previously been reported by Marggraf and British chemist William Lewis (1708–
1781) that solutions of platinum salts were not precipitated by sodium carbonate
(alkali minerale), which Bergman found hard to believe. Most metals form insoluble carbonates. He found that platinum salts indeed were precipitated by sodiumand potassium carbonate, ammonia and, to his surprise, ammonium chloride (salmiac). This is due to the precipitation of sparingly soluble ammonium tetrachloroplatinate (II), (NH 4 ) 2 [PtCl 4 ].
Bergman devised a method for purification of platinum. Thin platinum flakes
were boiled with hydrochloric acid to dissolve iron, the remaining metal dissolved
in Aqua regia, ammonium chloride was added and the precipitate melted with
ammonium sodium phosphate (microcosmic salt) to produce platinum. He investigated the effect of alkali on pure platinum chloride and showed that platinum
indeed is a unique metal with a characteristic solution chemistry.
Cobalt compounds have been known and used for millennia for colouring of
glass blue and painting porcelain. Metallic cobalt was, however, not reported until
1735 by Brandt [50]. It was Brandt’s students, Crosnstedt, who reported the discovery of nickel in 1751 [51]. Decades later, some chemists still doubted the
existence of cobalt and nickel. Experiments with impure materials had probably
added to the confusion.
In a paper published in 1780, Bergman reported precipitation experiments with
platinum, nickel, cobalt and manganese that finally showed that these metals where
unique elements, but he also showed that samples were frequently contaminated
[52]. Bergman mentioned that it had, for example, been suggested that platinum
was an alloy of gold and iron, and that nickel and cobalt were merely modifications
of iron. Among Bergman’s results was that he found that platinum could be precipitated from its solution in Aqua regia with zinc, but when zinc was added to a
solution of common nickel in nitric acid, arsenic was precipitated. He found that
zinc did not precipitate nickel, cobalt or manganese from pure metal salt solutions.
Bergman’s observation was correct.
15.7 Cerium—A Missed Opportunity
In 1751, Cronstedt described a mineral which he called Bastnäs tungsten (now
known as cerite), a heavy mineral discovered in the mines at Swedish Bastnäs [53].
In 1781, the 15-year old Wilhelm Hising (1766–1852), the son of a mine official at
Skinskatteberg, not far from Bastnäs, sent samples to Scheele and Bergman. This
mineral contains rare earth elements, mainly cerium and lanthanum, but Scheele
erroneously concluded that it was composed of silicon (silica), aluminium (clay),
carbonate (aerial acid) and traces of iron. d’Elhuyar was not more successful in
Bergman’s laboratory. He obtained iron, silica and lime [45]. Many years later, in
1803, Hisinger (as he was called after being adopted by his ennobled uncle) teamed
15.6 Establishing Platinum, Cobalt, Nickel and Manganese as Unique Metals
225
1781) that solutions of platinum salts were not precipitated by sodium carbonate
(alkali minerale), which Bergman found hard to believe. Most metals form insoluble carbonates. He found that platinum salts indeed were precipitated by sodiumand potassium carbonate, ammonia and, to his surprise, ammonium chloride (salmiac). This is due to the precipitation of sparingly soluble ammonium tetrachloroplatinate (II), (NH 4 ) 2 [PtCl 4 ].
Bergman devised a method for purification of platinum. Thin platinum flakes
were boiled with hydrochloric acid to dissolve iron, the remaining metal dissolved
in Aqua regia, ammonium chloride was added and the precipitate melted with
ammonium sodium phosphate (microcosmic salt) to produce platinum. He investigated the effect of alkali on pure platinum chloride and showed that platinum
indeed is a unique metal with a characteristic solution chemistry.
Cobalt compounds have been known and used for millennia for colouring of
glass blue and painting porcelain. Metallic cobalt was, however, not reported until
1735 by Brandt [50]. It was Brandt’s students, Crosnstedt, who reported the discovery of nickel in 1751 [51]. Decades later, some chemists still doubted the
existence of cobalt and nickel. Experiments with impure materials had probably
added to the confusion.
In a paper published in 1780, Bergman reported precipitation experiments with
platinum, nickel, cobalt and manganese that finally showed that these metals where
unique elements, but he also showed that samples were frequently contaminated
[52]. Bergman mentioned that it had, for example, been suggested that platinum
was an alloy of gold and iron, and that nickel and cobalt were merely modifications
of iron. Among Bergman’s results was that he found that platinum could be precipitated from its solution in Aqua regia with zinc, but when zinc was added to a
solution of common nickel in nitric acid, arsenic was precipitated. He found that
zinc did not precipitate nickel, cobalt or manganese from pure metal salt solutions.
Bergman’s observation was correct.
15.7 Cerium—A Missed Opportunity
In 1751, Cronstedt described a mineral which he called Bastnäs tungsten (now
known as cerite), a heavy mineral discovered in the mines at Swedish Bastnäs [53].
In 1781, the 15-year old Wilhelm Hising (1766–1852), the son of a mine official at
Skinskatteberg, not far from Bastnäs, sent samples to Scheele and Bergman. This
mineral contains rare earth elements, mainly cerium and lanthanum, but Scheele
erroneously concluded that it was composed of silicon (silica), aluminium (clay),
carbonate (aerial acid) and traces of iron. d’Elhuyar was not more successful in
Bergman’s laboratory. He obtained iron, silica and lime [45]. Many years later, in
1803, Hisinger (as he was called after being adopted by his ennobled uncle) teamed
15.6 Establishing Platinum, Cobalt, Nickel and Manganese as Unique Metals
225