The periodic table is the ultimate scientific infographic: very neat and highly informative, it summarises large amounts of information and it’s packed with ideas. Crucially, it helped chemists predict the properties of elements and compounds that were unknown when the table was created.
One element stands apart from all the others in the number of compounds it can form: carbon (because its atoms can combine to form chains and rings that incorporate other elements in numerous permutations). Here is a rather chaotic old infographic, drawn by father and son analytical chemists Benjamin and Wallace Nickels, that uses the metaphor of a genealogical tree to attempt to bring some order to the complexity of carbon chemistry. It depicts, perhaps too literally, a tree with massive trunk and numerous major and minor branches.
In an age when most useful carbon compounds are derived from petroleum, it seems curious that the trunk of the tree is boldly labelled COAL TAR. This sticky black by-product of the coal gas and coke industries was a major feedstock for the chemical industry from the 1850s, but its use declined after 1920 with the rise of the petrochemical industry. From 1960 the switch from coal gas (a mixture of hydrogen, carbon monoxide and methane, manufactured from coal) to natural gas (naturally occurring methane) for use in homes and industry all but killed off the remaining coal tar industry.
However, coke continued to be made because it is still used in the steel industry. Chemists have worked out numerous ways to re-use the wastes from this industry and thus improve its economics while reducing its environmental footprint. Some of these methods were known to the nineteenth century coal tar industry.
The prospect of ‘peak oil’ has also led to renewed interest in returning to the use of coal as a feedstock for the chemical industry. Perhaps a carbon tax will help make this an attractive option compared to burning coal to create power. Would locking up a substantial portion of the carbon in coal in long-lasting plastic products be preferable to spewing that carbon into the atmosphere as carbon dioxide and thence into the ocean as carbonic acid? Or would we continue to use plastic to make throw-away junk, a proportion of which ends up contaminating the ocean and reducing its potential to support life?
Coal tar links many objects in the Powerhouse Museum’s diverse collection: gas lamps, stoves, irons and engines; samples of coal, iron and steel; synthetic dyes plus textiles and clothing coloured with them; and synthetic perfumes and pharmaceuticals. The photo above shows some dyes on display in our Chemical attractions exhibition, where they illustrate the story of the beginning of the chemical industry in 1857: when chemistry student William Perkin tried to synthesise quinine and instead created some blackish gunk, he investigated it (rather than chucking it out), discovered that what he had made was a mauve compound suitable for dyeing fabric, and set up a factory to mass-produce it.
The dye industry developed first in England, but Germany’s chemists soon took its industry to world leadership. This carpet dye catalogue was made in Germany in 1899 by Meister Lucius & Bruning, which was later renamed Hoechst, merged with other firms to form the giant company IG Farben, reverted to the name Hoechst when IG Farben was demerged in 1951, grew to become a major pharmaceutical firm, and is now part of Sanofi-Aventis.
Through companies such as Hoechst, chemistry played a huge role in economics, politics and war during the twentieth century. A new battleground opened after the manufactured gas industry closed, as the sites of old gasworks became available for development and the need to remove dangerous coal tar compounds from the soil became obvious. Perhaps today’s chemists need to study our old tree chart to discover what nasty substances are in the soil and groundwater at sites such as Barangaroo in Sydney.