-
ents of the ore." When this is the case it is advisable to give such tail-
ings one or more preliminary water-washings, because the cyanide is
partly absorbed and partly decomposed by these substances, as seen in
the following equations:

FeSO^ + 2 KCy = FeCys + K2SO4
FeaSCSO^) + 6 KCy + 3 HgO = FcaOg -f 3(K2S04) -f 6 HCy '

From these equations it will be seen that the ferrous oxide combines
with cyanogen, and that the sulphuric acid, forming the second con-
stituent of the ferric salt, liberates hydrocyanic acid, which being vola-
tile is not available, and moreover constitutes a loss and a danger. The
action of the sulphates of alumina and magnesia has not been generally
and sufficiently recognized. These salts act practically as if they were
sulphuric acid: hydrocyanic acid is liberated and alumina or magnesia,
as the case may be, precipitated, as shown in the following equations:

Al23(S04) + 6 KCy -f- 3 H2O = AI2O3 -{- 3 (K2SO4) -f 6 HCy
MgSO^ + 2 KCy + H2O = MgO -f K2SO4 + 2 HCy

The remedy for these troubles is, as before stated, water-washing, in
some cases followed by a lime or soda treatment. Reference only has
been made to ferrous sulphate as a soluble salt, but it has been found
that the basic ferrous salts, which exist to a greater or less extent in
"weathered" tailings, are insoluble in water, and yet act detrimentally
on cyanide. In any case it is difficult to wash out the last traces of
any soluble substance, and it is wise to economize cyanide by an alkaline
treatment. "While ferrous salts, soluble or insoluble, exist in the
tailings, the lime or soda combines with the acid and deposits the
ferrous oxide or hydrate in the tailings. The ferrous oxide would still
absorb cyanogen if a cyanide solution were present, but if the air has
free access before a cyanide solution is applied, the ferrous oxide is
oxidized to ferric oxide, which does not combine directly with cyanogen.
It will thus be seen that where salts of iron have to be dealt with it is
advisable to make the alkaline treatment preliminary to permit of the
necessary oxidation; but where sulphates of alkaline earths only are in
question, the requisite lime or alkali may be added along with the
cyanide solution. Where soluble iron salts are present to any extent,
the washing should be very thorough, and the solution should be run
off from the vat through a separate pipe which has no connection with
any of the cyanide pipes" (or better, the washing should take place in
a special vat; see page 49). "This matter of salts formed by oxidation
arises chiefly in the case of tailings, but it may also happen with
concentrates and ores, in which case they are treated as tailings"
(MacArthur).

Butters and Clennell advance the following equations of possible
reactions accomjianying the action of cyanide on pyrites. They illus-
trate first the influence of oxygen on pyrites:

THE CHEMISTRY OF THE PROCESS. 19

FeSa + H2O + 70 = FeS04 + H2SO4

2 FeS04 H- = FezOg, 2 SO3 (Wittstein)

10 FeS04 + 50 = 2 Fe.^0^, 2 SO3 + 3 Fea (804)3 (Berzelius)

(Basic sulphate (Ferric sulphate

iusoluble.) soluble.)

They describe, then, the reaction of cyanide on such products:

FeS04 + 2 KCy = FeCyg + K2SO4
FeCy2 + 4KCy = K4FeCye

Ultimately giving rise to

3 K4FeCy6 + 6 FeS04 + 30 = Fe203 + 6 K2SO4 + FevCyjg

Ferric salts and cyanide give:

^62(804)3 + 6 KCy = Fe2Cye + 3 K2SO4
and,

Fe2Cye + 6 H2O = Fe2(0H)e + 6 HCy
Fe2(S04)3 + 6KCy+ 6 H2O = Fe2(0H)e + 6 HCy + 3 K2SO4

A mixture of ferrous and ferric sulphates on addition of cyanide will
form Prussian blue when the ferric salt is in excess:

18 KCy + 3 FeS04 + 2 Fe2(S04)3 = 9 K2SO4 + Fe4(FeCy6)3

and Turnbull's blue when ferrous salt is in excess:

12 KCy + 3 FeS04 + Fe2(S04)3 = 6 K2SO4 + Fe3(FeCy6)2

The reactions between the various iron and cyanogen compounds are
very complicated, and a number of possible reactions have been illus-
trated by equations by various writers, the discussion of which here
would take up too much space.

In cases where such conditions exist, a preliminary washing with
water alone, or with solutions of carbonates or hydroxide of sodium or
lime, as described, may be not only useful but imperative. A great sur-
plus of alkali should be avoided, on account of its action on the zinc in
the precipitation boxes. The loss of zinc will be larger the greater the
alkalinity of the solution; besides this, it is apt to form a sulphide of
sodium or potassium with the sulphur of ores, which interferes with the
extraclion of the silver. Further careful scientific researches in refer-
ence to secondary reactions, which accompany the cyanide process, will
probably lead to technically important results. The chemistry of
precii)itating the metals from cyanide solution will be discussed in con-
nection with the description of the various methods employed for that
purpose.

20 THE CYANIDE PROCESS.

IV. DEMONSTRATION OF THE PROCESS — METHODS OF

OPERATION.

The cyanide process is worked either by agitating the ore with the
solution ("the agitation process"), or by allowing the solution to pass
through the ore ("the percolation process").

A. The Agitation Process.

When cyanide treatment of ores was first attempted, it was done by
agitating the material under treatment with cyanide solution; Rae's
cyanide process of 1867 and Simpson's process of 1885 were agitation
processes. Generally speaking, agitation, as compared with percolation,
expedites and in instances increases extraction, but it requires motive
power, which is a source of expense. Wherever large quantities of ore
are being treated it has been abandoned in favor of the percolation
process. It is useful, however, in many instances where the ores are
hard and dense, and of a sufficient high value to pay for the necessary
motive power and permit a convenient method of filtration; it is applied
where the quantities are limited and is mostly used for treating concen-
trates, or such ores as make the treatment of limited parcels by them-
selves desirable. The importance of the cyanide agitation process has
not been so fully recognized as, in some instances, it deserves. It is
natural that if percolation gives as cheaply the same results it will be
preferred, but sometimes the agitation system has the advantage of
giving quicker, higher, and cheaper returns. Some ores, particu-
larly ores containing tellurides and sulphide of silver, give better
results by agitation than by percolation. The agitation process, in its
present form, is not well adapted to handling very large quantities of
ore without a considerable outlay of machinery. Technical improvements
of the system, which in suitable cases may make the whole process almost
a continuous one, may be expected. The chief appliances for the agita-
tion process are the agitator and the filter. Although any vat fitted
with revolving arms and barrels, similar to those employed in chlori-
nation, may be used successfully for agitation, still an agitator which
permits a charge and discharge quickly and safely, which has the least
wear and tear, does absorb neither gold nor cyanide, and is cheap in its
first cost, corresponds best with all requirements. I have been using
wooden barrels, wooden vertical agitators, iron pans, and steel cylindri-
cal agitators, and have found the latter construction best suited to the
purpose and satisfying all the above conditions. (For description of
such an agitator, see Utica cyanide plant, page 89.) ^

For the purpose of extraction, the ore and the cyanide solution are
agitated for a time, varying in accordance with the character of the ore,
generally ranging from six to twelve hours. I have extracted from com-
plex ores, in some instances, upwards of 90 per cent of the assay-value
in less than two hours, and in other instances I have found it necessary
to continue the operation for twenty-four hours. No general rule can
be given; each case has to be investigated and the modus operandi to be
selected according to circumstances. (See table showing rate of extrac-
tion in relation to time of agitation, attached to the description of the
Utica plant, page 94.) The strength of the cyanide solution and the

DEMONSTRATION OF PROCESS METHODS OF OPERATION. 21

volume required depend entirely on the character of the ore; as a rule,
solutions for agitation should be stronger than those for percolation.
Here, like in other matters in connection with cyanide treatment, experi-
mental investigation has to advise on best conditions. (See chapter on
laboratory work, page 44.) In using barrels as agitators, ore and solu-
tion will be charged before the barrel is revolved; if vertical vessels are
used, the solution will be charged first, then the stirrer Avill be set in
motion, and the ore added by degrees.

When the extraction is completed, the mass in the agitator is dis-
charged, and the cyanide solution, now containing the gold, is separated
from the solid material — i. c, the residues — by any method which local
conditions and the character of the ore suggest. Apparatus of different
principles have been used for this purpose. Filter presses of various
constructions, vacuum filters, and centrifugal machines have been
employed. Concentrates, coarse and slimy, can be successfully treated
by means of my vacuum filter (see description of Sylvia and Utica
plants, p. 79 and p. 89), which permits a quick filtration and a perfect
and speedy washing of the residues with a minimum of liquid. In some
instances I made successful use of centrifugal force for separating the
gold solution and washing the residues. For washing, weak cyanide
solutions from previous operations are used, and finally a water-wash is
given. The residues are then discharged. The gold solutions should,
for practical reasons, be kept separate according to their strength in gold
and cyanide; they pass through such appliances as are used for precipi-
tating the gold and silver, after which the "liquors" are collected in
sumps for use on subsequent charges of ore. In well-appointed works
no cyanide solution is allowed to run to waste, as the same amount of
liquid remains constantly in circulation.

The author took out early in 1893 a caveat in New Zealand for a cen-
trifugal apparatus, agitator and separator combined, for the treatment
of slimy ores by agitation with cyanide, and subsequent separation of
the gold solution by centrifugal force in the same apparatus. Experi-
ments have of late been made in the Thames School of Mines, New
Zealand, with the treatment of slimy ores by the agitation process in an
apparatus which is described as follows: The appliances used in the
operation consist of a shallow circular vat, a vacuum cylinder, and an air
pump. The vat is provided with four revolving arms, to which soft rubber
brushes are fixed. The bottom 'of the vat is fitted with a false bottom,
constructed of a wooden grating covered with wool packing. The opera-
tion is conducted as follows: The leaching solution, made up to the re-
quired strength, is first conducted into the vat. The revolving arms are
then set in motion, and the dry pulp or slimes introduced. The agitation
is continued for six hours, or until the extraction is complete. A stopcock
in a pipe connecting the false bottom of the leaching vat and vacuum cyl-
inder, is then opened and the air pump started. The effect is immediate.
At once the clear solution begins to drain over into the cylinder, the revo-
lution of the arms preventing the slimes from settling and choking up
the filter cloth. When the slimes have been drained down to a thick
paste, the first wash water is added, the pump again started, and the
slimes drained as before. The water-washings are carried on in the same
way, and when completed a plug or door is opened and the leached
slimes are sluiced out. The whole operation of leaching takes from
eighteen to twenty-four hours. The technical and economical practi-

22 THE CYANIDE PROCESS.

cability of this method of treating slimy ores appears doubtful and will
have to be proved.

B. Percolation Process.

Percolation is the method generally in use. It is being worked in the
United States, in the British Colonies of Australasia, and on a very exten-
sive scale in the South African gold fields, and therefore merits a full
description. Percolation consists in soaking cyanide solution through
ore. The character of the material to be treated, whether ores, concen-
trates, or tailings, will demand certain modificatioms of the treatment,
without interfering with the principle.

(a) Percolation of Ores. — It is advisable to dry-crush the ores;
the less dust produced the better for percolation. Screens of thirty meshes
to the lineal inch will be found satisfactory in most instances; in some
cases a coarser screen may do, or a finer one may be required. It is
desirable to crush as coarse as possible without interfering with the
percentage of extraction. Stamps are much in use for dry-crushing;
mortars with double discharge will give more product and less dust.
Rolls are to be preferred, on the ground of their giving a product of
greater uniformity. The ore is charged, either directly or through hop-
pers, into the vats in which the percolation is conducted. These vats,
or tanks, may be constructed of wood, brick and cement, concrete, iron,
or steel, and vary in size in accordance with local circumstances and
requirements. The largest in existence are the circular brick vats at
the Langlaagate Estate and Block B Company's works in Johannes-
burg; these vats have a capacity of about 400 tons, and are 40 ft. in
diameter by 10 ft. deep. A size in common use in Johannesburg is 20
ft. in diameter and about 6^ ft. in depth, inside measurement, of
which I give Mr. J. S. Mac Arthur's description: "This vat is made of
the best white pine; the staves are 7 ft. 3 in. long, 4 in. wide, and 2^ in.
thick, and fitted with a slight taper upwards, so that the diameter at
the top is about 4 in. less than it is at the bottom. The bottom is made
of the same kind of material, but is at least 3 in. thick. The pieces are
fitted together with dowel pins; it is then fitted into a groove cut in the
staves about 6 in. above the ground, and the whole vat is bound together
by steel hoops with a 6 in. over-lap an4 at least three rivets. No white
lead or packing of any kind should be used in making these vats. If
the faces of the wood are true no amount of white lead or other packing
can make them truer; if they are not true, neither white lead nor any
kind of packing will secure tightness. Besides this the cyanide solution
being alkaline would quickly combine with and remove the oil of the
white lead, if such were used, and make the vat positively worse than if
none had been employed. Circular pieces, cut out of the solid wood and
not bent by steam or moisture, are fixed by screws on the bottom of the
vat, about 1 in. from the staves, all around the circumference. These
circular pieces are about 3 in. thick and 3 in. wide, but the length of each
is immaterial, provided always that a complete ring is formed. Wooden
slats, about 1 in. thick and 3 in. high, are fixed about 6 in. apart all over
the bottom; and an iron pipe, generally 2 in. in diameter, is screwed in
from the under side near the center point. The 3 in. space from the
bottom to the top of the slats is filled in with round and clean pebbles.
Over this surface, formed by slats and pebbles alternately, is stretched

DEMONSTRATION OF PROCESS — METHODS OF OPERATION.

txi:

24 THE CYANIDE PROCESS.

a canvas cloth to act as a filter, which is fastened by stretching it over
a circle piece and ramming the cloth tight by pressing an inch rope into
the space between the circle pieces and the staves. The canvas filter is
made by shaping and sewing the canvas into a circle piece rather larger
than the area of the vat bottom. In practice the canvas filter is often
protected by covering it with old sacks or cocoa matting, which serves to
protect the filter proper from the wear and tear caused by the friction of
the ore or by the cutting of spades." (Special vat and tank construc-
tions will be given aside from this general description in reviewing large
and successful plants in different countries.) "The vat thus protected
and fitted is charged with ore, and the cyanide solution is run, prefer-
ably from the bottom, by a pipe and rises slowly through the crushed
ore. It must not be allowed to rush in or rise violently, as by so doing
channels will be formed through which the solution will pass without
acting on the ore. Such channels are apt to be formed under any cir-
cumstances, and should always be guarded against. After the upward
percolation, the stopcocks are shut, and opened again after the desired
time of contact has passed, so as to allow of a reversal and downward
percolation. The cyanide solution now containing gold is carried
through the precipitating appliances and from there into the sump, from
which it may again be used for percolation. It is not wise to attempt
to make the solution very rich in gold, and it is considered better prac-
tice to remove the gold frequently, as it is found that a cyanide solution
containing gold is not so active as a similar solution without any."

In some instances, however, it has been found of advantage to use
gold cyanide solution over again, without first passing the same through
the precipitation boxes. (See experiments made by the Robinson Com-
pany, in Johannesburg, page 65.) According to the richness of the ore
and the fineness of the grinding, percolation may be repeated several
times, but after the final percolation with the ordinary cyanide solution,,
a washing of weak or waste solution should follow, and the whole opera-
tion be completed by a water-wash, after which the residues are discharged.
The filling and discharging can be done either by hand or by mechanical
appliances. The various methods will be described in connection with
the process in South Africa.

(b) Tailings are treated in substantially the same way as ores, and,
the quantities being large and the grade low, the vats of the largest size
and the most complete arrangements for saving labor in charging and
discharging are necessary for profitable working; generally speaking, the
difficulty of discharging the vats is increased by the increase of their
diameter and their depth. " Several difficulties arise in the case of tail-
ings, which do not usually present themselves with ores. These diffi-
culties are chemical and mechanical. The chemical difficulties have
been described in the chapter on chemistry; no general rules can be
applied to them; each case has to be investigated and steps be taken
accordingly. The mechanical difficulties arise from the tailings being
derived from the operation of wet-crushing. When tailings are charged
in a wet state into the percolating vat, they are apt to remain in lumps,
from which the water has to be expelled by the cyanide solution before
the latter can effectually do its work. It is obvious that where tailings
are already saturated with water, the cyanide solution will have a diffi-
culty in penetrating, and this difficulty is increased when the wet tailings

DEMONSTRATION OF PROCESS — METHODS OK OPERATION. 25

are held together in masses between which the cyanide finds an easier
channel for flowing than by soaking through them. This is merely a
form of the channels above referred to. Assuming, however, that these
channels are not formed, the tailings in a wet state mass or pack together
to such an extent as seriously to retard percolation. Another difficulty
which arises from the tailings being wet is that in clayey ores the slimy
portion of the mass is apt to gather into a layer by itself, which if formed
of real clay, not only impedes but absolutely prevents percolation. In
order to overcome this difficulty the simple method of drying and mixing
should be adopted. The drying is a mere preliminary to the essential
of thorough mixing. Particles of clay, which are not kept apart by
sand, will agglomerate and form water-proof strata. It is impossible,
unless the whole material is perfectly dry, to get the particles of clay
separated from each other and allow the sand particles to intervene.
Even when this is done, the tendency of the clay particles to agglomerate
must be guarded against and prevented. The principal precaution
necessary is that the solution, whether applied from top or bottom, should
not flow more quickly than the dry tailings can absorb it. In many
respects upward percolation has an advantage, but principally because
the flow of solution is against gravitation. In downward percolation,
where the flow of solution and gravitation act together, the whole material
tends to become compressed into a cement, through w^iich the solution
penetrates but slowly, preferring to take the easier course down the sides
of the vat, and in fact going around rather than through the tailings.
Alternate upward and downward percolation may be found useful in
some cases."

The percolation vats are charged with tailings to within a few inches
from the top, and their surface is leveled. The cyanide solution of, say
from 0.2 to 0.8 per cent of strength, is then permitted to penetrate the
tailings, till the liquid covers them. The contents of the vat will settle
some inches, which shrinkage depends on the depth of the vat and the
percentage of moisture in the material. The solution is permitted to
remain undisturbed in contact for say twelve hours; after that time it
is allowed to drain ott". As the liquid is drawn off, it is replaced by
fresh solution. This operation is continued for a longer or shorter
period in accordance with the value of the tailings (about six to twelve
hours in the works of the Robinson Company at Johannesburg). After
this time, which is termed the "strong solution leaching," a weaker
solution, containing say from 0.2 to 0.4 per cent of cyanide, is turned
on, which filters through the ore for about eight to ten hours. This
weak solution, when drawn off, is treated separately (see above). At
last, water is run on the tailings for replacing the last weak cyanide
solution. The volume of solution in constant use and circulation
remains the same. The weak cyanide solution is the liquor which has
previously passed through the process by which the gold and silver are
precipitated and has from the sumps been pumped back into the vat.

The percolation vats, which used to be square, are, in new works,
round. The cyanide solution of the described strength has no appre-
ciable deleterious effect either on the wood of the vats or on the iron
pipes and iron valves of the pumps. Iron or steel vats may be protected
by a coating of coal tar and asphalt, or a solution of asphalt in turpen-
tine, preferably put on hot, if special reasons make such protection
desirable. The quantity of cyanide solution used for the treatment of

THE CYANIDE PROCESS.

PLA NT

TO TREAT

A MINIMUM OF 2000 TONS.
PER MONTH.

SaaZe. of Fe&t,

one ton of tailings amounts generally to half a ton of strong solution
and half a ton of weak solution and wash.

When the percolating process is finally completed, the exhausted tail-
ings, or "residues," are discharged in older works by being shoveled out
over the side. More modern works have trap-doors at the bottom of
their vats for discharge (see diagram, page 59). "Sluicing out" of the
residues is being practiced in several localities. The large vats of the
Langlaagte Estate Company's works at Johannesburg, which hold 400
tons of tailings each, are discharged by means of running cranes (see
diagram, page 57).

It must be always borne in mind that the most complete arrangements
for saving labor in charging and discharging large quantities of low-
grade material are necessary for profitable working. In order to achieve
that end, a plant should offer all such facilities which circumstances
permit; it should be so arranged that the tailings will not have to be
lifted, but can be dumped into the percolation vats. The size of the
vats has been constantly increased. New works, like the Roodeport
works at Johannesburg, are supplied with vats 40 ft. in diameter. The
table appended illustrates the dimensions of the percolation vats in some
of the more important cyanide extraction plants:

DEMONSTRATION OF PROCESS — METHODS OF OPERATION.

•^r*

•

o°^

•-'

0--

"oSV.

CUO

t>D

z,c o

_fl

a cj a>

•^

c a

<u o

<u a

'O--^

c3 .

■ 5 fK

TJ*

°2

(M_

t-_

I—

03_

° r<

i-T

»H

CO"

oo"

r-T

c<r

^-^

<♦-(

<4-l

SfH

<+-(

t-_

■^

-k^

-M

<+-<
■<*<

-p

-W

-t<

a""

-u

-S

-IJ

1 -^

-ij

««H

■4-H

e*-H

«*-<

<+H

««

«*H

**H

<*H

•H

T-H

■*

■q<

)-.

13
C

cr'

«2

CC!

•73

■73

■o

M •

•^

QJ ^

^tJ

fi>

•AO

;

•V

^1^

,__

,„_,

^__,

,_j

__,

,_,

__,

►J

a
a

3
O
CO

03
>

03
!>

03
cj

C
03

03
03
>
to
S
03

C3
03
>
m
C
oi

>
to

C
03

>
tn

C
03

03
03
>

C
03

<~,

;?;

>»

fjj

;

03
ft

'ft

03
ft

•a

c
a

c3
ft

r«=i

o
o

si
'A

S
o
O

0)
0)

O
o

o
n

O
O

o
ft

O
O

M
C

03
ft

-4H>

'60

C
■o3

c
o

o
o

s
&

"aj

"oS

i-i

'U'

irf

t-^

■<1<

28 THE CYANIDE PROCESS.

All vats should be some distance above the ground, so that leaking
can be easily detected; concrete foundations for the vats are generally
adopted. The wooden tank material is an absorbent of both cyanide
and gold, particularly when new. It has been found at the Salisbury
works, Johannesburg, that pine wood lying thirty-four hours in a 0.3
per cent cyanide solution reduced it to 0.05 per cent, while cement reduced
it to 0.24 per cent. Cement tanks have come into use of late, and have
proved satisfactory; such tanks and vats may advantageously be built
into excavations in solid ground. Many attempts have been made to
discharge tailings-pulp direct from the plates, or ore-pulp direct from
the mortars into the percolating vats, but their successful treatment by
cyanide when so discharged has been prevented by mechanical causes,
the reason being that the material packs so densely in the vats that it
makes percolation an extremely tedious operation, and in consequence of
the presence of slimes the results are unsatisfactory. The advantages
of wet-crushing over dry-crushing are, from an economical standpoint,
so obvious, however, that experiments will be continued, and ultimately
the drawbacks which now adhere to the method may be overcome.
Cyanide of potassium solution has been used, in some instances and in
an experimental way, in lieu of water in the mortars, when wet-crush-
ing was resorted to, but does not appear to be practiced anywhere at
present. An innovation in percolation consists in the circulating system,
which will be described in detail in connection with the practice of the
cyanide process in South Africa (see page 46).

(c) Percolation of Concentrates. — "These are treated similarly to
ores, but being generally richer require a greater number of percola-
tions, and thereby a much longer time. In most cases, their quantity
is limited, and the size of the percolation vats varies in accordance
with the quantity." I have, in most cases, given agitation the prefer-
ence to percolation for treatment of concentrates, on account of its
greater cheapness and rapidity; in Africa most companies prefer the
latter method. Percolation of concentrates requires about twenty days,
the reason for which will be found partly in the coarser character of the
gold, partly in its being in the form of amalgam, and mainly in the
difficulty the solution has in penetrating between the faces of the sul-
phuret crystals. A difficulty sometimes arises in the percolation of
concentrates, owing to the crystalline form of iron pyrites and galena.
These minerals crystallize in cubes, and when suspended partially or
wholly in a fluid tend to range themselves face to face, so that a section
of such a mass deposited from a fluid would resemble a brick wall in
structure. This difficulty does not arise in the case of sand or minerals
which crystallize in other systems. Whenever it occurs, it may be over-
come by mixing the cubical sulphurets with coarse sand.

C. Cyanide and Cyanide Solutions.

The best strength of solutions to use in either percolation or agitation
depends entirely upon the nature of the ore, and it is impossible to set
any rule. The strength of solutions generally used varies from one
eighth to one per cent of cyanide. (In reference to the determination of
the correct strength to be used in treating any class of ore, see chapter
on laboratory work, page 44.) " For convenience and economy of work,

DEMONSTRATION OF PKOCESS — METHODS OF OPERATION. 29

the solutions are generally divided into three classes: No. 1, No. 2, and
No. 3, of which No. 1 is the strongest and No. 3 the weakest. Assuming
that the material under treatment does not require a preliminary alka-
line wash, or that such treatment has already been completed, it is usual
to run on a weaker solution, say No. 2, in the first place, and after its
percolation to use No. 1, and then No. 3 in the same manner, finishing
with a water-wash, the first portion of which is run into and forms part
of the No. 3 solution. These different solutions are kept separate after
percolation, and when charged with gold are subjected by themselves to
the precipitating process. In some works sumps are used as reservoirs,
and the solution is pumped direct from them onto the ore; but space
permitting, it is considered better practice to have reservoirs for each solu-
tion above the percolation vats, from which the flow can be more easily
regulated." For the purpose of bringing weak solutions up to a certain
standard, it is advisable to use a very strong solution, of which enough
is added to bring the weak solution up to the required strength. This
method has to a great extent taken the place of the old method of using
solid cyanide to bring weak solutions up to high standards. The
strength of the cyanide solutions, which it is of great economical impor-
tance to determine, is tested according to Liebig's method by means of a
one tenth standard solution of nitrate of silver, which is made by dis-
solving seventeen grams of pure nitrate of silver in one litre (1,000 cc.)
of distilled water. Liebig's method is based on the fact that silver
cyanide is soluble in excess of potassium cyanide, with formation of a
double cyanide of silver and potassium:

KCy + AgN03 = AgCy + KNO3

(Potassic cyanide.) (Argentic nitrate.) (Argentic cyanide.) (Potassic nitrate.)

AgCy + KCy = KAgCy^

(Argentic cyanide.) (Potassic cyanide.) (Argentic potassic cyanide.)

As soon as the whole of the cyanide has been converted into a soluble
silver salt, an additional drop of silver nitrate will produce a permanent
precipitate of the insoluble simple cyanide of silver:

KAgCya + AgNOs = KNO3 + AgCy

(Argentic-potassic cyanide.) (Argentic nitrate.) (Potassic nitrate.) (Argentic cyanide.)

A measured portion of the perfectly clear cyanide solution which is to
be tested is taken; if necessary some distilled water is added, and the
standard silver solution is gradually added from a graduated burette,
until a permanent white cloud is formed. As each cubic centimetre of
the silver solution is equal to 0.013 grams of potassium cyanide, by
multiplying the number of cubic centimetres consumed by 0.013 the
amount of cyanide in the solution tested is found in grams, from which
the percentage can easily be calculated. A convenient silver solution
for the purpose of analyzing cyanide solutions is one of such strength
that every cc, added to 10 cc. of the solution which is to be tested, cor-
responds with 1 per cent pure cyanide of potassium. "The cyanide
solutions are apt to form, by continued exposure to the air, carbonate of
ammonia; and as this salt interferes very seriously with the determina-
tion of the cyanide, it is well to add a few drops of solution of iodide of
potassium, which forms a pale-yellow cloud insoluble in ammonia,

30 THE CYANIDE PROCESS.

which indicates completion of the reaction" (MacArthur). The mode
of analysis, as described above, calculates the amount of cyanide of
potassium in a solution by ascertaining its contents of cyanogen. If the
cyanogen is partly combined with sodium instead of potassium, the per-
centage of cyanide appears in the analysis higher than it really is; the
value of commercial cyanide of potassium should therefore be ascer-
tained by determining its contents of sodium, if any, as it is possible,
by manufacturing a mixture of cyanide of potassium and cyanide of
sodium, to produce cyanide, which according to the ordinary method of
estimation, contains apparently more than 100 per cent of potassium
cyanide. The analysis of cyanide solutions for gold and silver will be
described in the chapter on laboratory work (page 44).

The Cyanide usually employed for ore extraction is of two classes, one
of which, manufactured in Scotland, contains from 70 to 80 per cent of
pure potassic cyanide; the other is manufactured in Germany and con-
tains upwards of 98 per cent. The latter grade is preferable, because it
contains no carbide of iron, the presence of which in the former not only
involves periodical cleaning out of the dissolving tank, but also is liable
to precipitate gold should any of it come in contact with gold cyanide
solution. The price of the best quality of cyanide of potassium, guar-
anteed to contain upwards of 98 per cent cyanide, is at present 50 cents
per pound in the United States, delivered at seaports.

D. Treatment of the Gold Solutions (Recovery of the Bullion).

All methods of treating ores, as described, yield solutions containing
more or less gold and more or less cyanide of potassium. The next
step is to recover the gold and silver. The chief method for that end
consists in their precipitation by means of finely divided zinc; it forms
one of the patent-claims of MacArthur and Forrest, and is generally in
use. Another method is that of B. C. Molloy, of Johannesburg, who
decomposes the cyanide solution of gold by means of an alkali metal,
and amalgamates the bullion thus liberated; cyanide of potassium is
regenerated by this process. The Molloy process has been in use on a
small scale in South Africa, but has apparently gone into disuse again,
for the official list of the Chamber of Mines of Johannesburg for March
does not return any gold as extracted by that process, as had been the
case in former months. Other processes for bullion precipitation are:
The Siemens and Halske process of precipitating the noble metals by
electrolysis on lead sheets, which method is in use at the Worcester works
in Johannesburg; the Pielsticker process of using electrolysis, constantly
applied to the circulating solution; the Moldenhauer process of precipi-
tation by means of aluminium, and the Johnston process of using char-
coal as reducing agent. No information is available on the technical
application of the three processes last named.

(a) Bullion Precipitation by Zinc. — The solutions from the perco-
lation vats, or from the filter appliances if the agitation process is used,
are run through boxes which are divided into chambers with double
partitions. The first partition does not reach to the bottom of the box,
the next one not quite to the top, and so on; they compel the solution to
enter each chamber from below, and pass through a perforated bottom,.

DEMONSTRATION OF PROCESS — METHODS OF OPERATION.

^ Z

^ o

^ O

32 THE CYANIDE PROCESS.

on which the finely divided zinc is placed. After passing through the
zinc, the solution leaves the chamber at its top; then it descends between
the double partition to the space below the perforated bottom of the suc-
ceeding chamber, where it undergoes the same treatment, and so forth
in all successive ones (see sketches, pp. 31, 33). "This arrangement has
been adopted because the gold is precipitated on the zinc in a state of
fine division, and would, if deposited on the upper surface, prevent the
further flow of the solution; but being deposited on the under surface,
the gold precipitate falls ofl" and leaves the passage clear. Each precipi-
tating box may contain ten to twelve double chambers, and no matter
how rich the solution is at the inflow, it should not contain more than
a few grains per ton at the outflow." In some works the zinc boxes are
up to 40 ft. long. There is, however, no advantage in going beyond a
limited number of chambers, as precipitation of the metals takes place
chiefly in the first few compartments of the box. (See description of tJtica
plant, p. 89).

I give here Mr. J. S. MacArthur's description of his construction of
filter boxes, and the mode of working them which is used by the
MacArthur-Forrest patentees in South Africa: " The gold precipitate falls
through the gauze 'a' (see cut, p. 31) into a chamber which communi-
cates with an inclosed launder or gutter. From day to day fresh zinc is
added, always, adding it in the last chamber and bringing the partly
consumed zinc up a step, so that the first chamber contains zinc half
consumed and rich in gold, while the last chamber contains fresh zinc
containing no gold. At intervals of about two weeks, there is a clean-up,
and the gold is collected by stirring the zinc so as to cause the gold
precipitate to fall ofl". When this is done, the stopper ' b ' is raised and
the gold precipitates fall through the opening into the launder 'B.'
When this has been completed for each chamber, the launder is dis-
charged through the opening ' C " The precipitation boxes are usually
made of wood, and although I have been well satisfied with such mate-
rial (kauri-pine in New Zealand), I substituted it in California by steel,
which I found in every respect an excellent material for the purpose. I
could not ascertain any increased loss of cyanide by the use of iron as
box material; the galvanic action of iron and zinc in contact on the
cyanide seems by some writers overrated (see description of Utica plant,
p. 89). Of this apparatus, which is based on the same principle, but
which in its construction is simpler than the one described, I give the
appended diagram. The total length of the apparatus is 9 ft., the size"
of the chambers is 9 in. by 9 in. by 14 in. deep; the distance of the par-
titions between each chamber is 1 in. The perforated and movable
false bottom of each chamber is of steel, which is an advantage over wire
sieve bottoms, which easily become clogged b}^ bullion. The real bottom
of each chamber has a faucet of 1 in. diameter, which discharges the
liquid and the finely divided bullion into a tank below the apparatus,
from where, after settling (under addition of some alum, if saving of
time is an object), it is transferred to a vacuum filter, as described
further on.

"The zinc used for precipitation purposes should be the best quality
found in commerce, and should not contain arsenic or antimony; a small
percentage of lead, however, does no harm, but rather tends to promote
rapid action by forming a voltaic couple with the zinc" (MacArthur).
The metal is preferably used as shavings, or filiform, as these forms

DEMONSTRATION OF PROCESS — METHODS OF OPERATION.

give in practice the most surface for the least weight and do not pass
readily through a sieve, whereas the gold, which is precipitated as a fine
powder, does. Shavings have the advantage of not forming lumps so
easily in the precipitation boxes as filiform zinc; the latter has, however,
the greater advantage of being cheaper in its preparation, as no remelt-
ing of the commercial zinc is required. It is prepared by cutting sheet
zinc into disks, a number of which are placed together and turned on a
lathe with an ordinary chisel. The zinc linings of the cyanide packing-
cases, for which there is no market, may be turned to account in that
way.

3cp

34 THE CYANIDE PROCESS.

In reference to the cost of preparing the zinc, I may quote the Nigel
Gold Mining Company in Johannesburg, where one native, working
about eight hours a day, can easily keep the works going, with an output
of about two thousand ounces of gold monthly; the consumption of
zinc is about twenty pounds daily. As a rule, one cubic foot of zinc
shavings in the precipitating box is sufhcient for the precipitation of the
gold from two tons of solution per twenty-four hours, or, roughly speak-
ing, from the same weight of ore (see the zinc for bullion precipitation
in Africa on page 53). Zinc in sheets and granulated zinc have been
tried for bullion reduction, but with indifferent results, on account of
their limited surface. Zinc amalgam and zinc dust have not answered,
for mechanical reasons — zinc dust packing too tightly and zinc amalgam
not offering sufficient surface in proportion to its weight. The precipita-
tion of the metals in the zinc boxes takes place rapidly; the zinc in the
compartment near the influx will be much more quickly charged with
bullion than that in those more distant, and the zinc will be consumed
in proportion. Zinc on which bullion is already deposited is more active
than new zinc; it is therefore advisable to replace the dissolved zinc in
the upper by zinc from the lower chambers, and to add the fresh zinc in
the last compartment. The generation of hydrogen in the boxes is
liable, by polarization, to partly interfere with the bullion precipitation;
the zinc in the boxes should be stirred up occasionally to avoid this.

The zinc boxes are cleaned up once or twice a month; for that purpose
the inflow of the solution is stopped. The zinc shavings are stirred
with a rod, which causes the fine bullion to fall ofl" and to pass
through the perforations of the false bottoms, and through the faucets
at the real bottoms, into the box below, where it settles readily, on
the addition of a little alum. A jet of water will further wash
the zinc in the chambers. This method of operating takes only a
few minutes, and has been used by me in California. The liquid
standing above the settled bullion is returned to the zinc box; the
bullion itself, unavoidably mixed with fine zinc, is transferred through
a fine sieve onto a vacuum filter. If a final cleaning-up is desired, it
will be necessary to dissolve the whole of the zinc, impregnated with
bullion, in acid; such necessity will, however, rarely arise. The manip-
ulation itself if required, offers no difficulties. The precipitated bullion
is very finely divided, and provision should be made to prevent its flow-
ing away with the liquid out of the precipitation boxes (see page 52).

The process of bullion precipitation by zinc is, generally speaking, a
satisfactory one, although not free from objections; all operations with
and manipulations of the precipitated bullion require care to avoid loss.
The action of the zinc on gold solution is theoretically very simple —
a simple substitution of gold by zinc according to the equation:

2 KAuCy2 + Zn = K2ZnCy4 -f- 2 Au

(Auro-potassic cyanide.) (Zinc.) (Zinc-poiassic cyanide.) CGold.)

One pound of zinc should precipitate about six pounds of gold. The
actual consumption is, however, considerably larger, and amounts to
from 5 oz. to 1 lb. of zinc per ounce of gold recovered. A constant gen-
eration of hydrogen gas in the precipitation boxes proves the effect of
the potassic hydroxide on the zinc, and probably a decomposition of
cyanide of potassium, going on parallel with the decomposition of the

DEMONSTRATION OF PROCESS — METHODS OF OPERATION. oO

double gold cyanide. A considerable loss of zinc occurs generally
in refining the precipitated bullion, which always contains a high
percentage of that metal. The double salt of auro-potassic cyanide
appears to be one of the most stable of gold salts; its decompo-
sition by zinc is, however, practically complete; an excess of cyanide of
potassium in the solution does not redissolve precipitated gold in the
boxes as long as there is zinc present. The cyanide of potassium formed
into a double salt with zinc during the gold-reducing process is not
available for dissolving gold in new operations. If a surplus of caustic
soda has been used for neutralizing acid salts in the ore without follow-
ing washing, the loss of zinc will naturally be increased. A white pre-
cipitate is constantly accompanying the reduction of bullion in the zinc
boxes, undoubtedly the result of the action of alkali on the zinc and of
the zinc-potassium oxide on the double cyanide of zinc and potassium,
Avhich is always present in the solution, forming the insoluble cyanide
of zinc; ferrocyanide of zinc is also formed in the boxes. Ferrocyanide
of zinc is formed in the percolation vats when the double cyanide of
zinc and potassium comes in contact with the iron salts in the ore, and,
as it is insoluble, to this cause is due the constant removal of zinc from
the solution with the residues (Buckland). The gold precipitate on the
zinc is, as a rule, brown to black, with sometimes a metallic luster; it is
mostly slimy, and when dry it seldom contains more tban 40 or 50 per
cent of gold and silver, the remainder being finely divided zinc and its
accompanying impurities, such as carbonate of lead. It may also con-
tain copper, if that metal is present in solution. (In the instance of
treating concentrates containing carbonate of copper from the Sylvia
Mine, New Zealand, the gold solution contained a very appreciable
quantity of copper; this complicated matters by causing the copper to
precipitate with the gold and cover the zinc, thus forming a galvano-
plastic coating, which made it necessary to dissolve the whole of the zinc
for the purpose of obtaining the bullion, till I found an addition of
cyanide to the solution, before it enters the zinc boxes, useful for the
prevention of the deposition of the copper.)

I always found mercury in the zinc bullion in not inconsiderable
quantities when concentrates had been treated by agitation; such mer-
cury must have been derived from amalgam, and mercury saved with
the pyrites on the concentrators. Gmelin and others describe mercury
as absolutely insoluble in cyanide. There is, however, no doubt of the
correctness of my observations; the mercury must have been dissolved
in the cyanide solution, which entered perfectly clear into the zinc boxes;
solubility of gold amalgam in cyanide may offer the explanation. Traces
of antimony and arsenic have also been found in the bullion. The pre-
cipitation of silver goes on by zinc simultaneously with the gold; it is
even more rapid and complete than that of gold. (See my table on the
process in the Utica Works, page 91.)

Other apparatus than the described boxes have been suggested for
bullion precipitation by zinc — for instance, earthenware and porcelain
vessels have been recommended. They have the apparent advantnge of
cleanliness; tbeir construction, however, makes the cleaning-up of the
bullion difficult, the connection between the single cells being compli-
cated; they have not become a practical success in works of any extent;
they are all based on the principle of the solution penetrating the zinc
from below and running off at the top. The precipitates, obtained as

THE CYANIDE PROCESS.

-4-3-

described from the zinc boxes, are transferred to a sieve, made of No. 1
punched battery screen or a 40-mesh wire screen, through which they
are washed onto a filter in connection with a vacuum chamber, where
they are liberated from the adhering cyanide solution and reduced from
their very voluminous state into a more compact form. This filtration
will always be found slow on account of the extremely slimy character
of the bullion. For filtering and washing the bullion slimes, filter
presses may be suggested. By the screening process the coarser particles
of zinc are separated from the bullion, but the bullion still contains a
large percentage of very fine zinc, of which it is advisable to remove as
much as possible before melting.

Bullion Refining. — The means for this purpose are calcination or
roasting and acid treatment. I use for roasting (see description of
Sylvia plant, p. 79) a muffle furnace, where the slimes are dried, and
then calcined for the promotion of the oxidation of the base metals.
The calcining process is generally in use in South Africa, and will be
described with the cyanide practice in Johannesburg, page 54. I gener-
ally prefer sulphuric acid treatment, with following washing and drying
of the bullion. The acid treatment is a comparatively simple operation,
and does not require, even for large quantities of bullion, any other
apparatus than wooden tubs, the increased temperature produced by the
reaction of the acid on the zinc making application of artificial heat
superfluous. The separation of the acid solution from, and the Avashing
of, the bullion is best done by decantation, and completed on the bullion
filter mentioned above. It is advisable to liberate the bullion as much
as possible from base metal before melting, which is otherwise connected
with loss of gold by evaporation caused by the volatilization of zinc;
besides, the zinc fumes are very disagreeable. The presence of oxides
of base metals (as obtained by calcination) makes the melting tedious
and expensive on account of the detrimental influence of the slag on
the melting pots. The presence of a high percentage of base oxides pre-
vents the use of graphite crucibles and compels the use of clay pots.
Bullion, when treated by acid as described, does not offer any difficulties
in melting, if proceeded with in the following manner:

DEMONSTRATION OF PROCESS — METHODS OF OPERATION. 37

The bullion, after having been treated with sulphuric acid and washed
with water, is dried by suction on the vacuum filter as much as pos-
sible, after which it is easily detached from the filter cloth. The mass
is then charged into the muffle (see plans of Sylvia cyanide plant,
page 77). The heat is kept low to drive off the moisture; it is then
increased gradually to dark red; after about one hour's calcination,
during which time the oxidation of base metals which escaped removal
by acid treatment is going on, the mass presents a gray-brown appear-
ance. Attention has to be paid to the draught to prevent loss of the
fine precipitates. Bullion resulting from the treatment of concentrates
will invariably give off quicksilver vapors; condensation yielded only a
small quantity. The calcination process completed, the roasted bullion
is carefully transferred from the muffle, by means of a small shovel, into
a wrought-iron box for cooling purposes. It now presents itself in the
form of lumps, approaching more or less the spherical form, of the size
of peas, largely mixed with dust. When sufficiently cooled, it is charged
into a pulverizing cylinder of sheet-iron, 3 ft. long and 2 ft. in diameter,
which is revolved by means of a pulley. Large pebbles are charged into
the apparatus with the bullion to aid pulverization. Borax, with prefer-
ence borax glass, and soda ("ammonia-process soda") are added into
the barrel, in proportions according to experience, for securing a fusible
clear slag of light specific gravity. If the bullion is base on account
of a large proportion of zinc oxide, which happens only if acid treat-
ment was not properly conducted, a silicious flux, like sand or glass,
has to be added. Acid sulphate of soda and fluorspar have been occa-
sionally found useful as additional fluxes. During pulverization, a
thorough mixture of bullion and fluxes will take place. Moisture in
the fluxes should be avoided, as it is a certain source of loss in melting,
the escaping water carrying fine bullion out of the pot.

Plumbago crucibles are very well adapted for melting bullion, pre-
pared as above described; they stand almost as many operations as with
battery gold. In melting, some borax is first put into the crucible; the
bullion mixture from the pulverizing and mixing cylinder is not added
all at once, but as e,ach portion melts and sinks down, fresh quantities
of it are put in. The melting goes on speedily and in the most satisfac-
tory manner. When the whole quantity is finally charged, the tempera-
ture is kept very high for some time, to give the small bullion globules
a chance to collect. The contents of the pot are poured into a heaf-ed
mold in the usual manner. No chemical losses will be experienced by
this method of bullion melting. Bullion obtained by the described
manipulation will be found to be at least 950 fine. The bullion pi'o-
duced by cyanide works generally varies in fineness according to the
attention paid to its refining. Gold purchasers buy bullion on assay,
and refiners charge higher rates for baser bullion; it is therefore as a
rule cheaper in the end to produce clean bullion. Bullion precipitation
by means of zinc is not free from objections; its practice is connectetl
with a loss of cyanide and with the introduction into the process of a
new compound (the double zinc-potassium cyanide), which is, to say the
least, not an advantage; the consumption of precipitating agent (zinc)
is far in excess of the amount theoretically required, and no opportunity
is offered for a regeneration of the cyanide. The precipitation itself is,
however, a very efficient and simple procedure, not requiring either
motive power or more than ordinary attention, and the treatment of the

38 THE CYANIDE PROCESS.

precipitates cannot be said to offer any obstacles which would charac-
terize the process as metallurgically inefficient. In fact, generally speak-
ing, the clean-up of the bullion precipitated by zinc, if properly handled
on the lines explained above, will hardly be found more troublesome
than a mill clean-up.

Although the precipitation of the gold by zinc is unquestionably a
weak point in the cyanide process, no other method has as yet taken its
place to any extent. Had other methods, which require motive power,
careful adjustment of costly and delicate machinery, and constant
attention preceded it, its discovery would probably have been con-
sidered an improvement of importance.

(b) The MoUoy Process. — A method for precipitating bullion which
has obtained some technical importance has been advanced by B. C. Mol-
loy, of Johannesburg, whose process is protected by English letters
patent No. 3,024, dated 16th February, 1893. Molloy uses for precipita-
tion purposes sodium or potassium amalgam, which is formed electro-
lytically from a solution of carbonate in contact with a bath of mercury.
The alkali metal combines with the cyanogen of the gold compound,
forming an alkali salt of the cyanogen, while the gold is instantly amal-
gamated. This auriferous amalgam is then strained and melted as
in an amalgamation mill. The process of precipitating and collecting
the bullion is carried out in an amalgamating apparatus, the bottom of
which is partially covered with mercury. On this mercury rests the
solution from which the metals are to be precipitated. The mercury is
charged electrolytically with an alkaline metal (by the electrolysis of an
alkaline salt used in a porous vessel in contact with a mercury cathode).
The alkaline metal, or its amalgam, when coming to the surface of the
mercury and in contact with the water of the solution, decomposes the
water, the alkaline metal combining with the oxygen of the water to
form an alkaline oxide; the hydrogen of the decomposed water is at the
same time evolved in a nascent state from the surface of the mercury
which is in contact with the solution from which the gold is precipitated,
and absorbed by the mercury. The gold is released, from the mercury
in the ordinary manner by straining and distillation. Another, " though
much less advantageous method," suggested by Molloy, is the mechanical
addition to the mercury of potassium or other alkaline metals, or amal-
gam of the same. In both cases the original solution of cyanide of
potassium is regenerated and ready for use again. The reaction is aa
follows:

K.COg + elect, current = Ko + CO2 + 0.

KAuCya -f K = Au -f 2 KCy.

No information could be gained of the actual working results.
Other methods of bullion precipitation by means of the electric cur-
rent have been suggested.

(c) The Siemens and Halske Process for bullion precipitation
by electrolysis on lead sheets has become of technical importance. The
precipitation plant consists in boxes through which the gold solution
passes; these contain the anodes, Avhich are iron plates, and the cathodes,
which are lead sheets, stretched between iron wires fixed in a light
wooden frame, which is suspended between the iron plates. It is claimed

DEMONSTRATION OF PROCESS — METHODS OF OPERATION. 39

that the adoption of this method of bullion precipitation permits the use
of very weak cyanide solutions for extracting purposes, followed by a
•considerable reduction in the cost of treatment.

Mr. A. von Gernet has given the following details as to the practical
working results obtained at the Worcester works, in Johannesburg, with
the Siemens and Halske process, which has been tried there for four
months on a large scale, after long and exhaustive preliminary experi-
ments at the works of the Rand Central Ore-Reduction Company:

" There are now in use five leaching vats of 2 ft. in diameter with 10 ft.
staves, each holding 2,700 cub. ft. One tank is discharged and filled
every day. The strong solution used contains from 0.05 to 0.08 per cent
cyanide, and the weak washes 0.01 per cent. The actual extraction of
fine gold has averaged 70 per cent, while the consumption of cyanide
has been ^ lb. per ton of tailings treated.

"The precipitation plant consists of four boxes 20x8x4 ft. Copper
wires are fixed along the top of the sides of the boxes, and convey the
current from the dynamos to the electrodes. The anodes are iron plates
7 ft. long, 3 ft. wide, and ^ in. thick. They stand on wooden strips
placed on the bottom of the box, and are kept in vertical position by
Avooden strips fixed to its sides. In order to effect circulation in
solutions passing through the box, some of the iron sheets rest on
the bottom, while others are raised about 1 in. above the level of the
solution, thus forming a series of compartments similar to those of a
zinc box, the difference being that the solution passes alternately up and
down through successive compartments. The sheets are covered with
canvas to prevent short circuit. The lead sheets are stretched between
two iron wires, fixed in a light wooden frame, which is then suspended
between the iron plates. The boxes are kept locked, being opened once
a month for the purpose of the ' clean-up,' which is carried out in the
following manner: The frames carrying the lead cathodes are taken out
one at a time. The lead is removed and replaced by a fresh sheet, and
the frames returned to the box, the whole operation taking but a few
minutes for each frame. By this means the ordinary working is not
interrupted at all, and the cleaning out of the boxes, which is necessary
in the zinc process, is only required at very long intervals. The lead,
which contains from 2 to 12 per cent of gold, is then melted into bars
and cupelled. The consumption of lead is 750 lbs. per month, equal to
3 cents per ton of tailings. The working expenses, including filling and
discharging tanks, come to 80 cents per ton, which is divided as follows:
Filling and discharging, 20 cents per ton; cyanide, 12^ cents; lime, 2.4
<;ents; iron, 4.4 cents; caustic soda, 10 cents; lead, 2.2 cents; natives'
wages and food, 3.8 centos; coal, 9.2 cents; white labor, 9.2 cents; stores
and general charges, 6.5 cents; total, 80 cents. At the "Worcester works
100 tons are being treated per day; when working on a large scale it is
iinticipated that the expenses will be further reduced." (The Mining
Journal of London, October 27, 1894.)

The advantages claimed for this process are that electrical precii)ita-
tion is independent of the amount of cyanide or caustic soda contained
in the solution, therefore in the treatment of tailings very dilute solu-
tions can be used; for generating the current necessary in a 3,000-ton
plant, 2,400 Watts are required, equal, theoretically, to 3} horse-power,
and actually requiring about 5 indicated horse-power. The process has
produced 755 ozs. of gold during the month of July of this year.

,nd

40 THE CYANIDE PROCESS.

(d) The Pielsticker Process applies likewise the electric current
as the precipitating agent. A description of this process, illustrated hy
a diagram, will be found in the patent-specification (see Appendix).
No information in reference to practical results could be obtained. The
process attained of late a certain notoriety on account of the patent
litigation now pending between the owners of the MacArthur-Forrest
patent and the Cyanide Gold Recovery Syndicate (Limited) of London^
who control the Pielsticker patent.

(e) The Moldenhauer Process of bullion precipitation consists in
the application of aluminium, or alloys, or amalgam thereof, in the pres-
ence of a free alkali. It is claimed that aluminium separates the gold
very quickly from the cyanogen solution without entering into combina-
tion -with the cyanogen, but simply reacting with the caustic alkali
which is present at the same time, forming therewith an aluminate.
The precipitation of gold by aluminium takes place as follows:

6 AuK (CN)2 + 6 KHO + 2 Al -f 3 HoO =

6 Au + 6 KCN + 6 HCN + 6 KHO + AlgOg

6 Au + 6 KCN + 6 HCN + 6 KOH + Al203=

6 Au + 12 KCN + 6 H.O + AlgOg.

The whole of the cyanide of potassium which has been combined with
the gold is being regenerated, and the consumption of the cyanide is
limited to the loss involved by such secondary reactions as act decom-
posing. (See "chemistry of the process.") The discoverer of this method
of bullion precipitation claims that the quantity of aluminium required
for precipitating the same quantity of precious metal, is about four times
less than the amount of zinc required to produce the same effect. No
results of this process applied on a large scale have as yet been made
public.

(f ) The Johnston Process of abstracting gold and silver from their
solutions of alkaline cyanide (United States patent 522,260, see Appen-
dix) consists in the use of pulverized carbon, preferably in the form
of charcoal. "The pulverized carbon is placed upon suitable sup-
ports so as to form it into filters, through a series of which the cyanide
liquid is caused to pass successively, leaving the metal deposited upon
the carbon. The gold and silver are then recovered by carefully burning
the carbon and smelting the residue with the usual fluxes. By thus
employing a series of filters, through which the solution is passed suc-
cessively, 95 per cent of the precious metal contained in the solution is
recovered. When only one filter is employed, only about one fourth of
the gold can be extracted."

V. PERCENTAGE OF EXTRACTION.

The percentage of extraction depends on the character of the ore. As
I mentioned before, the process is suitable for many ores which for
chemical and mechanical reasons are refractory. The commercial ques-
tion in the selection of a metallurgical process for treatment of a certain

jcr cciii/ ui

^„„- ... biic guiu, iii&teuu ui oo pur cent us snown oy assay; ine

returns of the second month yielded 80 per cent, instead of 91 per cent;
after the third month the actual results came up to the extraction, as per
assay — 89 per cent. Similar experiences have been made in the Sylvia
Company in New Zealand and elsewhere. It has been recommended to

TABLE SHOWING RESULTS OF CYANIDE TREATMENT OF ORES.

Material.

Operator.

Assay per Ton.

Value per Ton.

Value.

Percentage
Extracted.

Cost of

Name of Mioe.

Character.

Quantity
Treated.

Gold.

silver.

Gold.

Silver.

In Ore
Parcel.

Extract
from Ore
Parcel.

Gold.

Silver.

per Ton.

Tons.
5

0.5

280

224

145

16.9

9.3

164

206

0.3
0.5
9.5
10.5
21
37.9
5
1
263.3
43.1
72.7
192
614
0.6
5
7

7.6
0.9
1
1
I
111
75
0.9
138
19
1
116
111
130
166
422
1,015
4.5
5

4.5
4.2
3

6.8
116
14.1
4.1
1.5
13.3
4.5
17.5
4.5
1,600
10.9
12.6
1.6
7.1
7.2
14
5.7
1,000
2.6
1.5
78
5.2
4.6
5

P.McIntyre

07.. dwt. gr.
1 10 16

... 8 4
1 6 2
1 2 20
1 2 20
1 2 1

1 18 10
3 15

2 14

15 8
7 5 7

1 6 23

2 11 10

2 8 4

1 6 12

3 6 23

3 16

4 3 7

3 17 22

2 6

4 2

1 10

2 8 4

2 19 21
1 12

148 15 8
222 7 12
324 8 10

'"3 '6 2.3

16 3
1 6 3
1 7 18

3 10 15
1 16 22

102 4 6
123 4 11

"b "e i2

oz. dwt. gr.

22 16 18
3 15
308 12 20
488 3 6
504 2 18

'2S ie 13
19 14

17 4 16

18 23
2 19 8
1 1 6

47 22
52 9 6

""6 "6 i7

84,1
90.0
86.3
81.8
91.1
822
90.7
91.3
87.0
87.2
88.0
88.0
85.1
91.2
90.3
89.3
80.3
lOO
96
88
85.5
87.7
83.3
86.0
91.09
90.6
93
93
93
94

90.29
81.18
84.37
80.78
90.20
86.31
97.90
97.20
86.11
86.34
88.70
80.32
77.90
89.10
91
89
91
91.6
91.8
91.8
79.4
82
82
9.S
90
80.2
71.77

"""98'"'"
90.3
90
98
84
96

"m""

"rob""

90
70
94

clacK jacK, A AuDtraifa'

Slimes

P.McIntyre

P.McIntyre..

Day Dawn, Block & Windham, Australia...
Day Dawn, Block & Windham, Australia...
Day Dawn, Block &. Windham, Australia..
Day Dawn, Block & Windham, Australia...
Day Dawn, Block & Windham, Australia...

General Grant, Australia -.-

Golden Gate, Australia

5
6

P.McIntyre....

P.McIntyre..

8
9
10
11
12
13

P.McIntyre

P.McIntyre.

P.McIntyre

Sludge....

Concentrates

Mills United, Australia

P.McIntyre

Mount Morgan, Australia

Ore, ironstone, and kaolin.

P.McIntyre

New Towers Fxtend Australia

P.McIntyre.

New Towers Extend., Australia

P.McIntyre...

•10

New Towers Extend., Australia..

P.McIntyre..

Sludge

Ore

Alhurnia, New Zealand...

Crown.New Zealand

56.78
70.5
79
79
79
94

79.78
77.06
83.70
74,60
16.10
35.16
100
97.10
67
68.7
59.58
60

64.45
28.46
61
46.6
49
49
49.8
49.8

""98""
98
83
61.65

"s'g'gs

54.47
3
83

$3 37

MacConnell

Crown' New Zealand

Ore . .

MacConnell

$41,350 00

3 50

Kenilworth, New Zealand

MacConnell

Ore

Silverton, New Zealand

Sylvia, Tararu, New Zealand

MacConnell

39
40

Concentrates, slimes

A. Scheidel

A. Scheidel....

A. Scheidel

A. Scheidel.

1^ 42,200 00

Sylvia, Tararu, New Zealand

42
43
44

Jigger concentrates

Coarse concentrates

Waihi, New Zealand

Robert Rose.

Robert Rose

G. & 8. Extr. Co. of Amer..

.1125 00
22 50
22 50

22 60

23 00
23 00

12 00

13 00
13 00

6 00
20 00
10 80

1.945 00
1,705 00
2,775 00
3,010 00
} 32,000 00

42 87
63 83
60 57

43 31
113 74

54'11
2,920 00
1,386 23
63 20
43 06
198 50
22 64
220 60
63 50

52"86'

166 42
66 70
253 68
301 16
487 20
157 63
«,0OO 00
16 03
56 24
4,240 OO
207 41
10 08
133 36

2 25

4li

1 76

Ore

1 50

Waihi, New Zealand

Boulder City, U.S. A

Boulder City, IT. S. A

1 38

4»

Ore

1 38

138

$0 60

60"

26 00

1 04

iei'is'

11 IS

2 46
1 40

3 51

"i'he

"""42
1 49
48 00
39 00
42 92
63 00

4 00

pi 00

66 65
61 20
44 20

138 00
69 26

"'"'l'i546"49"
79 97
49 23

233 07
25 95

262 60

67 42

6i"25"

183 62
67 50
289 63
340 17
915 60
170 50

2 25

2 60

3 00

ChicagcU. S. A

1 00

G. &S. Extr. Co.of Amer.

3 00

El Capitan. U. S. A. .

Eureka, Cal„ D. S. A

Flor do Marzo, U. S. A

Golden CloudLD. S. A.

Golden Rose, U, S. A

Gregory, U. S. A

KingsOre, U. S. A...

ELematite

Frue concentrates

1 13

57
5S

A. Scheidel

3 60
11 05

51)

8 40

28 80
16 00

9 10

15 00
11 20

""6 '20
13 20

"is '66"
4 00
2 40

27 00

10 40
8 80

38 00

"39'26"

16 40

29 04

2 50

2 86

til

4 00

3 00

t)3

Or5

McKeivie, tj. s. A, :::::;".:'.;:::;:::;'.;:::".'.:

Mercur, Utah, U. S. A

Old Charlie, U. S. A.

Siliciousore

""96""
33.6
84
87
83.4
62
82

2 25

Ore

Gill S.Peyton

2 40

ti«

1 50

Oro Grande U. .S. A

311. and pyrites

Ore with antimony

G. & 8. Extr. Co. ol Amer..
G. & 8. Extr. Co. of Amer..
G. & S. Extr. Co. of Amer.
G. &S. Extr. Co.of Amer..

1 21

Poorman, U. S. A

Poorman, U. S. A....

Poorman, U. S. A

Revenue, U. S. A :"."."."': "

Revenue, U. S. A.

R. M, Terror, U. S. A. .; ::.\V.:\[:^[[[[

Rosecrance, tJ. 8. A

Utica Mine, California, U. S. A '.'.'.'

Western Belle, U. 8. A

3 00
500

6 83

Stephanite

Siliciousore

6 49

2 00

Tailings

F. B. &R. B.Turner

G. & S. Extr. Co. of Amer.

6 78

3 75

"'4 "92"
2 24

4 29

36 63
62 62

"■"232'05
83 88
166 66

88.6

93.18

82.78

"6"8;6"'
48
61.32

2 50

Canvas concentrates

Silicions..

A. Scheidel

G. & 8. Extr. Co. of Amer..

3 27

4 40

Wolferine. U.S. A..

Chicago, Old Mexico...

600

3re

2 31

PERCENTAGE OF EXTRACTION. 41

ore has to be considered parallel with the chemical, and that process
should be adopted which permits the extraction of the largest percentage
of bullion at the lowest cost, and with the least investment of capital.
The cyanide process is, for this reason, the best yet discovered for the
treatment of the tailings of the South African gold fields, although
giving only an average of extraction of about 70 per cent, of which about
60 per cent is recovered (see page 52). No other process gave, at the
same expenditure, any results approaching it. The conditions of the
Witwatersrand ores are considered particularly favorable for the process,
yet the extraction figures are, in most instances, not high. The per-
centage of extraction in various mills in Johannesburg will be given in
the chapter on the process in Africa, page 60. The ores and tailings in
New Zealand, where cyanide treatment of dry-crushed ores is carried on
extensively, give better results. The Waihi ores, pure quartz, the gold
free, but exceedingly fine, the silver in form of sulphides, no sulphurets
of base metals, give an extraction of from 85 to 91 per cent of the gold
assay-value, the silver returns varying from 43 to 51 per cent. The ore
of the Crown mines, which resembles those of Waihi, but containing
occasionally telluride of gold, yields on an average 93 per cent of gold
and 79 per cent of silver. Concentrates, if satisfactory at all in cyanide
treatment, give as a rule very high figures. A considerable quantity of
concentrates from the Sylvia Mine in New Zealand, of a very complex
character, being composed chiefly of zinc-blende and copper pyrites,
with a large percentage of galena and iron pyrites, were treated by me
by cyanide, and gave very satisfactory results under conditions where
no other means of treatment were at disposal. The said concentrates
are classified by the dressing plant; the fine slimes rich in bullion and
galena gave as high an extraction as 95.43 per cent of the gold and
86.69 per cent of the silver; coarse concentrates gave an average of 80.32
per cent of the gold and 50 per cent of the silver. A large parcel of very
fine sulphurets (from the canvas plant) from the Utica Mine, California,
consisting of pure iron pyrites in finest division, mixed with more or less
fine sand and carbonate of lime, proved an excellent material for cyanide
treatment; the extraction averaged 93.18 per cent of the gold value, rising
in some instances as high as 96.57 per cent. The coarse concentrates from
the Frue vanners did not give such good results, if treated direct; their
reduction to greater fineness, however, improved results. An appended
table shows the results of successful treatment of parcels of ores from
various sources. It is to be regretted that no corresponding table, giv-
ing a like description of ores treated with unsatisfactory results, can be
produced for comparison, which would be useful and instructive.

The recovery of the bullion should correspond with the extraction
shown by assays; in practice, however, there is often a discrepancy, which
rnay be explained by various causes; new vats, particularly those of
wood, absorb both gold and cyanide, and considerable differences in the
returns will be felt during the first weeks of their use. In the Waihi
Company's works in New Zealand, for instance, 116 tons of ore, of an
assay-value of about -$25 per ton, returned after the first month only 75
per cent of the gold, instead of 85 per cent as shown by assay; the
returns of the second month yielded 80 per cent, instead of 91 per cent;
after the third month the actual results came up to the extraction, as per
assay — 89 per cent. Similar experiences have been made in the Sylvia
Company in New Zealand and elsewhere. It has been recommended to

(c
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the

PERCENTAGE OF EXTKACTION. 41

ore has to be considered parallel with the chemical, and that process
should be adopted which permits the extraction of the largest percentage
of bullion at the lowest cost, and with the least investment of capital.
The cyanide process is, for this reason, the best yet discovered for the
treatment of the tailings of the South African gold fields, although
giving only an average of extraction of about 70 per cent, of which about
60 per cent is recovered (see page 52). No other process gave, at the
same expenditure, any results approaching it. The conditions of the
Witwatersrand ores are considered particularly favorable for the process,
yet the extraction figures are, in most instances, not high. The per-
centage of extraction in various mills in Johannesburg will be given in
the chapter on the process in Africa, page 60. The ores and tailings in
New Zealand, Avhere cyanide treatment of dry-crushed ores is carried on
extensively, give better results. The Waihi ores, pure quartz, the gold
free, but exceedingly fine, the silver in form of sulphides, no sulphurets
of base metals, give an extraction of from 85 to 91 per cent of the gold
assay-value, the silver returns varying from 43 to 51 per cent. The ore
of the Crown mines, which resembles those of Waihi, but containing
occasionally telluride of gold, yields on an average 93 per cent of gold
and 79 per cent of silver. Concentrates, if satisfactory at all in cyanide
treatment, give as a rule very high figures. A considerable quantity of
concentrates from the Sylvia Mine in New Zealand, of a very complex
character, being composed chiefly of zinc-blende and copper pyrites,
with a large percentage of galena and iron pyrites, were treated by me
by cyanide, and gave very satisfactory results under conditions where
no other means of treatment were at disposal. The said concentrates
are classified by the dressing plant; the fine slimes rich in bullion and
galena gave as high an extraction as 95.43 per cent of the gold and
86.69 per cent of the silver; coarse concentrates gave an average of 80.32
per cent of the gold and 50 per cent of the silver. A large parcel of very
fine sulphurets (from the canvas plant) from the Utica Mine, California,
consisting of pure iron pyrites in finest division, mixed with more or less
fine sand and carbonate of lime, proved an excellent material for cyanide
treatment; the extraction averaged 93.18 per cent of the gold value, rising
in some instances as high as 96.57 per cent. The coarse concentrates from
tlie Frue vanners did not give such good results, if treated direct; their
reduction to greater fineness, however, improved results. An appended
table shows the results of successful treatment of parcels of ores from
various sources. It is to be regretted that no corresponding table, giv-
ing a like description of ores treated with unsatisfactory results, can be
produced for comparison, which would be useful and instructive.

The recovery of the bullion should correspond with the extraction
shown by assays; in practice, however, there is often a discrepancy, which
rnay be explained by various causes; new vats, particularly those of
wood, absorb both gold and cyanide, and considerable differences in the
returns will be felt during the first weeks of their use. In the Waihi
Company's works in New Zealand, for instance, 116 tons of ore, of an
assay-value of about .$25 per ton, returned after the first month only 75
per cent of the gold, instead of 85 per cent as shown by assay;' the
returns of the second month yielded 80 per cent, instead of 91 per cent;
after the third month the actual results came up to the extraction, as per
assay — 89 per cent. Similar experiences have been made in the Sylvia
Company in New Zealand and elsewhere. It has been recommended to

42 THE CYANIDE PROCESS.

soak the wooden parts of a new cyanide plant with paraffine to prevent
absorption; a coat of asphalt dissolved in bi-sulphide of carbon will be
found a good preventive for the absorption by wood. The chief sources
of chronic losses are to be found in the imperfect separation of the gold
solution from the exhausted ore residues, and in the faulty methods of
dealing with the bullion after its precipitation by zinc. There is no
reason why the actual returns should differ from the returns as estab-
lished by assay, provided all mechanical losses are prevented. In refer-
ence to the losses in the Johannesburg mills, see chapter on the process
in Africa, page 52.

VI. WORKING COSTS OF THE PROCESS.

As may be deduced from the whole tenor of this paper, the working
costs of the cyanide process vary within wide limits and depend on many
circumstances. Locality is a prime factor in the costs of working any
process, and expenses must be high where operations have to be carried
on in an inaccessible situation, or where there is dearth of fuel, water,
building material, etc. Apart from the question of locality, the cost
depends principally upon three factors:

The nature of the ore.

The price of labor.

The price of cyanide.

When an ore contains acid salts and demands an alkali treatment,
the price of the alkali must necessarily be added to other costs; and
where the ores are slimy, recourse must be had to drying and mixing
appliances, which also increase the cost to an extent depending on local
■circumstances. The principal labor involved in the process is the charg-
ing and discharging of the vats, or, if agitation is used, the charging of
the agitator and the removing of the exhausted material from the filter
appliances. The charging and discharging of the percolation vats may,
under ordinary circumstances, be contracted for at a rate of about 25
<jents per ton; the extent of the operations is naturally of great influence
in regulating the cost of handling. Very large works apply mechanical
means for discharging the vats, such as dredges and movable cranes,
which reduce the expense of labor per ton of ore to a minimum. To
give an instance of the labor employed in working the agitation process
I mention the Utica works in California, where the handling of the
ore and all the labor connected with the treatment amounts to $1 per
ton; this applies to concentrates*varying from $50 to $95 in value per
ton. The cost of the cyanide is one of the principal charges in the
process, and the cost of treatment depends to a great extent upon the
price of cyanide and on the amount consumed per ton of ore. The price
•of cyanide of from 95 to 98 per cent strength now averages about 50 cents
per pound, delivered at seaports, and for lower strength the rates are
somewhat better.

The amount of cyanide consumed per ton of ore is between 1 lb. and 3
lbs.; the character of the ore has, however, the greatest influence on the
consumption, and in many cases the cyanide process will be found the best,
cheapest, and quickest method, even if a considerably larger amount of
cyanide is consumed per ton. Naturally, as the quantity treated is greater
the cost becomes proportionally less. In some mines, as at the Primrose

WORKING COSTS, ETC. 43

Company, Johannesburg, tailings are treated for about $1 per ton, and it
is very seldom that the cost in the Transvaal exceeds $2 50. In the
Crown Reef works the cost of treatment ranges from $1 to $1 37 per
ton; this includes the royalty, which for the use of the MacArthur-Forrest
patents amounts in South Africa to $1 25 per standard ounce of gold.
In Revenue, Montana, the cost of treatment per ton of ore, including
crushing, amalgamating, cyanide treatment, and royalty of •$! per ton,
amounts to from $4 to $5 per ton. The cost of treatment of ore at the
Mercur Mine, Utah, amounts to $2 40 per ton, not including royalt}'.
The cost of ore treatment in the Crown mines. New Zealand, is from
$3 37 to $3 50; in the Waihi Company's works. New Zealand, the cost
amounted to $2 25 per ton of ore; the expenses are now reduced to
$1 25, cost of crushing and patent-royalty of 7^ per cent on the bullion
value not included. The treatment of concentrates is, as a rule, more
expensive than that of ore and tailings; their value is, however, in most
cases, considerably higher than that of those materials, so that the cost
per ounce of gold extracted is, with concentrates, generally much lower
than with ore and tailings. The agitation treatment of concentrates
(sulphurets) costs in the Utica works, California, from $3 25 to $3 50
per ton, labor included. " Ores yielding upwards of 90 per cent of their
gold assay-value have been treated at $1 25 per ton, and tailings con-
taining less than $3 have been worked profitably. It is therefore safe
to assume that under favorable circumstances, and apart from all costs
of mining and crushing, the cyanide process is capable of application at
a low figure."

VII. COST OF CYANIDE PLANTS.

The cost of cyanide plants varies naturally with the system applied
and the extent of the works. A well-equipped plant with a capacity of
50 tons per day will cost about $25,000, a 100-ton plant about $40,000.
I shall have occasion to give details on the cost of plants when describ-
ing prominent and successful plants in different parts of the world, and
I refer particularly to the corresponding chapter of the process in Africa,
page 55.

VIII. MACHINERY AND APPLIANCES.

In discussing the various methods of applying cyanide, the ma-
<:hinery for each purpose has been described (see Chapter IV). Gen-
erally speaking, all plants have the same main features; modifications,
however, will be suggested by special conditions of locality and char-
acter of ore. Economy in handling the ore is of the greatest impor-
tance, and should be made of first consideration in selecting the site
for the plant and in its arrangement. The crushing machinery, if ores
are to be treated without previous amalgamation, should be selected in
accordance with the character of the material. The proper prejjaration
of the ore is a very important item, and the crushing machinery should
be selected so as to produce the smallest amount of dust if dry-crushing
and of slimes if wet-crushing of the ore is practiced. For drv-crushing,
rolls should be preferred, on account of their giving a product of greater
uniformity than stamps, which are now used to a great extent. It is
with the cyanide process as with other leaching processes, the more

44 THE CYANIDE PROCESS.

equal in size the particles are, the better. Wet-crushing, with the
improvements necessary for mastering the slime difficulty, may ulti-
mately win. Pumps of all constructions may be used for the transporta-
tion of the solutions, provided their material is not attacked by the
alkaline cyanide solution. I shall refer to the general arrangement of
plants in the corresponding chapter of the process in Africa, page 55.

IX. LABORATORY WORK.

Exact laboratory experiments must precede all cyanide mill opera-
tions; the required fineness of the ore, the strength of the cyanide
solution, and the length of time for its action on the ore, have to be
established by experiment. The correct strength necessary for treating
any class of ore may be readily determined in the laboratory by treating
a weighed quantity of the ore with cyanide solutions of different strength
and for various periods of time. After treatment, the amount of gold
extracted and the quantity of cyanide consumed should be determined.
These results are then compared with the original contents of gold and
silver in the ores and the original strength of cyanogen in the solution
used. A method of rapidly determining the gold in the cyanide liquors
consists in evaporating a known quantity to dryness on lead foil (free of
■silver), and cupelling the lead in the usual manner. In the presence of
base metals, the liquor should be evaporated with the addition of litharge,
and the residue assayed for gold and silver in the usual manner. Tlie
point to be aimed at is to consume as little as possible of cyanide and to
extract at the same time as high a percentage of gold and silver as pos-
sible. The water used for making up the solutions should be examined
for carbonic acid, free sulphuric acid, and sulphates. A chief point to
be investigated in the laboratory is the " acidity " of the ore, by which
term is understood the presence of products arising from the decompo-
sition of sulphurets. These chiefly consist of free sulphuric acid and of
products derived from a more or less advanced oxidation of pyritic
matter, such as proto- and per-sulphates and basic iron salts. The exact
amount of free acid contained in an ore sample can be readily deter-
mined by shaking a certain weight with water, and adding standard
normal or one-tenth normal caustic soda solution, till the point of alka-
linity is reached, as indicated by litmus or some other indicator. The
means to prevent the ill effects of acidity have been discussed in the
chapter on chemistry. The amount of soda or lime required for the ore
is easily calculated from the consumption of normal soda solution as
shown by the above experiment. The cyanide solution will in many cases
contain after the treatment of ore the evidence of secondary reactions, and a
complete chemical analysis of the solution, before it comes into contact with
the zinc, should in all cases he made. The explanation of ^m satisfactory
results with cyanide treatment will be found in many instances by means of
such an examination.

The reasons why one ore yields its gold readily to cyanide treatment,
and others of a similar chemical composition do not, are not always
apparent; chemical analysis and microscopical examination should be
used along with practical tests. As a programme for the examination of
an ore in reference to its fitness for cyanide treatment, the following may
be suggested: (1) The ore shall be crushed and passed through a 30-mesh

LABORATORY WORK DANGER IN WORKING. 45

sieve, and part of it assayed. (2) The "acidity," if any, of the ore,
shall be determined, as described before, in say 100 grams; if necessary,
water and alkali washes will then be applied before the ore is submitted
to cyanide treatment. (3) Shaking tests in glass bottles with solutions
of various strength during various periods of time will determine the
amount of cyanide consumed by the ore, the strength of solution required,
and the time necessary for the reaction. Cyanide determination in the
solution and assay of the ore, after treatment, provide the required data.
Agitation tests will decide if an ore is suited for cyanide or not. In
cases of successful cyanide treatment by shaking tests, percolation tests
of samples should then be made. The simplest apparatus for the pur-
pose is a glass funnel of large size, the neck of which is closed by an
india-rubber pipe and clip; a lamp chimney closed at one end by a
stopper of india-rubber, which carries a glass tube, may be used for
the same purpose. The ore is placed on a filter-bed of pebbles, which
is covered by a piece of flannel or filter-paper. Experiments with equal
weights of ore, but with solutions of various strength, and exposed dur-
ing various periods of time, should be made simultaneously; analyses
of the percolated solutions and assays of the well-washed residues will
then show the best conditions of treatment. Small tests, if properly
conducted, are excellent guides as to the treatment of ore on a large
scale. In a cyanide plant there is ample employment for the chemist in
charge; all operations should be controlled by him by assays and
analyses; improvements on all parts of the process may be effected by
careful observation and continued investigation. The non-success of
the cyanide process in various mining camps may be attributed to the
incompetency of the men to whose care the works were intrusted.
Mine owners will find- it profitable to employ, at least during the first
time of their using cyanide, a competent man, instead of "finding out"
for themselves at the expense of much time and money. When the
process is once successfully and firmly established, an intelligent fore-
man will easily acquire the necessary knowledge to test and make up
the solutions.

X. DANGER IN WORKING THE PROCESS.

The deadly poisonous character of the reagent was once considered to
be a great obstacle in the way of its successful introduction. However,
in the first place, the solutions used are so diluted that the hydrocyanic
acid evolved from them is of no consequence if the works are properly
ventilated. For safety, as much as for practical reasons, all materials
should be tested for acid before treatment, and, if necessary, neutralized.
In the second place, there is no necessity for those working the process
to come into contact with cyanide, solid or in solution; even properly
conducted cleaning up does not require contact. Some, but very few,
have a susceptibility for cyanide, and with them the most diluted solu-
tions, if brought into contact with the skin, produce eruptions, which,
although not dangerous, are itching and annoying; such men should
not be employed in cyanide works. In case of bad ventilation, com-
plaints of headache, faintness, and dizziness may be heard. In instances
where circumstances require that hands and arms should be brought in
contact with the solution, I found a coating of oil or coal oil (kerosene)

46 THE CYANIDE PROCESS.

an eftective protection for the skin. The process is now used so generally^
and on such a gigantic scale, that many hundred men are constantly
employed in the works; considering the dangerous character of the
cyanide, the number of accidents is remarkably small, and it may
justly be said that no more danger is incurred in the working of the
cyanide process, under ordinary precautions, than there is in working
in establishments of chemical and metallurgical industries, where corro-
sive liquids and acids are constantly in use. Extraction of gold and
silver by cyanide will compare, as to fatal accidents, very favorably with
most chemical and metallurgical industries. It is, however, always well
to instruct the men how to act in cases of emergency: Put the patient into
a hot bath and apply cold water to his head and back. In cases of inter-
nal poisoning, vomiting by physical means, or by emetics, is advised.
Freshly precipitated carbonate of iron, obtained by mixing equal quan-
tities of sodium carbonate and ferrous sulphate, is recommended for
internal use; the two chemicals should be kept on hand ready for com-
pounding this antidote. If the poisoning is the consequence of inhala-
tion of hydrocyanic acid, it is advisable to make the patient inhale a
small quantity of chlorine gas, ammonia, or ether; rubbing with cam-
phor-alcohol is recommended. It has been reported of late that Dr.
Johann Antal, a Hungarian toxicologist, has notified the Hungarian
Society of Medicine that he had found a perfect antidote for prussic
acid in nitrate of cobalt; he quoted forty cases of its use with perfect
success.

XI. EXEMPLIFICATION OF THE PROCESS— THE PROCESS
IN VARIOUS COUNTRIES.

After having given the outlines of the process, and the various methods
of its use, I now propose to describe its practical application in different
parts of the world.

A. The Process in Africa.

The cyanide process has found its earliest application on a large ecale-
in the Witwatersrand gold fields of Johannesburg, South African Re-
public. The use of the process has since been extended to the difi'erent
gold fields of the republic, the output of which has gone on steadily
increasing, rather by application of improved machinery and the Mac-
Arthur-Forrest recovery process, than by the opening up of new mines.
In the following notes, describing the methods of cyanide treatment in
South Africa, I give chiefly the general information obtained from Mr.
J. M. Buckland, the General Manager of the African Gold Recovery
Company of Johannesburg, and embody in them, at the same time, the
special information obtained from other gentlemen in charge of promi-
nent companies and works.

The Ores. — "At the Witwatersrand, from which at present some forty-
five thousand ounces, or about 90 per cent, of the gold obtained in South
Africa by the cyanide process is obtained, the ore nwy be classed generally
as conglomerate, locally called 'banket' (almond-rock). This consists
practically of quartz pebbles embedded in a quartzose matrix, which last
carries the gold and a varying proportion of iron pyrites. There is also a
small quantity of alumina'in most 'banket,' existing in diverse forms of

EXEMPLIFICATION OF PROCESS THE PROCESS IN AFRICA. 47

corundum and (combined with silica) of clay. The latter is the cause
of much of the slimes formed during the crushing process, the cheap and
profitable treatment of which by cyanide still remains a difficult problem.
The iron pyrites almost invariably contain traces of copper and nickel
as sulpliides. Within 50 to 100 ft. of the surface, the 'banket' is
more or less weathered, and the iron exists in an oxidized form; but
below this depth the ore becomes paler in color, less friable, and conse-
quently more difficult to crush, and iron pyrites takes the place of the
iron oxide. The gold also is more difficult of extraction by amalgama-
tion or by cyanide; but whether in this latter case the cause is chemical
or mechanical is not yet determined. On the latter hypothesis, the
difficulty would consist in the fact that the particles of gold are so
imbedded between the cleavage planes of the pyrites as to prevent to a
great extent contact with cyanide solution; and, on the former, that the
gold exists chemically combined with certain constituents of the ore,
such as sulphur and arsenic — the cyanide having presumably not suffi-
cient affinity to act as a solvent by breaking up the bond of union.

" At the Sheba Mine, De Kaap District, the ore is a quartzite, contain-
ing a small amount of iron pyrites and talc. When crushed, there are
formed, owing to weathering, sulphates of iron and free sulphuric acid,
which react on the talc (silicate of magnesia), forming sulphate of
magnesia, and this salt may be observed as an efflorescence on many
of the tailings-dumps. This compound, like all others in which
the ' base ' is weaker than potash and the ' acid ' stronger than hydro-
cyanic acid, causes decomposition and loss of cyanide (see chapter
on chemistry). At the Barrett Company (Kaapsche Hoop), the ore is
a very soft, decomposed talcose slate, containing a large proportion of
hydrated iron oxide. Owing to the very fine nature of the gold the
solution of it is almost complete, but sufficient of the very finely divided
portion of the ore passes through the filter cloth, coats the zinc, and
prevents thereby the gold solution from coming into contact with it;
precipitation is consequently seriously interfered with. The difficulty
in such cases is met to a certain extent by the use of an extra vat,
placed between the leaching vats and the precipitating boxes, in which
the greater part of the suspended matter is allowed to settle, and tolera-
bly clear liquid is filtered off. This ore is of so soft a nature as not to
require any explosives in mining; it does not even require preliminary
crushing for the purpose of preparing it for treatment, but is simply
sifted through drums, and the portion which passes through the sieve,
when mixed with coarse tailings to assist filtration, is ready for cyanide
treatment.

Ore Reduction. — "At present, with the above-mentioned exception, all
ores in the Transvaal gold fields, which are treated by cyanide, have
previously undergone the ordinary crushing and amalgamation process
in the battery. The wet-crushing stamp-mill is the only machine
employed for ore reduction, apart from various grinding machines, such
as the Wheeler and Berdan pans, which are rarely used for the finer
reduction of tailings and concentrates. At the Rand ( Witwatersrand),
the average mesh employed for battery screens is thirty holes to the
linear inch (No. 30 screen), or 900 to the square inch. In some cases,
however, No. 24 screens are used. At mines, such as the Sheba, where
the gold is very fine, No. 40 screens are employed, but the tonnage per
stamp per twenty-four hours is in such cases not much more than twa

48 THE CYANIDE PKOCESS.

tons, as compared with the three and two thirds tons usual for mills
crushing Rand ' banket.'

" In an experimental way, a solution of cyanide has been used instead
of battery water; at present, however, water is invariably used in the
mortar boxes, sufficient success not having attended the other method.
The use of cyanide solution in the mortars would be of advantage only
when the pulp is directly delivered into the percolation vats; the for-
mation of slimes is fatal to this method. There is now no other process
than the cyanide process used in treatment of tailings, and no mill of
which the tailings are of sufficient value is considered complete without
a cyanide plant. On the Witwatersrand alone there are upwards of
forty cyanide plants in operation, and ten in process of construction;
the present quantity of tailings treated monthly is about 250,000 tons.
On the other gold fields — DeKaap, Lydenburg, and Klerksdorp — there
are in all ten cyanide plants in operation.

Method of Applying Cyanide. — " The method of applying cyanide to
gold extraction is that specified in the MacArthur-Forrest patents, of
which the African Gold Recovery Company holds the rights in Africa,
and lets out the right of using the process to gold-mining companies on
royalty, usually 10 per cent on the value of the gold produced. Nearly
all companies using the process erect and work their own plants, paying
royalty as above." Some custom-works will be mentioned later on.

The mode of procedure in applying the cyanide process in Africa is
generally that which has been outlined in the earlier part of this paper.
Some further details, however, will here be given and may prove of
interest. The general system of treatment is that of percolation in tanks.

The Vats. — "The percolation tanks, or leaching vats, vary greatly in
size and shape. Those first constructed were from 15 ft. to 20 ft. square,
and from 4 ft. to 5 ft. deep, the material used being boards 9 in. wide by
3 in. thick and as long as the side of the vat. Owing chiefly to the
difficulty of making these water-tight, oval and finally round vats, com-
posed of staves 2^ in. thick, 6 in. wide, and varying in length from 5 ft.
6 in. to 11 ft., were used. Vats now vary in diameter from 15 ft. to 40
ft., and in capacity from 30 to 600 tons. The employment of bottom
discharge, by which the exhausted tailings, or 'residues,' are shoveled
through a hole in the bottom directly into a truck below, has rendered
the great increase in depth possible. ' Side discharge ' through doors in
the side of the vat is also employed to some extent. Discharge over the
side into trucks on tram-lines is now used only in cases when first cost,
or ' want of fall,' in the dumping-ground is a serious consideration. The
loading into trucks does not cost more than 4 cents per ton, even under
unfavorable conditions, and is only 2 cents and even less per ton in some
cases. At the Barrett Company, the residues are shoveled through an
opening in the bottom of the vat into a launder, where a stream of water
carries them away." Some companies, like Le Champ d'Or French
Gold Mining Company, let the filling and emptying of their cyanide
tanks by contract.

"In some of the largest works cement vats are used, particularly for
' sumps,' or tanks, where the solution is stored after passing through
the precipitation boxes. Such vats are really excavations lined with
bricks, laid in hydraulic mortar, and plastered inside with cement;
these attain a capacity of 600 tons, being 50 ft. in diameter and 9 to
11 ft. deep. For discharging them, when they are used as percolation

EXEMPLIFICATION OF PROCESS THE PROCESS IN AFRICA. 49

vats, either tram-lines are laid down along the bottom, passing out
through doors, which are bolted and made water-tight when the vat is
in use, or else trucks are lowered by a steam crane into the vat, and
filled by natives, and again hoisted" (see diagrams, page 57). "At the
Salisbury works a tailings wheel lifts the pulp, after passing over the
amalgamating plates, to a flume, which carries it to a hydraulic sepa-
rator, which separates the slimes from the coarse tailings. This is done to
render the subsequent treatment of the tailings more economical, as easy
filtration is achieved when tailings free from slimes are treated. The
slimes are treated by themselves and filtered in filter-presses. Many
companies now run the material from the mill into intermediate settling-
vats, provided with bottom or side discharge, for convenience of loading
the trucks which transport it to the cyanide works. The difficulty of
insuring an equal mixture of fine and coarse tailings is met by means
-of a rotary distributor, pivoted above the center of the vat and discharg-
ing into it. This distributor consists of pipes of different lengths
diverging from a central basin into which the pulp is delivered. The
openings at the end of the pipes are so arranged that the stream of pulp
issuing therefrom causes the distributor to rotate." In the Nigel Com-
pany's works the slimes are separated from the sand by means of tailings-
pits, with overflow into pits where the slimes are collected; these are
dried, broken up, and delivered, mixed with the clean sand, into the
vats in the works.

Treatment of Concentrates. — " Concentrates are not now treated by agi-
tation in the Witwatersrand gold fields; percolation has been substituted
ior it. A period of contact and percolation, extending from two to four
weeks, is now usually employed. Agitation has been abandoned on
account of its cost, consequent upon the power and constant attention
required, and the necessarily small amount treated at one time. In
addition, it was found that the cyanide consumption was usually
increased by the solution becoming heated, owing to the friction of the
solid particles during an agitation of several hours. In treating by
ordinary percolation, the concentrates are usually mixed with a suffi-
cient amount of coarse tailings to insure filtration. Transferring the
material from one vat to another at intervals of a few days is sometimes
oonsidered beneficial, for the purpose of obtaining a supply of oxygen
as required by Eisner's equation." (See chapter on chemistry, p. 16.)

"Although pyrites themselves consume practically no cyanide, the
great difficulty incurred in the treatment of concentrates generally, and
of some tailings, is due to the fact of their having been partially oxidized
by exposure to the air." The reactions thereby taking place have
already been mentioned as detrimental in the chapter on chemistry,
and the remedies enumerated (see p. 18). "The water-washings em-
ployed to remove the 'acidity,' as it is termed, take place in a special
vat, as the traces of the cyanide retained by the filter-cloth, etc., of the
regular leaching vat are liable to dissolve gold, and thus cause loss.
Experiments have shown that a water-wash pure and simple will dis-
solve out of most tailings a minute quantity of gold, but this is so small
an amount that it may be neglected. If the ore is not very acid a solu-
tion of caustic soda is run on after the last water-wash, and the air
contained in the solution will serve to convert the ferrous hydrate
formed, which would otherwise subsequently form potassic ferrocyanide
4cp

50 THE CYANIDE PROCESS. •

with the potassic cyanide, into innocuous ferric hydrate. If very acid,
however, aeration, by changing to another vat, will be necessary.

" Lime sprinkled on the surface of the charge of ore, or mixed with it,,
is often preferred to caustic soda, and has the advantage of clarifying
solutions from organic compounds, which, if present, cause 'frothing'
in the zinc boxes. Lime does not form the yellowish-white precipitate
in the zinc boxes, which is mainly ferrocyanide of zinc, and liable ta
occur when caustic soda is used, and which, by coating the zinc, inter-
feres with the proper precipitation of the gold."

The Advisability of Ore Concentration. — " The question as to whether
it«is advisable to concentrate, or to allow the pyrites to remain with
the tailings for subsequent cyanide treatment, is at present under
discussion, and, like all other matters in gold extraction, resolves itself
into a question of cost. The general rule is, that with high-grade pyrites
concentration does pay, but with low-grade not." The Nigel Company
has abolished the use of concentrating machinery. They found that the
extraction of gold by cyanide treatment is equally as good from the ore
from which the concentrates have not been taken, as it was when using
True vanner concentrators. Their tailings are consequently of a high
grade, containing pyritic matter, and solutions of greater strength are
used than is the practice with other works on the Rand. (W. A. Radoe.)

The Cyanide Solutions. — "The strength of the solution before treat-
ment was some four years ago i and 1 per cent, but now 0.25 and 0.3
per cent may be taken as the usual amount of pure cyanide of potassium
contained in what are usually called strong solutions in South Africa.
In most works a constant quantity of this strong solution is run on
each charge of ore, having been made up from the ' weak' or dilute solu-
tion in stock by addition of a sufficient quantity of the solid salt, or a
concentrated solution prepared from it. Should the cyanide consump-
tion of the ore increase, the strength of the dilute solution, or that which
has been already used, decreases, and more solid cyanide is required,
and vice versa. Another method consists in always adding the same
amount of solid cyanide to the same amount of weak solution, and in
case the latter is below a certain point (say 0.1 per cent) to continually
use a larger quantity of strong solution for running on the ore until the
'weak' rises to 'normal' once more. If the strength of the stock solu-
tion falls too low, the precipitation of gold is imperfect, probably because
the cyanide of zinc formed in the precipitation boxes is not dissolved
and coats the zinc. If, on the other hand, it is too high, the consump-
tion of cyanide and zinc, by dissolution of the latter in the former, is
unnecessarily great. In this case, too, the loss of cyanide by atmos-
pheric decomposition is increased, and, while the same absolute amount
of solution is lost by leakage and in the form of moisture adhering to por-
tions of the residues, yet, the solution being stronger, more potassic cyanide
is lost. The quantity of strong solution employed per charge of ore
varies according to whether a preliminary washing with a dilute solution
has been employed or not. In the former case, it is about 25 per cent of
the weight of the ore, and in the latter case about 40 per cent, which last
quantity is usually sufficient to just cover the charge. The amount, how-
ever varies in different works, and, within reasonable limits, it is not a
matter of great importance, provided sufficient solid cyanide is added
daily to keep the stock of weak solution at the right strength. It is
desirable that the strong solution be of uniform strength throughout the

EXEMPLIFICATION OF PROCESS — THE PROCESS IN AFRICA. 51

whole charge of ore, and this object is attained, in great measure, by
using a preliminary washing with a dilute* solution; the cyanide of the
latter satisfies most of the components of the ore, which consume
cyanogen, so that the strong solution, which follows, is free to act on
the gold alone. This preliminary wash has also the advantage of satu-
rating lumps of slimes which may be in the tailings and would absorb
the strong solution, which would be lost when the residues are dis-
charged. Generally speaking, a larger quantity of the weaker solution
is preferable to a smaller quantity of strong solution, but exigencies of
time, capacity of the plant, filtering properties of the material, etc.,
cause modifications of this rule. When a charge has had more than its
own weight of washings passed through it, it becomes a question whether
there is suflBcient increase in yield by continuation of the process to
cover the cost of pumping, apart from the fact that if the solution be
run too fast through the zinc boxes not only is the gold it contains
imperfectly precipitated, but that already deposited is liable to be
haechanically carried into the sump by the force of the current."

The strength of cyanide solutions used in the Crown Reef Mine works
varies from 0.05 per cent to 0.35 per cent; they range after treatment
from nothing to 0.33 per cent. The total quantity of solution used, inclu-
sive of water-washes, is about 80 per cent of weight of charge; extraction
takes from forty to fifty hours. (G. E. Webber, Jr.) In the Nigel
Company, where, as already stated, concentration has been abandoned,
the conditions are in consequence somewhat different from those usually
prevailing in cyanide works; for tailings over 24 dwts. (about $18) in
value a solution of 0.6 per cent is used, preceded by a weak wash of
solution of 0.15 per cent and followed by two weak washes; the liquors
drain off at a strength of from 0.4 to 0.25 per cent of cyanide, the first
solutions draining off at a lower percentage than the last. The amount
of cyanide used per ton is about 3.8 or 3.5 lbs. per oz. of gold re.covered
(3.5 lbs. of 76 per cent cyanide). (W. A. Radoe.)

Precipitation by Zinc. — The precipitation process going on in the zinc
boxes has been fully discussed in a former part of this paper.

" After passing through the zinc box the solution should not contain
more than 50 cents of gold per ton, and in the majority of cases there will
be only a trace of gold present. If appreciable quantities of gold remain
unprecipitated, a certain amount is daily lost in the dilute cyanide
solution contained in the residues (see above). The latter should be
periodically tested for gold soluble in water, and gold soluble in cyanide
solution; imperfect precipitation will be discovered by the first, and too
short time of treatment by the second test."

Time of Treatment. — "The total time employed in the treatment of
a charge of tailings varies from three days to a week, and is dependent,
from a chemical point of view, upon the greater or less fineness of the
gold; the general rule is that the longer the time the better until the
increased cost of treatment more than counterbalances the improved
percentage of extraction."

Cyanide. — The cyanide usually employed contains from 70 to 80 per
cent of pure potassic cyanide, but another quality, containing upward of
95 per cent, imported from Germany, is also used, and is preferable for
the reasons explained in the chapter on cyanide (p. 30). The consump-
tion of cyanide is about 150 tons per month in the Witwatersrand mines.
Germany has sent out nearly 1,000 tons to the Transvaal this year.

52 THE CYANIDE PROCESS.

Value of Rand Tailings and Percentage of Extraction. — "The average
value of Rand tailings per ton, before treatment, is $5; of this $8, or 60
per cent, is actually obtained by the cyanide process, $1 50, or 30 per
cent, is left in the residue, and 50 cents, or 10 per cent, is unaccounted
for. Ores from DeKaap, containing a large amount of mispickel, gave
only an extraction of 9 per cent, but on roasting the extraction rose
to 83 per cent, the arsenic being presumably driven off. Owing, however,
to the cost of fuel, and the high cyanide consumption resulting from
sulphates formed by partial oxidation, roasting is never employed as
preliminarj^ to the cyanide process. The percentage of gold extracted
varies in different localities, but is usually between 70 and 80 per cent.
It depends chiefly upon the degree of fineness of the ore, and the degree
to which the gold it contains has been liberated from the matrix and
exposed to the action of the solution. (In comparing an ounce of like
particles of gV i^- diameter with an ounce of particles of similar shape
but -^ in. diameter, the surface exposed by the first lot is three fourths
of the surface exposed by the second lot — this being a particular
instance of the general law, that for equal weights of similar particles
the surface exposed varies inversely as the diameter.) There is little
doubt that the remaining 20 to 30 per cent in the residues consist of
particles of gold still incased in the matrix, and this is proved by the
fact that finer grinding renders almost complete extraction possible.
The limits of fine grinding on a working scale are fixed by the increased
difficulty of filtration. Even when only a No. 30 screen is used in a wet-
crushing stamp-mill, it is not possible to filter the pulp in its entirety,
on account of the slimes; the consequence of this is that with mod-
erately fine crushing only the coarser portion (possibly 80 per cent)
of the tailings is at present treated by cyanide. Slimes of sufficient
value are in some cases treated by drying, crushing, and mixing with a
sufficient amount of coarse tailings to allow filtration. A mixture of
equal parts of each take at least a week for treatment. The drying is
performed either by exposure to the sun, or, especially in the case where
much organic matter is present, by slightly calcining in a reverberatory
furnace, or in form of bricks in a kiln. In the last two cases, however,
the cyanide consumption is increased by the oxy-salts of iron formed,
and although usuall}'' remarkably good results may be reckoned upon,
yet the cost involved in so much handling is so high as to be prohibitive
for low-grade slimes." The treatment of slimes or of tailings-pulp con-
taining a high percentage of slimes, is still one of the unsolved prob-
lems of the cyanide process; at present most of the slimes are washed
away, and with them a large amount of gold is lost in Johannesburg.

It has been suggested to solve the difficulty of slime treatment by
mixing the slimes with 50 per cent of their weight of a solution contain-
ing cyanide of potassium and the double cyanide of manganese and
potassium. This mixture is pumped into a filter press under high
pressure; after filling the press, water is forced through, washing out
the gold solution. An extraction of 97.6 to 98.2 per cent is claimed.
(W. Bettel's process. E. & M. J.)

Loss of Gold, and its Causes. — "From leakage, and the loss consequent
upon the handling of gold slimes in the various stages of conversion
into bars of bullion, there is a certain amount of loss; but this, in prop-
erly conducted works, should be small. Even when experimental errors
of assay be also taken into account, the discrepancy between theoretical

EXEMPLIFICATION OF PROCESS THE PROCESS IN AFRICA. Oo

extraction, estimated on assay and tonnage, and actual extraction of
fine gold contained in the bullion, should not exceed 3 to 4 per cent.
As a matter of fact, chiefly from unskillful work, the bullion actually
recovered amounts in the Rand gold fields, on an average, to only 60
per cent; whereas the average extraction, as estimated by assaying the
material before and after treatment, amounts to 70 per cent. The chief
causes of error in the estimate of extraction arise from incorrectly calcu-
lating the tonnage, from faulty sampling of charges and residues, and
from careless assaying of too small samples. If truckloads of tailings
be weighed periodically and the percentage of moisture carefully tested;
if samples of tailings before treatment be taken from each incoming
truck and mixed thoroughly, and the residues after treatment be treated
likewise; and if assays be daily made in duplicate on not less than an
assay-ton of material, when this is low grade — then there should be little
difference between estimated and actual extraction, provided there is not
much leakage and the gold slimes are carefully handled. In many
works a serious loss is incurred by allowing solution, containing very
fine gold slimes in suspension, to enter the general stock of solution,
and to be ultimately discharged with the residues. So fine is some of
this material that it will even pass through the finest filter cloth and
remain suspended after hours of ' settling.' The most effectual way of
overcoming this difficulty is to run all solution, filtered or decanted,
from gold slimes during the process of 'cleaning-up' or separating
them from the zinc, into a separate vat, called a ' settler.' This is left
undisturbed for some days, after which the supernatant liquid may
be safely run off'. This settler should equal in capacity the united zinc
precipitation boxes, and may be cleaned up half-yearly. Filter presses
are sometimes used to remove as much solution as possible from the
gold slimes before drying the same." In large works, like those of the
Crown Reef Company, the actual returns of bullion amount to 95 per
cent of the calculated extraction. It is explained that the difference in
the estimation of the weight of tailings treated is sufficient to account
for the difference of 5 per cent (G. E. Webber, Jr.). The Nigel Company
recover about 93 per cent of the calculated extraction; the incomplete
recovery is attributed partly to the " soakage " of the vats, and particu-
larly to the treatment of the bullion, the slag sometimes containing as
much as two hundred ounces to the ton, of which only from 60 to 70 per
cent are recovered by amalgamation in a grinding-pan (W. A. Radoe).

The Zinc for Bullion Precipitation " is used in the form of thread-like
turnings, obtained as before described. A cubic foot of them weighs
from 3 to 6 lbs., and exposes forty square feet of surface per pound
weight. Granulated zinc is never used, as it exposes a very small sur-
face in proportion to its weight and is liable to clog in the extractors.
Aluminium in conjunction with an electric current has been suggested,
as also alternate sheets of iron and lead foil between which a current
of two hundred amperes and seven volts passes; but these methods are
still in the experimental stage. The consumption of zinc varies greatly
in different works, and is dependent upon causes other than the amount
of gold precipitated. The absolute amount varies from 2 to 8 oz. per
ton of ore, but of this, owing to waste in cutting out and turning, prob-
ably not more than one half goes actually into solution, when the finely
divided zinc included in the gold slimes be also taken into account.
The precipitation of the bullion is conducted as described before. The

54 THE CYANIDE PROCESS.

zinc consumption, above the amount required for gold precipitation
by the equation of the cliemical reaction, is due to its solution in the
caustic alkali formed as indicated, in the free cyanide and caustic alkali
present in the solution as it issues from the leaching vats, and also in
its precipitating action upon other substances in solution. An average
ore would probably consume about ten times as much zinc as it yielded
bullion, but if in treatment caustic soda has been used in excess, the
consumption will necessarily be higher."

Treatment of Precipitates — "Acid is occasionally used for making a
complete clean-up of all the zinc contained in the boxes, and also for
refining the amalgam (zinc, gold, and mercury) formed therein, when
the tailings have contained much * floured ' quicksilver. Its use, for refin-
ing generally, is not advocated in Johannesburg, as it involves washing
and filtration of the slimes, and loss of gold by the formation of regulus
in melting, if sulphates have remained in the slimes by fault of imperfect
washing. The method most in use for refining gold slimes in the
South African gold fields is by the use of nitre. The slimes are dried
till just before they become dusty; they are then mixed with powdered
nitre, the amount varying from 3 to 33 per cent of their weight, and
gently heated as a thin layer, either in a wrought-iron pipe (10 in.
diameter by 6 ft. length), or preferably in a tray of wrought-iron (f in.
thick, by 6 ft. by 3 ft. by 1 ft.), which may also be used for the drying
process. In neither case do the flames come into direct contact with the
slimes; a hood carries off the obnoxious fumes. By the use of nitre
everything in the zinc precipitation boxes which passes a sieve of three
of four meshes to the lineal inch may be refined, and thus the finely
divided zinc, which otherwise accumulates and clogs in the boxes, is
constantly removed. Less nitre is always used than is required to
oxidize all the base metals present, as otherwise the free nitre will
rapidly corrode the plumbago crucibles, Avhich subsequently are used
for melting; it is advisable, however, to remain as near as possible below
the limit, as the roasting which follows is thereby conducted quicker
and at a lower heat. Besides rendering the bullion finer — containing
say only 15 per cent base metals — this nitre-roasting gives a cleaner
slag and lessens by at least one half the time required for fusing the
gold slimes, and prevents violent ebullitions of vapor from the crucible.
From 3,000 to 4,000 oz. of bullion can be obtained in twenty-four Jiours
from roasted slimes containing 33 per cent of gold by the use of No. 70
plumbago crucibles, with good coke, in four box furnaces (20 in. square
by 22 in. deep). The following fluxes have been found to answer well:
When much metallic oxide is present — slimes six parts, borax four
parts, soda two parts, sand one part. When little metallic oxide is
present — slimes three parts, borax one part, soda two parts, sand one
part. The function of the sand is to form a fusible slag with the soda,
and also to protect the pots against metallic oxides and the potash
formed by the reduction of the nitre. The slag resulting from melting
slimes usually contains an appreciable quantity of gold. This, in the
absence of smelting works, is generally crushed by hand in a mortar or
by power in a smallest size Gates or Fraser & Chalmer's sample grinder.
It is then panned, and the tailings resulting, still rich as a rule, are
shipped to Swansea. In estimating the cost of a flux, it should be
remembered that a very small percentage of gold in the slag will pay

1^ IS 10 S o Ifl Ito 9o^__^o

EXEMPLIFICATION OF PROCESS — THE PROCESS IN AFRICA. 55

for an improved flux, and that flux which gives the cleanest, most fluid
slag is preferable."

I have given here the mode of bullion treatment in Johannesburg as
described by the African Gold Recovery Company; in addition to it, I
refer to my own way of procedure, as given on page 36, which may offer
some points of advantage.

Fineness of Bullion. — The bullion in the Robinson Works is about
650 fine; it is very hard and brittle, and the bars are by no means uni-
form, so that it is difficult to obtain an accurate assay; in addition to
zinc, they contain silver, lead, and sometimes a little copper (Butters
and Clennell). The bullion of the Crown Reef Company is 950 fine
(830 gold, 120 silver) (G. E. Webber, Jr.). The bullion of the Nigel
Company has been on an average 795 fine during the last seven months
(W. A. lladoe).

The Cost of Treatment " varies according to the size of plant and the
facilities for working, but exclusive of royalty may be taken at from
-$1 50 per ton for a 5,000-ton plant, to 87-i cents per ton for plants treating
20,000 tons monthly."

The Cost of Plants "varies according to the locality and the style in
which they are erected. To erect an average size plant costs at Johan-
nesburg about $6 25 per ton of ore it is intended to treat monthly; for
very large plants the cost would perhaps be $5 per ton." All plants
have the following main features: Leaching or percolation vats, zinc
boxes for bullion precipitation, sumps or tanks for storing solutions,
pumps for assisting filtration, and pumps for transporting the liquids.
The difference between the various plants consists in the size, form, and
material of the vats, the system of charging and discharging the tail-
ings, and the general arrangement of the different parts of the machinery.
The construction of vats and the handling of tailings has been discussed
above. In reference to the latter, I attach details of discharging ap-
pliances, taken from " Notes on Gold Extraction," by W. R. Feldtmann.

The General Arrangement may be of different kinds. "The most
convenient method is to have solution vats, leaching vats, extractors,
and sumps in four tiers, so that each series may be completely drained
into that next below it. B}'' this means sufficient solution can be stored
in the solution vats, and sufficient room left in the sumps to enable
work to proceed for from twelve hours to twenty-four hours without
pumping. Many plants, however, have the solution vats and sumps on
the same level as the leaching vats; in this case the solution issuing
from the last mentioned vats is run through precipitation boxes into a
small tank and is continually pumped back when required." I attach
plates, which illustrate the variations in the general design of plants
with regard to the relative position of the different parts, which with
their explanation are taken from " Notes on Gold Extraction by means
of Cyanide of Potassium, as carried out on the Witwatersrand Gold
Fields," by W. R. Feldtmann.

"In No. 1 design, the leaching vats are placed highest. The solution
gravitates from these through the zinc boxes into the storage vats, there
to be made up to strength ready for pumping up to the leaching vats
again. In the sketch the discharging of the tanks is assumed to be done
over the side. In No. 2 design the solution is either pumped direct
from the leaching vat, or, running into a small sump or an air-tight
receiver, is pumped from there into zinc boxes, and runs thence into*

THE CYANIDE PROCESS.

l/AR/AT/O/V/y^ 9.

— /)FSfc Afs or crA /v/d£'pl a a/ts. -

i?es/ cAfS or cyAr///?j>'/>AAA/TS. .

V V y ' ^

_ao

overhead storage vats. Having been made up to strength, it is ready
to run direct into the leaching vats again. The discharge system indi-
cated is the ' bottom discharge.' No. 3 design is a combination of the
two previous ones, and is advantageously fitted with a pipe service to
enable one, if desired, to run solutions up through the sand in the
leaching vats. As shown in the sketch, the plant is designed for side
discharge; but of course any system of discharge may be applied to
any of the three arrangements of plant.

EXEMPLIFICATION OF PROCESS — THE PROCESS IN AFRICA.

gji 15 TO y y ^p %° S o 4o

THE CYANIDE PROCESS.

Buildings. — " The majority of plants now erected have only the zinc
boxes inclosed in buildings, and there is little objection to having no
weather protection when cemented vats only are used, but with wooden
vats, exposure to the sun and weather undoubtedly causes increased
leakage.

-pv:7i. rELDT/iAAryv-'-

S/Z)r2?/SC//yi/)GE 4-r/^jE:/9CO^./l'r/OA^J<^7'S

■SCyt/ f 7 //vcAy^^Trcor-

Lahor. — "The men employed in a plant of average capacity (5,000
tons per month) are: One manager, one assayer, two shift men, one
mechanic, two native gangers, and the native crew." The Nigel Com-
pany employ two white men of twelve-hour shifts in the works, whose
duty it is to " make-up," pump in, and drain ofl" solutions, and to attend

EXEMPLIFICATION OF PROCESS — THE PROCESS IN AFRICA.

Cn.IiUTTEES' BOTTOM DISCHARGE AT PERCOLATTOy VATS.

n./j.iRrjyES bottom discuau<ie at fercolation vats .

Cop. fkom W R FELTMANN'C- Nohi. On Gold Extraction" Ltc.

60 THE CYANIDE PROCESS.

to things generally, and one white overseer over the natives (about
thirty in number), who attends to charging and discharging the vats
(W. A. Radoe). The Crown Reef Company employ one white man per
shift of eight hours and seventy native laborers, handling 500 tons of
tailings (G. E. Webber, Jr.). During 1893 about 500 vats were in use
on the South African gold fields, of a total daily capacity of 11,000 tons.

Results of the Process. — The process of treating tailings by cyanide was
first introduced on the Transvaal gold fields in 1890; the output of gold
by its means has since taken on enormous proportions. The gold pro-
duced by cyanide in 1890 amounted to 286 oz.; in 1891 to 34,862 oz; in
1892 to 178,688 oz.; in 1893 to 330,510 oz.; and during the first six
months of 1894 to 317,950 oz. I inclose a table giving the output of
gold in the Witwatersrand district by the milling and cyanide process.
The value of cyanide gold is on an average $15 per oz. The total value
produced by cyanide at the end of June amounted to $12,934,440. This
enormous amount has been almost entirely derived from low-grade tail-
ings, which were, before the introduction of MacArthur-Forrest'smethods,
practically valueless, for want of cheap and efficient means of extraction.
The working cost of treatment by the process is the lowest known in the
history of gold metallurgy, roasting never, and preliminary treatment
in exceptional instances, being required. The process is adopted, only
amongst others, by the following mines:

Robinson Company, 60 stamps; in 1892, 101,061 tons were crushed,
yielding 98,799 oz. of gold, an average of 19 dwts. 13^ grs. per ton;
the concentrates yielded 8,407 oz., and 75,375 tons of tailings by cyanide
treatment 27,577 oz.; the average from all sources was 1 oz. 6 dwts. 16
grs. per ton; the cost per ton about $5 50.

The Langlaagte Estate Company, with 120 stamps working, crushed
in 1892, 197,201 tons, yielding on an average 6 dwts. 23.81 grs. per
ton; twelve thousand tons of tailings are being worked per month at a
working cost of $1 per ton; this plant is being increased to treat
thirty thousand tons monthly; the total value of gold received, includ-
ing that from treatment of tailings by cyanide, amounted in 1892 to
$1,554,850. The Langlaagte Estate Company has been using cement
tanks with good results for sometime past; the vats and sumps are built
in excavations made in solid ground, the upper part being level with
the ground. A tram-line runs over the center of five large vats, each
holding 450 tons, for charging purposes. A steam crane, running on
rails, placed on each side of these vats, lifts and empties the tailings,
after treatment, into a movable chute placed over two parallel lines of
trucks. This chute fills two trucks at each lift at a cost of less than 2
cents per ton, including wear and tear and maintenance of the machinery .
The time necessary to empty each vat is fourteen hours.

The following description of the application of the cyanide process in
the very extensive works of the Langlaagte Estate and Gold Mining
Company in Johannesburg is derived from notes written by the com-
pany's assayer, Mr. Thomas Lockhart, which have been contributed by
the company's manager, Mr. James Ferguson, whilst this paper was in
press:

The ore is of a silicious nature, containing about 2 per cent of iron
pyrites, and very little base matter; it is not treated directly by cyanide,
but is first put through the battery-amalgamation process. Eight hun-
dred tons are crushed daily. The tailings leaving the plates are con-

EXEBIPLIFICATION OF PROCESS — THE PROCESS IN AFRICA. 61

centrated, and then run to three settling dams, each of which holds
7,000 tons. The slimes are here separated from the tailings and allowed
to run away, as they are greatly impeding the percolation of the cyanide
solution in the vats. The tailings, free from slimes, are hauled from
these dams in trucks, by means of two endless steel wire ropes, and run
onto an overhead tram-line, from where they are dumped directly
into the vats for treatment. The vats are built in excavations; their
tops are level with the surface of the gi'ound. Of these vats there are
fifteen; they are built of brick, and circular in form, of a diameter of 40
ft., and a depth of 9 ft. 3 in. Their sides are cemented, and the bottoms
laid with concrete; the latter slope gently to one side, where a 2 in. pipe
carries off' the solutions. The bottoms are covered with a filter-bed,
built of stones, about 3 in. deep, which are packed close together and
form a level surface, which is covered with cocoa matting. Each vat
holds about 450 tons of tailings, which remain in them under treatment
for three days. After the completion of the extraction, the residues are
discharged by means of trucks, which are lowered into the vats, filled
by Kaffirs, hoisted up by a crane, and run out on the dump by means
of an endless rope.

As a rule three vats are charged per day and three discharged.
During March 33,000 tons of tailings were treated on 31 working days,
or 1,064 tons per twenty-four hours. These tailings averaged before
treatment 4 dwts. 5 grs. of gold per ton; the residues, after treatment,
contained 17 grs., which corresponds with an extraction of 83 per cent,
but only 68 per cent of the assay gold-value was actually recovered.
The chief causes of the incomplete recovery of the gold are: The imper-
fect precipitation by zinc; the presence of slimes in the tailings, which
take up and retain some of the cyanide gold solution; the loss of gold
solution through leakages in tanks and pipes; and the mechanical
losses in manipulating the precipitates in drying, calcining, and melting.

The strength of the first or strong cyanide solution pumped onto
the tailings, varies from 0.32 to 0.38 per cent; it stands 3 or 4 in. above
the surface of the charge, and remains in contact for from eight to twelve
hours; after that time it is run off and passes through the zinc precipi-
tation boxes; it is then brought up to its original strength by adding
cyanide of potassium and used again on a next charge. The zinc boxes
are 18 ft. long by 5 ft. wide and 2^ ft. deep, and contain the usual divis-
ions. Five such boxes take the solution from ten vats.

The first part of the solution, when running off the charge, contains
about 0.02 per cent cyanide; the following portions are of greater strength
and rise up to 0.3 per cent. When the solution has drained off, the
second, or weak, solution, of about 0.2 per cent cyanide, is pumped on;
this percolates directly through and replaces the first solution, which has
remained in the material. A water-wash completes the treatment. This
wash remains in contact during some hours, and is then drained off as
usual; it forms the weak or second solution for a following charge.

The solutions are stored in vats 56 ft. in diameter and 9 ft. 3 in. in
depth. The consumption of cyanide amounted during the last six
months of 1893 to 0.55 lb. per ton of tailings.

The treatment of the concentrates (sulphurets) is conducted on the
same plan as that of the tailings. Two tanks, each 35 ft. in diameter
and 2\ ft, deep, serve the purpose. A solution of 0.6 per cent cyanide
is used; this remains in contact with the material for six hours; it is

62 THE CYANIDE PEOCESS.

then run oflf and the gold precipitated as usual in the zinc boxes, which
are 11 ft. long, 2 ft. deep, and 2 ft. wide. The solution is then restored
to the required strength and used over and over again till the assays of
the residues prove the termination of the extraction.

During the month of March 405 tons of concentrates were treated;
they averaged before treatment 2 ozs. 10 dwts. 4 grs. of gold per ton;
the residues contained 5 dwts. 14 grs., which corresponds with an ex-
traction of 89 per cent of the assay- value; this percentage is actually
recovered. The consumption of cyanide per ton of concentrates
amounted during the last half of the year 1893 to 0.5 lb. The cyanide
used contains 98 per cent of potassium cyanide. The zinc used for pre-
cipitating the gold contains 1-^ per cent impurities; it is applied in
filiform. For every one ounce of fine gold obtained 1.48 lbs. of zinc are
consumed. Cleaning up takes place twice a month. The gold precipi-
tates, mixed with finely divided zinc, are separated from the coarse zinc
by shaking; they are then dried and calcined. The calcination is carried
on on a heavy iron plate, which is heated to redness; it is continued till
the oxidation of the zinc is complete. The calcined mass is then
fused with borax, soda-ash, and sand. The mixture is charged into No.
50 plumbago crucibles and melted in a reverberatory hearth furnace,
which holds twenty-two crucibles at a time. The time required for melt-
ing varies from one and a half to three hours, according to the character
of the material and the temperature of the furnace. The molten mass
is poured into iron moulds; the bullion, thus obtained, is remelted into
bars of 600 oz. The fineness of the bullion varies considerably; that
obtained from tailings runs from 700 to 780; that from concentrates
from 750 to 820 fine. The weight of the fluxed precipitates which are
reduced per month amounts to about 9,000 lbs. Three shifts, of two
white men each, attend to the working of the process. Two twelve-
hour shifts, of five Kafiirs each, are constantly employed in cutting
zinc shavings. The charging and discharging of the percolation vats is
done by contract; 14 white men and 250 Kaffirs are employed for the
purpose. The buildings consist of wooden frame structures, covered on
all sides with corrugated iron.

The Langlaagte Company pays a royalty for the use of the Mac-
Arthur-Forrest patents, amounting to $1 25 per standard ounce of gold
extracted from tailings, and 62| cents per standard ounce of gold
extracted from sulphurets.

The Ferreira Company derived for the half year ending March 31,

1892, a profit of $22,030 on the treatment of 15,310 tons of tailings,
producing 3,495 oz. of gold at a cost of $2 91 per ton. Fort he year
ending March 31, 1893, the tailings treated by cyanide yielded 11,201 oz.
of gold, which means to say 4,592 dwts. of the value of -$4 16 per ton.

The Crown Reef Company has 210 stamps working. For the half
year ending March 31, 1893, the tailings treated by the process yielded
16,629 oz. of gold. The revenue from tailings and concentrates
amounted to 92 cents per ton.

The Henry Nourse Company treated, during the first six months of

1893, 12,640 tons of tailings by cyanide, yielding 3,040 oz., or 4.81 dwts.
of gold, at an average cost of $2 33 per ton.

The Meyer and Charlton Company treated during six months ending
June 30, 1893, 10,799 tons of tailings by the cyanide process, yielding
3,205 oz., or 5.93 dwts. per ton.

EXEMPLIFICATION OF PROCESS THE PROCESS IN AFRICA. 63

The Nigel Company obtained during twelve months 21,471 oz. of gold
by the process from tailings and concentrates.

The Rand Central Ore Reduction Company has been formed to pur-
chase tailings from companies who have not erected their own plants;
1,500 tons of tailings are treated in their works per twenty-four hours.
The vats, made of wood, hold from 75 to 600 tons. The tailings average
5 dwts. before and 1 dwt. after treatment. The strong solutions contain
about 0.3 per cent, the weak about 0.15 per cent of cyanide. The last solu-
tion runs off at about 0.08 per cent. All solutions together amount to
about 1 ton per ton of ore. The extraction takes about three days. The
cyanide used is of 98 per cent on the average. The extraction from the
tailings varies from 75 to 80 per cent of the assay-value, of which 80 per
cent are actually recovered; the clean-up is never complete and much
gold remains in the slag. The zinc consumption amounts to about 1 lb.
per ounce of gold recovered. Electricity is also used for bullion precipi-
tation. The bullion after melting is 750 to 850 fine. The total cost of
treatment is about $1 per ton. The cost of the plant amounted to $600,-
000; 200 white men and 800 Kaffirs are employed. (D. Ruston.)

The Langlaagte Royal Gold Mining Company is erecting a cyanide
plant for the treatment of 10,000 tons per month. The mentioned com-
panies, in conjunction with a number of others, more or less important,
treat upwards of 200,000 tons of tailings monthly. During June, 1894^
220,507 tons w^ere treated, with an average yield of $3 per ton. The
treatment of concentrates by chlorination has been abandoned in favor
of cyanide treatment by the Crown Reef and the Langlaagte Estate
works.

The large profits accruing to some of the mining companies are to a
large extent derived from their tailings-treatment. Individual returns
show that at several of the leading and most prosperous mines 35 to
50 per cent of their output is due to their using the cyanide process.
The Nigel Company's official report for the three naonths ending
September 30, 1893, shows that a net profit of $122,325 was made, of
which only $43,970 was derived from amalgamating, and $73,895 from
cyanide treatment of tailings and concentrates. The report of the Lang-
laagte Estate Company for the same period shows a net profit of $51,410,
derived from the same source. During 1892, 37,595 oz. were recovered
by the process from Robinson tailings, 19,482 oz. from Crown Reef, and
nearly 29,000 oz. from Nigel tailings. All companies mentioned use the
cyanide process as described in the MacArthur-Forrest patents, and use
zinc as bullion precipitant. The amount of gold recovered by the Mol-
loy process (see page 38) is insignificant. The two companies which
were described in the official list of the Witwatersrand Chamber of
Mines as using that process, are now mentioned as using the MacArthur-
Forrest process.

The cyanide plants at Johannesburg are, generally speaking, very
similar to each other in their construction, and the description of a
typical one, that of the Robinson Company, will sufficiently illustrate
their construction. The plant in question, of which the attached plans
were designed by Mr. Chas. Butters, consists of twelve circular open
leaching vats, each having a capacity of 2,000 cub. ft. and holding
100 tons of tailings and cyanide solution. The vats, built upon elevated
arched stone foundations, are filled from a high level tramway above
them, and emptied through trapdoors in the center into tramcars below.

64 THE CYANIDE PROCESS.

Next in order is a series of precipitating boxes, designed to continu-
ously precipitate gold from the solution as it passes from the leaching
vat to the sump. The boxes are 20 ft. long, 2 ft. wide, and 2 ft. deep;
they have inclined bottoms. They are divided into compartments a
20 in. in length each. Each chamber contains about 40 lbs. of zinc turn-
ings. Seven compartments in each box are filled with shavings; of
single compartment at the head is left empty to receive any sand that
may be carried through the filter by the solution from the tanks. A
double compartment at the foot is also left empty to allow any gold that
may be carried away by the stream of liquid to deposit before the solu-
tion flows into the sump. About 60 tons of solution, which is the quan-
tity required for treating the ordinary daily charge of 225 tons of
tailings, is allowed to run through two zinc boxes in about nine hours.
This solution may carry from 1 oz. to 3 oz. of gold per ton of liquid;
after passing through the zinc boxes it rarely contains more than $2,
and should not contain more than 50 cents if the precipitation has been
properly carried out (Butters and Clennell). Underneath the leaching
vats are four 200-ton sumps, brick and cemented tanks set in the ground.
In these sumps are prepared and stored the solutions for dissolving and
washing out the gold. On the top of them are placed a double set of
duplex pumps, so arranged that both, or either, will throw from any
sump into any leaching vat. On the tram-level above the vat is a 10
horse-power double-drum winding engine and boiler, employed to hoist
the tailings out of the settling pits. The plant includes four furnaces
of large capacity for smelting and refining bullion; also a laboratory
a,nd weighing-room. An elaborate system of tram-lines is laid down, on
both high and low levels, for delivering and discharging the tailings in
the most direct and efficient manner. Works, pits, and dumps are
lighted by electric light. Lathes for turning zinc are employed, and a
12 horse-power engine, with 16 horse-power boiler, supply all power.
The whole is covered by an airy building of wood and iron. The
methods of working are: Hoisting tailings and filling vats; pumping
cyanide solution onto the tailings in the vats to dissolve the gold; run-
ning ofl' this gold solution into zinc boxes and precipitating the gold;
return of the cyanide solution into the sump below for repeated use;
collecting, melting, and refining the precipitated gold (M. S. P.).

The report of this company for the year ending December 31, 1893,
shows that 55,200 tons of tailings were treated by the cyanide process,
yielding 17,921 oz. of gold. The cost at the cyanide works is given per
ton of tailings treated, as follows: Wages, 29.62 cts.; supplies, 12.24 cts.;
fuel,. 10.48 cts.; cyanide, 48.38 cts.; zinc, 2.26 cts.; filling and discharg-
ing vats, 37.62 cts.; royalty, 16.38 cts.; total cost, 173.86 cts. per ton.
The actual cost of treatment per ton, omitting royalty, was 156.98 cts.
The average extraction by the process M'as 68.7 per cent of the assay-
value of the tailings. An innovation in percolation in the Robinson
Works consists in the circulating system, which has been described by
Butters and Clennell as follows:

" It has been stated that in the usual method of working about a ton
of solution is employed in the treatment of a ton of ore. Since, with
free-milling ore, a much smaller quantity is sufficient to dissolve the
same percentage of gold, it was suggested that the solution from one
tank might be transferred to a second, and be made to dissolve an addi-
tional quantity of gold before being passed through the zinc boxes; for

EXEMPLIFICATION OF PROCESS THE PROCESS IN AFRICA.

example, it was found at the Robinson Works that 20 tons of solution
were amply sufficient to extract 40 oz. of gold from 75 tons of tailings in
one tank. It was found that 20 tons of solution sufficed to fill a tank
holding the usual charge of 75 tons of tailings, covering the charge to a
depth of three or four inches. Instead of replacing these 20 tons of
solution by fresh cyanide, the solution filtering through was continually
pumped back again into the same tank for about thirty-six hours and
then passed through the zinc box. The extraction of gold by this
circulation-system was equal to that obtained by the ordinary method,
and the consumption of cyanide was much less, since a much smaller
quantity of solution was exposed to the action of the zinc. A further
modification suggested itself, namely, the transference of the solution
charged with gold from one tank to a second and third, in order that it
might take up an additional quantity of gold from fresh tailings before
passing into the zinc boxes. The advantages of this method are that
the solutions from which the precipitate is obtained are much richer in
gold, giving a cleaner deposit on the zinc, with much less consumption
of cyanide."

In the Durban-Roodeport Company's works the extraction ranged
from 67 to 85 per cent. The cost of treating the tailings, including
patent-royalty, amounted to $1 54; the profit to $2 87 per ton. During
eleven months, in 1893, 79,765 tons of tailings were treated, producing
22,751 oz. of gold, adding about 33 per cent to the total revenue.

The New Chimes Gold Mining Company have commenced to treat
their tailings in their own cyanide works only since the beginning of
the year; during March, 4,180 tons of tailings realized 709.55 oz. of
bullion. The assay-value amounted to (fine gold) 3.33 dwts.; fine gold
saved, 2.25 dwts.; extracted, 67.56 per cent; lost in tailings, 32.44 per
cent; value of bullion per ton treated, $2 36; expenses, $1 02; profit per
ton, $1 32. (G. Halford Smith.)

The financial success of the cyanide process in South Africa is best
proved by the dividends paid by the mining companies which use cya-
nide for tailings treatment. The following is a list of dividends paid
during 1893 by companies under such conditions:

Names of Companies.

Dividends.

Amount-
ing to —

City and Suburban

Crown Reef...

Durban-Roodeport

Ferreira

Langlaagte Estate.
Meyer & Charlton .

New Primrose

New Rietfontein...

Robinson

Nigel --

100 per
50 per
4.5 per

KX) per
30 per
fiO per
40 per
25 per
8 per
50 per

cent
cent
cent
cent
cent
cent
cent
cent
cent
cent

1425,000
300,000
282,250
225,000
705,000
215,100
391,870
200,000

1,087,500
400,000

The total output of the Rand mines fOr the year ending June 30, 1893,
apart from the cyanide process, was 1,087,058 oz.; by the process this
quantity was increased by 226,078 oz., making a total of 1,313,136 oz.
From districts not included in the Rand proper, a further recovery of
2,395 oz. was returned, making in all 228,473 oz. due to the working of
the process. It will thus be seen that, by the use of the process, the
Rand production was increased by 21 per cent. At several of the lead-
5cp

66 THE CYANIDE PROCESS.

ing and most prosperous mines, 35 to 50 per cent of their gold output is
due to the use of cyanide. The report of the Witwatersrand Chamber
of Mines gives the output of that district of the Transvaal, for March of
this year, at 165,372 oz., from fifty-three mines and three custom works;
of which 44,664 oz., of the value of $668,655, were extracted by cyanide
from 204,421 tons of tailings, and 1,367 oz., of the value of $20,805, from
concentrates by the same means. The returns per ton of tailings aver-
aged 4.37 dwts.; 33.74 per cent of the total month's production of gold
is derived from very low-grade material by the process. The cyanide
process is the only one which is successfully treating tailings on a com-
mercial scale. Its economical importance for Johannesburg will be
evident from the following tables:

EXEMPLIFICATION OF PROCESS THE PROCESS IN AFRICA.

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THE CYANIDE PROCESS.

Table showing Companies in the Transvaal Treating Tailings and Concentrates by Cyanide

in 1893.

Company.

Tons.

Total Output in ounces for 1893.

Plates.

Concen-
trates.

Tailings.

Champ d'Or

City and Suburban

Crown Reef

Durban-Roodeport

Evelyn

Ferreira

Geldenhuis Main Reef..

Gipsy - ■

Henry Nourse

J. H. Burg, Pioneer

Jubilee

Langlaagte Estate

Langlaagte Block B

Marais Keef

May Consolidated

Meyer & Charlton

New Heriot

New Chimes

New Primrose

New Rietfontein Estate .

New Spec Bona

Nigel •

Orion

Paarl Central—

Randfontein -.

Robinson

Salisbury

Simmer & Jack - ■

Stanhope -.-

Treasury ■

Village Main Reef

Vulcan

Wemmer

Witwatersrand.--

Customs Works

17,896

49,805

118,244

78,651

5,722.7
37,777.14
51,688.0
37,883.6

723.2

47,376
9,495
3,931
19,749
17,606
43,673

222,732
64,066
935
60,298
34,197
21,455
33,641

141,464
24,048
2-2,289
22,273
34,657

43,978.1

3,417.7

1,563.6

15,329.18

9,073.0

24,774.10

65,812.12

19,621.4

937.5

24,957.4

27,328.12

14,089.2

14,510.9

57,574.8

28,168.12

8,784.5

25,455.0

8,318.3

36.0

9,047.11

100.0

79.18
'3,"5Y6"2"

54,652
94,842
24.786
103,798
22,858
12,429
11,607
2,766
27,654
34,081

23,310.16

104,222.17

19,268.18

38,904.12

10,790.8

7,587.12

6,143.17

764.5

22,705.13

12,441.13

10,659.18

38,574.0

1,787.17
9,034.3

29,679.14

22,751.0
2,545.19

11,697.19

372.17

712.14

6,893.3

1,120.4

5,254.16

30,050.15
6,869.19
419.10
2,875.0
6,854.2
8,689.18
7,296.16

26,203.18
6,957.15
1,040.0

17,036.8
9,677.15
957.15
6,623.14

17,921.4
5,587.6
767.0
3,873.16
4,284.16
1,996.8
50.0
3,063.8
7,882.18

35,669.2

Witwatersrand Customs Works, 189S.

African Gold Recovery
Company.

Rand Central Ore Red.
Company.

Robinson Company.

TotaL

Concen-
trates.

Tailings.

Concen-
trates.

Tailings.

Concen-
trates.

Tailings.

Concen-
trates.

Tailings.

463.18

4,130.6

9,774.7

31,538.16

28,335.15

38,574.0

35,669.2

Gold is valued at $17 50 for plate gold, and $15 for cyanide gold. (These figures are
taken from M. I., vol. 2.)

The table giving the monthly analysis of gold production in the
Witwatersrand district, for April, 1894 (see Appendix), which has been
published by the Witwatersrand Chamber of Mines, will further illus-
trate the importance of the cyanide process in that district.

Cape Colony.— In the British Colony at the Cape "the gold mining
industry has not developed to such proportions as to lead to the intro-
duction of the cyanide process." (Letter of Secretary of Agriculture,
27th April, 1894.)

EXEMPLIFICATION OF PKOCESS — THE PROCESS IN AUSTRALASIA. 69

B. Australasia.

(a) New Zealand. — A very successful field for the cyanide process
has been the eminently progressive British Colony of New Zealand, where
various classes of ore, tailings and concentrates, of a very refractory type,
have been and are being treated on a large and commercially successful
scale. The colony contains the largest cyanide plant outside of South
Africa, that of the Waihi Company, with thirteen vats, where ore is
treated at the rate of 2,000 tons and tailings at the same rate per
month. The Crown mine at Karangahake is equipped with a smaller
but equally efficient plant for ore treatment. Smaller plants for treating
ores and tailings are distributed over the Hauraki gold fields. An
extensive and very successful agitation plant for the treatment of concen-
trates is connected with the reduction works of the Sylvia Company,
Tararu, Thames. The first mine to adopt the process has been the
Crown mine in the Upper Thames District. The first plant was erected
in an almost inaccessible position in 1889, under conditions which pre-
cluded a success. New works have since been erected by Mr. MacCon-
nell, which are in full and successful operation. The ore is clean quartz,
with no sulphurets of base metals; the free gold is very finely divided.
The silver is in form of sulphide; some of the gold in form of a telluride.
The works are described in the New Zealand Government Mining Report
of 1893, by Mr. H. A. Gordon, the Government inspecting engineer, as
follows :

"The ore, when brought into the works, is first dumped onto a grizzly;
what will not go through the bars runs down to the rock-breaker and is
broken up to a maximum size of 2 in. diameter, and then falls into the
same hopper where the fine material went. The ore passes then into
the drying kilns, which are built of brick, the hot air being confined in
a long flue, having a series of steps to prevent the ore from traveling
down too fast before it gets thoroughly dried. There is a cast-iron plate
at the bottom of this flue, which can be turned to allow of the dried ore
to pass down into a large hopper, made of steel plates, 3% in. thick, from
which the Challenge ore-feeders are fed. These kilns are only for drying
the ore, and not in any way to calcine it. There are two of these kilns
built on a stone foundation and placed about 6 ft. apart, the foundation
going all the way across. The kilns themselves stand about 30 ft. in
height, the step-flue being at an angle of about 30'^ to 40° from the
vertical. There is a furnace at the bottom, where either coal or firewood
can be used to dry the ore.

"Stamp Mortars. — There is first a concrete foundation put in for the
stamps, and on the top of the concrete the stamp mortars are placed on
the end of a log of kauri, each 18 ft. in length, 4 ft. 8 in. one way, and
2 ft. 2 in. the other. These are firmly embedded in the concrete, and
all bolted together, so as to form a solid block of timber standing on
end, having a length of 18 ft. 8 in. by a width of 2 ft. 2 in., and on this
the four mortars are placed. They are fitted with screens, having the
top standing outward at a slight angle, and held to the face of the mor-
tars by means of a long wedge, the gratings being 30-mesh, equal to 900
holes to the square inch.

"Stamps. — The stamps are fitted with the latest appliances for raising
and holding them up, the cams and tappets being all constructed on the
American type. They are intended to make about ninety-two blows

70 THE CYANIDE PROCESS.

per minute, having a drop of six inches. The guides and framing are
made of wood. Each ten-head battery is driven by a separate belt, and
there is further provision made so that twenty additional stamps can
be erected should they at any time be required. The pulverized material
from the stamps falls into a chute and is conveyed into another set of
hoppers at a lower level than the stamp mortars, and from these hoppers
the pulverized dust is taken to the leaching vats.

*' Cyanide Plant. — This consists of twenty-four wooden vats, each 11
ft. long by 9 ft. wide, and 3 ft. 9 in. deep. In the bottom of these vats
there is a false bottom, or grating, placed about 3 in. above the ordinary
bottom, and on this false bottom a filter-bed is placed, about 4 in. in
thickness, the bottom layer being of coarse quartz-gravel and gradually
getting finer up to the top, the last coating being fine sand, having a
coarse cloth placed over the top of the filter-bed to prevent the sand
from being disturbed, as the vats get cleaned out after every charge of
pulverized ore. There are also 14 agitators, 8 of which are 5 ft. deep by
4 ft. 9 in. in diameter, and 6 of them 6 ft. deep and 5 ft. 6 in. in diameter.
The agitators and vats are all made of kauri timber, the staves of the
agitators being 3 in. in thickness, and the vats being made of partly
3 in. and partly 4 in. timber, and all bolted together. Into each of these
vats are placed three pipes, under the false bottom, so that the first,
second, and third solutions can be drawn off into separate channels. On
one side of each vat there is a door, which can be opened to admit of
the material being sluiced out after the whole of the cyanide solution is
completely washed out of the ore, the solution passing through a long
series of boxes filled with zinc shavings, which precipitate both the gold
and silver in the form of a blackish powder. There are also three
concrete sumps, each 15 ft. by 12 ft., and 6 ft. deep, capable of holding
about 30 tons of the cyanide solution; this is pumped up to the vats on
the floor above as required. It is in these concrete sumps where the
solution is always made up to the proper strength before being used.
It is also proposed to use a vacuum pump to assist the filtration of the
solution through the pulverized material in the vats. Annexed are plans
of the company's plant, to which the following description or reference
applies: At point A, the ore is delivered at the battery and tipped onto
grizzly, B; the 'fines' pass through and are conveyed to hopper, D;
the 'roughs' pass over the grizzly onto the stone-breaker floor and are
passed through stone-breaker, C, and fall into the hopper underneath,
marked D; the drying- kiln, E, is charged from this hopper. The ore,
after passing through the kiln, being perfectl}^ dry, is run into an iron
hopper, G, from where it is automatically fed into stamps, I, by self-
feeders, H; the ore, after passing through the stamps, is received in
hoppers, J, and then conveyed by means of revolving tube, K, either
into trucks for conveying ore to agitation-cylinders for treatment, or, if
the ore can be better treated by percolation, to store-hopper, R, in con-
nection with percolation plant, from where it is trucked along the top
of and tipped into percolation tanks, S, for treatment. The plant is
so arranged that the ore, after it is delivered above the stone-breaker,
passes from stage to stage by gravitation, requiring the least possible
handling, and thereby reducing the cost of labor to a minimum.

'^ Crushing Machinery. — One Lamberton stone-breaker, capable of
reducing 70 tons of ore per day fine enough to feed into stamps; and

^ .

IJ J

1 LT

iiiiiiini 1

IlllkO! 1

IIIIJUH! I

fe' 1

it^f^^i

ternfF^^I

mit|ai 1

EXEMPLIFICATION OF PROCESS — THE PROCESS IN AUSTRALASIA. 71

20 heads of 9 cwt. dry stamps, crushing 30 tons of ore per day through
a 30-mesh screen.

" The Percolation Plant consists of 24 tanks, capable of holding each a
xharge of 7 tons of finely pulverized ore. The bottom of each tank is
covered with a sand and gravel filter. The ore is trucked into the
tanks from the storage hoppers. A dilute solution of cyanide is then
run on the top, and allowed or assisted to percolate through the body of
the ore. As the solution percolates, it is carried away from underneath
the filters by means of iron pipes, and permitted to run through a series
of boxes of zinc turnings.

^'Agitation Plant. — This consists of sixteen wooden tubs, fitted with
revolving paddles, in which the ore and cyanide solution are agitated
together until the gold and silver are dissolved. The pulp is then fil-
tered by means of filter-presses, and the bullion deposited from the
solution on the zinc, as already described. The extraction of bullion is
given as 93 per cent of the gold and 79 per cent of the silver assay- value.
The cost of treatment is $3 50 per ton." This is the only company in
New Zealand which does not pay any royalty to the owners of the Mac-
Arthur-Forrest patents, the patentees owning part of the mine. The
total bullion-value produced by the cyanide process in these works
amounts to upward of $142,000.

Another mine of importance, the Waihi Company, has recently
adopted cyanide treatment for their ores, supplanting unsatisfactory pan-
amalgamation. The ore of that mine is very similar to that of the Crown
mines. The bullion recovered by amalgamation has never exceeded 66
per cent of the gold and 40 per cent of the silver assay-value. Experi-
ments on a large scale, made nine months ago, led to the construction of
an extensive percolation plant, by which upwards of 20,000 tons of ore
have been already successfully treated. The extraction varies from 89
to 91.8 per cent of the gold, the silver extraction from 46.5 to 51 per cent
of assay-value. The cost per ton for cyanide and zinc is $1 37^. The
gold returns from cyanide treatment are 25 per cent higher than from
pan-amalgamation. The ore, which required 60-mesh screens for amal-
gamation, is sufficiently fine for cyanide if passed through 40-mesh,
which means an increased output from the mill of at least 25 per cent,
the running expenses remaining virtually the same. Eventually 30-
mesh wire gauze may be used. The strength of solution used is from
0.25 to 0.4 per cent. The percolation and subsequent washings can be
done in four days. No difficulties have been found in percolation, as the
dry ore does not form slimes as wet ore probably would. After the first
percolation is finished, the subsequent washings are hastened by atmos-
pheric pressure by means of a vacuum pump. The extra profit by cya-
nide treatment of Waihi ores over pan-amalgamation amounts to about
$3 75 per ton. The company has been experimenting with the Otis
crusher, as a substitute for the dry-crushing stamp battery; the results
have been unsatisfactory. A royalty of 7^ per cent on the bullion pro-
duced is paid to the owners of the MacArthur- Forrest patents, the Cassel
Company of Glasgow. For the information in reference to the Waihi
Company's cyanide operations, I am indebted to the company's man-
ager, Mr. R. Rose.

A fuller description of the working of the process has since been given
by Mr. Barry in the report of Mr. H. A. Gordon, the Inspecting Engi-

72 THE CYANIDE PKOCESS.

neer of Mines to the New Zealand Government (New Zealand Mining
Report, 1894), as follows:

" The ore is first dried in open kilns, excavated in tufaceous sand-
stone. These are 37 ft. deep by 20 ft. in diameter at the top, and taper
down to the bottom, where they are finished off" with a brick arch, having
a door and an iron chute for discharging the dried ore into trucks.
These kilns are first charged with wood and ore in layers, each layer of
wood being about 5 ft. apart. After the kiln is fully charged, the wood
is lighted, and after being all burned up, about one half of the charge is
withdrawn — 50 tons — and another 50 tons of raw ore, together with
wood, added on the top; after which about 50 tons is withdrawn every
third day. This method of drying the ore is found to be very economical
as regards fuel, as there is not a large surface of cold material to heat
up, as is the case with smaller kilns, which are emptied at each charge.
The cost of firewood used in large kilns is 37^ cents per ton of ore dried.
After the ore is taken from the kilns, it is then put through the rock-
breaker, from which it falls into a hopper, and thence, by automatic
feeders, it is fed into the stamp-mortars, when it is pulverized until it
passes through a 30-mesh and sometimes a 60-mesh screen. It is in-
tended in the future to use a 40-mesh standard. As the pulverized dust
passes through the screens it falls into a narrow trough, when it is con-
veyed by means of an Archimedian screw into a dust-bin at one end of
the battery, and from this bin the pulverized material is lifted with a
bucket-belt elevator and discharged onto an 8 in. rubber belt with rope
edges, and conveyed to and across the hopper 110 ft. long, running the
entire length of the cyanide plant-house. This hopper has twenty doors
for discharging the sand into the trucks, which are then run straight
out over the percolating vats into travelers, running on rails, which are
fitted with hand-traversing gearing, enabling a truck to be tipped at any
part of the vat. This is an important point, as sand has a tendency to
pack if moved about or touched in any way after being tipped into the
vat. As a further preventive against packing, there is a small traveler
running under the main traveler, with a platform just at the height
that the sand is to be filled up to. All trucks are tipped over this plat-
form, which breaks the fall and throws the sand olf in a light shower
all round. When the vats are filled up to a depth of about 2 ft., a strong
solution of cyanide — 0.4 per cent — is introduced into the bottom of the
vat under the filter-cloth, and forced up through the sand until it stands
about 2 in. above it. The solution remaining under the filter-cloth is
then drawn off, and filtration commences; the 2 in. on the surface taking
about twenty-four hours to percolate through. After the whole of the
strong solution has been taken out of the ore, a weak stock solution is run
on the top of the ore to a depth of about 6^ in. The cock connecting with
the vacuum cylinder is then opened, and in about thirty hours the sec-
ond solution has passed through; after which about 10 in. of water is
run onto the top, and when this has gone through the ore the operation
is completed. The sludge-door in the vat is opened, and the sand
sluiced out by means of two 2 in. hose-pipes under a head of 150 ft.
The vats are all circular, 22 ft. 6 in. in diameter, and 4 ft. in depth, of
which 5 in. is taken up by the filter bottom, which consists of a wooden
grating with edges rounded off on the upper side, having a strong Hes-
sian cloth laid over the top, which acts as a filter. The vats are made
of kauri timber, 3 in. in thickness; the bottom is held together by six,

EXEMPLIFICATION OF PROCESS — THE PROCESS IN AUSTRALASIA. 73

bolts of f in. diameter. The staves are about 3 in. in \vidth, joined
close, having the bottom rebated into the sides. Each vat is held
together by live round-iron hoops, three of which are {■ in. and two 1 in.
in diameter, having three turn-buckles on each hoop. The plant con-
sists of thirteen of these vats and two sumps of the same diameter, but
6 ft. in depth. Each vat holds 30 tons of ore for treatment; and it takes
about four days to fill a vat, treat the ore, and have it ready for filling
again. The precipitation boxes are 16 ft. long, 2 ft. deep, and 17 in.
wide, divided into twelve divisions, of which the first and last are sand
filters, to clean the solution going in, and to prevent any gold slimes
from being washed out.

"The cost of treatment is being reduced every month; at the present
time it amounts to about $3 25 per ton. This includes drying, milling,
treatment by cyanide, and all expenses, except the royalty paid to the
owners of the ^MacArthur-Forrest patents, from the time it leaves the
mine-hopper until the bullion is in bars."

The tailings from the former pan-amalgamation process are being
worked in a cyanide plant erected for that purpose b}' the Cassel Gold
Extraction Company. These works were completed about the end of
February, 1894. Mr. H. A. Gordon gives the following description,
illustrated by plans which I reproduce: "The works are situated in a
hollow below the tailings dam, so as to allow the tailings to be run at a
good grade into the percolation vats, and from there to be discharged by
sluicing, without the necessity for any lifting or rehandling.

"The building has a frontage of 116i ft., and is 77 ft. in breadth, and
includes laboratories and oflSces, situated in a * lean-to' at one end and
communicating with the main building. The plant consists of eight
circular percolation vats 20 ft. in diameter and 4 ft. in depth (internal
measurement), arranged in two rows, and having an intermediate dis-
charge-launder, toward which the vats have a slope of 2 in. to facilitate
the flow of solutions and the sluicing-out of residues. All the vats are
built of specially selected and well seasoned heart-of-kauri, the timbers
being 3 in. thick. The sides are hooped with 1^ in. iron bolts, connected
and screwed up by nuts and cast-iron boxes, there being three boxes to
each ring. The bottom planks are bolted and dowelled tightly together
independently of the sides. The filters at the bottom consist of a founda-
tion of 2 by 3 in. slats, 9 in. apart, covered by 1 in. molding, which
supports the canvas strainer. This filter is very easily laid, and is most
efiFective in practice. Eech vat is provided with a cast-iron door 18 by
12 in., fixed at the bottom of the side near the discharge-launder, for
the sluicing of residues. There are two sumps of same size and design
as the percolators, and situated between the percolators and front of the
building, and on a sufiiciently low elevation. The sumps are floored
over. In the same line are placed the reservoir and cylindrical vacuum
chamber, 13 ft. by 3 ft. 9 in., under which latter is provided a small
rectangular tank, 12 ft. by 8 ft. by 18 in. deep, capable of holding con-
tents of vacuum chamber. The reservoir is 13 ft. 9 in. diameter by
5 ft. deep (inside measurement), and is at such an elevation as to
permit solutions to flow therefrom into percolators. There are three
extractor boxes, 12 ft. 8 in. by 19 in., with side discharge for slimes and
a settler for cleaning-up. The tank for dissolving the cyanide is an
iron pan about 3 ft. 6 in. in diameter by 2 ft. 6 in. in height, and is
capable of dissolving four boxes — i. e., 1,000 pounds — of cyanide per

THE CYANIDE PROCESS.

TAILINGS CYANIDE WORKS erected by the CASSEL GOLD EXTRACTING C? U^ —

— AT WAIHI NZ.-

^£r£ft£J>fC£. .

REFEJiESCE

A — Pfrcoialort.

B~Sumpi

C — fi€iervofr

D—Disiohttg Tank /or Cy<snt.{i.

E — V^ofUMm Chamber.

F— Taut to Ffant anient $ of E

G — Zate Exfratior BoJUi

H—Stmu SeaUr.

I— Dtsduxrgt Launder.

J— Waste Launder.

K — StrVng~ttqiU>r Launder % t Ht\

L~Atr-pvmp.

M-Centn/ugaJ Pmnp

N—Petitm Wheel Afotor.

O—Frtsh-valer Supply f'tpe*
P— Solulkm Pipet, Reservoir to Percolator.

^ nt t m n. I PercoLtttort to

Q- Weai-tUptor Ptpes j y^^^^^ chamber

R—Pump Pipes
S—Atr-pump Pipe.
T — TratKways
U— Melting Room
V — Assay Room
W — L^iboratory.
X—Batanee Rdom
Y—Dweltmg Rmn

. LONGtTVDtMAL StCTiOft .

EXEMPLIFICATION OF PROCESS THE PROCESS IN AUSTRALASIA. 75

day. It is so arranged that the requisite amount of strong solution may-
be run into the reservoir by simply turning a handle. A 4 in. centrif-
ugal pump serves for returning the solution from the sump to the reser-
voir, and also an 8 in. vacuum pump, which is capable of producing a
vacuum of 26 in. of mercury. A line of pipe runs along above each
row of percolation vats, with a connection at each tank for the hose and
nozzle. One man can empty a vat containing upward of 40 tons in
two hours. A tramway connects the tailings-dams with the w^orks, and
two sets of lines run over the top of each vat, so that the tailings may
be equally distributed without the necessity for handling. The chief
cliaracteristic of the plant is its extreme simplicity and the easy access
to any portion of it; the absence of any subdivisions or partitions within
the main building exposes the whole of the plant constantly to the eye
of the operator.

" The system employed of running the solutions into parallel launders
instead of pipes, enables the solutions from each vat to be separately and
readily sampled and any mishap may be at once detected. The usual
method of procedure is as follows: Side-tipping trucks are run from the
tailings-pit over the top of the vat which is to be charged. The contents
of the trucks are tipped onto cross-bearers resting on struts, which serve
to break the fall of the tailings, and to divide them equally over the
bottom of the vat. Both tramway and bearers are supported entirely
independent of the vats, so that no vibrations ma}'- be communicated to
the latter. A charge consists of sixty-five truck-loads — about 33 tons,
dry weight — and as soon as the vat is full, ' strong ' solution — about 6
tons of 0.7 per cent — is run onto the top from the elevated reservoir.
Provision is made for either upward or downward percolation, but the
latter is usually adopted. The solution is now permitted to gravitate
through the mass of the charge, and to eventually percolate through the
false bottoms into the series of launders in which it is conducted to No.
1, No. 2, or No. 3 zinc precipitation box, according to its strength in
bullion and cyanide. About twenty-four hours after the ' strong ' solu-
tion, about an equal amount of ' weak' solution (0.25 per cent) from the
sumps is pumped on and allowed to gravitate. The residues are now
washed with about 10 tons of water in two charges, which are rapidl}"
drawn off by suction, and which displace the ' weak ' solution and leave
the residues free of either dissolved bullion or cyanide. The solutions
run from the zinc boxes to the sumps, whence they are pumped to the
reservoir or percolation vats, to be used over again for sluicing or weak
solutions as required. A clean-up of the gold in the zinc boxes takes
place fortnightly."

The New Zealand Mining Report of 1893 contains the description of
an interesting experiment which was made some time ago in the Waihi
works, with an apparatus by which ore was intended to be rapidly
extracted by a cyanide solution acting in a jigging motion on the ore in
iron cylinders. The cylinders used were, however, too long and narrow,
containing as they did some 10 ft. in depth of ore, which the solution
had to be forced through. The effect of this was that the solution could
not be made to percolate through the whole of the ore, but passed up
between the cylinder and the ore, the solution being forced into the
cylinder by a pump, at a pressure of 100 lbs. per square inch. This
pressure should have been sufficient to force the solution through, but
as the pulverized material offered greater resistance than the contact

76 THE CYANIDE PROCESS.

between the material and the side of the cylinder, the solution went
through the weakest spot, and had little effect on the ore. The process
("the Bohm Process") proved a failure.

The unquestionable success of the percolation process with the Crown
and Waihi mines has led to its adoption by a number of other com-
panies which treat either ores or tailings by the process, as the Te
Komata and Waiorongomai mines at the Upper Thames, and two or
three companies on the Kuaotunu gold field. The Kuaotunu ore,
in which the gold is exceedingly fine, is especially adapted for the
treatment, the only difficulty experienced — a mechanical one — is
caused by the amount of slimes formed by some of the ores, which
interfere with filtration. The plants on that field do not offer any
special point of interest; they are of small extent and give satis-
factory results. The best one, that of the Tryfluke Company, will,
however, be described on account of the attempts made therewith to run
the tailings direct from the battery into the percolation vats. The plant
consists of four working tanks, each 12 ft. wide, 16 ft. long, and 4 ft.
deep, having a filter-bed of 3 in. in thickness, covered with a coarse
cloth. The depth of ore in the tanks is about 3 ft. 6 in. and about 6
tons of 0.25 per cent cyanide solution are used per charge. This is
what is termed the strong solution. The tap, which allows the filtrate
to flow away, is so regulated as to take about 24 hours for that purpose.
After flowing through six compartments of a filter box, which are filled
with fine zinc-turnings, the solution passes into a sump, 18 ft. long by
14 ft. wide and 4 ft. deep, from where it is pumped into the tank again,
thus forming the second solution. This latter is allowed to filter through
as fast as possible, and, after going through the boxes filled with zinc,
it flows into another sump of the same dimensions as that already men-
tioned. The ore is then washed with pure water, after which the
material is shoveled out of the tanks and run onto the waste dump.
The second solution in the sump, previously referred to, is pumped into
a reservoir placed at a higher level than the working tanks. This
reservoir is 10 ft. long, 8 ft. wide, and 5 ft. deep. The solution is made
up to the required strength before again being used. The company tried
to run the tailings directly into the tanks from the battery, but they,
like others, found that the amount of slimes in the ore prevented the
cyanide solution from filtering, and they are now making arrangements
to run the tailings into a large pit, from which they will be lifted into
the cyanide tanks. (Extract from N. Z. Gov. Mg. Rep.)

Ali works so far referred to are situated in the North Island; on the
large gold fields of the South Island the process has not found more than
experimental application. Experiments have been made with gold-bear-
ing cement from the extensive deposits on the west coast, where almost
inexhaustible quantities of conglomerates, containing black magnetic
oxide of iron and very small quantities of gold, are found. Such experi-
ments were made, for instance, in the Reefton School of Mines, by treating
the cement in lumps, but they were not always successful, apparently for
mechanical reasons. When the cement is crushed, a very good percent-
age is said to be extrd'cted, the gold being fine and well suited for the
purpose. Tests with tailings from the Inangahua River gold fields have
given good results, and a plant for working a considerable deposit of
tailings is nearing completion at Boatman's.

The only instance in New Zealand where the agitation system has

•XEMPLIFICATIOX OF PROCESS THE PROCESS IX AUSTRALASIA.

9-^

^^ si
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111

THE CYANIDE PROCESS.

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EXEMPLIFICATION OF PROCESS THE PROCESS IN AUSTRALASIA. 79

been worked on a large scale is in the works of the Sylvia Company in
Tararu, Thames, where concentrates of a very complex character have
been treated with full success by the author. The ore of the mine named
contains, in the deeper levels, a high percentage of galena, zinc-blende,
and copper and iron pyrites. Most of the bullion is contained in the
sulphurets and cannot be saved by amalgamation, nor is there any
opportunity for smelting the sulphurets after concentration or for
remunerative exportation of the same. After successful trials with the
concentrates subjected to cyanide treatment, I constructed an agitation
plant, of which I append my plans, reproduced from the N. Z. Gov. Mg.
Rep. 1892. The concentrates in question are classed as jigger concen-
trates, first-class slimes, second-class slimes, and huddle concentrates.
They are named in the order as they are obtained during the dressing
process. The finest products contain the most galena; they are the
richest in gold and silver, and give the highest percentage of extraction.
A detailed description of plant and extraction process is given in the
mining report above referred to. I give here only the most salient points:
The plant, constructed of wood (kauri pine), consists of three agitators, 6 ft.
in diameter by 6 ft. in depth; three Scheidel's vacuum filters (patented)
of 35 ft. square filter surface each ; the necessary solution tanks, pipes,
and pumps, and bullion roasting and melting furnaces. The experience
gained with this plant, which works well with the exception of the faults
which necessarily adhere to the use of wood for cyanide plants, induced
me to construct, later on, the plant for the Utica Mine, California, of
steel. This plant, being free from the only fault, that above mentioned,
answers the purpose to perfection. The results of extraction of the
Sylvia concentrates vary in accordance with the quality of the material,
the slimes giving generally better results than the coarser products, and
the richer first-class slimes return a higher percentage of gold and sil-
ver than the second-class slimes, which are of lower grade. Eminently
satisfactory results have been obtained from the best slimes, from which
as high as 96.45 per cent of the gold and 94.59 per cent of the silver assay-
value have been extracted. The average extraction of 100 tons amounted
to 86.11 per cent of the gold and 67 per cent of the silver; corresponding
with 85.22 per cent of the total value. The extraction of the least suited
material, the jigger concentrates, coarse and low grade, amounted to
80.32 per cent of the gold and 50 per cent of the silver. The average
extraction of all classes of concentrates amounted to 82.67 per cent of
,the assay- value. The total amount of bullion extracted by me from
about 300 tons of material amounted to upward of $51,000. The time
of agitation and the strength of solution vary in accordance with the
quality of the material. The quantity of cyanide used for the highest
grade ore amounted to less than 1 per cent, and for low-grade material
considerably below 0.5 per cent of the ore. The time of agitation varied
between six and twenty-four hours. The method of working the plant,
which permits the treatment of twenty tons per twenty-four hours, is
identical with that of the Utica plant, which I propose to describe in
detail. The Sylvia Company enjoyed, on account of the plant being the
pioneer plant of its kind, special privileges in reference to royalty for
the use of the reagent.

New Zealand is among the few countries, outside of Africa, where
cyanide treatment of ores, tailings, and complex concentrates has been
in all instances a perfect success. Many of the ores of the Colony are

THE CYANIDE PROCESS.

particularly suited to the treatment. Its still more extensive applica-
tion is prevented by the royalty charged by the owners of the MacArthur-
Forrest jjatents, in reference to which fact I quote the Government
Inspecting Engineer of the Colony, Mr. H. A. Gordon, who says (Gov.
Min. Rep. 1893):

" There is no gainsaying the fact that the cyanide of potassium is a
good reagent for gold, and undoubtedly the best agent for extracting
gold, especially w^here the latter is in a very finely divided state among
the ore; but the royalty charged is prohibitive, and it will never be
largely used until it is lowered. If the Cassel Company (the owners of
the MacArthur-Forrest patents) would have been content with about
2 per cent royalty, the process would have been almost universally
adopted by every company in New Zealand."

The following particulars represent the results of the working of the
cvanide process on the New Zealand gold fields up to the end of Decem-
ber, 1893:

Names of Companies.

Bullion,

in oz.

value.

15,064

$145,930

14,552

51,965

3,072

35,895

605

6,410

1,981

4,595

1,741

5,155

149

1,1^30

299

2,105

1,097

9,045

200

2,255

New Zealand Crown Mines, Karangahake, from ore

Sylvia Gold Mg. Co., Thames, from concentrates

Tryfluke Gold Mg. Co., Kuaotunu, from tailings

Great Mercur Gold Mg. Co., Kuaotunu, from tailings

Te Aroha Gold Mg. Syndicate, Waiorongomai, from ore and tailings

Te Koraata Gold Mg. Co., Upper Thames, from tailings

Red Mercury Gold Mg. Co., Kuaotunu, from tailings

Siiverton Gold Mg. Co., Waihi, from tailings

Waihi Gold Mg. Co., Waihi, from ore

Welcome Gold Mg. Tailings, Boatman's, from tailings

Totals -.-

38,760

$264,585

The returns by cyanide during the twelve months ending March 31st
last are: Bullion obtained from ore, 14,774 oz.; from tailings, 12,478 oz.
The year 1894 promises to be even a more successful one, six new
cyanide plants being in course of erection. The bullion obtained by
cyanide during the quarter ending 30th June amounted to 13,030 oz.
from ore, and to 7,073 oz. from tailings. Fifty-two per cent of the total
bullion product in the North Island of New Zealand was produced
during that period by the cyanide process.

In the other colonies of the Australasian group the process is compar-
atively slow in being introduced. The monetary crisis that has prevailed
in the colonies, combined with prejudice and skepticism on the part of
the mining community, have retarded its introduction.

(b) Tasmania. — In this colony the process has not yet been intro-
duced on a working scale. So far, the only use that has been made of it,
has been on a small and experimental scale, and in a very imperfect
manner. (Letter from Government Secretary for Mines, January 15,
1894.)

(c) Western Australia. — Here the process has not been adopted on
a large scale, "the mining industry being yet in its infancy. The
process is, however, considered the best known for Western Australian
gold ores, and some minor experiments have been made with tailings,
giving good results." (Letter from Government Secretarv of Mines,
January 19, 1894.)

EXEMPLIFICATION OF PROCESS — THE PROCESS IN AU^RALASIA. 81

(d) South Australia. — This colony has several plants for the work-
ing of the cyanide process, one of which, that at Mt. Torrens, is being
worked as a custom works by the Mines Department of the State for
the purpose of giving the mine owners an opportunity to have their
ores tested. A Government plant undoubtedly inspires miners and
prospectors with confidence. A charge just sufficient to cover cost of
treatment is made by the department.

" The plant has now been in operation for some weeks, and the treat-
ment of an ore parcel from the Blacksnake Mine has been completed.
The ore contained on an average 16 dwts. 15 grs. of gold; of this, 10 dwts.
8 grs. were saved by the battery, 4 dwts. 9 grs. by cyanide, leaving 1
dwt. and 22 grs. in the tailings. The ore contained quartz, hematite,
and about 4 per cent of iron pyrites." (Letter from Secretary for Crown
Lands, May 23, 1894.)

A plant for treating 500 tons per month is at work on tailings at the
Virginia Gold Mining Company's property, and is doing good work.
The tailings from the battery are allowed to dry, and are then trucked
into vats of a capacity of between 25 to 30 tons, 16 ft. in diameter by 5
ft. in depth. The sumps are built of cement, 16 ft. by 14 ft. by 12 ft.
The consumption of cyanide is about 1^ lbs. per ton of tailings. The
tailings before treatment assay from 10 to 15 dwts., after treatment, 1
dwt. 7 grs. per ton. The bullion is refined with nitre. The vats are
charged twice a week, (GovernJhent letter.)

(e) Queensland. — At Charters Towers, a plant capable of treating
800 tons per month has been erected by the Australian Gold Recovery
Company, Lim., the owners of the MacArthur-Forrest patents for Aus-
tralia, from which the following information has been obtained: It
is a custom plant. The chief material treated is sludges, which are
purchased from the surrounding mills in varying quantities. These
sludges are concentrates which have been submitted to fine grinding
and amalgamating in berdans; this material is, if necessary, mixed
with coarse sand or tailings, and treated by percolation; vacuum pumps
are used to assist. Difierent classes of ore of a refractory character are
treated in the works, and the conditions of treatment are varied with
the character of the ore. Operations were started in August, 1892, since
which date about 9,200 tons of sludges have been treated, with a
return of 9,633 oz. of gold. "At Croydon a tailings plant has been
erected at the Cumberland property of a capacity of 1,500 tons per
month. Plants for the treatment of 2,000 and 1,000 tons per month
are in course of erection for the Croydon Quartz Crushing Company and
the Pioneer Gold Mining Company, respectively." (Australian Gold
Recovery Company.)

(f) New South Wales. — In this colony the cyanide process is at
work only at the Mitchell's Creek gold mine, where the plant and
operations are described by Mr. James Taylor, the Government metal-
lurgist, as follows: "The works have been erected for the treat-
ment of a dump of old tailings estimated to contain about 18,000 tons,
and found by careful sampling to contain 8 dwts. 4 grs. of gold and
11 dwts. 10 grs. of silver per ton. The plant consists of two 400-
gallon iron tanks, two storage vats, six percolating vats, two sets of
ten precipitating boxes, two sumps, iron pipes for conveying the solu-

6cp

82 ' THE CYANIDE PROCESS.

tions and washes, side-tipping wagons and tram-rails for charging and
discharging the percolating vats, steam boiler and pump to return the
cyanide solution from the sump to the storage vat, small muffle furnace
for roasting the precipitated gold with its admixture of zinc and copper,
laboratory and assay furnaces.

"In the two iron tanks the cyanide stock solution is prepared by dis-
solving crude potassium cyanide, suspended in a wire gauze tray in
water. The crude salt contains about 75 per cent of pure potassium
cyanide, and the stock solution is made up to a strength of from 10 to
25 per cent. From the iron tanks the solution is run through a canvas-
bottomed box, which serves as a filter, into one or the other of two storage
vats, as it is needed to bring up the strength of the returned liquor to
the standard required for the treatment of the next charge of ore, say
about 0.7 per cent of cyanide. These two wooden storage vats are 16 ft.
in diameter and 5 ft. deep, and are placed sufficiently high to discharge
into the next series of vats by means of iron pipes. The six large
percolating vats, each 18 ft. in diameter and 5 ft. deep, are provided
with filter-bottoms, built up by laying ribs of Avood, notched on the
under side, along the bottom of the vat at regular intervals. On these
ribs is spread cocoanut matting, and over this comes a layer of wool-
pack. The edges of the filtering cloths are well caulked along the sides
of the vat. The vats are charged with tailings by means of side-tipping
wagons, carried on an over-head tram-line, and the exhausted tailings
are discharged by being shoveled through an 18 in. hole in the side of
the vat, near the bottom, into a wagon running on rails and leading to
the waste dump. Each percolation vat receives a charge of 35 tons of
tailings, and two vats are emptied and refilled daily during the day
shift, so that 70 tons of tailings are treated every twenty-four hours.
The fresh charge of tailings is first soaked with returned solution, which
begins to make its appearance at the bottom of the vat in about three
hours from the time of its application. A solution of 0.7 per cent is
then turned on, and this is allowed to act for about twenty-five to thirty
hours; it is then drawn off, running direct to the precipitating boxes.
About twenty inches of liquid from the storage vat is sufficient to soak
the charge, and a similar amount of the reinforced solution is enough
for the gold extraction, after the application of which water is run on to
wash out the cyanide solution. Each of the percolation vats can be
supplied with cyanide solution from the storage vats by means of a
21 in. pipe, and with water through a 2 in. pipe, for washing after the
cyanide solution has been drained off, or before the cyanide solution has
been added should that be found necessary, as is sometimes the case.
The tailings are under treatment in the vat during a period of about
sixty-four hours from the completion of charging to the commencement
of discharging the vats.

"An inch and a half pipe proceeding from the bottom of the percolat-
ing vats takes the gold solution to the precipitating boxes, where the
liquid is caused to pass upward successively through a series of ten
boxes, filled with fine zinc turnings, made on the spot from the zinc lin-
ings of the boxes in which the potassium cyanide has been imported.
The gold and silver are precipitated upon the zinc as a fine black slime,
accompanied by any copper that may have been taken up by the solution
from the tailings. After passing these boxes, the solution, almost or
altogether free from gold, is collected in a couple of sumps, each 16 ft. in

EXEMPLIFICATION OF PROCESS — THE PROCESS IN AMERICA. 83

diameter and 5 ft. deep, from which it is pumped back to the storage
vats, ready for another application, either for soaking, or, when suitably
reinforced, for gold extraction. When a clean-up is being made, the zinc
in the boxes is well stirred to shake off the slimes, which are then washed
out through a plug-hole into a launder, where they are collected, and
either roasted and melted with a little flux, or treated with acid and
then melted; the mode of procedure depends upon the amount of base
metal mined with the gold and silver. All solutions going from the per-
colating vats pass through the precipitating boxes, excepting of course
the wash water retained as moisture in the tailings when the vat is emp-
tied. The tailings contain, as noted, 8 dwts. of gold and 11 dwts. 10 grs.
of silver to the ton. The returns for a recent run of ten weeks show
that 64 per cent of the gold and about the same of silver was actually
recovered; but by assay of the tailings after treatment it appears that
70 per cent of the gold had been removed; hence something like 6 per
cent seems to be locked up in the plant, and may be obtained later.
The cost of cyanide during the same period of ten weeks amounted to
$2 58 per ton of tailings, and the total cost of treatment to $3 38 per
ton. The tailings contain from 0.25 per cent to 0.50 per cent of copper,
the presence of which increases the amount of cyanide used by from 75
cts. to $1 per ton, and further acts injuriously, as it is precipitated by
the zinc with the gold and silver and debases the bullion obtained, thus
necessitating refining operations. The force employed in the works
consists of one scientific manager, two men on alternate twelve-hour
shifts to attend to the circulation of the solutions, nine men to fill and
empty the vats, one man to prepare the cyanide solution and to do odd
jobs, and a laboratory boy. The cost of the plant was approximately
$10,000; it was erected under the auspices of the Australian Gold Recov-
ery Company, Limited" (MacArthur-Forrest patents). During six
months 9,972 tons have been treated, with an extraction of 2,512 oz. of
gold.

(g) Victoria. — "A plant of 2,000 tons per month is being constructed
at the New Golden Mountain Gold Mining Company's property, and it
is proposed to treat the ore at these works directly by cyanide, without
any previous treatment or battery amalgamation". (The Australian
Gold Recovery Compan3^)

C. The United States of America.

The introduction of the cyanide process in the United States as a
metallurgical process on a commercial basis has so far been slow; the ter-
ritory is vast, the mining districts are widely scattered, and there is an
almost invincible prejudice against any new process, particularly patent
processes, owing to the innumerable failures in which for years past
much money has been lost. Of late the process has been tested on
many ores from almost all mining camps in the United States. It has
been found successful, on a small scale, in many instances. Its tech-
nical application has, however, not always been the expected success, for
which fact various causes are responsible. In many instances plants
have been erected where either the ore is unsuited for the process or
where the supply of suitable ore is insufficient; in other instances the
working of the process has been intrusted to incompetent hands, which

84 THE CYANIDE PROCESS.

naturally led to a failure. The Mac Arthur-Forrest patents and the
Simpson patent are owned in the United States by the Gold and Silver
Extraction Company of America, Lim., of Denver. A number of extrac-
tion works have been erected all over the United States by mining com-
panies and other parties. To obtain reliable information of their results
and their plants has proved possible only in a few instances, and it is
hardly possible to form from such information an adequate idea about
the success of the process in this country.

(a) Utah. — The first mill to operate cyanide treatment in this Terri-
tory is owned by the Mercur Gold Mining and Milling Company. That
company had just completed a pan-amalgamation plant at a cost of
$30,000, which proved a failure, only 20 per cent of the gold being
recovered, when small tests with cyanide, followed by good results, led
to the introduction of the process on a large scale, which has since proved
a full success. For the following description, by Louis Janin, Jr., I am
indebted to the Engineering and Mining Journal (Oct. 7, 1893):

" The ore passes through a Dodge rock-breaker, and is crushed by two
sets of Wall's corrugated rolls; the first are set to one half inch, the
second to one quarter inch. This very coarse ore (over 20 per cent of
the product which goes to the leaching vats does not pass a half-inch
mesh) is treated by C3^anide percolation. The dimensions of the vats
are 12 ft. 8 in. diameter; depth to false bottom, 35 in.; giving a capacity
of about fourteen tons when the vats are filled to within 6 in. of the
top. In consequence of the crudeness of the crushing, the time of
leaching varies greatly; it occupies between ten and two hundred
and forty hours. It is claimed that the ore (which is a silicious sur-
face-ore with the gold finely divided) is singularly constant in value
and quality; the wide differences in the time of treatment are ascribed
to the differences in mechanical condition. As a rule, the cyanide solu-
tion is left standing with the ore for twelve hours; it is then passed
through continuously, until practically all gold is extracted; the time
required varies from thirty-six to forty-eight hours. The percolation
liquor passes through zinc boxes 40 ft. long, and is returned to the stock
solution tank, where its proper strength is made up again by addition of
cyanide. After the ore in the tank has been leached sufficientl}^, the tank
is allowed to drain. However, a considerable quantity of solution, about
400 lbs. to the ton, or, with the 0.25 per cent solution used, about 1 lb.
potassium cyanide to the ton of ore, remains in the vat. To dislodge
this, wash water is used, either plain water or sometimes a weak solu-
tion resultant from washing. In the latter case, the weak solution is
stored in separate tanks, and this arrangement allows washing with a
minimum wastage of solution. The extraction of the Mercur ore has
varied; at the beginning of operations it was considerably below 70 per
cent, but as experience with the process increased the results became
better; the average is now given as between 85 and 90 per cent. The cost
of treatment during an early period of the work is given at $2 40 per
ton, divided as follows: Potassium cyanide (1.27 lbs. per ton), 66 cts. ;
zinc (0.55 lb. per ton), 5 cts.; labor (seven shifts per twenty-four hours,
6 day and 1 night), $1 12; supplies, repairs, fuel, and freight, 57 cts.;
total (not including ofiice expenses, royalty, and superintendence),
'$2 40. Since that period, the expenses have been reduced as the amount
of cyanide lost per ton of ore has been diminished, and a larger quan-

EXEMPLIFICATION OF PROCESS THE PROCESS IN AMERICA. 85

tity of ore is reduced with the same amount of hxbor. Comparative
results by actual experience on the ore by amalgamation and cyanide
treatment are as follows: 1,500 tons of ore treated by amalgamation
gave an average extraction of 20 per cent at a cost of $4 25 per ton for
milling; 1,600 tons of ore, treated during 90 days by cyanide, averaged
an extraction of 88.5 per cent, at a cost of $2 25 for milling." The intro-
duction of the cyanide process has made the Mercur Company a remark-
able financial success; it paid during the first five months of this year
$150,000 in dividends. The plant is being increased to a capacity of
250 tons per day.

(b) Montana. — One of the first cyanide mills in this State was
erected by F. B. & R. B. Turner, in Revenue, Madison County, who
supplied the information which follows: The gold in the Revenue
ores has always been very hard to save, the best amalgamation
methods only saving from 25 to 27 per cent of the assay-value; the
application of the cyanide process increases the returns to from
80 to 87 per cent. Extensive tests have proved that the wet-crush-
ing and cyanide treatment is profitable only on low-grade ore, as
the loss of low-grade slimes connected with that method is consid-
ered immaterial. The most successful treatment with cyanide has
been found to be percolation of dry-crushed ore. The present plant (see
diagram, p. 86) is used for wet-crushing of low-grade ore. The tailings
from the battery pass into settling pits, and the slimes are allowed to flow
into a large reservoir below the mill for eventual future treatment. The
tailings settled in the pits are shoveled into the leaching tanks; the
running of the pulp direct into the percolation vats proved here, like in
many other localities, a failure, owing to the slimes. A dry-crushing
plant of 25 tons per day is now in course of construction (see diagram);
after its completion, ores of about $25 value will be crushed in the dry,
poorer ores in the wet mill. The Revenue ore is nearly pure silica, con-
taining from 1 to 2 per cent of iron peroxide and no sulphurets. It is
crushed and passed through a 30-mesh steel screen. Some of the per-
colation vats are of 10 ft. diameter by a depth of 4^ ft., others are of
12 ft. diameter by 4 ft. deep; they are made of 3-in. Oregon pine. The
strength of the solution varies from 0.6 to 1 per cent; percolation takes
from 24 to 36 hours, after which the solution, which is circulated or
pumped back, varies from 0.4 to 0.8 per cent of cyanide. One half ton
of solution, on an average, is used for treating one ton of ore. The total
extraction amounts to from 80 to 87 per cent of the assay-value of the
ore, 27 per cent of which is obtained from amalgamation on the plates.
Cyanide extracts from 73 to 79 per cent of the value left in the tailings
after amalgamation. No difficulty is being experienced in precipitating
the gold. The consumption of zinc amounts to about half a pound per
ton of ore. Sulphuric acid is used for bullion refining; the fineness of
melted bullion is from 920 to 940. The total cost of treatment amounts
to $5 per ton, including $1 patent-royalty, and consists of the following
items: Crushing and labor, $2; chemicals, $2; patent-royalty, $1. The
actual consumption of cyanide is from 2^ to 3 lbs. per ton of ore. The
total cost of the plant amounted to about $20,000, including engines,
boilers, stamps, and vats, all placed in position. Eight to ten men are
employed in the mill.

A cyanide mill erected by the Henderson Mountain Mining and

THE CYANIDE PROCESS.

Milling Company, near Cooke, Park County, was worked on surface
hematite ore for some time with fairly satisfactory results.

(c) Colorado. — The owners of the Mac Arthur-Forrest patents possess
a small plant for testing ore parcels in South Denver.

The Cripple Creek Gold Extraction and Power Company erected a
plant in Cripple Creek, in reference to which I received the following
communication from the technical manager (Mr. J. K. Turner):

"A small plant has been a remarkable success, and an addition to it
is now in course of erection, bringing its capacity up to 50 tons daily.
The machinery will finally consist of three Gates' crushers, two pulver-

EXEMPLIFICATION OF PROCESS THE PROCESS IN AMERICA. 8/

izers, four screens, four iron leaching vats of 20 ft. diameter, two solution
tanks of 15 ft. diameter, and four zinc boxes of 40 ft. length. The plant
is running as a custom mill, and many classes of ore are being treated;
at present about 30 tons per day. The ore is crushed dry and passed
through a 20-mesh screen. The cyanide solution used is 0.75 per cent, the
strength of which is by percolation reduced to 0.5 per cent. One half
ton of solution is required for the treatment of one ton of ore. The
extraction of gold averages 90 per cent, that of silver 84 per cent. Sul-
phuric acid is used for bullion refining; the bullion is from 775 to 790
fine. Copper and zinc compounds in some ores have been found to
interfere with extraction. The average value of the ore is $30 before
and $3 after cj^anide treatment. The cost of treatment amounts to $4 70
per ton. The cost of the plant was $20,000. Seven men are employed
in the works."

The successful cyanide treatment of Cripple Creek ores, as here de-
scribed, is very interesting, for the ores in that district contain a large
amount of telluride minerals. Many ores contain sylvanite, krennerite,
and calaverite.

The Puzzler Gold Mining and Milling Company of Denver have
ceased to work their cyanide plant at Ward, Boulder County, although
they were successful with the process.

A cyanide plant at Junction Creek is reported in successful operation.
(M. S. P.)

(d) Nevada. — A branch company was formed by the owners of the
MacArthur-Forrest patents for introducing the cyanide process on the
Comstock Lode. A number of laboratory experiments made in the Con.
Virginia and California Company did not lead to the adoption of the
process.

(e) Arizona. — No information can be obtained in reference to the
process in this Territory, where a company has been organized for its
introduction, with the exception of that obtained from the Champies
Mine, Yavapai County, where the results were unsatisfactory, appar-
ently on account of faulty technical manipulation.

(f) New Mexico.— The Deep Down Mine had adopted the cyanide
process, but abandoned it in favor of pan-amalgamation, the reasons
for which are explained (Engineering and Mining Journal) as consist-
ing in a change of the character of the ore.

(g) South Dakota.— The Black Hills Gold and Silver Extraction
Mining and Milling Company of Deadwood have of late erected a cyanide
plant, about which the general manager, Mr. I. S. Childs, gives the fol-
lowing details:

" The ore consists of from 80 to 95 per cent of silica, accompanied by
variable quantities of iron, both in the form of peroxide and the various
■conditions of partial oxidation, and contains traces of copper, manganese,
arsenic, and antimony. The ore is dry-crushed with rolls, and passes
through a 30-mesh screen. The percolation vats of steel are 24 ft. in
diameter by 3 ft. in depth. The cyanide solution is usually of 0.5 per
cent strength; its quantity amounts to half the weight of the ore. From.
85 to 90 per cent of the assay-value in gold and from 50 to 75 per cent

88 THE CYANIDE PROCESS.

of the silver value is extracted. All extracted bullion is recovered.
Lime is used with the ore and caustic soda with the concentrates to
remedy the 'acidity.' The consumption of zinc amounts to 0.55 lb. per
ounce of bullion recovered. The treatment takes from twenty-four to
forty-eight hours. The value of the material before treatment is $20;
the tailings assay from $2 to $3 in gold. The total expenses for treat-
ment, including $1 patent-royalty, are $3 50 per ton. The plant for the
treatment of 40 tons per twenty-four hours cost $25,000. Fifteen men
are employed per twenty-four hours."

The Golden Reward Chlorination Works, of Deadwood, are reported
as adding cyanide works to their plant. The works ar,e custom works.

Many tests with cyanide have been made in various other States, in
some instances leading to the adoption of the process on a commercial
scale; in others, experiments were conducted with little knowledge and
in a cursory manner; in other instances, again, the character and quali-
ties of the ore prevented cyanide treatment from being a success. One
instance, where the process was first used but afterwards abandoned, is
the Creighton Mining and Milling Company, Cherokee County, Georgia,
where the extraction from concentrates from old oxidized tailings, as
described by the general manager, was reasonably good, being 82 per
cent of the assay-value; from the fresh concentrates from deeper levels,
however, the returns were only 50 per cent, in consequence of which the
process was discarded and barrel chlorination introduced in its place
(H. T. Fisher). In other instances the value of the ore in the mine fell
off, so that not only the cyanide process, but all operations had to be
stopped. An instance in point offers — the Moratock Mine, Montgomery
County, North Carolina. The engineer in charge stated (Engineering
and Mining Journal) that he had no trouble in treating the ores of that
mine by cyanide and making a high extraction (95 per cent) at a mod-
erate cost. Cyanide solution of 0.25 per cent was used; the total cost of
mining, milling, and royalty amounted to about $3 75. The mine,
however, was shut down, the ore-value receding to $1 25.

(h) California. — The Shasta Gold Recovery Company erected a mill
under the direction of Mr. A. B. Paul. The mill has been working for
some time successfully. Mr. Paul was one of the first, if not the first,
who used wet-crushing of the ore with cyanide solution, instead of water,
in the mortars. No authentic information could be obtained in refer-
ence to his results.

A cyanide plant has been erected at the Gold Run Mine, Siskiyou
County, the working of which has been described in the California
Mining Report, No. 11, page 430.

The following information referring to the cyanide process in Kern
County, has been contributed by Mr. W. L. Watts, assistant in the field
to the California State Mineralogist: "A company which was organized
in St. Louis to reopen the Bright Star Mine in Kern County, attempted
to work several thousand tons of tailings at that mine by the cyanide
process. It is said that the leaching plant used for the purpose could
only handle six tons of tailings every twenty-four hours, and that about
45 per cent of the precious metal was recovered."

" The Cyanide Process at Havilah, Kern County. — In 1892, Meesi-s.
Stebbins and Porter commenced leaching at Havilah. They first treated

EXEMPLIFICATION OF PROCESS — THE PROCESS IN CALIFORNIA. 89

50 tons of heavy sulphuretted concentrates at the Reese mill. The assay-
value of these sulphurets ranged from $15 to $48 per ton. Owing to
leakage and other causes, their first experiments were not remunerative,
but the last and richest portion of this batch of concentrates was treated
with great success, 86 per cent of the precious metal being saved. One
difficulty encountered arose from the fact that, owing to the sulphurets
having long been exposed to the air, they were partially oxidized into
acid sulphates; the detrimental effect of these sulphates was eventually
overcome by neutralizing them with quicklime. One hundred tons of
tailings were then treated at the Hayes mill. These tailings showed an
assay-value of $20 per ton, and about 91 per cent of the precious metal
was saved. This last lot of tailings consumed 3 lbs. of potassium
cyanide to the ton of ore. The process employed is as follows: The
tailings are first treated in a tank 6 ft. long, 6 ft. wide, and 6 ft. deep,
and holding a charge of six tons of ore. In this tank the tailings are
saturated with a solution containing one half of one per cent, by weight,
of potassium cyanide. The tailings are allowed to stand in this solution
for forty-eight hours, and are then sluiced into 'filter-bottom tanks,'
where they are washed. These 'filter-bottom tanks' are 7 ft. long, 10
ft. wide, and 3 ft. deep. The tailings are sluiced from the saturating tank
with a stock solution which has a strength of one-fifteenth of one per
cent of potassium cyanide. About 1,000 gallons of stock solution are
used in sluicing six tons of ore. The filtrate is then tested to determine
whether a sufficient percentage of the gold and silver value of the pulp
(as shown by assay) has been dissolved. If the filtrate is found to con-
tain a sufficient percentage of the gold and silver, the solution is drawn
ofi" and the tailings are washed with fresh water; enough wash-water
is used to replace the amount of the solution taken up by the tailings.
The amount of water thus added to the solution is usually about 500
gallons to six tons of ore. If on testing the solution it is not found to
have dissolved a sufficient percentage of the gold and silver, the stock
solution is left on the ore until all the gold and silver which it is pos-
sible to extract by this process has passed into solution. The tempera-
ture of the solution employed has varied from 40° to 80° Fahr., and
within these limits no difference was experienced in the solubility of
the gold and silver. In this process it was found to be far better to
assay the filtered solution than the macerated pulp, for a perfect volu-
metric sample of the filtrate can be readily obtained. Test assays —
four assay-tons of the auriferous solution of cyanide of potassium are
evaporated, and the resultant auriferous compound is mixed with half
an assay-ton of litharge, and fluxed with glass. The assay is conducted
as an ordinary assay for gold and silver."

" In speaking of the different ores they have treated by the cyanide
process, Messrs. Stebbins and Porter state that it has been their expe-
rience that the majority of ores showing free gold also contain gold in
any sulphide which may be present; but that, except in the case of
sulph-arsenides, ores showing no free gold seldom contain auriferous
sulphides. In September, 1893, Messrs. Stebbins and Porter were building
a mill in which to treat ore by the cyanide process at the Iconoclast Mine."

A cyanide agitation plant was erected by me (the author) in 1893, at
the Utica Mine, Calaveras County, which, being successful in all details,
shall here be described in full. The Utica Mining Company are the
owners of an extensive milling plant, consisting of 160 stamps with Frue
vanners and Tulloch concentrators, and a canvas plant for tlie saving

90 THE CYANIDE PROCESS.

of the sulphuret slimes which escape from the concentrators. Up to last
year all concentrates were extracted by the Piattner chlorination process,
wliich treats the coarse vanner-py rites well; the fine slimes of the canvas
plant, however, do not give equally satisfactory results, on account of
their containing a very large percentage of carbonate of lime, which is
troublesome and involves loss in the roasting furnace on account of its
fineness and lightness, and is costly in chlorination on account of its
taking up chlorine. The slimes are also difficult to leach in the chlori-
nation vats. I examined the different classes of concentrates as to their
fitness for treatment with cyanide. The coarser sulphurets from the
concentrators did not give, without further grinding, sufficiently high
extraction results to warrant the substitution of the chlorination by the
cyanide process. The results of the experiments with the slimes from
tiie canvas plant, which were very satisfactory, led to the construction
of the present agitation plant. This plant (see illustration) is com-
pletely built of steel and iron, and consists of the following parts: A
vertical cylindrical agitator (constructed by Mr. C. D. Lane and myself),
5 ft. in diameter by 5 ft. high, of ^in. steel plate, with a cast-iron bottom
2 in. thick, with strengthening ribs underneath; to the bottom is cast a
cone, through w^hich passes the vertical shaft, which carries four arms.
To these are attached the four paddles of ^ in. steel, 6 in. wide, twisted
like the plates of a propeller. A ring connecting the four paddle arms
gives greater stability to them. The shaft with the paddles can be
raised, by means of a screw-spindle, 4 ft. above the bottom of the appa-
ratus. A wrought-iron ring, 3 in. wide and ^ in. thick, riveted outside
around the top of the agitator, strengthens the structure. The driving
gear is placed below. An opening, 4 in. diameter, in the bottom, dis-
charges the contents of the agitator through a pipe, furnished with a
stopcock, onto Scheidel's patent vacuum filter, placed on the floor
below and in front of it. Here a perfect separation of the cyanide
gold solution is effected from the residues. This filter (see diagram)
is built of i in. steel, with bottom ■§ in. thick; it forms a rectangular
box 3 ft. 6 in. deep, 7 ft. long by 5 ft. wide; 2 ft. above the bottom is a
perforated steel filter-bottom of | in. boiler plate, made in three mov-
able sections, supported by angle-iron running around the sides, and
by the vertical support of double T iron. The perforations are of ^ in.
diameter, at a distance of ^ in. from each other. This filter-bottom fits
closely to the sides of the apparatus; it is covered with a blanket, which
is kept in position by bars running along the four sides, and fastened
by thumb screws. A grating in three sections of f in. round iron serves
to protect the cloth; the intervals of 3 in. between the bars are filled
in with coarse sand. The filter partition divides the apparatus into
two compartments, one above the other; the lower forms a closed box,
which is in connection with a duplex vacuum pump, by means of which
the air can be rarefied when the filter-bottom is covered with pulp.
The upper part, above the filter-bottom, receives the contents of the agi-
tator. The real bottom of the apparatus has a discharge with a 3 in.
stopcock, for running off the filtered solution into either one or the
other of the two solution tanks, which are standing on the floor one step
lower, in front of the filter. All cocks and taps of the plant are of con-
siderable diameter, which secures a quick charge and discharge. The
filter is provided with a gauge to indicate the height of the solution
within, a gauge indicating the degree of vacuum, an air-tap to permit
influx of air when the filtered solution is being discharged, and a manhole.

^
^
^

T«HjCmku*v>tN**'>'>.

EXEMPLIFICATION OF PROCESS THE PROCESS IN CALIFORNIA. 91

The mode of working the plant is this: The cyanide solution is
charged into the agitator, the paddles are set in motion by revolving the
shaft, the ore is charged b}'- degrees, and the agitation is kept up for the
required time, after which the pulp is discharged from the agitator onto
the filter. The vacuum pump is then set in motion, and filtration under
the influence of atmospheric pressure will at once commence. The solu-
tion will soon be sucked through; then washing follows, first with liquor
from former operations, which has already passed through the zinc
boxes, and finally with clear water. These operations of filtering and
washing take about two hours. It is advisable to suck the tailings as
dry as possible before each new wash is put on, which permits the com-
plete removal of the gold solution with a very small amount of liquid,
one half ton of which is sufficient for washing a charge of two tons of ore.
If the filtration has been properly managed, no degree of continued
washing can improve the results. The -filtered solutions are clear. The
first or original solution, together with the first wash, will be run oft' into
one of the two solution tanks in front below the vacuum filter; the follow-
ing washes run into the other. These tanks are 8 ft. long by 3 ft. wide
and 3 ft. deep, made of i in. steel. Each of the tanks is in connection
with a zinc precipitation box, 9 ft. long by 21 in. deep and 9 in. wide,
divided into ten compartments; there is an interval of 1 in. between
each two compartments. The false perforated steel bottoms of the
chambers, which can be removed if desired, are 2^ in. above the true
bottom of the box (see diagram, p. 31). The bottom of the box has a
number of 1 in. iron faucets, one corresponding with the center of each
filter compartment; the sides of the box are 4 in. higher than the par-
titions within, which insures absolute safety against the liquid running
over the sides of the box, if one or the other compartments should become
blocked. The gold solution flows into the box through a 1 in. cock, enters
the first compartment from below through the perforated false bottom,
percolates the zinc shavings placed thereupon, leaves it, and enters the
second, and so forth. A steel settling tank. 12 in. deep, 12 in. wide, and
9 ft. 3 in. long, is placed below the precipitating box for receiving the
bullion when cleaning up (see general demonstration of process, above).
The zinc used consists in turnings of ^o o' i^^- thick, turned from cast
zinc cylinders on a lathe; 2 lbs. fill one compartment. The solution
passes through the box at the rate of 700 gallons in twenty-four hours.
The bullion precipitation of the solution is very efficient as it passes
from compartment to compartment, which amounts to passing ten times
through a zinc column of 14 in. high by 9 in. square. As shown by the
following table of analysis.

One Ton of Liquid contains—

Gold

Silver.

Originallv

Oz. Dwts.

5 14

Grs.

1
22

15.43
14.96
13..36
12.34

Oz. Dwts.
2 4
5
1

Grs.
g

After 14 in. of zinc column

After 28 in. of zinc column

3
10

After 42 in. of zinc column . .

After 56 in. of zinc column .-.

After 70 in. of zinc column

After 84 in. of zinc column

After 98 in. of zinc column

After 112 in. of zinc column .

After 126 in. of zinc column

After 140 in. of zinc column

THE CYANIDE PROCESS.

11X5

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j'£/)n>VArra F/i.reft eorroM,

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The solution leaving the zinc box contains only 12.34 grs. of gold,
or 0.0045 per cent of its original contents, and only 3 grs. of silver, or
0.0028 per cent of the original silver value. Simultaneously the solu-
tions were analyzed for available cyanide, but no decrease in the strength
of the solution, which remained constantly at 0.3185 per cent, could be
ascertained. "At another period I studied the solubility of zinc in

BXEMPLIFICATlON OF PROCESS — THE PROCESS IN CALIFORNIA. 93

cyanide solution, of which I give the following figures: 0.2634 grs. of
filiform zinc were submerged in 50 cc. cyanide solution of 0.26 per
cent; after seven days of frequent agitation these were reduced to 0.2584
grs., and after fifty-six days to 0.2252 grs., which means that after seven
days 1.98 per cent, and after fifty-six days 14.47 per cent of the zinc
were dissolved. From this observation it follows that the loss of cyanide
in the precipitating boxes, by means of its being taken up by zinc, is
sometimes overestimated." The washes pass through a similar precipi-
tating box. The liquids, when leaving these boxes, go as liquor No. 1
and liquor No. 2, into tanks of the same size as the solution tanks, from
where a pump will deliver them wherever wanted. Liquor No. 1 serves
for making up the new solution for the next charge; liquor No. 2 is used
for washing purposes on the vacuum filter. No liquor ever leaves the
works; the quantity in circulation remains stationary. The bullion
obtained from the zinc boxes is passed, as formerly described, through
a sieve onto the bullion vacuum, which itself is a miniature reproduc-
tion of the vacuum filter (see diagram). It has the following dimen-
sions: Length, 2^ ft.; width, 2 ft.; total depth, 1 ft. 6 in. The per-
forated filter-bottom is fixed 12 in. above the true bottom. The bullion
is very slimy; in fact, it is the more slimy the freer it is from zinc; its
filtration and washing take some time. When the mass is tolerably
dry, it is put into a wooden tub and treated with diluted sulphuric acid.
The heat of the reaction I have always found sufiicient to make the
operation a speedy and satisfactory one; the bullion is then permitted
to settle, the liquid is siphoned off through the bullion filter, and the
solid matter is washed by decantation with water. This washing process
is continued until all soluble salts are removed. The bullion is then par-
tially dried on the filter, and finally dried in a small muffle furnace;
complete drying of the bullion by artificial heat before the acid treatment
is not advisable. The thoroughly dry bullion is pulverized and well
mixed with soda and borax, and melted in a plumbago crucible as
described before. The bullion thus obtained is 946 fine; the slag is
clean, it contains the usual few granules of bullion, but, freed from them,
does not give any assay results. The bullion could be still further
refined, but to no commercial advantage. The steel of the tanks has
not as yet shown any effects from cyanide, nor does it exercise any
influence on the solutions. All apparatus is composed of plates and
sheets riveted together; leakages, if any, can be easily stopped by a
varnish made of asphaltum dissolved in bi-sulphide of carbon. As
mentioned, this plant has been constructed for the treatment of slime
concentrates from the canvas plant; such concentrates contain a vary-
ing percentage of carbonate of lime, in some instances as much as 95
per cent, which, however, does not interfere mechanically or otherwise
with their satisfactory extraction by cyanide. Such conditions would
make chlorination all but impossible, as alluded to before. For agita-
tion the material requires an amount of solution equal to 30 per cent of
its weight, and six hours of time. The described plant is capable of treat-
ing a much larger amount of slimes than are usually produced per day
by the canvas plant; its services are therefore only periodically required.
The average consumption of cyanide, calculated from a large tonnage of
slimes treated, amounted to 4.3 lbs. per ton, costing $2 27; the labor
amounts to $1; the total expenses of treatment by cyanide to $3 50 per
ton. The average extraction amounts to 93.18 per cent of the gold, and

THE CYANIDE PROCESS.

90 per cent of the silver assay-value; as high as 96.57 per cent of the
gold has been extracted in some instances. The extraction of the gold
during the agitation goes on as shown by this table:

Treatment of Slimes by Agitation.

Gold per
Ton.

Extraction—
Per Cent.

Sample before treatment

Sample after 1 hour's agitation
Sample after 2 hours' agitation
Sample after 3 hours' agitation
Sample after 4 hours' agitation
Sample after 5 hours' agitation
Sample after 6 hours' agitation
Sample after 7 hours' agitation
Sample after 8 hours' agitation

$88 00

13 00

11 00

7 00

6 00

5 00

85.23
87.50
92.05
92.05
93.18
94.31
94.31
94.31

Within the first hour 85.23 per cent of the gold are extracted; during
the following five hours the increase of extraction is slow and irregular;
after six hours no further extraction takes place. For experimental pur-
poses I continued agitation up to twelve hours without improving on the
result. The treatment of the slime concentrates by agitation was pre-
ferred on account of its quicker, cheaper, and better results, as compared
with percolation. All Utica concentrates, as in fact all concentrates I
ever had to deal with, contain a small amount of amalgam, part of
which is found on the bottom of the agitator; part of it leaves the works
with the tailings, and is recovered in Hungarian riffles and on amal-
gamated silver plates; part of the mercury goes undoubtedly into the
cyanide solution, and is precipitated with the bullion in the zinc boxes.

Other sulphurets, such as the Frue vanner concentrates of the Utica,
Madison, and Eureka mines, were treated on a more or less extensive
scale by the same plant; results were, however, not very satisfactory on
account of their coarseness. All sulphurets of the Utica Mine are pure
sulphide of iron. The fine canvas-plant concentrates, although less
clean, are as a rule richer in gold; their extraction averaged 93.18 per
cent, whereas the vanner concentrates gave only 81.38 per cent, which,
although reasonably good at the rate of -$4 per ton cost of treatment,
cannot compete with a chlorination treatment, which yields 90 per cent
of a $50 ore at a cost of $6 50. (The large size of the Utica chlorination
works oflers special advantages and permits chlorination at this figure,
which is much lower than the cost anywhere else in California.) A large
number of tests proved that a high percentage of the gold is contained in
the coarser particles of the sulphurets; this will account to some extent
for the comparatively low percentage of cyanide extraction. It would
lead too far to give here the results of the large number of experiments
in reference. The experiments were extended to roasted concentrates
after their reduction to uniform size, which gave on a small scale excellent
results (98.09 per cent extraction). I am indebted to Colonel Hay-
ward, Mr. Charles D. Lane, and Mr. James Cross, of the Utica Mine,
for their permission to publish the diagrams and the described results
of the cyanide works which I erected for them. The cost of the plant
is divided as follows:

Grading and foundations - - $200 00

Biiilding 300 00

Shafting, belting, and puttmg into place 135 00

Agitator 260 00

Vacuum filter --- - -- 165 00

EXEMPLIFICATION OF PROCESS — THE PROCESS IN MEXICO, ETC. 95

Three tanks - $160 00

Two zinc boxes 260 0<J

Two steel tanks ^5 00

One vacuum pump 235 00

One liquid pump 130 00

Pipes, stopcocks, faucets, etc. 70 00

Total $2,000 00

The Standard Consolidated Mining Company, Bodie, California, started
a 100-ton cyanide plant (50-ton vats) on September 17th for the treat-
ment of tailings.

The amount of ores, fine concentrates, and tailings suitable for
cyanide treatment is considerable in this State. There is no doubt that
a great amount of gold is now being lost with the slimes in most mills
here, as elsewhere, and in many instances dry-crushing of the ore and
direct cyanide treatment would vastly increase the returns. Coarse
gold, if present, can be saved by amalgamation at some later stage of
the manipulation.

Generally speaking, the number of commercial successes of the process
in the United States is limited, although the number of tests and trials
on a smaller or larger scale have been very numerous. The amount of
ores suitable for the treatment is large, and the process is becoming
more and more an established and acknowledged fact with the mining
public. The miners of this country have long been looking for a process
for the treatment of low-grade sulphurets which is cheaper in its appli-
cation than chlorination. Under certain conditions the cyanide process
meets the requirements, and will be found particularly valuable in
remote places to which the freight expenses are high. The weight of
chemicals used in chlorination amounts to about 5 per cent of the ore
weight, but only to about 1 per cent in the case of cyanide treatment.
By chlorination one ton of chemicals will treat about twenty tons of
ore, whereas by cyanide one ton will treat 100 tons; moreover, the
cyanide process does not require a special treatment of the ore for the
extraction of the silver. No statistics in reference to the gold produced
in the United States of America by the cyanide process could be obtained
by the author.

D. Mexico, Etc.

A MacArthur-Forrest company is introducing the process in that old
mining country. No information, however, could be obtained from
that company in reference to their results. In other parts of the
world, attempts have been made, chiefly by the owners of the Mac-
Arthur-Forrest patents, to introduce the cyanide process. Ores from
the republic of Colombia are reported as having been treated with
success, and the introduction of the process into that country is now
intended. Negotiations for the introduction of the process into the
Straits Settlements, Borneo, the mining States of South America, and
that great gold-producing country, Russia, are now pending.

I have in this paper been following the cyanide process in its workings
and results through the chief places of its application. The process, like
most metallurgical processes, has its weak points, which by continued
investigations may be strengthened; its strong points are evident from
the description of its successful application. Whatever may be the merit
of the controversy on the subject of patent-rights in connection with this

96 THE CYANIDE PROCESS.

process, there is no doubt that Messrs. MacArthur and Forrest deserve
the credit of having first, on a large scale, practically and successfully
applied the cyanide process for working ores.

SUMMARY AND CONCLUSIONS.

Generally speaking, the cyanide process is better suited for the treat-
ment of gold ores than of silver ores, one of the reasons of which may be
found in the great variety of compounds in which the silver occurs, and
a number of these offer difiiculties in treatment. The required long
contact of cyanide, connected with the large consumption of reagent,
prevents the treatment of silver ores in some instances from being a
commercial success, even when chemically a high extraction is obtained.
In reference to the general characteristics of ores which can be success-
fully treated, it must be said that no definite specification can be given.
The question, Is an ore suited for cyanide treatment? can only be decided
experimentally. Preliminary but exhaustive experiments on a limited
scale should precede all operations on a large scale. Many of the prob-
lems of the process are of a chemical nature; many of its difficulties are,
however, of a mechanical character, and experience and judgment must
guide in the selection of the plant to make the venture a financial suc-
cess. One of the great mechanical difficulties has been, and is still, the
treatment of the slimes, by which is meant the very finest parts and the
clayey portion of ores and tailings. The final solution of the difficulty
in their treatment will probably be found in dry-crushing the ore and
direct treatment of the crushed material with cyanide. In cases where
coarse gold is present, the amalgamation of such may be introduced at
some later periods of the manipulation. Practical experience with the
process extends over only a few years. It has been found to be well
adapted for free-milling ores with finely divided gold, particularly
so-called float gold, and has given great satisfaction with some pyritic
ores. Even complex ores containing tellurides have been treated to
advantage. The process has fourtd its most extensive application on
the Transvaal gold fields; although the average extraction is not
high, it answers there better than any other process attempted for
working the tailings. In other parts of the gold-producing world, its
application is gaining way by degrees. Like all metallurgical pro-
cesses, its success depends on the character of the ore and local cir-
cumstances, and failures had to be recorded where these were not
sufiiciently considered. It is certain that our knowledge is as yet
incomplete, and there is still a large amount of ground for the metallur-
gist and chemist to explore. We have yet particularly to learn how
to extend the application of the process to more common use. A com-
parison of the cyanide process with other processes is a futile task; the
great merit of the treatment is that it comes to fill a want long felt — that
of treating low-grade ores and tailings in a simple and inexpensive way.
It is here that the process antagonizes no other methods, and simply
takes its place in gold metallurgy as a new and powerful means to con-
quer nature. Wherever the process gives satisfactory results, it offers
great advantages: it does not require roasting furnaces; ores containing
lead, zinc, or earthy carbonates, which cannot be worked to a profit by
chlorination, may be easily and profitably treated by it; as it does not

SUMMARY AND CONCLUSIONS. 97

require smelters, coal, and fluxes, it may be successfully used in remote
situations, where smelting is absolutely impossible. One of its great
advantages is, it does not require extra treatment for silver, invariably
associated with gold in ore. I have generally spoken about gold only
in this paper. The remarks referring to it and to its extraction apply
with equal force to the silver associated with it. A well-constructed
plant and efficient chemical and metallurgical supervision are, however,
conditions always necessary to make its application a commercial suc-
cess. The process is only in its infancy; many of the various and
complex problems it has given rise to — such as the reduction in the
consumption of cyanide and its regeneration — are still open questions.
Its possibilities are great; chemical and mechanical improvements will
enlarge the range of its application and usefulness. If it has not proved
itself to be the metallurgical panacea that some enthusiasts expected,
it has certainly during the four years of its technical application devel-
oped into a process of enormous economical importance, and one which
justly may be considered a most valuable addition to gold metallurgy.

7cp

APPENDIX.

UNITED STATES PATENT OFFICE.

JULIO H. REA, OF Syracuse, New York.
IMPROVED MODE OF TREATING AURIFEROUS AND ARGENTIFEROUS ORES,

Specification forming part of Letters Patent No. 61,866, dated February 5, 1867.

To all whom it may concern:

Be it known that I, Julio H. Rae, of Syracuse, in the county of Onondaga and State of
New York, have invented a new and useful Improvement in Treating Auriferous and
Argentiferous Ores; and I do hereby declare that the following is a full, clear, and exact
description thereof, which will enable those skilled in the art to make and use the same,
reference being had to the accompanying drawing, forming part of this specification, in
which —

Figure 1 represents a transverse vertical central section of thfi apparatus which may be
used in carrying out this invention.

Figure 2 is a plan or top view of the same.

Similar letters of reference in both views indicate corresponding parts.

This invention consists in treating auriferous and argentiferous ores with a current of
electricity or galvanism for the purpose of separating the precious metals from the
gangue. In connection with the electric current suitable liquids or chemical prepara-
tions, such, for instance, as cyanide of potassium, are used, in such a manner that by the
combined action of the electricity and of the chemicals, the metal contained in the ore
is first reduced to a state of solution and afterwards collected and deposited in a pure
state, and that the precious metals can be extracted from the disintegrated rock or ore
at a very small expense and with little trouble or loss of time.

In carrying out this process a jar. A, may be used such as shown in the drawing.
This jar is made of glass or other suitable material (the size depending upon the elec-
tric battery to be used in connection therewith), and into said jar is placed the pulver-
ized rock, filling the same half full or more. On the rock is poured the proper chemical
preparation in a fluid state, such, for instance, as cyanide of potassium. Tlirough the cen-
ter of the jar passes a vertical shaft C, whicn terminates upon a metal plate, a, by pref-
erence of platma, which rests on the bottom of the jar, and to said shaft is attached a
cage, B, of platina wire or other suitable material. This cage is made in the form of a
truncated cone, its base extending close to the inner circumference of the shaft, or it may
be made in any other suitable form or shape, a series of spirals, for instance, which will
produce the same effect. On the shaft G is mounted a pulley, E, which may be con-
nected with any suitable mechanism for the purpose of imparting a rotary motion to said
shaft and the cage connected therewith, so that the contents of the jar will be agitated
and each particle of the pulverized rock shall come in contact with the metal cage B
and plate a. The shaft C is connected by a wire, 6, with one, say the positive pole of the
battery, thus converting the shaft, the cage, and the plate a into an electrode, and the
other or negative pole of the battery connects by a wire, c, with a thin slip or coil, d, of
copper or other suitable material, forming a base on wliich the precious metals are
deposited. By the action of the electric current the action of the chemicals on the met-
als contained in the rock is materially faciliated and a perfect solution thereof is
effected, and from this solution the precious metals are precipitated upon the base d,
whence the same can be easily collected. By this process gold or silver can be extracted
from rock in an absolutely pure state and with very little expense.

What 1 claim as new, and desire to secure by Letters Patent, is —

1. The within-described process of treating auriferous or argentiferous rock by expos-
ing the same to the combined action of a current of electricity and of suitable solvents
or chemicals, substantially such as herein specified, or any others which will produce
the same effect.

2. Separating gold or silver from the rocks containing the same by the action or aid
of electricity, substantially as described.

3. Using the agitator B as an electrode substantially as and for the purpose set forth.

JULIO H. RAE,
Witnesses:
W. Haxjff.
Geo. F. Southern.

102

THE CYANIDE PROCESS.

J. H. RAL
Treating Ores.

No. 61.866.

Patented Feb. 5, 1867.

..^Zf^ -^

Jhoy^riti?/*

PATENT-SPECIFICATIONS. ' 103

UNITED STATES PATENT OFFICE.

THOMAS C. CLARK, of Oakland, assignor to JAMES STRATTON, of samk
PLACB, AND RICHARD E. COADY, of Alameda, California, one fourth to each.

EXTRACTING PRECIOUS METALS FROM ORES.

Specification forming part of Letters Patent No. 229,586, dated July 6, 1880.
(Application filed December 27, 1879.)

To all whom it may concern :

Be it known that I, Thomas C. Clark, of Oakland, county of Alameda, and State of
California, have invented an Improvement in Extracting Precious Metals from ores ;
and I hereby declare the following to be a full, clear, and exact description thereof.

The object of my invention is to perform the disintegration and desulphurization of
ores so as to bring the said ore into proper condition for easy pulverization and the
precious metals contained therein into a suitable form for amalgamation by freeing
them from the union and influence of baser metals. In order to accomplish this object
the ore is crushed into pieces about the size of ordinary Indian corn. That portion
containing sulphurets generally becomes finer, since it is more friable. The object of
crushing it to this size is to prevent loss of gold and to facilitate washing operations.

The ore, after being crushed as described, is placed in an ordinary roasting-furnace.
After being roasted for a suitable length of time the heat is raised, so the sulphur will
burn freely, after which the heat is let down again, a free supply of oxygen being fur-
nished during the whole process of roasting.

After the ore has become dead and lies like sand in the furnace, and no more scintilla-
tion is apparent, it is heated up to a good red heat, but not made too hot.

In a suitable receptacle beside the furnace I form a cold bath, into which the ore is
drawn while in its heated condition fresh from the furnace. This bath is formed of a
solution of salt, prussiate of potash, and caustic soda or caustic potash.

For one ton of gold ore containing five per cent or less of sulphurets, I form my bath
in about the following proportions: I take about thirty gallons of cold water, to which
common salt is added until a saturated solution is formed. I then dissolve one pound of
prussiate of potash in water and pour it into the solution, and also dissolve one pound
of caustic soda in water and add it to the solution. The bath then contains chloride of
sodium, prussiate of potash, and caustic soda. For the latter caustic potash may be
substituted with a like result.

The red-hot ore being drawn into the cold solution described, a complete desulphur-
ization is effected, as well as a disintegration.

Where there is a higher percentage of sulphur in the ore, additional quantities of the
prussiate of potash and caustic soda are added, the proportions of the solution being
thus altered to suit the requirements of the class of ore under treatment. The propor-
tions may also be modified for ore of different character.

I am aware that ore has frequently been roasted and dumped while red hot into cold
water or into cold solutions, and I therefore do not claim, broadly, such process ; but

What I do claim as new, and desire to secure by Letters Patent, is —

The process of disintegrating and desulphurizing ores and freeing the precious metals
therein contained, consisting m first roasting the ore to a red heat, and while in that
condition placing it in a cold bath composed of a solution of salt, prussiate of potash,
and caustic soda or caustic potash, in about the proportions named, substantially as
herein described.

In witness whereof I have hereunto set my hand.

THOMAS C. CLARK.

Witnesses :

Chas. G. Yalb. I

S. H. NotTBSE.

104 THE CYANIDE PROCESS.

UNITED STATES PATENT OFFICE.

HIRAM W. FAUCETT, of St. Louis, Missoubi.
PROCESS OF TREATING ORE.

Specification forming part of Letters Patent No. 236,424, dated Janiiary 11, 1881.

(Application filed July 13, 1880. No specimens.)

To all whom it may concern:

Be it known that I, Hiram W. Faucett, a citizen of the United States, residing at St.
Louis, in the county of St. Louis and State of Missouri, have invented new and useful
Improvements in Process of Treating Ores, of which the following is a specification.

The object of my invention is to treat all refractory ores containing gold and silver
for the purpose of separating such metals from the ore.

It is well known that the chemical nature of all refractory ores is more or less of a
silicious character, and by desulphurizing or roasting such ores they are rendered porous.
Taking advantage of this fact, I subject the silicious ore to a proper chemical bath
under pressure, which effectually disintegrates the ore by decomposing or destroying
the silica therein, which silica is the chemical agent in the ore which holds or locks the
ore together in a compact mass.

To this end my invention consists, broadly, in subjecting hot crushed ores to the
action of disintegrating chemicals in solution while under pressure, the pressure being
effected by the steam generated by the contact of the hot ore and the chemical solution
in a closed vessel.

In carrying out this process I take the ore, crushed as ordinarily for stamp-mill or
smelter, and heat the same in any suitable furnace to a sufiicient degree and for a proper
time to desulphurize it. I then draw the ore, while at red heat, into an iron retort of
proper strength to withstand the proposed pressure, and provided with a steam-tight
door, and into this retort, through a suitable aperture, after closing the door, I introduce
the chemicals in a state of solution, the steam generated creating such pressure within
the retort that the chemicals are forced into the silica or rock of the ore, thoroughly
disintegrating the same and freeing the metals therefrom, so that the latter are ren-
dered susceptible of ready amalgamation. The process will be facilitated by agitating
the retort.

I use different chemicals, according to the different kinds of ore to be treated, and the
quantity required depends upon the quantity of silica or other refractory substances to
be decomposed to effect a thorough disintegration of the ore.

For the treatment of most of the refractory ores I use chloride of sodium as a base,
and in connection therewith nitrate of potash, cyanide of sodium, and about equal
parts of sulphate of protoxide of iron and sulphate of copper, the proportions being
about as follows, viz.: chloride of sodium, from thirty to forty pounds to the ton ;
nitrate of potassium, from one to two pounds to the ton ; cyanide of sodium, from two
to four pounds to the ton ; sulphate of protoxide of iron, from one to two pounds to the
ton ; sulphate of copper, from one to two pounds to the ton. These chemicals are to be
dissolved in boiling or hot water of sufficient quantity to cover the ore in the retort. If
the ores to be treated are unusually hard or refractory, I add to the above one to two
pounds of hydrofluoric acid, or one to two pounds of fluoride of potassium or fluoride
of sodium, according to the character of the ore. After the ore has been agitated in the
retort a proper time — say from ten to fifteen minutes — under from fifty to one hundred
pounds pressure to the square inch, it may be removed while hot to the pulverizer, then
passed through any convenient and desired amalgamating process.

It should be here stated that while the ore is in the chemical bath, the latter acts to
disintegrate the ore by decomposing or destroying the silica therein, and the ore is
thoroughly impregnated with the chemicals, thereby effectually disengaging the parti-
cles of metal from the silica, which, if not disengaged, will not amalgamate with the
quicksilver in the amalgamating-machines.

To facilitate the carrying out of the process, I prefer to use a cylindrical retort
mounted on axial trunnions, in order that it may be rotated for the purpose of agitat-
ing its contents. The door of the retort should be in its side, and at each end there
should be a projecting coupling-nipple provided with a cut-off cock, to which may be
connected pipes, one of which leads from the top, and the other from the bottom, of an
elevated steam-tight receiver provided with safetj'-valve, both pipes being provided with
suitable cocks. The chemical solution is then placed in the elevated cylinder, and, after
the retort has received its charge of heated ore and been closed, the pipes from the
receiver are connected to the coupling-nipples and the cocks all opened. The solution
will flow from the bottom of the tank to the retort, and the steam generated in the latter
will flow to the top of the cylinder, creating a pressure therein which will force the solu-
tion rapidly into tne retort. After the pressure has decreased, the cocks may then be

PATENT-SPECIFICATIONS. 105

closed, the pipes disconnected from the retort, and the latter rotated for the purpose of
agitating its contents.

The apparatus thus partially described will form the subject of a separate application
for Letters Patent.

I do not confine myself to the chemicals or quantities thereof herein enumerated, as
they may be varied as required by the character of the ores to be treated.

I am aware that crushed ores have been subjected to the action of chlorine gas under
pressure, and that unroasted pulverized ores have been treated with chemical solutions
in a closed vessel under pressure created by the injection of steam, and also that hot
roasted ores have been treated by placing cold chemical solutions in contact therewith
in the open air, or not under pressure ; and I do not claim any of such modes of treat-
ment.

What I claim is —

1. The process herein described for separating metals from ores, the same consisting
in subjecting hot crushed ores to the action of disintegrating chemicals in solution under
pressure, the pressure being effected by the steam generated by the contact of the hot
ores with the chemical solution in a closed vessel, substantially as specified.

2. The process herein described for treating refractory ores for disengaging the precious
metals therefrom, the same consisting in subjecting hot crushed ores to the action of a
solution of chloride of sodium, nitrate of potash, cyanide of sodium, sulphate of pro-
toxide of iron, and sulphate of copper, under pressure, with or without admixture of
hydrofluoric acid, fluoride of potassium, or fluoride of sodium, the pressure being effected
by the steam generated by the contact of the solution with the hot ore, substantially as
set forth.

In testimony whereof I have hereunto set my hand in the presence of two subscrib-
ing witnesses.

HIRAM W. FAUCETT.
"Witnesses :

RoBT. Harbison,
Jno. C. Orrick.

106 THE CYANIDE PROCESS.

UNITED STATES PATENT OFFICE.

JOHN F. SANDERS, of Ogden, Utah Tbrritoey.
COMPOSITION FOR DISSOLVING THE COATING OF GOLD IN ORE.

Specification forming part of Letters Patent No. 244,080, dated July 12, 1881.
(Application filed April 16, 1881. No specimens.)

To all whom it may concern.

Be it known that I, John F. Sanders, of Ogden, in the county of Weber and Terri-
tory of Utah, have invented an improved Composition for Dissolving the Coating of
Gold in Ore, of which the following is a specification :

The coatings that envelop gold in the ore, and that consist usually of various metallic
oxides and of silver, have thus far been difficult to remove, except under the influence
of extreme heat, which it is not possible at all places to apply, or by the waste of much
valuable time. I have found that a mixture of cyanide of potassium and phosphoric
acid, in about the proportions hereinafter mentioned, constitutes a powerful solvent for
these coatings of gold ore. .

I use in my mixture about sixteen parts of cyanide of potassium to one part glacial
phosphoric acid. These two ingredients I mix shortly before the mixture is to be used.
The mixture I place into the vessel that contains the covered ore. This vessel preferably
is a rotating barrel made of iron or other proper material, and the composition above
named is added with sufficient water to form a thick pulp with the raw gravel. The
proportions of my improved mixture to the ore will vary, of course, with the varying
thickness of covering of the gold. They will, however, be readily ascertained by testing
with samples of the ore to be treated. The barrel is rotated or agitated in suitable
manner for from fifteen to sixty minutes, as may be required. After agitation the mixt-
ure above mentioned will be found, on investigation, to have dissolved the oxides and
the sulphurous coatings of the ore, and the agitation of the barrel or vessel removes the
dissolved impurities, leaving the gold free and exposed, and permitting it to be amal-
gamated by the addition of quicksilver, in the usual manner.

The amalgam may be separated from the impurities which have joined with the
improved mixture in the manner in which amalgams are usually separated from
impurities.

I am aware that cyanides have already been used in the extraction of gold ; also, that
gold-bearing ores have been disintegrated in the presence of heat by various chemicals.
This I do not claim. By using phosphoric acid in the presence of cyanide of potassium
1 am enabled to dissolve the impurities in a raw state and with great rapidity.

I claim —

The composition of cyanide of potassium and phosphoric acid, in about the pro-
portions mentioned, for the purpose of dissolving the impure coatings of gold, substan-
tially as specified. JOHN F. SANDERS.

"Witnesses :

Willy G. E. Schultz,
William H. C. Smith.

PATENT-SPECIFICATIONS. 107

UNITED STATES PATENT OFFICE.

JEROME "W. SIMPSON, of Newark. New Jerskt.
PROCESS OF EXTRACTING GOLD, SILVER, AND COPPER FROM THEIR ORES.

Specification forming part of Letters Patent No. 323,222, dated July 28, 1885.
(Application filed October 20, 1884. No specimens.)

To all whom it may concern :

Be it known that I, Jerome W. Simpson, a citizen of the United States, residing at
Newark, in the county of Essex, and State of New Jersey, have invented certain new
and useful improvements in processes of extracting gold, silver, and copper from their
ores; and I do hereby declare the following to be a full, clear, and exact description of
the invention, such as will enable others skilled in the art to which it appertains to
make and use the same.

The object of this invention is to extract certain metals from their ores more effect-
ually and at a reduced cost; and it consists in the processes hereinafter set forth, and
finally embodied in the clauses of the claims.

To carry my invention into effect, I first grind or crush the ore containing the metal
to be extracted to a powder of more or less fineness. This powder is then treated with
certain salts in solution adapted to combine chemically witn the metal in said ore and
form therewith a soluble salt. After thorough agitation to mix the solution with the
ore, the mixture is allowed to stand until the solid matter is settled and the solution
has become clear. I then suspend a piece or plate of zinc therein, which causes the
metal dissolved in the salt solution to be precipitated thereon, from which it can be
removed by scraping or by dissolving the zinc in sulphuric or hydrochloric acid. The
precipitated metal may then be melted into a button.

The salt solution I use for dissolving the metal from the ore is composed of one pound
of cyanide of potassium, one ounce carbonate of ammonia, one half ounce chloride of
sodium, and sixteen quarts of water, or other quantities in about the same proportions.

This solution is particularly adapted for ores containing gold, silver, and copper in
the form of sulphurets.

For an ore containing gold and copper only I use cj'^anide of potassium and carbonate
of ammonia about in the proportions named.

For ores rich in silver I employ a proportionately larger quantity of chloride of
sodium.

I am aware that cyanide of potassium, when used in connection with an electric
current, has been used for dissolving metal, and also that zinc has been employed as a
precipitant, and the use of these I do not wish to be understood as claiming, broadly.

I am also aware that carbonate of ammonia has been employed for dissolving such
metals as are soluble in a solution thereof, and the use of this I do not claim; but

What I claim as new is —

1. The process of separating gold and silver from their ores, which consists in subject-
ing the ore to the action of a solution of cyanide of potassium and carbonate of ammonia,
and subsequently precipitating the dissolved metal, substantially as set forth

2. The process of separating metals from their ores, to wit: subjecting the ore to the
action of a solution of cyanide of potassium, carbonate of ammonia, and chloride o
sodium, and subsequently precipitating the dissolved metals.

In testimony that I claim the foregoing, I have hereunto set my hand this 15th day
of October, 1884.

JEROME W. SIMPSON.
"Witnesses:

Oliver Drake.
Chablbb H. Pbi<i<.

108 THE CYANIDE PROCESS.

[Fifth Edition.]

No. 14,174. A. D. 1887.

Date of application, 19th Oct., 1887; complete specification left, 26th July, 1888 — Accepted

10th Aug., 1888.

PROVISIONAL SPECIFICATION.

IMPROVEMENTS IN OBTAINING GOLD AND SILVER FROM ORES AND OTHER

COMPOUNDS.

We, John Stewart MacArthur, Analytical Chemist, of 15 Princes Street, PoUokshields,
in the County of Renfrew, North Britain, Robert Wardrop Forrest, M.D., and William
Forrest, M.B., both of 319 Crown Street, Glasgow, in the County of Lanark, North Britain,
do hereby declare the nature of this invention to be as follows:

This invention has principally for its object the obtaining of gold from its ores or
other compounds, but it is also applicable for obtaining silver from its ores or com-
pounds ; and it comprises an improved process, which, whilst applicable to ores or com-
pounds generally, is effectual with ores and compounds from which gold or silver have
hitherto not been easily obtainable.

In carrying out the invention the ore or other compound in a powdered state is treated
with a solution containing cyanogen or a cyanide (such as the cyanides of potassium,
sodium, or ammonium), or other substance or compound containing or yielding cyanogen,
till all or nearly all of the gold and the silver are dissolved; the operation being conducted
in a wooden vessel or a vessel made of or lined with a material not acted on to any consider-
able extent by the solution or substances contained therein. The solution is then drawn
off and the metal or metals are recovered by any suitable process, and the cyanogen,
cyanide, or substance containing or yielding cyanogen may be regenerated. The cyano-
gen or substance containing or yielding cyanogen may be used as such, or such materials
may be taken as will by mutual action form cyanogen or substances containing or yield-
ing same.

Under certain circumstances it may be found desirable to conduct the operation
under pressure, in which case a closed vessel must be employed, and in any case, if
found advisable, such operation may be carried on under varying conditions of temper-
Dated this 19th day of October, 1887.

ALLISON BROS.,
Agents for the Applicants.

COMPLETE SPECIFICATION.
Improvements in Obtaining Gold and Silver from Ores and Other Compounds.

This invention has principally for its object the obtaining of gold from its ores or
other compounds, but it is also applicable for obtaining silver from its ores or com-
pounds; and it comprises an improved process, which, whilst applicable to ores or com-
pounds generally, is effectual with ores and compounds from which gold or silver have
hitherto not been easily obtainable because of the presence of various other metals or
their compounds, or because of the physical or chemical condition of the gold or silver
in the ores or compounds.

In carrying out the invention the ore or other compound in a powdered state is treated
with a solution containing cyanogen or cyanide (such as cyanide of potassium, or of
sodium, or of calcium), or other substance or compound containing or yielding cyano-
gen. In practice we find the best results are obtained with a very dilute solution, or a
solution containing or yielding an extremely small quantity of cyanogen or a cyanide,
such dilute solution having a selective action such as to dissolve the gold or silver in
preference to the baser metals. In preparing the solution we proportion the cyanogen
to the quantity of gold or silver or gold and silver estimated by assay or otherwise to be
in the ore or compound under treatment, the quantity of a cyanide or cyanogen-yielding
substance or compound being reckoned according to its cyanogen. We mix the pow-
dered ore, or compound, with the solution in a vessel made of or lined with wood or any
other convenient material not appreciably acted on by the solution. The process is

PATENT-SPECIFICATIONS. 109

expedited by stirring the mixture of ore and solution intermittently, or continuously
for which purpose any convenient mechanical agitator may be fitted to the vessel
When all or nearly all the gold or silver is dissolved the solution is drawn off from the
ore or undissolved residue, and is treated in any suitable known way, as for example
with zinc, for recovering the gold and silver. The residuary cyanogen compounds may
also be treated by known means for regeneration or reconversion into a condition in
which they can be used for treating fresh charges of ores or compounds.

Any cyanide soluble in water may be used, such as ammonium, barium, calcium,
potassium, or sodium cyanide, or a mixture of any two or more of them, or any mixture
of materials may be taken which will, by mutual action, form cyanogen, or a substance
or substances containing or yielding cyanogen.

In dealing with ores or compounds containing, per ton, twenty ounces or less of gold
or silver, or gold and silver, we generally use a (Quantity of cyanide, the cyanogen of
which is equal in weight to from one to four parts in every thousand parts of the ore or
compound, and we dissolve the cyanide in a quantity of water of about half the weight
of the ore. In the case of richer ores or compounds, whilst increasing the quantity of
cyanide to suit the greater quantitj'^ of gold or silver, we also increase the quantity of
water so as to keep the solution dilute. In using free cyanogen, the cyanogen obtained
as a gas in any well known way is led into water to form the solution to be used in our
process; or any suitable known mode of setting cyanogen free in solution may be
employed.

In some circumstances it may be found desirable to conduct the operation under
pressure in a closed vessel ; and a higher than the ordinary temperature may be used if
found desirable.

Having now particularly described and ascertained the nature of our said invention
and in what manner the same is to be performed, we declare that what we claim is —

1. The jjrocess of obtaining gold and silver from ores and other compounds, consisting
in dissolving them out by treating the powdered ore or compound with a solution con-
taining cyanogen or a cyanide or cyanogen-yielding substance, substantially as herein-
before described.

2. The process of obtaining gold and silver from ores and other compounds, consisting
in dissolving them out by treating the powdered ore or compound with a dilute solution
containing a quantity of cyanogen or a cyanide or cyanogen-yielding substance, the
cyanogen of which is proportioned to the gold or silver or gold and silver, substantially
as hereinbefore described.

Dated this 16th day of July, 1888.

ALLISON BROS.,
Agents for the Applicants.

110 THE CYANIDE PROCESS.

UNITED STATES PATENT OFFICE.

JOHN STEWART MacARTHUR, of Pollokshiblds, County of Renfrew, and ROB-
ERT W. FORREST AND WILLIAM FORREST, of Glasgow, County of Lanark
Scotland.

PROCESS OF OBTAINING GOLD AND SILVER FROM ORES.

Specification forming part of Letters Patent No. 403,202, dated May 14, 1880.

(Application filed November 9, 1887. Serial No. 254,699. (No specimens.) Patented in England,
October 19, 1887, No. 14,174; in Cape of Good Hope, January 7, 1888, No. 6-101; in Victoria, Jan-
uary 19, 1888, No. 5,572; in New South Wales, January 21, 188^1, No. 453: in South Australia, Jan-
uary 2,'?, 1888, No. 948; in Tasmania, January 24, 1888, No. 529; in New Zealand, February 1, 1888,
No. 2,775; in Canada, February 6, 1888, No. 28,471; in France, April 6, 1888, No. 189,808; In Bel-
glum, July 24, 1888, No. 82,673; in Brazil, August 23, 1888, No. 619; in Portugal, August 30, 1888,
No. 1,272; in Italy, September 30, 1888, No. 23,852, and in Spain, October 2, 1888, No. 8,538.)

To all whom it may concern:

Be it known that we, John Stewart MacArthur, a subject of the Queen of Great Brit-
ain, residing at 15 Princes Street, Pollokshields, in the County of Renfrew, Scotland,
and Robert Wardrop Forrest and William Forrest, both subjects of the Queen of Great
Britain, residing at 319 Crown Street, Glasgow, in the County of Lanark, Scotland, have
invented certain new and useful Improvements in Processes of Obtaining Gold and Sil-
ver from Ores (for which we have obtained patents in the following countries: Great
Britain, No. 14,174, dated October 19, 1887; Cape of Good Hope, No. 6-101, dated January 7,
1888; Victoria, No. 5,572, dated January 19, 1888; New South Wales, No. 453, dated Jan-
uary 2i, 1888; South Australia, No. 948, dated January 23, 1888; Tasmania, No. 529, dated
January 24, 1888; New Zealand, No. 2,775, dated February 1, 1888; Canada, No. 28,471,
dated February 6, 1888; France, No. 189,808, dated April 6, 1888; Belgium, No. 82,673, dated
July 24, 1888; Brazil, No. 619, dated August 23, 1888; Portugal, No. 1,272, dated August 30,
1888; Italy, No. 23,852, dated September 30, 1888, and Spam, No. 8,538, dated October 2,
1888) ; and we do hereby declare that the following is a full, clear, and exact description
of the invention, which will enable others skilled in the art to which it appertains to
make and use the same.

This invention has principally for its object the obtaining of gold from ores; but it is
also applicable for obtaining silver from ores containing it, wnether with or without
gold, and it comprises an improved process which, while applicable to auriferous and
argentiferous ores generally, is advantageously and economically effective with refrac-
tory ores, or ores from which gold and silver have not been satisfactorily or profitably
obtainable by the amalgamating or other processes hitherto employed, such as ores con-
taining sulphides, arsenides, tellurides, and compounds of base metals generally, and
ores from which the gold has not been easily or completely separable on account of its
existing in the ores in a state of extremely fine division.

The invention consists in subjecting the auriferous or argentiferous ores to the action
of a solution containing a small quantity of a cyanide, as hereinafter set forth, without
any other chemically-active agent, such quantity of cyanide being reckoned according
to its cyanogen, and the cyanogen being proportioned to the quantity of gold or silver,
or gold and silver, estimated by assay or otherwise to be in the ores under treatment.
By treating the ores with the dilute and simple solution of a cyanide the gold or silver is,
or the gold and silver are, obtained in solution, while any base metals in the ores are left
undissolved, except to a practically inappreciable extent, whereas when a cyanide is
used in combination with an electric current or in conjunction with another chemically-
active agent— such as carbonate of ammonium, or chloride of sodium, or phosphoric
acid— or when the solution contains too much cyanide, not only is there a greater expendi-
ture of chemicals in the first instance, but the base metals are dissolved to a large extent
along with the gold or silver, and for their subsequent separation involve extra expense,
which is saved by our process.

In practically carrying out our invention we take the ore in a powdered state and mix
with it the solution of a cyanide in a vessel made of or lined with any material not
appreciably acted on by the solution. We employ a vessel made of or lined with wood;
but it may be made of or lined with any ordinary inert material — such as stone, brick,
slate, rubber, gutta-peiicha, cement, glass, earthenware, iron (plain, tinned, or enameled),
or lead. The process is expedited by stirring or triturating the mixture of ore and solu-
tion intermittently or continuously, for which purpose any convenient mechanical
agitator may be fitted to the vessel. A pan-mill with edge runners or other known trit-
urating device may be advantageously used. The solution is allowed to act on the ore
until the gold or silver is all or nearly all dissolved, and the solution is then drawn off
from the ore or undissolved residue.

Any cyanide soluble in water may be used — such as ammonium, barium, calcium,,
potassium, or sodium cyanide, or a mixture of any two or more of them. We regulate
the quantity of cyanide so that its cyanogen will be in proportion to the quantity of

PATENT-SPECIFICATIONS. Ill

gold or silver or gold and silver in the charge of ore; but in all cases we dissolve it in
suflBcient water to keep the solution extremely dilute, because it is when the solution is
dilute that it has a selective action such as to dissolve the gold or silver in preference to
the baser metals.

In dealing with ores containing per ton twenty ounces or less of gold or silver or gold
and silver, we find it most advantageous to use a quantity of cyanide the cyanogen of
which is equal in weight to from one to four parts for every thousand parts of the
ore, and we dissolve the cyanide in a quantity of water of about half the weight of the
ore. We generally use a solution containing two parts of cyanogen for every thousand
parts of the ore. In the case of richer ores, while increasing the quantity of cyanide to
suit the greater quantity of gold or silver, we also increase the quantity of water so as
to keep the solution dilute. In other words, the cyanide solution should contain from
two to eight parts, by weight, of cyanogen to one thousand parts of water, and the
quantity of the solution used should be determined by the ricnness of the ore. After
the solution has been decanted or separated from the undissolved residues the gold and
silver may be obtained from it in any convenient known way — such as evaporating the
solution to dryness and fusing the resulting saline residue, or by treating the solution
with sodium amalgam.

Having fully described our invention, what we desire to claim and secure by Letters
Patent is —

The process of separating precious metal from ore containing base metal, which process
consists in subjecting the powdered ore to the action of a cyanide solution containing
cyanogen in the proportion not exceeding eight parts of cyanogen to one thousand parts
of water.

JOHN STEWART MacARTHUR.
ROBT. W. FORREST.
W. FORREST.
Witnesses:

robt. dunlop,
William Brunton,

Law clerks, both of 160 West George Street, Glasgow.

112 THE CYANIDE PROCESS.

UNITED STATES PATENT OFFICE.

JOHN STEWART MacARTHUR, of Pollokshields, County of Rknfekw, Scotland.

METALLURGICAL FILTER.

Specification forming part of Letters Patent No. 418,138, dated December 24, 1889.

(Application filed November 13, 1889. Serial No. 330,195. No model.)

To all whom it may concern :

Be it known that I, Jotin Stewart MacArthur, a subject of the Queen of Great Britain,
residing at Pollokshields, in the county of Renfrew, Scotland, have invented a new and
useful Improvement in Metallurgical Filters, of which the following is a specification:

This invention relates to a filter for precipitating and separating precious metals from
solutions containing them — such, for instance, as chlorides, bromides, theosulphates
(sometimes called "hyposulphites"), or sulphates obtained in the well-known Plattner,
von Patera, Russell, Ziervogel, and Augustine extracting processes.

The object of the invention is to provide a filter having a large active surface for the
metals in solution.

In the accompanying drawings. Figure 1 is a sectional elevation of a series of these
improved filters. Fig. 2 is a longitudinal vertical section of a filtering apparatus com-
prising two of these improved filters constructed in modified form. Fig. 3 represents a
zinc filiform sponge, constituting the principal feature of this improved filter, the fila-
ments of the sponge being represented on an enlarged scale.

Similar numerals of reference indicate corresponding parts in the different figures.

This improved filter comprises a containing-vessel 10 and a zinc sponge 11, disposed
therein. The zinc sponge is preferably supported on a perforated false oottom 12, dis-
posed within said vessel near the bottom proper thereof. The vessel is provided with an
inlet-tube 13 and an outlet-tube 14, the inlet-tube being preferably disposed near the
bottom of the vessel and the outlet-tube near the top thereof, each of said tubes being
provided with a coupling-nut 15 when the vessels are used in series.

A number of these filters are preferably arranged in series, as represented in Fig. 1,
from six to ten being ordinarily employed. When so arranged, the filters are connected
by pipes 16, which extend from the outlet near the top of one vessel to the inlet near the
bottom of the adjacent vessel. A reservoir or tank 17 for containing the solution hold-
ing the precious metals is disposed adjacent to the first filter of the series and elevated
a sufficient distance to secure a proper flow of the liquid through the filters. This tank
is provided with an outlet-tube 18 near its bottom, said tube being provided with a stop-
cock 19, and connected by pipe 20 with the inlet-tube of the first filter of the series. The
zinc sponge, which constitutes the filtering material and precipitant, is preferably com-
posed of fine threads or filaments of zinc interlocked together. The zinc threads from
which the sponge is formed are cut by a turning tool from a series of zinc disks held be-
tween lathe-centers and turned ; or the zinc sponge may be formed by passing molten
zinc, at a temperature just above the melting-point, through a fine sieve and allowing
it to fall into water. This improved zinc sponge presents a very large contact-sur-
face for the action of the solution, and it does not become easily choked. Each contain-
ing-vessel may be provided with a vertical partition or partitions 21, as illustrated in
Fig. 2, whereby the vessel is divided into two or more compartments or filtering-cham-
bers. These partitions extend to a point near the bottom or top of the vessel, as the case
may be, or they are provided with holes near the top or near the bottom of the vessel.
In case the vessel has three or more filtering-chambers, the partitions are provided with
communicating-openings, disposed alternately near the bottom and top of the vessel,
whereby the passage of the solution is downward through one of the filtering-chambers,
upward through the adjoining filtering-chamber, and downward again through the
third filtering-chamber, and so on.

In the use of this improved filtering apparatus the solution containing the precious
metal is placed in the tank 17 and the cock 19 is opened. In case a series of separate
filters is employed, as represented in Fig. 1, the solution passes from the tank through
the pipe 20 and into the first filter of the series, near the bottom thereof, beneath the
false bottom 12, thence upward through the zinc sponge within the filter, thence out-
ward near the top of the first filter, thence through the connecting-pipe to the next filter
of the series, where it again enters near the bottom and passes upward through the zinc
sponge to the top of the second filter of the series, and so on. The metal which is not
precipitated by the first filter is caught in the zinc sponge of the su-cceeding filters of
the series.

In case filters having a number of compartments are employed, the solution is perfer-
ably admitted to the first compartment at the top thereof, and passes down through the
zinc sponge contained in said compartment to near the bottom thereof, and thence
passes into the second compartment and upward through the zinc sponge therein con-
tained to near the top of said compartment, and thence downward through the next

PATENT-SPECIFICA.TIONS.

113

(No Model.)

No. 418.138.

J. S. MacARTHUR.

METALLURGICAL FILTER.

Patented Deo. 24, 1889.

T^cy d.

WITJVESS£S

IJVVEJ^rTOE

^€<:^

Attorney

8cp

114 THE CYANIDE PROCESS.

compartment, and so on through the several compartments of the compound filter, and
thence to the next compound filter of the series and through its several compartments.
The precious metal may be separated from the zinc sponge by distillation, or the zinc
sponge containing the precious metal may be placed in a suitable sieve and subjected to-
a screening operation, preferably under water. In this operation the greater part of the
precious metal will pass through the sieve and the greater part of zinc sponge will
remain therein.
I claim as my invention —

1. A metallurgical filter for separating a precious metal from a solution containing
said metal, consisting of a vessel provided with inlet and outlet openings, and a zinc
sponge disposed in said vessel between said openings, substantially as described.

2. A metallurgical filter for separating a precious metal from a solution containing
said metal, consisting of a vessel provided with inlet and outlet openings and a filiform
zinc sponge disposed in said vessel between said openings, substantially as described.

3. A metallurgical filter for separating a precious metal from a solution containing
said metal, consisting of a vessel provided with a perforated false bottom, a zinc sponge
within said vessel above said false bottom, and inlet and outlet openings above and
below said sponge, substantially as described.

4. A metallurgical filter for separating a precious metal from a solution containing-
said metal, consisting of a vessel provided with a perforated false bottom, a filiform zinc
sponge within said vessel above said false bottom, and inlet and outlet openings above
and below said filiform sponge, substantially as described.

5. A nietallurgical filtering apparatus for separating a precious metal from a solution
containing said metal, consisting of a series of vessels, a zinc sponge in each of said ves-
sels, pipes connecting the outlet-tube of one vessel of the series with the inlet-tube of the
adjacent vessel of the series, and a reservoir for supplying the solution to the first vessel
of the series, substantially as described.

6. A metallurgical filtering apparatus for separating a precious metal from a solution
containing said metal, consisting of a series of vessels, each of which has an inlet-tube
near its bottom, an outlet-tube near its top, and a perforated false bottom above the
inlet-tube, zinc sponges disposed in the several vessels, pipes connecting the inlet and
outlet-tubes of the several vessels, and a reservoir for supplying the solution to the first
vessel of the series, substantially as described.

7. A metallurgical filter for separating a precious metal from a solution containing
said metal, consisting of a vessel provided with a partition dividing said vessel into a
plurality of filtering-chambers, said partition being provided with openings near one
end, and zinc sponges disposed in said compartments, substantially as described.

JOHN STEWART MacARTHUR.

Witnesses:

F. C. Somes.
Gordon Wilson, Je.

PATENT-SPECIFICATIONS. 115

UNITED STATES PATENT OFFICE.

JOHN STEWART MacARTHUE, of Pollokshields, County of Renfrew, and
ROBERT WARDROP FORREST and WILLIAM FORREST, of Glasgow, County
OF Lanark, Assignors to the CASSEL GOLD EXTRACTING COMPANY
(Limited) of Glasgow, Scotland.

PROCESS OF SEPARATING GOLD AND SILVER FROM ORE.

Specification forming part of Letters Patent No. 418,137, dated December 24, 1889.

(Application filed April 4, 1889. Serial No. 305,998. [Specimens.] Patented in Natal, September 11,
1888, No. 32; in New South Wales, September 27, 1888, No. 965, and in Tasmania, September 29,
1888, No. 609.)

To all whom it may concern:

Be it known that we, John Stewart MacArthur, residing at Pollokshields, in the
county of Renfrew, and Robert Wardrop Forrest and William Forrest, both residing at
Glasgow, in the county of Lanark, Scotland, all subjects of the Queen of Great Britain,
have invented certain new and useful improvements in the process of separating gold
and silver from ores (for which we have received Letters Patent in Natal, No. 32, dated
September 11, 1888 ; New South Wales, No. 965, dated September 27, 1888, and Tasmania,
No. 609, dated September 29, 1888) ; and we do hereby declare that the following is a full,
clear, and exact description of the invention, which will enable others skilled in the art
to which it appertains to make and use the same.

This invention relates to an improvement in the process of separating precious metals
from ores described in Letters Patent of the United States, No. 403,202, granted to us
May 14, 1889. In that process a cyanide is used as the separating agent, and it has been
found tRat ores containing pyrites or sulphurets which have been exposed to the
weather and become partially oxidized absorb a comparatively large quantity of the
cyanide.

'The object of this invention is to economize the process by preventing the absorption
of the cyanide.

The invention consists in separating precious metals from ores by first nevitralizing
the ore by the addition of an alkali or alkaline earth and then leaching such prepared
charge with a cyanide solution.

In carrying out the first or preparatory step of this improved process, we take ore
containing iron pyrites or other compound which has become partially oxidized by
exposure to the weather and mix with it, when in a powdered state, a sufficient quan-
tity of potash, lime, or other alkali or alkaline earth, to neutralize the salts of iron or
other objectionable ingredients formed by the partial oxidation.

The quantity of alkali or alkaline earth to be employed will depend upon the nature
of the ore, and must be determined by first taking a test quantity of the particular ore
to be treated and adding the alkali or alkaline earth thereto until the alkali ceases to be
absorbed. When this condition is reached the liquid will cause red litmus-paper to
turn blue. The proportion of the alkali or alkaline earth so absorbed will indicate the
proper proportion thereof to be added to the bulk of the ore to be treated. In case lime
is employed, 1 per cent of the alkali to 99 per cent of ore will generally be found suffi-
cient. After this prejiaratory treatment the ore (which may consist of tailings or resi-
dues from other processes or operations) is treated with the cyanide solution by being
agitated therewith or by being ground therewith in a pan-mill or other suitable grind-
ing-mill ; or, as we find preferable in the case of some ores, the cyanide solution maj' be
made to percolate through said ores one or more times until all or nearly all the
precious metals are dissolved. For this percolation very simple tanks, vats, or vessels
may be used, such vessels being provided with permeable false bottoms or any suitable
filtering apparatus. The cyanide solution containing the gold or silver is next made to
pass through a sponge of zmc, whereby said metal is precipitated from the solution and
retained in the sponge. The zinc sponge is preferably composed of fine threads or fila-
ments of zinc. These zinc threads are formed in shavings cut by a turning tool from
a series of zinc disks held in a lathe ; or the sponge may be formed by passing molten
zinc at a temperature just above the melting point through a fine sieve and allowing it
to fall into the water. The sponge thus formed presents a very large contact surfacelor
the solution, and it does not oecome easily choked.

The precious metals maybe separated from the zinc sponge by distillation; or the
zinc sponge containing the precious metal may be placed in a suitable sieve and sub-
jected to a screerrtng operation, preferably under water. In this operation the greater
part of the precious metal will pass through the sieve and the greater part of the zinc
sponge will remain therein.

116 THE CYANIDE PROCESS.

We claim as our invention —

1. The process of separating precious metals from an ore, which consists in neutraliz-
ing the ore by the addition of an alkali or alkaline earth, and then leaching the neu-
tralized ore with a cyanide solution.

2. The process of separating precious metal from an ore, which consists in neutralizing
the ore by the addition of an alkali or alkaline earth, then leaching the neutralized ore
with a cyanide solution, and then passing the cyanide solution containing the precious
metal through a sponge of zinc, substantially as set forth.

JOHN STEWART MacARTHUR.
ROBERT WARDROP FORREST.
WILLIAM FORREST,
Witnesses :

Robert Jamikson MacKinlat,
Chaeles Keith Ritchie,
Both of 160 West George Street, Glasgow, Clerks at Law.

PATENT-SPECIFICATIONS. 117

UNITED STATES PATENT OFFICE.

EDWARD D. KENDALL, of Brooklyn, New York.
COMPOSITION OF MATTER FOR THE EXTRACTION OF GOLD AND SILVER FROM ORES.

Specification forming part of Letters Patent No. 482,577, dated September 13, 1892.
(Application filed May 27, 1892. Serial No. 434,528. No specimens.)

To all whom it may concern:

Be it loiown that I, Edward D. Kendall, a citizen of the United States, residing at
Brooklyn, in the county of Kings and State of New York, have invented a new and use-
ful composition of matter to be used for the extraction of gold and silver from ores,
so-called "tailings," and other matters containing one or both of these metals, of whicli
composition the following is a specification.

My composition consists of the following ingredients, combined as hereinafter stated :
water (hot or cold), potassium ferricyanide (or other soluble ferricyanide), and potas-
sium cyanide (or other soluble cyanide). The best proportions of the two last men-
tioned constituents vary somewhat with the different ferricyanides and cyanides, and
may be determined by calculation based on the molecular weights of the salts or the
chemical equivalents of their elements, and also by considering that the purpose of my
composition is to set free cyanogen to form — for example, when the potassium salts are
used — the soluble double cyanide of gold or silver and potassium, and by applying my
theory of the chemical reactions which occur, set forth in the following formula:

4 Kg (CslSra)^ Fe2 + 16 KCN + 8 Au = 4 Kg (CsNa)^ Fez -f 8 K Au (CN)2.

The indicated proportions are therefore, practically, by weight, two and one half parts
of potassium ferricyanide and one part oi potassium cyanide, and these proportions I
have found satisfactory in practice ; but they may be varied within wide limits without
departing from my invention. The potassium ferricyanide, which is a product of the
chemical action, facilitates the solution of the resulting cyanides, and after the separa-
tion of the precious metal from the menstruum by appropriate means, may be utilized
by a process which I propose to make the subject of a separate application.

To prepare my composition, I dissolve the ferrocyanide in one portion of water and
the cyanide in another portion, and mix the two solutions ; or either salt, in solid form,
may by added to the solution of the other. In dissolving the salts I do not always
confine myself to a specific proportion of water. More or less water may be used. As
a rule, the more concentrated the composition the more energetic its action, but the
more costly. Except in treating substances very rich in gold or silver, my composition
will always be used in a more or less dilute condition.

In using the herein-described composition, the gold- and silver-bearing minerals, tail-
ings, and other matters, cold or while moderately heated, with or without prior chemical
or mechanical treatment, should be placed in tanks, or troughs, or other receptacles
made of any suitable material, as wood (if of wood, preferably lined with stoneware
slabs), and thoroughly drenched, soaked, or impregnated with my composition, which
is, after a time, to be drawn off and washed out, or displaced with water, in order that
the contained precious metal may be separated by subsequent operations.

The composition may be used hot or cold. The effect of heat is to hasten the chem-
ical and solvent action.

What I claim, and desire to secure by Letters Patent of the United States, is—

The before-described composition of matter — to be used for extracting gold and silver
from minerals, tailings, and other matters containing one or both of these metals — con-
sisting of water, one or more soluble ferricyanides, and one or more soluble cyanides,
prepared and combined as herein stated.

EDWARD D. KENDALL.

Witnesses :

Edward M. McCook.
• S. J. Stokes.

118 THE CYANIDE PROCESS

[Second Edition.]

No. 3,024. A. D. 1892.

Date of Application, 16th Feb., 1892.

Complete Specification Left 16th Nov.. 1892— Accepted 16th Feb., 1893.

PROVISIONAL SPECIFICATION.

IMPROVEMENTS IN PRECIPITATING AND COLLECTING METALS FROM SOLUTIONS
CONTAINING THEM.

A communication by Bernard Charles Molloy, Member of Parliament, Barrister at Law,
of the Middle Temple, London, temporarilj'^ residing in Jolaannesburg, South Afri-
can Republic.

I, Alfred George Brookes, of 55 and 56 Chancery Lane, in the county of London, Char-
tered Patent Agent, do hereby declare the nature of this invention to be as follows :

This invention consists in a new method of precipitating and collecting gold and other
metals from solutions containing these metals, such as bromide, chloride, and cyanide
solutions.

In some cases these solutions are acid, but under the action of this process these solu-
tions are rendered neutral and alltaline, so that the solutions are, or become, alkaline
solutions of the metals which are soluble in alkaline solution.

The application of this process may be carried out in apparatus of many forms of con-
struction and under many and differing conditions, depending on the character of the
work required to be done.

The following example will, however, explain the nature of the process, and how it
may be carried out:

Take a tray or tank constructed of wood, cement, or other suitable material and of a
size as may be necessary.

Cover, or partially cover, the bottom of the tank with mercury. On this mercury will
rest the solution from which the metals are to be precipitated. This mercury is then
charged electrolytically with ammonium, sodium, potassium, or other alkaline metal,
which is then amalgamated by the mercury. These alkaline metals, or the amalgams of
these metals, when they come to the surface of the mercury and in contact with the
water of the solution, decompose the water, the alkaline metal combining with the oxy-
gen of the water to form an alkaline oxide, and so rendering the solution alkaline if not
previously so, and the hydrogen of the decomposed water is at the same time evolved
in a nascent state from the surface of the mercury in contact with and against the solu-
tion from which the metal in solution (say the gold) is to be precipitated and collected.

Under this action the metals in solution (such as gold) will be precipitated and ab-
sorbed by the merctiry, from which it can be released in the ordinary manner by the
action of heat.

In the above-described case the charging of the mercury with the alkaline metal has
been effected electrolytically by the electrolysis of say an alkaline salt of the alkaline
metal used in a porous vessel in contact with a mercury cathode or other convenient
method.

Another though much less advantageous method is the mechanical addition to the
mercury, of potassium or other alkaline metal or amalgam of the same, when the nascent
hydrogen with an equivalent of the alkaline oxide will be produced.

These are some methods by which the process may be carried out, but there are others,
as is evident, which may be employed.

In carrying out this process a solution of bromine, chlorine, or cyanogen may be used
to dissolve the gold and other metals from their compounds, and then the process here
described may be used to precipitate and collect the metals.

It is evident that generation of nascent hydrogen in contact with an alkaline solution
of metals, soluble in such solution, may be obtained by other means, though not detailed
here.

Dated the 16th day of February, 1892.

WM. BROOKES & SON,
55 and 56 Chancery Lane, London, Agents for the Applicant.

PATENT-SPECIFICATIONS. 119

COMPLETE SPECIFICATION.

IMPROVEMENTS IN PRECIPITATING AND COLLECTING METALS FROM SOLUTIONS CON-
TAINING THEM.

A communication by Bernard Charles Molloj'-, Member of Parliament, Barrister at Law,
of the Middle Temple, London, temporarily residing in Johannesburg, South Afri-
can Republic.

I, Alfred George Brookes, of 55 and 56 Chancery Lane, in the county of London,
Chartered Patent Agent, do hereby declare the nature of this invention and in what
manner the same is to be performed, to be particularly described and ascertained in and
by the following statement :

This invention consists in a new method of precipitating and collecting the gold and
other metals from the solutions containing these metals, such as bromide, chloride, and
cyanide solutions, when such are employed for dissolving out the precious metals from
compounds containing the same.

In some cases these solutions are acid, but under the action of this process these solu-
tions are rendered neutral and alkaline, so that the solutions are, or become, alkaline
solutions of the metals, which are soluble'in alkaline solutions.

The application of this process may be carried out in apparatus of many forms of con-
struction, and under many and differing conditions, depending on the character of the
work required to be done.

The following example of the treatment of a gold-bearing compound will, however
explain the nature of the process, and how it may be carried out:

The crushed ore is treated, say, with a solution of cyanide of potassium, the quantity
and saturation being in proportion to the work to be done. When the solvent solution
is sufficiently charged, then the precipitation of the gold, the regeneration of this solvent,
and the collection of the gold, is effected as follows:

Take a tray, or tank, constructed of wood, cement, or other suitable material, and of a
size as may be necessary. Cover, or partially cover, the bottom of the tank with mer-
cury.

On this mercury will rest, or pass over, the solution from which the metals are to be
precipitated. This mercury is then charged electrolytically with ammonium, sodium,
potassium, or other alkaline metal. These alkaline metals, when they come to the sur-
face of the mercury and in contact with the water of the solution (now containing gold)
decompose the water, the alkaline metal combining with the oxygen of the decompose(i
water to form an alkaline oxide, rendering the solution alkaline, if not previously so,
and the hydrogen of the decomposed water is at the same time evolved in a nascent
state from the surface of the mercury in contact with and against the solution from
which the metal in solution (say the gold) is to be precipitated and collected. While
the current continues to pass, the required nascent hydrogen and oxide will be produced
and act on the solution containing the gold.

Under this action the metals in solution such as gold will be precipitated and ab-
sorbed by the mercury, from which it can be released in the ordinary manner by the
action of heat.

In the above-described case, the charging of the mercury with the alkaline metal has
been effected electrolytically by the electrolysis of, say, an alkaline salt of the alkaline
metal used in a porous vessel in contact with the mercury cathode or other convenient
method.

Another though less advantageous method is the mechanical addition to the mercury
of potassium, or other alkaline metal, or amalgam of the same, when the nascent hydro-
gen, with an equivalent of the alkaline oxide, will be produced.

These are some methods by which the process maybe carried out, but there are others
as is evident, which may be employed instead. '

The action may be concisely aescribed as follows :

The precious metal is dissolved out say by a solution of potassium cyanide. The solu-
tion is then brought into contact with mercury, charged, as described, with potassium.
The potassium on coming into contact with the water of the solution decomposes it
with the evolution of nascent hydrogen and the formation of the oxide of the alkaline
metal. The hydrogen decomposes the solution of the new cyanide of gold— and sets the
gold free, which is precipitated upon and collected by the mercury.

The metal of the alkaline oxide reacts upon the cyanogen compound, and so reforms
or reproduces the cyanide of potassium. The original solution (of cyanide of potas-
sium) is thus regenerated, and is then ready for re-use, thus effecting a great economv.

The following equations roughly represent the various reactions when cvanogen "is
the solvent :

H,0 + -f4 KCN -1-2 Au = 2 (KAu(CN),) -f- 2 KOH 2 (KAu(CN),) -f 2 H =
2 KCN -f 2 CNH -}- 2 Au 2 CNH -f- 2 KOH = 2 KCN -f- 2 HjO

In carrying out this process a suitable solution of a solvent for gold, such as bromine
or chlorine, or cyanogen, or their compounds, mav be used to dissolve out the gold and!
other metals from their ores or compounds, and then the process more particularly
described for precipitating the metals in such solution, and in some cases regenerating
the solvent solutions and obtaining the metals.

120 THE CYANIDE PROCESS.

It is evident that generation of nascent hydrogen in contact with an alkaline solution
from which metals soluble in such solution are to be precipitated, may be obtained
without the employment of a cathode of mercury, and using instead thereof another
known cathode.

Although I have hereinbefore indicated some methods by which it may be worked,
variations in detail may be effected without departing from the essential features of my
invention.

Having now particularly described and ascertained the nature of my said invention,
and in wnat manner the same is to be performed, I declare that what I claim is —

1. The method of obtaining gold and other metals from solutions which have been
employed in dissolving out such precious metals from ores, or compounds, containing
the same, substantially in the manner and for the purpose hereinbefore set forth.

2. The described method of precipitating and collecting gold and other metals from
solutions, such as referred to, containing them, by the action of the alkaline metals, in
the manner hereinbefore set forth.

3. The extraction of gold or other metals from ores, or other compounds, by solutions
of cyanogen, or its compounds, the precipitation of gold or other metals from such solu-
tions, the regeneration of such solutions, and the collection of the gold or other metal,
all substantially as and for the purpose set forth.

4. The described method of precipitating gold and other metals from alkaline solutions,
such as indicated, containing them, by the action of nascent hydrogen, in the manner
hereinbefore set forth.

5. The precipitation of gold, and other precious metals from solutions, such as indi-
cated, containing them, by means of the alkaline metals, or amalgams of the same,
obtained electrolytically, substantially as and for the purpose set forth.

6. The separation and collection of gold or other precious metals from their ores or
compounds by means of a suitable solvent for said metals, an electrolyte of the alka-
line metals, a current of electricity, a mercury cathode, all substantially as set forth.

7. The employment of bromine, chlorine, iodine, and cyanogen, or their compounds,
as solvents for gold or other metals, in combination with the above-described process
for effecting the precipitation and collection of the gold and other metals in solution
therein, substantially as set forth.

Dated the 16th day of November, 1892.

WM. BROOKES & SON,
55 and 56 Chancery Lane, London, Agents for the Applicant.

PATENT-SPECIFICATIONS. 121

[Second Edition.]

No. 12,641. A. D. 1892.

Date of Application, 8th July, 1892.
Complete Specification Left 10th April, 1893— Accepted 8th July, 1893.

PROVISIONAL SPECIFICATION.

IMPROVEMENTS IN THE EXTRACTION OF GOLD AND SILVER FROM ORES OR COM-
POUNDS CONTAINING THE SAME, AND IN APPARATUS APPLICABLE FOR USE IN
THE TREATMENT OF SUCH MATERIALS BY MEANS OF SOLVENTS.

I, John Cuninghame Montgomerie, of the "Water of Ayr" and "Tarn O'Shanter"
Hone Works, Dalmore, Stair, in the county of Ayr, manufacturer, do hereby declare the
nature of this invention to be as follows :

This invention relates to the treatment of auriferous and argentiferous ores or com-
pounds, for the purpose of separating and collecting the gold and silver contained
therein, by means of solvent agents — as, for example, cyanide of potassium— and to
apparatus applicable for use in processes of this description.

According to the method usually employed in the recovery of gold and silver by
means of cyanide of potassium, the ore or other material having been reduced to a
finely-triturated state is placed, along with the solvent, in a barrel or other vessel and
is there subjected to agitation. After the lapse of a few hours the conte'uts of the barrel
are removed to a filter, where the liquid portion of the charge (containing the precious
metals in solution) is separated from the ore. The latter is further washed for the
removal of any gold or silver remaining (in solution) therewith. The cyanide solution
of gold and silver (as also the wash-water) is then treated for the recovery of the pre-
cious metals by precipitation.

When a cyanide solvent is employed as hereinbefore described, the proportion of
cjranide is necessarily considerably in excess of that required for chemical combination
with the gold and silver present in the ore. This excess remains with the liquor after
the precious metals have been precipitated therefrom, and is either run to waste or is
subjected to a separate process for the recovery of the cyanide.

My improvement in the process of extraction by the method hereinbefore referred to
consists in applying the cyanide solution of gold and silver, after having been separated
from the ore by filtration, to a subsequent charge or to subsequent charges of fresh ore
prior to treating the solution for the separation of the precious metals by precipitation,
care being taken that the original quantity of water is made good. With this object
the requisite quantity of water is preferably added as soon as the surface of the ore
contained in the filter presents a dry appearance, the added water displacing the liquid
remaining in the ore and permitting the same (which is highly charged with the sol-
vent and with the precious metals in solution) to be discharged. The solution is then
tested for cyanide of potassium (or such other solvent agent as may be employed), and
the deficiency supplied by the addition of a suitable quantity of cyanide of potassium
(or other solvent agent), thereby restoring the solvent solution to its original strength
before adding the same to the fresh charge of ore. Before being added to the fresh
charge of ore, the solution is made slightly alkaline by the addition of an alkali, prefer-
ably caustic soda.

Where cyanide is employed, it is necessary for the ore to be thoroughly neutralized
before treatment; and in some cases it is advantageous to have it slightly alkaline,
especially where oxygen is used under pressure. The tailings are then further washed'
to remove the last trace of gold and silver remaining in solution, and the resultant
wash-water is treated in the usual way for the recovery of the precious metals contained
therein.

By this mode of procedure considerable economy is effected, both in the quantity of
cyanide or other solvent used and in the cost of working, the quantity of liquid sub-
jected to treatment for the recovery of the gold and silver by precipitation being at the
same time greatly reduced.

My invention relates secondly to the construction of the barrel or other vessel in
which the ore is subjected to the action of the solvent.

If this barrel or vessel be formed of metal, its internal surface is rapidly acted upon
by cyanide of potassium or other solvent of the precious metals ; and if a lining of wood
or similar material be employed, the latter is incapable of withstanding the chemical
action of the solvent and the abrasive action of the ore for any length of time.

With a view to overcoming these difficulties, I line the barrel or vessel with tiles or
segments composed of glass or glazed porcelain or similar solvent- and acid-resisting
material, the same being set in cement adapted to withstand the chemical action of the
cyanide or other solvent employed.

122 THE CYANIDE PROCESS,

My invention relates thirdly to the construction of the filter or leaching vat employed
for separating the ore from the cyanide or other solution of gold and silver, or from the
wash-water.

A filter constructed according to my improved method comprises an upper vessel for
the reception of the mixture of ore and solvent, and a lower vessel in which the solution
is received after passing through the filter-bed. The latter is formed of filter cloth
carried on wire gauze coated with an acid-proof enamel and supported on wooden laths.
The upper vessel is attached to the lower vessel by means of bolts, and is so arranged
that the bottom edge of the former rests upon the periphery of the filter cloth and grips
the same in a recess formed in the upper edge of the lower vessel, thereby securing a
water-tight joint between the two vessels and at the same time holding the filter cloth
securely in position.

The filter or leaching vat may be lined with segments or tiles in the manner herein
before described with reference to the barrel or other vessel in which the ore is subjected
to the action of the solvent.

Dated the 6th day of July, 1892.

G. G. M. HARDINGHAM,
191 Fleet Street, London, E.G., Chartered Patent Agent.

COMPLETE SPECIFICATION.

IMPROVEMENTS IN THE EXTRACTION OF GOLD AND SILVER FROM ORES OR COM-
POUNDS CONTAINING THE SAME, AND IN APPARATUS APPLICABLE FOR USE IN
THE TREATMENT OF SUCH MATERIALS BY MEANS OF SOLVENTS.

I, John Cuninghame Montgomerie, of the "Water of Ayr" and "Tarn O'Shanter"
Hone Works, Dalmore, Stair, in the county of Ayr, Scotland, manufacturer, do hereby
declare the nature of this invention, and in what manner the same is to be performed, to
be particularly described and ascertained in and by the following statement:

This invention relates to the treatment of auriferous and argentiferous ores or com-
pounds, for the purpose of separating and collecting the gold and silver contained
therein, by means of solvent agents— as, for example, cyanide of potassium — and to
apparatus applicable for use in processes of this description.

According to a method commonly employed in the recovery of gold and silver by
means of cyanide of potassium, the ore or other material having been reduced to a
finely-triturated state is placed, along with the solvent, in a barrel or other vessel, and
is there subjected to agitation. After the lapse of a few hours, the contents of the barrel
are removed to a filter, where the liquid portion of the charge (containing the precious
metals in solution) is separated from the ore. The latter is further washed for the
removal of any gold or silver remaining (in solution) therewith. The cyanide solution
of gold and silver, as also the wash-water, is then treated for the recovery of the precious
metals by precipitation in a zinc filter or percolator.

When a cyanide solvent is employed as hereinbefore described, a certain portion
thereof is taken up by base metals and other impurities invariably present in greater or
less proportions in the ore. The solvent is also contaminated *by the zinc dissolved
whilst the mixture of ore and solvent is under treatment in the zinc percolator ; both of
these causes resulting in a considerable waste of the cyanide, and in its contamination
with deleterious matter.

My improvement in the process of extraction by means of the kind hereinbefore
referred to, consists in adding sodium oxide (caustic soda), or other suitable oxide of the
alkalies, to the cyanide solution before (or whilst) mixing the same with the ore,
thereupon agitating or otherwise treating the resultant mass for the time requisite for
enabling the gold and silver to be dissolved by such a solution, then discharging the
same into a filter and drawing off the original quantity of water employed, the same
being highly charged with the unconsumed cyanide and sodium oxide, and with the
preciou% metals in solution.

By the employment of sodium oxide in the manner hereinbefore described, particu-
larly where the alkali is in excess, I have found that the proportion of cyanide or other
solvent may be considerably reduced and an important economy in the cost of working
effected.

In carrying out this stage of the process, a sufficient quantity of water is added to the
surface of the ore in the filter as soon as it becomes dry, the added water displacing the
liquid remaining in the ore and permitting the latter to be discharged. The liquid
obtained is then tested for cyanide of potassium and sodium oxide, and the deficiency
supplied by the addition of the necessary quantity of these agents so as to restore the
son'ent solution to its original character and strength. This solution is now applied to
a fresh charge of ore, and the same operation is repeated with successive charges till it
is found necessary to discharge the solution with a view to precipitating the gold and
silver in the usual manner. Experiment alone can determine the quantity of solvent
and of sodium oxide appropriate, and the period of time requisite to insure the greatest
extraction of the precious metals with the least consumption of the solvent, as these
will vary according to the nature of the ore operated upon. (It may be mentioned by

PATENT-SPECIFICATIONS.

123

AD. 1892. JuLT 8. N" 12,641.
MONTGOMERIE'S Complbte Specification.

124 THE CYANIDE PROCESS.

way of illustration that for an ore containing about 4 ozs. of gold and 12 ozs. of silver
per ton, 12 lbs. of cyanide of potassium and 3 lbs. of sodium oxide would be suitable.)
The tailings are then further washed to remove the last trace of gold and silver remain-
ing in solution, and the resultant wash-water is treated in the usual way for the recovery
of the precious metals contained therein.

By this mode of procedure, the quantity of liquid subjected to treatment for the
recovery of the gold and silver by precipitation is greatly reduced.

My invention relates secondly to the construction of the barrel or other vessel in
which the ore is subjected to the action of the solvent.

If this barrel or vessel be formed of metal, its internal surface is rapidly acted upon
by cyanide of potassium or other solvent of the precious metals; and if a lining of wood
or similar material be employed, the latter is incapable of withstanding the chemical
action of the solvent and the abrasive action of the ore for any length of time.

With a view to overcoming these difficulties, I line the barrel or vessel with tiles or
segments composed of glass or glazed porcelain, or similar solvent- and acid-resisting
material, the same being set in cement adapted to withstand the chemical action of the
cyanide or other solvent employed.

My invention relates thirdly to the construction of the filter or leaching vat employed
for separating the ore from the cyanide or other solution of gold and silver, or from the
wash-water.

Apparatus constrticted according to my invention is illustrated in the accompanying
drawings, w^hereof Fig. 1 is a vertical section, and Fig. 2 a plan. The apparatus com-
prises an upper vessel A for the reception of the mixture of ore and solvent, and a lower
vessel B in which the solution is received after passing through the filter-bed. The
latter is formed of filter-cloth C carried on wire gauze D coated with an acid-proof enamel
and supported on wooden laths E on the top of the vessel B. The vessel A is attached
to the vessel B by means of bolts F and nuts Fi, and is so arranged that its bottom edge
rests upon the circular margin of the filter-cloth 0, which it presses against the bottom
of a recess or socket formed in the upper edge of the vessel B, thereby securing a water-
tight joint between the two vessels and at the same time holding the filter-cloth
securely in position. G is a draw-off cock; H being the exhaust cock. The vessels A
and B are lined with segments or tiles K, composed of glass, glazed porcelain, or similar
solvent- and acid-resisting material, set in cement adapted to withstand the chemical
action of the cyanide or other solvent employed. When a barrel is used, it may be lined
with segments or tiles set in a similar manner.

Having now particularly described and ascertained the nature of this invention, and
in what manner the same'is to be performed, I claim —

1. The improved process of extracting gold and silver from ores or compounds con-
taining the same, substantially as herein described; the same consisting in mixing the
ore with a solution of cj'anide of potassium or other cyanide solvent rendered alkaline
by the addition of sodium oxide or an eqi^ivalent alkaline oxide, filtering or otherwise
separating the liquid (containing the gold and silver in solution) from the ore, and
treating the former, by precipitation or other known mode, for the recovery of the
precious metals.

2. In the extraction of the precious metals by a solvent process of the general char-
acter herein referred to, applymg the solvent solution, after separation from the first
charge of ore, to a subsequent charge or successively to subsequent charges of fresh ore,
the solution being fortified at each operation by the addition of a suitable quantity of
the chemical agents employed, and ultimately treating the liquid (consisting of a more
or less saturated solution of gold and silver) by any known means for the separation
and recovery of the precious metals.

3. In the process of extracting gold and silver by means of cyanide of potassium or
other cyanide solvent, the addition of sodium oxide or other suitable alkaline oxide to
the solvent, either prior to or during its admixture with the ore, for the purpose of
economizing the solvent and expediting its action.

4. In the extraction of the precious metals by a solvent process of the general char-
acter herein referred to, discharging the solvent remaining with the ore after filtration
by adding water to the surface of the ore and thereby displacing the solvent containing
the precious metals in solution, substantially as herein described.

5. In apparatus adapted for use in the treatment of ores or compounds containing
gold or silver, a barrel, filter, or leaching vessel such as A or B lined with tiles K set in
an acid- or solvent-resisting cement, substantially as herein described.

6. The herein described apparatus for use in the treatment of ores or compounds con-
taining gold and silver by means of solvents, the same comprising an upper vessel A for
the reception of the ore and solvent, a lower vessel B in wnich tne solution is received,
a filter cloth C held between the lower part of the vessel A and a socket in the upper
part of the vessel B, wire gauze D on which the filter cloth lies, and bars E for support-
ing the wire gauze.

7. The herein described apparatus for use in the treatment of ores or compounds con-
taining gold and silver by means of solvents, the same comprising an upper vessel A
lined with tiles K, a lower vessel B also lined with tiles K, a filter cloth C held between
the vessels A and B, wire gauze D under the filter cloth, bars E for supporting the wire
gauze, a draw-off cock G, and an exhaust cock H.

Dated the 8th day of April, 1893.

G. G. M. HARDINGHAM,
191 Fleet Street, London, E.G., Chartered Patent Agent.

PATENT-SPECIFICATIONS. 125

UNITED STATES PATENT OFFICE.

ALEXIS JANIN and CHARLES W. MERRILL, of San Francisco, California.
PKOCESS OF LEACHING ORES WITH SOLUTIONS OF ALKALINE CYANIDES.

Specification forming part of Letters Patent No. 515,148, dated February 20, 1894.
(Application filed June 12, 1893. Series No. 477,.338. No specimens.)

To all whom it may concern:

Be it known tliat we, Alexis Janin and Charles W. Merrill, citizens of the United
States residing in the city and county of San Francisco, State of California, have invented
an Improvement in Processes of Leaching Ores with Solutions of Alkaline Cyanides; and
we hereby declare the following to be a full, clear, and exact description of the same:

Our invention relates to an improvement in the art of leaching ores with solutions of
alkaline cyanides, and consists in, first, precipitating and separating, in the form of silver
sulphide, by means of an alkaline sulphide or of sulphuretted hydrogen gas, all or the
greater portion of the silver dissolved from the ore by such solutions, and then precipi-
tating in the metallic state, by means of metallic zinc, the gold contained in the same
solution, together with any silver which has escaped precipitation as a sulphide.

In the usual method of leaching ores with a solution of potassium cyanide, the gold
and silver extracted are both precipitated from the solution in the metallic state, with
metallic zinc. When much silver is present, this method involves a large consumption
of zinc and consequent contamination of the cyanide solution by the zinc dissolvec^ and
unless the contact between the zinc and the silver- bearing solution be greatly prolonged,
the precipitation of the silver is imperfect. Furthermore, the potassium cyanide which
combines with the zinc dissolved is practically lost. When the silver is precipitated
from its solution in potassium cyanide by means of an alkaline sulphide an alkaline
cyanide is regenerated, which is again available for leaching. If sulphuretted hydrogen
gas be used to precipitate the silver there is also formed free hydrocyanic acid, but if the
solution of potassium cyanide contains free alkali, or if such be added to the solution, no
free hydrocyanic acid will escape, either because the sulphuretted hydrogen gas first com-
bines with the alkali, to form a sulphide which precipitates the silver in the manner
described, or because any hydrocyanic acid generated will also combine with the free
alkali to form an alkaline cyanide.

We have found that, whereas, silver is not precipitated at all, or only very imperfectly,
from strong solutions of potassium cyanide, by means of the agents hereinafter men-
tioned, yet when the silver-bearing solution contains only about one and one half per
cent, or less, of pure potassium cyanide (KCN) or its equivalent, then the silver can be
thoroughly precipitated by means of the sulphides of sodium, potassium, or ammonium,
or by sulphuretted hydrogen gas, and the precipitation of the silver becomes more imper-
fect as the strength of the solution in potassium cyanide is increased. Therefore when
leaching silver-bearing ores we employ solutions containing, at the most, two per cent
of potassium cyanide or its equivalent. As a precipitating agent we employ preferably
a solution of sodium sulphide, approaching, as nearly as practicable, to the composition
of a monosulphide, in order to avoid, as much as possible, the separation of free sulphur
in precipitating the silver.

In practice we leach ores containing both gold and silver, with a solution of potassium
cyanide containing not more than two percent of KCN or its equivalent, or as much
weaker as is consistent with a thorough extraction. The solution, after passing through
the ore, is run into precipitating vats, where a solution of sodium sulphide is added in
suflScient quantity to convert the silver present into sulphide of silver, or in a little less
than that amount, in order to avoid the possibility of any excess of the precipitating
agent remaining in the solution which might be prejudicial in its further use. The
precipitate of silver sulphide is allowed to settle, the supernatant solution of potassium
cyanide is then drawn off, and the gold, together with any silver remaining in solution,
is precipitated by means of metallic zinc.

Having thus described our invention, what we claim as new, and desire to secure by
Letters Patent, is—

The improvement in the art of leaching ores with solutions of alkaline cyanides, which
consists in first leaching the ore with such solutions, then adding to the solution an
agent which will precipitate the silver present as a sulphide, and then precipitating the
gold in the solution with metallic zinc, substantially as herein described.

In witness whereof we have hereunto set our hands.

ALEXIS JANIN.
CHARLES W. MERRILL.

Witnesses:

s. h. noursk.
Wm. F. Booth.

126 THE CYANIDE PROCESS.

NEW ZEALAND PATENT OFFICE.

JOHN STEWART MacARTHUR and CHARLES JAMES ELLIS.

APPLICATION FOR LETTERS PATENT FOR IMPROVEMENTS IN EXTRACTING GOLD
AND SILVER FROM ORES AND THE LIKE.

We, John Stewart MacArthur, Managing Director of the Cassel Gold Extracting Com-
pany (Limited), and Charles James Ellis, technical chemist to the said company, both
of 157 West George Street, Glasgow, in the county of Lanark, North Britain, do declare
the nature of our invention for "Improvements in extracting gold and silver from ores-
and the like," and in what manner the same is to be performed, to be particularly
described and ascertained in and by the following statement:

Our said invention relates to what is known as the "MacArthur-Forrest process" for
extracting gold and silver from ores and the like by means of cyanides, and has for its
object to increase the efficiency and economy of that process in cases in which, from the
nature of the ores treated, or other circumstances, it is found that in the solution of cya-
nide as heretofore used there is formed, or becomes present, a sulphide soluble therein
which retards and objectionably affects the action of the cyanide on the precious metals.

Our invention consists in removing or rendering inert such sulphide by adding to the
solution of cyanide, or to the ore, or to the mixture of ore and cyanide solution, a
suitable salt or compound of a metal which will form with the sulphur of the sulphide
a sulphide which is practically insoluble or inert in the cyanide solution, or which
will materially diminish the objectionable action.

In carrying out our invention, we may use any one or more of various metallic salts
or compounds, of which the following may be mentioned, by way of example, preference
being given to them in the order in which they are noted, namely : Salts or compounds
of lead, such as plumbates, carbonate acetate, or sulphate of lead; or salts or compounds
of other metals, such as sulphate or chloride of manganese, zincates, oxide, or chloride
of mercury, and ferric hydrate, or oxide. The proportion to be used in any case will
depend on the proportion of soluble sulphide which has to be dealt with in the cyanide
solution applied to the particular ore, and is easily and most conveniently ascertained
by trials of a few samples in each case. In the case of some ores containing sulphur, we
find the addition of salts or compounds, as and for the purpose hereinbefore referred to,
and especially those of lead and mercurj', increases the percentage of precious metals
obtained.

Having now particularly described our said invention, and in what manner the same
is to be performed, we declare what we claim is —

1. In the MacArtliur-Forrest process for extracting gold and silver from ores and the
like, the addition to the cyanide solution, or to the ore, or to the mixture of ore and
cyanide, of salts or compounds of lead, substantially as and for the purposes herein-
before described.

2. In the MacArthur-Forrest process for extracting gold and silver from ores and the
like, the addition to the cyanide solution, or to the ore, or to the mixture of ore and
cyanide, of any one or more of the metallic salts or compounds hereinbefore indicated,
and capable of forming insoluble sulphides, as and for the purposes hereinbefore
described.

Dated June 29, 1893.

JOHN STEWART MacARTHUR.
CHARLES JAMES ELLIS.

PATENT-SPECIFICATIONS. 12'i

NEW ZEALAND PATENT OFFICE.

CARL MOLDENHAUER.

APPLICATION FOR LETTERS PATENT FOR IMPROVEMENTS IN RECOVERING GOLD
AND OTHER PRECIOUS METALS FROM THEIR ORES.

I, Carl Moldenhauer, of Frankfort-on-Main, in the Empire of Germany, do hereby
declare that the nature of my invention for improvements in recovering gold and other
precious metals from their ores, and the manner in which the same i"s to be used, are
particularly described and ascertained in and by the following statement:

This invention relates to extracting gold and other precious metals from their ores by
means of a solution of cyanide of an alkali or an alkaline earth, and has for its object
to render the process more expeditious and considerably cheaper than heretofore.

The invention consists, firstly, in adding to the cyanide solution an artificial oxidizing
agent; and secondly, in precipitating the extracted precious metal out of its cyanide
solution by means of aluminium or alloys or amalgam thereof.

As to the first part of my invention, I have found that the dissolving action of the
cyanide solution on the precious metal is highly expedited, and much cvanide is saved,
if an artificial oxidizing agent is added to the said cyanide solution. As such an arti-
ficial oxidizing agent, I use, by preference, ferricyanide of potassium, or another ferri-
cyanogen salt of an alkali or of an alkaline earth. In either case the ferricyanogen salt
is preferably employed in alkaline solution. The result of this addition of an artificial
oxidizing agent is that the dissolving action of the solvent is rendered more energetic,
and consequently a considerably smaller quantity of the'solvent is required. Thus, by
the addition of ferricyanide of potassium or other ferricyanogen salt in alkaline solu-
tion, as much as 80 per cent of the potassium may be saved. The proportions preferred
are from one half to two parts of ferricyanide to one part of cyanide.

It may be remarked that the ferricyanide of potassium alone will not dissolve the gold,
and does not, therefore, come under the category of the solvent heretofore employed in"
processes of extraction. It does not, therefore, render unnecessary the employm'ent of
the simple cyanide as a solvent, but only reduces the amount required, owing to the
capacity of the ferricyanide to act as an oxidizing agent; consequentiv the cyanogen of
the ferricyanide is not used to form the gold cyanide compound. I'may also employ
permanganate of potash as the oxidizing agent instead of the ferricyanide. The said
permanganate of potash is also added in solution and in the same proportions as before
namely, from one half to two parts of permanganate to one part of cyanide.

In lieu of permanganate of potash, any other suitable oxidizing agent can be used in
carrying out my invention in practice, the invention not being restricted to the use of
any special oxidizing agent, but includes the use of an agent that exerts an oxidizing
action in the cyanide solution. The process can be carried out in a ball-mill lined with
porcelain, wood, or other substance unattackable by the chemicals employed.

I may also use the cyanide solution and the oxidizing agent in combination with a
preliminary treatment of the ore with any acid or salt that renders the precious metal
better adapted to the subsequent treatment of the cyanide solution.

The second part of the process consists in precipitating the dissolved gold or precious
metal out of its cyanide solution by means of aluminium alloy or aluminium amalgam-
but this can also be applied with advantage to sulphurized" solutions containing free
alkali— that is to say, solutions which contain gold in the form of sulphuret, or hyposul-
phide of gold.

Zinc has heretofore been employed in practice by preference in precipitating gold
from the cyanide solutions obtained by leaching auriferous ores. The employment of
zinc for this purpose is found, however, to be attended with serious disadvantages. Now
I have discovered that aluminium can be employed for this purpose in place of zinc'
without the disadvantages attending the use ot the latter. '

Whilst zinc forms a combination with the bound or free compound of cyanogen and
alkali contained in the cyanide solution, aluminium separates the gold very quicklv from
the cyanogen solution without entering into combination with the cyanogen, but simplv
reacting with the caustic alkali which is present at the same time. By the action o"f
aluminium the cyanide of potassium employed for leaching the gold out of its ore is
regenerated, which is not the case when zinc is employed. But the zinc does not con-
fine itself to entering into combination with the cyanogen of the cyanogen compounds
of the gold, but also acts upon the free cyanide of potassium conta"ined in the solution
so that a great part of the latter is consumed; but this is not the case when aluminium
is employed.

These results are of the greatest importance when the solutions separated from the
gold is to be employed in subsequent -gold-extracting operations, as the whole of the
cyanogen in the regenerated and liberated cyanide of potassium is enabled to renew its
aetion; but the lyes resulting from the employment of zinc cannot be employed with

128 THE CYANIDE PROCESS.

the same advantage in subsequent operations for the extraction of gold. Numerous
attempts have been made to regenerate the zinc, but are found to be inconvenient and
costly. It is consequently evident that an important saving in cyanide of potassium is
obtained by the employment of aluminium.

Aluminium acts in a like manner in a sulphurized alkaline solution — that is to say,
in a solution containing the gold in the form of sulphuret of gold or hyposulphide of
gold. It does not enter into combination with the sulphur in a solution of this descrip-
tion. _ This great and important advantage attending to the employment of aluminium,
aluminium alloys, or aluminium amalgam, is combined with other advantages, as follows:

Aluminium is far less subject to oxidation than is zinc, so that it can be sent from its
place of production in the form in which it is to be used for the precipitation, whereas
when zinc is employed it is considered to be an important advantage to reduce it to the
required form at the place where it is employed, and immediatelj' before using it. For
the same reason, the repeated employment of the aluminium is admissible for con-
tinuous precipitation.

Finally, the quantity of aluminium required for precipitating the same quantity of
precious metal is about four times less than the amount of zinc required to produce the
same effect.

I am aware that attempts have been made to employ aluminium for precipitating
precious metals from acid or neutral solutions, but in this case it offers no advantages
as compared with zinc and iron.

On the other hand, the practical precipitation of precious metals from alkaline
cyanide solutions or sulphurized solutions by means -of aluminium was not known,
neither was it known that by the employment of the same in the presence of free alkali
it was possible to obtain the important advantages hereinbefore set forth.

Of course, instead of pure aluminium, alloys or an amalgam thereof can be used with
a like advantage; furthermore, I do not confine myself to the use of the aluminium, its
alloys or amalgam, in any special form, as it may be used in any sxiitable form without
departing from my invention.

Having particularly described and ascertained the nature of my said invention, and
in what manner the same is to be performed, I declare that what I claim is —

1. Extracting gold and other precious metals from their ores by subjecting the ores to
the dissolving action of a cyanide of an alkali or an alkaline earth in the presence of an
oxidizing agent, substantially as and for the purpose hereinbefore set forth.

2. Extracting gold from its ores by subjecting the ores first to the action of an acid
and subsequently to the dissolving action of cyanide of an alkali or an alkaline earth in
the presence of an oxidizing agent, substantially as and for the purpose hereinbefore
set forth.

3. Extracting gold from its ores by subjecting the ores to the dissolving action ol
cyanide of an alkali or an alkaline earth in a ball-mill, substantially as and for the pur-
pose hereinbefore set forth.

4. Precipitating gold or other precious metals out of their solutions by means of
aluminium, aluminium alloys, or aluminium amalgam, in the presence of a free alkali,
substantially as hereinbefore described.

Dated August 31, 1893.

CARL MOLDENHAUBR.

PATENT-SPECIFICATIONS. 129

NEW ZEALAND PATENT OFFICE.

CARL MARIA PIELSTICKElf.

APPLICATION FOE LETTERS PATENT FOR IMPROVEMENTS IN THE EXTRACTION OF
GOLD AND SILVER FROM ORES.

I, Carl Maria Pielsticker, of No. 43 Connaught Road, Harlesden, in the county of Mid-
dlesex, England, engineer, do hereby declare the nature of my invention for Improve-
ments in the Extraction of Gold and Silver from Ores, and in what manner the same is
to be performed, to be particularly described and ascertained in and by the following
statement :

My invention has for its object the extraction of gold and silver, particularly from
sulphide, and from such ores in which the precious metals exist in a state of extremely
fine division, and it consists essentially in treating the powdered ore with a solution of
cyanide of potassium or a cyanide or cyanogen-yielding substance in conjunction with
an electric current, continuous circulation of the solvent, continuous precipitation of
the dissolved precious metals by electrolysis, and continuous regeneration of the solvent.

In carrying out my invention, I employ a tank, marked A on the accompanying
drawing, which I call the ore-tank, in which the ore is subjected to the treatment with
cyanide of potassium in conjunction with an electric current. About 3 inches from the
bottom I place a perforated plate, H, preferably of iron or carbon, covered with a porous
material, such as cocoanut matting. The plate H serves as anode, and is insoluble, or
practically so, in cyanide of potassium.

If made of iron, I prefer a highly carburetted iron, or ore containing a high percentage
of silicum. Near the top of the ore-tank I place a second perforated plate, G, which
serves as cathode. Both these plates are connected by means of insulated wires, e — e,
with a dynamo, D, or other source of electricity.

The ore-tank A is connected near its top by means of a pipe with a second tank, B, con-
taining a number of baffle plates, K, or their equivalent, which are destined to arrest any
suspended matter flowing over with the solution from the ore-tank, and which otherwise
would greatly interfere with the precipitation of the dissolved precious metals in the
following tank, C, connected with the tank B near the top by means of a pipe. The pre-
cipitating-tank C contains one or more pairs of electrodes, M and N, connected with the
dynamo D, or other source of electricity, by means of the insulated wires, g and gi, of
which the anode preferably consists of carbon or other material, insoluble, or practically
so, in cyanide of potassium. A pump P is connected with the ore-tank A under the
anode H on the one hand, and with the top of the depositing-tank C on the other hand,
enabling me to maintain a circulation of tne solvent througn the set of tanks.

In operating my invention, I fill the ore-tank A between the electrodes H and G with
powdered ore, and admit into the three tanks A, B, and C, a solution of cyanide of
potassium, filling them above the level of the pipes which connect one tank with the
other. The strength of the cyanide solution may vary, care being taken to have suffi-
cient cyanogen present to bring the gold and silver in the ore into the solution, the
amount of which has previously been ascertained by assay. I connect the electrodes H
and G in the ore-tank A, and ]M and N in the depositing-tank C, with the dynamo D, or
other source of electricity, and force the cyanide solution from below through the ore in
the tank A.

The solution pregnant with dissolved precious metals overflows into the settling-tank
B, where it clears itself from suspended matter, and becomes thus fit to part with the
dissolved precious metals on overflowing into the depositing-tank C, where the latter are
precipitated on the cathode, and from which they are recovered by amalgamation or
otherwise. The cyanide solution, freed from dissolved metals, and therefore in a better
condition to dissolve more metal than when loaded with metal in solution, is pumped
from the depositing-tank C, again through the ore in the tank A, where it dissolves a
fresh proportion of precious metals, and so on, continuously, until the precious metals
contained in the ore under treatment are dissolved.

In this manner my process becomes a continuous one, of dissolving the precious metals
from the ore, preparing the solution pregnant with dissolved metals for electrolysis by
separating continuously the suspended matter therefrom, precipitating continuously
the dissolved metals by electrolysis, and regenerating continuously the solvent for
further action on the undissolved precious metals still contained in the ore. Very little
of the precious metals are precipitated on the cathode G in the ore tank, as the amount
of the suspended matter present in the solution interferes with precipitation in this tank.

The electric current in the depositing-tank must be of lo.w tension, and so regulated
as to be of just sufficient strength to deposit the gold and silver without also decompos-
ing the cyanide of potassium ; the gold and silver, being more readily precipitated from
their double salts of cyanide of gold (or silver) and potassium than the cyanogen, is set
free from the simple salt of cyanide of potassium so long as the current of electricity
is sufficiently low in tension, and so long as there are metals present in the solution.

9cr

130 THE CYANIDE PROCESS.

The original solution can therefore be used over and over again for a long time, and
only the loss made good occasionally.

In practice I find that an electro-motive force of about one volt, and an intensitjr of
about ten amperes per square meter of surface of cathode, is well adapted for depositing
the gold and silver in the tank C. I may find it desirable to employ a current of elec-
tricity of greater potential in the ore-tank A and of lesser potential in the depositing-
tank 0.

The great advantage in treating ores with cyanide of potassium in conjunction with
an electric current lies in the fact that the precious metals are attacked by the cyanide
solution more energetically in conjunction with a current of electricity than without
one; furthei, when the dissolved precious metals are precipitated by means of an elec-
trical current and an insoluble anode very little cyanide and no metal is consumed, as
is the case when, for instance, zinc is used as a precipitant, when not only zinc is con-
sumed, but also cyanide of potassium in the formation of a double salt of cyanide of
zinc and potassium. Moreover, serious losses in gold and silver are occasioned in the
recovery of the precious metals from the zinc slimes, whereas nothing can be simpler
than their recovery from the cathode by amalgamation. Again, the precipitation of
gold and silver is greatly accelerated by the electric current.

When these metals are precipitated by zinc without a current of electricity, the latter
goes into solution as a double salt of cyanide of zinc and potassium, but the amount of
zinc which is converted into cyanide of zinc is directly proportionate to the time dur-
ing which it is in contact with the cyanide solution. Therefore, the more time is con-
sumed in precipitating the gold and silver, the more cyanide and the more zinc will be
wasted.

The cyanide process is most advantageously employed on ores in which either the
gold is so finelj' divided in a free state that it is difficult to retain it by older methods, or
for sulphide ores. Free gold is certainly more quickly dissolved by cyanide of potas-
sium in conjunction with an electrical current than without one. As regards pyritic
ores, if they are simply iron pyrites, as they are in a great number of cases, a cyanide of
potassium solution, whatever its strength may be, has as little action on them when
used in conjunction with an electric current of the strength I use as without one. only
the gold and silver in the ore are more quickly dissolved in conjunction with an elec-
trical current than without one.

If the ores contain sulphides, oxides, or carbonates, for instance, of coppei and zinc,
these are as easily dissolved by a cyanide of potassium solution, whether employed by
itself or in conjunction with an electric current such as 1 use. Such ores, however, I
prefer to treat first with, say, a 5 per cent sulphuric acid or other acid solution in water,
or a strong solution of sulphurous acid in water in sufficient quantity to dissolve such
metals, then leach with water, and then treat with the cyanide solution in conjunction
with the electric current.

I would have it understood that I do not limit myself to the precise details herein set
forth and illustrated on the drawing— for example, the number, nature, and position of
electrodes, of the sources of electricity, and of the number, shape, and position of the
tanks; all may be varied while retaining the construction and combinations for the
proper carrying out of my process of extraction of gold and silver from their ores;
further, I am aware that cyanide of potassium has been used in conjunction with an
electric current for like purposes, and I make no broad claim thereto.

Having now particularly described and ascertained the nature of my said invention,
and the manner in which the same is to be performed, I declare that what I claim is—

1. The process of separating gold and silver from their ores, which consists in treating
the powdered ore with a solution of cyanide of potassium in conjunction with an electric
current, depositing the precious metals constantly by means of a current of electricity
of low tension and electrodes, of which the positive one is insoluble in cyanide of potas-
sium, and bringing the cyanide of potassium solution thus freed from dissolved metals
constantly again into contact with the ore, whereby I obtain a continuous process of
extraction and precipitation, all substantially as herein described.

2. In the process of separating gold and silver from their ores by means of a solution
of cyanide of potassium in conjunction with an electric current, bringing the cyanide of
potassium solution freed from dissolved metals continuouslj'^ into contact with the ore,
substantially as described.

3. In the above-described process of separating gold and silver from ores by means of
a solution of cyanide of potassium in conjunction with an electric current, depositing
the dissolved metals by means of electrodes contained in depositing-tank or tanks,
an electric current being passed through the ore-tank and depositing-tank, substantially
as set forth.

4. In the above-described process of separating gold and silver from their ores by
means of a solution of cyanide of potassium in conjunction with an electric current,
treating the ore with an acid in combination with a subsequent treatment of cj'anide of
potassium in conjunction with an electric current and continuous circulation of the
solution, substantially as described.

5. In the above-described process of separating gold and silver from their ores by
means of a solution of cyanide of potassium in coni unction with an electric current,
subjecting the ore and solution in the ore-tank to an electric current of greater potential,
and depositing the dissolved metal in a depositing-tank by an electric current of lesser
potential, substantially as described.

PATENT-SPECIFICATIONS.

131

132 THE CYANIDE PROCESS.

6. In the above-described process of separating gold and silver from their ores in con-
j unction with an electric current, the use of a current of electricity of sufficient strength
to decompose the double salt of cyanide of gold or silver and potassium without decom-
posing the cyanide of potassium itself.

7. In the above-described process of separating the gold and silver from their ores in
conjunction with an electric current, the combination of an ore-tank with a settling-
tank and a depositing-tank, substantially as described.

CARL PIELSTICKER.
By W. H. Quick, His Agent.
Dated this 14th day of December, 1893.

PATENT-SPECIFICATIONS. 133

UNITED STATES PATENT OFFICE.

WILLIAM DAVID JOHNSTON, of San Francisco, California.

METHOD OF ABSTRACTING GOLD AND SILVER FROM THEIR SOLUTIONS IN POTAS-
SIUM CYANIDES.

Specification forming part of Letters Patent No. 522,260, dated July 3, 1894.
(Application filed November 20, 1893. Serial No. 491,473. No specimens.)

To all whom it may concern:

Be it known that I, William David Jolmston, a citizen of the United States, residing
in the City and County of San Francisco, State of California, have invented an Improve-
ment in Methods of Abstracting Gold and Silver from their Solutions in Potassium
Cyanide ; and I hereby declare the following to be a full, clear, and exact description of
the same :

Heretofore when solutions of gold and silver have been made in potassium cyanide,
the metals have been recovered from their solution by the use of zinc in various' forms.

The object of my invention is to recover the metals in a shorter time, and more eco-
nomically, by the use of pulverized carbon, preferably in the form of charcoal.

To carry my invention into effect, I take carbon in a pulverized form as above, and
place it upon suitable supports so as to form it into filters, through a series of which the
cyanide liquid is caused to pass successively, leaving the metal deposited upon the
carbon. The gold and silver are then recovered from the carbon by carefully burning
the carbon, and smelting the residue with the usual fluxes. By thus employing a series
of filters through which the solution is passed successively, I am able to recover upward
of 95 per cent of the precious metal contained in the solution.

When only one filter is employed, only about one fourth of the gold can be extracted.

Having thus described my invention, what I claim as new, and desire to secure by
Letters Patent, is —

1. The process of abstracting gold and silver from their solution in potassium cyanide,
consisting in passing the liquid through a series of carbon filters within which the gold
is arrested, suDstantially as described.

2. The process of abstracting gold and silver from their solution in potassium cyanide,
consisting in passing the liquid through a series of carbon filters within which the gold
is arrested, and then recovering the metal by burning the carbon and smelting the
residue with suitable fluxes, substantially as described.

In witness whereof I have hereunto set my hand.

WILLIAM DAVID JOHNSTON.
Witnesses:

S. H. NOUBSK.
H. F. ASCHBCK.

Note. — The patents, where the country is not mentioned, are to be
understood as being issued in Great Britain.

California _ go

Capacity, daily, of South African plants ..J "" 60

Cape Colony. _ V [."V.[ I 68

Carbonate of ammonia and cyanide " H

Cement tanks 22-61

MONTHLY ANALYSIS OF GOLD PRODUCTION IN THE WITWATERSRAND DISTRICT— APRIL, 1894.
Peepahid bi WITWATEKSKAND CHAMBER OF MINES. A. K. GoLDBms, Secretary.

, City and Suburban

. Crown Reef

. Durban Roodeport

. Dashwood Synaicate

. Ferreira

. Geldenhuis Estate -

I. Geldenhuis Main Reef

. Ginsberg _

. Glencairn

:. George Goch (amalgamated) .

. George and May. -

. Henry Nourse --

I. .Tohannesburg Pioneer

'. jubifee ."r;;;""."!'/';".";

. Knight's Tribute Syndicate . .

. Langlaagtc Estate

. Idnglaagt« Block 6

. Langlaagtc Royal

. Langlaagtc United

. Ltiipaarda Vlei Estate

. May Consolidated

. May I)eep L/evel-

32. NewHeriot ...

33. New Primrose .

34. New Chimes...

35. New Aurora Wi

36. New Blue Sky .

. Princess Estate ,

. Paarl Central

. Paarl Central (tailings)..

'. Kandfontein

. Robinson -.

. Salisbury

. Treasury
. United Mi
. Van Ryn Estate

Reef (Roodeport) .
Village Main Reef"!"'.'.*

. Worcester

. Wolhuter

Vogelstruisfonteii

Rand Central Ore Rednc

Rand Central Ore Reduction Co. .

Robinson Company

Received by banks from other sou:

Totals 237,213 2,376

799 10
1,234 7
2,212 16

1,262 13
1,120 6
1,817 18

26.81 3.72 111,716 14

Value of Yield.

9,770
S,959
24,756
11,716

14,300
12,531
2,863

6,179
3,760
6.455

2,918
4.622
8,187

10,192
19,205
7,101

6,045
5,646
10,319
11,086

MacArthur-F. .

Chlorination ..

From ConcentiatcB.

Yield of Gold.

Chlorination .

Value of Yield.

3,380
9,417

-MacArthur-F.
MacArthur-F. ,
MacArthur-F. .
MacArthui^F. .
MacArthur-F. ,
MacArthur-F.

MacArthur-F.
MacArthnr-F.
MacAithur-F.

MacArthur-F. .

MacArthur-F.
MacArthur-P.
MacArthur-F.
MacArthur-F.
Mac.\rthur-F.
MacArthur-F.

MacArthur-F.

MacArthur-P. .
MacArthur-F. .
MaoArthnr-F. .
MacArthur-F. .
MacArthur-F. .
MacArthur-F. .

MacArthur.F.
MacArthur-F.
MacArthur-F.
MacArthur-F.
MacArthur-F.

MacArthur-F. ,
MacArthur-F. .
MacArthur-F. ,

MacArthur-P. .
MacArthur-'F.".

7,915
1,300
2,910

6,651
19,416
1,320

Yield of Gold.

211,764 47,147 4.42

Value of Yield.

14,806
6,337
1,149

1 2 10
14 6
13 11
14 7

1,049
2,610
14,088

1,366
4,205
1,109

16 1
17 11
10 8
7 10
10 2

3,622 19

3,507 4

12,063

6,344 12

2,260 14
13,003 U
2,787 12

241 19

3,841 2

6,803

2,486 11

1,719

616 19

1,479 17

1,908 14

1,122

3,628 6

3,034 6

1,120 5

2,581 10

271 18

3,630 14

12,372 18

3,019

3,889 3

2,377 17

2,628 14

18,063
1,149
17,630

2,031
12,961
6,179
3,750

42,660
9,455
13,172

10,862
13,679
8,620
8,874

Coucentrales Produced
During the Month, f

Value
per Ton,

63.00 2.20

10.00 4.00

82.00
94.00
67.76

J. Falk, tributor.
25 per cent dividend.

Concentrates treated by Rand Central Ore Reduction Co.

Milling for five days in March included.

Tailings sold to Rand Central Ore Reduction Co. Concentrates to Robinson Co.

Tailings treated by Lace and Thompson.

Six days' milling in March included.

Concentrates sold to Rand Central Ore Reduction Co.

10 per cent dividend.
Alluvial from 5,304 loads.

Where the value of the gold i

In calCQlfttiDg the total averages, allowance is made for defecti'

10s. per oz. for mill gold, i

ubllBbed on the leBpoQaiblltty of the companies concerned.

Prom Mill 111,715

Prom Concentrates. 5,618

From Tailings 47,147

From Alluvial 142

From othersources. 4,121

Totals 168,745

£402,500
21,476
142,013

INDEX.

Page.

Absorption of cyanide by wood 28

Accidents in cyanide works... 45

Acidity ; 45

determination of 44

Advisability of tailings concentration. 50

Aeration of ore _. 50

Africa _ 5-46

African Gold Recovery Company 46-55

Agitation and filtration by tne same apparatus 21

Agitation process 20

advantages and disadvantages 20

time of ^ 20

Agitator at Utica Mine _ . . 90

of steel .'. 20

Alkali, action on the zinc 34-35

Alum, addition of, for bullion settling 34

Aluminium for bullion precipitation 40

Amount of cyanide solution used for tailings 25

Antidote to cyanide poisoning 46

Antimonial ores and cyanide 15-16

Antimony in zinc bullion 35

Arizona 87

Arrangement of plants 55

Arsenic in zinc bullion _. 35

Arsenides I5

Australasia 69

Australian Gold Recovery Company _ gi

Australian ores, cyanide experiments with n

Bagration, Prince Pierre 6 9

Banket '"] 45

Barrels for agitation 20

Barrett Company, South Africa 47-48

Barry [."l'[l[[[] 71

Bettel process 52

Black Hills, Gold and Silver Mining Company, South Dakota ..[-.-T. .'"! 87

Bohm process 76

Borneo .'../.. 95

Bottom discharge for tailings .1.'".. 59

Bright Star Mine, California ..... 88

Buckland, J. M. .........5-25-^6

Bullion, calcining process of 36-54

fineness of ........ 55

filter in Utica Mine ..... 92

fluxes ........ 37

left in slag... 1.1^1.1.11!!. 54

melting "l.."'.. 37

precipitation in Utica Mine ...111.1111111 91

precipitation by, zinc 111111111' 34

precipitation by charcoal 1. 1. "Villi 40

precipitation by lead 1!1.1111 33

pulverizer , 1111!! 1 37

refining by nitre 1!1!.!1111'! 54

refining by sulphuric acid . '"' 36

Butters, Chas... 1111111!!! 118^55-59-63

California gg

Capacity, daily, of South African plants ..."... ll!!! 60

Cape Colony lllllllllll! 68

Carbonate of ammonia and cyanide l.llllll n

Cement tanks 111!!!! 22-61

INDEX.

Page.

Absorption of cyanide by wood 28

Accidents in cyanide works... 45

Acidity ." 45

determination of 44

Advisability of tailings concentration... 50

Aeration of ore 50

Africa _ .. 5-46

African Gold Recovery Company 46-55

Agitation and filtration by the same apparatus 21

Agitation process _.. 20

advantages and disadvantages 20

time of - .- 20

Agitator at Utica Mine.-- - - . . 90

of steel - ■. 20

Alkali, action on the zinc _ 34-35

Alum, addition of, for bullion settling 34

Aluminium for bullion precipitation 40

Amount of cyanide solution used for tailings 25

Antidote to cyanide poisoning 46

Antimonial ores and cyanide 15-16

Antimony in zinc bullion 35

Arizona 87

Arrangement of plants 55

Arsenic in zinc bullion 35

Arsenides 15

Australasia 69

Australian Gold Recovery Company 81

Australian ores, cyanide experiments with 11

Bagration, Prince Pierre 6,9

Banket 46

Barrels for agitation 20

Barrett Company, South Africa 47^8

Barry 71

Bettel process 52

Black Hills, Gold and Silver Mining Company, South Dakota 87

Bohm process 76

Borneo 95

Bottom discharge for tailings 59

Bright Star Mine, California _ 88

Buckland, J. M ...5-35-46

Bullion, calcining process of 36-54

fineness of 55

filter in Utica Mine 92

fluxes 37

left in slag _ 54

melting _._ 37

precipitation in Utica Mine 91

precipitation by, zinc _ 34

precipitation by charcoal 40

precipitation by lead _ 33

pulverizer 37

refining by nitre 54

refining by sulphuric acid 36

Butters, Chas i8^55-5&-<33

California 88

Capacity, daily, of South African plants ...*... qq

Cape Colony 68

Carbonate of ammonia and cyanide 11

Cement tanks 22-61

136 INDEX.

Page.

Centrifugal agitator and separator ., 21

Champie's mine, Arizona 87

Charter's towers, Queensland 81

Chemistry of process . 6-16

Childs^ I. S 87

Chronic losses of bullion 42

Circulating system in Robinson works 25

Clark, T. C ...10-103

Cleaning up of bullion .. 34

Clenell 18-55

Coating of gold ores 15

iron and steel vats . 25

wooden vats ...- 25

Colorado ' 86

Colombia, Republic of. 95

Consumption of cyanide in Johannesburg 51

Consumption of zinc in Johannesburg 53

Con. Virginia and California Company _ 87

Copper compounds, refractory 15

cyanide, consumption by 16

Copper in gold precipitates 35

Cost of cyanide plants 43

in Johannesburg 55

Cost of cyanide treatment in Johannesburg 55

Cost of Utica plant 94

Crawford, J. J., State Mineralogist, California 5

Cripple Creek Gold Extraction and Power Company 86

ores 87

Cross James.. 94

Crown mine plant of Karangahake, N. Z. 69

Crown Reef Company, Johannesburg 55-60-62-65

Croydon, Queensland 81

Custom Mill, Government, Mt. Torrens, South Australia 81

Custom works in Johannesburg 68

Cyanide.. 28-30-51

process 5

application of, in South Africa 48

poisoning, treatment of 46

price of.- 30

returns in New Zealand.. 70

solutions -. '. 28-50

analysis of 29-44

determination of strength required 44

in the mortar boxes 28-48

strength of.. 28

volume of 29-65

Danger in working the process 45

De Kaapsehe District 47

Deep Down Mine, New Mexico 87

Demonstration of process 6-20

Determination of gold and silver in cyanide solution 44

Difficulties in percolating concentrates 28

Discharge of residues 56-61

Dividends, list of, in South Africa 65

Dixon, J - 6,11

Durban Roodeport Company's works 65

Effect of cyanide on wooden vats 28

Electric methods 38-40

Molloy 38

Pielsticker 40

Siemens & Halske ' 38

Electro-plating 9

Elkington, G. R. and H 6-9

Ellis, C.J ....9-14-126

Eisner, L. <>

Endlich, F. M :... 6-11

Errors in the estimate of extraction 53

Exemplification of the process 46

INDEX. 137

» Page.

Faraday 6-9

Faucett, H. W 10-104

Feldtmann, W. R 55-58

Ferreira Company 62-65

Ferricyanide and cyanide, Moldenhauer process 14

Ferrocyanide experiments &-11

Ferrocyanide for extracting gold and silver 9-11

Filling" and discharging of vats 26

Filter 79

Filter presses 21

Filter presses for slime treatment 52

Filtration by centrifugal force 21

Financial success of cyanide process in South Africa 60

Fineness of bullion in Crown Eeef Company.. 55

Nigel Company 55

Rooinson Company 55

Utica Company 43

Fineness of ore _ 22

Fitness of ore for cyanide treatment .; 96

examination for 44

Fisher, H. T 88

Forest, R.W. and W. ...6-12-110-115

Generation of hydrogen in the zinc boxes. 34

of hydrocyanic acid... 17

Gernet, A. von _ 39

Gmelin 35

Gold and Silver Extraction Company of America, Limited 84

Gold production of South Africa ._ 67

Gold Run Mine 88

Gold solutions, treatment of 30

Golden Reward works 88

Gordon, H. A. ..69-71-73

Greighton Mining and Milling Company, Georgia 88

Hagen 6-9

Halske. See Siemens & Halske •. 38

Hay ward, A 94

Hauraki gold fields, cyanide plants on the 69

Havilah, Kern County, California 88

Henderson Mountain Mining Company, Montana 85

Henry Nourse Company, JohannesDurg 62

History of process. 6-9

Hydraulic slime separator at Salisbury works 49

Iconoclast Mine, Cal... 89

Irvine, W. E 59

Janin, A 6-14-125

Janin, Louis, Jr 6-11-84

Johannesburg ores -. 46

Johnston, W. D. 5^14-40

Kendall, E. D 14-117

Kuaotunu gold field 76

Labor in cyanide works 68

Laboratory work 44

Lane, C. D 90

Langlaagte Estate Company 22-60-63-65

cement tanks 22

Royal Gold Mining Company 63

liebig's method of testing cyanide 29

138 INDEX.

Page.

Lime treatment, preliminary of ore 18-50

Loss of cyanide by absorption in vats and tanks 17-28

by action of carbonic acid. -. 17

by hydrolysis 17

gold in Johannesburg 52

zinc by galvanic action ..- 32

MacArthur, J. S 5-12-110-112-115-126

Machinery and appliances . - - 43

McLaurin 17

Mercur Mining and Milling Company, Utah _ 84

Mercury in zinc boxes 35

Merrill, C. W ..6-14-125

Methods of operation ... 20

Meyer and Charlton Company 62-65

Mexico - 95

Mineralogist, California, State 5

Mitchell Creek Gold Mine, New South Wales 81

Moldenhauer, Carl 14-40-127

Molloy, B. C -.6-13-38-118

Molloy process for bullion precipitation ^.. ... 38

Molloy separator ... 13

Montana 85

Montgomery, T. C 13-121

Moratock Mine, N. C... 88

Mortars with double discharge 22

Mt. Morgan Mine 15

Muffle furnace for bullion refining 36

Miihlenberger, N. H _ 6-11

Nevada --- - 87

New Golden Mountain Gold Mining Company, Victoria. 83

New Mexico 87

New South Wales . 81

New Zealand 69

Nigel Company ...49-53-55-63

Nitre for bullion refining in South Africa. 54

Number of plants in South Africa , . ... 48

Otis crusher. 71

Output, total, of Rand mines 65-66-87

Oxygen, action of, in cyanide treatment . 9

P
Patents 6

Patent royalty in New Zealand . 80

Paul, A. B 36-88

Percentage of extraction 40-52

in South Africa 41

in New Zealand 41-79

in United States of America 41

Percolation of concentrates - .- 28

ores .._- .- 22

tailings. _ --- .-- 24

process - - .... 20-22

Pielsticker, Carl M - - ....14-40-129

Plant in South Denver 86

Precipitation of bullion by aluminium 40

by charcoal 40

by electricity - 38-40

by zinc - - 34

Preliminary experiments .- 44

Primrose Company, Johannesburg 65

Profits of cyanide treatment in South Africa 65

Puzzler Gold Mining and Milling Company. 87

Q
Queensland ■ --- — 81

INDEX. 139

Page.

Radoe, W. A 53-55-60

Rae, Julio H ...6-9-101

Rand Central Ore Reduction Company 39-63

Rate of gold extraction at Utica Mine 94

Reactions, secondary 17

Recovery of bullion 30-53

Recovery ot bullion at Nigel Company 53

Reese Mill, Cal 89

Refractory ores, definition ot ._ 15

Residues, discharging of, by running cranes 26

sluicing out of--- 26

Returns per ton of tailings in Johannesburg -. 66

Revenue, jNIontana --. .._ 85

Revivification of cyanide 38

Robinson Company _.. 25-55-60

plant - 63

Rolls for dry-crushing - _- 42

Rose, R. ..- - _- - 71

Rotary distributor for mixing coarse and fine tailings - 49

Russia - - - -.. 94

Salisbury works, Johannesburg 28-49

Sanders, I. F ___ 106

Scheidel, Dr. A ..- 3^7-33^77-78-89-92

Scope of process 6-15

Screens for dry crushing 22

Selection of site for plant - 43

Shasta Gold Recovery Company 88

Sheba Mine -- - 47

Side discharge of tailings .-- - 48

Siemens and Kalske process - 38

Silver, precipitation by zinc 92

Simpson, Jerome W -.6^10-107

Slimes, deleterious to percolation - 52

Smith, Halford G __ 65

Soda treatment of ore 18

Sodium amalgam for bullion precipitation 38

Solubility of gold and silver in cyanide 9

South America .-. _ _ 95

South Australia -_ 81

South Dakota 87

Standard Mine, California .- _. 95

Stebbins and Porter... _ 88

Straits settlements _, 95

Strength of solution in Crown Reef works 61

Strength of solutions in Johannesburg 50

Strong solution leaching 50

Sulphates of alumina, action of on cyanide 1. 18

Sulphates of magnesia, action of on cyanide * is

Sulphides _ " 15

Sulphuric acid, preliminary treatment by ig

Summary and conclusions __ qq

Sylvia Mine, Tararu, New Zealand _ ...16-35-41-79

Tailings .. _ 24

channel formation in percolation - 24

mechanical difficulties in percolation "_ 25

shrinkage in vats " 25

Tasmania "" 80

Taylor, James - - ^_ 81

Te Komata Mine - ..11" 76

Tellurides "ll[""l[. 20

Tellurides in Cripple Greek - 1111 87

Time of treatment-- 1.111 25

Time required for percolation of concentrates 1... 111111 28

Total production by cyanide process ll_] 5

Trap doors at vats HH 26

Treatment of gold solutions —11.1111 30

ore and tailings pulp direct from the battery 111111 28

precipitates in Johannesburg H 54

140 INDEX.

Page.

Tryflnke Company, plant of - 76

Turner, F. B. and R. B. 85

Turner, J. K 86

United States oi America _._ 83

Utah 84

Utica Mining Company, Cal 7&-89

Vacuum filter, Scheidel's 21-79-90

at Utica Mine — -. 90

Value of cyanide gold in South Africa 60

Rand tailings 52

Vats of brick and cement 22-28-48

circular , 48

false bottoms of --. - 23

made of iron or steel. 22

made of wood - - - - --- 22

wooden, MacArthur construction 22

size of, in common use « 22

table giving dimensions and materials of ..-•. 27

Victoria -. .- - 83

Virginia Gold Mining Company, South Australia 81

Waihi Company, New Zealand 69-71

Waiorongomai Mines - 76

Watts, W.L - 88

Webber, G. E., Jr 51-53-55

Western Australia 8('

Witwatersrand gold fields 46

custom works 68

Worcester Works 39

Working costs of process 42

in Utica cyanide works, California --- 93

Wright, Dr 6-9

Zinc amalgam as precipitant - ..- 34

as precipitant -- - 30

box, MacArthur's description of .-- .-- 32

boxes, material of --- — 32

box, Scheidel's construction .♦ 32

dust as precipitant - - - 34

ferrocyanide of - 35

filter, A. B. Paul's ..-- 36

filters of earthenware and porcelain 35

final cleaning up of .- 34

for precipitation of bullion 53

loss of^ by alkali 19-54

precipitation of gold and silver, theory of -. 34

preparation of filiform --- 33

preparation of shavings 34

quality of, used for precipitation 32

THIS BOOK IS DUE ON THE LAST DATE
STAMPED BELOW

JUL

AN INITIAL FINE OF 25 CENTS

WILL BE ASSESSED FOR FAILURE TO RETURN THIS BOOK
ON THE DATE DUE. THE PENALTY WILL INCREASE TO
50 CENTS ON THE FOURTH DAY AND TO $1.00 ON THE
SEVENTH DAY OVERDUE.

HU ^^1981

JUN 1 9 1981

APR 3 1989
JUNi^9
JAN04199r

NOV 28 1389:!t5

RECEIVED
M07 2 ^ 1989
PHSYSCIUBRARy

APR OLW^l

RECaVEDj

MftR2« 1991

■fl

Book SIip-15H<-8,'57(,CS107s4)456

16)^P>9?

California. Dept. of
natural resources. Di-
vision of mines.

PHYSICAL
SCIENCES
LIBRARY

Call Number:

TN21;

A3
no, 5

Ttv2-4
C3

vno. ^

UNIVERSITY OF CALlFO««
DAVIS

164892