106 OF THE INORGANIC 



t 



tained in the soil itself is inexhaustible in comparison 

 with the quantity removed by plants. 



But when we increase the crop of grass in a 

 meadow by means of gypsum, we remove a greater 

 quantity of potash with the hay than can, under 

 the same circumstances, be restored. Hence it 

 happens, that after the lapse of several years, the 

 crops of grass on the meadows manured with gyp- 

 sum diminish, owing to the deficiency of potash. 

 But if the meadow be strewed from time to time 

 with wood-ashes, even with the lixiviated ashes 

 which have been used by soap-boilers, (in Germany 

 much soap is made from the ashes of wood,) then 

 the grass thrives as luxuriantly as before. The 

 ashes are only a means of restoring the potash. 



A harvest of grain is obtained every thirty or 

 forty years from the soil of the Luneburg heath, 

 by strewing it with the ashes of the heath-plants 

 (Erica vulgar is) which grow on it. These plants 

 during the long period just mentioned collect the 

 potash and soda, which are conveyed to them by 

 rain-water ; and it is by means of these alkalies, 

 that oats, barley, and rye, to which they are indis- 

 dispensable, are enabled to grow on this sandy 

 heath. 



The woodcutters in the vicinity of Heidelberg 

 have the privilege of cultivating the soil for their 

 own use, after felling the trees used for making tan. 

 Before sowing the land thus obtained, the branches^ 

 roots and leaves are in every case burned, and 



