312 A CENTURY OF SCIENCE 



phuric acid industry, while other important applications 

 of platinum as a " catalytic agent " have also been made. 

 Wolcott Gibbs and Carey Lea have contributed perhaps 

 more than any other recent chemists to a knowledge of 

 the platinum metals. Carey Lea (38, 81, 248, 1864) 

 dealt chiefly with the separation of the metals from each 

 other, while Gibbs 's work (31, 63, 1861; 34, 341, 1862) 

 included investigations of many of the compounds. 

 ^ It may be mentioned that while platinum and its asso- 

 ciates were formerly known only in the uncombined con- 

 dition in nature, the arsenide sperrylite, PtAs 2 , was 

 described by the late S. L. Penfield, and the senior writer 

 of this chapter, in articles published in the Journal (37, 

 67, 71, 1889). 



Applications of the Spectroscope. The discovery in 

 certain mineral waters of the rare alkali-metals rubidium 

 and caesium by Bunsen and Kirchoff in 1861 was in conse- 

 quence of the application of spectroscopy by these same 

 scientists a short time previously to the identification of 

 elements imparting colors to the flame. Since that time 

 the employment of the spectroscope for chemical pur- 

 poses has been much extended, as it has been used in the 

 examination of light from electric sparks and arcs, as 

 well as from Geissler tube discharges and from colored 

 solutions. 



The metals rubidium and caesium are interesting in 

 being closely analogous to potassium and in standing at 

 the extreme electro-positive end of the series of known 

 metals. It should be noticed here that Johnson and 

 Allen of our Sheffield Laboratory, having obtained a 

 good supply of rubidium and caesium material from the 

 lepidolite of Hebron, Maine, made some important 

 researches upon these elements, accounts of which were 

 published in the Journal (34, 367, 1862; 35, 94, 1863). 

 They established the atomic weight of caesium, thus cor- 

 recting Bunsen 's determination which was unsatisfac- 

 tory on account of the small quantity and impurity of his 

 material. Pollucite, a mineral rich in caesium, which had 

 been found in very small amount on the Island of Elba, 

 has more recently been obtained in large quantitieshun- 

 dreds of pounds at Paris, Maine, and its vicinity. 

 This American pollucite was first analyzed and identi- 



