334 Professors Kirchhoff and Bunsen on Chemical 



We have assured ourselves in a series of spectrum-analytical 

 investigations, which we here omit, as we shall return to the 

 subject when discussing the properties of the csesium . com- 

 pounds, that in almost all mineral springs containing chloride 

 of sodium, traces of rubidium compounds accompany the salts of 

 potassium and sodium ; so that, although rubidium is found in 

 but small quantities, it is by no means a body of rare occurrence. 



II. Of Metallic Rubidium and some of its compounds. 

 a. The Metal. 



As the total quantity of pure material which we possessed 

 scarcely exceeded one ounce, it would have been unwise to waste 

 the whole of this in one experiment upon the reduction of the metal 

 from the carbonate, and we therefore for the present confined 

 ourselves to separating the metal by means of electrolysis. If a 

 current be passed through fused chloride of rubidium, the posi- 

 tive pole consisting of a rod of graphite, and the negative pole 

 being formed of an iron wire, the metallic rubidium, is seen to 

 rise to the surface of the liquid from the latter, and burns with 

 reddish colour on coming in contact with the air. When the 

 iron wire is surrounded by a small glass bell through which a 

 current of pure dry hydrogen is led, the metal does not burn, 

 but it does not collect in the hollow bell, as it disappears as soon 

 as it is liberated, uniting with the chloride to form a subchloride, 

 which dissolves in the fused mass. This subchloride imparts a 

 deep blue colour to the salt in the neighbourhood of the iron 

 pole ; and although this blue mass is perfectly transparent and 

 does not exhibit, either when examined by the naked eye or with 

 the microscope, any trace of a metallic substance, it decomposes 

 water with evolution of hydrogen and with formation of a colour- 

 less solution having a strong alkaline reaction ; chloride of potas- 

 sium also forms, under similar circumstances, a blue subchloride. 

 If the reduction be repeated with a mixture containing an equal 

 number of atoms of chlorides of calcium and rubidium at the 

 temperature, almost below redness, at which this mixture fuses, a 

 mass is obtained which evolves large quantities of hydrogen when 

 thrown into water, and from which small grains of metal arc 

 thrown out, which ascending take fire spontaneously on coming 

 into contact with the air. The metal cannot, however, be ob- 

 tained in this way in sufficient quantity to be properly investi- 

 gated. The amalgam of rubidium can, on the contrary, be very 

 easily prepared from a concentrated solution of chloride of 

 rubidium when metallic mercury is used as the negative pole, 

 and a platinum wire is employed as the positive pole. The 

 mercury is thus quickly changed into an amalgam of rubidium, 

 which on cooling appears as a solid crystalline brittle mass of a 



