FRENCH CHEMIST AND SURGEON
Nicolas Leblanc invented a method of making alkali soda from salt that became one of the most important chemical processes of the nineteenth century. Leblanc was born in Issoudun, France; his father managed an iron-works. After completing his medical education in about 1780, Leblanc became a private physician in the house of Philippe Égalité, duc d'Orléans (1747–1793). France had been suffering from an acute shortage of alkali from traditional vegetable sources. Alkali was critical in the manufacture of glass, textiles, paper, soap, and other products. In 1775 the French Royal Academy offered a prize to anyone who could develop a process for transforming common salt (sodium chloride) into soda ash. With Égalité's support, Leblanc achieved the goal by 1789 and opened a small factory at Saint Denis that began production in 1791.
What became known as the Leblanc process was actually several inter-related processes. Salt was first reacted with sulphuric acid in a cast-iron pan, then in a reverberator furnace (in which heat was applied from a flame blown from a separate chamber, not in direct contact with the salt), to produce saltcake (sodium sulphate), with hydrochloric acid released as a waste gas. Saltcake was used to make sodium carbonate, or roasted with limestone (calcium carbonate) and coal or coke to produce "black ash." This mixture of sodium carbonate, calcium sulphide, sodium sulphide, lime, salt, carbon, and ash could be treated further with hot water to produce impure sodium carbonate in solution, evaporated into soda crystals (washing soda), or heated to yield anhydrous sodium carbonate. The latter, in turn, could be reacted with lime to made caustic soda (sodium hydroxide), the strongest commercial alkali then available.
Leblanc personally benefited little from his innovation. The National Assembly granted him a fifteen-year patent in September 1791, but three years later the revolutionary government sequestered his factory and made his patents public, giving Leblanc only meager compensation for his assets. Napoléon Bonaparte returned the plant to him in 1802, but by then Leblanc was too poor to resume production and, in 1806 he took his own life. (In 1855 Napoléon III gave Leblanc's heirs a payment in lieu of the 1775 prize.)
Leblanc's process—by greatly reducing the cost and boosting the efficiency of alkali for the key industries that depended on it—boosted European industrialization for two generations. The year of Leblanc's suicide, the Saint Gobain Company opened a soda ash factory; by 1818 French producers were turning about roughly 10,000 to 15,000 tons of Leblanc soda ash per year. British producers, discouraged until a prohibitive tax on salt was repealed in 1823, embraced the new process and surpassed the French by the middle of the century. U.S. alkali makers remained wedded to potash but imported Leblanc soda ash after 1850. Germany took the lead in Leblanc soda production in the 1870s.
By that time the Leblanc process was facing competition from the newer Solvay (ammonia soda) alkali. The dominance of Leblanc soda was extended by improvements, most notably the Deacon process (1868), which converted the wasteful and harmful hydrochloric acid gases into chlorine, and the Chance process (1882), which recovered waste sulphur. By the turn of the twentieth century, however, the Leblanc and Solvay processes were eclipsed by new electrolytic methods for making chlorine and caustic soda.
Haber, L. F. (1958). The Chemical Industry during the Nineteenth Century: A Study of the Economic Aspect of Applied Chemistry in Europe and North America. Oxford, U.K.: Clarendon Press.
Landes, David S. (1972) The Unbound Prometheus: Technological Change and Industrial Development in Western Europe from 1750 to the Present. Cambridge, MA: Harvard University Press.
Morgan, Sir Gilbert T., and Pratt, David D. (1938). British Chemical Industry: Its Rise and Development. London: Edward Arnold & Co.