‘Coming the acid’: Leather’s Chemical Works, Bradford

This North Brook Vitriol Works was situated between Wharf Street and Canal Road near the end of Bradford’s canal spur. It claimed to be one of the world’s oldest chemical plants. Its origin lay in the work of John Roebuck of Birmingham, who in 1746 had adapted a method of burning sulphur with saltpetre to form sulphur trioxide within lead-lined, acid-resistant, chambers. The sulphur trioxide resulting was dissolved in water to produce sulphuric acid. These lead chambers were larger, stronger and cheaper than the previously employed glass vessels. The process was essentially in use for the next two centuries. The chambers produced sulphuric acid of 35-40% concentration. The chemists Gay-Lussac and Glover replaced the chambers with towers to obtain a more concentrated product. Sulphuric acid or vitriol was the starting point for the production of the other mineral acids, but was also important in fertiliser production, metal surface treatments, and a cloth bleaching process.

Vitriol and aquafortis (nitric acid) were first made in Bradford at the North Brook Works by Benjamin Rawson. Using the lead chamber process he was certainly in operation by 1792, and perhaps earlier. Shortly afterwards he purchased the Lordship of the Manor of Bradford which he and his daughters held for more than sixty years. By 1802 the works were leased to James Broadbent but were bought outright in 1838 by Broadbent’s son Samuel. Additional chemicals were now being sold: spirits of salts (hydrochloric acid), ammonia and Epsom salts (magnesium sulphate). Samuel Broadbent lived in Northbrook House, which had a garden leading down to the canal. The house was later used as offices. One of Samuel’s daughters married George Henry Leather, a worsted spinner, and he it was who took over the enterprise when Samuel died. After 1844 it was generally known as Leather’s Chemical Works and in due course Leather built the Zetland Mill for his textile interests. In 1854 the works were offered for sale by auction, as advertised in the Bradford Observer, but in fact the family connection seems to have continued.

Leather’s now also sold chloride of lime as a disinfectant, which may have been needed since the smell of the vitriol works, the canal, and nearby tipped human waste, was described in the press as ‘abominable’. Chloride of lime (calcium hypochlorite) was made by exposing slaked lime to an atmosphere of chlorine in brick built sheds. Lime kilns were present on the nearby canal-side which could have provided the slaked lime easily enough. It is a shock to learn that as recently as 1849 this chemical was being used to combat an outbreak of cholera in Bradford. It is also a shock to learn that at one works the employees raked over the lime to hasten its absorption of chlorine with no protection from the deadly atmosphere except face masks. Victorian industrialists were seldom health and safety conscious.

The product of the Gay-Lussac towers was about 78% sulphuric acid. The manufacture of some dyes, and nitrocellulose, required a more concentrated product still which in the 19th century was still made by the dry distillation of green vitriol or hydrated iron II sulphate. This material could be made by burning the mineral pyrite (iron sulphide) in oxygen, or leaving pyrite nodules exposed to water and atmospheric oxygen for several years. Leather’s adopted the former process in the 1870s, but it was relatively expensive. In the sources I have seen there is a material described called spent oxide. I assume this was the residual iron oxide remaining after the iron sulphate was dry distilled.

Meanwhile ‘back in Bradford’ the family connection with chemicals was maintained. Another of Samuel’s daughters married the Rev John Eccleston Burnet and their son Henry took over when George Leather died, full of years, in 1897. Henry died himself in 1940 when his own sons, David & Ronald Burnet assumed responsibility. The site was still a chemical works as recently as 1970. It was sold to Occidental Petroleum in 1972/73 but shortly afterwards Bradford Council purchased the site for road widening; chemical production was transferred to St Helen’s & Manchester.

The West Yorkshire Archives (Bradford) curate many documents relating to this site of chemical production. They have the monthly output figures for the years 1844 – 1928 with figures being given in glass carboys holding 10 gallons. In the first years the main products were OV (brown Oil of Vitriol), SS (spirits of salts or hydrochloric acid) and liquid ammonia. By 1859 no ammonia was being produced. The basic raw materials were brimstone (sulphur) and nitrate of soda. In 187, for example, over 1200 tons of sulphur was purchased for conversion to acid. Pyrite purchase was first mentioned in 1875-76 (305 tons) and within a year more pyrite than sulphur was purchased. After five more years pyrite was only used in some years, although ‘oxide’ was always bought. I don’t know enough inorganic chemistry to work out exactly what was going on and why.

Other raw material purchases included coal for fuel and the metal copper. Was there a requirement for copper sulphate to be used with lime in Bordeaux mixture against potato blight? It looks as though the company bought in chemical stocks itself when demand exceeded what could be supplied. The problem of getting 100% concentrated sulphuric acid remained. In 1887 Leather’s explored, with the famous company James Fison & Sons of Thetford, Norfolk, the possibility of purchasing a platinum still which cost £5,600. These could apparently be bought from Johnson Matthey & Co of Hatton Gardens. This company is still big today in precious metal products.

Oddly platinum had already provided the solution to the sulphuric acid concentraion problem. in 1831 British vinegar merchant Peregrine Phillips devised the ‘contact process’ in which sulphur dioxide and oxygen were reacted together at a relatively high temperature to produce sulphur trioxide directly. The reaction procedes very slowly unless a catalyst is provided and platinum is one possibility in this role. There were many difficulties in producing a commercially acceptible version of the contact process which was not generally adopted before the early 20th century. I have no evidence that it was ever used at Leather’s.

The world changes. Platinum has now been abandoned and vanadium is used as the contact process catalyst. But in this changing world two pieces of wisdom still stand as immutable as stone. One is that it is always wise to say on being offered yet another drink to say ‘no thank you I have had quite sufficient for one evening’. The second demands that when diluting concentrated sulphuric acid you murmur ‘add acid to water, never water to acid’.

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