COMMERCIAL FERTILISERS 379 



this plant food. The nitrogen in it is nearly as 

 quickly available to plants as that in nitrate of 

 soda. It should not be mixed with muriate of 

 potash, as the muriate causes a loss of ammonia. 

 Less important sources of nitrogen are the fol- 

 lowing animal products: hoof meal, dry ground 

 fish, tankage, Peruvian and other guanos, horn 

 and hoof meal, wool and hair waste, dried meat or 

 meal; and two vegetable products, linseed meal 

 and castor pomace. These materials are usually 

 obtained with greater difficulty and are less 

 valuable for the farmer unless he is so situated 

 that he can buy them advantageously. The 

 amount of plant food in each of these is given 

 in the Appendix. 



SOURCES OF PHOSPHORIC ACID 



The principal sources of phosphoric acid are 

 phosphate rocks and bones. In most cases the 

 phosphoric acid is in combination with lime, mak- 

 ing a phosphate of lime. Only a fertiliser that 

 contains phosphoric acid is a "phosphate," 

 but this term is often applied by farmers to 

 all fertilisers. For many years bones were the 

 main source of phosphoric acid and they are 

 still largely used. 



Raw Bone is that which has not been treated 

 in any way, except by grinding. It should 

 contain about 4 per cent, of nitrogen and 22 

 per cent, of phosphoric acid ; but only 5 to 7 per 

 cent, of the phosphoric acid is soluble, the 

 remainder being insoluble. For this reason the 

 phosphoric acid in raw bone is but slowly avail- 

 able to plants, its usefulness extending over 

 several years. 



