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 his patron Count Trissino. In 1547 he returned to Vicenza where he designed a very large number of fine buildings—among the chief being the Palazzo della Ragione, with two storeys of open arcades of the Tuscan and Ionic orders, and the Barbarano, Porti and Chieregati palaces. Most of these buildings look better on paper than in reality, as they are mainly built of brick, covered with stucco, now in a very dilapidated condition; but this does not affect the merit of their design, as Palladio intended them to have been executed in stone. Pope Paul III. sent for him to Rome to report upon the state of St Peter’s. In Venice, too, Palladio built many stately churches and palaces, such as S. Giorgio Maggiore, the Capuchin church, and some large palaces on the Grand Canal. His last great work was the Teatro Olimpico at Vicenza, which was finished, though not altogether after the original design, by his pupil and fellow citizen Scamozzi.

In addition to his town buildings Palladio designed many country villas in various parts of northern Italy. The villa of Capra is perhaps the finest of these, and has frequently been imitated. Palladio was a great student of classical literature, and published in 1575 an edition of Caesar’s Commentaries with notes. His I quattro libri dell’ architettura, first published at Venice in 1570, has passed into countless editions, and been translated into every European language. The original edition is a small folio, richly illustrated with well-executed full-page woodcuts of plans, elevations, and details of buildings chiefly either ancient Roman temples or else palaces designed and built by himself. Among many others, an edition with notes was published in England by Inigo Jones, most of whose works, and especially the palace of Whitehall, of which only the banqueting room remains, owed much to Palladio’s inspiration. The style adopted and partially invented by Palladio expressed a kind of revolt against the extreme licence both of composition and ornament into which the architecture of his time had fallen. He was fascinated by the stateliness and proportion of the buildings of ancient Rome, and did not reflect that reproductions of these, however great their archaeological accuracy, could not but be lifeless and unsuited to the wants of the 16th century. Palladio’s carefully measured drawings of ancient buildings are now of great value, as in many cases the buildings have altogether or in part ceased to exist.

 PALLADIUM (Gr.  ), an archaic wooden image ( ) of Pallas Athena, preserved in the citadel of Troy as a pledge of the safety of the city. It represented the goddess, standing in the stiff archaic style, holding a spear in her right hand, in her left a distaff and spindle or a shield. According to Apollodorus (iii, 12, 3) it was made by order of Athena, and was intended as an image of Pallas, the daughter of Triton, whom she had accidentally slain, Pallas and Athena being thus regarded as two distinct beings. It was said that Zeus threw it down from heaven when Ilus was founding the city of Ilium, Odysseus and Diomedes carried it off from the temple of Athena, and thus made the capture of Troy possible. According to some accounts, there was a second Palladium at Troy, which was taken to Italy by Aeneas and kept in the temple of Vesta at Rome. Many cities in Greece and Italy claimed to possess the genuine Trojan Palladium. Its theft is a frequent subject in Greek art, especially of the earlier time.

 PALLADIUM [symbol Pd, atomic weight 106·7 (0＝16)], in chemistry, a metallic element associated with the platinum group. It is found in platinum ores, and also in the native condition and associated with gold and silver in Brazilian gold-bearing sand. Many methods have been devised for the isolation of the metal from platinum ore. R. Bunsen (Ann., 1868, 146, p. 265), after removing most of the platinum as ammonium platinochloride, precipitates the residual metals of the group by iron; the resulting precipitate is then heated

with ammonium chloride and evaporated with fuming nitric acid, the residue taken up in water, and the palladium precipitated as potassium palladium chloride. This is purified by dissolving it in hot water and evaporating the solution with oxalic acid, taking up the residue in potassium chloride, and filtering off any potassium platinochloride formed. The filtrate deposits potassium palladium chloride, which on heating in a current of hydrogen leaves a residue of the metal. Roessler (Zeit. f. chemie, 1866, p. 175) precipitates both platinum and palladium as double chlorides, the resulting mixed chlorides being reduced to the metals by ignition in hydrogen, taken up in aqua regia, the solution neutralized, and the palladium precipitated by mercuric cyanide. See also T. Wilm (Ber., 1880, 13, p. 1198; 1881, 14, p. 629; 1882, 15, p. 241) on its separation as palladosammine chloride, and Cox (Phil. Mag., 1843, 23, p. 16) on the separation of palladium from Brazilian gold sand. Pure palladium may be obtained by the reduction of the double chloride (NH4)2 PdCl4 in a current of hydrogen, or of palladious chloride with formic acid.

It is a ductile metal of silvery lustre, with a specific gravity of 11·97 (0°C.). It is the most easily fusible of the metals of the platinum group, its melting-point being about 1530–1550° C. (L. Holborn and F. Henning, Sitzb. Akad. Berlin, 1905, p. 311). It readily distils when heated in the electric furnace. Its mean specific heat between 0° and t°C. is 0·0582 + 0·000010t (J. Violle, Comptes rendus, 1879, 89, p. 702). Palladium finds application in the form of alloys for astronomical instruments, in dentistry, and in the construction of springs and movements of clocks. Native palladium is dimorphous. It is soluble in nitric acid, more especially if the acid contains oxides of nitrogen, and when obtained in the finely divided condition by reduction of its salts, it is to some extent soluble in hydrochloric acid. It also dissolves in boiling concentrated sulphuric acid and in hydriodic acid. It oxidizes when fused with caustic alkalis. It combines with fluorine and with chlorine at a dull red heat, but not with iodine, whilst bromine has scarcely any action on the metal. It combines with sulphur directly, and according to T. Wilm (Ber., 1882, 15, p. 2225) forms the oxide Pd₂0, when heated in a current of air.

