66 AMERICAN MANURES. 



of gypsum is not due to its lime, except in a 

 slight degree. 



One great benefit derived from the use of gyp- 

 sum, is in fixing the ammonia contained in the 

 oil and the atmosphere. When gypsum and 

 carbonate of ammonia are brought into contact, 

 under certain conditions, double decomposition 

 takes place, resulting in the formation of sul- 

 phate of ammonia, and carbonate of lime. These 

 facts prove that the benefits derived from the 

 application of gypsum are principally due to its 

 sulphuric acid, which we have already treated 

 under that head. 



If lime is the substance needed, it can be ap- 

 plied more cheaply as quicklime. The applica- 

 tion of gypsum in small or large quantities is 

 often attended with equally beneficial results. 

 This can be explained by the fact that it requires 

 from four to five hundred pounds of water to 

 bring one pound of plaster into solution ; hence 

 only a small quantity of it can become available 

 in a season, and only that amount need be ap- 

 plied. 



MAGNESIUM. 



Magnesium is a white, malleable solid, resem- 

 bling silver. It is not altered by dry air, at the 

 ordinary temperature, but is tarnished when ex- 

 posed to moisture. When heated to dull red- 



