Coal tar, also known as liquor carbonis detergens (LCD), is a very thick, dark liquid with a number of medical and industrial uses. As a medication it is used to treat psoriasis and dandruff. Industrial uses include preservation of railway ties and improving the surface of roads.
Coal tar was discovered around 1665 and used for medical purposes as early as the 1800s. It is on the World Health Organisation's List of Essential Medicines, the most effective and safe medicines needed in a health system and it was one of the key starting materials for the early pharmaceutical industry. Other early colourful uses include:
The 1st artificial dye
In 1849, phenol was being extracted from creosote distillate and, when nitrated to make trinitro phenol (picric acid) this was used as a yellow dye for wool, cotton and silk. This was the first artificial dye.
‘Mauve’ – the 1st aniline dye
In 1856, William Perkin, attempting to make quinine, oxidised aniline with potassium dichromate and obtained a black precipitate, which was soluble in alcohol giving a colour, which he called 'mauve'. The American Section of the Society of Chemical Industry awarded William Perkin a Medal in 1906 to mark the 50th anniversary of his discovery. The Perkin Medal is now awarded annually at the Plaza Hotel in New York and by tradition, all the men wear Mauve bow-ties with their Dinner suits!
Mauve was the first aniline dye. A year later Perkin set up the first dyestuffs factory in the world at Greenford Green, Middlesex. As aniline was obtained from benzene there was a rise in the demand for benzene from the tar industry. However in 1874 Perkin sold his works and the British dyestuff industry went into decline being unable to compete with the huge German artificial colour industry.
Jeyes Fluid!
In 1865, phenol became prominent again when Lister introduced his antiseptic surgery. In 1877, Jeyes Ltd started production of a phenolic disinfectant. They used light creosote, with phenols present, mixed with rosin and caustic soda, which formed a white emulsion with water. This is still known as 'Jeyes Fluid'.
Turkey Red dye – the rise and fall
The artificial dye industry was becoming established when, in 1869, Caro, Graebe and Lieberman in Germany and Perkin in England, independently devised methods for producing the essential dye of madder, alizarin, from anthracene. Up to this time anthracene had been used as a cheap axle grease! It suddenly became very valuable and the tar industry extracted anthracene from its heavy creosote to meet the new demand. This resulted in the demise of the cultivation of madder, the natural source of Turkey Red dye, which had been in use from the time of the ancient Egyptians.
Indigo In 1880, Adolf von Baeyer synthesised indigo from naphthalene but it was not until 1897 that it was produced on a commercial scale in Germany. Tar distillers extracted the naphthalene from their oils and the growing of indigo plants in India ceased.
John Bethell
John Bethell was born in Bristol in 1804. He was a Solicitor in London from 1825-54 and was also a prolific inventor. In 1835 he patented a complete system of diving apparatus! However, he is best remembered for his patent AD 1838, BP 7731, which employed among other things coal tar thinned with 'deadoil', or creosote oil as it is known today, to preserve timber. Isambard Kingdom Brunel heard about Bethell’s patent and as he was then building miles of railway lines for the Great Western Railway and needed a good preservative for his wooden sleepers he jumped at the opportunity. With the financial support of Roberts and Daines, Iron Masters in St Philips, and the lease & technical expertise of Bethell, he set up a Tar Works at Crew’s Hole in 1843. In the early days, under the name Roberts & Daines, the principal product was creosote, the raw material was coal-tar, the residue from gas production.