Meanwhile the nature of the earth with which the sulphuric acid was combined remained unknown to chemists. Stahl worked at the problem and came to the conclusion that it was lime. The younger Geoffroy, a famous pharmacist of Paris, ascertained (1728) that the earth of alum was identical with that of argillaceous earth and Alumina was for some time called Argile. Marggraf observed that he could not get alum crystals from a combination of argile and sulphuric acid, but noting that in the old factories it had been the custom to add putrid urine to the solution, for which carbonate of potash was subsequently substituted, went so far as to make the salt, but did not appreciate that it was actually a double salt. The name alumina which the earth now bears was given to it by Morveau. It was Vauquelin (another pharmacist) who clearly proved the composition of alum, and Lavoisier first suggested that alumina was the oxide of a metal. Sir Humphry Davy agreed with this view but failed to isolate the metal. Oersted was the first to actually extract aluminium from the oxide, but his process was an impracticable one, but in 1828 Woehler, and in 1858 Deville, found means of producing the metal in sufficient abundance to make it a valuable article of industry.
The chemical history of ammonia commences in Egypt with Sal Ammoniac. This is mentioned by Pliny under the name of Hammoniacus sal. Dioscorides also alludes to it; but in neither case does the description given fit in satisfactorily with the product known to us. Dioscorides, for instance, states that sal ammoniac is particularly prized if it can lie easily split up into rectangular fragments. It has been conjectured that what was called sal ammoniac by the ancient writers was, at least sometimes, rock salt.
The name is generally supposed to have been derived from that of the Egyptian deity, Amn or Amen, or Ammon as the Greeks called him, and in the belief that he was the same god as Jupiter he is referred to in classical literature as Zeus-Ammon or Jupiter-Ammon. The principal temple of this god was situated in an oasis of the Libyan desert which was then known as Ammonia (now Siwah), and if, as is supposed, the salt was found or produced in that locality its name is thus accounted for. Gum ammoniacum was likewise so called in the belief that it was obtained in that district, though the gum with which we are familiar and which comes from India and Persia, is quite a different article from the African gum the name of which it has usurped. Pliny derives the name of the salt from the Greek “ammos,” sand, as it was found in the sand of the desert; an explanation which overlooks the fact that the stuff was called by a similar name in a country where the sand was not called ammos. In old Latin, French, and English writings “armoniac” is often met with. This was not inaccurate spelling; it was suggested by the opinion that the word was connected with Greek, armonia, a fastening or joining, from the use of sal ammoniac in soldering metals.