COBALT AND NICKEL. 159 



9. Compounds of chromium impart a green color to the 

 borax bead. 



Cobalt and Nickel, Co = 59, Ni = 59. These two metals have 

 not only the same atomic weight, but show also much resem- 

 blance to each other in their chemical and physical properties, 

 and occur in nature associated with each other as sulphides or 

 arsenides. 



Both metals are nearly silver-white; the salts of cobalt show 

 generally a red, those of nickel a green color. The solutions of 

 both metals give a black precipitate of the respective sulphides 

 on the addition of ammonium sulphide. Ammonium hydrate 

 produces in solutions of cobalt a blue, in solutions of nickel 

 a green precipitate of the hydrates, both of which are soluble 

 in an excess of the reagent; potassium or sodium hydrate pro- 

 duces similar precipitates, which are insoluble in an excess. 



Cobalt is chiefly used when in a state of combination (for 

 coloring glass blue); nickel, when in the metallic state. (German 

 silver is an alloy of nickel, copper, and zinc.) 



QUESTIONS. 



251. How is manganese found in nature? 



252. Mention the different oxides of manganese. What is the bin- 

 oxide used for ? 



253. What is the color of manganese salts, of manganates, and of 

 permanganates ? 



254. How is potassium permanganate made ; what are its properties, 

 and what is it used for ? 



255. Give tests for manganese. 



256. State composition and properties of potassium dichromate. 



257. How is chromium trioxide made ; what are its properties ; what 

 is it used for ; and under what other name is it known ? 



258. By what process may chromium sesquioxide be converted into 

 chromates ? 



259. What is the composition of the oxide and hydrate of chromium, 

 and how are they made ? 



260. Mention tests for chromates and chromium salts. 



