the Rubidium Compounds. 49 



Chloride of sodium 35*77 



Chloride of potassium 33*37 



Chloride of rubidium 19*75 



Chloride of lithium 0*19 



Chloride of caesium (present in too 



small quantities for estimation). 



Chloride of strontium .... traces 



Water . . 10*92 



100*00 



This source of rubidium accordingly contains 3 ounces of chloride 

 of rubidium per pound *. 



The preparation of the chloride of rubidium is effected best as 

 follows : a kilogramme of the salt is dissolved in 2*5 kilogs. of 

 water, and precipitated in the cold by a solution of about 30 

 grms. of platinum in aqua regia. As soon as the yellow preci- 

 pitate has sufficiently subsided, the supernatant liquid is poured 

 into a large beaker-glass, and the precipitate brought into a basin 

 in order to boil it out twenty-five consecutive times with small 

 quantities of water. For this purpose about 1*5 kilog. of water, in 

 all, may be used ; and the operation is best performed in a large 

 platinum capsule, from which the volume of water used for boil- 

 ing out the precipitate is poured boiling-hot into the original 

 decanted liquid. A new precipitate then falls down from the 

 liquid, now amounting to about 4 kilogs. The liquid poured off 

 from this precipitate is next boiled down until, on adding it 

 again to the precipitate, the volume is not greater than it was at 

 the commencement of the operation. The platinum obtained by 

 reducing the purified precipitate in hydrogen is dissolved in 

 aqua regia, and this added to the boiled-down liquid ; the preci- 

 pitate which falls, as well as the supernatant liquid, is then 

 under the same conditions as it was at the beginning of the pre- 

 paration. Precipitate and liquid can therefore be treated again 

 in the manner just described. 



When these operations have been repeated seven or eight 

 times, the greater part of the chloride of rubidium contained in 

 the original kilogramme of salt has been extracted. Each of the 

 seven or eight platinum -precipitates is dried at 100° C. in the 

 dish in which it was boiled, then brought into a glass tube and 

 reduced in a current of hydrogen at a temperature below a red heat, 

 and below the melting-point of the chloride of rubidium. By di- 

 gesting the black reduced mass with warm water, the soluble chlo- 

 ride of rubidium is easily extracted from the platinum, which, as 



* This salt can now be obtained from Dr. Struve's mineral-water manu- 

 factory in Leipzig at a price of 6 thalers the kilogramme, or about 9s. per 

 pound. 



Phil Mag. S. 4. Vol. 24. No. 158. July 1862. E 



