500 Professors Kirchhoff and Bunsen on Chemical 



e. Nitrate of Casium. 

 This salt contains no water of crystallization, it does not un- 

 dergo alteration in the air, and may be obtained from its aqueous 

 solution in the form of small shining crystals of a prismatic form, 

 in which the faces of the prism are generally better defined than 

 those at the summits. The crystals obtained by slow evapora- 

 tion at 14° C. belong to the hexagonal system, and are isomor- 

 phous with nitrate of rubidium. The primary form is an obtuse 

 hexagonal dodecahedron, with polar angles of 142° 56', and basal 

 angles of 78° 58', corresponding to the following relation of the 

 axes 



1:« = 1: 071348. 



The faces which could be observed (see Plate V. fig. 1) are as 

 follows : — 



P.ooP.P2.ooP2.0P.fP. 

 r p r x 2 } \ ° Q' 





Calculated. 



Found. 



P~P\ ' • 



. 150 6 



149 59 



V\~P - ' 



. 150 



149 58 



r —px* . 



, 



129 29 



r\-~P\ 



. 125 30 



125 28 



r —r y 



. 161 28 



161 41 



r — q 



. 172 14 



172 



r, — o 



. 144 30 



144 39 



If the primary form be taken to be a hexagonal dodecahedron 

 of the second order, the corresponding hexagonal dodecahedron 

 of the first order yields as a hemihedral form a rhombohedron 

 having polar angles of 106° 40'. Through this form, therefore, 

 the isomorphism of the nitrates of caesium and rubidium, and the 

 potash and soda nitre, becomes apparent. We have — 



Nitrate of caesium .... 106 40 

 Nitrate of potassium . . . 106 30 

 Nitrate of sodium .... 106 36 



When crystallized quickly, the salt separates out in long needle- 

 shaped prisms, longitudinally striated. It has the same saline 

 bitter cooling taste as saltpetre — so much so that these salts can- 

 not thus be distinguished from each other. On heating, the 

 salt melts to a thin liquid at temperatures almost below the red 

 heat j and when more strongly heated it evolves oxygen, and is 

 converted first into nitrite, and afterwards, by absorption of 

 moisture from the air, into caustic hydrate of caesium, which 



* This angle served as basis of calculation for the primary form. 



