630 STATE BOARD OP^ AGRICULTURE, 



certainty of its composition and the difficulty of its preparation, East- 

 man and Hildebrand (15) suggested that a solution of the normal salt 

 which is slightl}^ alkaline be substituted for it. The technic described 

 in the present paper eliminates botli of these objections to the use of 

 the neutral solution and consequently eliminates any advantage in this 

 regard which 1lie solution of the normal salt possesses. Using the 

 methods described a perfectly neutral solution of ammonium citrate 

 may be easily and accurately prepared. 



In one respect the neutral solution possesses a slight advantage over 

 the solution of normal triammonium citrate in that with most com- 

 mercial fertilizers its reaction apparently remains constant throughout 

 the determination. This, however, is but of small importance as the 

 reaction of the alkaline solution is but little altered. 



The chief recommendation for the retention of the neutral solution is 

 perhaps simply that there is now no reason for abandoning it and 

 since it has been prescribed for use, and supposedly has been used, for 

 years it should still be used. 



In conclusion a few words ma^' be said regarding the proposed sub- 

 stitutes for ammonium citrate. These have included such solutions 

 as dilute acids and salts other than ammonium citrate. In no case 

 does any seem to present material advantages over the reagent at present 

 in use. The method which seemingly is somewhat preferable is tliat 

 suggested by Olsen (40) using ammonia. He claims to be able to 

 accurately determine the three forms of calcium phosphate in com- 

 mercial products. He criticises the present method for including the 

 phosphoric acid of iron and aluminum phosphates in the available frac- 

 tion, implying that his own method does not though he later states that 

 in the presence of iron and aluminum phosphates "the problem of differ- 

 entiating is somewhat complex." 



CONCLUSIONS. 



The indicators commonl3' used are unsuitable for the accurate prepar- 

 ation of neutral ammonium citrate solution although the results may be 

 improved by tlie use of Hand's (25) technic. 



Accurate results are obtainable with physical chemical methods, 

 Hildebrand's (27) for the preparation of either neutral solutions or 

 solutions of the normal salt, and that of Hall & Bell (23) (42). for pre- 

 paring the latter, but the apparatus and technic preclude their common 

 adoption. 



• Analytical methods give accurate results for making any solution 

 whose composition is fixed. 



Methods relying upon the autoneutralizatiou of the solution by means 

 of the heat of reaction, etc. are absolutely unreliable. 



The adjustment of the reaction of the solution using phenol red as 

 the indicator and comparing the solution colori metrically with standard 

 solutions whose reactions are known gives accurate results and permits 

 the rapid and convenient adjustment and control of citrate solutions. 

 It possesses advantages over any other method. 



The composition of a neutral solution of ammonium citrate having a 

 S. G. 1.09 at 20^ lias been found to be 45.33 g. NH,, and 172.00 g. 

 C.HsO, per liter. The ratio of NIIgrCoHsO- is 1:3.794. 



With commercial fertilizers the reaction of acid or neutral citrate solu- 



