nitrate which do not contain water of crystallisation. In parallel with Bergman,
Richard Kirwan was working along similar lines determining the chemical composition of salts, and in the English translation of Bergman’s manual, published in 1784
[32], the translator has added footnotes with analytical results reported by Kirwan for
comparison. Bergman’s way of expressing the composition of salts is ambiguous to a
modern chemist. For instance, the composition of potassium sulphate is given as 52
parts of vegetable alkali, 40 parts of sulphuric acid and 8 parts of water per 100 parts
of salt. In reality, potassium sulphate is not composed of potassium hydroxide and
sulphuric acid, but water is eliminated when the acid and base react. Therefore, it is
not absolutely clear what this actually means, or whether the values of Bergman and
Kirwan are comparable. When it comes to non-hygroscopic metal salts, the values are
easier to interpret, as we can compare the true metal content and the true water
content with Bergman’s and Kirwan’s reported results. For example, copper(II)
sulphate pentahydrate contains 25% copper and 36% water. Bergman reported 26%
copper and 28% water, while Kirwan reported 27% copper and 43% water. Iron(II)
sulphate heptahydrate contains 20% iron and 45% water. Bergman reported 23% iron
and 38% water, while Kirwan reported 25% iron and 55% water. Zinc sulphate
heptahydrate contains 23% zinc and 44% water. Bergman reported 20% zinc and
40% water, while Kirwan reported 20% zinc and 58% water. Thus, Bergman’s values
seem to be somewhat more reliable than those of Kirwan.
Bergman’s methods of water analysis were employed by many chemists of the
time [33] and were very influencing. However, Bergman’s analyses suffered from
one serious problem. He collected salts as hydrates, but since the water content in
these salts often varied, so did Bergman’s results. Unfortunately, Bergman’s untimely death in 1784 prevented him from perfecting his methods. The work was,
however, taken up by others. Bergman’s methods were rationalised by Fourcroy
and important contributions came from Klaproth, who heated the salts to constant
weight, and isolated anhydrous salts rather than hydrates. Based on these contributions, the methods were perfected by Kirwan at the end of the century [34].
23.4 Mineral Analysis in Solution
Bergman’s work on mineral water analysis led him to the idea of analysing minerals
by wet methods, a very important step in the development of analytical chemistry.
Bergman’s first contribution to the field, a paper on the analysis of gems[35] was
written in 1777, but the publication of the third volume of Nova Acta, including
Bergman’s paper, was delayed to 1780 [36, 37].
In this paper, Bergman analysed the composition of gems (emerald, sapphire,
topaz, hyacinth, ruby and diamond) by a combination of dry methods (blow-pipe;
Sect. 23.5) and wet methods. He found that acids (sulphuric, hydrochloric and nitric
acid) extracted small amounts of calcium (lime) and traces of iron from all of the
stones except diamond. As the main part of the samples was insoluble in acids, he
proceeded by fusing them with sodium carbonate (fixed alkali). The method of
318
23 Bergman as an Analytical Chemist
Richard Kirwan was working along similar lines determining the chemical composition of salts, and in the English translation of Bergman’s manual, published in 1784
[32], the translator has added footnotes with analytical results reported by Kirwan for
comparison. Bergman’s way of expressing the composition of salts is ambiguous to a
modern chemist. For instance, the composition of potassium sulphate is given as 52
parts of vegetable alkali, 40 parts of sulphuric acid and 8 parts of water per 100 parts
of salt. In reality, potassium sulphate is not composed of potassium hydroxide and
sulphuric acid, but water is eliminated when the acid and base react. Therefore, it is
not absolutely clear what this actually means, or whether the values of Bergman and
Kirwan are comparable. When it comes to non-hygroscopic metal salts, the values are
easier to interpret, as we can compare the true metal content and the true water
content with Bergman’s and Kirwan’s reported results. For example, copper(II)
sulphate pentahydrate contains 25% copper and 36% water. Bergman reported 26%
copper and 28% water, while Kirwan reported 27% copper and 43% water. Iron(II)
sulphate heptahydrate contains 20% iron and 45% water. Bergman reported 23% iron
and 38% water, while Kirwan reported 25% iron and 55% water. Zinc sulphate
heptahydrate contains 23% zinc and 44% water. Bergman reported 20% zinc and
40% water, while Kirwan reported 20% zinc and 58% water. Thus, Bergman’s values
seem to be somewhat more reliable than those of Kirwan.
Bergman’s methods of water analysis were employed by many chemists of the
time [33] and were very influencing. However, Bergman’s analyses suffered from
one serious problem. He collected salts as hydrates, but since the water content in
these salts often varied, so did Bergman’s results. Unfortunately, Bergman’s untimely death in 1784 prevented him from perfecting his methods. The work was,
however, taken up by others. Bergman’s methods were rationalised by Fourcroy
and important contributions came from Klaproth, who heated the salts to constant
weight, and isolated anhydrous salts rather than hydrates. Based on these contributions, the methods were perfected by Kirwan at the end of the century [34].
23.4 Mineral Analysis in Solution
Bergman’s work on mineral water analysis led him to the idea of analysing minerals
by wet methods, a very important step in the development of analytical chemistry.
Bergman’s first contribution to the field, a paper on the analysis of gems[35] was
written in 1777, but the publication of the third volume of Nova Acta, including
Bergman’s paper, was delayed to 1780 [36, 37].
In this paper, Bergman analysed the composition of gems (emerald, sapphire,
topaz, hyacinth, ruby and diamond) by a combination of dry methods (blow-pipe;
Sect. 23.5) and wet methods. He found that acids (sulphuric, hydrochloric and nitric
acid) extracted small amounts of calcium (lime) and traces of iron from all of the
stones except diamond. As the main part of the samples was insoluble in acids, he
proceeded by fusing them with sodium carbonate (fixed alkali). The method of
318
23 Bergman as an Analytical Chemist