RHCENT WORK IN AGRICUIJURAL SCIENCE. 



AGRICULTURAL CHEMISTRY— AGROTECHNY. 



The quantitative determinations of mono-, di-, and tricalciuni phosphates 

 and their application, G. A. Olson {Was/iinf/ion >St(i. Bid. IIG {t!ll/f), pp. IS). — 

 A critical discussion of the metliods iu use for determining the value of ferti- 

 lizers as regards the pliosphoric acid available to the plant. 



The author believes that all chemical tests of phosphate fertilizers should be 

 limited to the determination of total phosphoric acid and that which is not 

 precipitated with an alkaline solution such as ammonium hydroxid. As am- 

 monium citrate acts upon tricalciuni phosi)liate as well as dicalcium phosphate 

 the method in use for determining phosi)horic acid at the present day is deemed 

 emjurical. 



" Substances soluble in ammonium citrate are not necessarily mono- and di- 

 calcium phosphate, but also tricalcium, iron, and aluminum phosphates. Am- 

 monium citrate-soluble is not a measure of the phosphoric acid contained in a 

 fertilizer available for plants. If it is desirable to estimate the mono-, di-, 

 and tricalcium phosphates, this can be done in a scientific manner by dissolving 

 the substance in nitric acid and precipitating the solution with ammonium 

 hydroxid. For the monocalcium phosphate two-thirds of the phosphoric acid 

 will be present in the filtrate, and for the dicalcium phosphate one-third the 

 pliosi)horic acid will be i)resent in the filtrate. Upon these bases the three forms 

 of calcium phosphate can be differentiated and determined quantitatively in 

 the presence of each other. 



"The ammonium hydroxid method is applicable for the testing of the purity 

 of phosphate chemicals. It can also be applied to differentiate between the 

 different forms of phosphoric acid that may be present iu soiLs, plant, and 

 animal tissue. Indirectly, by adding the equivalent of a base with calcium the 

 different forms of phosphate salts can be determined. In soil mono- and di- 

 calcium phosphates tend to react, forming tricalcium phosphate. There is 

 then nothing to be gained by applying either superphosphate or reverted phos- 

 phoric acid to soil." 



A comparison of neutral ammonium citrate with sodium citrate and tenth- 

 normal citric acid, P. Rudnick, W. B. Derby, and W. L. Latshaw {Jour. 

 Indus, and Engin. Chcm., 6 (1914), No. 6, pp. 486, //8?).— The figures for phos- 

 phoric acid obtained with a sample of acid phosphate by treatment with sodium 

 citrate solution of the concentration described by Bosworth (E. S. II., 31, p. 714) 

 were much higher than those yielded by the neutral ammonium citrate solution., 

 When, however, the concentration was Increa.sed the results compared more 

 favorably with those with neutral ammonium citrate. 



" The disadvantages of working with heavy solutions suggested the possibility 

 of using a citric acid solution of suitable concentration as a substitute. After 

 trying various strengths ranging from 2 per cent, as used for l)asic slag analyses, 

 downward, it was found that a tenth-normal solution of citric acid gave results 

 approximating quite closely to tho.se obtained with neutral ammonitnn citrate." 



The substances studied in addition to the acid phosphate mentionei^l above 

 were tankage, raw bone meal, and complete fertilizer. Tenth-normal citric 



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