in the free as in certain combined states, came to be looked upon
as a powerful medicinal agent.
Occurrence.—Mercury occurs in nature chiefly in the form of a red sulphide, HgS, called cinnabar (q.v.), which, as a rule, is accompanied by more or less of the reguline metal—the latter being probably derived from the former by some secondary reaction. The most important mercury mines in Europe are those of Almaden in Spain and of Idria in Illyria; and in America those of California and Texas. Deposits also occur in Russia, the Bavarian palatinate, in Hungary, Italy, Transylvania, Bohemia, Mexico, Peru and in some other countries.
Mercury occurs in formations of all ages from the Archean to the Quaternary, and it has been found in both sedimentary and eruptive rocks of the most varied character, e.g. conglomerates, sandstones, shales, limestones, quartzites, slates, serpentines, crystalline schists, and eruptive rocks from the most acid to the most basic. It appears that nearly all known deposits occur along lines of continental uplift, where active shearing of the formations has occurred. Large deposits are seldom found in eruptive rocks, but generally near such formations or near active or extinct hot springs. The deposits are of many types, simple fissure veins being less usual than compound, reticulated or linked veins. Segregations and impregnations are very common. The form of the deposit seems to depend chiefly on the physical properties and structure of the enclosing rocks and the nature of the fissure systems that result from their disturbance. The principal ore is cinnabar, though metacinnabarite and native mercury are often abundant; the selenide (tiemannite), chloride, and iodide are rare. Of the associated heavy minerals, pyrite (or marcasite) is almost universal, and chalcopyrite, tetrahedrite, blende and realgar are frequent. Many deposits contain traces of gold and silver, and some deposits, as the Mercur in Utah, are more valuable for their gold than their mercury content. The usual gangue-forming minerals are quartz, dolomite, calcite, barite, fluorspar and various zeolites. Some form of bituminous matter is one of the most universal and intimate associates of cinnabar. Formerly quicksilver deposits were supposed to be formed by sublimation, but from a careful study of the California occurrences S. B. Christy was convinced as early as 1875 that this was unlikely, and that deposition from hot alkaline sulphide solutions was more probable. By treating the black mercuric sulphide with such solutions, hot and under pressure, he succeeded in producing artificial cinnabar and metacinnabarite. He also showed that the mineral water at the New Almaden mines, when charged with sulphydric acid and heated under pressure, was capable of effecting the same change, and that this method of production agreed better with all the facts than the sublimation theory. (See “Genesis of Cinnabar Deposits,” Amer. Jour. Science, xvii. 453.) The investigations of Dr G. F. Becker on the “Quicksilver Deposits of the Pacific” (U.S. Geol. Survey, Mon. xiii., 1888) established the correctness of these views beyond doubt.
Production.—At one time the world’s supply of mercury was almost entirely derived from the Almaden and Idrian mines; but now the greater proportion is produced in California and Texas, where cinnabar was used by the Indians as a pigment, and first turned to metallurgical purpose in 1845 by Castellero. In the United States mercury has also been found in Utah, Nevada, Oregon and Arizona. In the 16th century the Almaden and Idrian mines were practically the only producers of this metal; statistics of Almaden dating from 1564 and of Idria since 1525 are given in B. Neumann, Die Metalle (1904). Spain produced 1151 metric tons in 1870, and in 1889 its maximum of 1975 tons; since then it has, on the whole, been decreasing. The Austria-Hungary output steadily increased to about 550–600 tons at which it appears to remain. In 1887 Russia produced 64 tons, and has steadily improved. The United States output was over 1000 tons, in 1871, and declined to 800–900 in the period 1889–1892; it has since increased and surpassed the supply from Spain. The following table gives the production in various countries for selected years:—
| Spain. | United States. |
Russia. | Austria- Hungary. |
Italy. | Mexico. | Total (Metric Tons). | |
| 1901 | 754 | 1031 | 368 | 558 | 278 | 128 | 3120 |
| 1902 | 1425 | 1208 | 416 | 556 | 259 | 191 | 4056 |
| 1903 | 914 | 1288 | 362 | 567 | 314 | 188 | 3633 |
| 1904 | 1020 | 1192 | 393 | 581 | 357 | 1901 | 3733 |
| 1905 | 800 | 1043 | 318 | 564 | 370 | 1901 | 3285 |
1 Estimated.
Mercury is transported in steel bottles closed by a screw stopper; the Almaden and Idrian bottles contain 76 ℔; and until the 1st of June 1904, the Californian bottles contained 7612 ℔ of mercury; they now hold 75 ℔. From the smaller works the metal is sometimes sent out in sheepskin bags holding 55 ℔ of mercury.
Metallurgy.—Chemically speaking, the extraction of mercury from its ores is a simple matter. Metallic mercury is easily volatilized, and separated from the gangue, at temperatures far below redness, and cinnabar at a red heat is readily reduced to the metallic state by the action of iron or lime or atmospheric oxygen, the sulphur being eliminated, in the first case as iron sulphide, in the second as calcium sulphide and sulphate, in the third as sulphur dioxide. A close iron retort would at first suggest itself as the proper kind of apparatus for carrying out these operations, and this idea was, at one time, acted upon in a few small establishments—for instance, in that of Zweibrücken in the Palatinate, where lime was used as a decomposing agent; but the method has now been discarded. In all the large works the decomposition of the cinnabar is effected by the direct exposure of the ore to the oxidizing flame of a furnace, and the mercury vapour, which gets diffused through an immense mass of combustion gases, is recovered in more or less imperfect condensers.
With the exception of the massive deposits of Almaden in Spain and a few of those in California and Idria, cinnabar occurs in forms so disseminated as to make its mining very expensive. Rude hand-sorting of the ores is usually practised. Wet concentration has not been successful, because it necessitates ore crushing and extensive slime losses of the brittle cinnabar. As a rule low-grade ores can be roasted directly with less loss and expense. At Almaden in Spain the ores average from 5 to 7%, but in other parts of the world much poorer ores have to be treated. In California, in spite of the high cost of labour, improved furnaces enable ores containing not more than 12% to be mined and roasted at a profit.
The furnaces originally used at Almaden and Idria differ only in the condensing plant. The roasting was carried out in internally fired, vertical shafts of brickwork, and, at Almaden, the vapours were led through a series of bottles named aludels, so arranged that the neck of one entered the sole of the next; and at Idria the vapours were led into large brickwork chambers lined with cement, and there condensed. The aludel furnace, which was designed in 1633 by Lopez Saavedra Barba in Huancavelica, Peru (where cinnabar was discovered in 1566), and introduced at Almaden in 1646 by Bustamente, by whose name it is sometimes known, has now been entirely given up. The Idrian furnace was designed in 1787 by von Leithner; it was introduced at Almaden in 1800 by Larranaga, and used side by side with the aludel furnace. The crude mercury is purified by straining through dense linen or chamois leather bags.
The most important improvements in the metallurgy of mercury are the introduction of furnaces for treating coarse ores, and the replacement of the old discontinuous furnaces by those which work continuously. The most successful of these continuous furnaces was a modification of Count Rumford’s continuous lime-kiln. This furnace was introduced at New Almaden by J. B. Randol, the author of many improvements in the metallurgy of mercury. The success of the continuous coarse-ore furnace at New Almaden led Randol to attempt the continuous treatment of fine ores also, and the Huettner and Scott continuous fine-ore furnace, which was the result of these experiments solved the problem completely. It contains several vertical shafts in which the descending ore is retarded at will by inclined shelving, which causes it to be exposed to the flames as long as may be necessary to roast it thoroughly. The time of treatment is determined by the rapidity with which the roasted ore is withdrawn at the bottom. Several similar furnaces are in use, as the Knox and Osborne, the Livermore and the Cormak-Spirek. The fumes from the roasting furnaces are received in masonry chambers, usually provided with water-cooled pipes; from these they pass through earthenware pipes, and finally through others of wood and glass. Not all the yield is in liquid mercury; much of it is entangled in masses of soot that cover the condenser walls, and this is only recovered after much labour.
The conditions for effective condensation are: (1) The furnace gases should be well oxidized, to avoid the production of an excess of soot. Gas firing would meet this requirement better than the use of wood or coal. (2) The volume of permanent gases passing through the furnace should be reduced to a minimum consistently with complete oxidation. (3) The cross-section of the condensers should be sufficient to reduce the velocity of the escaping gases, and the surface large enough for cooling and for the adhesion of condensed mercury. The latter requirement is best provided for by hanging wooden aprons in the path of the cooled gases. (4) The temperature of the escaping gases should not exceed 15° to 20° C., but cooling below this temperature would not give any adequate return for the expense. Cooling by water is quicker, but more expensive than by air. Water sprays, acting directly on the fumes, have not given good results, on account of the difficulty of recovering “floured” quicksilver from the water. (5) The use of an artificial inward
draught is absolutely necessary to control the operation of the
