The Microscope. 45 



He immediately had forty-four tons of this water evaporated, from 

 which he obtained two new metals in very minute quantity. He 

 called them caesium and rubidium. Since their providential discov- 

 ery, these two metals have been found in many of the most celebrated 

 springs in the old world. The quantity of the two new metals thus 

 obtained by the evaporation of the forty-four tons of water was nearly 

 200 grains. This eminent chemist succeeded in separating these two 

 metals and to establish their properties chemically and spectrosco- 

 pically. 



The springs of Bourbon les Bains, Baden-Baden, Vichy, Gastein, 

 Nauheim, Karlsbad and others contain either the one or the other, 

 or both these alkaline metals in minute quantities, and much of the 

 curative powers of these springs may be due to their presence, 

 although in such minute quantities. 



Rubidium has a wider distribution than Csesiuni, especially in 

 the vegetable kingdom. We find it in the beet, in tobacco, in the 

 ash of the oak (the quercus pubescens), in coffee, tea, as well as in 

 cocoa. 



Not long after this, in 1861, the third new metal was discovered 

 by means of the spectroscope by W. Crooks. This new metal bears 

 the name of thallium. 



Reich and Richter, of Freiburg, Saxony, discovered a fourth 

 new metal, indium, by the spectral test. 



Another, the fifth, named gallium, was discovered by Lecoc de 

 Boisbaudran. 



Great as these discoveries were, thus initiated by the eminent 

 men in Heidelberg and elsewhere, there were still higher triumphs 

 in store for the prismatic test. In 1859 Kirchhof desired to ascer- 

 tain the accuracy of the often asserted coincidence of the bright 

 sodium line, produced by burning the metal sodium, and the dark 

 or black solar D line seen in the spectroscope. 



He placed a burning sodium flame before the slit of his spectro- 

 scope, and lo! he saw the dark D line change into a beautiful yellow 

 bright line. Then he directed bright solar light to pass through the 

 sodium flame, and beheld the bright line changed back again to the 

 dark D line. Thus he found the solution of his inquiry. The two 

 lines were coincident, identically the same. These experiments led 

 him to the logical conclusion that the dark D line I'esulted from 

 burning sodium in the sun, and that there must be some vaporous 

 envelope which absorbed the yellow bright line, and converted it into 

 a dark line ; he further concluded that both the bright and the dark 



