94 SCHOOL AND HOME GARDENING 



ground very fine, treated with sulfuric acid and dried. Some 

 nitrogen is usually found in bone tankage because of the waste 

 meat which it contains. Pure animal bone fertilizer con- 

 tains, on an average, four per cent of nitrogen and twenty 

 per cent of phosphoric acid. Fertilizers that derive their 

 phosphate from animal bone are usually more expensive than 

 those derived from phosphate rock, even when the composition 

 is taken into account. 



4. Phosphorus. — ^Common friction matches have phosphorus 

 mixed with sulfur and other materials. Moisten the head of a 

 match and rub it a, little, being careful to not touch it with the 

 finger-nails. The white fumes which appear are caused by the phos- 

 phorus in the match uniting with the oxygen in the air. These 

 white fumes are phosphoric acidr — exactly the same material found in 

 fertilizers (P2O5). 



Phosphoric acid is one of the three or more main ingre- 

 dients which we apply to soils in commercial fertilizers. 

 Mtrogen, phosphorus and potash are always found in com- 

 plete fertilizers. Lime is sometimes present. Phosphoric 

 acid or mineral phosphate in fertilizers is obtained from 

 phosphate rock, ground bone, bone tankage, fish scraps, and 

 other sources. 



5. Making Phosphoric Acid. — ^Put a few teaspoonfuls of ground 

 phosphate rock in a drinking glass or large test-tube. Pour over it 

 about the same amount of strong sulfuric acid. Stir these together. 

 An importg.nt chemical action will take place. The lime present in 

 the rock is taken by the acid, and a mineral acid is left in the tube. 

 This is the phosphoric acid of commerce. 



The method used in this exercise is exactly similar to that 

 used on a commercial scale in the manufacture of phosphoric 

 acid as a farm and garden fertilizer. 



The phosphate rock for these exercises may be obtained by 

 asking for a sample from any fertilizer company or from local 

 dealers. The sulfuric ncid may be obtained from a drug 

 store or high school laboratory. It is the same acid as that 

 used in testing milk samples. 



