silver chloride, while the apparently higher affinity of sodium for sulphuric acid
than for hydrochloric acid is due to the volatility of hydrogen chloride and the
increase in entropy accompanied by the evolution of gas. There is one important
exception. Examining the order of the metals in the acid columns (i.e. the precipitation of one metal from its salts by a second metal) reveals a good correlation to
the so-called electrochemical or electromotive series found in modern chemistry
textbooks. Ordering the metals with increasing
1 standard reduction potential
reveals a reasonable agreement with the order found by Bergman:
Bergman
Zn
Mn
Fe
Pb
Sn
Co
Cu
Ni
Bi
Hg
Ag
Modern
Mn
Zn
Fe
Co
Ni
Sn
Pb
Bi
Cu
Hg
Ag
Bergman’s system works fairly well for acids, bases and metals but, unfortunately, he also included columns like water, ethanol, ether and oils. These columns
do not describe chemical reactions and should not have been included.
Bergman had to account for several anomalies. For example, it had been
reported by Baumé in 1760 that when nitric acid was added to an aqueous solution
of potassium sulphate, potassium nitrate crystallised leaving sulphuric acid in
solution. On the other hand, it was well known that heating potassium nitrate with
concentrated sulphuric acid gave nitric acid and potassium sulphate (actually
potassium hydrogen sulphate). While other authors had attributed this to what they
called reciprocal attractions, Bergman clearly attributed this to a chemical equilibrium: “Acidum vitrioli [sulphuric acid] in sufficient amount decomposes nitrum
[potassium nitrate] completely, even via humida [i.e. in solution] whence it appears
to have more power of attraction than does acidum nitri [nitric acid]” [10]. This was
an important statement, as it anticipated the discovery of the law of mass action by
25 years. The law of mass action was first clearly stated by Claude Louis Berthollet
in 1801 [11] but already Boyle had pointed in the right direction in 1674: a large
amount of a substance can compensate for a low affinity [12].
The fifth form of attraction discussed by Bergman was double elective attractions (Attractio duplex elective) which correspond to what a modern chemist would
call metathesis reactions (or double decomposition in older literature). These are
reactions between four components, e.g. two salts. One example would be the
reaction between aqueous solutions of sodium sulphate and barium chloride, which
yields insoluble barium sulphate and a solution of sodium chloride. Of course,
Bergman did not attempt to represent these in a table.
An unexpected application of Bergman’s theories of elective attractions is found
in Goethe’s novel Elective Affinities (Die Wahlverwandtschaften) originally published in 1809. This book tells the story of a couple, Eduard and his wife Charlotte.
To bring some excitement to their slightly dull life, they invite Eduard’s friend Otto
and Charlotte’s young niece Ottilie. Soon enough, attractions arise between Eduard
and Ottile and between Charlotte and Otto. Written by Sturm und Drang author
1
In modern textbooks the order would be reversed.
20.1 Bergman’s Essay on Elective Attractions
273
than for hydrochloric acid is due to the volatility of hydrogen chloride and the
increase in entropy accompanied by the evolution of gas. There is one important
exception. Examining the order of the metals in the acid columns (i.e. the precipitation of one metal from its salts by a second metal) reveals a good correlation to
the so-called electrochemical or electromotive series found in modern chemistry
textbooks. Ordering the metals with increasing
1 standard reduction potential
reveals a reasonable agreement with the order found by Bergman:
Bergman
Zn
Mn
Fe
Pb
Sn
Co
Cu
Ni
Bi
Hg
Ag
Modern
Mn
Zn
Fe
Co
Ni
Sn
Pb
Bi
Cu
Hg
Ag
Bergman’s system works fairly well for acids, bases and metals but, unfortunately, he also included columns like water, ethanol, ether and oils. These columns
do not describe chemical reactions and should not have been included.
Bergman had to account for several anomalies. For example, it had been
reported by Baumé in 1760 that when nitric acid was added to an aqueous solution
of potassium sulphate, potassium nitrate crystallised leaving sulphuric acid in
solution. On the other hand, it was well known that heating potassium nitrate with
concentrated sulphuric acid gave nitric acid and potassium sulphate (actually
potassium hydrogen sulphate). While other authors had attributed this to what they
called reciprocal attractions, Bergman clearly attributed this to a chemical equilibrium: “Acidum vitrioli [sulphuric acid] in sufficient amount decomposes nitrum
[potassium nitrate] completely, even via humida [i.e. in solution] whence it appears
to have more power of attraction than does acidum nitri [nitric acid]” [10]. This was
an important statement, as it anticipated the discovery of the law of mass action by
25 years. The law of mass action was first clearly stated by Claude Louis Berthollet
in 1801 [11] but already Boyle had pointed in the right direction in 1674: a large
amount of a substance can compensate for a low affinity [12].
The fifth form of attraction discussed by Bergman was double elective attractions (Attractio duplex elective) which correspond to what a modern chemist would
call metathesis reactions (or double decomposition in older literature). These are
reactions between four components, e.g. two salts. One example would be the
reaction between aqueous solutions of sodium sulphate and barium chloride, which
yields insoluble barium sulphate and a solution of sodium chloride. Of course,
Bergman did not attempt to represent these in a table.
An unexpected application of Bergman’s theories of elective attractions is found
in Goethe’s novel Elective Affinities (Die Wahlverwandtschaften) originally published in 1809. This book tells the story of a couple, Eduard and his wife Charlotte.
To bring some excitement to their slightly dull life, they invite Eduard’s friend Otto
and Charlotte’s young niece Ottilie. Soon enough, attractions arise between Eduard
and Ottile and between Charlotte and Otto. Written by Sturm und Drang author
1
In modern textbooks the order would be reversed.
20.1 Bergman’s Essay on Elective Attractions
273