The X-ray photograph

shows a human stomach. It is visible only because the patient has swallowed a "barium meal." This sub­stance contains barium sul­fate, a substance that is opaque to X rays.

Fact entries

Berylliumwas discovered in the silicon-containing mineral beryl (from which its name derives) in 1798 by the French chemist Louis Vauquelin (1763-1829). The free metal was first isolated in 1828 by the German chemist Fredrich Wohler (1800-1882) and, independ­ently, by the French chemist Antoine Bussy (1794-1882). At. no. 4; at. mass 9.0128; m.p. 1278+5° C;b.p. 2970° C.

Magnesiumwas first iso­lated as the free metal in 1808 by the British scientist Humphry Davy (1778-1827), although its compounds (for

example, Epsom salts and magnesia) were known much earlier. The element is named after the ancient Creek region of Magnesia. At. no. 12; at. mass 24.305; m.p. 650° C; b.p. 1110+10° C.

Calciumwas first isolated as the free metal in 1808 by Humphry Davy. Its name is derived from the Latin calx, meaning lime—a calcium compound known since an­cient times. At. no. 20; at. mass 40.08; m.p. 839° C; b.p. 1484° C.

Strontiumwas first found at Strontian (hence, the ele-

ment's name) in Scotland in 1790 by the British scientist Adair Crawford. The metal itself was isolated in 1808 by Humphry Davy. At. no. 38; at. mass 87.62; m.p. 769° C; b.p. 1384°C.

Bariumderives its name from the Greek barys— meaning heavy—although the metal is not particularly dense. It was first detected in 1774 by the Swedish chemist Karl Scheele (1742-1786). The free metal was isolated in 1808 by Hum­phry Davy. At. no. 56; at. mass 137.33; m.p. about 725° C; b.p. about 1140° C.

Radiumwas discovered in the radioactive mineral pitchblende (a uranium ore) in 1898 by the French scien­tist Pierre Curie (1859-1906) and his Polish-born wife Marie (1867-1934). The metal itself was isolated in 1910 by Marie Curie. Its name is de­rived from the Latin radius, meaning ray. At. no. 88; at. mass 226.025; m.p. about 700° C; b.p. about 1140° C; half-life (of stablest isotope) 1,600 years.

Zinc, cadmium, and mer-curyconstitute Group 2B of the periodic table. They are chemically similar to each other. However, they are physically dissimilar.

The suspended steel pipes/right/ have just been galvanized. This means they have just been coated with a layer of zinc by being dipped into a bath of the molten metal. The zinc coat­ing on galvanized steel pre­vents the steel from rusting. The zinc itself does not cor­rode easily because, in air, a thin film of zinc oxide forms on its surface. This protects the underlying metal.

Date: 2015-12-11; view: 878