EXPERIMENT STATION BULLETINS. 



623 



ing tlie digestion mixture. This was later changed to a bath temperature 

 of 65°. This decision gave rise to considerable discussion as to the 

 exact time allowable in raising the temperature to the final maximum, 

 the outcome of which was the adoption of a temperature inside the 

 flask of G5°, the bath being held at such a temperature as would main- 

 tain this for 30 minutes and the temperature to be brought to this point 

 before the introduction of the sample. To prevent the escape of ammonia 

 it is prescribed that the flask shall be tightly stoppered. 



From the above discussion it is perfectly plain that the selective 

 solvent action of ammonium citrate is purely a relative matter. This 

 is further confirmed by an examination of the results of experiments 



P.O. 



involving the ratio . Ilerzfeld and Fcuerleiu (26), Gladding 



Eeagent 

 (18), Koenig (32), Johnson (30), and Huston (29) have all offered 

 evidence in proof of the statement tliat an increase in the relative amount 

 of solution increases the quantity of phosphoric acid removed. Since 

 these two points are of minor importance in the present work further 

 discussion of them will be postponed. 



To more thoroughly test these points the four solutions previously de- 

 sciibed (page 16) Avere used for the analysis of twelve samples of com- 

 mercial phosphates having citrate-insoluble fractions running from 

 about one-half of one per cent to over ten per cent. The determinations 

 were made in duplicate and showed good agreement. The average avail- 

 able PjOj, together Avith the results obtained in the regular fertilizer 

 inspection work, are given in Table IV. 



TABLE IV. 

 Average Available P2O5. 



It may be well to state that these solutions cover a range probably 

 wide enough to include those prepared by the usual methods using ordi- 

 nary care. Consequently the results represent the practical extremes 

 which could be anticipated from solutions made in different laboratories 

 or by different analysts. Two of the solutions, "B" and "C" possess 

 particular interest in that the former is strictly neutral and the latter 

 a solution of the triammonium citrate. 



The results are of interest in that they show no large variation in 

 the values for available PoO., with variation in reaction. Those with 

 the acid solution "A" and the neutral solution "B" are generally the 



