Page:The American Cyclopædia (1879) Volume XIV.djvu/315

RHODES > Turkish mosque. There are no considerable remains of an earlier time than the residence of the knights of St. John, among which is a moated castle of great size and strength, con- taining the cloisters of the knights. The city of Rhodes, which in 304 B. 0. withstood a RHODIUM 299 famous siege by Demetrius Poliorcetes, is de- scribed by Strabo as superior to all other cities for the beauty and convenience of its ports, streets, walls, and public edifices, all of them profusely adorned with works of art. There are said to have been about 3,000 statues in Rhodes, from the hill northwest of the city. the city. It contained one of the seven won- ders of the ancient world in its brazen statue of Apollo, commonly called the colossus of Rhodes. (See COLOSSUS.) RHODES, Inner and Onter. See APPENZELL. RHODEZ. See RODEZ. RHODIUM, a metal belonging to the platinum group, discovered by Wollaston in 1803. He found 0'4 per cent, in ore from Brazil, and in a specimen from another locality as much as 3 per cent. It usually forms about one half of one per cent, of the ore. It may be extracted from the solution from which platinum and palladium have been separated in the manner which has been described. (See OSMIUM, PAL- LADIUM, and PLATINUM.) The solution is mixed with hydrochloric acid and evaporated to dry- ness, and the residue is treated with alcohol of sp. gr. 0'837 ; this dissolves everything except the double chloride of sodium and rhodium, which remains behind as a red powder. This is dissolved in water, and the rhodium precipi- tated by the action of metallic zinc, or the salt may be reduced by heating it in a current of hydrogen gas. Rhodium is white and very hard. When quite pure it is malleable after fusion upon lime, and is then of sp. gr. 12'1. "Wollaston's estimate was 11, but he experi- mented on the unfused metal. The fusing point of rhodium is higher than that of plati- num, and it will only melt in the voltaic arc or in the oxyhydrogen furnace ; the precise degree cannot be estimated. Its symbol is Ro ; its atomic weight 104 or 104-3. It is un- alterable in the air at ordinary temperatures, but oxidizes, and also combines with chlorine, at a red heat. It resists the action of the strongest acid, singly or combined, unless al- loyed with some other metal, when it will dis- solve in nitro-muriatic acid. Rhodium forms four oxides : a monoxide, RoO ; a sesquioxide, RoaOs ; a dioxide, RoO a ; and a trioxide, RoO$. The principal oxygen salts are the acetate, ni- trate, phosphate, sulphate, and sulphite. There are two sulphides, RoS and Ro s S 3 . According to Berzelius, there are three chlorides, RoCla, Ro01 6 , and Rods ; but more recent investi- gations by Glaus make it probable that there is only one, the trichloride, Rods, which forms double chlorides with the alkalies. The best known salt of rhodium is the sodic rhodic chloride, which is obtained in the extraction of the metal as described above. The rhodic salts generally form rose-colored solutions, and are decomposed by metallic iron or zinc, with precipitation of metallic rhodium. Potassic and sodic hydrates added to rhodic salt solu- tions slowly precipitate a yellow hydrated rhodic oxide, which is soluble in excess of al- kali as well as in acids. Potassic iodide pre- cipitates a sparingly soluble yellow tri-iodide of rhodium. Sulphuretted hydrogen in hot