142 



Three different states of Oxide of Iron are visible in this; 

 viz. the black-brown, the red, and the Roman Ochre ; and 

 I conceive an indefinite number of Oxides may be formed 

 by the blending of these : nor do I think Iron is capable of 

 taking oxygen from water, Sec, in these different degrees 

 which colour seems to represent; but when blueish or pur- 

 plish, or any variety exists, it may depend upon Carbonic 

 Acid, Hydrogen, Phosphorus, Manganese, &c, which 

 may be known by their external appearance. 



