Transferring Electrons for Work or Pleasure
In addition to his well-known books on neurology such as An Anthropologist on Mars, Oliver Sacks wrote an engaging memoir of his childhood and his love of chemistry in his formative years. Not only does it describe part of his own own intellectual development, but Uncle Tungsten, Memories of a Chemical Childhood offers one of the most accessible histories of chemistry ever written, providing fascinating insights into the intellectual developments of an entire field of study. Students in John Bullock’s Foundations of Physical Science used one particular chapter out of this book as an entry to the study of magnetism, electricity, and batteries. In it Sacks describes his own experiences in reproducing the metallic “trees” discovered by alchemists. For example, placing copper wire in a solution of silver nitrate, would result in “shining, almost fractal, arborescent growth” of metallic silver on the wire (see above).
These changes result from a simple oxidation-reduction (redox) reaction in which electrons are transferred from dissolved silver ions to metallic copper. Such redox reactions are the source of the electric current provided by all batteries and fuel cells (and the electron transport chain). As part of the investigation of these topics, students used readily available materials such as aluminum cans and copper wire to construct simple electrochemical cells. Pictured below, students hook two such cells together to form a battery with a potential of about 3 volts; here they are using it to power a dc motor.
Footnote: In Uncle Tungsten, Oliver Sacks explains his peculiar use of footnotes as a sort homage to Dmitri Mendeleev, the nineteenth-century Russian chemist who, being unable to resist the temptation to include seemingly endless examples of tangential materials in his texts, used them promiscuously. Sacks characteristically included the following note to provide some explanation for the names of the metallic trees he was so fond of:
“These names for metallic trees came from the alchemical notion of the correspondence between the sun, the moon, and the five (known) planets with the seven metals of antiquity. Thus gold stood for the sun, silver for the moon (and the moon goddess, Diana), mercury for Mercury, copper for Venus, iron for Mars, tin for Jupiter (Jove), and lead for Saturn.”