acid can not be dried even at a temperature under 100° in vacuum 

 over phosphorus pentoxide without undergoing a very considerable 

 decomposition with liberation of free phosphoric acid. Attempts to 

 synthesize the substance by subjecting mixtures of inosite and phos- 

 phoric acid to a high temperature would appear, therefore, to be 

 doomed to failure. 



METHODS FOR ESTIMATING INOSITE PHOSPHORIC ACID 



Inosite phosphoric acid or its salts can not be extracted from plant 

 material and quantitatively determined by any direct method. Indi- 

 rect methods of estimation, therefore, were developed and used. More 

 recently efforts have been made to perfect direct volumetric methods 

 for the determination of the acid. The earlier methods consisted in 

 extracting the plant material with dilute hydrochloric or acetic acids 

 and determining the inorganic phosphoric acid and the total soluble 

 phosphorus in the resulting extract. The difference between the two 

 values thus obtained was regarded as phytin phosphorus. Ammonium 

 molybdate precipitates the inorganic phosphoric acid but not organic 

 phosphoric acids, hence it was possible to effect an approximately 

 accurate separation of inorganic phosphate in the presence of inosite 

 phosphoric acid. The total soluble phosphorus in the extract was 

 determined after destroying organic matter by the Neumann method. 



Hart and Andrews (1903) worked out the first method along the 

 line mentioned above for determining organic and inorganic phos- 

 phorus in plant material. They employed a practically neutral solu- 

 tion of ammonium molybdate. These authors believed that it was 

 necessary to restrict as much as possible the amount of free acid in 

 the precipitating mixture in order to prevent hydrolysis of the organic 

 phosphorus compound by the nitric acid. They examined a large 

 numiber of plant products and found that practically all of the phos- 

 phorus was present in organic combination. The method which they 

 employed has been criticised by several authors, but their results have 

 in general been confirmed by all other investigators. Various modi- 

 fications have been proposed for the indirect estimation of organic or 

 phytin phosphorus in plant material by several investigators, among 

 whom may be mentioned Schulze and Castoro (1904), Stutzer (1908), 

 Vorbrodt (1910) and Rising (1911) in Europe and particularly Forbes 

 and his co-workers (1914, 1915, 1916) in this country. It was shown 

 by Suzuki and Yoshimura (1907) that the ordinary nitric acid solu- 

 tion of ammonium molybdate could be used for precipitating inor- 

 ganic phosphate in the presence of organic or phytin phosphorus without 

 effecting a notable cleavage of the organic phosphorus compound. Plim- 

 mer (191 3) (2) has also shown. that it is necessary to heat phytin 

 dissolved in N/1 or 2N/1 nitric acid for several hours to 75° or higher 



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