SOILS. 21 



stroy bad odors and also for bleaching straw bonnets, 

 hats, and other goods (14). Sulphur in combination 

 with oxygen and hydrogen forms sulphuric acid, or 

 "oil of vitriol," one of the strongest of the acids. 

 This acid forms compounds known as sulphates, as 

 calcium sulphate, or gypsum, and magnesium sulphate, 

 or Epsom salts (15). 



35. Phosphorus is a soft, slightly yellow solid, 

 that gives off a white smoke when exposed to the 

 air and takes fire very easily. This white smoke is 

 caused by the slow burning of the phosphorus (16). 

 This element forms a large percentage of the bones 

 of animals, and is found in soils and in plants, espe- 

 cially in the seeds. Phosphorus takes fire so easily in 

 the air that it must be kept under water. It is used 

 for making matches. When the end of a match is 

 rubbed against a rough surface, enough heat is pro- 

 duced to set fire to the phosphorus; this inflames the 

 sulphur on the match, and the sulphur sets fire to the 

 wood of which the match is made (17). 



36. Phosphoric acid is a compound of phos- 

 phorus with oxygen and hydrogen (18). When cal- 

 cium takes the place of hydrogen in this acid it forms 

 calcium phosphate, or bone phosphate, the chief con- 

 stituent of bones. This acid forms a large class of 

 salts called phosphates. As animals get their food 

 from plants and plants their food from the air and 

 soil, it is necessary for soils to contain phosphorus. 

 When a deficiency of this element does exist in a 

 soil, it is usual to supply it by means of bones. 



