In 1773, Bergman published his results in an important paper entitled On Aerial
Acid in the Transactions [27]. After keeping a sample of pure alkali (K 2 CO 3 or
Na 2 CO 3 ) for 4 years on the attic, he had found no traces of sulphuric acid (vitriolic
acid), and explained previous reports of sulphuric acid in the atmosphere by
impurities in the alkali used or acid vapours present in laboratories, and he wrote
that such experiments could not be carried out in a laboratory where acids were
handled or stored. He then discussed Aër fixus (carbon dioxide), referring to Boyle
and Hales, and then discussed the theories of Black and Meyer. Bergman summarised the general properties of acids, and set out to investigate if carbon dioxide
fulfilled these criteria. A substance as sublime as carbon dioxide needed a vehiculum, i.e. it had to be dissolved in a solvent rather than being investigated in
gaseous state. Bergman concluded that aqueous solutions were appropriate. Water
saturated with CO 2 had a sour taste and was similar to Pyrmont water (Sect. 17.4)
or Champagne. He found that CO 2 gave salts with bases, and that bases could be
over-saturated, i.e. he had noticed the formation of HCO 3
- ; he mentioned both
NaHCO 3 and Ca(HCO 3 ) 2 . Aqueous calcium hydroxide solution (lime water) first
gives a precipitate (CaCO 3 ) with CO 2 that dissolves in the presence of excess CO 2
due to the formation of unstable water-soluble Ca(HCO 3 ) 2 . When the solution is left
in the sunshine, CaCO 3 is re-precipitated as CO 2 escapes. Bergman recognised the
geological effect of carbon dioxide saturated water on limestone. He correctly
defined lime (CaCO 3 ) as a salt, and found that CaO kept in a closed vessel is
unaffected over time. Just as Lane had reported, Bergman found that aqueous
solutions of CO 2 can dissolve iron. Bergman found that aqueous CO 2 solutions
colour litmus solution red and that the solution turned blue with time, as the
dissolved CO 2 escaped. Bergman described carbon dioxide as a glue that held the
elements (principa proxima, see Sect. 22.2) together in substances. He attributed
the alleged property of CO 2 to prevent scurvy and putrefaction to this fact. He
concluded his paper with a number of precipitation experiments with metal salts.
In 1775, Bergman published an extended version of his paper in Latin [28].
A revised version of this paper appeared in the first volume of his Opuscula, and
was translated to English, German, French, Italian and Spanish [29]. This paper
starts with a discussion of fixed air, a word that may have two meanings according
to Bergman: either any gas trapped in a solid, or more specifically the gas now
known as carbon dioxide, or aerial acid (luftsyra) as Bergman called it. He then
described the three main methods of preparing pure CO 2 : heating of carbonates,
addition of acid to carbonates and fermentation. Next, he described the general
properties of acids and the properties of aqueous CO 2 solution: it has a sour taste
and acts as a weak acid. The bulk of the paper discussed different carbonates. He
determined their compositions and the amount of different mineral acids required to
saturate them. In the case of Na 2 CO 3 , he was quite close to the truth. He found 100
parts of fresh crystals of aerated mineral alkali (Na 2 CO 3 Á 10 H 2 O) to be composed
of 16 parts CO 2 (fixed air), 64 parts water and 20 parts of pure alkali (NaOH). The
true values are 15, 56 and 24, respectively.
18.3 Bergman and the Aerial Acid
249
Acid in the Transactions [27]. After keeping a sample of pure alkali (K 2 CO 3 or
Na 2 CO 3 ) for 4 years on the attic, he had found no traces of sulphuric acid (vitriolic
acid), and explained previous reports of sulphuric acid in the atmosphere by
impurities in the alkali used or acid vapours present in laboratories, and he wrote
that such experiments could not be carried out in a laboratory where acids were
handled or stored. He then discussed Aër fixus (carbon dioxide), referring to Boyle
and Hales, and then discussed the theories of Black and Meyer. Bergman summarised the general properties of acids, and set out to investigate if carbon dioxide
fulfilled these criteria. A substance as sublime as carbon dioxide needed a vehiculum, i.e. it had to be dissolved in a solvent rather than being investigated in
gaseous state. Bergman concluded that aqueous solutions were appropriate. Water
saturated with CO 2 had a sour taste and was similar to Pyrmont water (Sect. 17.4)
or Champagne. He found that CO 2 gave salts with bases, and that bases could be
over-saturated, i.e. he had noticed the formation of HCO 3
- ; he mentioned both
NaHCO 3 and Ca(HCO 3 ) 2 . Aqueous calcium hydroxide solution (lime water) first
gives a precipitate (CaCO 3 ) with CO 2 that dissolves in the presence of excess CO 2
due to the formation of unstable water-soluble Ca(HCO 3 ) 2 . When the solution is left
in the sunshine, CaCO 3 is re-precipitated as CO 2 escapes. Bergman recognised the
geological effect of carbon dioxide saturated water on limestone. He correctly
defined lime (CaCO 3 ) as a salt, and found that CaO kept in a closed vessel is
unaffected over time. Just as Lane had reported, Bergman found that aqueous
solutions of CO 2 can dissolve iron. Bergman found that aqueous CO 2 solutions
colour litmus solution red and that the solution turned blue with time, as the
dissolved CO 2 escaped. Bergman described carbon dioxide as a glue that held the
elements (principa proxima, see Sect. 22.2) together in substances. He attributed
the alleged property of CO 2 to prevent scurvy and putrefaction to this fact. He
concluded his paper with a number of precipitation experiments with metal salts.
In 1775, Bergman published an extended version of his paper in Latin [28].
A revised version of this paper appeared in the first volume of his Opuscula, and
was translated to English, German, French, Italian and Spanish [29]. This paper
starts with a discussion of fixed air, a word that may have two meanings according
to Bergman: either any gas trapped in a solid, or more specifically the gas now
known as carbon dioxide, or aerial acid (luftsyra) as Bergman called it. He then
described the three main methods of preparing pure CO 2 : heating of carbonates,
addition of acid to carbonates and fermentation. Next, he described the general
properties of acids and the properties of aqueous CO 2 solution: it has a sour taste
and acts as a weak acid. The bulk of the paper discussed different carbonates. He
determined their compositions and the amount of different mineral acids required to
saturate them. In the case of Na 2 CO 3 , he was quite close to the truth. He found 100
parts of fresh crystals of aerated mineral alkali (Na 2 CO 3 Á 10 H 2 O) to be composed
of 16 parts CO 2 (fixed air), 64 parts water and 20 parts of pure alkali (NaOH). The
true values are 15, 56 and 24, respectively.
18.3 Bergman and the Aerial Acid
249