with something yet unknown gave hydrochloric acid. When these acids were mixed
with earth, middle salts (salts in our modern definition) were obtained [29]. This is a
system that Wallerius has drawn from literature sources, and for which he could not
have found any support by experiments.
To get an idea of Wallerius’ ways of thinking, his explanation of the so-called
cold-short iron is instructive. Cold-short iron is iron which is brittle in the cold state
due to contamination with phosphorus. It was Scheele who proved in 1785
(Chap. 15) that cold-short iron owed its brittleness due to the presence of phosphorus. He did this by dissolving the iron in acid, boil the residue with alkali and
dissolve it in nitric acid. He then precipitated mercury(II) phosphate from the
solution and reduced the precipitate to phosphorous with charcoal [30]. Wallerius,
in 1750, used a completely different strategy to explain the phenomenon [31]. He
argued that the malleability and ductility of metals were due to phlogiston (he used
the terms “fire matter” or “inflammable matter”). When metal was deprived of its
phlogiston, it turned into a brittle calx (metal oxide in modern words). He had also
performed an experiment where he heated potassium carbonate (Sal tartari) with
charcoal (rich in phlogiston) and found the residue
5 so soft that it could be beaten
with a hammer without cracking. From these two phenomena, he drew the, in our
eyes far-fetched, conclusion that cold-shortness in iron was caused by too low
phlogiston content. Red-short iron (iron which is brittle due to a high sulphur
content) was, according to Wallerius, brittle due to high phlogiston content. Since
Wallerius believed in the transmutation of metals in the Earth’s crust, he finally
came to the conclusion that red-short iron came from ore which was young and not
ripe, while the cold-short iron came from ores which were too old. Neither Scheele
nor Bergman would ever have used such analogies to draw conclusions about a
completely unrelated chemical system.
9.2 Bergman’s First Chemical Study
Bergman had probably never paid much attention to chemistry, but the illness of
Wallerius gave him a reason to do so. As he saw no openings for a professorship in
physics,
6 the chair in chemistry was a possibility. Probably, he initially saw it as a
step towards a future professorship in physics. Although the branches of natural
sciences were not as differentiated as they are today and the step from physics to
chemistry not as great as it would be today, Bergman definitely needed more
chemical experience in order to be appointed professor. He had studied chemistry
under Wallerius but had only received the second-lowest grade on a four-step scale
(admittitur cum approbatione) [32]. Of all his publications, only Physical
Description of the Earth approached the field of chemistry. Most probably, the
5
No chemical reaction is expected in this case.
6
The chair in physics was held by Samuel Duræus (1718–1789). As a former student of
Klingenstierna, he became acting professor when Klingestierna applied for leave of absence in
1752 and finally succeeded Klingenstierna in 1757. As it happened, he would outlive Bergman.
118
9 Bergman Becomes a Chemist
with earth, middle salts (salts in our modern definition) were obtained [29]. This is a
system that Wallerius has drawn from literature sources, and for which he could not
have found any support by experiments.
To get an idea of Wallerius’ ways of thinking, his explanation of the so-called
cold-short iron is instructive. Cold-short iron is iron which is brittle in the cold state
due to contamination with phosphorus. It was Scheele who proved in 1785
(Chap. 15) that cold-short iron owed its brittleness due to the presence of phosphorus. He did this by dissolving the iron in acid, boil the residue with alkali and
dissolve it in nitric acid. He then precipitated mercury(II) phosphate from the
solution and reduced the precipitate to phosphorous with charcoal [30]. Wallerius,
in 1750, used a completely different strategy to explain the phenomenon [31]. He
argued that the malleability and ductility of metals were due to phlogiston (he used
the terms “fire matter” or “inflammable matter”). When metal was deprived of its
phlogiston, it turned into a brittle calx (metal oxide in modern words). He had also
performed an experiment where he heated potassium carbonate (Sal tartari) with
charcoal (rich in phlogiston) and found the residue
5 so soft that it could be beaten
with a hammer without cracking. From these two phenomena, he drew the, in our
eyes far-fetched, conclusion that cold-shortness in iron was caused by too low
phlogiston content. Red-short iron (iron which is brittle due to a high sulphur
content) was, according to Wallerius, brittle due to high phlogiston content. Since
Wallerius believed in the transmutation of metals in the Earth’s crust, he finally
came to the conclusion that red-short iron came from ore which was young and not
ripe, while the cold-short iron came from ores which were too old. Neither Scheele
nor Bergman would ever have used such analogies to draw conclusions about a
completely unrelated chemical system.
9.2 Bergman’s First Chemical Study
Bergman had probably never paid much attention to chemistry, but the illness of
Wallerius gave him a reason to do so. As he saw no openings for a professorship in
physics,
6 the chair in chemistry was a possibility. Probably, he initially saw it as a
step towards a future professorship in physics. Although the branches of natural
sciences were not as differentiated as they are today and the step from physics to
chemistry not as great as it would be today, Bergman definitely needed more
chemical experience in order to be appointed professor. He had studied chemistry
under Wallerius but had only received the second-lowest grade on a four-step scale
(admittitur cum approbatione) [32]. Of all his publications, only Physical
Description of the Earth approached the field of chemistry. Most probably, the
5
No chemical reaction is expected in this case.
6
The chair in physics was held by Samuel Duræus (1718–1789). As a former student of
Klingenstierna, he became acting professor when Klingestierna applied for leave of absence in
1752 and finally succeeded Klingenstierna in 1757. As it happened, he would outlive Bergman.
118
9 Bergman Becomes a Chemist