56 THE ELEMENTS OF PLANT FOOD 



Magnesium sulphate (MgSO 4 ), Epsom salts, found 

 in many mineral waters, is a very common drug used 

 in medical practice. 



Magnesium carbonate (MgCO 3 ) is frequently used as 

 an adulterant of face powder. This is the magnesia of 

 commerce or magnesia alba. It is often combined with 

 calcium carbonate and then is called dolomite or dolo- 

 mitic limestone. The soft crayon used in schools is 

 made by mixing magnesia with a fine clay to give it 

 strength. 



SULPHUR (S) 



Description and Occurrence. Sulphur exists in 

 various forms as an element. It may be melted and 

 run into molds, making the common form sold in the 

 stores as brimstone. It may be vaporized and collected 

 on the cool walls of the chamber containing the vapor. 

 It then appears as a yellow powder called flour ol 

 sulphur. If boiled and poured slowly into cold water, 

 it becomes dark colored and non-crystalline, or amor- 

 phous. In this form it has much of the elasticity of 

 rubber. 



Large quantities of sulphur are mined on the island 

 of Sicily, from which source has come in the past 

 most of the world's supply. In recent years, Louisiana 

 and Texas have supplied very much of the sulphur for 

 this country. 



Sulphur is found in compounds in nearly all plants 

 and animals. The color of the hair is probably due 

 to some organic compound of S. The sulphides of the 

 common metals, lead (PbS), zinc (ZnS), iron (FeS 2 ), and 

 copper (CuS), are combinations with sulphur. FeS 2 

 is a low grade of iron known as iron pyrites. It is 



