PLANT FOOD AND PLANT GROWTH 41 



The proteid of milk, called casein, has the following composition : 



Carbon .... 53.30 per cent. 

 Hydrogen . . . 7.07 per cent. 

 Oxygen . . . . 22.03 P er cent. 

 Nitrogen . . . 15.91 per cent. 



Sulfur 82 per cent. 



Phosphorus . . .87 per cent. 



A ton of wheat bran contains about 24 pounds of phosphorus, 

 or 1.22 per cent. About 86 per cent of the total phosphorus in 

 bran is soluble in water, and, according to Patten and Hart (New 

 York State Agricultural Experiment Station Bulletin 250), this 

 water-soluble phosphorus is contained in the salt of an organic 

 acid, which is probably identical with a compound investigated 

 by Posternak, and called by him anhydro-oxymethylene diphos- 

 phoric acid, the formula being C 2 H 8 P 2 O 9 . As determined by Patten 

 and Hart, the complex salt of this acid which constitutes the prin- 

 cipal phosphorus compound in wheat bran, has the following 

 composition, as found by the ultimate analysis of the isolated 

 compound : 



Calcium 1.13 per cent. 



Potassium 2.60 per cent. 



Magnesium 5.80 per cent. 



Carbon 17.30 per cent. 



Hydrogen 3.63 per cent. 



Phosphorus 16.38 per cent. 



Oxygen (by difference) . . . 53.16 per cent. 



The free acid was found to contain 10.63 per cent of carbon, 

 3.38 per cent of hydrogen, and 25.98 per cent of phosphorus, which 

 corresponds fairly closely, especially in phosphorus, with the 

 theoretical percentages, which any one can compute for the for- 

 mula C 2 H 8 P 2 Oa. 



m 9 m 9 



The mineral part of animal bone consists largely of tricalcium 

 phosphate, Ca 3 (PO 4 ) 2 , which, when pure, contains 20 per cent of the 

 element phosphorus, as can be easily computed by any one who 

 knows the atomic weights. In 100 pounds of raw bone are about 



