did not even bother discussing Scheele’s theories: “I shall forbear entering on
discussion of antiquated opinions long ago exploded, and also of that of Mr.
Scheele, which has scarcely been embraced by any body, and has been sufficiently
refuted by Mr. Lavoisier, and the experiments of Dr. Fordyce” [51]
While Scheele appears to have regarded nitrogen (ruined air) as an element,
Bergman was more cautious. In his Instructions to Lectures in Chemistry, he wrote
that its “true nature and inner properties” are still unresolved [52]. He wrote that
because oxygen (pure air) can be completely destroyed by combustion or respiration, and become unsuitable to sustain fire and life, there are reasons to regard
nitrogen as phlogisticated. Later on the same page, he wrote: “Since the pure air
[oxygen] with something phlogistic appears to constitute such a harmful matter as
ruined air [nitrogen]…” Here Bergman appears to regard nitrogen as phlogisticated
air, and thus approach the views of Priestley (Sect. 21.6). Although Scheele’s
theories sometimes are somewhat naïve (e.g. his theories on the interactions of heat
and atoms), this is an example where Scheele was closer to the truth than Bergman.
When Scheele learned of Lavoisier’s work on the weight increase of sulphur and
phosphorus on combustion, and of Cavendish’s discovery in 1783 that combustion
of hydrogen in pure oxygen gave rise to water, he was forced to modify his theory.
In a paper in Crell’s Chemische Annalen, published in 1785 [53], Scheele proposed
oxygen to be a compound of Principum salinum, water and enough phlogiston to
render the product gaseous. Upon combustion, the hypothetical Principum salinum
gave heat and light with phlogiston, while the water was absorbed by the burning
material, explaining the weight increase. Hydrogen was considered by Scheele as a
compound of phlogiston and heat [54], and thus its combustion gave water and
heat.
In Sweden, Scheele and Bergman were in good company holding on to phlogiston. von Engeström had also hard to believe in the new theory of Lavoisier [55].
He used arguments put forward by a de la Folie who argued against Lavoisier’s
initial theory that it was carbon dioxide (fixed air) that was absorbed by metals
during calcination. Twelve lod (160 g) lead absorbed 700 cubic inches (4,300 L) of
air on calcination, but von Engeström found it unlikely that such a large volume of
air could be compressed into such a small volume of lead oxide (lead calx). von
Engeström assumed that the absorbed air was fixed air, i.e. carbon dioxide. Another
relevant point highlighted by von Engeström was the calcination of mercury. On
heating mercury, it first forms mercury clax (it is oxidised by oxygen to mercury
(II) oxide), but at a slightly higher temperature mercury is reformed (mercury
(II) oxide decomposes to mercury and oxygen above 500 °C). This was difficult to
explain by the prevalent theories of affinity.
Earlier authors have often been surprised or perhaps even embarrassed, that
Scheele and Bergman did not convert to Lavoisier’s theory, but it should be kept in
mind that Lavoisier’s theories did not receive widespread recognition until about
1785 [56], and by that time Bergman was dead and would soon be followed by
Scheele. Also, Lavoisier’s theory could not explain redox-reactions not involving
oxygen, e.g. the reactions between metals and metal salt solutions investigated by
21.5 Scheele’s and Bergman’s Views on Oxygen, Heat and Phlogiston
293
discussion of antiquated opinions long ago exploded, and also of that of Mr.
Scheele, which has scarcely been embraced by any body, and has been sufficiently
refuted by Mr. Lavoisier, and the experiments of Dr. Fordyce” [51]
While Scheele appears to have regarded nitrogen (ruined air) as an element,
Bergman was more cautious. In his Instructions to Lectures in Chemistry, he wrote
that its “true nature and inner properties” are still unresolved [52]. He wrote that
because oxygen (pure air) can be completely destroyed by combustion or respiration, and become unsuitable to sustain fire and life, there are reasons to regard
nitrogen as phlogisticated. Later on the same page, he wrote: “Since the pure air
[oxygen] with something phlogistic appears to constitute such a harmful matter as
ruined air [nitrogen]…” Here Bergman appears to regard nitrogen as phlogisticated
air, and thus approach the views of Priestley (Sect. 21.6). Although Scheele’s
theories sometimes are somewhat naïve (e.g. his theories on the interactions of heat
and atoms), this is an example where Scheele was closer to the truth than Bergman.
When Scheele learned of Lavoisier’s work on the weight increase of sulphur and
phosphorus on combustion, and of Cavendish’s discovery in 1783 that combustion
of hydrogen in pure oxygen gave rise to water, he was forced to modify his theory.
In a paper in Crell’s Chemische Annalen, published in 1785 [53], Scheele proposed
oxygen to be a compound of Principum salinum, water and enough phlogiston to
render the product gaseous. Upon combustion, the hypothetical Principum salinum
gave heat and light with phlogiston, while the water was absorbed by the burning
material, explaining the weight increase. Hydrogen was considered by Scheele as a
compound of phlogiston and heat [54], and thus its combustion gave water and
heat.
In Sweden, Scheele and Bergman were in good company holding on to phlogiston. von Engeström had also hard to believe in the new theory of Lavoisier [55].
He used arguments put forward by a de la Folie who argued against Lavoisier’s
initial theory that it was carbon dioxide (fixed air) that was absorbed by metals
during calcination. Twelve lod (160 g) lead absorbed 700 cubic inches (4,300 L) of
air on calcination, but von Engeström found it unlikely that such a large volume of
air could be compressed into such a small volume of lead oxide (lead calx). von
Engeström assumed that the absorbed air was fixed air, i.e. carbon dioxide. Another
relevant point highlighted by von Engeström was the calcination of mercury. On
heating mercury, it first forms mercury clax (it is oxidised by oxygen to mercury
(II) oxide), but at a slightly higher temperature mercury is reformed (mercury
(II) oxide decomposes to mercury and oxygen above 500 °C). This was difficult to
explain by the prevalent theories of affinity.
Earlier authors have often been surprised or perhaps even embarrassed, that
Scheele and Bergman did not convert to Lavoisier’s theory, but it should be kept in
mind that Lavoisier’s theories did not receive widespread recognition until about
1785 [56], and by that time Bergman was dead and would soon be followed by
Scheele. Also, Lavoisier’s theory could not explain redox-reactions not involving
oxygen, e.g. the reactions between metals and metal salt solutions investigated by
21.5 Scheele’s and Bergman’s Views on Oxygen, Heat and Phlogiston
293