THE ELEMENTS OF PLANT FOOD 45 



act on it, a disagreeable odor is produced. The fumes 

 are PzOf,. P^O^ unites readily with H 2 O. 



Phosphoric Water Phosphoric 



pentoxide acid 



P 2 O 5 + 2H 2 O 2H 3 PO 4 



Notes. Phosphorus may be obtained by treating bones wit 

 after the animal matter has been burned out of them. This changes the 

 calcium phosphate to calcium superphosphate and calcium sulphate. The 

 sulphate is removed by filtration and the superphosphate is mixed with 

 powdered charcoal, heated and distilled, and the distillate collected under 

 water. The phosphorus is then melted under hot water and run into 

 molds. 



Matches owe their inflammability to the presence of the phos- 

 phorus in the head of the match. To make the sulphur matches 

 the end of a small piece of wood is stuck in a paste, made of phos- 

 phorus, sulphur, and glue, and the whole is coated with glue to protect 

 the phosphorus from the air. To make the cracking matches the paste 

 is made of phosphorus, chlorate of potash, and glue. The heat pro- 

 duced by the friction of the match is sufficient to ignite the phosphorus ; 

 this produces heat enough to cause the sulphur or the chlorate of pot- 

 ash to burn, and this, in turn, causes the end of the stick to burst into 

 flame. Safety match boxes have red phosphorus and powdered glass on 

 the sides, and the matches are tipped with sulphide of antimony and 

 chlorate of potash. Unless the match is scratched on the preparation 

 on the match box, it will not ignite. 



Phosphates. --The element phosphorus is taken 

 up in considerable quantities by nearly all food-pro- 

 ducing plants. It is found in the fruits and in the 

 grains. Although the plant takes the largest amount 

 of P during the early part of its growth, this element 

 is stored up in the fruit or the grain before maturity. 

 If the element is not present in the soil in available 

 forms, the plant dies of starvation. 



