ERBACH

erbach, a town of germany, in the grand-duchy of hesse-darmstadt, on the mumling, 22 m. s.e. of darmstadt. it has cloth mills and ivory-turning, for which last branch it possesses a technical school. wool and cattle fairs are held twice a year. pop. 2800. the castle contains an interesting collection of weapons and pictures, and in the chapel are the coffins of einhard, the friend and biographer of charlemagne, and his wife, emma. erbach has long been the residence of the counts of erbach, who trace their descent back to the 12th century, and who held the office of cupbearer to the electors palatine of the rhine until 1806. in 1532 the emperor charles v. made the county a direct fief of the empire, on account of the services rendered by count eberhard during the peasants' war. since 1717 the family has been divided into the three lines of erbach-furstenau, erbach-erbach and erbach-schonberg, who rank for precedence, not according to the age of their descent, but according to the age of the chief of their line. in 1818 the counts of erbach-erbach inherited the county of wartenberg-roth, and in 1903 the count of erbach-schonberg was granted the title of prince. the county was mediatized in 1806, and is now incorporated with the duchy of hesse-darmstadt. see simon, _die geschichte der dynasten und grafen zu erbach_ (frankfort, 1858). erbium (symbol, er; atomic weight, 165-166), one of the metals of the rare earths. the first of the rare earth minerals was discovered in 1794 by j. gadolin and was named gadolinite from its discoverer. in 1797 ekeberg showed that gadolinite contained another rare earth, which was given the name yttria. yttria is an exceedingly complex mixture, which has been decomposed, yielding as an intermediate product terbia. this latter substance in its turn has been split by j.l. soret, p.t. cleve, lecoq de boisbaudran and others into erbia, holmia, thulia and dysprosia, but it is still doubtful whether any one of these four splitting products is a single substance. the rare earth metals are found in the minerals gadolinite, samarskite, fergusonite, euxenite and cerite. they are separated from the minerals by converting them into oxalates, which by ignition give the corresponding oxides. the oxides are then converted into double sulphates which are separated from each other by repeated fractional crystallization or by fractional precipitation with ammonia or some other base. erbium forms rose-coloured salts and a rose-coloured oxide. the oxide dissolves slowly in acids; it is not reduced by hydrogen and is infusible. the salts show a characteristic absorption spectrum. see j.f. bahr and r. bunsen (_ann._, 1866, 137, p. 1); a. v. welsbach (_monats._, 1883, 4, p. 641; 1884, 5, p. 508; 1885, 6, p. 477); p.t. cleve (_comptes rendus_, 1879, 89, p. 478; 1880, 91, pp. 328, 381; 1882, 95, p. 1225; _bull. de la soc. chim._, 1874, 21, p. 196; 1883, 39, p. 287); c. marignac (_ann. chim. phys._, 1849 [3] 27, p. 226); b. brauner (_monats._, 1882, 3, p. 13); w. crookes (_proc. roy. soc._, 1886, 40, p. 502); lecoq de boisbaudran (_comptes rendus_, 1886, 102, p. 1005); a. bettendorf (_ann._, 1892, 270, p. 376); m. muthmann (_ber._, 1898, 31, p. 1718; 1900, 33, p. 42); g. kruss (_zeit. f. anorg. chem._, 1893, 3, p. 108).