The so-called natural sal ammoniac was for centuries brought from Egypt, and was supposed to have been mined in the earth or sand of that country. In 1716 the younger Geoffroy came to the conclusion that it must be a product of sublimation, and he read a paper to the French Academy giving his reasons for this opinion. Homberg and Lemery opposed this view with so much bitterness, however, that the paper was not printed. In 1719 M. Lemaire, French Consul at Cairo, sent to the Academy an account of the method by which sal ammoniac was produced in Egypt, and this report definitely confirmed the opinion which Geoffroy had formed. It was, said M. Lemaire, simply a salt sublimed from soot. The fuel used in Egypt was exclusively the dung of camels and other animals which had been dried by the sun. It consisted largely of sal ammoniac, and this was retained in the soot. For a long time an artificial sal ammoniac had been manufactured at Venice, and a commoner sort also came from Holland. These were reputed to be made from human or animal urine. The manufacture of sal ammoniac was commenced in London early in the eighteenth century by a Mr. Goodwin. A formula for Sal Ammoniacum Factitium in Quincy’s Dispensatory (1724) is as follows:--Take of Urine lb. x.; of Sea-salt lb. ii.; of Wood soot lb. i.; boil these together in a mass, then put them in a subliming pot with a proper head, and there will rise up what forms these cakes. Dr. James (1764) states that at Newcastle one gallon of the bittern or liquor which drains from common salt whilst making, was mixed with 3 gallons of urine. The mixture was set aside for 48 hours to effervesce and subside. Afterwards the clear liquor was drawn off and evaporated in leaden vessels to crystallisation. The crystals were sublimed. A sal ammoniacum volatile was made by subliming sal ammoniac and salt of tartar (or lime or chalk) together. Sometimes some spices were put into the retort. This salt was used for smelling-bottles. Aqua regia was made by distilling sal ammoniac and saltpetre together. Sal Volatile Oleosum was introduced by Sylvius (de la Boe) about the year 1650. It became a medicated stimulant of the utmost popularity, and there were many formulas for it. One of the most famous was Goddard’s Drop. (See page 319). Ammonia in gaseous form was first obtained by Priestley in 1774. He called it alkaline air. Scheele soon after established that it contained nitrogen and Berthollet proved its chemical composition in 1785. SPIRITUS AMMONIÆ AROMATICUS