PHOSPHORUS FROM CASEINOGEN. 457 



with ammonia in the usual way and excess of magnesia mixture was 

 added. This gave immediately a small white precipitate, which caused 

 the values to be erroneous as the figures show : 



50 c.c. oxidised and precipitated by Neumann's method gave 27-01 mgm. P 2 O 5 . 

 50 c.c. precipitated by magnesia mixture gave 36-13 mgm.) mean _ 35.10 mam p o 

 50 34-23 ,, i 



This error, however, was entirely obviated by employing the mag- 

 nesium citrate method instead of magnesia mixture for precipitating 

 the phosphoric acid. No precipitation occurred on its immediate addi- 

 tion, but the ammonium magnesium phosphate was thrown down on 

 stirring vigorously : 



50 c.c. precipitated by magnesium citrate gave 25*74 mgm. \ 



50c - c - " " " 27 ' 13 " I mean = 26-42 mgm. P.O.. 



50 c.c. ., ,, 27-05 ( 



50 c.c. ,, ,, 25-74 J 



The phosphoric acid is thus completely precipitated by this method, 

 the small difference of 0'59 mm. being due to experimental error and not 

 to incomplete precipitation in presence of albuminous matter. We 

 have proved this by making further determinations in the presence 

 of a known volume of standard acid potassium phosphate solution 

 (10 c.c. = 20 mm. P 2 O 5 ) as follows: 



) c.c. + 10 c.c. KH.,P0 4 solution precipitated by magnesium citrate gave 46-40 mgm."| mean 



) c.c. + 10 c.c. KH 2 P0 4 ,, ,, ,, 46-15 ,, I =46-19 mgm. 



) c.c. + 10 c.c. KH 2 P0 4 ,. ,, ,, 46-02 J P A 



Hence 50 c.c. gave 26-19 mgm. P 2 5 . 



Thus, the soluble P 2 O 5 split off from caseinogen by the action of 

 1 per cent, caustic soda consists entirely of inorganic phosphoric acid. 

 The small quantity of less than one milligramme which is not precipi- 

 tated is negligible. It could be demonstrated by oxidising the filtrate 

 from the ammonium magnesium phosphate by Neumann's method and 

 precipitating as ammonium phospho-molybdate. In all probability it is 

 derived from the small quantity of nucleoproteid present in the 

 caseinogen as above mentioned. 



(2) The soluble P 2 O 3 obtained by the action of trypsin. The 

 solution remaining in Experiment (5) was employed after the digestion 

 had been continued for nearly two months. It contained a small 

 precipitate from which it was filtered and the filtrate was examined in 

 the following way : 



