Wells & Foote — One Hundred Years of Chemistry. 283 



It is in the same periodic group as thallium and indium, 

 and it has a remarkably low melting point, just above 

 ordinary room-temperature. It has been among the 

 rarest of the rare elements, but within two or three years 

 a source of it has been found in the United States in cer- 

 tain residues from the refining of commercial zinc. The 

 recent issues of the Journal (41, 351, 1916; 42, 389, 1916) 

 show that Browning and Uhler of Yale have availed 

 themselves of this new material in order to make import- 

 ant chemical and physical researches upon this metal. 



Germanium. — The discovery of germanium in the min- 

 eral argyrodite in 1886 by Winkler revealed a curious 

 metal which gives a white sulphide that may be easily 

 mistaken for sulphur and which is volatilized completely 

 when its hydrochloric acid solution is evaporated, so that 

 it is evasive in analytical operations. This element had 

 been predicted with much accuracy by Mendeleeff, and 

 it is rather closely related to tin. 



A few vears after the discovery of germanium, Pen- 

 field published in the Journal (46, 107, 1893; 47, 451, 

 1894) some analyses of argyrodite, correcting the for- 

 mula given by Winkler to the mineral ; also he described 

 canfieldite, an analogous mineral from Bolivia, in which 

 a large part of the germanium was replaced by tin. 



The Rare Earths. — Before the year 1818 two rare 

 earths, the oxides of yttrium and cerium, were known 

 in an impure condition. Since that time about fourteen 

 others have been discovered as associates of the first 

 two. The rare earths are peculiar from the fact that 

 many of them are always found mixed together in the 

 minerals containing them, and also from the circum- 

 stance that most of them are remarkably similar in their 

 chemical reactions and consequently exceedingly difficult 

 to separate from each other. In many cases multitudes 

 of fractional precipitations or crystallizations are needed 

 to obtain pure salts of a number of these metals. The 

 solutions of the salts of several of these elements give 

 characteristic absorption bands when examined spectro- 

 scopically by the use of transmitted light. 



No important practical application has been found for 

 any of these earthy oxides, except that about one per cent 

 of cerium oxide is mixed with thorium oxide in incandes- 

 cent gas-mantles in order to obtain greatly increased 

 luminosity. 



