Analysis by Spectrum-observations. 337 



moistened with a solution of carbonic acid in water, and again 

 dried in the same way until no further loss of weight occurred. 

 The salt then weighed 0*6878 grm. Hence it is seen that the 

 bicarbonate of rubidium has a composition analogous to bicar- 

 bonate of potassium, or is represented by the formula — 







Calculated. 



Found. 



RbO . . 



. 93-36 



63-79 



63-72 



2C0 2 . . 



, . 44-00 



30-06 





HO. . . 



, . 9-00 



6-15 





146-36 100-00 



e. Nitrate of Rubidium. 



This salt crystallizes from aqueous solution, when quickly 

 cooled, in long indistinct crystals. When the crystallization is 

 conducted more slowly, double hexagonal prisms terminated with 

 less distinct double hexagonal pyramids are obtained in a state 

 fit for measurement. The crystals invariably incline to a prismatic 

 form, and belong to the hexagonal system, corresponding to a 

 ratio of the axes of 



l:«as 1 : 0-7097. 



This ratio belongs to an obtuse hexagonal dodecahedron, having 

 polar angles of 78° 40', and basal angles of 143° 0'. The pyra- 

 midal faces were very imperfectly formed, so that the measure- 

 ment of the angles could not be very exactly made. The faces 

 P . go P . P2 . go P2, Plate V. fig. 1, were the only ones observed. 

 Found. Calculated. 



p- Pl . . . 149 49 150 

 Pl -p . . . 149 53 150 

 r- p* ... 129 20 



The nitrate of potassium crystallizes, as is well known, in the 

 rhombic system, but according to Frankenheim it occurs some- 

 times as a secondary hexagonal form whose hemihedral form 

 corresponds to a hexagonal dodecahedron having polar angles of 

 106° 40'. This form corresponds to a hexagonal dodecahedron 

 of another order than that in which nitrate of rubidium cry- 

 stallizes ; to this, however, we will recur in speaking of the nitrate 

 of caesium. 



The nitrate of rubidium is anhydrous, but, like saltpetre, it 

 contains water enclosed in the pores of the crystals, which there- 

 fore decrepitate on heating. Near red heat it fuses without 

 decomposition to a clear liquid, and on cooling solidifies to a 

 striated crystalline mass. When heated to a higher point it 

 loses oxygen, and forms nitrite together with caustic oxide of 

 * This angle served for the calculation of the ratio of the axes. 



