His next paper on electricity concerned the rubbing of silk ribbons of different
colours [26]. The idea of using ribbons of different colours may sound naïve today,
but originated from Robert Symmer (1707–1763) who had reported that when
white and black silk stockings were rubbed against each other, the former became
positively charged and the latter negatively charged. Bergman built a devise where
a silk ribbon was attached and stretched. The ribbon was then rubbed with another
silk ribbon, either along or against its direction. The sign of the charge was
determined with a piece of gold leaf attached to a charged silk thread. The most
important conclusion was that if a ribbon was heated before rubbing, it would
acquire a negative charge on rubbing. As expected, the colour of the ribbon was
found to have no effect on the charge. In a paper on the rubbing of glass plates,
published in 1765 [27], Bergman concluded that (1) there are two types of electricity, having the same effects but annihilating each other and (2) both types of
electricity consists of an excess of a particular substance. The particles of the two
substances can saturate each other giving rise to an inactive compound. In the
natural (uncharged) state, any substance is saturated with this inactive compound.
Thus, Bergman did not agree with Franklin and proposed a chemical view of
electricity.
Bergman’s final paper on electricity appeared in 1766 and concerned the electrical properties of tourmalines [28], a study which British chemist Thomas
Thomson (1773–1854), the author of the influential book History of Chemistry
regarded as important [29]. Tourmalines were mined in Sri Lanka and brought to
Europe by the Dutch East Indian Company. They were very expensive and had
attracted much attention, also among scientists. Axel Fredrik Cronstedt (the discoverer of nickel) had asked mineralogist Bengt Qvist (1733–1790), who was in
Amsterdam at the time, to acquire tourmalines on the behalf of the Royal Swedish
Academy of Sciences in Stockholm. These stones, there were five of them (three
from Sri Lanka and two from Brazil), were investigated by mineralogist Sven
Rinman and by Bergman. Rinman analysed the composition of small fragments,
which had come loose during the shipping to Sweden [30]. Wilcke, finally, wrote a
review article summarising the known literature on tourmalines, including the
works by Rinman and Bergman [31] and a fourth paper on tourmalines from Brazil
was published later the same year by Rinman [32]. Rinman (Fig. 5.3), who would
become an important friend for Bergman, was born in Uppsala in 1720. He studied
chemistry for Wallerius and became an auscultator (a civil servant position) at the
Board of Mines (Bergskollegium) in 1740. In 1746, he left Sweden to undertake a
study trip through Europe: the Netherlands, Germany and France. In 1762, he left
Board of Mines to take up a position as inspector for the Swedish Steel Association
(Jernkontoret). Rinman was not particularly happy with this job [33], since the
position meant that he had to constantly travel across the country to inspect the
different iron works and in addition he had to deal with problems of little scientific
challenge. Largely disconnected from libraries and scientific news, Bergman
became an important link to the scientific community for Rinman. In 1773, he could
64
5 Bergman’s Early Scientific Career
colours [26]. The idea of using ribbons of different colours may sound naïve today,
but originated from Robert Symmer (1707–1763) who had reported that when
white and black silk stockings were rubbed against each other, the former became
positively charged and the latter negatively charged. Bergman built a devise where
a silk ribbon was attached and stretched. The ribbon was then rubbed with another
silk ribbon, either along or against its direction. The sign of the charge was
determined with a piece of gold leaf attached to a charged silk thread. The most
important conclusion was that if a ribbon was heated before rubbing, it would
acquire a negative charge on rubbing. As expected, the colour of the ribbon was
found to have no effect on the charge. In a paper on the rubbing of glass plates,
published in 1765 [27], Bergman concluded that (1) there are two types of electricity, having the same effects but annihilating each other and (2) both types of
electricity consists of an excess of a particular substance. The particles of the two
substances can saturate each other giving rise to an inactive compound. In the
natural (uncharged) state, any substance is saturated with this inactive compound.
Thus, Bergman did not agree with Franklin and proposed a chemical view of
electricity.
Bergman’s final paper on electricity appeared in 1766 and concerned the electrical properties of tourmalines [28], a study which British chemist Thomas
Thomson (1773–1854), the author of the influential book History of Chemistry
regarded as important [29]. Tourmalines were mined in Sri Lanka and brought to
Europe by the Dutch East Indian Company. They were very expensive and had
attracted much attention, also among scientists. Axel Fredrik Cronstedt (the discoverer of nickel) had asked mineralogist Bengt Qvist (1733–1790), who was in
Amsterdam at the time, to acquire tourmalines on the behalf of the Royal Swedish
Academy of Sciences in Stockholm. These stones, there were five of them (three
from Sri Lanka and two from Brazil), were investigated by mineralogist Sven
Rinman and by Bergman. Rinman analysed the composition of small fragments,
which had come loose during the shipping to Sweden [30]. Wilcke, finally, wrote a
review article summarising the known literature on tourmalines, including the
works by Rinman and Bergman [31] and a fourth paper on tourmalines from Brazil
was published later the same year by Rinman [32]. Rinman (Fig. 5.3), who would
become an important friend for Bergman, was born in Uppsala in 1720. He studied
chemistry for Wallerius and became an auscultator (a civil servant position) at the
Board of Mines (Bergskollegium) in 1740. In 1746, he left Sweden to undertake a
study trip through Europe: the Netherlands, Germany and France. In 1762, he left
Board of Mines to take up a position as inspector for the Swedish Steel Association
(Jernkontoret). Rinman was not particularly happy with this job [33], since the
position meant that he had to constantly travel across the country to inspect the
different iron works and in addition he had to deal with problems of little scientific
challenge. Largely disconnected from libraries and scientific news, Bergman
became an important link to the scientific community for Rinman. In 1773, he could
64
5 Bergman’s Early Scientific Career