Coal Tar: Mauve and More

Following the practice of one of President Jefferson's thrifty yeoman farmers, that of "using all of the pig but its oink," the coal industry has developed many uses for the black viscous liquid called coal tar, the main leftover when bituminous coal is cooked to produce coke. Gases also are drawn out of the coke oven and burned as coal gas for heating factories and homes in nations that don't have the generous supplies of cleaner-burning natural gas found in the United States. This process was one of the first uses of chemistry as an applied science. And, as with so many scientific discoveries, the beginning of the coal tar products industry was an accident.

An eighteen-year-old Englishman, William Perkin,1 was trying to make artificial quinine—the treatment for malaria, a mosquito-borne illness that affected the Lewis and Clark Expedition. "Doctor" Lewis gave the men Peruvan bark from his medicine chest when they suffered malarial chills and fever; unknown to anyone at the time, quinine was the bark's active ingredient.

Instead of quinine, though, young Perkin was left with some purplish powder. More experimentation led him to realize that this substance worked as a textile dye, producing a light pinkish-purple shade he called mauve.

Perkin's 1856 "failure" was the discovery of the first synthetic dye. When Queen Victoria wore mauve to the wedding of one of her five daughters, the color became high fashion, and the future of dyes derived from coal tar was guaranteed. Later, the color even was used to name part of her era.2 Synthetic dyes also could create many more colors than were available from organic sources. Perkin became a rich man, but remained torn between his love of theoretical chemistry and his success with its applied form.

Besides dye, many other coal tar byproducts are still in use, although similar materials derived from petroleum and natural gas have joined them, and replaced some. Here are some of coal's byproducts:

Benzene is a light, very flammable solvent, which is used in such different applications as perfume-making, dry cleaning, and gasoline production (where it cleans grease out of petroleum).

Creosote (CREE-oh-soat) can be made from coal tar, as well as from the wood tar that is a byproduct of charcoal making. Used to preserve wood exposed to the elements, it has been soaked into every telephone or power pole, and railroad tie, in sight. It also can be a component of cough syrup!

(Kerosine, also miscalled "coal oil," is actually a petroleum product. The name stuck, though, after Canadian geologist Abraham Gesner first extracted it from coal in 1854. In short order, kerosine was made from petroleum. It was the major source of lighting through the mid- to late19th century.)

Naphtha, a very flammable liquid, is used as a spot remover and as the solvent in varnish.

Paraffin, odorless, wax-like, and solid at room temperature but easy to melt, comes from coal tar as well as from crude oil. It is molded into candles, and poured atop jars of jam and jelly to seal them.

Toluene (TALL-you-ween), another flammable light solvent, is a component in an amazing array of products: explosives like TNT (trinitrotoluene), antiseptic, paint, saccharin, cosmetics, and textile dye.

1. Simon Garfield, Mauve: How One Man Invented a Color that Changed the World (New York: W.W. Norton & Company, 2001) is the biography of Perkin, whose work moved chemistry from theory to application.

2. Thomas Beer, The Mauve Decade: American Life at the End of the Nineteeth Century (1926; reprint Carroll & Graf, 1997). Journalist Beer quoted the definition of mauve as "pink trying to be purple," and used it to label the boastful, optimistic, ambitious, and sometimes downright greedy life in the United States of the 1890s, the last decade of the Gilded Age, which he detailed in this book.

Funded in part by a grant from the Montana Committee for the Humanities.