Analysis by Spectrum-observations. 335 



silver-white colour. This amalgam decomposes water at the 

 ordinary temperature, absorbs oxygen from the air, becoming hot, 

 and being covered with a white coating of caustic hydrated oxide 

 of rubidium. Rubidium amalgam is strongly electro-positive in 

 respect to potassium-amalgam when a circuit is completed with 

 both by means of the chlorides of rubidium and potassium. 



Potassium, therefore, can no longer be considered as the most 

 electro-positive element, for in the foregoing experiment it has 

 been shown to be more electro-negative than rubidium. 



b. Hydrated Oxide of Rubidium. 



This substance is best prepared from the sulphate ; the latter 

 salt is dissolved in 100 parts of water, and the solution boiled 

 for some time to free it from air ; to the boiling solution hydrate 

 of baryta is cautiously added ; the sulphate separates quickly out, 

 so that the point of complete precipitation is easily and accurately 

 reached. If the liquid be now quickly evaporated in a silver 

 basin, the hydrated oxide is obtained as a white, or greyish-white, 

 porous mass, which melts and fuses quickly almost below a red 

 heat. It does not lose its water of hydration at a red heat; 

 on cooling, it solidifies to a brittle though not easily breakable 

 mass, which does not exhibit any crystalline structure. This 

 substance is completely and quickly volatilized when placed 

 in a flame ; and placed in contact with water, it dissolves with 

 evolution of great heat. Placed on the skin it acts as a powerful 

 caustic, resembling the hydrate of potash. Exposed to the air 

 it rapidly deliquesces, forming a syrupy liquid which possesses 

 the peculiar oily feeling, when placed on the finger, characteristic 

 of the common alkalies ; and it gradually absorbs carbonic acid, 

 at first becoming carbonate, and at last forming bicarbonate of 

 rubidium. Alcohol dissolves this substance as easily as it does 

 caustic potash, and a thick oily liquid is produced. As regards 

 alkaline reaction and alkaline taste, it is not surpassed by potash. 

 The alkali cannot be evaporated in platinum vessels, as it attacks 

 this metal as strongly as caustic potash. 



0*7200 grm. of this hydrated oxide of rubidium yielded 

 , 9286 grm. of sulphate. Hence it consists of — 



Calculated. Found. 



RbO . . . 93-36 91-21 90-29 



HO . . . 9-00 8-79 9-71 



102-36 100-00 100-00 



The somewhat large excess of water here found is explained by 

 the difficulty of obtaining the salt perfectly free from carbonic 

 acid. We have, as yet, not made experiments to determine 

 whether rubidium possesses any higher or lower oxides. 



