Brandt's research involved investigating metals. He coined the term semi-metals to describe elements that have both metal and non-metal characteristics. These elements are now called metalloids. Metaloids are the elements in the region between metal and non-metal elements on the periodic table (see here) In 1733 he investigated arsenic and its compounds. In 1735 he postulated that the blue color in an ore known as smalt was due to an unknown metal or semi-metal. In 1742 he was able to isolate this unknown blue metal which he named cobalt, taking the name from the old Teutonic word kobold meaning demon. Cobalt is atomic number 27 and is represented by the chemical symbol Co.
Brandt's later research involved using hot acid solutions to dissolve gold. Brandt's later publications dealt with criticism of the alchemical belief that other "base" metals could be transformed into gold. It has been said that he did more than any other chemist to clarify that transmutation of other metals into gold was impossible and that claims of alchemists that they could create gold from other metals were false.
Brandt died on April 29, 1768 in Stockholm, Sweden of prostate cancer.
Morris, Richard; The Last Sorcerers; Joseph Henry Press; 2003
"Brandt, Georg" in Complete Dictionary of Scientific Biography; Charles Scribner's Sons; 2008
Georg Brandt Wikipedia Entry