ALKALIMETRIC ESTIMATION l6l 



tightly with a smooth rubber, and shake violently until the filter 

 paper is reduced to a pulp. Place the flask in the bath and main- 

 tain it at such a temperature that the contents of the flask will 

 stand at exactly 65. Shake the flask every five minutes. At the 

 expiration of exactly 30 minutes from the time the filter and 

 residue are introduced, remove the flask from the bath and im- 

 mediately filter the contents as rapidly as possible. Wash thor- 

 oughly with water at 65. Transfer the filter and its contents to 

 a crucible, ignite until all organic matter is destroyed, add from 

 10 to 15 cubic centimeters of strong hydrochloric acid, and digest 

 until all phosphate is dissolved ; or return the filter with contents 

 to the digestion flask, add from 30 to 35 cubic centimeters strong 

 nitric acid, from five to 10 cubic centimeters strong hydrochloric 

 acid, and boil until all phosphate is dissolved. Dilute the solution 

 to 200 cubic centimeters. If desired, the filter and its contents 

 may be treated according to the methods in paragraph 61 under 

 methods of solution. Mix well ; filter through a dry filter ; take 

 a definite portion of the filtrate and proceed as under total phos- 

 phoric acid. 



(6) In Non-Acidulated Samples. In case a determination of 

 citrate-insoluble phosphoric acid is required in non-acidulated 

 samples it is to be made by treating two grams of the phosphatic 

 material, without previous washing with water, precisely in the 

 way above described, except that in case the substance contains 

 much animal matter (bone, fish, etc.) the residue insoluble in 

 ammonium citrate is to be treated by one of the processes de- 

 scribed under methods of solution, paragraph 61. 



Citrate-Soluble Phosphoric Acid. The sum of the water-solu- 

 ble and citrate-insoluble subtracted from the total gives the cit- 

 rate-soluble phosphoric acid. 



144. Alkalimetric Estimation of Phosphoric Acid in Connection 

 with the Incineration by Acid Mixture. Neumann recommends 

 the following process, which is a variation of the ordinary volu- 

 metric method in common use in this country for the estimation 

 of phosphoric acid in organic matters which . have been incin- 

 erated by the wet acid method described by him. 20 For carrying 

 10 Zeitschrift fiir physiologische Chemie, 1902-3, 37 : 115. 



