SIGNING, SEALING, AND DELIVERY-SIKHS. pass the Privy Seal, required first to have the signet affixed, and passed from the Signet-office to the office of the Privy Seal in the form of signet bills, verified by the signet-seal and superscription and the signature of the Clerk of the Signet. By act 11 and 12 Vict. c. 82, however, warrants under the royal sign-manual, countersigned by one of the principal secretaries of state, have been made per se sufficient authority for the Privy Seal to be affixed, and the Signet-office has been abolished. The signet in Scotland is a seal which seems to have been originally intended to authenticate royal warrants connected with the administration of justice. The principal class of agents or attorneys in Scotland are called Writers to the Signet, it is said from their having been originally clerks in the office of the Secretary of State, by whom writs passing the signet were prepared. See WRITERS TO THE SIGNET. SIGNING, SEALING, and DELIVERY of a deed, in English Law, is the mode of executing a deed. The main acts are, however, the sealing and delivery, for signature is not absolutely essentialat least in some kinds of deeds known to English authenticating deeds, still kept up in England, though long superseded in Scotland by simple subscription. In practice, a wafer or seal is attached to the end of the English deed, and the party who executes it must, after signature, put his finger on the seal, and say: 'I deliver this as my act and deed,' at the same time handing the deed to the person who is to have the custody thereof. law. The use of the seal is an ancient form of SIGN-MANUAL, ROYAL, the subscription of the sovereign, which must be adhibited to all writs which have to pass the Privy Seal or Great Seal. When attached to a grant or warrant, it must be countersigned by one of the principal secretaries of state, or by the Lords of the Treasury. The signmanual, in practice, consists but of the initial of the sovereign's name, with the letter R added, for Rex or Regina. SIGOURNEY, MRS LYDIA HUNTLEY (Huntley being her maiden name), American authoress and poet, was born at Norwich, Connecticut, in 1791. She was, like most young ladies of ability in New England at that period, early engaged in teaching, and much of her early writings consists of tales, essays, instructive letters, and poems, for her pupils and the young. Her first published work was a volume of poems in 1815. In 1819, she was married to Mr Charles Sigourney, a merchant of Hartford. In 1822, she published a descriptive poem on the Traits of the Aborigines of America; and in 1824, a Sketch of Connecticut Forty Years Since. These were followed by Pocahontas and other Poems, Lays of the Heart, Tales in Prose and Verse, &c. In 1840, Mrs S. visited Europe, and on her return, with a freedom common to American authors, wrote her Pleasant Memories of Pleasant Lands. piled amusing and instructive books for the young, and was a constant contributor to magazines and other periodicals of poems, whose subjects, style, and sentiment gave her the designation of the American Hemans.' She died at Hartford, June 1865. SIHU'N. See JAXARTES. She com SIKHS. The term Sikh, a corruption of the Sanscrit s'ishya, signifying disciple,' is applied to a community of which the Punjab, in Northern India, constitutes, substantially, the confines. Less commonly, even among themselves, the members of this community are also known as Sinhs (vulgarly Singhs), that is, lions,' a title given them by Govind, the last and most influential of their hierarchs. Every name of a Sikh male now terminates with the word Sinh. Originally a body of mere religionists, the Sikhs, what from the energy which they developed under repression, and the inducements to join them which they offered as proselytisers, grew, by degrees, in strength and numbers, and ended in a formidable nationality. Their originator, Nanak, was born in 1469, in the vicinity of Lahore, and died in 1539, not far from the place of his nativity. To him succeeded, in turn, nine pontiffs, each of whom, like himself, is popularly denominated guru, or 'teacher.' These were Angad, Amardâs, Râmdâs, Arjunmall, Hargovind, Harrây, Harkrishna, Teghbahâdar, and, finally, Govind. The aim of Nanak was pointedly humanitarian, and designed to combine Hindus and Mohammedans, at the cost of what he held to be only unimportant compromise, into one harmonious brotherhood. Sufficient proof of the comprehensive character of his scheme is afforded by the circumstance that he accepted concurrently the incarnations of Neo-Brahmanism and the mission of the Arabian prophet. His three immediate successors, while zealously protecting the interests of the infant sect, avoided secular pursuits, and held themselves aloof from political complications. Arjunmall, however, not content with signalising himself as compiler of the Adigranth, and as founder of Amritsar, the holy city of the S., engaged with ardour in trade, and rendered himself conspicuous as a partisan of the rebellious Prince Khusrû, son of Jahangir. Hargovind, who came after Arjunmall, called the S. to remitted nothing of his assiduity as a guru, became arms, led them in person to battle, and, though he an active and useful, though sometimes refractory, adherent of the Great Moghul, against whom his predecessor had plotted. Harray subsequently espoused the part of Dârâ Shukoh, when contending krishna, son of Harrây, died a child, and was only nominally a guru. Teghbahâdar, after a career of turbulence, was executed as a rebel, by command of Aurangzeb, at Delhi. However deficient in the qualifications demanded for spiritual leadership, it can scarcely be doubted that he contributed, to an important degree, in preparing for the complete change of Sikhism which was effected by his son, Govind. The chief motive that instigated Govind, the tenth of the teachers,' to bring about this change was, with some probability, a desire to avenge the ignominious death of his father. resolved to combat the Mohammedan power and, in deviation from the principles enunciated by Nânak, the Mohammedan religion as well. But Hinduism, with its social restrictions of caste, its fantastic fictions, and its irrational idolatry, likewise fell under his ban. God, he inculcated, is not to be found save in humility and sincerity. In what measure he was a man of thought is evinced by his legacy to his co-religionists, the second volume of the Sikh scriptures. A Sikh, it is therein taught, is to worship one God, to eschew superstition, and to practise strict morality, but equally is to live by the sword. The purport of this last injunction is unmistakable. Govind was assassinated, while in the imperial service, in 1708, on the banks of the Godâvari. He died, it is true, without beholding the fulfilment of the purpose for which he had striven; but he had, nevertheless, succeeded in stirring his followers to an ambition for political independence-an idea which was ultimately transformed into a reality. His successor, but only as a temporal leader, Banda, suffered a cruel death. He did but little to advantage his sect; and his memory is not held in reverence. with his brothers for the throne of India. Har He SIKHS-SIKH WARS. With the decline of the Moghul Empire, the might of the S., in spite of their intermittent reverses, steadily increased, until, in 1764, they convened a general assembly, formally assumed the character of a substantive nation, and issued coin from which the name of the emperor was omitted. Their commonwealth was still denominated, as it had been by Govind, Khâlsa; and the component states of the federation, ordinarily said to have been twelve in number, were thenceforward distinguished as Misls. Foremost in influence among these states was that of Sukarchakiyâ, the chieftain of which was Mahâ Sinh, for whose son, the famous Ranjit Sinh (Runjeet-Singh, q. v.), it was reserved to consolidate the Misls into a unity subject to his own undivided control. The virtual headship of Ranjit Sinh dates from the year 1805, though it was not until 1838 that he attained the zenith of his ascendency. He died in the year following, at the age of 59. During 1845 and 1846, the S. ceased to exist as a nation; and their country has since been ruled by the English. Yet every loyal Sikh is still confident that his people is suffering but a transitory depression, and that it is destined to retrieve, and even to surpass, its bygone glory. In the meantime, the reputed son of a wife or concubine of Ranjit Sinh, Dilip Sinh, is a pensioner of the British government, has professed Christianity, and has taken up his abode in England. Ethnologically considered, the S. are, in large proportion, of Jât origin; the Jâts, whom some take to be one with the classical Getæ, being a tribe extensively diffused over the north of India. But other Hindus have helped to swell their ranks, and also not a few Mohammedans. The ten gurus are accounted Kshatriyas, or of the second Brahmanical caste, the martial. The descendants of these several races, from intermarriage and other causes, cannot, however, now be discriminated; and there is no division of the multiform population of India that strikes more than the S., as respects physical uniformity. For symmetry and comeliness, and, it may be added, for courage and powers of endurance, the Lions of the Punjab are altogether remarkable. Nânak's was, undoubtedly, by far the most successful of the repeated attempts which have been made to fuse together the incompatible dogmas of Hinduism and Islamism. None of the authors of these attempts seem, indeed, to have been acquainted with other than the mere surface of the two religions which they would have blended into one. With the Mohammedan, the existence of the Deity as a pure spirit, and his creatorship of the world, are fundamental postulates. On the other hand, the radical doctrine of the Hindu is pantheism, agreeably to which the universe, alternatively God, is a single eternal substance, under the twofold aspect of spirit and matter. These sets of first principles, which Nanak and his fellow-reformers could never have clearly apprehended, are palpably impossible of reconciliation. Without rejecting all that is distinctive of his creed, no Hindu can assent to the theology of Islam; and, conversely, every intelligent follower of the Arabian prophet must be aware that the monism and the metempsychosis of Brahmanism are utterly antagonistic to the leading positions of his own faith. Govind, as we have seen, openly repudiated the notion of amalgamating Hinduism and Mohammedanism. But a critical acquaintance with his real views, in their fulness, and of those of Nanak, must remain a matter of conjecture until we possess a detailed translation, executed by some scholar competently versed in Hindu philosophy, of the Adigranth (The Original Record) and the Daswîn Pâtsâhî dâ Granth (The Record of the Tenth King). These voluminous compositions are metrical throughout, and are chiefly in Hindi and Panjâbî; the former containing, additionally, a little Sanscrit, and the latter, a long chapter in Persian. They are written in the same character as the Sanscrit, the values of the letters being altered, though their forms are retained. Among the numerous divisions into which Sikhism, as a system of belief and practice, has ramified, two, at least, apart from the great central sect, deserve specification. First are the Udâsis, professors of indifference to mundane concerns sect whose origin is attributed to S'richand, a son of Nânak. These recluses, whom Amardâs refused to recognise as genuine S., have, to this day, numerous disciples. The Akâlîs sprang up just after the time of Govind. For extravagance of fanaticism, these Ishmaelites have, it is hoped, no rivals; and the style of their piety is comparable with that of a Thug. a As specimens of the superstitions of the S., it may be noted that, like the Hindus, they look upon the eating of beef as a deadly offence, and that, like the modern followers of Zoroaster, they attach sinfulness to the act of extinguishing a light with the breath. Some illustrations of practical Sikhism may also be gathered even from the few remarks that have been made touching the gurus. It is not irrelevant to add, that Amardâs humanely discountenanced the cremation of widows, and that Arjunmall committed suicide. The morality of ordinary S. is as positively maintained by one class of writers as it is denied by another. Evidence should seem to shew that the agriculturists among them are much on a par, as to correctness of life, with other Indian cultivators of the soil. As to their soldiers, however, it has been observed that they are deeply tainted with those repulsive impurities for which the Persians are so infamous. Though forbidden the use of tobacco, they are under no restriction as concerns indulgence in bhang, opium, and intoxicating drinks; and it would be gross flattery to commend them on the score of sobriety. As regards morality, there is reason to believe that they have greatly degenerated since the days of Govind. The gross Sikh population has been most variously estimated by different statisticians, some of whom compute it at considerably less than half a million of persons, while others deem a million and a quarter, or even a million and a half, to be not excessive. For the most satisfactory extant treatment of the subject of this article, the reader is referred to Captain J. D. Cunningham's History of the Sikhs. Sir J. Malcolm's Sketch of the Sikhs; The Asiatic Researches, vols. i. and xi.; the collective works of Professor H. H. Wilson, vols. i. and ii.; and The Calcutta Review, vols. xxxi. and xxxiii., may likewise be consulted with advantage. SIKH WARS, two brief but desperate contests waged between the British power in India and the the destruction of the latter as an independent nation. Sikhs in 1845-1846, 1848-1849, which resulted in The first had its origin in the dissensions which convulsed the Sikh country after the death of Runjeet Singh (q. v.), and which necessitated the exercise of a wary regard on the part of the flushed with their triumph over all lawful authority Calcutta authorities. At length an army of Sikhs, extended their ravages over British territory; in their own country, crossed the Sutlej, and but their advanced guard was met by Sir Henry Hardinge, the governor-general, at the head of four regiments of infantry and one of dragoons, and routed at Mudki (q. v.) with heavy loss. Three days after, their main body, which had meantime crossed the river, and intrenched itself at Feroze SI-KIANG-SILESIA. Shah (q. v.), was attacked by a larger force of British under Gough and Hardinge, and after a bloody conflict, which lasted two days, also routed. Still undismayed by these reverses, they again intrenched themselves at Sobraon; but a fresh body which had just crossed the Sutlej at Aliwal (q. v.), 19,000 strong, with 68 pieces of cannon, was wholly routed and driven across the river by Sir Harry Smith, at the head of 7000 men, with 32 guns; and their main body was soon after similarly dispersed at Sobraon (q.v.). The British then crossed the river, took Lahore, and restored the authority of the young Maharajah, from whom they took the territory between the Beas and the Sutlej, the treaty confirming this settlement being made at Lahore, 9th March 1846. But the internal disturbances in the kingdom of Lahore soon became as active as before, and induced the Maharajah's prime-minister to put the country under the Company's protection; and a residency with a guard of regular troops was then established in the capital. On April 20, 1848, two British officers were murdered by a Sikh chief, the dewan Moolraj of Multan; and as this was found to be but a premonitory symptom of a general outbreak, a small force of British under Lieutenant Edwardes, aided by a body of Sikhs, under the Rajah of Bhawalpur, gallantly attacked the army of Moolraj, which, after a desperate conflict of nine hours, they defeated on June 18, and, both sides in the meantime having received reinforcements, again on July 1. Multan was then laid siege to, but the defection of 5000 auxiliary Sikhs under Shere Singh (the son of the Sirdar Chuttur Singh, the governor of Hazara, who had been for some time in revolt, and had driven the British from his district) compelled the British to retreat. For some time, the British authorities in the Punjab were hampered by a want of military force, and though the Maharajah and much of his army still opposed the Sikh rebels, little reliance could be placed upon most of it. Shere Singh now succeeded in raising his army to 40,000, but was defeated by Lord Gough at Ramnugger (November 22). The inconsiderate haste of Gough at Chillianwalla (January 13) nearly lost him that great battle, which was saved only by the extreme valour of his soldiers; but amends for this fault were made at Gujerat (q. v.), where the power of Shere Singh and his allies was completely broken. Meanwhile, the fortress of Multan had, after a protracted bombardment, been captured; and the Company, seeing no other mode of protecting their territories from annoyance by these warlike fanatics, annexed the Punjab, March 29, 1849, thus terminating the existence of the Sikhs as an independent nation. SI-KIA'NG, or WESTERN RIVER, a river at the southern extremity of China Proper. It has lately been ascertained by our surveyors to be navigable for vessels not drawing more than 16 feet of water for about 100 miles from its mouth. The S. is remarkable for the purity and clearness of its waters. It is at present chiefly useful in conveying the sugar-cane that grows in its vicinity, as well as rafts of timber from the forests of Kwangse, to the markets of Canton. SILE'NÉ, a genus of plants of the natural order Caryophyllacea with a tubular 5-toothed calyx; five notched or bifid petals, which terminate in a narrow claw at the base, spring from the stalk of the germen, and have each an appendage forming a Corona (q. v.) in the mouth of the corolla; ten stamens; three styles; the capsule 3-celled, 6-toothe, many-seeded. The species are numerous, mostly natives of the temperate parts of the northern hemisphere, annual and perennial plants; nine or ten of them natives of Britain, and others frequent in flower-gardens. One of the species most common in America, but introduced from Europe, is the BLADDER CAMPION (S. inflata), a perennial, which grows in fields and dry pastures, and has a branched stem fully a foot high, ovate-lanceolate bluish-green leaves, panicles of white flowers, and an inflated calyx, with a beautiful network of veins. The young shoots are sometimes used like asparagus, and have a peculiar but agreeable flavour, somewhat resembling that of peas. They are best when most blanched. The cultivation of this plant was long ago strongly recommended, but it has not obtained a place among garden plants.-The MOSS CAMPION (S. acaulis) is a pretty little plant, with beautiful purple flowers growing in patches so as to form a kind of turf, one of the finest ornaments of the higher mountains of Scotland, and found also in Cumberland and Wales. --Many species, some of them American, are popularly called CATCHFLY, from their viscidity, as S. regia and S. Virginica, found in open woods or on the prairies of Ohio, Kentucky, and southwards. In most generally represented as the chief of the Sileni or SILE NUS, son of Pan and Gæa (the Earth), is older Satyrs (q. v.), and the inseparable companion of Bacchus, with whom he took part in the contest against the Gigantes, slaying Enceladus. respects he seems to have resembled the other satyrs, and to have borne a strong likeness to Sir John Falstaff, being in addition noted for his wisdom and his power of prophecy. S. had a temple at Elis. SILE'SIA, a province of the kingdom of Prussia, included in the limits of the new German empire, lies south of the provinces of Brandenburg and Posen, and is bounded on the E. by the Polish provinces of Russia and Austria, and on the S. and W. by the Austrian provinces of Silesia and Bohemia, and the kingdom of Saxony. It is divided into three governments: Liegnitz, in the west, Breslau, in the east, and Oppeln, in the south; and these, again, are subdivided into circles. Total area, 15,547 English sq. m., with a pop. (1867) of 3,585,752, of whom 1,811,805 are Catholics, 1,711,569 Protestants, and 44,822 Jews. Of the population, 4th speak Polish, more than 90,000 employ other Slavic dialects, and the rest use the German language. This province, by far the largest and most populous of the Prussian provinces, is crossed from north-east to south-west by a broad strip of mountainous country, which widens out at each extremity; and along the whole eastern boundary, and in the south, are ranges of low hills; in the north-west and centre, the surface is flat and heathy, or sandy, with numerous stagnant pools. S. is almost wholly included in the basin of the Oder (navigable as far south as Ratibor), which flows through it from south-east to northwest, and receives from each side numerous tributaries; but a small portion in the extreme south is drained into the Vistula, which here takes its rise. The soil is altogether fertile and well cultivated, cereals of all kinds, oil-plants, beet, hops, occamore so, however, in Lower than in Upper S.; and sionally vines, and above all, flax and hemp, are the crops of the province; but of late years the cultivation of tobacco, and of plants yielding dyestuffs, has been receiving increased attention. Cattle and sheep, the latter excellent in quality, and partly of pure or mixed merino blood, are reared in the high-lands, the annual produce of wool averaging fully 140,000 cwt. The mines of S. are of great importance; iron, copper, and lead are the chief SILESIA-SILICON. products; coal is found in abundance. The manufacture of lace, averaging in annual value £1,500,000, is carried on in the mountainous districts, chiefly around Schweidnitz; and the production of other fabrics, as linen, cotton and woollen goods, paper, iron, leather, glass, and earthenware, is vigorously carried on throughout the province. The Oder, and the great central railway from Berlin and Posen to Vienna, atford ample facilities for commerce. There are a university at Breslau, gymnasia in the principal towns, and a great number of professional and S. was inhabited at the beginning of the Christian industrial schools. which silica is the principal ingredient. See This SI'LHOUETTE, the name given to a profile or shadow-outline of the human figure, filled in of a dark colour, the shadows and extreme depths being sometimes indicated by the heightening effect of gum or some other shining material. species of design was known among the ancients, and was by them carried to a high degree of perfection, as the monochromes on Etruscan vases amply testify; but the name S. is quite modern, dating from about the middle of last century. It was taken from Etienne de Silhouette, the French era by the Quadi and Lygii, who, like the other German tribes, advancing westward in the 6th c., were succeeded by Slavic tribes. It formed part of the Slavic kingdom of Moravia, was next joined to Bohemia, and in the beginning of the 10th c. to Poland. In 1163, it was separated from the kingdom of Poland, but was ruled by dukes who were of the royal line of Piast; these dukes, to repeople the country, which had been devastated by the numerous civil wars, encouraged the settlement of German colonies, especially in Lower Silesia. The practice of division and subdivision of territory prevailed so extensively in S., that at one time it had no less than 17 independent dukes, and to save itself from re-incorporation with Poland, it acknowledged the sovereignty of the kings of Bohemia, with which, and with Germany, from the time of the Emperor Karl IV., it was indissolubly connected. In 1537, the Duke of Liegnitz, one of the numerous Silesian princes, entered into an agreement of mutual succession succession (Erbverbrüderung) with the Elector of Brandenburg, on the extinction of either reigning line; and the other ducal lines becoming gradually extinct, their possessions fell to Liegnitz or to Bohemia, or lapsed to the emperor. In 1675, when the last ducal family, that of Liegnitz, failed, his territories of Liegnitz, Brieg, and Wohlau, would have fallen to Prussia, but the emperor of Germany refused to recognise the validity of the agreement of 1537, and took possession of the Liegnitz duke's dominions, as a lapsed fief of Bohemia. The remainder of S. was thus incorporated into the Austrian empire. In 1740, Frederick II. of Prussia, taking advantage of the helpless condition of Maria Theresa of Austria, laid claim, on the strength of the agree-out pockets-was styled à la Silhouette; and ment of 1537, to certain portions of S.; and without declaring war, marched into, and took possession of the province, maintaining his hold despite the utmost efforts of Austria in 1740-1742, and 1744 1745, called the first and second Silesian wars. After the third Silesian war, better known as the SEVEN YEARS' WAR (q. v.), it was finally ceded (1763) to Prussia. SILESIA, AUSTRIAN, a duchy and a Cisleithan province of Austria, bounded on the N.E. by Prussia, and on the S.W. by Moravia. Area, 1963 sq. m.; pop. (1869) 511,581. It is mountainous in the west, where the Spieglitzer Schneeberge, a summit of the Sudetic chain, rises to the height of 4512 feet. The province comprises 1806 sq. m. of level land, of which by far the greater portion is arable or under wood. The climate, though rough, is healthy, and the soil produces good crops of rye, oats, barley, flax, &c. Within the province rise the Oder and the Vistula. Cattle-breeding and bee-keeping are important branches of industry; 170,000 head of sheep belong to the province. Iron, lead, and coal mining are profitably pursued. The manufactures are principally spirits, copper and iron wares, and linen and cotton fabrics. SI LEX (Lat. flint), a generic name given by some mineralogists to all those minerals of 410 Silhouette of Robert Burns. minister of finance in 1759, who, to replenish the treasury, exhausted by the costly wars with Britain and Prussia, and by excessive prodigalities, inaugurated numerous reforms, and the strictest economy of expenditure. His extreme parsimony in all finance matters made him a choice subject for caricature; so that any mode or fashion that was plain and cheap-'surtouts' without plaits, trousers with profiles made by tracing the shadow projected by the light of a candle on a sheet of white paper being then much in vogue, have continued to bear the name. Although without merit as a work of art, the S. presents a clear and well-marked profile, and such instruments as the Pantograph (q. v.), &c., used to be frequently employed to obtain profiles of a reduced size direct from the human features.-Profiles cut out of black paper with scissors also receive the name of silhouettes. SI LICA. See SILICON. elements. SILICON, or SILICIUM (sym. Si, eq. 28, spec. grav. 2:49), is one of the metalloids, or non-metallic lt may be obtained in three different forms or modifications-viz., the amorphous, the graphitoid, and the crystalline. It is the first of these, the amorphous silicon, which is obtained by the processes in common use, the second and third being obtained from this first modification. Amorphous silicon presents the appearance of a insoluble in water and in nitric and sulphuric acids, dull brown powder, which adheres to the finger, is but readily soluble in hydrofluoric acid, and in a hot solution of potash. It is a non-conductor of electricity, and when heated in air or oxygen, its external surface burns brilliantly, and is converted into silica, which fuses from the extreme heat, and forms a coating over the unburned silicon. Graphitoid 721 SILICON. silicon is obtained by exposing the amorphous variety to an intense heat in a closed platinum crucible. This form of silicon will not take fire when heated in oxygen gas, and resists the solvent action of pure hydrofluoric acid, although it rapidly dissolves in a mixture of nitric and hydrofluoric acids; moreover, as another point of difference, it is a conductor of electricity. For the description of crystallised silicon, we may refer to a treatise by Deville (in the Ann. de Chimie, 3d ser. vol. 49, p. 65), | who obtained it in regular double six-sided pyramids of a dark steel-gray colour. Silicon, in a state of combination with oxygen, is the most abundant solid constituent of our globe; and, in less proportion, is an equally necessary ingredient of the vegetable kingdom, while in the animal kingdom it occurs in mere traces, except in a few special cases. It is never found in nature except in combination with oxygen; but by a somewhat difficult process-which we need not here describe it may be separated as a dark brown powder. It was first isolated by Berzelius in 1823. For our knowledge of the other modifications, we are indebted to Wöhler and Deville. acid. The amorphous form exists naturally in opal, and is obtained artificially as gelatinous silica, &c.; it differs from the former in its specific gravity, being about 2.2, and in its being rapidly dissolved by potash and by hydrofluoric acid. Pure silica (as it occurs in rock-crystal, for example) is perfectly transparent and colourless, and is sufficiently hard to scratch glass. The heat of the oxyhydrogen blowpipe is required for its fusion, when it melts into a transparent glass, capable of being drawn out into elastic threads. Perfectly pure silica in its amorphous form may be obtained by various chemical processes. If a solution of silicate of potassium or sodium be treated with hydrochloric acid, the silicic acid separates as a hydrate, and on evaporating this to dryness, and treating it with boiling water, silicic acid remains as an amorphous powder, which, after being washed, dried, and exposed to a red heat, may be regarded as chemically pure. The hydrated silicic acid mentioned in the above experiment is soluble in water, and more freely in acids and alkalies. The solubility of hydrated silicic acid in water accounts for the presence of silicic acid in mineral springs and in the Geysers of Iceland, as well as for its gradual Silicon forms two oxides, one of which is only separation from these waters in the form of petrifacknown in the hydrated state, while the other is tions. That silica or silicic acid is a true acid (althe well-known compound, silica or silicic acid. though a feeble one) is obvious from its uniting with Hydrated oxide of silicon is represented by the bases, especially those which are capable of undergoing formula Si40.4H2O, and silicic acid by SiO,. The fusion and forming true salts, known as silicates. hydrated oxide exhibits many interesting chemical These silicates occur abundantly in nature; all the properties, but is of no practical importance. forms of clay, felspar, mica, hornblende, augite, serpentine, &c. being compounds of this description. Silicic acid combines with bases in various proportions. The following table exhibits the composition of the several groups of natural silicates, with the ratio of the quantity of oxygen contained in the base and acid (SiO2) in each case: Silicic acid or silica exists both in the crystalline and in the amorphous form. The best examples of the crystalline form are rock-crystal, quartz, chalcedony, flint, sandstone, and quartzose sand. Silica in this form has a specific gravity of about 2·9, and is only attacked with difficulty by potash or hydrofluoric joints, and is known as Tabasbeer), in the equisetæ, &c. In the above formulæ, MO stands for 1 equivalent | the The following are the general characters of the silicates: Most of them are fusible, the basic silicates fusing more readily than those which are either neutral, or contain an excess of acid. Excepting the silicates of the alkalies, no silicates are soluble in water. The anhydrous, neutral, and acid silicates of the earths resist the action of all acids except the hydrofluoric. In conclusion, we may remark that silica derives its name from silex, flint, of which it is the essential constituent, and that it is largely employed in the manufacture of glass, china, and porcelain. For these purposes, it is obtained in a finely comminuted state by heating flints or portions of colourless quartz to redness, and plunging them in cold water. The silica splits up into a friable mass, which may be easily ground to a fine powder. The use of silica in giving firmness and rigidity to various parts of the animal organs, is exemplified in its free occurrence in the quill-part of the feather of birds, in the shields of certain infusoria, and in the spicula occurring in sponges; while its similar use in the vegetable kingdom is seen in its more or less abundant presence in the stalks of the grasses, more particularly in the cereals and in the bamboo (where it is especially deposited about Silicon may be made to combine with several other elements besides oxygen, but, with the exception of silicofluoric acid, these compounds are of no practical value. Thus silicon and hydrogen form a hydride of silicon, a colourless and spontaneously inflammable gas. Nitride of silicon is a bluish fibrous body, while sulphide of silicon is a white earthy powder. Silicon unites with chlorine, bromine, and probably iodine and fluorine, in two proportions corresponding to its oxygen compounds. Fluoride of silicon (SiF2) is a colourless pungent gas, liquefiable under strong pressure, and solidifying at -220°, inflammable, and a non-supporter of combustion. It is obtained by heating powdered glass with 12 times its weight of oil of vitriol, and when a stream of this gas is transmitted through water, a reaction takes place; two atoms of water and three atoms of the fluoride of silicon yielding silicofluoric acid (SiH2F6), which remains in solution, and silicon, which is deposited. A saturated solution of this acid forms a very sour fuming liquid, which does not directly attack glass, but if allowed to evaporate on it, causes erosion from the fluoride of silicon becoming evaporised, and free hydrofluoric acid being left. A dilute solution is frequently employed in the laboratory as a precipitant of potash, which it throws down in a transparent gelatinous form. |
