SiF 4 ðgÞ þ 4H 2 OðlÞ ! SiðOHÞ 4 ðsÞ þ 4HFðaqÞ:
In his letter to Troil in June 1776 (Sect. 7.3) he wrote:
Mr. Scheele has discovered the formation of the flint
1
; and I myself have found out, within
these two year, a method of obtaining, with help of some fluor acid [hydrofluoric acid],
thirteen precipitated crystals of sizes of small peas. Theses artificial pebble in all experiments, both in the wet and dry method, and even in focus of a burning-glass, in piece that I
sent to Mr. Macquer, discovered exactly to him the same qualities as the natural one. All
these circumstances, therefore, prove, that the pebble [kisel (= quartz) in the original
Swedish text] is a saline earth, which is composed of fluor acid, and an original substance
existing in the watry exhalations. It is not quite simple; but however, I have not been able to
consider it as any other than an elementary earth: indeed my judgement is, that it cannot be
compounded from any other principle. [25]
In a dissertation defended in November 1779 [26], Bergman argued that the
formation of siliceous earth from hydrofluoric acid and water indicated that siliceous earth was composed of hydrofluoric acid and the principle of water. In his
Instructions to Lectures in Chemistry, published the same year, he wrote “That acid
of fluor-spar is present in silica is without doubt, but the basis in this earth, which
appears to be the solid part of water, is still unknown” [5]. Still, the other primitive
earths had not been decomposed, and until further experiments had proven the
compounded nature of siliceous earth, he preferred to treat it as a primitive earth
[27].
The nature of magnesium oxide (magnesia) was studied in a dissertation, de
Magnesia alba, defended by one of Bergman’s students in 1775, adding further
evidence to the elemental nature of magnesium [28]. Two years later, a Johan
Berger, apparently of military background, claimed in a paper on potassium nitrate
(saltpetre) production that calcium (lime) could be converted to magnesium
(magnesia) [29]. Berger’s paper is followed by a short paper by Bergman, where he
proved Berger wrong [30]. Bergman insisted that magnesia and lime were independent primitive earths, referring to the works of Black, Marggraf and his own
dissertation on Magnesia alba. The problem was that when magnesium nitrate
(Magnesia nitri) was removed from the potassium nitrate solution by precipitation
with potassium carbonate, it yielded a precipitate which readily dissolved in sulphuric acid, but after calcination (i.e. decomposition to magnesium oxide), it
became much less soluble in sulphuric acid, and was thus confused for calcium
oxide (lime) by Berger. Bergman showed that there was no conversion of
magnesium to calcium, but upon calcination the precipitate (magnesium carbonate
hydroxide) lost carbon dioxide and water (turning to magnesium oxide) which
dissolves more slowly in sulphuric acid.
In addition to the four generally accepted earths and the recently discovered
barium oxide, Bergman also suspected the presence of sixth elemental earth, earth
of gems, in diamonds [11], a view that he later had to abandon after realising that
1
kisel in the original Swedish text (kisel = quartz).
306
22 Bergman’s and Scheele’s Theories of Elements and Atoms
In his letter to Troil in June 1776 (Sect. 7.3) he wrote:
Mr. Scheele has discovered the formation of the flint
1
; and I myself have found out, within
these two year, a method of obtaining, with help of some fluor acid [hydrofluoric acid],
thirteen precipitated crystals of sizes of small peas. Theses artificial pebble in all experiments, both in the wet and dry method, and even in focus of a burning-glass, in piece that I
sent to Mr. Macquer, discovered exactly to him the same qualities as the natural one. All
these circumstances, therefore, prove, that the pebble [kisel (= quartz) in the original
Swedish text] is a saline earth, which is composed of fluor acid, and an original substance
existing in the watry exhalations. It is not quite simple; but however, I have not been able to
consider it as any other than an elementary earth: indeed my judgement is, that it cannot be
compounded from any other principle. [25]
In a dissertation defended in November 1779 [26], Bergman argued that the
formation of siliceous earth from hydrofluoric acid and water indicated that siliceous earth was composed of hydrofluoric acid and the principle of water. In his
Instructions to Lectures in Chemistry, published the same year, he wrote “That acid
of fluor-spar is present in silica is without doubt, but the basis in this earth, which
appears to be the solid part of water, is still unknown” [5]. Still, the other primitive
earths had not been decomposed, and until further experiments had proven the
compounded nature of siliceous earth, he preferred to treat it as a primitive earth
[27].
The nature of magnesium oxide (magnesia) was studied in a dissertation, de
Magnesia alba, defended by one of Bergman’s students in 1775, adding further
evidence to the elemental nature of magnesium [28]. Two years later, a Johan
Berger, apparently of military background, claimed in a paper on potassium nitrate
(saltpetre) production that calcium (lime) could be converted to magnesium
(magnesia) [29]. Berger’s paper is followed by a short paper by Bergman, where he
proved Berger wrong [30]. Bergman insisted that magnesia and lime were independent primitive earths, referring to the works of Black, Marggraf and his own
dissertation on Magnesia alba. The problem was that when magnesium nitrate
(Magnesia nitri) was removed from the potassium nitrate solution by precipitation
with potassium carbonate, it yielded a precipitate which readily dissolved in sulphuric acid, but after calcination (i.e. decomposition to magnesium oxide), it
became much less soluble in sulphuric acid, and was thus confused for calcium
oxide (lime) by Berger. Bergman showed that there was no conversion of
magnesium to calcium, but upon calcination the precipitate (magnesium carbonate
hydroxide) lost carbon dioxide and water (turning to magnesium oxide) which
dissolves more slowly in sulphuric acid.
In addition to the four generally accepted earths and the recently discovered
barium oxide, Bergman also suspected the presence of sixth elemental earth, earth
of gems, in diamonds [11], a view that he later had to abandon after realising that
1
kisel in the original Swedish text (kisel = quartz).
306
22 Bergman’s and Scheele’s Theories of Elements and Atoms