of gold in Aqua regia.
17 It had been known since the days of the alchemists in the
middle ages, but its instability still today makes chemical studies difficult. Bergman
correctly found that ammonia was essential for the explosive properties of the
precipitate, other bases formed non-explosive precipitates with gold. As a noble
metal, Bergman wrote, gold in its calcined state (i.e. an oxidation number higher
than 0) has a very strong affinity for phlogiston. Thus, the gold calx (gold oxide)
attracted phlogiston from ammonia liberating large volumes of elastic fluid (gaseous nitrogen). Bergman could not identify the gas but found that it was at least not
carbon dioxide (fixed air). Bergman determined that fulminating gold evolved four
times more gas per weight than black powder, and wrote that an explosion is
nothing else but a rapid evolution of gas. Fulminating gold was also studied by
Scheele [88], who also found it to be composed of gold calx and ammonia (alkali
volatile). The gas evolved on detonation, he found to be identical to the gas (i.e.
nitrogen) evolved by decomposition of ammonium chloride (salmiack) with MnO 2 .
As will be seen in the next section, Bergman’s thesis led to an infected dispute with
Wallerius.
In 1770, Bergman started his important studies of water analysis (Chap. 17) with
a thesis by Bergman and Dubb [89]. The same year he also published the first part
of a long review on the chlorides of mercury [90], the third and last part of which
appeared in 1772. This work is essentially a literature study but Bergman has made
occasional control experiments. It is also here that we find the first seed to his
chemical nomenclature (Chap. 26) in the form of the name Mercurius Nitratus for
mercury nitrate.
Of more interest is his paper on the preparation of more durable bricks and roof
tiles [91]. Bergman complained that the quality of bricks had decreased in recent
years, so that it almost seemed like the knowledge of preparing bricks had been lost.
Brick walls could be protected by cement rendering, but roof tiles made from clay
was a more serious issue. Clay tiles were the perfect material for roofs, Bergman
wrote, as wooden boards, wood shingles or sod used up much more valuable
resources. The tiles that Bergman saw around him were too porous, which caused
the roofs to leak and the water-soaked tiles cracked by freezing in the winter. A few
years earlier, Bergman had visited a tile factory belonging to the university and he
had found the manufacturing process unsatisfactory.
By reading the works of Macquer,
18 Bergman had found out that pure clay
mixed with lime does not melt on heating. On addition of silica, however, the
mixture melts on heating, but as the silica content was increased still further, the
melting point increased. Bergman had made experiments with both lime-free clays
and lime rich clays (marl) from the Uppsala area and mixed them with sand in
different proportions. He found that bricks made from pure clay shrunk and cracked
on burning, so the addition of sand was necessary. Too much sand, however,
prevents proper sintering. The degree of heating was also critical. The tiles must be
17
Fulminating gold is a mixture of different species but appears to be square planar Au(III)
complexes with chloride and ammonia ligands.
18
Pierre Macquer (1718 − 1784). See Sect. 14.7.
132
9 Bergman Becomes a Chemist
17 It had been known since the days of the alchemists in the
middle ages, but its instability still today makes chemical studies difficult. Bergman
correctly found that ammonia was essential for the explosive properties of the
precipitate, other bases formed non-explosive precipitates with gold. As a noble
metal, Bergman wrote, gold in its calcined state (i.e. an oxidation number higher
than 0) has a very strong affinity for phlogiston. Thus, the gold calx (gold oxide)
attracted phlogiston from ammonia liberating large volumes of elastic fluid (gaseous nitrogen). Bergman could not identify the gas but found that it was at least not
carbon dioxide (fixed air). Bergman determined that fulminating gold evolved four
times more gas per weight than black powder, and wrote that an explosion is
nothing else but a rapid evolution of gas. Fulminating gold was also studied by
Scheele [88], who also found it to be composed of gold calx and ammonia (alkali
volatile). The gas evolved on detonation, he found to be identical to the gas (i.e.
nitrogen) evolved by decomposition of ammonium chloride (salmiack) with MnO 2 .
As will be seen in the next section, Bergman’s thesis led to an infected dispute with
Wallerius.
In 1770, Bergman started his important studies of water analysis (Chap. 17) with
a thesis by Bergman and Dubb [89]. The same year he also published the first part
of a long review on the chlorides of mercury [90], the third and last part of which
appeared in 1772. This work is essentially a literature study but Bergman has made
occasional control experiments. It is also here that we find the first seed to his
chemical nomenclature (Chap. 26) in the form of the name Mercurius Nitratus for
mercury nitrate.
Of more interest is his paper on the preparation of more durable bricks and roof
tiles [91]. Bergman complained that the quality of bricks had decreased in recent
years, so that it almost seemed like the knowledge of preparing bricks had been lost.
Brick walls could be protected by cement rendering, but roof tiles made from clay
was a more serious issue. Clay tiles were the perfect material for roofs, Bergman
wrote, as wooden boards, wood shingles or sod used up much more valuable
resources. The tiles that Bergman saw around him were too porous, which caused
the roofs to leak and the water-soaked tiles cracked by freezing in the winter. A few
years earlier, Bergman had visited a tile factory belonging to the university and he
had found the manufacturing process unsatisfactory.
By reading the works of Macquer,
18 Bergman had found out that pure clay
mixed with lime does not melt on heating. On addition of silica, however, the
mixture melts on heating, but as the silica content was increased still further, the
melting point increased. Bergman had made experiments with both lime-free clays
and lime rich clays (marl) from the Uppsala area and mixed them with sand in
different proportions. He found that bricks made from pure clay shrunk and cracked
on burning, so the addition of sand was necessary. Too much sand, however,
prevents proper sintering. The degree of heating was also critical. The tiles must be
17
Fulminating gold is a mixture of different species but appears to be square planar Au(III)
complexes with chloride and ammonia ligands.
18
Pierre Macquer (1718 − 1784). See Sect. 14.7.
132
9 Bergman Becomes a Chemist