244 AGRICULTURAL ANALYSIS 



determined with potassium permanganate in the usual way. 

 The phosphoric acid and iron having been thus determined, the 

 alumina is estimated by difference. The chief objection to this 

 process is in the excessive quantity of acetic acid used and the 

 danger of solution of the precipitated phosphates caused thereby. 



215. Estimation of the Lime and Magnesia. The filtrate and 

 washings from the first precipitation, (paragraph 213) of iron and 

 alumina in the method ( of Krug and McElroy, above described, 

 are collected and sufficient ammonium oxalate is added to precipi- 

 tate the calcium. The precipitated calcium is very fine and 

 should be collected on a gooch, without pressure. The filtrate 

 and washings from the calcium precipitate are again collected, 

 and a solution of sodium phosphate added to precipitate the 

 magnesia. The solution must be kept cool and slightly alkaline 

 with ammonia during the above operations in order to prevent 

 the separation of molybdic anhydrid. 



216. Separation of Iron and Aluminum Phosphates from the 

 Calcium Compound. There are many points of difference noted 

 in the descriptions given by authors of the deportment of the iron 

 and aluminum phosphates in presence of a large excess of the 

 calcium salt. Especially is this true of the statements made by 

 Hess and Glaser. 3 The subject is of such importance, from a 

 analytical point of view, as to merit a careful study. 



In the laboratory of the Division of Chemistry a thorough in- 

 vestigation of the mutual deportment of these three phosphates 

 has been made by Brown with the following results :* When 

 a mixture containing a known weight of the salts is treated exact- 

 ly as Hess directs, in no case is there a complete separation of the 

 iron aluminum phosphate from the calcium salt. In order to dis- 

 cover the cause of the failure, pure solutions of calcium and iron 

 aluminum phosphates are treated under identical conditions by 

 the necessary reagents. Fifty cubic centimeters of a solution of 

 calcium phosphate, containing about one gram of the salt, are 

 treated with 100 cubic centimeters of water and 50 cubic centime- 

 ters of the commercial ammonium acetate containing 150 grams 



* Zeitschrift fur angewandte Chemie, 1894, 7 : 679, 701 ; 1889, 2 : 636. 



* Report to Author by W. G. Brown, 1894. 



