Sect. III. Agriculture and Vegetation. 59 



IT turns the fyrup of violets red j which 

 (hows, that it contains an acid : whereas 

 marl, like all abfbrbent earths, gives it a 

 green colour. 



THESE qualities are fufficient to teach 

 the farmer how to diflinguifh this poifon- 

 ous body from marl, and how to fhun it. 

 Let us now try if we can difcover on what 

 principles this poifonous quality depends ; 

 for if we can inveftigate its nature, we may 

 perhaps find out a cure for it. Befides, all 

 purfuits of this kind lead us directly to the 

 true fyftem of vegetation. The vegetable 

 is like the animal body, whofe nature is 

 afcertained as well by what does it harm, 

 as by what does it good. 



FROM my experiments in die fedtion on 

 till, I imagined that its poifonous quality 

 might depend on its containing fome fait of 

 iteel. I, therefore, directed moft of my trials 

 on this body with that view. 



Exp, 



