AMERICAN INSTITUTE. 365 



The principal sources of lime in agriculture are limestones, cLalk, cal- 

 careous marls, and tlie shells of crustaceous animals. In all of these, the 

 lime exists in comhiuation with carbonic acid and water, being mild, 

 almost inert, and hardly soluable in water. To render these forms fit for 

 use in agriculture, it is necessary that the}' be reduced to fine powder. In 

 the softer chalks and marls, this is eflFected readily by mere exposure to 

 frost. Limestones might be pulverized by mechanical means, but as a 

 general rule they can be more readily and cheaply reduced to powder by 

 burning to quick-lime, and slaking by the effusion of water. The pow'der 

 thus obtained attracts carbonic acid from the atmosphere, and finally be- 

 comes as mild as the limestone whence it was prepared. This method, 

 however, ought not to be applied to shells. They contain an animal mat- 

 ter, highly valuable as a manure, wiiich is destroyed by heat ; they there- 

 fore ought to be crushed- — and there are cases, as in planting trees, when 

 the entire shells, buried deep in the earth, are to be preferred. 



Except in the third of the cases for which lime had been said to be use- 

 ful, namely, to liasten the decomposition of inert organic matter, lime ought 

 to be rendered perfectly mild by the absorption of water and carbonic acid, 

 before it is mixed with the soil. In conformity with this rule, it is usual 

 to leave the slaked lime in heaps, until it is thoroughly deprived of its 

 causticity by the absorption of carbonic acid from the atmosphere. Even 

 for the correction of acidity, the mild form is to be preferred, unless the soil 

 is also covered with moss and other vegetables difficult of eradication, in 

 which case the caustic lime speedily destroys them. 



The President next went on to remark' that although lime, except in 

 small c^uantities, did not enter into the material of plants, it was, notwith- 

 standing, absolutely essential to the constitution of a soil fertile in the 

 cereal gramina, and particularly in wheat. This was remarked first by Sir 

 Humphrey Davy, who stated that he had examined no soil of acknowledged 

 fertility, which did not show indications of the presence of carbonate of lime. 

 These indications consist in effervescence with acids. ' But lime in some 

 other form, as for instance the sulphate and oxalate, may be present, 

 although no effervescence take place. 



The President was inclined to refer the well known fact, that lands cul- 

 tivated by farmers of German descent in Pennsylvania, were maintained in 

 good heart by the application of lime, although the plow often turned up 

 fragments of limestone, to the conversion of the carbonate into sulphate 

 and iron, probably oxalate. How oxalic acid might be generated in the 

 soil, would require him to enter into a discussion of probabilities, instead of 

 facts, both too tedious and too vague for the present occasion. 



He next proceeded to the third branch of his subject — the proper quan- 

 tity of lime to be applied. In some countries, as in England, Scotland 

 and Belgium, the application of lime served as the basis of all cultivation. 

 It was, however, well understood that of itself it was of little value, and 

 might be positively hurtful, were no putrescent manures largely and habit- 

 ually used on the lands previously limed. The application of lime took 



