46 PRACTICAL FARM CHEMISTRY. 



process takes place, we have the so-called "reverted 

 phosphoric acid." 



Neither the element potassium, nor its compound 

 with oxygen (potassium oxide, ordinarily called 

 * 'potash") is ever met with in nature in a free form. 

 The form in which everybody is familiar 

 with it, is "carbonate of potash," a com- 

 pound of potassium oxide (or potash) with carbonic 

 acid. This compound is readily soluble in water. 

 It appears in fresh wood ashes, in corn cob ashes, in 

 cotton seed hull ashes, etc. ; and no better form is 

 known in which potash could be applied to the soil, 

 or utilized as plant food. 



In chloride of potassium we have a simple com- 

 pound of the metal potassium with chlorine. This 

 is found in sea water, and in the potash salts mined 

 at the salt mines near Stassf urt in Prussia, Germany, 

 and known as muriate of potash. Sulphate of pot- 

 ash, obtained from the same source, is a compound 

 of potash with sulphuric acid, and kainit a sulphate 

 of lower grade. 



One of the most valuable, but also expensive, 

 forms of potash, is the compound of potash with 

 nitric acid, known as nitrate of potash or saltpetre. 

 This furnishes two elements of plant food at the 

 same time, potash and nitrogen (the latter in the 

 available nitrate form), and is found in large beds 

 in South America, and also produced naturally in 

 any soil containing decaying vegetable matter and 

 potash, or artificially in so-called nitre beds. Potash 

 also exists in combination with several other acids, 

 as with oxalic acid in rhubarb, with citric acid in 

 lemons, oranges, etc., and with tartaric acid in 

 grapes. 



