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The viceroyalty extended over an area of about 1,500,000 miles; the Argentine republic comprises about two thirds of this surface, with a population estimated at 2,000,000, of which 600,000 are Spanish creoles, 600,000 mestizoes, 800,000 Indians, and 25,000 negroes. This part of the country was first discovered by Juan Diaz de Solis, in 1517, and was further explored by Sebastian Cabot, then in the service of Spain, in 1526. In 1553, the first Spanish colony was founded here by don Pedro de Mendoza, who built Buenos Ayres. The government was at first dependent upon that of Peru, and, in consequence of the restrictions imposed on its commerce, had no other conimunication with other parts of the world than by the annual fleet from Spain. But as the population multiplied, and the agricultural produce increased, some relaxations in the monopoly system took place, and finally, to put a stop to the smuggling, which had been carried on to a great extent, register ships were allowed to sail, under a license from the council of the Indies, at any time. The annual flotilla sailed for the last time in 1748; in 1774, a free trade was allowed between several of the American ports, and, in 1778, several Spanish ports were allowed an open trade to Buenos Ayres. In the same year, the viceroyalty of Buenos Ayres was constituted, and, as it included the rich provinces of Upper Peru, became not only important as an agricultural colony, but for its valuable mines. The commerce continued to increase in value until the war between England and Spain (1797), after which it never revived, and has been entirely annihilated by the recent events. In 1806 and 1807, the inhabitants, having victoriously repelled the attacks of the English, under generals Beresford and Whitelocke, learned to know their own strength, and, in 1810, the first insurrection against the mother country broke out at Buenos Ayres. In none of the Spanish colonies were there so few blacks; none had been so much neglected by the mother country; hence in none were shown a greater unanimity of purpose, and firmness in resistThe inhabitants of this colony were, also, superior to most of the colonists in cultivation and character. Liniers, a French officer who had conducted the successful resistance to the British, was declared viceroy, in the place of the Spanish governor. But as he favored the cause of Joseph Napoleon, he was soon after deposed, and the junta of the province of Buenos Ayres managed

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the government under Cisneros, the new Spanish viceroy; the latter, however, was deposed by the junta, on account of his attempts to revive the old Spanish policy, and sent home. The junta took upon itself the administration, in the name of Ferdinand VII. Chile followed this example, and sent troops to the assistance of Buenos Ayres. The insurgents likewise took possession of Upper Peru, where an insurrection had already broken out at La Paz, Aug. 16, 1809. Liniers, who was supported by some of the internal provinces, made an unsuccessful attempt against Buenos Ayres; he was deserted by his troops, and, having been made prisoner with some of his adherents, was shot. The other provinces joined Buenos Ayres, and the creoles were every where victorious. In 1811, the junta was dissolved, in consequence of the intrigues of its president; and a congress, assembled at Buenos Ayres, vested the executive power in the hands of a triumvirate; but the progress of the Spanish arms in Peru led the congress, in 1814, to name Pozadas suprerne director of the republic, with a council of seven; and the government thus acquired more unity and vigor. Monte Video was yet occupied by a Spanish garrison, but was soon after taken by the Buenos Ayrean forces; Artigas, the commander in the Banda Oriental, then declared himself independent, defeated the troops of Buenos Ayres, and took possession of Monte Video, which, in 1817, fell into the hands of a Brazilian force. (See Artigas, and Banda Oriental.) At the same time, Paraguay, under doctor Francia, declared itself independent. (See Francia, and Paraguay.) In 1816, a new congress met at Tucuman, which named Pueyrredon director of the republic, on July 19, declared the countries on the Plata independent, and, having transferred its sessions to Buenos Ayres, issued a declaration (Manifestacion historica y politica de la Revolucion de la America, Oct. 25), containing a list of twenty-eight grievances. The republic now assumed the title of United Provinces of South America, and, Dec. 3, 1817, proclaimed a reglamento provisorio as preliminary to a constitution. The congress, chosen in compliance with the reglamento, was opened in February, 1819, and, on the 25th of May, the new constitution was published. It was on the model of that of the U. States, and secured personal freedom and equality, liberty of conscience and of the press, and the right of suffrage. Pueyrredon, who declined re

election to the place of supreme director, the Banda Oriental. Garcia, who was was succeeded in that post by general sent by Rivadavia to negotiate a peace, Rondeau. The country still continued in, having ceded the Banda Oriental to the a disturbed state, and, in 1820, colonel Rodriguez was placed at the head of affairs by the federalists. The nomination of Rivadavia, who had previously been plenipotentiary to Paris and London, to the place of secretary of state in 1821, contributed to restore order; the province of Buenos Ayres yielded its claims to superiority over the other provinces, which established separate provincial governments, and sent deputies to a general congress at Buenos Ayres, May 1, 1822. The treaties of peace and amity, concluded with Santa Fé, Entre Rios and Corrientes, restored peace, and general amnesty established domestic tranquillity. The confederacy now consisted of the nine provinces of Buenos Ayres, Tucuman, Cordova, Salta, Cujo, Potosi, Cochabamba, La Paz and Puno. The vigilant and prudent policy of Rivadavia, who was also at the head of the department of foreign affairs, changed the condition of the country. The revenue of 1823 exceeded the expenditures; the customs, in particular, were much increased by the commercial prosperity. In 1822, the congress of the U. States, considering that the provinces of Buenos Ayres, after having, from the year 1810, proceeded in their revolutionary movements without any obstacle from the government of Spain, had formally declared their independence in 1816; and that, after various intestine commotions and external collisions, those provinces had attained domestic tranquillity, and a good understanding with all their neighbors, and actually exercised, without opposition from within or the fear of annoyance from without, all the attributes of sovereignty,-resolved that they ought to be recognised as an independent nation; and a minister plenipotentiary was, therefore, appointed to Buenos Ayres (1824). In 1825, a treaty of peace, commerce and navigation was concluded with Great Britain. At this time the republic assumed the title of United Provinces of La Plata. The principal functions of government were discharged for several years by a constituent congress, the executive power being intrusted to the provincial government of Buenos Ayres. In February, 1826, Rivadavia was chosen president of the United Provinces. In December preceding, the emperor of Brazil had declared war against the Argentine republic, in consequence of its having taken possession of

emperor, the president was induced, by the general dissatisfaction with this step, to resign. The successes of the Argentine arms led to articles of agreement with Brazil (August, 1828), by which it was stipulated that the Brazilians should evacuate the disputed province, which was declared an independent state. (See Monte Vidco.) On the resignation of Rivadavia, congress dissolved, each of the provinces again became independent, and colouel Dorrego was chosen governor of the province of Buenos Ayres. The new governor was expelled from the city in December of the same year, by general Lavalle, the head of the Unitarios, who caused himself to be proclaimed governor, and, having made Dorrego prisoner, caused him to be shot on the spot. A civil war of the most bloody description ensued, and, in August, 1829, general Lavalle found himself compelled to resign. He was succeeded by general Viamont, who was at the head of the federal party, who, in turn, gave way to general Rosas in December of the same year.-See Funes, Historia civil del Paraguay, Buenos Ayres y Tucuman (Buenos Ayres, 1825); Nuñes, Historical, political and statistical Account of the United Provinces of La Plata (translated from the Spanish, London, 1825); Head's Journey across the Pampas; Miers, Travels in Chile and La Plata (2 vols., London, 1826); Haighs, Sketches in Peru, Chile and Buenos Ayres (London, 1831); Miller's Memoirs (2 vols., London, 1828); the American Annual Register (I, II, III, IV).

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PLATEE; a town in Baotia, celebrated for the battle in which the Persians, under Mardonius, were defeated by the Greeks, B. C. 479. After Xerxes had been defeated at Salamis (q. v.), he returned with the greatest part of his forces, but left 300,000 men, under Mardonius, in Thessaly, to influence the negotiations of that commander with the Greeks. the failure of his attempts to negotiate, Mardonius advanced towards Attica, and laid waste every thing with fire and sword. One hundred thousand Greeks, under Pausanias and Aristides, having solemnly sworn to prefer death to subjugation, advanced against the Persians, and the two armies met near the small town of Platææ, September 25. The loss of the Greeks was inconsiderable. Mardonius fell, and hardly one tenth part of his army escaped by flight; but few ever returned to their

country. On the same day, the remnant of the Persian fleet, which had escaped from Salamis, was destroyed off Mycale by the Greeks, under the Athenian Xanthippus and the Spartan Leotychides. From that time, Greece was freed from invasions from Persia. The Plateans distinguished themselves both at Marathon and Platææ.

PLATE GLASS. (See Glass.)

PLATINA is a metal of modern discovery, and owes its name to the idea at first entertained of its being related to silver, it being a diminutive of the Spanish word plata. We shall first describe its ore, denominated in mineralogy native platina. It occurs in very small, irregularly formed grains, of uneven surface, usually flattened, and having the appearance of being worn by attrition. They are destitute of cleavage, and possessed of a hackly fracture; lustre metallic; color perfect steel-gray; streak unchanged and shining; ductile; hardness a little above that of fluor; specific gravity 17.3. It generally contains a little iron, and is accompanied, besides, by iridium, osmium, rhodium, palladium, and also by copper, chrome and titanium. It is very refractory, and soluble only in nitro-muriatic acid. The pieces in which it occurs rarely exceed a few grains in weight. It has been found principally in secondary deposits, and was first brought from Peru, and from Choco, in New Grenada. It also occurs in Brazil and St. Domingo; but of late comes, in the largest quantity, from Siberia, where it is found in the auriferous sands of Kuschwa, in the Uralian mountains. The richest beds of these sands are from two and a half to five feet in thickness, and yield from one to three pounds of metal for about 3700 pounds of sand. Native platina is also abundant on the western slope of the Uralian mountains. More recently, it has been found in a sienitic rock, along with oxide of iron and gold. The grains in which it occurred, possessed the same shape as those found in the sands. This locality is near Santa Rosa, in the province of Antioquia. To procure the pure metal from its ore has been one of the most difficult problems in metallurgy; and all the processes formerly employed have given way to the ingenious one invented and practised, for a long time privately, by doctor Wollaston, and which he made public, through the Philosophical Transactions, in 1829. The crude platina is dissolved in nitro-muriatic acid (formed in the proportion of three pounds of muri

atic acid to two of the simple aqua fortis). The acid should be allowed to digest three or four days, with a heat which ought gradually to be raised. The solution, being then poured off, should be suffered to stand until a quantity of fine pulverulent ore of iridiuni, suspended in the liquid, has completely subsided, and should then be mixed with a solution of muriate of ammonia (the salt being dissolved in five times its weight of water). A yellow precipitate of platina will immediately fall, which must be well washed in order to free it from the various impurities known to exist in native platina, and must ultimately be well pressed in order to remove the last remnant of the washings. It is next to be heated, with the utinost caution, in a black lead pot, with so low a heat as just to expel the whole of the muriate of ammonia, and to occasion the particles of platina to cohere as little as possible; for on this depends the ultimate ductility of the product. When turned out of the crucible, it will be found of a gray color, and, if prepared with due precaution, lightly coherent. It now requires to be rubbed between the hands, in order to procure, by the gentlest means, as much as can possibly be so obtained of metallic powder, so fine as to pass through a fine lawn sieve. The coarser parts are then to be ground in a wooden bowl, with a wooden pestle, but on no account with any harder material, capable of burnishing the particles of platina (because burnished particles of platina will not weld); and indeed every degree of burnishing would prevent the particles from cohering in the further stages of the process. And since platina cannot be fused by the utmost heat of our furnaces, and consequently cannot be freed, like other metals, from its impurities during igneous fusion by fluxes, nor be rendered homogeneous by liquefaction, the mechanical diffusion through water should here be made to answer, as far as may be, the purposes of melting, in allowing earthy matters to come to the surface by their lightness, and in making the solvent powers of water effect, as far as possible, the purifying powers of borax and other fluxes, in removing soluble oxides. By repeated washing, shaking and decanting, the finer parts of the gray powder of platina may be obtained as pure as other metals are rendered by the various processes of metallurgy; and if now poured over, and allowed to subside in a clean basin, a uniform mud, or pulp, will be obtained, ready for the further process of

casting. The mould to be used for casting the metallic powder, is a brass barrel, 6 inches long, turned rather taper within, with a view to facilitate the extraction of the ingot to be formed, being 1.12 inches in diameter at top, and 1.23 inches at a quarter of an inch from the bottom, and plugged at its largerextremity witha stopper of steel, that enters the barrel to the depth of a quarter of an inch. The inside of the mould being now well greased with a little lard, and the stopper being fitted tight into the barrel by surrounding it with blotting paper (for the paper facilitates the extraction of the stopper, and allows the escape of water during compression), the barrel is to be set upright in a jug of water, and is itself to be filled with that fluid. It is next to be filled quite full with the mud of platina, which, subsiding to the bottom of the water, is sure to fill the barrel without cavities, and with uniformity—a uniformity to be rendered perfect by subsequent pressure. In order, however, to guard effectually against cavities, the barrel may be weighed after filling it; and the actual weight of its contents, being thus ascertained, may be compared with that weight of platina and water which it is known, by estimate, that the barrel ought to contain. A circular piece of soft paper first, and then of woollen cloth, being laid upon the surface of the barrel, allow the water to pass during partial compression by the force of the hand with a wooden plug. A circular plate of copper is then placed upon the top, and thus sufficient consistency is given to the contents to allow of the barrel being laid horizontally in a forcingpress. After compression, which is to be carried to the utmost limits, the stopper at the extremity being taken out, the cake of platina will easily be removed, owing to the conical form of the barrel; and, being now so hard and firm that it may be handled without danger of breaking, it is to be placed upon a charcoal fire, and there heated to redness, in order to drive off moisture, burn off grease, and give to it a firmer degree of cohesion. The cake is next to be heated in a wind-furnace; and, for this purpose, it is to be raised upon an earthen stand, about two and a half inches above the grate of the furnace, the stand being strewn over with a layer of clean quartzose sand, on which the cake is to be placed, standing upright on one of its ends. It is then to be covered with an inverted cylindrical pot of the most refractory crucible ware, resting at its open end on the layer of sand; and

care is to be taken that the sides of the pot do not touch the cake. To prevent the blistering of the platina by heat, which is the usual defect of this metal in its unmanufactured state, it is essential to expose the cake to the most intense heat that a wind-furnace can be made to receive, more intense than the platina can well be required to bear under any subsequent treatment, so that all impurities may be totally driven off. The furnace is fed with coke, and the action of the fire maintained for about twenty minutes from the time of lighting it. The cake is now to be removed from the furnace, and, being placed upright upon an anvil, is to be struck, while hot, upon the top, with a heavy hammer, so as at one beating effectually to close the metal. If in this process the cylinder should become bent, it must on no account be hammered on the side, by which treatment it would be cracked immediately, but must be straightened by blows given upon the extremities, dexterously directed, so as to reduce to a straight line the parts that project. The ingot of platina, when cold, may be reduced by the processes of heating and forging, like any other metal, to any form that may be required. After forging, the ingot is to be cleaned from the ferruginous scales which its surface is apt to contract in the fire, by smearing over its surface with a moistened mixture of equal parts, by measure, of crystallized borax and common salt of tartar, which, when in fusion, is a ready solvent of such impurities, while it does not act, like caustic alkali, upon the platina itself. It is then to be exposed upon a platina tray, under an inverted pot, to the heat of a windfurnace. The ingot may then be flattened into leaf, drawn into wire, or submitted to any of the processes of which the most ductile metals are capable. The mean specific gravity of the metallic cake of platina powder, when taken from the press, is 10; that of the cake fully contracted by heat, before forging, is from 17 to 17.7; that after forging is about 21.25, and that of wire, 21.5, being the maximum density of this metal. Pure platina has a white color, very much like that of silver, but is inferior in lustre to that metal. Its malleability is far less than that of gold or silver, but superior to that of tin. It may be drawn into wires that do not exceed the 2000th part of an inch. It is a soft metal, and, like iron, admits of being welded at a high temperature. A wire one tenth of an inch supports 590 pounds without breaking. As a conductor of heat, it ranks between gold

and silver. It undergoes no change from the combined agency of air and moisture, and it may be exposed to the strongest heat of a smith's forge without suffering either oxidation or fusion. On heating a small wire of it, by means of galvanism, or the compound blow-pipe, it is fused, and afterwards burns with the emission of sparks. Platina is not attacked by any of the pure acids. Its only solvents are chlorine and nitro-muriatic acid, which act upon it with greater difficulty than on gold. The resulting orange-red colored liquid, from which the excess of acid should be expelled by cautious evaporation, may be regarded as containing either chloride of platinum, or the muriate of its oxide. According to Berzelius, there are two arides of this metal, the oxygen of which is in the ratio of 1 to 2. The protoride prepared by the action of potash on protochloride of platina is of a black color, and is reduced by a red heat. The peroride is obtained with difficulty; for, on attempting to precipitate it from the muriate, by means of an alkali, it either falls as a sub-salt, or is held altogether in solution. It is of a yellowish-brown color, resembling rust of iron when dry, and is nearly black when anhydrous. Like peroxide of gold, it is a very feeble base, and is much disposed to unite with alkalies.Chlorides of platina. The perchloride is procured by evaporating muriate of platina to dryness, by means of a gentle heat. It is deliquescent, and is soluble in water, alcohol and ether. The muriate of platina is the protochloride, and is resolved, on heating, into platina and chlorine. According to Mr. E. Davy, there are two phosphurets and three sulphurets of platina. The salts of platina have the following general characters: their solution in water is yellowish-brown; sulphureted hydrogen throws down the metal in a black powder; hydriodic acid produces a thin film of platina upon the surface of the solution, after a few hours standing. The sulphate of platina is formed by the action of nitric acid upon the sulphuret, or hydrosulphuret. It is soluble in water, alcohol and ether. When a strong aqueous solution of it is mingled with alcohol, in equal volumes, and heated, it will deposit a black powder, which, on being washed and dried, and heated to the temperature of 400°, explodes with violence. This detonating compound is analogous to those which ammonia forms with the oxides of gold and silver. The useful alloys of platina are not numerous. With silver it forms a tolerably fusible white 16

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alloy, malleable and brilliant when polished; but it scales and blackens by work ing. Gold, by a forge heat, combines with platina, and the alloys, in all proportions, are more fusible than platina. In the proportion of 38 grs. to 1 oz., it forms a yellowish-white, ductile, hard alloy; it is so elastic after hammering, that it has been proposed to use it for watch-springs. Mercury, by trituration with spongy platina, forms an amalgam at first soft, but which soon becomes considerably firm, and has been much used in obtaining malleable platina. A coating of platina can be given to copper and other metals, by applying to them an amalgam of spongy platina, and five parts of mercury; the latter metal is then volatilized by heat. Lead combines with platina readily; and iron and copper in like manner: the last mentioned, when added in the proportion of 7 to 16 of platina and 1 of zinc, and fused in a crucible, under charcoal powder, forms the alloy called artificial gold. Steel unites with platina in all proportions, and, especially in the proportion of from 1 to 3 per cent. of platina, forms a tough and tenacious alloy, well adapted for cutting instruments. Arsenic unites easily with platina, and was once employed for rendering the latter metal fusible. Platina is a metal of great utility. It is used for the construction of large boilers for the concentration of sulphuric acid, the larger ones of which cost upwards of 300 guineas. Its uses in chemistry are numerous, and very important. It is also employed for staining pottery; and has lately been coined in Russia, and forms a part of the circulating medium of that country.

PLATO (from λarus, broad). The celebrated Greek philosopher of this name was so called on account of the breadth of his chest and forehead. His original name was Aristocles. He was the son of Ariston and Perictione, and was born about 429 B. C. Among his ancestors were king Codrus and the lawgiver Solon. Circumstances were favorable to his early education: his body and mind were equally developed. In gymnastics, he was instructed by Ariston, in the rudiments of letters by the grammarian Dionysius, in painting and music by Draco and Metellus, in philosophy at first by Cratylus. Until his twentieth year, the gifted youth tried his creative power in epic, lyric and dramatic poetry with much ardor. Nothing satisfied him. We now see him introduced by his father to the wise Socrates, who, the story says, was just relating to his pupils a dream, in

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