ACTION OF SALTS. 97 



and alkaline bases of earths, united to a mineral 

 acid, such as sulphuric, muriatic, phosphoric. These 

 salts are taken up by the roots of plants when dis- 

 solved in water, and thus form a constituent of veg- 

 etables. Secondly, a large quantity of alkali and 

 alkaline earths, is united in plants, with a vegetable 

 acid. In this case, the salts of the soil, have been 

 decomposed by the living plant. What is the con- 

 sequence ? The base, if alkali, lime, alumina, mag- 

 nesia, iron, acts upon geine, rendering that soluble, 

 and it is then taken up as such, or it forms an alka- 

 line or earthy, or metallic geate, which entering the 

 plant as such, is there decomposed by the vegetable 

 acid produced in the living plant ; while the acid of 

 the salt thus let loose in the soil, acting on the sili- 

 cates, forms new salts, which in their turn, play a 

 similar part to that produced by the original salt. 



148. The effect of this action of salts is, that 

 they continually reproduce themselves. The effect 

 may be illustrated by yeast, which added to dough, 

 begets a new portion of the fermenting principle, 

 which again added to new dough, still begets new 

 leaven, and this without end. It is not to be under- 

 stood, from this illustration, that the action of salts 

 is fermentation. 



149. But let this action be farther illustrated ; 



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