364 Elements of Mineralogy. 



4. It is true, that in feme circumftances glafs 

 may be tinged blue by iron, as Mr. Gmelin 

 has learnedly fhewn in the jth part of Mr. 

 Cre/fs Chymical Journal ; but this iron is 

 not transformed into cobalt ; for if that glafs 

 be digefted in aqua regia, the folution will 

 not form a fympathetic ink ; but, on the con- 

 trary, will manifefl every property of iron $ 

 whereas glafs tinged blue by cobalt will,when 

 digefted with aqua regia, afford fympathetic 

 ink, and manifeft the other diftinctive cha- 

 racters of cobalt. 



Nickel 



5. Mr. Monnet thinks that cobalt and 

 nickel are one and the fame metal, which 

 when united to iron, exhibits the properties 

 of, and is called cobalt, but when free from 

 iron, is called nickel; fo that nickel is the 

 fimple fubftance, and cobalt the compound. 

 The folutions of cobalt he adds are red, merely 

 on account of the iron, otherwife they would 

 be green like thofe of nickel ; the blue tin- 

 ging matter he fays is inherent in cobalt, but 

 it cannot be developed without the addition 

 of iron and arfenic. This opinion carries 

 its own refutation with it, for common nickel 

 always contains at leaft as much iron as cobalt 

 does, and yet conftantly gives glafs a reddifh 

 yellow colour, and if ever the addition of 



arfenic 



