THE PREPARATION OF RUBIDIUM Rubidium i s pe@red by distillation from a mixture of rubidium chloride and calcium metal. I t belongs to the ~olassiumfamily and reacts readily with the oxygen and moisture in air. For this reason it must be pre@red and collected i n an evacuated ap@ratus.
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The writer was recently given a quantity of rubidium chloride to be converted into the metal for museum samples. The problem was to prepare several small glass tubes, each containing about a half-gram of rubidium. This metal belongs to the potassium family. It oxidizes readily and reacts with the moisture in air, hence it must be prepared in a sealed and evacuated a p p a r a t u s . The method of preparation is to heat a m i x t u r e of rubidium chloride and calcium metal to 900 or 1000°C. in an electric resistance furnace. The calcium replaces the rubidium, which distils over and is collected in a suitable reservoir. After the reaction is complete the metal, which melts a t 38'C., is run over into the tubes in which it is to be exhibited. The apparatus used is shown in the figure. It is constructed of Pvrex glass. A is a tube made of heavy sheet iron, containing theoretically equivalent quantities of rubidium chloride and calcium filings. Its purpose is to prevent the sides of the outer glass tube from collapsing in the furnace. After this tube is loaded and placed in position, the outer glass tube is sealed off a t B and is placed in the furnace up to the top of the iron tube. A vacuum pump is connected to C and the furnace is turned on. A Bunsen flame applied a t D will keep the metal in the liquid or gaseous state until it reaches the collecting reservoir ( E ) . After the reaction is complete the tube is sealed off a t F, so that the reservoir and its side tube may be easily tilted to one side. A Bunsen flame applied to the bottom of the reservoir will then melt the metal so that some of it can be poured over into the bottom of the side tube. I t is possible to calculate to what depth this tube (Continued a page 12 f i ) 1274
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JOURNAL OF CHEMICAL EDUCATION
JULY.
1932
(Continued from page 1274)
must be filled to give the required amount of the sample (in this case a halfgram). The tube is then sealed off a t G and each of the successive sections filled and sealed off a t the next constriction, in the same manner. If it is desired to obtain the metal in a purer form, several of the collecting tubes ( E ) may be connected in series, and the metal may then be distilled from one tube into the next and finally poured into the side tube after E several redistillations. The side tube was weighed empty and filled, and it was found that about six grams of the metal had been obtained. This is about fifty per cent. of the theoretical yield from the eighteen grams of rubidium chloride used. A comparatively large amount of the metal seemed to wet the glass and stuck to the inside of the reservoir so that it could not be poured over into the side tube. This probably could have been prevented, and a larger yield obtained, if the inside of the apparatus had been more thoroughly cleaned a t the start. Any metal remaining in the reservoir may be dissolved out with hydrochloric acid and recovered as the chloride. Cesium, the fifth member of the potassium family, may be prepared from its chloride in the same manner as rubidium.
