250 CHEMISTRY. 



therefore, that they were mocked in these results by the 

 earth-spirits of the mines, the Kobolds, as they were called, 

 and so named the ore after them. The name which the 

 metal now bears is a corruption of that which was orig- 

 inally bestowed by the miners upon the ore. 



349. Chloride of Cobalt. The solution of this salt makes 

 a beautiful sympathetic ink. It being of a pink color, what 

 is written upon pink paper will be invisible. If the paper 

 be warmed, the letters will become of a bright blue color, 

 and then they will fade again as the paper becomes cool. 



This is owing to the difference of color between the hy- 

 drated and the anhydrous salt. 



350. Nickel. This is a white metal, and takes a good 

 polish. One of its chief uses is in making the alloy called 

 German silver. It is an ingredient in the meteorites, as 

 already noticed. Both cobalt and nickel are commonly 

 found in company with iron, and these three metals are the 

 only ones which are magnetic. The beautiful stone called 

 chrysoprase is quartz colored an apple-green by oxide of 

 nickel. 



Nickel almost deserves to be classed among the noble 

 metals, it is so little prone to oxidize. Since nickel-plating 

 has been perfected we see nickel -covered objects in com- 

 mon use. The one-cent and five-cent coins are alloys of 

 copper and nickel. Nickel forms two oxides, only one, 

 NiO, being of importance. 



351. Salts of Nickel. The most abundant ore of nickel 

 is niccolite, an arsenide of nickel. Nickel dissolves in ni- 

 tric acid, forming a beautiful green nitrate of nickel. The 

 carbonate, sulphate, chloride, hydrate, etc., are well-known 

 salts, which have not obtained any extensive use in the 

 arts. A double salt, sulphate of nickel and ammonium, is 

 used in nickel-plating. 



352. Chromium. This is not very abundant in the earth. 



