Bergman devoted much effort to the identification of the classes and genera of
minerals. As in Sciagraphia, Bergman adopted the classes devised by Cronstedt but
changed their order. Salts, the first class in Bergman’s system, were soluble in
water, their water solutions had taste and their densities were generally less than
twice that of water. Earths had neither taste nor solubility in water. They had higher
densities than salts, but no known earth had a density exceeding 4.5 (Bergman is
probably referring to barium carbonate which has a density of 4.43 gcm
−3 ). Metals
were insoluble in water, had “a peculiar splendour” and high density, at least six
times that of water. Phlogistic bodies, the fourth and last class, had low densities
and were combustible. Bergman then discussed in detail different physical properties such as taste, colour and density and affinities (Chap. 20).
As most minerals are not pure elements, it was not trivial in which genus a
specific mineral should be classified. Bergman suggested that the weights of the
different components could be used; if a compound is composed of the proximate
principles (Chap. 22) A and B, the mineral will belong to genus A if it contains
more A than B. Thus, metal compounds, for instance, were classified under the
corresponding metal. Some exceptions were possible; if B was more important or
more valuable than A, the mineral was more conveniently classified in the genus of
B. Bergman could, for example, have referred to ores of precious metals such as
gold or silver. As in Cronsted’s book, Bergman suggested putting mechanically
mixed rocks in appendices.
When classifying minerals composed of different earths, Bergman devised a
system of formulae for describing their composition. As in Berzelius’ system from
1813, the system still used by chemists today, Bergman used Latin letters to denote
the constituents: p for ponderous earth (barium), c for calcareous earth (calcium),
m for magnesia (magnesium), a for argillaceous earth (aluminium) and s for
siliceous earth (silicon). Berzelius had the advantage of being able to determine
empirical formula and denoting the number of atoms with coefficients; Bergman did
not have this luxury, let his formulae are semi-quantitative. The order of the letters
in Bergman’s formulae denoted the composition: the earth appearing in the largest
proportion was given first and thus determined the genus, followed by the other
constituents in decreasing order. In Bergman’s system, cas would be a calcium
aluminium silicate. He also devised a system for denoting rocks of mixed composition using upper case letters: S for salt, T for earth (Terra in Latin), M for metal
and I for phlogistic bodies. Unfortunately, in the English translation (volume 3 of
his Chemical and Physical Essays), lower case letters were used, making the
meaning of symbols s and m ambiguous.
Shortly before his death, Bergman wrote to Crell that he was preparing a new
edition of his mineralogy and was eager to get hold of any mineral that he had yet
not studied [23]. This was a plea to the readers of Crell’s journal to send him
specimens.
348
25 Bergman’s Contributions to Mineralogy
minerals. As in Sciagraphia, Bergman adopted the classes devised by Cronstedt but
changed their order. Salts, the first class in Bergman’s system, were soluble in
water, their water solutions had taste and their densities were generally less than
twice that of water. Earths had neither taste nor solubility in water. They had higher
densities than salts, but no known earth had a density exceeding 4.5 (Bergman is
probably referring to barium carbonate which has a density of 4.43 gcm
−3 ). Metals
were insoluble in water, had “a peculiar splendour” and high density, at least six
times that of water. Phlogistic bodies, the fourth and last class, had low densities
and were combustible. Bergman then discussed in detail different physical properties such as taste, colour and density and affinities (Chap. 20).
As most minerals are not pure elements, it was not trivial in which genus a
specific mineral should be classified. Bergman suggested that the weights of the
different components could be used; if a compound is composed of the proximate
principles (Chap. 22) A and B, the mineral will belong to genus A if it contains
more A than B. Thus, metal compounds, for instance, were classified under the
corresponding metal. Some exceptions were possible; if B was more important or
more valuable than A, the mineral was more conveniently classified in the genus of
B. Bergman could, for example, have referred to ores of precious metals such as
gold or silver. As in Cronsted’s book, Bergman suggested putting mechanically
mixed rocks in appendices.
When classifying minerals composed of different earths, Bergman devised a
system of formulae for describing their composition. As in Berzelius’ system from
1813, the system still used by chemists today, Bergman used Latin letters to denote
the constituents: p for ponderous earth (barium), c for calcareous earth (calcium),
m for magnesia (magnesium), a for argillaceous earth (aluminium) and s for
siliceous earth (silicon). Berzelius had the advantage of being able to determine
empirical formula and denoting the number of atoms with coefficients; Bergman did
not have this luxury, let his formulae are semi-quantitative. The order of the letters
in Bergman’s formulae denoted the composition: the earth appearing in the largest
proportion was given first and thus determined the genus, followed by the other
constituents in decreasing order. In Bergman’s system, cas would be a calcium
aluminium silicate. He also devised a system for denoting rocks of mixed composition using upper case letters: S for salt, T for earth (Terra in Latin), M for metal
and I for phlogistic bodies. Unfortunately, in the English translation (volume 3 of
his Chemical and Physical Essays), lower case letters were used, making the
meaning of symbols s and m ambiguous.
Shortly before his death, Bergman wrote to Crell that he was preparing a new
edition of his mineralogy and was eager to get hold of any mineral that he had yet
not studied [23]. This was a plea to the readers of Crell’s journal to send him
specimens.
348
25 Bergman’s Contributions to Mineralogy