62O AGRICULTURAL ANALYSIS 



4. Determination of Phosphoric Acid. (a) In an aliquot por- 

 tion of the hydrochloric acid solution, corresponding to 0.2 to one 

 gram of ash, determine the phosphoric acid by any of the me- 

 thods described for total phosphoric acid in fertilizers. 



(b) The determination can also be made directly in the plant 

 substances after incineration as prescribed in the methods for 

 phosphoric acid, in fertilizers using sufficient material to give from 

 0.2 to one gram ash in the aliquot portion of the solution used 

 for the phosphoric acid determination. 



5. Determination of Sulfuric Acid. Heat an aliquot of solu- 

 tion A, corresponding to from 0.5 to one gram of ash, to boiling 

 and add barium chlorid solution in small quantities until no fur- 

 ther precipitation is produced, and proceed in the usual manner 

 to determine the barium sulfate. 



6. Determination of Chlorin. Determine the chlorin as silver 

 chlorid, either gravimetrically or by one of the standard volumet- 

 ric processes, in a nitric acid or aqueous solution of the ash. Ni- 

 tric acid may be used as the solvent in 2 (c) and the solution em- 

 ployed for this purpose. 



7. Potassium in Plants. Potash may be determined as directed 

 under fertilizers for potash in organic compounds, using suf- 

 ficient plant material to get from 0.5 to one gram ash in the ali- 

 quot portion of the solution used for the potash determination. 



8. Sulfur in Plants. Peroxid Method. Provisional. Place 

 from 1.5 to 2.5 grams of material in a nickel crucible of about 

 100 cubic centimeters capacity and moisten with approximately 

 two cubic centimeters of water. Mix thoroughly, using a nickel 

 or platinum rod. Add five grams of pure anhydrous sodium 

 carbonate and mix. Add pure sodium peroxid, small amounts 

 (approximately 0.50 gram) at a time, thoroughly mixing the 

 charge, after each addition. Continue adding the peroxid un- 

 til the mixture becomes nearly dry and quite granular, requir- 

 ing usually about five grams of peroxid. Place the crucible 

 over a low alcohol flame (or other flame free from sulfur) and 

 carefully heat with occasional stirring until contents are fused. 

 Should the material ignite, the determination is worthless. After 

 fusion remove the crucible, allow to cool somewhat, and cover 



