38 Literature on Inosite-Phosphoric Acid [Sept 



The term soluble phosphorus above and elsewhere means of course 

 the phosphorus Compounds which dissolve in cold acidulated water ; 

 the amount is obtained by evaporating the extract and destroying 

 the organic matter with sulphuric and nitric acids according to the 

 method of Neumann,^^ after which the phosphorus is determined 

 by the usual ammonium molybdate and magnesia mixture method 

 as described by Sonnenschein and later modified by Woy. As ex- 

 tracting agents both acetic acid and hydrochloric acid have been 

 used. 



The first method to approximate an accurate determination of 

 inorganic phosphorus in the presence of soluble organic phosphorus 

 was that used by Hart and Andrews in 1903. Their extracting 

 agent was 0.2 per cent. hydrochloric acid Solution, a solvent which 

 has since been used by most investigators. Hart and Andrews 

 noted that ammonium molybdate did not precipitate the phytin 

 phosphorus, and used this fact to devise a method for separating 

 the two kinds of phosphorus combination in Solution. They 

 had some apprehension lest the strong acid in the usual molybdate 

 Solutions would hydrolyze some of the organic phosphorus Com- 

 pounds and thus yield high results for the inorganic portion. They 

 determined the minimum amount of nitric acid necessary to give a 

 rapid, complete, and crystalline Separation of the yellow precipitate 

 (2 c.c. of nitric acid, specific gravity 1.2, in each 250 c.c. of Solu- 

 tion) and added to the liquid of this acidity neutral ammonium 

 molybdate Solution. 



Vorbrodt, in his excellent monograph on " phytin," developed a 

 method which is based on a triple precipitation of the inorganic 

 phosphorus, first precipitating in general by means of magnesia 

 mixture and dissolving the precipitate in the least amount of 

 nitric acid. This is diluted to 50 c.c, heated to 100° C, and treated 

 with an equal volume of ammonium molybdate Solution. The 

 yellow precipitate is dissolved in ammonia water, 25 c.c. of 5 per 

 cent. barium chlorid are added,^^ and the precipitate after being 

 washed and dried is weighed; or the phosphorus may be precipi- 

 tated with magnesia mixture and weighed as magnesium pyro- 

 phosphate. 



"Neumann: Zeit, für physiol. Chetn., 1902, 37, 115. 

 "Riegler: Zeit. Anal. Chem., 1902, 41, 675. 



