http://www.etymonline.com/index.php?search=chemistry&searchmode=none
chemistry 1605 (see chemical), originally "alchemy;" the meaning "natural physical process" is 1646, and the scientific study not so called until 1788. The figurative sense of "instinctual attraction or affinity" is older, c.1600, from the alchemical sense.
alchemy 1362, from O.Fr.
alkemie, from M.L.
alkimia, from Arabic
al-kimiya, from Gk.
khemeioa (found c.300 C.E. in a decree of Diocletian against "the old writings of the Egyptians"), all meaning "alchemy." Perhaps from an old name for Egypt (Khemia, lit. "land of black earth," found in Plutarch), or from Gk.
khymatos "that which is poured out," from khein "to pour," related to
khymos "juice, sap." The word seems to have elements of both origins.
"Mahn ... concludes, after an elaborate investigation, that Gr. khymeia was probably the original, being first applied to pharmaceutical chemistry, which was chiefly concerned with juices or infusions of plants; that the pursuits of the Alexandrian alchemists were a subsequent development of chemical study, and that the notoriety of these may have caused the name of the art to be popularly associated with the ancient name of Egypt." [oed]
The
al- is the Arabic definite article, "the." The art and the name adopted by the Arabs from Alexandrians and thence returned to Europe via Spain. Alchemy was the "chemistry" of the Middle Ages and early modern times, since c.1600 applied distinctively to the pursuit of the transmutation of baser metals into gold, which, along with the search for the universal solvent and the panacea, were the chief occupations of early chemistry.