EXPERIMENT STATION BULLETINS. 393 



variation below the average is only 0.26 and the maximum variation 

 above the average is 0.17. 



These differences might well be considered within experimental error. 



Ratio of Ammonia to Citric Acid. 



Dr. McCandless, the referee on phosphoric acid for the Association of 

 OflScial Agricultural Chemists in 1909 suggested a reagent be used 

 which should have the same ratio of ammonia to citric acid as the 

 pure trianmionium salt. This ratio is 1 :3.7G5. He made some coopera- 

 tive tests with three other chemists, in which solutions were obtained 

 having ratios from 1:3.775 to 1:4.189. Some time later the division 

 of Fertilizer Chemists of the American Chemical Society recommended 

 a solution in which the ratio of ammonia to citric acid was 1 :4.2o. A 

 neutral solution was made up by the conductivity method and the 

 ratio of ammonia to citric acid determined. An average of three de- 

 terminations gave a ratio of 1 :3.785. This would probably have ap- 

 proached still closer to the theoretical ratio if the neutral solution had 

 been made up immediately after making the conductivity measurements. 

 During the several days that elapsed between the determinations of the 

 quantity of dilute ammonium hydroxide solution required to give per- 

 fect neutrality and the actual preparation of the neutral solution, the 

 strength of the dilute ammonium hydroxide solution was probably 

 changed. It seems probable that this method could be used to give 

 more satisfactory results than the present official method. 



Conclusions. 



The present oflScial method for preparing a neutral solution of am- 

 monium citrate is extremely unreliable. 



The purified litmus method gives somewhat better results although 

 the limit of error is too great for reliable work. 



The conductivity method, on the other hand, is reliable and not 

 difficult of operation and the results obtained by different workers agree 

 very closely. 



