The Salt-Based Chemical Industry

Salt was not a promising raw material. However heating vitriol (alias copperas or IronII sulphate) gave sulphuric acid (oil of vitriol) which reacts with salt to give Spirits of Salt.(HCl). In the age of the alchemist this was about the limit of salt’s involvement. Plus they were unaware that salt had contributed in the formation of the Aqua Regia which dissolved gold.

Sulphuric acid and later Spirits of salt replaced buttermilk as a souring aid in textile bleaching but the breakthrough came in 1773 when the Swedish chemist Scheele reacted Spirits of Salt with manganese dioxide and thereby discovered chlorine. His observation that chlorine was able to bleach vegetable matter was applied by the French chemist Berthollet in 1785 to the bleaching of textiles using a weak solution of chlorine in alkali as an industrial bleach. Prominent in the early use of chlorine bleach were James Watt in Scotland and Thomas Henry in Manchester. This early application of chlorine bleach required the on-site generation of chlorine from a mixture of salt, sulphuric acid and manganese dioxide. In the 1790’s this became unnecessary with the introduction of a readily transportable bleaching powder by Tennant and Macintosh at Glasgow where Charles Tennant established the St Rollox Works.

The basic requirement for the expansion of the chemical industry in the 19th century was the chemical production of alkali from common salt and early experiments were under way in the mid 18th century.

A leading figure in this research was James Watt and it is interesting to note that as early as 1766, there were attempts to produce alkali by the reaction of salt with lime in the presence of coal. James Keir, in the 1780’s, had achieved some success and making alkali from potassium / sulphate waste product (from his nitric acid works) mixed with lime and coal. He established a large soap works at Tipton, Staffs.

James Watts’s lobbying of Parliament failed to obtain a rebate of the Salt Tax for chemicals manufacture. This greatly inhibited the growth of a salt based alkali industry in Britain and the ultimate credit was to go to the Frenchman Nicholas Leblanc. An alkali works based on the Leblanc process was established on Tyneside by William Losh and Lord Dundonald in 1795. The Napoleonic Wars brought an excessive increase of the level of salt taxation and little incentive for the growth of a chemical industry based on duty paid salt. Some alkali manufacturers took advantage of Ireland as a tax-free salt haven while on Tyneside and at Glasgow there was considerable activity by William Losh and several other manufacturers making alkali from duty free coal-contaminated salt and the waste sulphate by-product from nitric acid manufacture.

Thus in the thirty years before the repeal of the Salt Tax the main centres for Leblanc manufacture of alkali were to be found on Tyneside and in Scotland . Alkali manufacture on Merseyside was to await the arrival of James Muspratt, from alkali manufacture in Ireland, to Liverpool where he established the Vauxhall Works in 1823.