VIII.J 



POTASH 



217 



The Absorption of Potash. 



In all respects the absorption of potash follows the 

 same laws as that of ammonia : Le. y caustic potash 

 is absorbed directly, but sulphate, nitrate, and chloride 

 of potash undergo a double decomposition, by which the 

 potash is retained and calcium sulphate, nitrate, or 

 chloride, appear in the water draining through the soil. 

 Voelcker found in laboratory experiments with small 

 quantities of soil that potassium carbonate was more 

 freely absorbed than sulphate, and that clays, marls, 

 and pasture soils were more effective in retaining potash 

 than light loams or sands, which latter had but little 

 absorbing power. 



The following table shows some of the results 

 obtained when potash and soda salts were compared : — 



Both the humus and the zeolitic double silicates take 

 part in the retention of the potash salts, the reactions 

 being exactly similar to those taking place with the 

 ammonium salts. In some of Way's experiments with 

 pure clays the application of potash salts was followed 

 by the appearance of the corresponding sodium salts in 

 the percolating water, though with most soils it is 

 calcium that is turned out of combination. Potash salts 

 applied to the soil also react to a certain extent with the 

 calcium carbonate, giving rise to a little potassium 

 carbonate, the bad effect of which upon the tilth of the 



