56 AGRICULTURAL ANALYSIS 



to be considered, the operation to determine them must be con- 

 ducted on a separate part of the sample. 



The methods of analysis which have been adopted by associa- 

 tions of chemists should be given the preference in the conduct of 

 the work, although it must be admitted that they may contain 

 sources of error, and may be in no respect superior to processes 

 employed by chemists in their private capacity. In this country 

 the methods adopted by the Association of Official Agricultural 

 Chemists should be followed as closely as possible. The great 

 merit of other methods, however, must not be denied. Espe- 

 cially those methods which shorten the time required or diminish 

 the labor and expense of the analysis are worthy of careful con- 

 sideration. In factory work, for instance, it is often far more 

 important for the chemist to be able to rapidly determine the 

 phosphoric acid in a great number of samples with approximate 

 accuracy than to confine his work to one with absolute precision. 

 Some of the shorter methods, moreover, notably the citrate or ti- 

 tration process, appear to be quite, if not altogether, as reliable 

 as the molybdate method, while in the case of the uranium volu- 

 metric process, it must not be forgotten that it has been largely 

 practiced in France. Other volumetric processes are given 

 in full, as, for instance, the one perfected by Pemberton and Kil- 

 gore, and data are at hand to justify their strong recommendation. 

 It should be remembered that this manual is not written for the 

 beginner, but rather for the chemist already acquainted with the 

 principles and practice of general chemical analysis, and it is, 

 therefore, expected that each analyst will make intelligent use of 

 the data placed at his disposal. 



63. Preparation of Reagents. Ammonium Citrate Solution. 

 (a) Mix 370 grams of commercial citric acid with 1500 cubic 

 centimeters of water, nearly neutralize with commercial ammonia, 

 cool, add ammonia until exactly neutral (testing with saturated 

 alcoholic solution of corallin) and bring to a volume of two liters. 

 Determine the specific gravity, which should be 1.09 at 20, be- 

 fore using. 



(&) Optional Method. To 370 grams of commercial citric 

 .acid add commercial ammonia, of 0.96 specific gravity, until near- 



