STIMULATING MANURES. /tl 



Magnesian earths possess but little fertility ; and when 

 the lime employed for agricultural purposes contains mag- 

 nesia, its beneficial effects do not follow. In order to ac- 

 count for this difference of action, it is necessary to take 

 into consideration, that magnesia has less affinity for car- 

 bonic acid than lime has, and that, consequently, when 

 the two earths are mingled together, the magnesia pre- 

 serves its causticity, even when the lime is saturated with 

 carbonic acid, and brought back to the state of lime-stone. 

 Thus it appears that magnesia can preserve its caustic 

 properties, and exercise its deleterious effects upon vege- 

 tation, during a long time. 



The use of plaster, or gypsum, which has become com- 

 mon in Europe as a manure, is one of the most important 

 improvements that has ever been made in agriculture. It 

 has even been introduced into America, where it was 

 made known by Franklin upon his return from Paris. 

 As this celebrated philosopher wished that the effects of 

 this manure should strike the gaze of all cultivators, he 

 wrote in great letters, formed by the use of the ground plas- 

 ter, in a field of clover lying upon the great road to Wash- 

 ington, " This has been plastered." The prodigious vege- 

 tation which was developed in the plastered portion led 

 him to adopt this method. Volumes upon the excel- 

 lences of plaster would not have produced so speedy a revo- 

 lution. From that period the Americans have imported 

 great quantities of plaster of Paris. 



There are, however, some tracts of country where the 

 use of plaster has been attempted without success. But 

 this arose from its being one of the original constituents 

 of the soil, which derived no advantage from the addition 

 of a new quantity. The existence of this salt, naturally, 

 in those lands upon which plaster produced little or no 

 effect, has been proved by analysis. 



Gypsum is a compound of sulphuric acid and lime, con- 

 taining more or less of the water of crystallization. A 

 moderate heat deprives it of its water of crystallization, 

 and renders it opaque. It can then be reduced to powder, 

 and employed in that state. Though the prepared gyp- 

 sum absorbs water with avidity, and its consistency is 

 affected by the mixture, it may be preserved many months 

 without its properties being sensibly affected. Nothing 

 more is necessary for this purpose than to head it up in 

 tight casks. 



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