DOMAIN XI. DECOMPOSED. 



oxygenated, become purple, red, orange, 

 and finally pale yellow ; the latter becomes 

 at first blue, then purple, red, &c. 



" Iron in its perfect metallic state, or at 

 least but slightly oxygenated, also decom- 

 poses water ; but if exposed to the air, it 

 becomes farther oxygenated ; and the com- 

 pound into which it enters gradually 

 withers, as Dr. Higgins observed, in imi- 

 tating pouzzolana (on Cements, 124). 



" But stones, into whose composition 

 calces of iron highly oxygenated seem to 

 have originally entered, are very difficultly 

 decomposed, as red jaspers, &c. as they 

 already possess nearly as much as they can 

 absorb. 



" Manganese, when slightly oxygenated, 

 is known to attract oxygen strongly, par- 

 ticularly with the assistance of heat and 

 moisture ; hence it is, in many cases, a 

 principle of decomposition, as in siderocal- 

 cites, &c. ; it also frequently assists or pro- 

 motes that effected by calces of iron. 



" Lime, from its attraction to fixed air, Lime,&c. 

 and its solubility in water, must promote, 



