tot Cobalt* 



from iron, yet no one dreams of attributing 

 their peculiar properties to an alloy of iron, 

 and any other metal ; and indeed if this 

 manner of reafoning were of any weight, 

 no properties could be attributed to any fimple 

 fubftance ; for what fubftance can be procured 

 abfolutely pure ? When was water rigoroufly 

 pure ever found or procured, or gold of 24 

 carats ? Unlefs therefore we can produce by 

 art a compound fimilar to that which we pre- 

 fume to be a mixture, or Ihew fome good 

 reafon why fuch a compound cannot be arti- 

 ficially produced, or unlefs we can decom* 

 pofe fuch fubftance, and thereby deftroy its 

 peculiar properties, or at leaft alter them by 

 the fubftra&ion of any one of its fuppofed 

 conftituent parts, we muft look upon the 

 fuppofition that fuch fubftance is effentially a 

 compound^ as groundlefs relatively to the pre- 

 fent ftate of our knowledge, on which alone, 

 and not on mere poffibiiities, we can ra- 

 tionally found any aflertion. The word mo- 

 dification has been ftrangely abufed on this 

 occafion. Cobalt, nickel and manganefe, 

 have been faid to be only modifications of 

 iron ; but as long as it is not known wherein 

 that modification confifls, this word prefents 

 no idea whatfoever, and any other infignifi- 

 cant word may as well be ufed. If it be laid 

 that it denotes iron 'with the addition of fome 

 unknown fubftance, then it would follow at 

 B b 2 leaft, 



