IN 1819, thirty-eight-year-old John Walker opened a pharmacy at 59, the High Street, in his hometown of Stockton-on-Tees. He had at one time studied surgery under Watson Alcock, physician to local landowner the Marquis of Londonderry, but after a brief spell in London he had retrained as a pharmacist in Durham and York.

He was little like the spare and haggard apothecary in Shakespeare’s ‘Romeo and Juliet’. The work of a pharmacist could be laborious but Walker was always ready with a joke, and his sunny smile was one of his most trusty remedies. He had an inquiring turn of mind, and like many of his fellow chemists made experiments with the combustible properties of various compounds, perhaps with an eye to the gun trade. One day in 1826, when working with a mixture of sulphide of antimony, chlorate of potash and gum, Walker accidentally dropped his mixing stick onto the hearth. The stick glanced aside and burst into flame, and at the same instant an idea kindled in Walker’s imagination.