132 CHEMISTRY OF FARM PRACTICE 



Basic calcium nitrate contains about 10 per cent of 

 nitrogen. 



96. Ammonium Sulphate. This material is a by-prod- 

 uct of the gas-works, bone distilleries, and coke-ovens. It 

 contains about 24 per cent of ammonia, and is soluble in 

 water. Its action in the soil has already been discussed. 

 It is a good source of nitrogen for plant food, but it is 

 higher in price than is nitrate of soda. 



97. Organic Sources of Nitrogen. The organic com- 

 pounds containing nitrogen vary greatly in their agri- 

 cultural value. 



Animal Sources: (a) Dried blood is a by-product of 

 the slaughter-houses. It is carefully saved, because of 

 its high value as a source of nitrogen. The fresh blood 

 contains about 2| per cent of nitrogen, but, after drying, 

 the product contains from 12 to 14 per cent. Blood is 

 an excellent quickly available source of nitrogen for use 

 on sandy land, and is highly prized as a source of nitro- 

 gen for sugar cane and tobacco. It nitrifies much more 

 rapidly than the other organic forms of nitrogen. 



(6) Dried ground fish is an important source and con- 

 tains from 7 to 10 per cent of nitrogen, and usually from 

 6 to 9 per cent, of total phosphoric acid. This material is 

 obtained as a mixture of refuse and whole fish from the 

 herring, pilchard, and mackerel fisheries. Fish has long 

 been used as a fertilizer. The first colonists found the 

 Indians using it as a fertilizer for corn. Fish is more 

 slowly available than blood, and consequently more lasting 

 in its effects. This fact enforces the importance of using 

 at least two sources of nitrogen on farm crops having a 

 long growing season. 



(c) Tankage. This term, variously modified, is employed 

 to designate quite a range of fertilizing materials, and the 

 modifying words should be carefully noted. There is a 

 great difference between first-class slaughter tankage, con- 

 sisting of the waste products of slaughter-houses, such as 



