
• (n.) A white amorphous or granular substance which consists principally of potassium carbonate, and has a strong alkaline reaction. It is obtained by lixiviating wood ashes, and evaporating the lye, and has been an important source of potassium compounds. It is used in making soap, glass, etc.
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http://thinkexist.com/dictionary/meaning/pearlash/
 Pearl'ash`  noun  (Chemistry)
Pearl'ash`  noun  (Chemistry) A white amorphous or granular substance which consists principally of potassium carbonate, and has a strong alkaline reaction. It is obtained by lixiviating wood ashes, and evaporating the lye, and has been an important source of potassium compounds. It is used in making ...
Found on 
http://www.encyclo.co.uk/webster/P/38
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