I expect everyone will remember dilute sulphuric acid from school chemistry, or the contents of car batteries. In the Middle Ages alchemists made the concentrated acid, vitriol, by heating crystals of hydrated iron II sulphate (green vitriol). This is a topic I will return to when I describe copperas manufacture at Denholme in a future article. In the eighteenth century vitriol was needed for manufacturing chemicals like nitric and hydrochloric acids, and in an early industrial process for making washing soda. Hydrochloric acid was the starting point for chlorine production and the gas made was in turn used in a textile bleaching process. The synthesis of important fertilisers in the nineteenth century, like ammonium sulphate and super-phosphate, required large amounts of sulphuric acid. Some of the documents relating to a Bradford works mention ‘manures’ by which name, I assume, the artificial fertilisers were once known.
In 1746 John Roebuck (Birmingham) had adapted a process of burning sulphur with saltpetre to form sulphur trioxide, within acid-resistant chambers made of lead. Sulphur trioxide was then dissolved in water to form the vitriol. Lead was chosen for the chambers since it was the cheapest acid-resistant metal available. These large, strong and cheap receptacles produced 35-40% acid. The chemists Gay-Lussac and Glover replaced the chambers with towers, obtaining a more concentrated product. The manufacture of some dyes, and nitrocellulose, required an even more concentrated acid which could still be produced by the dry distillation of hydrated iron II sulphate.
North Brook Vitriol Works was situated between Wharf Street and Canal Road. Vitriol and aquafortis (nitric acid) were first made there by Benjamin Rawson (1758-1844). He is believed to have been in operation by 1792 which makes the works one of Britain’s first chemical plants. In this and much else Bradford was ahead of the game. Shortly afterwards Rawson purchased the Lordship of the Manor of Bradford, a role in which he and his two daughters, Mary and Elizabeth, will be familiar to local historians. In 1838, before Rawson’s death, the works were bought by Samuel Broadbent. He lived in Northbrook House and his garden led to the canal. Additional chemicals were now sold: spirits of salts (hydrochloric acid) and ammonia.
Mid-nineteenth century plan showing the relationship between Northbrook House, the Vitriol Works and the Canal
Northbrook House was later used as offices and one of Samuel’s daughters married George Henry Leather, a worsted spinner. Leather took over when Samuel died and after 1844 the whole plant was known as Leather’s Chemical Works, a name which was familiar to Bradfordians within living memory. Leather also sold chloride of lime as a disinfectant, which may have been needed since the smell of the works, the canal, and nearby tipped human waste, was described in the Bradford Observer as ‘abominable’. Chloride of lime (calcium hypochlorite) was made, by exposing slaked lime to gaseous chlorine in brick built chambers. One of the most interesting documents I read in the West Yorkshire Archives when researching this subject was a memorandum of 1887 to Leather’s Chemical Works from the famous fertilizer company, Jas. Fison & Sons of Thetford. An enquiry from Leather’s revealed that Fisons were using a platinum still, presumably to concentrate and purify their sulphuric acid. The still cost £5,600 and was bought from Johnson Matthey & Co of Hatton Gardens, London. This company was brought to public notice recently by the failure of its banking subsidiary, JMB, in 1984. The parent company is heavily involved in precious metals, and chemicals, today.
Samuel’s grandson Henry Burnet took over when George Leather died in 1897. By this time a new means of making the acid, the Contact Process, was becoming widely employed. I’ve found no evidence that this was adopted in Bradford. Possibly keeping the existing plant required little capital expenditure and the decision to stick with older technology was essentially a financial one. I understand that the site was still a chemical works as late as 1970. Then it was initially sold to Occidental Petroleum but Bradford Council purchased the site a year or two later and demolished the works.
There is one small puzzle. In his book The History & Topography of Bradford John James describes a bizarre incident. About 50 years before he wrote a group of gentlemen founded a Bradford Philosophical Society. One of the members, a chemist, after many experiments discovered a way of rendering oils ‘pure and transparent’ by application of a strong acid. One of the other philosophers thought he would try cleaning the working parts of the watches and clocks of the town with the same acid. As a result all the clockwork corroded. If James was being exact the date of the trials would have been 1791. The reaction between sulphuric acid and vegetable oils is quite complex but no one could call the result transparent. The acid would attack all eighteenth century known metals except lead and gold. It does seem probable that experiments were being made with the newly available cheap vitriol but please, please, do not try these at home.
If you want to explore vitriol making further I would suggest:
AE Musson (ed), Science, technology and growth in the eighteenth century, 1971.
Documents and photographs of Leather’s Chemical Company are held by West Yorkshire Archives (Bradford): 30D90.
Derek Barker, Local Studies Library Volunteer