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.
Authorities.—Montanari, Vita di Andrea Palladio (1749); Rigato, Osservazioni sopra Andrea Palladio (1811); Magrini, Memorie intorno la vita di Andrea Palladio (1845); Milizia, Memorie degli architetti, ii. 35-54 (1781); Symonds, Renaissance in Italy—Fine Arts, pp. 94–99; Zanella, Vita di Andrea Palladio (Milan, 1880); Barichella, Vita di Andrea Palladio (Lonigo, 1880).
PALLADIUM (Gr. παλλάδιον), an archaic wooden image
(ξόανον) 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.
Two series of salts are known, namely, palladious salts and palladic salts, corresponding to the two oxides PdO and PdO2. Of these the palladious salts only are stable, the palladia salts readily passing into the palladious form on boiling with water. The palladium compounds show a complete analogy with the corresponding platinum salts. All the salts of the metal when heated decompose and leave a residue of the metal; the metal may also be obtained from solutions of the salts by the addition of zinc, iron, formic acid, phosphorus and hot alcohol. Sulphuretted hydrogen gives with palladium salts a precipitate of palladium sulphide which is insoluble in ammonium sulphide; mercuric chloride gives the characteristic yellowish precipitate of palladious chloride, and potassium iodide the black palladious iodide which dissolves en addition of excess of the precipitant. These two latter reactions may be used for the recognition of palladium, as may also the behaviour of the salts with ammonia, this reagent giving a brown precipitate, which turns to a red shade, and is soluble in a large excess of the precipitant to a clear solution, from which by adding hydrochloric acid a yellow precipitate of palladosammine chloride, Pd(NH3)2Cl2, is obtained. Palladium is permeable to hydrogen at a temperature of 240° C. and upwards. It absorbs hydrogen and other gases, the heat of occlusion being 4640 calories per gram of hydrogen. The occluded hydrogen is strongly bound to the metal, only traces of the gas being given off on standing in vacuo, but it is easily removed when heated to 100° C. T. Graham (Phil. Mag., 1866–1869) was of the opinion that the occluded hydrogen underwent great condensation and behaved as a quasi-metal (to which he gave the name “hydrogenium”). forming an alloy with the palladium; but L. Troost and P. Hautefeuille (Ann. chim. phys., 1874. (5) 2, p. 279) considered that a definite compound of composition Pd2H was formed. The more recent work of C. Hoitsema (Zeit. phys. chim., 1895, 17, p. 1) however, appears to disprove the formation of a definite compound (see also J. Dewar, Phil. Mag., 1874, (4) 47. pp. 324, 342). A palladium hydride was obtained by Graham by the reduction of palladious sulphate with sodium hypophosphite. It is an unstable black powder, which readily loses hydrogen at 0° C. C. Paal and J. Gerum (Ber., 1908, 41, p. 818) have shown that when palladium black is suspended in water one volume of the metal combines with 1204 volumes of hydrogen, or in the atomic proportion Pd/H＝1/·98.
