248 INORGANIC CHEMISTRY 



curious metal melting at 50, gallium. Winkler, after very delicate 

 analysis, obtained germanium from Freiberg argyrodite. Also, in 

 1886, the author of this lecture succeeded in isolating fluorin, which, 

 though having a fairly wide distribution in nature, had previously 

 resisted the efforts of Humphry Davy, Louyet, the Knox brothers ( , 

 Fremy, and Gore. 



Within the last few years, another series of discoveries has aroused 

 the keen interest of the scientific world. As the result of delicate 

 experiments for determining the density of nitrogen when prepared 

 by chemical reaction, and when obtained from the air, Lord Rayleigh 

 declared that the difference, which affected only the third decimal 

 of his figures, was to be attributed to the existence of a gaseous ele- 

 ment heavier than nitrogen, present in the atmosphere. Following up 

 this physical determination, Lord Rayleigh and Sir William Ramsay 

 isolated argon; and Sir William Ramsay obtained the satellites of 

 argon, such as krypton, xenon, and neon. These studies led him also, 

 turning his attention to the surface of the earth, to observe and study 

 helium, the spectrum of which had been simultaneously discovered 

 in the sun's rays by Sir Norman Lockyer and by Janssen. 



These are splendid results, and they are the more curious since 

 they deal with a series of gaseous bodies which, because of their chem- 

 ical inertness, are a great embarrassment to the scientist and the 

 philosopher. 



But there is a group of metals which, in spite of the continued 

 efforts of chemists, has never yet been fully studied. I refer to the 

 rare earths, divided into the two series of cerium and yttrium. 



In 1751, Cronstedt discovered cerite in a mine at Bastnaes. In 1794, 

 Gadolin pointed out a rare earth, yttria, in a heavy black mineral 

 which was found abundantly in the neighborhood of Ytterby, and 

 which was afterwards named gadolinite. Cerium was characterized 

 as an element, in 1804, by Berzelius and Hisinger in Sweden, and by 

 Klaproth in Germany. 



This first work was followed by numerous rather confused investi- 

 gations, until Mosander, in 1839 and 1842, separated lanthanum and 

 didymium from the true cerium. The study of cerium and its com- 

 pounds was completed by the masterly researches of Cleve, and by 

 Marignac, Brauner, Wyrouboff , and Verneuil. Still later, Mosander's 

 didymium was separated by Auer von Welsbach into two elements, 

 praseodymium and neodymium. 



Samarium was studied by Cleve, Lecoq de Boisbaudran, Demargay, 

 Brauner, and Bettendorf. While examining the action of samarium, 

 Demarcay proved the existence of a new element, europium. 



Terminating his work on cerium, Mosander at once took up the 

 study of yttria and from it separated erbia and terbia. This study was 

 continued by Cleve, Marignac, Crookes, Delafontaine. In 1879, Cleve 



