280 Wells £ Foote — One Hundred Years of Chemistry, 



powders and of mixtures used for fireworks. It is also 

 used in making certain light alloys. 



After almost innumerable attempts to isolate fluorine, 

 during a period of nearly a century, this was finally 

 accomplished in 1886 by Moissan in France by the elec- 

 trolysis of anhydrous hydrogen fluoride. The free 

 fluorine proved to be a gas of extraordinary chemical 

 activity, decomposing water at once with the formation 

 of hydrogen fluoride and ozonized oxygen. This fact 

 explains the failure of many previous attempts to pre- 

 pare it in the presence of water. 



Early Discoveries of Neiv Elements. — The remarkable 

 activity of chemical research at the beginning of our 

 period is illustrated by the fact that three new elements 

 were discovered in 1817. In that year Berzelius had dis- 

 covered selenium, Arfvedson, working in Berzelius 's 

 laboratory had discovered the important alkali-metal 

 lithium, and Stromeyer had discovered cadmium. 



In 1826 Ballard in France discovered bromine in the 

 mother-liquor from the crystallization of common salt 

 from sea-water. Bromine proved to be an unusually 

 interesting element, being the only non-metallic one that 

 is liquid at ordinary temperatures, and being strikingly 

 intermediate in its properties between chlorine and 

 iodine. It has been obtained in large quantities from 

 brines, and is produced extensively in the United States. 

 The elementary substance and its compounds have found 

 important applications in chemical operations, while the 

 bromides have been found valuable in medicine and 

 silver bromide is very extensively used in photography. 



In 1828 Berzelius discovered thorium. The oxide of 

 this metal has recently been employed extensively as the 

 principal constituent of incandescent gas-mantles, and 

 the element has acquired particular importance from the 

 fact that, like uranium, it is radio-active, decomposing 

 spontaneously into other elements. 



Vanadium had been encountered as early as 1801 by 

 Del Eio, who named it ' i erythronium, ' ' but a little later 

 it was thought to be identical with chromium and was lost 

 sight of for a while. In 1830, however, it was re-discov- 

 ered by, and received its present name from Sefstrom in 

 Sweden. Berzelius immediately made an extensive 

 study of vanadium compounds, but he gave them incor- 

 rect formulas and derived an incorrect atomic weight for 



