A word of explanation as to what is meant by phosphoric 

 acid, potash and nitrogen. 



'^y phosphoric acid \% meant a white powder which is made 

 up of the metal phosphorous and the gas oxygen. Chemists ex- 

 press this as PgOcj which means two parts by volume. of phos- 

 phorus and five parts of oxygen. 



^y potash is meant a white substance made up of the metal 

 potassium and the gas oxygen, expressed as KgO, or two parts 

 by volume of potassium and one of oxygen. 



By nitrogen is meant the gas which is abundant in its free 

 form in the air. Chemists indicate this by the letter N. 



The term ammonia is used and often misunderstood. It 

 means one part by volume of nitrogen and three parts of the gas 

 hydrogen, or in chemical work written NH3. It must be re- 

 membered that when a fertilizer is said to contain a certain 

 amount of ammonia that it really means that it contains nitrogen, 

 but that the amount of nitrogen is only -j-f as much as the 

 amount of ammonia. 



To illustrate this explanation take sulphate of ammonia in 

 the following table. It contains on an average twenty per cent, 

 of nitrogen, that is, one hundred pounds of the sulphate of am- 

 monia as bought has twenty pounds of the gas nitrogen (N) and 

 it is this twenty pounds that the plant demands, but we might 

 say that the same sulphate of ammonia had twenty-four and one- 

 third per cent, of ammonia (NH3), hence, if manufacturers print 

 the per cent, of amnonia in their goods the farmer must remem- 

 ber that only -J-^, or eighty-two per cent, of this is plant food, 

 that is, nitrogen. 



If a fertilizing material contains fifty per cent, of potash, it 

 means that each one hundred pounds has in it fifty pounds of 

 actual potash (KgO), or a bone meal that contains twenty-four 

 per cent, of phosphoric acid, has in every hundred weight twen- 

 ty-four pounds of phosphoric acid (PaOs)) but fertilizers and fer- 

 tilizing chemicals have their phosphoric acid in three forms, one 

 soluble, that is, it will dissolve in water ; another, reverted, that is, 

 not soluble in water, but soluble in ammonium citrate solution, 

 this solution having been agreed upon by chemists, and it is as- 

 sumed that the roots of plants have the power of taking up phos- 

 phoric acid in this form, hence, it is common to speak of the 



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