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for this or that crop or kind of land, should be generally under- 

 taken. 



As to the earthy and siliceous matter which, in some lime- 

 stones daily used for agricultural purposes, forms a considerable 

 percentage, I have stated that, during the burning, it combines 

 with the lime and forms silicate of lime. It is not known, 

 however, what purpose this silicate of lime serves in reference to 

 vegetation. 



Does it merely, in proportion to its quantity, lessen the 

 ordinary effects which would be produced by an equal weight 

 of pure lime ? Is it a mere inert mixture ? 



Or does it, as some suppose, supply silica to the growing 

 plant in a state in which it can be taken up, and does it thus 

 in reality render the lime which contains it more valuable ? 



These are questions which can only be solved by comparative 

 experiments. 



1. With silicate of lime. This compound is not manufac- 

 tured for experimental purposes, but it exists abundantly in 

 many districts as a refuse slag of the iron furnaces, and is much 

 used in mending the roads. With this form of silicate of lime 

 I would suggest that experiments should be made. 



a In place of ordinary lime, chalk, or marl, on soils and crops 

 of all kinds. Of course, whatever its action may be, it must 

 not be expected to be so speedy as that of quicklime, or even 

 of chalk. 



In regard to corn crops, it should be specially observed if it 

 has the effect of strengthening the straw, as the silica it con- 

 tains might lead us to suppose. If it has, this slag would then 

 acquire a definite value, because of its being applicable to a 

 definite purpose. 



b This possible effect of strengthening the straw recommends 

 the trial of the slag on peaty soils, which are accustomed to 

 produce a weak, yellow, and sickly straw. While, by its 

 weight, the slag will consolidate such soils, the acid of the 

 peaty matter will decompose the silicate of lime, and, while it 

 becomes itself neutralised, will liberate silica in a form in which 

 it may be useful to the plant. 



For the purpose of being applied in this way, the slag ought 



