CHEMICAL CHANGES 243 



phates. If calcium carbonate is also present, the distribution of 

 the phosphoric acid will be modified by the quantitative relation 

 between the fixing materials, and the change to iron and aluminium 

 phosphates may be reduced or even reversed. 



On the other hand, decaying vegetable matter may reduce 

 ferric to ferrous phosphates, with the production of more soluble 

 bodies. 



