146 



DISCUSSION OF RESULTS. 



P. Rudnick (results by G. F. Beyer): Commenting on the results in general, I do not 

 believe that any of the methods proposed are preferable to the modified Von Grueber 

 method in point of simplicity, rapidity, accuracy, and general applicability to various 

 kinds of rock. Although the results obtained for ferric oxid in the synthetic solution 

 prepared in this laboratory are high, they agree very well with the results obtained 

 by the determination of iron in the precipitate from the method proposed by you, 

 and the results on aluminum by the modified Von "Grueber method are certainly very 

 close to the calculated quantity. Although I have not had time nor opportunity to 

 prove the point, I am inclined to believe that ammonium acetate is not sufficient to 

 prevent the partial hydrolysis of the aluminum phosphate, and that ammonium nitrate 

 is more efficient in this respect. I believe the fairly good agreement between the 

 results by the Glaser method and the modified Von Grueber method obtained in this 

 work, as well as at other times, supports this view. 



S. H. Wilson: For simplicity and ease of execution the McCandless laboratory 

 method leaves little to be desired. 



Remarks by the referee: On the whole the results seem to be encouraging and to show 

 that all three of the methods for which instructions were sent are capable of giving 

 good results. One analyst used the Von Grueber method, another the Veitch method. 

 A study of the results on the synthetic solution, in which the percentages of iron 

 and alumina are accurately known, reveals a tendency on the part of those getting 

 the lowest results on the phosphate rocks to get them also on the solution and vice 

 versa; excluding the lowest and highest results, the agreements and approximations 

 to the truth are about as good as would be found in the determination of other ele- 

 ments, as, for instance, phosphoric acid by the accepted methods. 



The referee would call attention to the fact that this subject has been taken up 

 by the National Fertilizer Association, and would recommend cooperation between 

 the next referee and the committee of that association, with a view to reaching a 

 decision as to what method shall be adopted. 



EFFECT OF DILUTE AND CONCENTRATED HYDROCHLORIC ACID ON PYRITES IN PHOS- 

 PHATE ROCK. 



The referee also requested the analysts cooperating to test the effect of dilute 

 (1 to 1), and concentrated hydrochloric acid as to its solvent effect on pyrites, present 

 to a greater or less extent in nearly all phosphate rock. 



It has been claimed on the one hand that dilute hydrochloric acid (1 to 1) fails to 

 dissolve all the iron and alumina, especially when the latter is present in the form 

 of clay; it has been claimed, on the other hand, that concentrated hydrochloric acid, 

 while it dissolves the alumina and iron oxids better than the dilute, also decom- 

 poses pyrites present in the phosphate rock and therefore yields too high a percentage 

 of iron. It is desired that the analysts test this latter point as follows: 



Procure a sample of freshly pulverized pyrites and weigh half a gram into a 250 cc 

 flask, cover with 25 cc of hydrochloric acid (1 to 1), heat just below boiling for thirty 

 minutes, dilute with 100 cc of water, shake, allow to settle, decant the liquid, repeat 

 the washing by two or more treatments with 125 cc of cold water slightly acidulated 

 with hydrochloric acid, followed by decantation. This preliminary treatment is to 

 remove any oxid or sulphate of iron already existing in the pyrites. Have ready 2.5 

 grams of phosphate rock, add it to the flask on top of the washed pyrites, then cover 

 with 30 cc of concentrated hydrochloric acid, heat just below boiling for thirty minutes, 

 cool and make up to the mark. Determine the iron volumetrically in an aliquot 

 of the solution and compare the results with that obtained from a similar treatment 

 of phosphate rock and pyrites with dilute hydrochloric acid (1 to 1) the second time. 



Only two chemists beside the referee took part in this work. 



