fusing minerals with sodium carbonate is still used on large scale today in the
extraction of chromium from its ores. The residue was treated with hydrochloric
acid,
6 which left small amounts of silicon dioxide undissolved. Potassium hexacyanoferrate(II) (alkaline phlogisticated lixivium) was added to the solution to
precipitate iron, and the earths were then precipitated with alkali carbonate (fixed
alkali). The precipitate was treated with acetic acid (vinegar). In the cold, calcium,
magnesium and barium carbonates were dissolved, leaving aluminium carbonate
undissolved.
7 Magnesium, calcium and barium were re-precipitated with alkali
carbonate and treated with dilute sulphuric acid. Barium sulphate (spatum ponderosum) is insoluble. Calcium sulphate (gypsum) is five hundred times less soluble
in water than magnesium sulphate (Epsom salt) and the two are easily separated. As
only minute amounts of samples could be used due to the high cost, the analysis of
precious stones presented a great challenge.
Due to the delayed publication of the earth of gems paper, a paper on brown
tourmalines[36] was actually published before the earth of gems paper, although
written later. It describes brown tourmalines from Tyrol that Bergman recently had
received and compared with tourmalines brought from Sri Lanka (Ceylon) by
Linnaean apostle Carl Peter Thunberg (1743–1828). Thunberg visited Sri Lanka on
the way home from his successful journey to Japan, where he compiled the first
Japanese flora. After a crystallographic investigation, Bergman proceeded with a
chemical analysis. He started with a traditional blow-pipe analysis and proceeded
by noting that the stones were hardly soluble in nitric or hydrochloric acid. He then
gave an account of the method described in the earth of gem paper, fusing the
stones with sodium carbonate (alkali sodæ) and heating the residue with
hydrochloric acid to bring the components into solution. He concluded that the
tourmalines consisted of clay, silica, lime and iron, the reported quantitative analysis from the two kinds of tourmalines being quite similar. As tourmalines have
very complex compositions, the accuracy of Bergman’s analyses is hard to estimate. It should be recalled from Sect. 5.2 that Bergman’s friend Rinman had
examined tourmalines a few years earlier. Rinman’s method was to observe the
changes of the samples when fused using a blow-pipe, both alone and with different
fluxes (e.g. borax, calcium fluoride and calcium carbonate). He observed that
tourmalines did not dissolve in boiling sulphuric acid (Oleo vitrioli), nitric acid
(Aqvafort) or hydrochloric acid (Spiritu Sali), but that they dissolved in nitric acid
after fusion with borax leaving a gelatinous residue [SiO 2 ] which he did not
6
The mixture must be heated to assure precipitation of silica. When I applied Bergman’s method to
a sample of feldspar, addition of hydrochloric acid at ambient temperature gave no precipitate, but
the following day the whole solution had formed a gel.
7
Indeed, it is found that the precipitate formed by mixing 0.1 M solutions of calcium nitrate and
sodium carbonate is instantaneously dissolved upon addition of acetic acid at 0 ºC, while the
corresponding precipitate obtained from aluminium nitrate and sodium carbonate takes minutes to
dissolve. The method is not perfect, as aluminium carbonate is not completely insoluble, but it is
still an evidence of Bergman’s ingenious ways of solving chemical problems. To find this method
either required a deep chemical knowledge or a large number of trial-and-error experiments. If
Bergman had heated the carbonate precipitate before treatment with acetic acid, virtually insoluble
aluminium oxide would have formed.
23.4 Mineral Analysis in Solution
319
extraction of chromium from its ores. The residue was treated with hydrochloric
acid,
6 which left small amounts of silicon dioxide undissolved. Potassium hexacyanoferrate(II) (alkaline phlogisticated lixivium) was added to the solution to
precipitate iron, and the earths were then precipitated with alkali carbonate (fixed
alkali). The precipitate was treated with acetic acid (vinegar). In the cold, calcium,
magnesium and barium carbonates were dissolved, leaving aluminium carbonate
undissolved.
7 Magnesium, calcium and barium were re-precipitated with alkali
carbonate and treated with dilute sulphuric acid. Barium sulphate (spatum ponderosum) is insoluble. Calcium sulphate (gypsum) is five hundred times less soluble
in water than magnesium sulphate (Epsom salt) and the two are easily separated. As
only minute amounts of samples could be used due to the high cost, the analysis of
precious stones presented a great challenge.
Due to the delayed publication of the earth of gems paper, a paper on brown
tourmalines[36] was actually published before the earth of gems paper, although
written later. It describes brown tourmalines from Tyrol that Bergman recently had
received and compared with tourmalines brought from Sri Lanka (Ceylon) by
Linnaean apostle Carl Peter Thunberg (1743–1828). Thunberg visited Sri Lanka on
the way home from his successful journey to Japan, where he compiled the first
Japanese flora. After a crystallographic investigation, Bergman proceeded with a
chemical analysis. He started with a traditional blow-pipe analysis and proceeded
by noting that the stones were hardly soluble in nitric or hydrochloric acid. He then
gave an account of the method described in the earth of gem paper, fusing the
stones with sodium carbonate (alkali sodæ) and heating the residue with
hydrochloric acid to bring the components into solution. He concluded that the
tourmalines consisted of clay, silica, lime and iron, the reported quantitative analysis from the two kinds of tourmalines being quite similar. As tourmalines have
very complex compositions, the accuracy of Bergman’s analyses is hard to estimate. It should be recalled from Sect. 5.2 that Bergman’s friend Rinman had
examined tourmalines a few years earlier. Rinman’s method was to observe the
changes of the samples when fused using a blow-pipe, both alone and with different
fluxes (e.g. borax, calcium fluoride and calcium carbonate). He observed that
tourmalines did not dissolve in boiling sulphuric acid (Oleo vitrioli), nitric acid
(Aqvafort) or hydrochloric acid (Spiritu Sali), but that they dissolved in nitric acid
after fusion with borax leaving a gelatinous residue [SiO 2 ] which he did not
6
The mixture must be heated to assure precipitation of silica. When I applied Bergman’s method to
a sample of feldspar, addition of hydrochloric acid at ambient temperature gave no precipitate, but
the following day the whole solution had formed a gel.
7
Indeed, it is found that the precipitate formed by mixing 0.1 M solutions of calcium nitrate and
sodium carbonate is instantaneously dissolved upon addition of acetic acid at 0 ºC, while the
corresponding precipitate obtained from aluminium nitrate and sodium carbonate takes minutes to
dissolve. The method is not perfect, as aluminium carbonate is not completely insoluble, but it is
still an evidence of Bergman’s ingenious ways of solving chemical problems. To find this method
either required a deep chemical knowledge or a large number of trial-and-error experiments. If
Bergman had heated the carbonate precipitate before treatment with acetic acid, virtually insoluble
aluminium oxide would have formed.
23.4 Mineral Analysis in Solution
319