112 The Phosphates of America. 



Assuming that A leaves nothing to be desired, the bulk of our 

 average raw phosphates still offers two difficulties of considerable 

 magnitude. If they are treated with the theoretical amount of 

 acid, as in our example, they may yield a Avet, pasty mass or mud 

 which can only be dried with difficulty, and which therefore remains 

 long unmarketable. If, on the other hand, something less than 

 the theoretical quantity of acid be taken, a certain proportion of 

 the substance remains unattacked and therefore becomes neither 

 "water" nor "citrate" soluble. This is because there is in their 

 composition, either a lack of some needed, or an excess of some 

 objectionable constituent, and we are hence led to quite naturally 

 inquire, what we are to regard as a defective phosphate. 



The result of prolonged investigations pursued under many 

 and varying conditions has proved to us, that next to an insuffi- 

 ciency of the phosphoric acid itself, a lack or insufficiency of car- 

 bonate of lime is the most serious defect. This defect is aug- 

 mented in the presence of iron and alumina in any form. 



In Europe, and especially in England, high-grade phosphates 

 have great commercial value, but they lose part of it when the 

 oxides of iron and alumina, taken together, exceed three per cent. 



This is because the market price of the English manufactured 

 fertilizer is made dependent upon its percentage of water-soluble 

 phosphoric acid, and because, even when all other conditions are 

 favorable, the presence of iron and alumina gradually causes 

 "water "-soluble to revert into "citrate "-soluble phosphates when 

 kept for a short time ready made in the factory. When an acid of 

 greater average strength than 50 B. is used for the attack on the 

 phosphate and stronger acids are frequently necessary free phos- 

 phoric acid is at first almost exclusively produced as a result of 

 the reaction. After a little time, when the temperature is at its 

 maximum, this free phosphoric acid commences to react upon the 

 undecomposed material, and first of all upon any iron and alumina 

 that may be present. Bodies insoluble in water result from this 

 reaction, and hence the English fertilizer makers studiously avoid 

 all mineral phosphates containing more than the stated maximum. 



In this country we are not handicapped by any such foolish 

 prejudices. Our farmers are hard-headed and practical and have 

 no marked preference for water-soluble phosphoric acid. They 

 have been taught by theory and have proved by their own field 

 practice, that citrate-soluble phosphates are readily transformed 

 into plant food by the elements in the soil. This being the case, 



