614 AGRICULTURAL ANALYSIS 



treat the residue in the dish with another portion of alkali. Finally 

 wash with hot water till the alkaline reaction disappears, then 

 with weak hydrochloric acid, then with water until chlorids dis- 

 appear. The washed mass on the filter is transferred to a plati- 

 num dish and ignited. The weight obtained represents sand. 



Separation of Phosphoric Acid. The united filtrates from the 

 two determinations are placed in a graduated flask and made up 

 to the mark. An aliquot portion of this solution representing 

 half a gram of the original ash or any other convenient quantity 

 is transferred to a beaker and a solution of ferric chlorid added 

 until ammonia produces a brown precipitate in the mixture. Neu- 

 tralize with ammonia and hydrochloric acid alternately until the 

 liquid is as little acid as it can be and still remain clear. Add 

 from 10 to 20 cubic centimeters of a solution of sodium ace- 

 tate (1:10) and bring to a boil. The liquid should be quite 

 dilute. Filter and wash free of chlorids with boiling water con- 

 taining some sodium acetate. 



Manganese. Make the filtrate faintly alkaline with ammonia 

 and add ammonium sulfid. Any manganese sulfid which may 

 form is separated by filtration, treated with dilute acetic acid and 

 the resulting solution, which should be clear, heated to boiling, 

 nearly neutralized with caustic soda, and mixed with bromin 

 water. The resultant manganese dioxid is to be filtered into a 

 gooch, ignited and weighed as Mn 3 O 4 . 



Lime. Reacidify the filtrate from the manganese sulfid with 

 acetic acid, heat to boiling and add ammonium oxalate: Allow 

 to stand over night, filter through a gooch and wash with water 

 containing acetic acid. The calcium oxalate can be weighed as 

 such, but it is preferable to dry thoroughly and then heat in a 

 small bunsen flame until a change can be noted passing over the 

 precipitate. If this is carefully done the residue will be calcium 

 carbonate. In any case, the result is to be checked by igniting 

 over the blast-lamp to constant weight and weighing the lime 

 thus obtained. 



Magnesia. In the filtrate the magnesia can be determined by 

 sodium phosphate in the usual manner. In very accurate work 

 the calcium oxalate obtained as directed above can be dissolved 



