higher in cast iron than steel. According to Thomson, “this study contributed very
materially to advance the knowledge of the cause of the difference between iron and
steel” [37].
15.5 Isolation of Tungstic Acid and the Discovery
of Tungsten
After his successful investigation of molybdæna, Scheele turned his attention to a
mineral now known as scheelite (CaWO 4 ; Fig. 15.5) [38]. To Scheele, however, the
mineral was known by the Swedish name tungsten, literally meaning “heavy stone”
due to its high density of c. 6 g cm
−3 . The idea to study scheelite most likely came
from Bergman, as he apparently had studied the same mineral a few years earlier.
From the preserved correspondence between Scheele and Bergman, it appears
likely that Scheele’s investigations started during the summer of 1780; in August he
wrote to Bergman and reported that the mineral was composed of calcium (lime)
and a special acid. In November, he wrote to Hjelm: “I have investigated tungsten.
It is composed of lime and an acid, which is similar to acidum molybdenæ [MoO 3 ],
but in some circumstances different”. Scheele had found that the mineral was partly
soluble in nitric acid, giving a solution of calcium nitrate and a yellow residue,
soluble in aqueous ammonia. The ammoniacal solution gave a precipitate with
nitric acid, and this precipitate was Scheele’s acid of tungsten (tungstic acid,
H 2 WO 4 ∙ H 2 O; Fig. 15.6). It had a sour taste and coloured litmus tincture red.
Scheele reported his results in a paper published in spring 1781; [39] this short 5 ½
page paper is important, since it is the first investigation of the chemistry of
tungsten.
Directly following Scheele’s paper on tungstic acid is a paper by Bergman, [29]
who had studied the same mineral a few years earlier. Bergman had suspected the
presence of barium (heavy earth) in the mineral, but had found it to contain calcium
(lime), just like Scheele. The only additional experimental contribution by Bergman
Fig. 15.5 Scheelite or
tungsten, as it was known to
Scheele. Photo Petra
Rönnholm
222
15 New Metals
materially to advance the knowledge of the cause of the difference between iron and
steel” [37].
15.5 Isolation of Tungstic Acid and the Discovery
of Tungsten
After his successful investigation of molybdæna, Scheele turned his attention to a
mineral now known as scheelite (CaWO 4 ; Fig. 15.5) [38]. To Scheele, however, the
mineral was known by the Swedish name tungsten, literally meaning “heavy stone”
due to its high density of c. 6 g cm
−3 . The idea to study scheelite most likely came
from Bergman, as he apparently had studied the same mineral a few years earlier.
From the preserved correspondence between Scheele and Bergman, it appears
likely that Scheele’s investigations started during the summer of 1780; in August he
wrote to Bergman and reported that the mineral was composed of calcium (lime)
and a special acid. In November, he wrote to Hjelm: “I have investigated tungsten.
It is composed of lime and an acid, which is similar to acidum molybdenæ [MoO 3 ],
but in some circumstances different”. Scheele had found that the mineral was partly
soluble in nitric acid, giving a solution of calcium nitrate and a yellow residue,
soluble in aqueous ammonia. The ammoniacal solution gave a precipitate with
nitric acid, and this precipitate was Scheele’s acid of tungsten (tungstic acid,
H 2 WO 4 ∙ H 2 O; Fig. 15.6). It had a sour taste and coloured litmus tincture red.
Scheele reported his results in a paper published in spring 1781; [39] this short 5 ½
page paper is important, since it is the first investigation of the chemistry of
tungsten.
Directly following Scheele’s paper on tungstic acid is a paper by Bergman, [29]
who had studied the same mineral a few years earlier. Bergman had suspected the
presence of barium (heavy earth) in the mineral, but had found it to contain calcium
(lime), just like Scheele. The only additional experimental contribution by Bergman
Fig. 15.5 Scheelite or
tungsten, as it was known to
Scheele. Photo Petra
Rönnholm
222
15 New Metals