teeth. The metal is quite permanent in dry air, but in moist air it becomes coated with a superficial layer of the oxide; it burns on heating to redness, forming a brown coloured oxide; and is readily soluble in mineral acids with formation of the corresponding salts. Cadmium vapour decomposes water at a red heat, with liberation of hydrogen, and formation of the oxide of the metal.
Cadmium oxide, CdO, is a brown powder of specific gravity 6.5, which can be prepared by heating the metal in air or in oxygen; or by ignition of the nitrate or carbonate; by heating the metal to a white heat in a current of oxygen it is obtained as a dark red crystalline sublimate. It does not melt at a white heat, and is easily reduced to the metal by heating in a current of hydrogen or with carbon. It is a basic oxide, dissolving readily in acids, with the formation of salts, somewhat analogous to those of zinc.
Cadmium hydroxide, Cd(OH)2, is obtained as a white precipitate by adding potassium hydroxide to a solution of any soluble cadmium salt. It is decomposed by heat into the oxide and water, and is soluble in ammonia but not in excess of dilute potassium hydroxide; this latter property serves to distinguish it from zinc hydroxide.
The chloride, CdCl2, bromide, CdBr2, and iodide, CdI2, are also known, cadmium iodide being sometimes used in photography, as it is one of the few iodides which are soluble in alcohol. Cadmium chloride and iodide have been shown to behave in an anomalous way in aqueous solution (W. Hittorf, Pogg. Ann., 1859, 106, 513), probably owing to the formation of complex ions; the abnormal behaviour apparently diminishing as the solution becomes more and more dilute, until, at very high dilutions the salts are ionized in the normal manner.
Cadmium sulphate, CdSO4, is known in several hydrated forms; being deposited, on spontaneous evaporation of a concentrated aqueous solution, in the form of large monosymmetric crystals of composition 3CdSO4·8H2O, whilst a boiling saturated solution, to which concentrated sulphuric acid has been added, deposits crystals of composition CdSO4·H2O. It is largely used for the purpose of making standard electric cells, such for example as the Weston cell.
Cadmium sulphide, CdS, occurs naturally as greenockite (q.v.), and can be artificially prepared by passing sulphuretted hydrogen through acid solutions of soluble cadmium salts, when it is precipitated as a pale yellow amorphous solid. It is used as a pigment (cadmium yellow), for it retains its colour in an atmosphere containing sulphuretted hydrogen; it melts at a white heat, and on cooling solidifies to a lemon-yellow micaceous mass.
Normal cadmium carbonates are unknown, a white precipitate of variable composition being obtained on the addition of solutions of the alkaline carbonates to soluble cadmium salts.
Cadmium nitrate, Cd(NO3)2·4H2O, is a deliquescent salt, which may be obtained by dissolving either the metal, or its oxide or carbonate in dilute nitric acid. It crystallizes in needles and is soluble in alcohol.
Cadmium salts can be recognized by the brown incrustation which is formed when they are heated on charcoal in the oxidizing flame of the blowpipe; and also by the yellow precipitate formed when sulphuretted hydrogen is passed though their acidified solutions. This precipitate is insoluble in cold dilute acids, in ammonium sulphide, and in solutions of the caustic alkalis, a behaviour which distinguishes it from the yellow sulphides of arsenic and tin. Cadmium is estimated quantitatively by conversion into the oxide, being precipitated from boiling solutions by the addition of sodium carbonate, the carbonate thus formed passing into the oxide on ignition. It can also be determined as sulphide, by precipitation with sulphuretted hydrogen, the precipitated sulphide being dried at 100° C. and weighed.
The atomic weight of cadmium was found by O. W. Huntington (Berichte, 1882, 15, p. 80), from an analysis of the pure bromide, to be 111.9. H. N. Morse and H. C. Jones (Amer. Chem. Journ., 1892, 14, p. 261) by conversion of cadmium into the oxalate and then into oxide, obtained values ranging from 111.981 to 112.05, whilst W. S. Lorimer and E. F. Smith (Zeit. für anorg. Chem., 1891, 1, p. 364), by the electrolytic reduction of cadmium oxide in potassium cyanide solution, obtained as a mean value 112.055. The atomic weight of cadmium has been revised by G. P. Baxter and M. A. Hines (Journ. Amer. Chem. Soc., 1905, 27, p. 222), by determinations of the ratio of cadmium chloride to silver chloride, and of the amount of silver required to precipitate cadmium chloride. The mean value obtained was 112.469 (Ag=107.93). The mean value 112.467 was obtained by Baxter, Hines and Frevert (ibid., 1906, 28, p. 770) by analysing cadmium bromide.
CADMUS, in Greek legend, son of Agenor, king of Phoenicia and brother of Europa. After his sister had been carried off by Zeus, he was sent out to find her. Unsuccessful in his search, he came in the course of his wanderings to Delphi, where he consulted the oracle. He was ordered to give up his quest and follow a cow which would meet him, and to build a town on the spot where she should lie down exhausted. The cow met him in Phocis, and guided him to Boeotia, where he founded the city of Thebes. Intending to sacrifice the cow, he sent some of his companions to a neighbouring spring for water. They were slain by a dragon, which was in turn destroyed by Cadmus; and by the instructions of Athena he sowed its teeth in the ground, from which there sprang a race of fierce armed men, called Sparti (sown). By throwing a stone among them Cadmus caused them to fall upon each other till only five survived, who assisted him to build the Cadmeia or citadel of Thebes and became the founders of the noblest families of that city (Ovid, Metam. iii. 1 ff.; Apollodorus iii. 4, 5). Cadmus, however, because of this bloodshed, had to do penance for eight years. At the expiration of this period the gods gave him to wife Harmonia (q.v.), daughter of Ares and Aphrodite, by whom he had a son Polydorus, and four daughters, Ino, Autonoë, Agave and Semele—a family which was overtaken by grievous misfortunes. At the marriage all the gods were present; Harmonia received as bridal gifts a peplos worked by Athena and a necklace made by Hephaestus. Cadmus is said to have finally retired with Harmonia to Illyria, where he became king. After death, he and his wife were changed into snakes, which watched the tomb while their souls were translated to the Elysian fields.
There is little doubt that Cadmus was originally a Boeotian, that is, a Greek hero. In later times the story of a Phoenician immigrant of that name became current, to whom was ascribed the introduction of the alphabet, the invention of agriculture and working in bronze and of civilization generally. But the name itself is Greek rather than Phoenician; and the fact that Hermes was worshipped in Samothrace under the name of Cadmus or Cadmilus seems to show that the Theban Cadmus was originally an ancestral Theban hero corresponding to the Samothracian. The name may mean “order,” and be used to characterize one who introduces order and civilization.
The exhaustive article by O. Crusius in W. H. Roscher’s Lexikon der Mythologie contains a list of modern authorities on the subject of Cadmus; see also O. Gruppe, De Cadmi Fabula (1891).
CADMUS OF MILETUS, according to some ancient authorities the oldest of the logographi (q.v.). Modern scholars, who accept this view, assign him to about 550 B.C.; others regard him as purely mythical. A confused notice in Suidas mentions three persons of the name: the first, the inventor of the alphabet; the second, the son of Pandion, “according to some” the first prose writer, a little later than Orpheus, author of a history of the Foundation of Miletus and of Ionia generally, in four books; the third, the son of Archelaus, of later date, author of a history of Attica in fourteen books, and of some poems of an erotic character. As Dionysius of Halicarnassus (Judicium de Thucydide, c. 23) distinctly states that the work current in his time under the name of Cadmus was a forgery, it is most probable that the two first are identical with the Phoenician Cadmus, who, as the reputed inventor of letters, was subsequently transformed into the Milesian and the author of an historical work. In this connexion it should be observed that the old Milesian nobles traced their descent back to the Phoenician or one of his companions. The text of the notice of the third Cadmus of Miletus in Suidas is unsatisfactory; and it is uncertain whether he is to be explained in the same way, or whether he was an historical personage, of whom all further record is lost.
See C. W. Müller, Frag. Hist. Graec, ii. 2-4; and O. Crusius in Roscher’s Lexikon der Mythologie (article “Kadmos,” 90, 91).
CADOGAN, WILLIAM CADOGAN, 1st Earl (1675–1726), British soldier, was the son of Henry Cadogan, a Dublin barrister, and grandson of Major William Cadogan (1601–1661), governor of Trim. The family has been credited with a descent from Cadwgan, the old Welsh prince. Cadogan began his military career as a cornet of horse under William III. at the Boyne, and, with the regiment now known as the 5th (Royal Irish) Lancers, made the campaigns in the Low Countries. In the course of these years he attracted the notice of Marlborough. In 1701 Cadogan was employed by him as a staff officer in the complicated task of concentrating the grand army formed by contingents from
