PHOSPHORUS 117 



c. Nitrate of soda, or Chile saltpeter, contains about 

 fifteen per cent nitrogen ; and dried blood, tankage, and 

 bone meal carry from three to fifteen per cent nitrogen. 

 These last three fertilizers are products of the slaughter- 

 house. In all these commercial compounds, nitrogen costs 

 three to four times as much as an equal weight of phosphoric 

 acid or potash in their commercial compounds. 



d. The best way to get nitrogen into the soil is to grow 

 clover or alfalfa or other leguminous plants in a rotation 

 upon it. The ancient Chinese said, " Beans are good 

 for the ground " ; but they did not know why it was so. 

 We know now that plants of the clover family assist the 

 growth of certain bacteria in the soil about their roots, 

 and that these bacteria "fix" free nitrogen from the air 

 into compounds suitable for plants to use. Nearly all 

 crops leave the soil poorer ; but clover crops usually leave 

 it richer by the addition of this costly and essential food 

 for other crops. 



75. In the world of life, nitrogen is the great builder. 

 All protoplasm, the primary substance out of which all 

 organisms build their bodies, contains this element. 

 Work may go on for a time, or heat may be produced, 

 without nitrogen ; but no plant or animal structure can 

 be built up without its aid. It does not build alone, but 

 its presence is always required for building. A little 

 nitrate of soda, scattered on the sod beneath a languish- 

 ing tree, will commonly tend to stimulate its growth and 

 tint its foliage with a healthy green color. 



76. Phosphorus forms the principal element of phosphoric 

 acid, a compound of phosphorus and oxygen, one pound 

 of phosphorus forming nearly three and one third pounds 

 of phosphoric acid. Pure phosphorus is a straw-colored 

 solid, having the consistency of beeswax. The whitish 

 smoke which appears when a phosphorus match is first 



