ELISHA MITCHELL SCIENTIFIC SOCIETY. 



11 



method. Being one of the alternate methods of the A. (). A. 

 C, he had no reason to doubt it.s adequacy. 



Having looked at one side of the determination of available 

 phosphoric acid in fertilizers containing cotton seed meal, let us 

 turn to the other, namely, the determination of insoluble. As 

 almost the entire content of phosphoric acid in the meal has been 

 shown to be available, it might be anticipated that there would 

 be likely not to be much difference in the determination of 

 insoluble whether the citrate-extracted residue is first incinerated 

 or dissolved directly in acid. Such was found by experimenta- 

 tion to be the fact. In fact, in every case but one (and this was 

 the same fertilizer that was the exception to the total rule, 

 namely, the old one brought from the previous season) a slightly 

 higher insoluble was found by dissolving in acid directly than 

 after incineration. 



The details of the two methods of determining the insoluble 

 were these: After filtering from the citrate and thoroughly wash- 

 ing, the filter and contents were in the first instance incinerated 

 and the ash dissolved in nitric acid (designated in the table 

 below as '' incineration"), and in the second instance the filter 

 and contents were introduced directly into flasks and completely 

 dissolved with nitric acid and a little hydrochloric acid (the 

 ^'acid solution'' of the table below). The samples used were 

 the same as those used in the total experiments, with the excep- 

 tion of 110, which was not used. 



Whether the excess of insoluble by direct acid solution was 

 due to mechanical loss in the incineration by the other method 

 (whieh in tliese instances is not at all apprehended, though it is 

 believed that care is necessary to with certainty guard against 



