"28 DEPARTMENT OF AGRICULTURE GEORGIA. [314] 



Gypsum is known agriculturally as " land plaster," and, 

 for some crops, is highly valued as a fertilizer. 



" Plaster of Pans," is made by heating gypsum to such a 

 temperature that all the water will be driven off, and a 

 white powder left. 



This has the power of absorbing water and becoming 

 very hard. It is used in making casts and moulds, and in 

 cementing articles. For this purpose a thick paste is 

 made of it with water, and used immediately, allowing it 

 to stand for some hours, until perfectly hard. 



Phosphate of Lime, which is, as before stated, a com- 

 pound of phosphoric acid with lime, forms the chief con- 

 stituent of bones, and is a valuable fertilizer ; especially 

 when reduced to the condition of super-phosphate, or sol- 

 uble phosphate, by treatment with sulphuric acid. 



Chloride of Lime forms the well-known bleaching pow- 

 der of commerce. Its effect is limited to vegetable stains 

 and colors, and is due to the chlorine. 



Magnesium is a white, light metal, which burns in the air 

 with a very bright light. . It is largely used in photogra- 

 phy, for which purpose it is prepared in the form of wire 

 or tape. 



Magnesia; or Oxide of Magnesium^ is found in many 

 rocks, especially in dolomite or magnesian limestone. 



It forms an important constituent of agricultural plants, 

 occurring in considerable quantity in the seeds of cereals, 

 ranking next to potash and phosphoric acid in quantity. 

 "In the ash of small grain cereals it ranges from 8 to 12 per 

 cent. , and in Indian corn runs up as high as 14. 6 per cent. " 

 (Pendleton.) 



It exists in sufficient quantity in most soils, but its ap- 

 plication in small quantities is desirable on lands that have 

 been long cultivated. 



Aluminum is the lightest metal known. 



Its oxide, alumina, occurs naturally in large quantities, 

 forming as a silicate, the clay of our soils. While it does 



