144 THE ART OF CULTURE. 



If, now, we calculate from these data, and from 

 the specific weights of the different substances, 

 how much potash must be contained in a layer of 

 soil, which has been formed by the disintegration 

 of 40,000 square feet (1 Hessian acre) of one of 

 these rocks to the depth of 20 inches, we find that 

 a soil of 



Felspar contains 1,152,000 Ibs. 



Clink-stone , from 200,000 to 400,000 ,, 



Basalt 



Clay-slate 



Loam 



47,500 75,000 



100,000',, 200,000 



87,000 300,000 



Potash is present in all clays ; according to Fuchs, 

 it is contained even in marl ; it has been found in 

 all the argillaceous earths in which it has been 

 sought. The fact that they contain potash may 

 be proved in the clays of the transition and strati- 

 fied mountains, as well as in the recent formations 

 surrounding Berlin, by simply digesting them with 

 sulphuric acid, by which process alum is formed. 

 (Mitscherlich.) It is well known also to all manu- 

 facturers of alum, that the leys contain a certain 

 quantity of this salt ready formed, the potash of 

 which has its origin from the ashes of the stone 

 and brown coal, which contain much argillaceous 

 earth. 



When we consider this extraordinary distribu- 

 tion of potash over the surface of the earth, is it 

 reasonable to have recourse to the idea, that the 

 presence of this alkali in plants is due to the gene- 

 ration of a metallic oxide by a peculiar organic 



