RECENT WORK IN AGRICULTURAL SCIENCE. 



CHEMISTRY. 



The determination of citrate soluble phosphoric acid in 

 Thomas slag, O. Bottchek (Chem. Ztg., 21 {1897), No. 19, pp. 

 168, 169). — A brief statement of Wagner's method for the determina- 

 tion of citrate-soluble phosphoric acid in Thomas slag is followed by a 

 description of several proposed substitutes, which are claimed to be 

 simpler and equally reliable. 



(1) Dissolve 5 gui. of the slag in ammonium citrate according to 

 Wagner. To 50 cc. of this citrate solution in a platinum dish add a 

 spoonful of nitrate of soda, evaporate to dryness, incinerate, moisten 

 with hydrochloric acid, and dry for 2 hours to render the silica insol- 

 uble. Dissolve the residue in hydrochloric acid with the aid of heat, 

 dilute with water, filter, wash with hot water, and in the filtrate deter- 

 mine the phosphoric acid by the citrate method. 



(2) In 50 cc. of the Wagner citrate solution of slag, precipitate the 

 phosphoric acid directly by the citrate method, filter through a paper 

 filter, wash with 5 per cent ammonia water, incinerate the moist filter 

 in a platinum crucible. Dissolve the ash in hydrochloric acid with the 

 aid of heat, filter, wash with hot water, and determine the phosphoric 

 acid in the filtrate by the citrate method. 



(3) Instead of incinerating the moist filter above, dry at 120° and 

 then proceed as directed. 



It has been objected that in this modified citrate method the pyro- 

 phosphate is not completely reconverted into the orthophosphate aud 

 hence low results are obtained. The untenableness of this is shown by 

 the fact that (2) and (3) give concordant results, while one does and 

 the other does not contain the pyrophosphate to be reconverted during 

 the process. To further disprove the validity of the objection a given 

 weight of the pyrophosphate was dissolved in hydrochloric acid and 

 made up to 500 cc. The phosphoric acid was determined by the citrate 

 method, in some portions directly, in others after boding with fuming 

 nitric acid. The results in the two cases agreed closely. 



As a result of his researches the author concludes that the ordinary 

 citrate method, as applied in the determination of water soluble and 

 total phosphoric acid in other fertilizers, need not be modified m 



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