air…”.. In addition, the second edition was supplied with an index and a foreword
by Leonhardi. Altogether, the additions amount to 120 pages, nearly doubling the
number of pages compared to the first edition. The copperplate is clearly printed
from the same matrix as in the original edition, while a new copper plate had been
engraved to illustrate the paper “On the amount of pure air…”. It is quite
remarkable that both the translations and the second edition contain Kirwan’s essay,
which cannot have pleased Scheele and which contains little of value.
In 1788, i.e. after Scheele’s death, a Latin translation by Heinrich Schafer
appeared in the Latin edition of Scheele’s collected works, published on initiative
by Ernst Benjamin Hebenstreit (1753–1803) [38]. The German text, including
Kirwan’s essay and Priestley’s letter, was reprinted as the first volume in the
German edition of Scheele’s collected works in 1793 [39], and the second edition
(excluding Bergman’s preface and all additions) was reissued as volume 58 in
Ostwald’s Klassiker der Exakten Wissenschaften in 1894. The title page gives the
impression that the first edition was used, which is not true. Probably the editor,
physical chemist and later Nobel laureate Wilhelm Ostwald, did not have access to
a copy of the rare first edition. The original 1777 edition was finally published in
facsimile in 1970 with comments by Scheele scholar Uno Boklund.
21.5 Scheele’s and Bergman’s Views on Oxygen, Heat
and Phlogiston
Scheele found that air was lost in a closed vessel containing air and potassium
polysulphide (liver of sulphur), potassium sulphite, turpentine, iron(II) sulphate
solution, nitrogen monoxide or copper(I) chloride solution. Of course, this is due to
the absorption of oxygen by the readily oxidisable materials. Scheele first considered two possible explanations: either phlogiston caused the air to loose elasticity,
and thus decrease in volume, or a part of the air was absorbed by the material (liver
of sulphur, etc.). Scheele correctly excluded the first possibility, as he found that the
air lost not only volume but also weight. Unfortunately, he also excluded the
second, true explanation, since he failed to extract air from the oxidised materials.
Scheele apparently had the erroneous impression that any gas absorbed by a solid
material would behave as carbon dioxide (fixed air): it was well known that carbon
dioxide could be absorbed—fixed—by strong bases such as potassium hydroxide or
calcium oxide. When carbon dioxide reacts with potassium hydroxide it generates
potassium carbonate which gives a precipitate with calcium hydroxide solution
(lime water). When Scheele found that oxidised turpentine failed to give a
precipitate with lime water, he concluded that it contained no “fixed air”. This was
the largest mistake in Scheele’s entire career, and given Scheele’s extensive
knowledge, it is a quite remarkable error. At this point, Scheele could have been the
one to realise the true role of oxygen in combustion and to overthrow the phlogiston
theory; as Blomstrand put it: “A few seconds of thought in the right direction,
would have been all needed” [40]. However, it is not likely that Scheele would have
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21 The Discovery of Oxygen
by Leonhardi. Altogether, the additions amount to 120 pages, nearly doubling the
number of pages compared to the first edition. The copperplate is clearly printed
from the same matrix as in the original edition, while a new copper plate had been
engraved to illustrate the paper “On the amount of pure air…”. It is quite
remarkable that both the translations and the second edition contain Kirwan’s essay,
which cannot have pleased Scheele and which contains little of value.
In 1788, i.e. after Scheele’s death, a Latin translation by Heinrich Schafer
appeared in the Latin edition of Scheele’s collected works, published on initiative
by Ernst Benjamin Hebenstreit (1753–1803) [38]. The German text, including
Kirwan’s essay and Priestley’s letter, was reprinted as the first volume in the
German edition of Scheele’s collected works in 1793 [39], and the second edition
(excluding Bergman’s preface and all additions) was reissued as volume 58 in
Ostwald’s Klassiker der Exakten Wissenschaften in 1894. The title page gives the
impression that the first edition was used, which is not true. Probably the editor,
physical chemist and later Nobel laureate Wilhelm Ostwald, did not have access to
a copy of the rare first edition. The original 1777 edition was finally published in
facsimile in 1970 with comments by Scheele scholar Uno Boklund.
21.5 Scheele’s and Bergman’s Views on Oxygen, Heat
and Phlogiston
Scheele found that air was lost in a closed vessel containing air and potassium
polysulphide (liver of sulphur), potassium sulphite, turpentine, iron(II) sulphate
solution, nitrogen monoxide or copper(I) chloride solution. Of course, this is due to
the absorption of oxygen by the readily oxidisable materials. Scheele first considered two possible explanations: either phlogiston caused the air to loose elasticity,
and thus decrease in volume, or a part of the air was absorbed by the material (liver
of sulphur, etc.). Scheele correctly excluded the first possibility, as he found that the
air lost not only volume but also weight. Unfortunately, he also excluded the
second, true explanation, since he failed to extract air from the oxidised materials.
Scheele apparently had the erroneous impression that any gas absorbed by a solid
material would behave as carbon dioxide (fixed air): it was well known that carbon
dioxide could be absorbed—fixed—by strong bases such as potassium hydroxide or
calcium oxide. When carbon dioxide reacts with potassium hydroxide it generates
potassium carbonate which gives a precipitate with calcium hydroxide solution
(lime water). When Scheele found that oxidised turpentine failed to give a
precipitate with lime water, he concluded that it contained no “fixed air”. This was
the largest mistake in Scheele’s entire career, and given Scheele’s extensive
knowledge, it is a quite remarkable error. At this point, Scheele could have been the
one to realise the true role of oxygen in combustion and to overthrow the phlogiston
theory; as Blomstrand put it: “A few seconds of thought in the right direction,
would have been all needed” [40]. However, it is not likely that Scheele would have
290
21 The Discovery of Oxygen