IRON. 69 



one equivalent of iron combined with one equiva- 

 lent of oxygen. 



Peroxide of Iron, or red rust, is composed of 

 two equivalents of iron combined w^ith three 

 equivalents of oxygen, and is technically called 

 " sesquioxide of iron." The presence of oxidiz- 

 ing iron in a soil liberates free hydrogen, which, 

 uniting with the nitrogen contained in the soil, 

 forms ammonia. As the rust of iron has slight 

 acid properties, it has an affinity for ammonia, 

 and fixes and retains this valuable substance in 

 a soluble form in the soil. Quite probably the 

 injurious effect of the presence of a large amount 

 of iron in any cultivated soil, is due to its attrac- 

 tion of oxygen, thus interfering with the oxida- 

 tion of organic substances in the soil. Such 

 soils should be frequently cultivated, and the 

 particles pulverized as fine as possible, so as to 

 expose every part of it to the action of the oxy- 

 gen of the atmosphere, which facilitates the for- 

 mation of the peroxide or red rust of iron ; hence 

 soils containing a large amount of iron acquire 

 a deeper red color under cultivation. Two ad- 

 vantages are gained by cultivating such soils : 

 First, The hastening of the formation of the per- 

 oxide of iron ; Second, The benefits derived by 

 the action of this oxide, in absorbing certain 

 kinds of plant-food present in the soil. Thus 



