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of iron. The iron in the clay iron stones is generally in this form. See Iron, Metallurgy Of.

Side-saddle Flower. See Pitcher Plant.

Sidgwiek, Henry. LL.D.. D.C.L.. b.1838. Prof. Cambridge 1883. Methods of Ethics, 1874; Political Economy, 1883; Hist. Ethics, 1886; Politics, 1891.

Sidmouth, Henry Addington, Viscount, 1757-1844. M.P. 1783; Speaker 1789-1801; Premier 1801-4; Viscount 1805; Privy Seal 1806-7; Home Sec. 1812-21; reactionary.

Sidney, or Sydney, Algernon, 1622-1683. Officer in Parliamentary army; Gov. of Dublin 1646; a judge at the trial of Charles I. 1648; member of Long Parliament, of Council of State, and Ambassador to Denmark 1659: in exile until 1677; charged with high treason (Rye House Plot) 1683, and beheaded Dec. 7. Discourses concerning Government, 1698.

Sidney, Sir Philip, 1554-1586. English poot and courtier, admired and remembered not more for his gifts and accomplishments than for the beauty of his character; knighted 1583; mortally wounded at Zutphen, fighting for Dutch liberty. His romance, ^lrcadin, Defense of Poesy, sonnets, psalm versions, and songs appeared posthumously, and were collected

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by which it was eclipsed; famed for its maritime power and for the manufacture of glass: conquered by Cyrus ab.537 B.C.; taken from the pasha of Egvpt bv Turkey, aided by British ships, Sept. 1840.

Sldonius Apollinaris, ab.430-483. Son-in-law of the Emperor Avitus; Bp. of Clermont 472; author of panegyrics, epithalamiums, and letters.

Sidra, Gulf Of. See Syrtis.

Siebcngeblrge. Seven mountains in Rhenish Prussia on the right bank of the Rhine 20 m. above Cologne. The highest is Olberg, 1,522 ft., and the most famous DrachenFels (q.v.).

Siebold, Philipp Franz Von. 1796-1866. German botanist, in Japan 1823-30; Dutch Baron 1831. Flora Japonica, 1835-44. — His brother, Karl Theodor Ernst, 1804-1S85, prof. Munich 1853, wrote on natural history. Invertebrata, tr. 1857.

Siege. Operations of placing an army before a military

f>osition and attempting its capture by the method of regtiar approaches. Lines of circum- and counter- vallation are first established as a security against sorties from the besieged atui attacks from the enemy's forces from without. After the investment is complete and depots are established the first parallel is constructed. This is a line of intrenchment of sufficient extent to embrace at least the capitals of the two salients adjacent to that of attack. At least three parallels are required, although there are instances of five or more having become necessary: the first should be beyond the destructive cannon range of the besieged, the second at the limit of the dangerous zone of small-arm fire, and the third where the full protection of the double sap is needed to protect the sappers from the direct front and slant lire of the infantry. Connecting the parallels and advancing upon the capitals are the zigzags or boyaux, by means of which the besiegers are enabled to gain ground toward the fortified place.

Siege Artillery. Pieces of heavier weight and greater caliber than those required for field service: designed to batter

down the permanent defenses of a fortified place, and to destroy or dismount its armament. These are, in the U. S. service. 5-in. and 7-in. steel breech-loading rifles and 7-in. steel mortars, weighing 3,660. 3,710, anil 1,715 lbs. respectively; the projectiles for them weigh 45, 105, and 125 lbs. respectively.

Siege Carriages. The 5-in. gun and 7-in. howitzer carriages are mounted on wheels and when united to their limbers form wheeled carriages. When in place the carriage is connected with platform by hydraulic buffers to check recoil. The mortar carriage is not wheeled; when in position it rests on three traverse circles to obtain the proper azimuth for firing, and its recoil is checked by hydraulic buffers and coiled springs inclosed in a strong case.

Siegfried. See Nibelungenlied.

Siemens, Sir William. F.R.S.. 1823-1883. German engineer and electrician, in England from 1844. His greatest invention is the regenerative gas furnace, invented with his brother Friedrich 1857, and first successfully applied 1861. In 1862 he took up making steel by fusing malleable iron with cast-iron, and after several years perfected the Siemens' steel process. He was one of the earliest workers at the electric light, designed the steamer Faraday, which laid the lirst transatlantic cable, devised an electric furnace, an electric pyrometer, a direct process of making iron and steel from their ores, and a regenerative gas-burner.—His brother Ernst Werner, 18161892, shared in several of his inventions.

Siena, Guido Da, 13th cent. Italian painter.

Slenkiewiez, Henryk, b.1845. Polish novelist: ed. Slowo, 1880. With Fire and Sirord. 1884. The Deluge, 1890, and Pan Michael, tr. 1894, form a long historical romance of great power. Pisma, 1880; Without Dogma, tr. 1894; Quo Vadis, tr. 1897.

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1555; held by Florence from 1557; once an important art center; noted for its duomo or cathedral. Its univ. was founded 1203. Pop. ab.28,000.

Sierra. Applied to a range of mountains in Spanishspeaking countries.

Sierra Leone, British colony on w. coast of Africn, w. of Liberia; area ab.lS.OOOsq. m. Along the shore the land is low and unhealthy, rising inland into hills. The rainfall reaches 170 in. annually. Pop.. 1890, 75.000, including 224 whites, the balance negroes, one-half of whom are the descendants of liberated slaves.

Sierra .Yladre. Mountain range of w. Mexico, extending from the U. S. border to Guadalaxara, ab.300 m.; height seldom over 10,000 ft.

Sierra lllorena. Mountain range of s. Spain, separating the basins of the rivers Guadiana and Guadalquivir. The highest summit, Aracena, is ab. 5,500 ft. above sea.

Sierra Nevada. 1. Range of s. Spain, s. of the Guadal1390


quivir; greatest altitude 11,660 ft. 2. Principal range of Cal. It extends along: most of the e. border, with long spurs descending w. to the valley of Cal., and a short precipitous descent e. Its height increases s., and reaches its maximum in Mt. Whitney, near its s. end, 14,898 ft.

Sieve-Cells. Elongated cells of the fibro-vascular system of plants, characterized by their walls being finely perforated in certain well-defined panels or plates, called sieve-plates; also known as cribrose-cells and sieve-tubes.

Sieveking, Amalie, 1794-1859. Founder of a nursing sisterhood at Hamburg 1832, nucleus and model of others throughout Germany.

Sievcrs, Eduard, b.1850. Prof. Jena 1876, Tubingen 1883, Halle 1887, and Leipzig 1892; prolific writer on philology. Anglo-Saxon Grammar, 1881, tr. 1887.

Sievcrshausen. Near Hanover; scene of a defeat of Albert of Culmbach, 1553, by the imperial troops under Maurice of Saxony, who was slain.

Sieve-Tubes. See Sieve-cells.

Sieves, Emmanuel Joseph, 1748-1836. French priest, who, by pamphlets on human rights and the Third Estate, 1788-89, profoundly influenced the early course of the Revolution; Deputy 1789; one of the Directory 1799, and of the three Consuls.


Emmanuel Joseph Sieves.

having planned the movement of 18th Brumaire with Bonaparte, who made him a count. Thinker rather than politician, the servant of fixed ideas, he bore no part in the Reign of Terror, lived in retirement under Napoleon, and was in exile 1815-30.

Sigel, Franz, b. 1824. Leader in German insurrections 1848-49; in America from 1852; Brig.-gen. U. S. Vols. 1861, Major-gen. 1862-65; prominent in Mo. and Va.; journalist, lecturer, and official in New York since 1867.

Sighing. Deep and long-drawn inspiration chiefly through the nose, followed by a somewhat shorter, but correspondingly large, and audible expiration; it is manifested frequently during profound mental impressions, as of grief.

Sight. Sensations Of. Changes of consciousness aroused by stimulation of the retina of the eye; of two distinct kinds, sensations of light, supposed to be due to rapid vibrations of luminous ether, and of color, due to differences in rapidity of vibration. Sight is probably the most presentative of all the senses by which we acquire direct knowledge of the external world. See Eye, After Images, Color, Color-blindness, Double Images, and Horopter.

Sights. Attachments used for pointing a gun. The front sight is a fixed point, a thin edge, or cross wires in a protecting tube: the rear sight consists of a rod, bar or standard, graduat"d in degrees or ranges, fixed in a socket on the breech of the gun corresponding in position with the front sight. It carries a sliding notch or small aperture which can be adjusted

to any height corresponding to a given range or elevation: the notch has also a motion at right angles to the rod to correct for drift, wind velocity, or other causes of lateral deflection. The sights used in small arms consist of a fixed point of metal for the front sight and agraduated metal leaf carrying a notch arranged for adjustment for all ranges.

Sigillaria. Genus of extinct Lepidodendreje (q.v.).

Sigillum Confessionis. Seal of confession. In R. C. Ch., the obligation of a confessor not to divulge the secrets of the confessional.

Sigismund, 1368-1437. German emperor from 1411; son of Charles IV.; King of Hungary 1387: defeated at Nicopolis, by the Turks, 1390; imprisoned by the usurper Ladislaus of Naples, 1401-3. He convoked the Council of Constance 1414: consented to the condemnation of Huss. in- violation of his own safe-conduct; sold Brandenburg to Frederic of Zollern, and defeated the Turks. 1416 and 1419. His succession to the Bohemian throne, 1419. was successfully resisted by the Hussites (q.v.), but obtained 1436, by concessions to the Calixtines, which he afterward withdrew. His death averted civil war. He did little for the empire.

Sigismund I., 1466-1.548. King of Poland from 1507; able and prosperous ruler, patron of letters and of the Refi ormation.— II. (augustus), 1520-1572, his son and worthy successor.—III., 1566-1632; his nephew, King of Poland 1587, and of Sweden 1592-1604. His reign was warlike and injurious.

Slginaringen. See Hohenzollern.

Sigmoid. In Botany and Geology, S-shaped structures.

Slgnay. Joseph, D.D., 1778-1850. Bp. of Quebec 1833; Abp. of the province 1844.

Sign. Symbol of operation, direction, character, relation, as distinguished from symbols of quantity or mere abbreviations.

Signal Code. Signals by means of which messages maybe sent in the presence of the enemy without being intelligible to them. The code is usually based upon a small number of elementary signals; that of the army is one of three elements, a motion to the right, one to the left, and a forward motion. The first two signals, designated 1 and 2, may by combination give all the letters of the alphabet and the third designate the completion of a word or sentence. The code may be transmitted by flags, torches, semaphores or telegraph. The signals are interpreted by a signal book.

Signal Service. Organization for display of signals for any purpose; especially, meteorological branch of office of Chief Signal Officer U.S.A., the military duties of which were imposed on it 1862: the meteorological work was added in February 1870. The chief is by law a brig.-gen. The chiefs have been: A. J. Meyer 1862-80; Wm. B. Hazen 1880-87: A. W. Greely, since 1887. The meteorologists have been: Wm. Ferrel, 1881-87, Cleveland Abbe, since 1871. By act of Congress all the meteorological duties of this service were July 1, 1891, transferred to the new weather bureau of the Department of Agriculture.

Signature. In Printing, the figure or letter at the lower part of the first page of a sheet, intended to facilitate the gathering of the sheets for binding them.—Also the sheet when folded ready to gather.

Signature of Plants. In early medicine, a belief that the external formation or color of plants indicated that they were adapted for particular diseases; as Lungwort and Liverwort.

Sign Boards. House signs were indispensable in city life when few could read and write. As education spread, they

] were less needed, and when the system of numbering houses was introduced in the last century, their original value lin

| gered on, usually as business advertisements. Sign boards

I appear to have been adopted from the Romans, examples of whose pictorial signs have been excavated at Herculaneum.

I See Shop Signs.

Signet. In England, the king's seal, used in sealing his private letters, and all such grants as pass his majesty's hand by bill signed.

Significant Figures. In Arithmetic, those having quantitative value; distinguished from zero and other symbols of position in the scale.

Sign Language. See Deaf Mutes.

Sign Manual, Royal. The signature or subscription of the king or queen is termed the sign manual. This is done

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chapel. His great work is the series of frescoes in the chapel of the cathedral of Orvieto painted after 1499. In painting them he was assisted by his pupil Girolamo Genga.

Sigourney, Lydia Howard (huntley). 1701-1865. American poet, once very popular. Letters of Life, 1866.

Slgucnza j Gongora, Carlos, 1645-1700. Mexican author.

Slgwart, Christoph Von. Ph.D.. b.1880. Prof. Tubingen 1863. Logic, 1873-78, tr. 1804.

Sikcs, William Wirt, 1836-1883. U. S. Consul at Cardiff from 1876; journalist and author.—His wife, Olive (logan), b. 1841, m. 1871, is an actress and writer.

Sikhs. Sect in India, rejecting idolatry and caste distinctions, and infusing much of Buddhism and Mohammedanism into Hinduism; founded by Nanak, a Hindu, 1469-1538. They became a great military power in the 18th century; but submitted to the English 1848, when the Punjab was annexed to the British empire, and furnish ab. 14,000 soldiers to the British army.

Silage. Fodder material preserved in the fresh state in a silo by the process of Ensilage (q.v.). It usually takes also the name of the fodder so preserved: e.g., corn silage, clover silage. The former is the best silage plant in America.

Silcnus. Satyr, companion and instructor of Bacchus; gifted with the power of prophecy; represented as a fat, bald, jovial, old man, intoxicated, and often riding on an ass.

Silesia. S.e. province of Prussia; early occupied by German tribes, succeeded, as they moved w., by Slavs: joined, successively, to Moravia, Bohemia, and Poland; separated from Poland 1163, but ruled by dukes of the Piast line, who encouraged German colonies; then held by Bohemia, and thus connected with Germany. An agreement of succession, made 1587, made Prussia heir to parts of it; but Austria seized them as a lapsed fief of Bohemia, the remaining portions having previously fallen to her. This claim was resisted by Frederick II., and after the Seven Years' War (q.v.), Silesia was ceded, 1763, to Prussia. Capital Breslau. Area 15,557 sq. m.; pop., 1890, 4,224.458.

Silesia. Austrian. Duchy and crown-land in the n.e. of Moravia; province of Austrian empire. Area 1,987 sq. ni.; pop., 1890, 602.117.

Silcslus, Angelus. See Scheffler, J.

Silcx. See Silica.

Silhouette. Profile drawn in black, the shadows and extreme depths being indicated by the heightening effect of gum

or some other shining material; named from Etienne de Silhouette, 1709-1767, French Minister of Finance 1759, and noted


Silhouette Portraits.

for reforms in the interest of economy. SilhouetU s were known to the ancients, as is shown on vases.

Silica. SiO,. Chemical compound consisting of silicon and oxygen, occurring in nature by itself in the three forms of quartz, opal, and tridymite, and in combination with various bases in the class of minerals known as silicates; made by melting sand with sodium carbonate, and treating with hydrochloric acid; insoluble in water and the ordinary acids, soluble in alkalies and hydrofluoric acid; fusible with difficulty; found in plants, straw, and eggs; used extensively in the manufacture of glass and porcelain.

Silicate Cotton. This was first made by a steam-blast on a stream of melted slag; invented by John Player, of England, as made at the present. Owing to sulphur in furnace slags, which when wetted would corrode iron, rocks are fused and treated in the same manner, 4 parts of orthoclase with 6 parts of dolomite. It is usually white, and is used as a nonconductor to prevent freezing of water pipes, cooling of steam pipes and dampness in buildings, to keep out vermin, and to prevent the spread of fire, it being non-combustible. It came into general use 1871. It occurs in nature as Pele's Hair (q.v.).

Silicates. Derivatives of silicic or. of the polysilicic acids; family of minerals, numbering several hundred species, consisting of silicon and oxygen, combined in many different proportions with aluminium, calcium, magnesium, sodium, potassium, iron, and many other chemical elements. Except sandstones and limestones, almost all the common rocks are made up to a large extent of silicates.

Silicic Acids. These are numerous. All may be regarded as derived from normal silicic acid, Si(OH)4. The simplest form is H^SiO,, made by decomposing a silicate in solution with dilute hydrochloric acid. When the solution is evaporated to dryness, the residue is no longer soluble. Disilicic acid, H^Si,05, is derived from two molecules of the ordinary form by abstracting one molecule of water; trisilicic acid, H»Si,Oio, from three molecules of the ordinary acid by abstracting two molecules of water. Other trisilicic acids are derived in a similar way. Many minerals are derivatives of some form of silicic acid.

Silicide of Carlton. See Cakborundum.

Silicifled Wood. Wood in which the organic matter has been removed and its place taken by silica, usually in the form of agate (agatized wood), or of opal. Tree trunks, three or four feet in diameter or more, have been found in considerable quantity in the silicifled condition in Arizona and elsewhere. When polished, these masses exhibit a beautiful variety of colors. See Petrified Wood.

Silicic. Short form of the fruit called a silique, found in

Peppergrass, Shepherd's Purse, and other plants of the Mustard family.

Silicon. Si. At.wt. 28.4, sp. gr. 2.49, sp. ht. .167, Valence IV.; discovered by Berzelius 1823. Next to oxygen it is the 1392


chief constituent of the earth's crust, probably one-fourth. It occurs in crystallized and amorphous forms. The former may be made by fusing potassium fluosilicate with sodium and zinc. As a brown amorphous powder, it is obtained by passing the vapor of silicon tetrachloride over heated sodium. Amorphous silicon is not dissolved by sulphuric or nitric acids, but is readily soluble in hydrofluoric acid and potassium hydroxide.

Silicon Bromoform. SiHBr,. Colorless liquid, spontaneously inflammable in the air; bpt. 115°-117° C; sp. gr. 2.7; formed by treating silicon chloroform with hydrobromic acid; analogous to bromoform, CHBr,.

Silicon Carbide. SiC. Transparent, rhombic tablets, of brilliant luster, not soluble in the common acids; decomposed by fusion with caustic alkalies; hardness 9.5, sp. gr. 8.22; made by treating silica with carbon at a temperature of ab. 3,500°C.; used for polishing purposes and for the manufacture of polishing apparatus. See Carborundum.

Silicon Chloroform. SiHCU. Colorless, mobile, fuming liquid of a strong odor, very inflammable and unstable; so called on account of its compositional resemblance to chloroform.

Silicon Hexabromide. Si,Br„. Liquid boiling at 240° C. It forms a white substance with water, and is made by the action of bromine upon silicon hexiodide dissolved in carbon disulphide.

Silicon Hexachlorldc. SiaCl„. Colorless, mobile, fuming liquid; bpt. 146°-148°C. It solidifies at 14° to large white leaf-like crystals. It is made by passing the tetrachloride over • fused silicon.

Silicon Ilexiodiile. 8i,I,. Colorless, doubly refracting prisms or rhombohedra; nipt. 250° C. (in vacuum); made by heating the tetraiodide with finely divided silver to 290°-300°C.

Silicon Hydride. 8iH4. Colorless gas, made by treating a compound of magnesium and silicon with hydrochloric acid. Prepared in this way. it takes fire in the air.

Silicon Iodoform. Si III,. Colorless, strongly refractive liquid; bpt. 220° C. sp. gr. 3.36; made by passing hydriodic acid gas over heated silicon.

Silicon Tclrabromide. SiBr4. Colorless, fuming liquid; bpt. 149° C, sp. gr. 2.81; made by heating the elements together.

Silicon Tetrachloride. SiCl4. Acrid, fuming, colorless liquid, made by passing chlorine over a strongly heated mixture of silica and charcoal; decomposed by water.

Silicon Tetrafliioride. SiF,. Strongly fuming, colorless gas of a pungent odor, made by treating calcium fluoride and silica with sulphuric acid.

Silicon Tetraiodide. Sil,. Colorless, transparent, regular octahedra, isomorphous with carbon tetraiodide; mpt. 120.5° C, bpt. 290° C; made by passing iodine vapors over heated silicon.

SilicoMkelcta. Sub-class of Radiolaria, including the orders Peripyl.ea, Monopyl^ea, and Ph^eodaria (q.v.).

Siliculo§a. Order of the Linnaean class Tetradynamia, including those cruciferous plants which bear short round pods called silicles.

Silique. Two-valved, capsular fruit, each valve having a parietal placenta, from which the valves break away wiien mature, as in many plants of the Mustard family.

Sillquosa?. Order of the Linnaaan class Tetradynamia, including those cruciferous plants which bear elongated, slender pods called siliques.

Sllistrla. Town of Bulgaria on the Danube; besieged in

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sians 1854 and many times assaulted in vain. June 15th the garrison assumed the offensive, crossed the river, defeated the Russians, destroyed the siege works, and raised the siege. Its principal redoubt was ordered to be destroyed by the Congress of Berlin, 1878. Pop., 1893, 11,710.

Siliu§ Itallcus, 25-101. Latin epic poet, Consul 69. His Puniea, in 17 books, describing the second Punic war, is extant. His meter is good, but the work is too close an imitation of Virgil and Homer to claim much originality.

Silk. Fine, lustrous fiber produced by the larvae of certain moths, the best by the Silkworm (see BOMBYCINA), an annual, and a native of China. The moth is white, about 1 in. long, and lays many eggs, as large as mustard seeds. About six weeks after hatching the worm begins to spin the cocoon, which is completed in a week. The worm is 8} in. long, of a cream color, and feeds on white-mulberry leaves. The silk is produced by the two glands opening in the underlip. The cocoon is egg-shaped, and about li in. long. An equal number of male and female cocoons are selected for breeding, the latter being the larger, and placed in a room ab. 70° F., when the moth develops, lavs its eggs, and dies. The diseases of the silkworm are muscadine, due to a fungus, and pebrine and flacherie, due to bacteria; they have entailed great losses on silk growers. Pasteur suggested remedies, which have been largely efficacious. The remainder of the cocoons are placed in hot water or an oven to kill the chrysalis. The fiber is as fine as jlxs in. diameter, each cocoon yielding ab. 300 yds. The outer floss silk is separated, the cocoons floated in hot water and the silk reeled off, 2 to6 cocoons being run into one thread. The cocoons yield ab. 10 per cent of raw silk. The raw silk contains up to 25 per cent of gum. which is removed by boiling with soap. The silk is used in the raw and in the boiled state, several threads being twisted into one. It is dyed in the thread, or in the piece after weaving. The fabrics are often loaded with tannic acid and metallic salts in the dyeing to increase their weight. The world's annual production of raw silk is estimated at 30.000,000 lbs., China and Japan furnishing onehalf, Italy one-third, and France, the Levant and India the balance. The annual silk manufactures of the world are valued at $320,000,000, of which $120,000,000 are by France, $80,000,000 by the U. S.. Switzerland and Germany each $20,000,000, and England $5,000,000; Japan also largely manufactures. In 1896 there was imported into the U. S. silk manufactures valued at $26,652,768, and unmanufactured silk valued at $26,753,428. The price of raw silk in New York, Jan. 1898, was from $2.25 to $4.50 per lb. Good silk, rated as No. 1, was from $3.50 for Japanese to $3.90 for Piedmont, Italian.

Silk. In Botany, long styles of the flowers in an ear of maize.

Silk-Cotton Trees. Of the Mallow family, of the genera Bombax, Pachira and Eriodendron, natives of tropical Asia and America, bearing very large flowers and seeds provided with long, silky hairs.

Sllkweed. See Milkweed.

Silkwor m. See Bombycina.

Silkworm Out. Material prepared in Italy and Sicily, and used by anglers for dressing the hook end of a fishingline. The worms, about to begin spinning, are immersed in vinegar for ab.12 hours, when they are pulled apart, exposing two transparent yellowish-green cords, which are stretched on a board to dry.

SHI. In Mining, horizontal piece of timber laid to support the vertical or inclined legs of a set of timbers.

Sill,Edward Rowland, 1841-1887. Prof. Univ. Cal. 1874-82; poet.

Sill, Joshua Woodrow, U.S.A., 1831-1862. Brig.-gen. U. S. Vols.; killed at Murfreesboro.

Sillery. Village near Rheims, France, famous for its champagne. Pop. 400.

Silllman, Benjamin, M.D., LL.D., 1779-1864. Prof, of Chemistry at Yale 1802-53: founder of its museum of geology, and of the American Journal of Science and Arts, 1818; eminent as a phvsicist and geologist. Chemistry, 1830.—His son. BENJAMIN, M.D., LL.D.. 1816-1885, was Prof. Yale from 1846. co-editor Journal of Science from 1845, and author of several text-books and many monographs.

Sillimanlte. Al,Si06. Aluminium silicate, commonly found as an accessory ingredient in several kinds of metaniorphic rock; also called flbrolite.

Silo. See Ensilage and Silage.

Siloam. Fountain and pool of Jerusalem, connecting with a second pool by an aqueduct, mentioned in O. T. and

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Pool of Siloam.

a tunnel from a spring to the pool. In 1889 a second conduit was discovered 20 ft. below the ground.

Silt. Fine, impalpable mud collecting in lakes and estuaries; often all calm and gradual deposits of mud, clay, or fine sand.

Sllurcs. Ancient people, probably of a non-Aryan stock, being dark and curly-haired, inhabiting the s.e. of South Wales. They were warlike and resisted fiercely the Roman generals who invaded their territory.

Silurian. Series or system of fossiliferous rocks lying immediately below the Devonian; first studied in Wales by Murchison, who named them from the Silures. an ancient British tribe. This term has been gradually restricted, and is now applied only to Murchison's upper division, the lower being called Ordovician. See Column.

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Siluridae. See Nematognathi.

Silva, Antonio Jose Da, 1705-1739. Portuguese dramatist, b. in Brazil; burned at Lisbon, with his mother and wife, as Jews.

Silva, Jose Laurencio, 1792-1873. Venezuelan officer, prominent in the liberation of Colombia and Peru; Major-gen. 1828; exiled 1831-35; Lieut.-gen. and Sec. of War 1855.

Sllva Lifsboa, Jose Da. 1756-1835. Brazilian historian and statesman, Senator 1826.—His brother, Balthazar, 17611840, pub. Annals of Rio Janeiro, 7 vols., 1834.

Silver (argentum). Ag. At.wt. 107.92, sp. gr. 10.5, sp. ht. .057, mpt. 954° C, valence I. It unites directly with the halogens, forming insoluble compounds. Treated with hydrochloric acid, it becomes covered with a layer of the insoluble chloride. It is soluble in concentrated sulphuric acid; the best solvent is nitric acid. It is used for coins and silverware. Its salts, which are affected by light, are used in photography.

Silver, Metallurgy Of. Silver occurs most abundantly in the following ores: Native silver, Argentite, Pyrargyrite, Proustite. and Cerargyrite. Besides these there are several other ores with sulphur, arsenic, bromine, etc.; and it is also found in small amount in the ores of other metals, notably in tetrahedrite. Pure silver is white, soft, very malleable, very ductile, the best known conductor of heat and electricity. Its mpt. is 954° C.J it boils below the mpt. of platinum (1,775° O), and has been distilled; its vapor is greenish. Thin leaf is blue by transmitted light. It crystallizes usually in octahedrons. When melted, it absorbs 22 times its volume of oxygen, which it gives out suddenly when setting, producing a spitting. It does not oxidize in dry or damp air, but is easily blackened by vapors containing sulphur, forming' silver sulphide. It alloys easily with melted lead, copper, zinc, and many other metals; it dissolves in cold mercury, more easily in hot.

Three principal methods are used in treating the ores. The most usual is to smelt the silver ore together with lead ore, the lead obtained carrying all the silver. This may be accomplished in any of the ways used for treating lead ores (see Lead, Metallurgy Of). This silver-bearing lead can be desilverized by several processes. Another method is to convert the silver into chloride, then dissolve this in a salt solution, from which it is afterward precipitated. Another is to amalgamate the silver by grinding t he ore up with mercury, and distilling the mercury from the amalgam.

Amalgamation processes are very old, and are conducted as follows: the barrel amalgamation makes use of tight, revolving barrels. If the ore is not native silver or the chloride, it is first roasted with common salt, which converts the silver into chloride. The charge of a barrel, in Freiberg, was 1,500 lbs. of roasted ore, 300 lbs. of water, 120 lbs. of lumps of iron. The barrel was turned 12 times a minute for 2 hours, then stopped, and 300 to 500 lbs. of mercury put in, and ro

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tated again 20 times a minute for 18 hours. The barrel was then filled two-thirds full of water and turned two hours longer. The amalgam thus obtained was squeezed through canvas bags, and the pasty, rich amalgam put into retorts in which the mercury was distilled off, leaving nearly pure silver. The cost of treating an ore by this method is $10 to $20 per ton, making it profitable to treat only ores over 25 to 50 ounces of silver per ton.

The same process can be conducted more economically in iron pans, in which the finely-divided ore is ground with hot water and mercury. This is called the Washoe process, and can be operated for $5 to $7 per ton. The same principle is again employed in the more primitive Patio process, in which the preliminary grinding of the ore is done in an Arrastra (q.v.j, and the amalgamation is done by spreading the fine ore on a cemented or paved courtyard, making a mud of it, sprinkling it over with salt, and then treading it by driving mules through. After the salt is worked in, mercury and some sulphate of iron and copper are added, and trodden in. The whole working of a heap takes 15 to 45 days. The mass is then washed in tanks, the amalgam separated, squeezed through canvas bags, and distilled. This process was largely used in Mexico and Spanish-American countries from 1600 nearly to the present.

The wet processes of silver extraction depend on the fact that silver chloride, while not soluble in water, is soluble in solutions of common salt, sodium hyposulphite, copper hyposulphite, etc. If the ore is a chloride, bromide, or iodide ore, it can be treated directly. If not, it is first roasted carefully with common salt, an operation called chloridizing roasting, whereby silver chloride is formed. The ore containing the silver as chloride is then placed in tanks having false or perforated bottoms, and is washed with a strong brine (Augustin's process), or sodium hyposulphite (Patera), or calcium thiosulphate (Kiss), or hyposulphite of sodium and copper (Russell). All these solutions dissolve notable quantities of silver chloride, and are mostly precipitated by putting into them strips of copper, which throws down pure silver. Russel's process can be applied to most silver ores without preliminary chloridizing roasting, and he prefers to precipitate the silver as sulphide by adding sodium sulphide. The precipitated silver sulphide is filtered out, dried, and gently roasted in air to silver. These wet processes are in extensive use, and can treat very poor ores.

The concentration of silver in lead furnishes work-lead, which must be desilverized. The oldest method of accom

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