Jabir ibn Hayyan introduces the systematic experimental method into medieval alchemy, turning it into a practice of observation and verification: he describes processes of distillation, calcination, sublimation, and evaporation with reproducible procedures. The Kitāb al-Kīmiyāʾ contains the first systematic classification of chemical substances into three categories (spirits, metals, stones), the synthesis of ammonium chloride by chemical means from organic matter, and the preparation of nitric and hydrochloric acid. Translated into Latin by Robert of Chester in 1144 as Liber de Compositione Alchemiae, it was the reference text of European alchemy until the 15th century. The Arabic term 'al-qaliy' (plant ash) enters Latin as alkali through his works.