SECT. IT. R UBIDIUM AND CAESIUM. 1 3 5 



belonged to a new rnetal ; and having obtained about 200 

 grains of the substance by the evaporation of forty tons 

 of the water, he found that they contained the chlorides 

 of the two new metals in question. Moreover he per- 

 ceived that these metallic chlorides resemble the chloride 

 of potassium so nearly in spectrum and chemical cha- 

 racter, that a refined prismatic analysis could alone 

 determine the difference. He thus ascertained that the 

 spectra of all the three have two red lines in the red ( 

 part of their spectrum, and two violet lines in the indigo, 

 while the middle part is occupied by a continuous, 

 diffused light. The only difference is that the two red , 

 lines in the rubidium spectrum are less refrangible than , 

 the red lines in the potassium spectrum, and that the 

 csesium spectrum is distinguished by two bright blue 

 lines in the diffuse middle part. Rubidium received its , 

 name from rubidus, on account of the dark red of its . 

 lines., and csesium from its sky-coloured blue lines. 



M. Bunsen thinks that there can hardly be a doubt 

 of rubidium having been mistaken for potassium, but he 

 has shown that they may be distinguished by the 

 difference in the solubility of the double salts which the 

 chlorides of these two metals form with the chloride of 

 platinum. An aqueous solution of the bichloride of 

 platinum and potassium gives an insoluble yellow pre- 

 cipitate, consisting of the bichlorides of platinum and 

 potassium. An aqueous solution of the bichlorides of 

 platinum and rubidium gives an insoluble yellow preci- 

 pitate of the bichlorides of platinum and rubidium. 

 These two precipitates are undistinguishable to the eye. 

 Now if a solution of platinum be added to the first, no 

 further precipitate can take place, but if a solution of 

 rubidium be added to it, a yellow precipitate is formed 

 consisting of the bichloride of rubidium and potassium, 

 because the chloride of rubidium resolves the precipitate, 

 combines with the chloride of potassium, and sets the 



