Charles Tennant (1768–1838)

The ability to bleach products was increasingly important during the Industrial Revolution as industries such as cotton manufacturing and papermaking grew rapidly. In traditional bleaching, materials were laid in sunlight to whiten or disinfect them or prepare them for further processing. Chlorine bleach was used in the late eighteenth century. However its powdered form, invented by Charles Tennant, made it far easier to transport and use. It became a pillar of the new chemical industries.

Charles Tennant was born into a farming family in Ayrshire, south-west Scotland. As a boy he was apprenticed to a hand-loom weaver at Kilbarchan, west of Glasgow. This introduced him to methods of bleaching and the limits which the slow process placed on cotton production. In 1788 he started a bleaching field at Darnley, on the edge of Glasgow, where he and his partners boiled cloth in a weak alkali solution then placed it in daylight. They began experimenting with more efficient methods and in 1798 Tennant patented a process to make a compound of chlorine and lime. It was soon discovered that other producers were using a similar method already. However, Tennant obtained another patent in 1799 for making ‘bleaching powder’ by treating slaked lime with chlorine gas. The process may have been devised mainly by one of his partners, Charles Macintosh (1766-1843). The powder was far safer to make and handle than the previous chlorine, which was processed with sulphuric acid.

With four partners, in 1799 Tennant set up the St Rollox bleach works on the north-east side of Glasgow to exploit the invention at a commercial scale using coal fuel brought by canal. They relocated their existing work from the Darnley bleachfields and sold large quantities of bleaching powder to other consumers. Production grew rapidly and they soon employed 1,000 people and opened a second plant at Hebburn near Newcastle-upon-Tyne. Tennant bought out his partners to take sole ownership of the company.

Tennant was the chief promotor of one of the first public railways in Scotland, the Garnkirk and Glasgow Railway (opened 1831), which allowed him to cut the costs of delivering coal to his works. His process remained the principal one in use to make bleach until the 1860s, when techniques were developed to make chlorine as a biproduct in the Leblanc process. Tennant’s son John led Charles Tennant and Company for the next 40 years and it continues today.