Strontium

Strontium

Stontium is an alkaline earth metal element denoted by the atomic symbol, Sr. It has an atomic weight of 87.62 and has an atomic number of 38. It is a silvery-white metal that oxidizes rapidly in air, forming a pale yellow crust of oxide on any freshly cut surface. It exists in three allotropic forms and has a melting point of 1,430.6°F (777°C) and a boiling point of 2,519.6°F (1,382°C).

Credit for the discovery of strontium probably should be divided among three men, Adair Crawford (1767-1813), Thomas Charles Hope (1766-1844), and Humphry Davy. Crawford was a physician and professor of chemistry at Woolwich. He first recognized in 1790 that an ore found in the lead mine at Strontian, in Argyleshire (Scotland), contained " a new species of earth" unlike anything that had been described to that time.

Beginning in 1791, Hope continued the study of this new earth. Hope was professor of chemistry at the University of Edinburgh. He presented the results of his investigations in papers read at the College Literary Society of Edinburgh in March 1792 and the Royal Society of Edinburgh in November 1793. In those talks, he described in great detail the properties of Crawford's new earth, strontia, and compared it to the closely related earths known as lime (calcium hydroxide) and baryta (barium hydroxide).

He pointed out that strontia could be distinguished from its two close cousins on the basis of flame tests. Calcium produced a red flame, barium a green flame, and strontia a brilliant red flame that was strikingly different from that of calcium.

Isolation of the metal itself did not occur until 1808 when Davy used electrolysis to produce it, calcium, magnesium, and barium.

Strontium's chemical behavior is similar to that of calcium, but it has relatively few commercial applications since it is rarer and more expensive than that element. The beautiful crimson flame produced by its compounds when ignited accounts for its major uses in fireworks, signal flares, and tracer bullets. Strontium is also used in the production of glass for color televisions and as a gemstone.

The radioactive isotope, strontium-90, was the source of considerable concern during the period of atmospheric testing of nuclear weapons. A by-product of these weapons, strontium-90 fell back to earth as a fine powder, coated grass and surfaces, was ingested by cows, and became incorporated into their milk. When the milk was drunk by children, the strontium-90 followed the same metabolic path as calcium and became incorporated into their teeth and bones. The health threat it posed thereby was an important factor in convincing nations to discontinue atmospheric testing of nuclear weapons. Now, this radioactive isotope is being considered as a source of electric energy.