192 Mr. 0. D. Allen on Casium and Rubidium. 



dium-salts twenty to thirty extractions of the carbonates with 

 boiling absolute alcohol (Phil. Mag. for July 1862, p. 50), 

 that I have made various attempts to discover a simpler 

 method. 



In the first place, a trial was made with the picrates of the new 

 metals. To a concentrated solution of their mixed chlorides an 

 alcoholic solution of picric acid was added. The liquid imme- 

 diately filled with fine acicular crystals. These were rinsed with 

 water and successively recrystallized from fresh portions of water 

 eleven times. Portions of the first, second, third, fourth, seventh, 

 and eleventh crops of crystals were separately examined in the 

 spectroscope, the picrates being converted into chlorides for this 

 purpose by treatment with aqua regia. No difference being 

 observable between the spectra of the various crops, no further 

 experiments were made in this direction. It may be here 

 remarked that the mixed picrates crystallize with great facility 

 in needles an inch in length, and perfectly resemble the corre- 

 sponding potassium-salt. 



A second series of trials was made with the platinobromides 

 of potassium, rubidium, and csesium. The platinobromide of 

 potassium is known to be readily soluble in water. The platino- 

 bromides of csesium and rubidium readily separate from dilute 

 solutions of these three metals, but carry down potassium 

 with them. For the removal of the latter metal from the new 

 alkalies, the platinobromides appear to have no advantage over 

 the platinochlorides, while they are equally inadequate to the 

 separation of csesium and rubidium from each other. In ex- 

 ternal characters the three platinobromides closely resemble 

 each other. 



Finally, recourse was had to the bitartrates, and with satisfac- 

 tory results. Carbonates of caesium and rubidium were first 

 prepared from the chlorides by converting them into sulphates, 

 separating the sulphuric acid with caustic baryta, and removing 

 the excess of baryta by carbonic acid. To the alkaline solution 

 thus obtained, twice as much tartaric acid was added as was 

 necessary to neutralize it. This solution was concentrated till it 

 was nearly saturated at 100° C. The crystals which deposited 

 on cooling, when examined by the spectroscope, showed the 

 rubidium lines more intensely than did the original mixture, 

 while the caesium lines were much fainter. This product was 

 dissolved and recrystallized from hot saturated solutions three 

 times. The caesium reaction in these successive crops diminished 

 until in the fourth it disappeared, leaving the rubidium spectrum 

 in entire purity. 



In order to ascertain whether the more soluble bitartrate of 

 csesium could be purified from rubidium by fractional crystalli- 



