58 VERMONT AGRICULTURAL REPORT. 



Concerning the artificial forms it may be said: 



1. Oxide. Quicklime is derived from the calcining or "burning" of 

 limestone or oyster shells in a kiln, the carbonic acid gas being water 

 off by the heat. The oxide thus formed is very alkaline, absorbs water 

 and carbonic acid from the air with eagerness, and "slakes" with the 

 production of great heat. Quicklime is the most energetic form of lime. 



2. Hydrate. Slaked lime as such is used but little in agriculture. Its 

 action is much the same as that of air slaked lime. • 



3. Impure hydrate and carbonate. Air slaked lime is perhaps the 

 most common form used in those regions where the custom of liming 

 obtains. Quicklime slowly changes from the oxide to the hydrated 

 (or watered) form through the action of the air, absorbing at the same 

 time more or less carbonic acid therefrom and thus becoming less viru- 

 lent in its action. Complete slaking seldom occurs. Like the oxide, 

 this form of lime is an active one and may well be termed available. 



4. Impure carbonate. Ashes contain usually from 30 to 40 per cent, 

 of lime as carbonate, which is sometimes termed "vegetable lime." It 

 is an active form of this ingredient, though a somewhat less energetic 

 one than the others. Ashes furnish a form of lime which is probably 

 quite as available as any and, if not too costly, often prove a desirable 

 purchase. 



5. Phosphate. Phosphate of lime treated with an adequate quantity 

 of sulphuric acid forms more or less free phosphoric acid, soluble and 

 reverted phosphoric acid, and sulphate of lime; and usually some re- 

 mains unaltered. About one-third of the lime in such materials is left 

 united with the phosphoric acid while two-thirds joins with the sulphuric 

 acid. The lime in these altered compounds is more or less soluble in 

 water and all of it is quite available. It is less powerful in some ways 

 than the other forms. 



FUNCTION OF LIME IN SOILS. 



Nitrogen, phosphoric acid and potash are deficient elements or com- 

 pounds of plant food. Soils become deprived of them and plants get 

 hungry for them. That is why they are used. Lime, on the contrary, 

 is more commonly used on account of its indirect action. In other 

 words, it promotes plant growth through its effect on the soil, rather 

 than because it adds any needed plant food to the soil. Hence it fol- 

 lows that the functions of the lime are somewhat complex and, more- 

 over, that one needs to consider its effect on the soil rather than upon 

 the plant. 



We have viewed nitrogen, phosphoric acid and potash solely from the 

 standpoint of the plant and studied their effects upon plant life. They 

 do not modify the character of the soil on which they are placed. Lime, 

 however, has a more pronounced action and may profoundly affect the 

 soil to which it is added. The influence of lime on a soil may be felt 

 in three ways: 



1. Upon its mechanical condition. 



2. Upon its chemical composition. 



3. Upon its biological condition. 



