F. R. Fraprie — Chromates of Caesium. 309 



Art. XXVII. — On the Chromates of Caesium / by Frank Roy 



Fraprie. 



Or salts of caesium and chromic acid, there have been 

 described a chromate and a bichromate, neither of which have 

 been thoroughly investigated. Caesium chromate was appar- 

 ently first made by Retgers,* who studied its isomorphism 

 with the other alkaline chromates without describing the salt 

 itself. It was prepared in " beautiful clear yellow needles 

 several centimeters long " by Chabrief in 1901, after the pre- 

 sent study was begun. The bichromate was first mentioned 

 in 1885 by Soret,^: who prepared caesium chrome alum from 

 commercial bichromate, and was described by Chabrie (loc. cit.) 

 as " small crystals of a brilliant clear red." 



In the present investigation the following salts have been 

 prepared : 



Cs 2 Cr0 4 a (Rhombohedral-hemihedral) 



Cs 2 Cr0 4 (3 (Orthorhombic) 



Cs 2 Cr 2 0, (Triclinic) 



Cs 2 Cr 3 O 10 (Rhombohedral-hemihedral) 



Caesium Chromate a, Cs 2 Cr 0^ 



This salt was prepared in Cambridge in 1901-2 by adding an 

 excess of silver chromate suspended in water to a solution of 

 caesium chloride. The caesium chloride used was prepared by 

 Mr. E. H. Archibald for the determination of the atomic 

 weight of caesium, and was spectroscopically free from traces 

 of other alkali metals. The caesium chromate was filtered by 

 suction and evaporated to small bulk, when a small quantity 

 of silver chromate separated. This was filtered off, and the 

 nearly saturated solution was allowed to crystallize in a desic- 

 cator. The crystals obtained at ordinary temperatures, instead 

 of being orthorhombic, like-the potassium and ammonium salts, 

 were long hexagonal prisms, of a very pale yellow color, almost 

 colorless when transparent. They are perfectly stable in either 

 dry or moist air. They contain no water of crystallization. 

 An analysis for chromium gave .the following result : 



Barium % Cr0 3 



Salt taken. chromate. found. Calculated. 



0-2874 g. 0-1900 g. 26-12 26'22 



A crystallographic examination of the crystals was made. 



They consisted of a combination of the hexagonal prisms of 



the first and second order equally developed, with a single 



*Retgers, Ztschr. physikal. Cheni., 1891, viii, 24-63. 



f Chabrie, Comptes rendus, 1901, cxxxii, 678-681 ; Ann. chim. phys., 1902, 

 (7)xxvi, 212-228. 



JSoret, Arch. sci. phys. nat., 1885, (3) xiv, 96; Comptes rendus, 1885, 

 ci, 156-157. 



Am. Jour. Sci. — Fourth Series, Vol. XXI, No. 124. — April, 1906. 

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