57.6 PRINCIPLES OF CHEMISTBY 



whether any other as yet unknown metals might not occur in different 

 natural products together with lithium, potassium, and sodium, and he 

 soon discovered two new alkali metals showing independent spectra. 

 They^ire named after the characteristic coloration which they impart to 

 the flame. One which gives a red and violet band is named rubidium, 

 from rubidius (dark red), and the other is called ccesium, because it 

 colours a pale flame sky blue, which depends on its containing bright 

 blue rays, which appear in the spectrum of caesium as two blue bands 

 (table on p, 565). Both metals accompany sodium, potassium, and 

 lithium, but in small quantities ; rubidium occurs, in larger quantity 

 than caesium. The amount of the oxides of caesium and rubidium in 

 lepidolite does not generally exceed one-half per cent. Rubidium has also 

 been found in the ashes of many plants, while the Stassfurt carnallite 

 (the mother-liquor obtained after having been treated for KC1) forms 

 an abundant source for rubidium and also partly for caesium. 

 Rubidium also occurs, although in very small quantities, in the majority 

 of mineral waters. In a very few cases caesium is not accompanied by 

 rubidium ; thus, in a certain granite on the Isle of Elba, caesium has 

 been discovered, but not rubidium. This granite contains a very rare 

 mineral ceMedpollux, which contains as much a% 4 per cent, of caesium 

 oxide. Guided by the spectroscope, and aided by the fact that the 

 double salts of platinic chloride and rubidium and caesium chlorides 

 are still less soluble in water than the corresponding potassium salt, 

 K 2 PtCl 6 , 41 Bunsen' succeeded in separating both metals from each 

 other and from potassium, and demonstrated the great resemblance 



41 The salts of the majority of metals are precipitated as carbonates on the addition 

 of ammonium carbonate for instance, the salts of calcium, iron, &c. The alkalis whose 

 carbonates are soluble are not, however, precipitated in this case. On evaporating the 

 resultant solution and igniting ihe residue (to remove the ammonium salts), we obtain 

 salts of the alkali metals. They may be separated by adding hydrochloric acid together 

 with a solution of platinic chloride. The chlorides of lithium and sodium give easily soluble 

 double salts with platinic chloride, whilst the chlorides of potassium, rubidium, and 

 caesium form double salts which are sparingly soluble. A hundred parts of water at 

 dissolve 0'74 part of the potassium platinochloride ; the corresponding rubidium 

 platinochloride is only dissolved to the amount of 0'184 part, and the caesium salt, 

 0'024 part; at 100 6'18 parts of potassium platinochloride, K 2 PtClg, are dissolved, 

 0'634 part of rubidium platinochloride, and 0'177 part of caesium platinochloride. 

 From this it is clear how the salts of rubidium and caesium may be isolated. The 

 separation of caesium from rubidium by this method is very tedious. It can be better 

 effected by taking advantage of the difference of the solubility of their carbonates in 

 alcohol; caesium carbonate, Cs 2 C03, is soluble in alcohol, whilst the corresponding salts 

 of rubidium and potassium are almost insoluble. Setterberg separated these metals as 

 .alums, but the best method, that given by Scharples, is founded on the fact that from 

 a mixture of the chlorides of potassium, sodium, caesium, and rubidium in the pre- 

 sence of hydrochloric acid, stannic chloride precipitates a double salt of caesium, which 

 is very slightly soluble. The salts of Eb and Cs are closely analogous to those of 

 potassium. 



