ELEMENTS NECESSARY FOR PLANT GROWTH 39 



to make applications of it in a commercial form. It is a 

 necessary constituent of the bones of animals, which are 

 composed in part of calcium phosphate. Phosphorus has 

 an important part to play in the formation of the seeds of 

 plants and in hastening their maturity. When freshly 

 prepared and kept in the dark, the element phosphorus is 

 an almost colorless or slightly yellow, waxlike solid. It 

 has a remarkably low kindling temperature, and therefore it 

 is a very inflammable substance, and must be kept under 

 water. Phosphorus appears luminous in the dark, due to 

 its slow oxidation to phosphorous trioxide (P2Os) when 

 in contact with moist air. Phosphorus fumes are very 

 poisonous. When yellow phosphorus is heated to 240-250 

 Centigrade, it is changed to the red or amorphous form, 

 which has a much higher kindling temperature than the 

 yellow form. When heated to 260 C., it is again changed 

 to the yellow form. 



34. Sulphur. Sulphur occurs as yellow crystals, and 

 also as opaque crystalline masses. It is found in nature 

 in the free state, most frequently in volcanic regions. Com- 

 pounds of sulphur with metals are known as sulphides; 

 and when these compounds are more completely oxi- 

 di/^ed, they become sulphates. Compounds of sulphur are 

 found widely distributed in both plants and animals. 

 Small amounts of it occur in hair and in wool, while about 

 1 per cent of it is present in the albuminous substances 

 which are present to a large extent in both plants and 

 animals. Sulphur is mined in large quantities in Louisiana, 

 where the supply of the United States is produced. It 

 is also produced in Sicily and Japan. Most of our soils 

 contain sufficient sulphur for plant growth. 



35. Potassium. Potassium is rather abundant in nature, 

 and especially so in soils that result from the decompo- 

 sition of igneous rock. The minerals feldspar and mica 

 contain potassium in large amounts. Granite rock con- 

 tains over 3 per cent of potassium. Sea water contains 



