3S4 STATE BOARD OF AGRICULTURE. 



NEUTKAL AMMONII'M CITRATE SOLUTION 



Technical Bulletin No. 12. 



A. J. PATTEN AND C. S. RORINSON, 



Since the proiK)sal of the amnioniiim citrate method for the deteriniua- 

 tion of available phosphoric acid, much trouble has been experienced 

 in preparing a strictly neutral solution of the reagent. The weakness 

 of both the acid and tlio base renders the end ])oint quite indistinct with 

 ordinaiy indicators, and much time and patience are reipiired on the 

 part of the operator to obtain the desired i*esulls. Several modifications 

 of the simple titration method have been proposed, but each has objec- 

 tions which prohibit its common accc])tation by practical chemists. The 

 imi)ortance which the method has assumed in agricultural work de- 

 mands, however, that some convenient means be devised for preparing 

 the necessary solution. Such a method has recently been proposed by 

 ITall and BelP and was later shown by Hall- to be quite suitable for 

 laboratory use. At the time these articles appeared, the authors of this 

 paper were engaged in working out the same method, and the results 

 are here offered, not with the hope of claiming the credit for originating 

 the method, but simjjly as corroborative evidence in favor of its general 

 adoption. 



Of the several methods proposed as substitutes for the present official 

 method, that recently suggested by Hand^ using purified litmus solution 

 or azolitmin seems to be the most i>romisiiig. In order to test it out 

 and compare it with the official corallin method as well as to obtain some 

 data as to the accuracy of the latter an acid solution of ammonium 

 citrate was made up and neutralized by these two methods by each of 

 four analysts working indeiiendently. 



An acid citrate solution was chosen of Avhich 50 c.c. required 7.50 c.c. 

 of the dilute ammonia solution for neutralization as determined by the 

 conductivity method to be described later. The dilute ammonium 

 hydroxide solution (about 3 per cent) was kept in a burette enclosed 

 in opacjuo i>a])er to prevent the residing being taken until the supposed 

 neutral jmint had been reached. In this way each operation was made 

 independently of the others. Great care was taken that no loss of 

 ammonium hydroxide should occur during the process. The results are 

 given in Tables I and II. 



•Jour, of Am Ch<^m. Sor. .33. 711 fl911>. 

 *.Toiir. of Inrl. aiui Fnj? Chem. .3. 559 riOll). 

 »U. S. Dept. of Agric. Bur. of Chcm. Bui.' 132. P. 11. 



