PLAT JEM PLATINA. 



581 



movements without any obstacle from the govern- 

 ment of Spain, had formally declared their indepen- 

 dence in 1816; and that, after various intestine 

 commotions and external collisions, those provinces 

 had attained domestic tranquillity, and a good under- 

 standing with all their neighbours, and actually 

 exercised, without opposition from within, or the fear 

 of annoyance from without, all the attributes of sov- 

 ereignty, resolved that they ought to be recognised 

 as an independent nation ; and a minister plenipo- 

 tentiary 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 in- 

 trusted to the provincial government of Buenos 

 Ayres. In February, 1826, Rivadavia was chosen pre- 

 sident of the United Provinces. In December pre- 

 ceding, the emperor of Brazil had declared war 

 against the Argentine republic, in consequence of 

 its having taken possession of the Banda Oriental. 

 Garcia, who was sent by Rivadavia to negotiate a 

 peace, having ceded the Banda Oriental to the em- 

 peror, the president was induced, by the general 

 dissatisfaction with this step, to resign. The succes- 

 ses of the Argentine arms led to articles of agreement 

 with Brazil (August, 1828), by which it was stipu- 

 lated that the Brazilians should evacuate the disput- 

 ed province, which was declared an independent 

 state. (See Monte f'ideo.) On the resignation of 

 Rivadavia, congress dissolved, each of the provinces 

 again became iudependent, and colonel 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 com- 

 pelled 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 Decem- 

 ber of the same year. See Funes, Historia civil del 

 Paraguay, Buenos Ayresy Tucuman (Buenos Ayres, 

 1825) ; Nunnes, Historical, political and statistical 

 Account of the United Provinces of La Plata (trans- 

 lated from the Spanish, London, 1825) ; Head's 

 Journey across the Pampas ; Miers, Travels in Chile 

 and La Plata (2 vols., London, 1826); Haigh's 

 Sketches in Peru, Chile and Buenos Ayres (London, 

 1831); Miller's Memoirs (2 vols., London, 1828); 

 the American Annual Register (I. II. III. IV.). 



PL AT^EiE ; a town in Bceotia, 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 he returned with the 

 greatest part of his forces, but left 300,000 men, 

 under Mardonius, in Thessaly, to influence the nego- 

 tiations of that commander with the Greeks. On 

 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 PlataMC, 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 Plat- 

 aeans distinguished themselves both at Marathon and 

 Plateae. 



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 ; colour perfect steel-gray ; streak un- 

 changed and shining ; ductile ; hardness a little 

 above that of fluor ; specific gravity 17.3. It gen- 

 erally contains a little iron, and is accompanied, 

 besides, by iridium, osmium, rhodium, palladium, and 

 also by copper, chrome and titanium. It is very re- 

 fractory, 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 abun- 

 dant on the western slope of the Uralian mountains, 

 More recently, it has boen 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, 

 iu 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 dissolv- 

 ed in nitro-muriatic acid (formed in the proportion 

 of three pounds of muriatic acid to two of the sim- 

 ple aqua fortis). The acid should be allowed to di- 

 gest 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 quan- 

 tity of fine pulverulent ore of iridium, 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 plat- 

 ina, and must ultimately be well pressed in order to 

 remove the last remnant of the washings. 1 1 is next 

 to be heated, with the utmost 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 pro- 

 duct. When turned out of the crucible, it will be 

 found of a gray colour, 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 platiua (because 



