PALLADIUM. A rare metal, possess ed of valuable properties, was discovered in 1803, by Dr. Wollaston, in native plat inum. It constitutes about 1 per cent. of the Columbian ore, and from t to 1 per cent. of the Uralian ore of this metal ; occurring nearly pure in loose grains, of a steel-gray color, passing into silver white, and of a specific gravity of from 11.8 to 12.14; also as an alloy with gold in Brazil, and combined with selenium in the Harz near Tilkerode. Into the nitro-muriatie solution of native platin um, if a solution of cyanide of mercury be poured, the pale yellow cyanide of pal ladican will be thrown down, which be ing ignited affords the metal. This is the ingenious process of Dr. Wollaston. The palladium present in the Brazilian gold ore may be readily separated as fol ows : melt the ore along with two or three parts of silver, granulate the alloy, and digest it with heat in nitric acid of speci fic gravity 1.3. The solution containing the silver and palladium, for the gold does not dissolve, being treated with com mon salt or murnitic acid, will part with all its silver in the form of a chloride. The supernatant liquor being concentrat ed and neutralized with ammonia, will yield a rose-colored salt in long silky crys tals, the ammonia-muriate of palladium, which being washed in ice-cold water, and ignited, will afford 40 per cent, of metal.
Pure palladium resembles platinum, but has more of a silver hue ; when plan ished by the hammer into a cup, such as that of M. Breant, in the Museum of the
Mint at Paris, it is a splendid steel-white metal, not liable, like silver, to tarnish in the air. Another cup made by M. Breant, weighing 2 lbs. (1 kilogramme), was pur chased by Charles X., and is now in the garde-meuble of the French crown. The specific gravity of this metal, when lam inated, is stated by Dr. Wollaston at 11.8, and by Vauquelin at 12.1. It melts at from 150° to 160°1Vedgewood ,• and does not oxidize at a white heat. When a drop of tincture of iodine is let fall upon the surface of this metal, and dissipated over a lamp flame, a black spot remains, which does not happen with platinum. A slip of palladium has been used with advan tage to inlay the limbs of astronomical in struments, where the fine graduated lines are cut, because it is bright, and not li able to alteration, like silver.
There are a protoxide and peroxide of palladium. The proto-chloride consists of 60 of metal and 40 of chlorine ; the cy anide of 67 of metal, and 83 of cyanogen. PALLETS, in clock and watch work, are the pieces connected with the pendu lum or balance which receive the imme diate impulse of the swing-wheel, or bal ance-wheel. They are, of various forms and constructions, according to the kind of escapement employed.