MANURES AND FERTILIZERS. 129 



six per cent, while phosphoric acid ranges from seven to 

 eighteen per cent, averaging eleven per cent. It is cus- 

 tomary to sell the phosphoric acid as bone phosphate of 

 lime, which runs much larger than the actual phosphoric 

 acid, and farmers often confuse the term, thinking they 

 are the same. Phosphoric acid is combined with lime 

 in the ratio of one to 2.183; that is, one per cent of 

 phosphoric acid is equivalent to 2.183 of bone phos- 

 phate of lime. And when tankage contains eleven per 

 cent of phosphoric acid it contains twenty-four per cent 

 of bone phosphate. The term phosphate of lime looks 

 big and is often used by manufacturers to describe the 

 phosphoric acid present in commercial fertilizers, thereby 

 conveying the impression that a much larger quantity of 

 phosphoric acid is contained than is actually present. 

 It is one of the "tricks of the trade." A similar con- 

 fusion exists between nitrogen and ammonia, as explained 

 on Page 123. 



When tankage runs largely to bone, there is little 

 difference between it and ordinary bone meal. For to- 

 bacco, the presence of bone in tankage is of little ad- 

 vantage, since the crop requires but a small quantity of 

 that element. In selecting tankage for this crop, care 

 should be taken to choose that which runs high in 

 nitrogen and low in phosphate. The presence of the 

 bone increases the selling price, especially when a fair 

 proportion of nitrogen is present, so that tankage cannot 

 be considered an economical nitrogen supply, since it 

 requires the purchase of a large quantity of unnecessary 

 bone. For other crops, however, where phosphoric acid 

 is needed, it is a good purchase, a better one than bone. 



The meat of tankage is in a very fine state and is 

 easily disintegrated in the soil. It has been supposed 

 to be more readily available for plant food than the 

 organic matter of cottonseed meal and castor pomace-, 

 as animal matter appears to ferment and disintegrate 



