Component Parts of the Soil on Vegetation, SI 



part of the bottom earth, especially in districts where the 

 latter arises from gneuss or micaceous schistus. Having a 

 greater affinity for the sulphuric acid, it can effect a neutra- 

 lization of this acid, as it unites with it to produce sul- 

 phate of magnesia. In this form, when dissolved in water, 

 it can be conveyed into vegetables, from which we can ex- 

 plain the existence of magnesia in the residuum of the de- 

 composition of plants, without admitting it as an essential 

 component part of vegetables, 



5th, Iron is found also in some kinds of soil, but never 

 in a metallic form : it is always in the oxidated state iu 

 which it is dispersed almost over the whole surface of the 

 earth; with the free sulphuric acid it forms vitriol of iron, 

 which exercises a corrosive action on the roots of plants, 

 and makes them smutty. When dissolved in water in the 

 state of carbonic acid, it perhaps may be capable of pass- 

 ing into vegetables, which explains it;: being found in them. 



6th, Free .yitlphuric acid lixiviated by water from clav 

 occurs here and there : its property of charring the roots ot 

 plants is the most probable cause of the production of strata 

 of turf; for the basis of these is always clay and stagnant 

 water, by which the sulphuric acid is lixiviated. The growth 

 of turf may therefore be promoted by not suifering the 

 water to drain off from a dug stratum of it. 



Ingenhous recommended manuring with sulphuric acid; 

 and it is evident that it may be of use in calcareous soil, 

 and in the neighbourhood of great cities where the fields 

 arc rich in black mould, as the carbonic acid is driven off 

 by it, rendered free, and nourishment thus conveyed to the 

 vegetables : but this method is too expensive to be gene- 

 rally employed. 



7th, Phosphoric acid. The existence of this acid in ani- 

 mal matters was known :-but it is now known that it oc- 

 curs also in the mineral kingdom, as we are acquainted 

 with a combination of it with iron, to which the cold short 

 property of the latter is ascribed. It is doubtful whether 

 it has any useful influence on vegetation. From what 

 matters it is formed in marshy meadows is not known ; but 

 it is believed that it is the cause of the sourness of fodder 

 in places were there is no argillaceous earth. 



From the future progress of chentical research there is 

 Teason to expect that more effectual means will be discovered 

 of bringing n)atters back to their original component parts. 

 Phosphorus, sulphur, &c. were for a time considered as 

 gubstances or piinciplcs, merely because it was impossible 

 to decompose them, though there are phicnomcua wl)ich 



Vol. XVUI. Mo. Gy. '^ F give 



