MM. Becquerel on Electro-chemical Reductions. 383 



one-twelfth, to get rid of the greater part of the salts. Hydro- 

 chloric acid is then added to decompose the carbonates, sulphides, 

 and hyposulphites ; and to the filtered liquid, nitric acid is added 

 to remove iodine and bromine. The liquid then contains nothing 

 but sulphates and chlorides. It is diluted, heated to boiling, and 

 a saturated boiling solution of chloroplatinate of potassium added. 

 The precipitate formed consists mainly of chloroplatinate of rubi- 

 dium, which may be purified by treatment with hot water. The 

 chloroplatinate of rubidium is reduced in a current of hydrogen. 

 The residue, treated by water, dissolves out chloride of rubidium. 



M. Grandeau has also found rubidium among the salts in 

 Havanna and Kentucky tobacco, in the ashes of coffee and of 

 tea, and in small quantity in the mother-liquors from the pre- 

 paration of crude tartar. 



Than has also* found rubidium in the ashes of the Quercus 

 pubescens. 



The MM. Becquerel have resumed the researches on the elec- 

 tro-chemical phenomena produced by electrical forces of low in- 

 tensity. They describe the results obtained with solutions of 

 cobalt, nickel, gold, silver, and platinum. 



Cobalt. — This metal is readily obtained pure by the action of 

 a feeble current on a concentrated solution of chloride of cobalt 

 to which an excess of alkali has been added. The metal is depo- 

 sited in brilliant white coherent tubercles, or in uniform layers, 

 according to the intensity of the current. During its formation 

 some chlorine is disengaged, and some remains in solution as 

 hydrochloric acid; when the solution has attained a certain 

 degree of acidity, the deposit ceases to have the metallic aspect, 

 and takes a blackish appearance. When the solution is again 

 saturated with ammonia, the deposit resumes the metallic lustre. 

 The intensity of the solution must always have a certain relation 

 to the density of the liquid to be decomposed. 



The cobalt thus obtained is hard and brittle ; reduced at a suit- 

 able temperature in hydrogen, it becomes very malleable, and 

 may be worked. With suitable moulds, cylinders, bars, and 

 medals are obtained. 



If the solution contains salts of lead or manganese, they are 

 decomposed, and the two metals deposited as peroxide on the 

 positive electrode. Iron remains in solution ; no trace is found 

 in the metallic deposit, which is then very pure. The cylinders 

 or bars withdrawn from solution are magnetic, and they have the 

 polarity due to the action of the earth or of the current. 



Nickel. — The method is the same ; sulphate of nickel is used, 

 to which ammonia must be added. As the decomposition pro- 



* Liebig's Annalen (Supplement 1), 1862. 



