METHODS FOR THE PREPARATION OF NEUTRAL 

 SOLUTIONS OF AMMONIUM CITRATE^ 



BY JAM?^S M. BELL AND CHARLES F. COWELL 



The method at present approved hj the Association of Official 

 Agricultural Chemists^ for the preparation of neutral solutions 

 of ammonium citrate requires the use of an alcoholic solution of 

 corallin as indicator. It is common knowledge that this method 

 is not accurate. The method proposed bj Hand,^ using purified 

 litmus solution, has been thoroughly tried by Patten and Robin- 

 son'* and like the corallin method has proven much less satis- 

 factory than the conductivity method proposed by Hall and 

 Bell.^ By this conductivity method a series of solutions is 

 prepared containing constant quantities of citric acid and vari- 

 able quantities of ammonia in a constant volume. It was found 

 that the solution just neutral has the highest electrical con- 

 ductivity, the plot for conductivity and quantity of ammonia 

 consisting of two curves intersecting at the neutral point. Up 

 to that point the solutions consist of mixtures of ammonium 

 citrate and free citric acid, and beyond the break the solutions 

 consist of mixtures of ammonium citrate and free ammonia. 



The conductivity method requires some temperature control, 

 for the temperature coefficient of conductivity is large enough 

 to cause serious errors in the final result unless the maximum 

 variations in temjDerature are but very slight. Two further 

 methods are here presented for the determination of the neutral 

 point, neither of which requires careful temperature regulation. 

 In one method there is an indirect determination of the excess 

 of ammonia just past the neutral point by the use of chloroform 

 as solvent. This method is called the "extraction method." The 

 second method like the conductivity method is a i^hysical method 

 depending on the great heat evolution when ammonia and citric 

 acid solutions are mixed. This has been called the "tempera- 

 ture method." 



"Reprinted from The Journal of the American Chemical Society, Vol. XXXV. 

 No. 1. January, 1913. 



^Bureau of Chemistry, BvU. 107 (revised), 1. 

 ^Bureau of Chemistry, Bull. 132, 11. 

 V. Ind. Eng. Chem., 4, 443 (1912). 

 V. Am. Chem. Soc, 33, 711. (1911.) 



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