HISTORY OV COBALT AND NICKEL. 57 



Heated under charcoal in a spoon of platina, the arsenic is 

 quickly dissipated, and oxide at a minimum remains. 



The arseniat, heated in a tube, loses its colour with its Arsem'aL. 

 water ; becomes transpaient and of a hyacinth red ; but if the 

 heat be carried to redness it turns of a pale yellow, and remains 

 unalterable. 



In the spoon the arseniat turns white, and grows red hot 

 without melting, or emitting the least arsenical fume. To 

 decompose it an obscure flame is required. 



Recapitulation. 



From the preceding facts, and others which he has given in Most metals 

 different memoirs, Mr. Proust concludes, that cobalt, nickel, have but two 

 and most of the well known metals, have but two very decided 

 degrees of oxidation. He dots not mean to say, that a metal 

 can absorb oxigen in too proportions only : he only asserts, that at leaetthafc are 

 it is too soon to admit all the oxides which have been mention- vetknovvD » 

 ed by chemists, and of which neither the quantity of oxigen, 

 nor the combinations they are capable of forming with acids, 

 can be considered as determined ; and that colour is not a 

 character sufficient to constitute a distinction. 



There are but too metals, that have hitherto afforded him' The only ex- 

 more than two oxides. These are tin and lead. However, the f e P tin S tin an * 



lead, 

 quantity of oxigen in that oxideof tin, which constitute s the base 



of mosaic gold, is not yet known ; or that of the oxide of nitrat 



of lead made by boiling with plates of this metal. '.- ■ * 



It seems, that the different oxides of the same metal can mil- Oxides of the 

 tually dissolve each other, and form true combinations, Thus same . metaI 

 the green oxide of cobalt is a combination of the blue and black m i ca iiy. 

 oxides. 



Is not minimum a combination of the brown oxide of lead Minimum per- 



and oxide at per cent, in a similar manner ? ba -V s a c " m " 



1 . . pound. 



Finally, all the magnetic ores of iron, and magnetic sands are Magnetic iron 



mixtures or combinations of this order. If this were not the oles *? coai " 



pounds. 



case what would prevent the minimum oxide from being raised to 

 a maximum of oxidation ? The, oxide of a gun- barrel that has 

 been used for decomposing water is likewise in a similar state, 

 k is composed of two oxides. 



XI. 



