HYDRATES AND CARBONATES OF THE ALKALI-METALS, ETC. 463 



impurity of any kind or magnitude, a quantity of the carbonate was fused in instalments 

 over the blowpipe in a platinum crucible, the fused salt dissolved in water, the filtered 

 solution treated with carbonic acid, to saturate any caustic alkali and then again evapor- 

 ated to dryness in platinum, and dehydrated without fusion. The experiment was then 

 repeated with the purified salt, i.e., a quantity of it was heated in carbonic acid, first for 

 one hour with a small, and then for an hour and a half with a larger Bunsen, and 

 allowed to cool in C0 2 . The product this time had no brownish tinge about it ; some 

 parts of it had that glassy appearance which I had noticed in the corresponding kind of 

 carbonate of soda. It was analysed twice, with the following results :■ — 



(1) (2) Mean. 



Substance, . . . 1-4442 1-9376 



Carbonic acid obtained, . 04594 - 6169 



Percentage of carbonic acid, 31-809 31-838 31-824 



Pure K 2 C0 3 contains, by calculation, 3L821 per cent.* 



Mr Henderson applied the chloride of barium method, and found no caustic alkali. 

 The experiment is interesting chiefly as showing how perfectly normal fused K 2 C0 3 can 

 be prepared. 



Experiments with Carbonate of Rubidium. 



Let me state at once, that the word " Rubidium " in this heading means " a mixture 

 of rubidium and caesium, consisting chiefly of the former." The research on the " Chloro- 

 platinate Method for the Determination of Potassium," &c, which I carried out sometime 

 ago with Mr MAcARTHUR,t had left me in possession of a number of residues, from which 

 such " rubidium " could be and was extracted by known analytical methods. The 

 extracted rubidium was converted into normal sulphate, with the view, originally, of con- 

 verting this into hydrate by means of baryta water, and the hydrate into carbonate by 

 combination with carbonic acid. But caustic rubidia must be presumed to attack glass 

 very strongly, and we had not at the time a large enough platinum vessel to spare, which 

 would have enabled us to avoid contact of the caustic rubidia with glass. I therefore 

 caused Mr Henderson to try and convert the sulphate into carbonate more directly by 

 treatment with carbonate of baryta, water and carbonic acid, which last-named reagent 

 was intended to convert the alkaline carbonate into bicarbonate as quickly as it is pro- 

 duced, and to act as a solvent for the carbonate of baryta. To my surprise this very 

 plausible method would not work ; the process stopped long before the whole of the 

 sulphuric acid had assumed the form of baryta salt. 



I therefore proposed to substitute oxalate for the carbonate of baryta, and was glad 

 to find that the decomposition this time went on as desired. To produce an oxalate of 

 baryta sure to be free of alkali, this salt was made by addition of a solution of pure oxalic 

 acid to its calculated equivalent of pure baryta water, and then rendering the mixture 



* If K = 39-136, as found by Stas. If K = 39-00, the percentage becomes 31-884. I am far from taking it for 

 granted that the close agreement of our number with Stas's is not a mere accident. 

 + Transactions of the Royal Society of Edinburgh for 1887, p. 618. 



