26 DEPARTMENT OF AGRICULTURE GEORGIA. [3 12] 



are small, as in fine table salt ; and when very slowly, a 

 much coarser kind, called bay salt, is produced. That pro- 

 duced by slow evaporation is much stronger than the finer 

 kind, and is generally used for preserving meat and fish in 

 brine. 



From common salt is obtained all of the other com- 

 pounds of soda, by certain processes, which it is not 

 necessary to describe here. 



Carbonate of soda is used very extensively in the manu- 

 facture of glass, soap, etc. 



Sulphate of soda, or Glauber's salts, as medicine. 



Chillian saltpetre, or nitrate of soda, as a fertilizer. 



Bicarbonate of soda is used in connection with sour milk 

 in making bread. 



Lime is a compound of oxygen with a metal called 

 calcium, and, while its salts are generally known as those of 

 lime, yet the term calcium is often used ; thus, sulphate of 

 lime is the same as calcium sulphate. 



As with the metals, potassium and sodium, the metal 

 calcium is of little use, and is kept, like them, out of contact 

 with air or water. 



Lime exists, in nature, in many forms, entering into the 

 composition of nearly all rocks. 



Caustic, or quick lime is made by heating limestone or 

 any other carbonate of lime. 



The heat drives off the carbonic acid gas, and leaves a 

 hard and dry rock. By long exposure to air, this crumbles, 

 or is " air-slaked," by the absorption of moisture and 

 carbonic acid from the air; but, if water be poured on it, 

 the rock takes it up so vigorously that great heat is evolved, 

 and the lime immediately slaked. 



In slaking, it is found that 28 pounds of lime will absorb 

 9 pounds of water, and swell to three times its original 

 bulk. 



Carbonate of lime occurs abundantly in limestone, mar- 

 ble, chalk, marl shells, etc. 





