88 Fertilizers 



alumina in the raw material, the nature of the reaction is 

 not well understood, and is, consequently, not so easily 

 demonstrated as in the former case. Where iron is present 

 in the form of pyrites, or ferrous silicate, it does not seem 

 to cause reversion. It is only when it is present in the 

 form of oxide (and in most raw phosphatic materials it is 

 generally in this form) that it causes reversion in the 

 phosphate." 



Aikman also discusses the value of reverted phosphates, 

 showing the estimation in which they are held in England : 

 "The value of reverted phosphate is a subject which has 

 given rise to much dispute among chemists. That it has a 

 higher value than the ordinary insoluble phosphate is now 

 admitted, but in this country, in the manure trade, this is 

 not as yet recognized. At first it was thought that it was 

 impossible to estimate its quantity by chemical analysis. 

 This difficulty, however, has been overcome, and it is 

 generally admitted that the ammonium citrate process 

 furnishes an accurate means of determining its amount. 

 Both on the continent and in the United States reverted 

 phosphate is recognized as possessing a monetary value in 

 excess of that possessed by the ordinary insoluble phos- 

 phates. The result is, that raw mineral phosphates con- 

 taining iron and alumina to any appreciable extent are 

 not used in this country, although they do find a limited 

 application in America and on the continent." 



As stated by Aikman, the reverted phosphoric acid due 

 to the presence of undecomposed phosphate, as well as 

 the reverted due to the presence of iron and alumina, are 

 recognized by the chemists in this country, and this 

 recognition is strongly encouraged by commercial interests, 

 because of the fact that our mineral phosphates contain, 

 as a rule, iron and alumina, which by their action reduce 



