two steps: at 420–630 °C, MoO 3 is reduced to MoO 2 and, at 820–870 °C, reduction
to metallic molybdenum takes place [30]. At higher temperatures, however, the
produced molybdenum reacts with carbon to generate molybdenum carbides and
some metallurgic experience was required to optimise and control the reaction
conditions. Thus, Scheele sent a sample of about 6 g (nearly ½ lod) of molybdic
acid to Hjelm with the request that Hjelm attempted to reduce it to metal. [31].
Scheele corresponded with Hjelm in Stockholm about molybdæna and molybdic
acid, and it is possible that Hjelm visited Scheele in Köping. At least Scheele wrote
to Hjelm in June 1779 and thanked him for the honour of a forthcoming visit in
Köping, and asked him to bring some different samples of blyerts (molybdæna or
plumbago). It appears like they planned to carry out some experiments together.
Hjelm, working in a metallurgical laboratory, was more successful, and his
experiments resulted in the isolation of metallic molybdenum in 1781. The samples
of molybdenum obtained by Hjelm were never very pure, but contained high levels
of carbon since he used charcoal and linseed oil as a reductant; he never reported
higher densities than 7.4, while pure molybdenum has a density of 10.2 gcm
−3 . It
would take another century until pure molybdenum could be prepared in any
quantity. Hjelm brought the positive results to Scheele in September 1781, and
Scheele answered in November: “It delights me that we now again have a new
metal, molybdænum. I think I already can hear at least the French deny its existence, since they are not themselves the inventors of it”. The first printed account of
the new metal appeared in the preface of Hjelm’s Swedish translation of Bergman’s
treatise on blow pipe analysis (Sect. 23.4) published the same year [32]. A more
detailed account of the metal and its properties was published 1788–1791 in a series
of seven papers by Hjelm in the Transactions of the Royal Swedish Academy of
Sciences.
Scheele could show that plumbago was indeed very different from molybdæna
[33]. Upon strong heating with potassium nitrate (saltpetre) or arsenic acid it gave
carbon dioxide, and hence it was a form of carbon [34]. Similar conclusions were
made about the same time by the French mineralogist Jean-Babtiste Romé de I’lse
(1736–1790). Scheele was probably the first to realise that the difference between
steel and cast iron is its carbon content, and that the powder remaining after dissolving cast iron in acid is graphite. This was an important discovery for the
growing metal industry. Rinman had previously noted in a paper about etching of
steel and iron that a “blyerts-like” residue remained after dissolving cast iron in
acids, [35] but he made no further investigation of this material. From the correspondence between Bergman and Scheele, it can be concluded that Scheele’s
investigation of graphite was carried out in the summer of 1779; the manuscript for
the paper was sent to Wargentin in September that year.
The difference between iron and steel was also studied in 1781 by Bergman and
his student Gadolin, who examined 89 iron samples in an attempt to determine their
phlogiston content [36]. In order to do so, they determined the amount of hydrogen
evolved upon dissolution in dilute sulphuric acid, and found that pure malleable
iron evolved more hydrogen than steel which in turn evolved more hydrogen than
cast iron. The amount of insoluble residue (graphite) left after dissolution was
15.4 The Discovery of Molybdenum
221
to metallic molybdenum takes place [30]. At higher temperatures, however, the
produced molybdenum reacts with carbon to generate molybdenum carbides and
some metallurgic experience was required to optimise and control the reaction
conditions. Thus, Scheele sent a sample of about 6 g (nearly ½ lod) of molybdic
acid to Hjelm with the request that Hjelm attempted to reduce it to metal. [31].
Scheele corresponded with Hjelm in Stockholm about molybdæna and molybdic
acid, and it is possible that Hjelm visited Scheele in Köping. At least Scheele wrote
to Hjelm in June 1779 and thanked him for the honour of a forthcoming visit in
Köping, and asked him to bring some different samples of blyerts (molybdæna or
plumbago). It appears like they planned to carry out some experiments together.
Hjelm, working in a metallurgical laboratory, was more successful, and his
experiments resulted in the isolation of metallic molybdenum in 1781. The samples
of molybdenum obtained by Hjelm were never very pure, but contained high levels
of carbon since he used charcoal and linseed oil as a reductant; he never reported
higher densities than 7.4, while pure molybdenum has a density of 10.2 gcm
−3 . It
would take another century until pure molybdenum could be prepared in any
quantity. Hjelm brought the positive results to Scheele in September 1781, and
Scheele answered in November: “It delights me that we now again have a new
metal, molybdænum. I think I already can hear at least the French deny its existence, since they are not themselves the inventors of it”. The first printed account of
the new metal appeared in the preface of Hjelm’s Swedish translation of Bergman’s
treatise on blow pipe analysis (Sect. 23.4) published the same year [32]. A more
detailed account of the metal and its properties was published 1788–1791 in a series
of seven papers by Hjelm in the Transactions of the Royal Swedish Academy of
Sciences.
Scheele could show that plumbago was indeed very different from molybdæna
[33]. Upon strong heating with potassium nitrate (saltpetre) or arsenic acid it gave
carbon dioxide, and hence it was a form of carbon [34]. Similar conclusions were
made about the same time by the French mineralogist Jean-Babtiste Romé de I’lse
(1736–1790). Scheele was probably the first to realise that the difference between
steel and cast iron is its carbon content, and that the powder remaining after dissolving cast iron in acid is graphite. This was an important discovery for the
growing metal industry. Rinman had previously noted in a paper about etching of
steel and iron that a “blyerts-like” residue remained after dissolving cast iron in
acids, [35] but he made no further investigation of this material. From the correspondence between Bergman and Scheele, it can be concluded that Scheele’s
investigation of graphite was carried out in the summer of 1779; the manuscript for
the paper was sent to Wargentin in September that year.
The difference between iron and steel was also studied in 1781 by Bergman and
his student Gadolin, who examined 89 iron samples in an attempt to determine their
phlogiston content [36]. In order to do so, they determined the amount of hydrogen
evolved upon dissolution in dilute sulphuric acid, and found that pure malleable
iron evolved more hydrogen than steel which in turn evolved more hydrogen than
cast iron. The amount of insoluble residue (graphite) left after dissolution was
15.4 The Discovery of Molybdenum
221