EXPERIMENT STATION REPORTS. 



177 



To ascertain whether or not these differences in the citrate solution 

 would produce marked dift'erences in the results of analyses made with 

 them, several actual determinations were made. The solutions used were 

 conductivity solution No, 2 (Co) R. II, PI and MI. A sample of com- 

 mercial fertilizer was used which had been analyzed during the fer- 

 tilizer cami)aign of 1911, and the result recorded at that time for in- 

 soluble phosphoric acid, was 2.48%. Unfortunately the conductivity of 

 the solution was not obtained. 



The four solutions were carefully diluted to a specific gravity of 1.09. 

 Two samples were weighed out for each solution and the official method 

 for insoluble phosphoric acid was followed very closely. The results 

 are given in Table 3. 



TABLE ITI. 



The duplicate results agree very closely in every case with the ex- 

 ception of solution Rj^. Here we find one result (.0230) as low as 

 the lowest result obtained with the conductivity solution and one result 

 (.0249) higher than any obtained with solution P^. When, however, 

 we consider the average of the results, we find the result for solution 

 Rji falls between those obtained with the C, and P^ solutions. 



The results obtained with the three solutions Co, R^i and PJ are very 

 close and for fertilizer work, at least, would be considered identical in effi- 

 ciency since variations in the manipulation of the method might cause 

 greater differences than are here reported — However, the fact cannot 

 be denied that solutions R^^ and P^ are not strictly neutral and that 

 they give slightly higher results for insoluble phosphoric acid. And 

 furthermore, the solution M^ adds emphasis to the fact that the present 

 official method cannot be relied upon to give a strictly neutral solution 

 nor even solutions of the same degree of neutrality in the hands of all 

 chemists because it is very difficult to detect just when the change of 

 color takes place. 

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