The Leblanc Process

From the 1760’s there were was an increased interest in the use of salt as the a raw material for the production of alkalies. An Act of 1768 allowed to use of soiled salt and pan scale as a fertiliser by farmers at a greatly reduced rate of tax. Meanwhile in Edinburgh, James Watt, Joseph Black and James Keir were actively researching the process and lobbying Parliament for the raw material salt to be free of duty. In 1771, James Keir applied unsuccessfully for a Patent for making soda from common salt, but nevertheless went ahead with a process using the potassium and sodium sulphate waste product from his nitric acid manufacture as raw material. This was reacted with lime. He established an alkali and soap works at Tipton in Staffordshire which was famous in its day. By using these cheap sulphate by-products, Keir avoided the high excise duty on common salt, but his process was slow and the yield poor. Watt gave up chemistry for steam power and with his partner Matthew Boulton established the Soho Foundry; equally famous in its day.

Another significant advance was that of George Fordyce, a London physician and chemist. He set up a works at South Shields to manufacture hydrochloric acid and sodium sulphate by the reaction of salt with sulphuric acid. Here was the first major step towards the production of alkali from salt, although Fordyce’s main objective was the supply of the “Marine acid” as a superior bleaching agent to “Oil of vitriol” which for some thirty years had been used as an alternative to the traditional buttermilk. Here was the production of sodium sulphate (salt-cake) which became the vital first-stage of the chemical route from salt to alkali. Again, profitability was threatened by the tax on salt and Fordyce’s 1780 petition to both the Salt Office and Parliament for salt, free of duty, was blocked by the Board of Customs who saw this as threat to the high revenue they received on imported barilla and potash. Eventually in 1782 concessions were granted for duty-free salt in respect of sodium sulphate to be used in glassmaking but any alkali produced was subject to a duty of 20s per ton.

Meanwhile in France in 1775 the Duke of Orleans, who had been in correspondence with Joseph Black, offered a prize for a process of making alkali from salt and in, 1783, this was awarded to Nicolas Leblanc. A Patent was awarded in 1791 and the Duke built a works at St Denis. However the Duke was executed in 1793 and the works confiscated. Although returned by Napoleon in 1802, Leblanc was destitute and unable to operate it, and died by his own hand in 1805. He did, however, give his name to a process which was at the centre of the Chemical Revolution. In Britain, processes very similar to Leblanc’s were already being worked by James Keir and several other chemical manufacturers. William Losh in partnership with Lord Dundonald and others established in 1795 a works on the Tyne which was equivalent to the Leblanc patent. But all these developments were handicapped by the high rate of salt duty which had been raised by Pitt to provide additional wartime revenue. In 1796 Pitt appointed an independent review of the working of the Salt Office and in 1798 it was disbanded and administration of the Salt Tax was returned to the Board of Excise.

The end of the Napoleonic wars brought increased pressure for a repeal of the salt tax from an expanding alkali industry, particularly in Scotland and on the Tyne where the Leblanc process was in full operation and in 1823 James Muspratt established his alkali works at Vauxhall Liverpool. The campaign to abolish the tax was successful following a Parliamentary inquiry which highlighted the gross inefficiency of the Tax and from 1823 it was progressively reduced and repealed completely in 1825.

The repeal of the Salt Tax stimulated a rapid expansion of the salt industry to meet an increased market demand particularly from a rapidly growing chemical industry. In Cheshire, large salt works were established at Winsford and along the Trent and Mersey canal at Anderton where the canal passed close to the Weaver. Elsewhere along the Trent and Mersey canal at Middlewich Wheelock and Lawton the canal passed close by long established salt works and these were given new life. With the growth of the Empire, Cheshire salt was exported worldwide; to West Africa, (a legacy of the slave trade) and to North America, India, Australia and New Zealand.

The extension of the canal network and especially the building of the railways brought cheap overland transport which enabled the Cheshire and Worcestershire salt makers to distribute their low price salt nationwide. Small inland and coastal salt makers could not compete and they gradually went out of business.

From being a food related commodity, white salt became predominantly a chemical raw material for the expanding bleach and Leblanc alkali industries. For this, the bulk unstoved common salt was most suitable. The common pans, of typical size 25ft by 100ft, were also able to produce a coarse fishery grade salt which matched the traditional Bay Salt.

The expansion of the salt industry in the 19th century inevitably led to overproduction and unstable prices and there were successive attempts to form a trade association to control production and prices. By the 1880’s the demand for common salt for chemical production declined due to competition from the expanding Ammonia-Soda alkali industry based on brine, and exports declined as countries abroad developed their own salt industries. In 1888 this situation resulted in the merger of some 90% of the industry to form the Salt Union Limited The need to close ranks by both the white salt makers and the Leblanc alkali makers resulted in the formation of the Salt Union in 1888 and the United Alkali Company in 1890, each representing about 90% of their respective industries.

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