process employed was barrel chlorination similar to that employed in South Carolina and the Black Hills, South Dakota.

The cyanide process was introduced about the same time, the first mill having been built at Bodie in 1892. Another mill was built at Florence, in 1895, by the Metallic Extraction Company, which when completed had a capacity of 170 tons per day. From that time on there grew up a keen competition between the two processes, and from appearances the chlorination process seems to have gained the ascendency. Further, improved railroad facilities, connecting the mines with the low lands and valleys, where reduction works could be placed to an advantage, made it possible to build up large smelting centers, such as Colorado Springs and Florence, where the ores are treated under the most favorable circumstances. In 1899 there were four plants operating at Cripple Creek, while in 1903 there were three, which included two small mills for direct cyaniding.1

In 1904 the kind and distribution of the plants were as follows:

The combined capacity of these mills is over 2,200 tons, or about 800,000 tons per year, and therefore represents a larger tonnage than is produced in the district.

Although the charge for the two processes varies somewhat with the grade of the ore yet for 1904 it did not exceed $9 per ton for 3 to 5-ounce ore, the range being $5.50 to $9 for to 5-ounce ores, which also includes freight charges.2

The use of cynide of potassium as a solvent for gold had been known to chemists and metal workers for many years prior to its

1 Geology and Gold Deposits of the Cripple Creek District, Colorado. U. S. G. S., Professional Paper No. 54, pp. 138–139, 1906.

1 Geology and Gold Deposits of the Cripple Creek District, Colorado. U. S. G. S., Professional Paper No. 54, p. 39, 1906.

application to the extraction of values from ores. The adaptation of this solvent to the commercial treatment of ores was made by J. S. MacArthur in 1886.1

For an historical account of the cyanide process and its development the reader is referred to the following works."

We are especially interested in this connection with the introduction and development of the process in the United States.

Probably the first use to which potassium cyanide was put in the treatment of ores in the United States was the removal of the coatings from rusty gold, especially in pan amalgamation. It was also used at an early date in dressing the outside amalgamating plates in stamp mill work.

The following summary of the early work in the development of the cyanide process is given by C. E. Munroe, in his paper on the Cyanide Process: 3 "The first instance of an attempt to apply this solvent action of the cyanides to the extraction of precious metals from their ores or other bodies containing them appears in United States Patents 61866 and 62776, issued to Dr. Julio H. Rae, of Syracuse, N. Y., on February 5 and March 12, 1867. Dr. Rae claimed the use not only of potassium cyanide as a solvent for the precious metals in the ore, but also of an electric current in precipitating them from the solution, and of rotatory or movable electrodes. This was followed by United States Patent 229586, of July 6, 1880, to Thomas C. Clark, of Oakland, Cal., who roasted his ore to a red heat, and placed it, in this condition, in a cold bath containing salt, prussiate of potash, and caustic soda; United States Patent 236424, of January 11, 1881, to H. W. Faucett, of St. Louis, Mo., who subjected hot crushed ones, under pressure, to the action of sodium cyanide in solution; and United States Patent 244080, of July 12, 1881, to John F. Sanders, of Ogden, Utah, who treated his ore with potassium cyanide and glacial phosphoric acid.

"In 1884 Astley P. Price applied for British Patent 5125 for the use of zinc in a state of fine division in precipitating gold or silver from solutions containing them. On July 28, 1885, United States Patent 323222 was issued to Jerome W. Simpson, of Newark, N.J.,

1 Eng. and Min. Jour., Vol. 80, p. 241.

2 Histoire de Chemie, Vol. 1, p. 226, The Metallurgy of Gold, 1896, p. 378; The Art of Electro-Metallurgy, 1877, pp. 19-20; California State Bureau, Bull. No. 5, 1894, p. 9, and Special Rept. of the Census Office, Mines and Quarries, 1902, p. 595; Min. and Sci. Press, Vol. 95, pp. 655–657.

Special Rept. Census Office, Mines and Quarries, 1902, pp. 596-597.

covering the extraction of gold, silver, and copper from their ores by means of solutions containing potassium cyanide, ammonium carbonate, and sodium chloride, and the subsequent precipitation of the dissolved metals by means of pieces or plates of zinc suspended in the solution. A caveat for the use of cyanide was filed in the United States Patent Office by F. M. Endlich and N. W. Mühlenberger, during the same year, but was subsequently abandoned. At Park City, Utah, about the same time, Louis Janin, Jr., made experiments with cyanide in extracting silver and gold from ores, which led to his filing a caveat on May 1, 1886. He did not press this to an issue, but he published his results in the Engineering and Mining Journal,

W. A. Dixon, also made experiments with cyanide on Australian ores, and recorded his results in a paper read before the Royal Society of New South Wales. "

The development and application of the cyanide process in England and South Africa is given in the same paper as follows: 1

"The cyanide process acquired commercial value in 1887, when John S. MacArthur and W. Forrest, of Glasgow, Scotland, applied, on October 19, for their English patent covering the use of dilute solutions of cyanides in the extraction of the precious metals. Later they obtained a patent for the use of zinc as a precipitant in a particular state of subdivision.

"The commercial value of the cyanide process was demonstrated by the tests made on a large scale, with ore from the New Zealand Crown mine, in June and July, 1888. Commercial success dates from the introduction of the MacArthur-Forrest process, in 1890, in the Witwatersrand gold fields in South Africa, the first cyanide plant in the world for treating tailings having been erected at Johannesburg in April, 1890. In the Witwatersrand alone, at the end of 1891, there were 6 companies treating tailings by the cyanide process; at the end of 1892 there were 22, and at the end of 1893 there were 32, with a record of 143,500 tons per month treated. By the use of this process there were recovered in the Rand 286 ounces of gold in 1890, 34,862 ounces in 1891, 178,688 ounces in 1892, 330,510 ounces in 1893, 714,122 ounces in 1894, 753,490 ounces in 1895, and 703,704 ounces in 1896; the output then increased up to September, 1898, when the commencement of active hostilities in the Boer War interfered with the active workings of the mines." The cyanide process was first successfully and commercially employed in the United States in extracting gold from ores at the Mercur 1 Special Rept. Census Office, Mines and Quarries, 1902, p. 596.

mines, Utah, about 1891. The process was introduced by Captain J. R. De La Mar, owner of the properties.1

Experiments on Gold Hill mine ores, North Carolina, by Mr. Richard Eames in May, 1892, gave an extraction of 60 per cent of the assay value. During the summer of 1893 a 10-ton cyanide plant was in operation at the Moratock mine, North Carolina, but owing to the leanness of the ore it was discontinued. In the same year another plant was operating at the Gilmer mines, Goochland County, Virginia, but with apparently little success. At the Franklin mine, Georgia, work with the cyanide process preceded that of chlorination, and was successful as applied to the more or less oxidized ore of the dumps, but failed of economical extraction when applied to the fresh sulphides.

The Sawyer mine, Randolph County, North Carolina, was the scene of further cyanide work in 1895, but the work soon stopped owing to lack of results. Two other plants were installed in North Carolina during 1896; one at the Russell mine, the other at the Cabin Creek mine, but they did not pass the experimental stage in their operations.

The Hunt and Douglas process was installed at the Conrad Hill mine, North Carolina, in 1880, which consisted of treating roasted sulphides with a ferrous chloride solution, by which the copper was rendered a soluble chloride, being precipitated by scrap iron as metallic cement.

The Designolle process, by which roasted ore was treated with corrosive sublimate in iron vessels, was only partially successful owing to the formation of base bullion, the iron of the containing vessel precipitating the soluble salts resulting from roasting. This process was applied to the ores of Charlotte, North Carolina, during 1882-83; also at the New Discovery mine, Rowan County, North Carolina, in 1883; and at the Haile mine, South Carolina, in 1883.

Another plant for extracting the gold from sulphurets (concentrates) together with the recovery of sulphuric acid was installed at Blacksburg, South Carolina. In connection with this process was a Walker-Carter muffle furnace and lead chambers. The oxidized ores being treated in turn by the Caloric Reduction Company's process, which consisted of volatilization of mercury through the mass of the ore followed by a condensation of the same. The pro

cess never attained any success and was abandoned. The so-called Eng. and Min. Jour., Vol. 68, p. 754.

Phelps process was similar to the last mentioned, being tried without success in 1877 at Philadelphia, on North Carolina ores. 1

Probably the first successful application of the cyanide process to low-grade Southern ores was at the plant of the Colossus Gold Mining and Milling Company in 1904.2

The Cyanide process was established at Bodie and the SmugglerUnion mines, Colorado, in 1892 and 1902, respectively. A mill was built at Florence in 1895. There were four cyanide plants at Cripple Creek in 1899, similarly in 1903, three of the four in the latter case being direct acting.3

According to the Report of the Director of the Mint for the calendar year 1901, there were eleven cyanide plants in active operation in South Dakota which had a capacity aggregating over 1,500 tons daily.'

METHODS OF EXTRACTION.

It is obviously impossible in a work of this character and scope to more than outline the methods and processes employed in the treatment of ores and the extraction of the contained values. But, owing to the fine spirit of coöperation exhibited by the experienced and highly skilled engineers of all countries our technical literature has been enriched by elaborate and painstaking descriptions of the various operations of extraction, which may serve equally well as a guide to those who wish to follow after or deviate somewhat from the beaten path of practice. It is from such sources that much of the information found in the following pages has been derived. Extracts of papers descriptive of the various typical operations which have been successfully applied to certain ores under fixed conditions are given, the selection and arrangement of which have been made with an idea more for brevity and clearness than technical detail.

MILLING.

Reduction. In the treatment of certain ores, either owing to the fineness of dissemination of the useful mineral or metal, or to its being chemically combined, it is obviously necessary to reduce the

1

1 U. S. G. S., 20 Ann. Rept., Pt. 6, pp. 121–122, 1898–99.

2 Min. and Sci. Press, Vol. 88, p. 146.

U. S. G. S., Professional paper No. 54, pp. 138-139, 1906.

Special Rept. Office of the Census Bureau, Mines and Quarries, 1902, p. 602, and Production of the Precious Metals during 1901, p. 201, 1902.