AND AGRICULTURE. 69 



quick-lime. It is most beneficial in localities dis- 

 tant from the sea, or where the land is sheltered 

 from the winds by high hills. Near the sea- 

 shore salt is never needed, because the winds 

 carry with them, in passing over the sea, no 

 small portion of the spray, sprinkling it over the 

 soil to a distance of many miles from the sea- 

 coast. 



Gypsum, or plaster of Paris, is a white sub- 

 stance, composed of sulphuric acid and lime. 

 Forty pounds of sulphuric acid and twenty-eight 

 and one-half pounds of lime make sixty-eight 

 and one-half pounds of burned gypsum. The 

 same proportions of acid and lime, with eighteen 

 pounds of water, compose the unburnt gypsum. 

 Native gypsum loses, by calcination, about twen- 

 ty-one pounds of water, and becomes burned 

 gypsum. 



All saline (salt-like) substances should be 

 applied to the soil in still weather, to insure their 

 being equally spread ; and immediately before or 

 after a rain, that they may be readily dissolved. 



Questions. Where is salt most usefully applied ? Of 

 what is plaster of Paris composed ? In what proportions ? 

 What is the difference between burned and unburned gyp- 

 sum ? When ought salts to be applied to the soil ? 



