II \ov.. 



191 



Wlicat and it 6 Cultivation. 



69: 



super. undergoes 



change and becomes 

 converted into less 

 soluble forms. This 

 change in the solu- 

 bility is known as 

 " reversion." Such 

 reversion, whatever 

 may be its cause, 

 obviously depreciates 

 the value of the 

 manure. 



This reversion may 

 be considerable in 

 manures made from 

 raw phosphate con- 

 taining large per- 

 centages of iron and 

 alumina compounds. 

 For this reason, 

 manufacturers gene- 

 rally refrain from 

 using natural phos- 

 phates containing 

 much iron and alu- 

 mina. A slight 

 amount of reversion 

 may take place when 

 super, is kept for any 

 length of time. This 

 is due to the fact 

 that manufacturers 

 usually iLse less sul- 

 phuric acid than is 

 actually required to 

 change the whole of 

 the triealcic phos- 

 phate to soluble phos- 

 phate, in order to 

 avoid the presence of 

 free acid in the 

 manure. Hence, the 

 undissolved triealcic 

 phosphate reacts with 

 the soluble and forms 

 reverted phosphate. 

 When applied to the 

 soil, however, the 

 process of reversion 

 goes on at a Avhole- 

 :sale rate, due to 





