NITRE  , the name given to naturally occurring

potassium nitrate; " cubic nitre " is sodium nitrate . The word is adapted from Lat. nitrum, which is itself adapted from Gr. virpov . These words were originally applied to the naturally occurring sodium carbonate; the connexion with potassium nitrate (sal petrae or sal petrosum) may be traced to Raimon Lull's name sal nitri, which substance, however, he distinguished from nitrum . In the 16th century the ancient nitrum became altered to natron, a term still used for native sodium carbonate, while nitrum, and its adaptation nitre, were retained for potassium nitrate or saltpetre (q.v.) .