638 STATE BOARD OF AGRICULTURE. 



density of 1.105. They claimed that such a solution was neutral to 

 litmus. 



The A. O. A. C. (3) adopted a method in 18S5 calling for the neutral- 

 ization of the bulk of the citric acid with solid ammonium carbonate, 

 the final adjustment being made with ammonia and testing with deli- 

 cate red and blue litmus paper. 



Richardson (44) reported to the Association the results of his studies 

 of several indicators used for this purpose including coralline, cochineal 

 and litmus paper. He said: 'Trom the results I was led to conclude 

 that coralline and litmus paper, carefully prepared by the method given 

 by Sutton, and immersed in the citrate solution, are the only indicators 

 available for determining neutralit}' of citrate of ammonia with a de- 

 cided preference for the coralline." 



Dircks and Werenskiold (14) discussed at length the difficulty in 

 obtaining a neutral solution and selected rosolic acid as being prefer- 

 able to litmus as an indicator for this purpose. 



Huston (29) some years later studied the question and proposed the 

 alcoholic calcium chloride method which was adopted by the Associa- 

 tion. At the same time Cooke (12) suggested the preparation of a 

 solution of the normal salt by analysis. He found such a solution to 

 be alkaline. 



In 189G Lord (35) suggested a method for neutralizing the solution 

 in question using litmus as the indicator which, as later modified by 

 Hand (25), has also found a place in the Official Methods. This method 

 was based on the superposition of two tubes, containing equal con- 

 centrations of litmus in an acid and alkaline solution respectively and 

 the addition of acid or alkali to a mixture of the citrate solution and 

 litmus until its color just matched the composite color in the two 

 standard tubes. This method must be acknowledged to be a long step 

 in advance toAvards the solution of the problem, but the unfortunate 

 choice of an indicator which had already been shown in a practical way 

 to be particularly unsatisfactory for the purpose in hand and whose 

 general unreliability was later so thoroughly demonstrated by the care- 

 ful studies of Walpole (51), largely vitiated the value of an otherwise 

 admirable procedure. 



Cook (11), some time later, proposed a method which does not differ 

 materially from that used by Herzfeld and Feuerlein. It consisted in 

 allowing the heat of neutralization to drive off the excess ammonia. 



In 1908 McCandless (37) proposed the preparation of the solution 

 by analysis, an idea suggested some years previously by Cooke (12). 

 According to this method citric acid is almost neutralized, the solution 

 then being analyzed for its citric acid and ammonia content and the 

 amount of ammonia necessary to neutralize the excess of the former 

 calculated and added. The density of the solution is finally brought to 

 1.09. This method was the subject of considerable discussion cluring 

 the years immediately following its proposal. In 1908, while referee 

 on phosphoric acid, its autlior suggested the use of a reagent in which 

 the ratio of ammonia to citric acid should be 1 : 3.7G5, this being the 

 ratio for a solution of triammonium citrate. Subsequently the Division 

 of Fertilizer Chemists of the American Chemical Society (1) proposed 

 a solution in wliicli the ratio of these ingredients should be as 1:4.25. 



In 1911 appeared the first method based upon the elcctrometric ad- 



