POTASH-CONTAINING SUBSTANCES 137 



The chief potash manures in use are : — 



The low-grade materials like kainit, carnallit, and the potash 

 manure salts contain large proportions of the sulphate and chloride 

 of magnesium and of common salt. Sulphate of lime is also likely 

 to be present in small quantity. 



125. Wood Ashes, 



A small quantity of wood chips or sawdust is 

 incinerated at low temperature. The ash is extracted 

 by boiling with water and the extract filtered. It will 

 be found to be alkaline to litmus. The filtrate is 

 neutralised with dilute HCl (note the effervescence), 

 and tested for potassium with platinic chloride or 

 sodium cobaltinitrite solution. 



126. Potash Felspar. 



Some orthoclase or other potash-containing felspar 

 is ground to a fine powder and equal quantities are 

 • treated as follows : — 



{a) Extracted by shaking with 2 per cent, citric 



acid solution. 

 {b) Extracted by boiling with strong HCl. 

 {c) Moistened with water, fused with seven times 



its weight of ammonium fluoride, and then 



extracted with dilute HCl. 



In each case the filtered extract is tested for potassium, 

 and an attempt made to obtain some indication of 

 how much potash has been removed by each treatment. 



