before appreciable quantities of inorganic phosphoric acid are split off. 

 In view of these facts, it appears to be unnecessary to determine inorganic 

 phosphate in plant material in the presence of a minimum quantity of acid. 

 If the usual quantity of nitric acid is present the precipitation of the phos- 

 phomolybdate is more rapid and complete. Many determinations of inor- 

 ganic phosphate in plant material have been made by using the ordinary 

 ammonium molybdate solution and there appears to be no reason to believe 

 that these results are very far from the truth. 



Starkenstein (1911) studied the direct determination of inosite 

 phosphoric acid by titrating with uranylacetate, using cochineal or 

 ferrocyanide as indicator. The most promising method for the direct 

 determination of inosite phosphoric acid is undoubtedly that proposed 

 by Heu'bner and Stadler (1914). This method is based upon the fact 

 that the iron salt of inosite phosphoric acid is very sparingly soluble 

 in dilute acid. It is possible, therefore, to determine the amount of 

 inosite phosphoric acid in the presence of phosphoric acid or other 

 phosphoric acid esters whose salts are soluble in dilute hydrochloric 

 acid by titrating with ferric chloride, using ammonium thiocyanate as 

 indicator. The method has recently been used by Rather (1917) in 

 determining the percentage of inosite phosphoric acid present in a 

 number of feeding materials. 



OTHER PHOSPHORIC ACID ESTERS OF INOSITE 

 OCCURRING IN PLANT MATERIAL 



Evidence of the existence of various phosphoric acid esters of 

 inosite formed by hydrolysis from phytic acid or inosite hexaphos- 

 phoric acid was obtained in our study of the properties of phytic acid 

 (Anderson 1914 (4) ). At that time, however, no definitely homo- 

 geneous compound could be isolated. Clarke (1914) reported that he 

 had obtained from wild Indian mustard compounds which corre- 

 sponded to inosite tetra- and di-phosphoric acid. 



Probably the most interesting substance of this kind that has been 

 obtained from plant material is the inosite monophosphoric acid which 

 was isolated from wheat bran (Anderson 1914 (6) ). The properties of 

 this acid differ from those of all other inosite phosphoric acids so far 

 described. When pure it crystallizes very easily and may be purified 

 by recrystallization from dilute alcohol or water. All other inosite 

 phosphoric acids have been obtained only as non-crystallizable syrups. 

 Inosite monophosphoric acid separates in beautiful, colorless crystals 

 which melt under decomposition at 190°. All of the salts of this acid, 

 with the exception of the lead salt, are easily soluable in water, whereas 

 other, inosite phosphoric acids are precipitated by the alkaline earth 

 and heavy metals. In addition to obtaining this acid from wheat bran 



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