OFFICIAL AND PROVISIONAL METHODS OF ANALYSTS, 

 ASSOCIATION OF OFFICIAL AGRICULTURAL CHEMISTS. 



[Superseding Bulletins 46 and 65 on methods of analysis.] 



I. METHODS FOR THE ANALYSIS OF FERTILIZERS. 



[The word " water " whenever used throughout this bulletin means " distilled " water.] 

 1. Preparation of Sample. Official. 



Grind the sample to pass through a sieve having circular perforations 1 mm 

 in diameter, and then thoroughly mix. Perform the grinding and sifting as 

 rapidly as possible, to avoid loss or gain of moisture during the operation. 



2. Moisture. Official. 



Heat 2 grams, or 5 grams if the samples be very coarse, for five hours in a 

 water oven at the temperature of boiling water. In potash salts, sodium 

 nitrate, and ammonium sulphate heat from 1 to 5 grams at about 130 C. until 

 it ceases to lose weight. The loss in weight is considered as moisture. 



3. Phosphoric Acid. Official, 

 (a) GRAVIMETRIC METHOD. 



(1) PREPARATION OF REAGENTS. 



(a) Ammonium citrate solution. Dissolve 370 grams of commercial citric acid 

 in 1,500 cc of water; nearly neutralize with commercial ammonium hydroxid; 

 cool ; add ammonium hydroxid until exactly neutral (testing with saturated 

 alcoholic solution of corallin), and dilute to a volume of 2 liters. Determine 

 the specific gravity, which should be 1.09 at 20 C. 



(6) Optional method for ammonium citrate solution. To 370 grams of com- 

 mercial citric acid add commercial ammonium hydroxid until nearly neutral; 

 reduce the specific gravity to nearly 1.09 and make exactly neutral, testing as 

 follows : Prepare a solution of fused calcium chlorid, 200 grams to the liter, 

 and add four volumes of strong alcohol. Make the mixture exactly neutral, 

 using a small amount of freshly prepared corallin solution as preliminary 

 indicator, and test finally by withdrawing a portion, diluting with an equal 

 volume of water, and testing with cochineal solution; 50 cc of this solution 

 will precipitate the citric acid from 10 cc of the citrate solution. To 10 cc of 

 the nearly neutral citrate solution add 50 cc of the alcoholic calcium chlorid 

 solution, stir well, filter at once through a folded filter, dilute with an equal 

 volume of water, and test the reaction with neutral solution of cochineal. If 

 acid or alkaline, add ammonium hydroxid or citric acid, as the case may be, 



For special treatment of Thomas or basic slag, see Appendix, page 233. 



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