(29 Dec 1766 - 25 Jul 1843)
Charles Macintosh was born in Glasgow, Scotland. He first began to work as a clerk with a Glasgow merchant. By age 19, he instead pursued his interest in chemistry and science derived from his father, George Macintosh who was a well-known and inventive dyer. Charles was prepared with university studies at Glasgow and as a student of Joseph Black at Edinburgh. By the time he was twenty, Charles had opened a plant in Glasgow to produce sal ammoniac (ammonium chloride) and Prussian blue dye. He also introduced the manufacture of lead and aluminum acetates to Britain, and developed new processes to dye cloth.
In 1797, he established Scotland’s first alum works at Hurlet, Renfrewshire. He found a source of the alum in waste shale from coal mines. Additional chemical works followed later.
In the same area, Charles Tennant, had a chemical works at St. Rollox, near Glasgow, where he made a bleaching liquor by passing chlorine through a stirred mixture of lime and water. The liquor came from Tennant’s old bleaching process at Darnly, which used a combination of boiling textiles in weak alkali followed by months of exposure to sunlight. In 1799, Tennant patented a process to form a dry bleaching powder by substituting dry slaked lime. The process was worked out in partnership with Macintosh, who remained associated with the St. Rollox chemical works until 1814. The ease of transportation made their new dry bleaching powder a desirable product and made a considerable fortune for the two men. The success of the plant made it for a while the largest chemical works in Europe. Bleaching powder was used industrially to bleach cloth and paper until the 1920’s.
A yeast factory which Macintosh set up in 1809 failed because of opposition from London brewers.
Meanwhile, he continued to buy all the ammonia and the tar waste byproducts from the Glasgow coal-gas works. He utilized the ammonia in the production of cudbear, a useful dye extracted from various lichens. By varying the choice of mordant used with this dye, manufacturers could colour textiles in a range of shades from pink to blue. The tar could be distilled to produced naphtha - a volatile, oily liquid hydrocarbon mixture. Although this could be used in flares, from 1819, Macintosh continued to experiment to find more ways to utilize naphtha, so that the original tar waste could yield more value.
The invention for which Macintosh is best known came when these investigations of naphtha yielded a process for waterproofing fabric. When the fabric was later used to make a raincoat, it was called by his name as the mackintosh (in which the extra “k” is unexplained).
In June 1823, Macintosh patented his process using a solution of india-rubber in naphtha soaked between two layers of cloth forming a sandwich that was pressed together. The rubber interior provided a layer impermeable to water, though still flexible. His patent, No. 4,804, described how to “manufacture for rendering the texture of hemp, flax, wool, cotton, silk, and also leather, paper and other substances impervious to water and air.” (The sandwich-type construction was not totally new, for it had been devised by Spanish scientists to make leak-proof containers for mercury, and also Charles Green in 1821 had made a balloon envelope that applied the same principle.)
In another application of his inventiveness, Macintosh developed improved methods of iron production, which was much faster than the existing methods. He patented a method for converting malleable iron into steel (1825) in which the iron was raised to white heat in a current of coal gas which provided a carbon content. The process was unsuccessful in commercial application because of the problem involved in keeping a furnace gas-tight. He then assisted Beaumont Neilson in bringing hot blast into use in blast furnaces (1828). By introducing hot air into the furnace, instead of cold air, the smelting process was made more efficient. In return, he was given a share in Beaumont’s patent. This was more of a loss than a gain because of protracted litigation concerning the patent that lasted until 1843.
Macintosh was to become most successful with his waterproof fabric. After experimenting in Glasgow, Macintosh set up for manufacturing in Manchester with several partners. One was H.H. Birley who was a cotton spinner and weaver. As one of the first to light his mills with coal-gas, he also had that particular interest in common with Macintosh. New buildings were constructed in 1824-25 for the production of the new waterproof compound fabric.
The engineer, Peter Ewart was called upon to install the necessary machinery, powered with steam a engine from the company of Boulton and Watt. Naturally, Macintosh had a convenient supply of naphtha from his own Glasgow works, but there remained difficulties in the process. One was the spreading of the solution onto the cloth. In cold weather the fabric became stiffer and in hot weather the fabric became sticky. Stitching holes make leaks at seams. When used with wool fabrics, the natural oil in wool caused the rubber cement to deteriorate.
The first noteworthy use of the rainproof cloth was to outfit the Arctic Expedition led by Sir John Franklin (1924). The material was also purchased by the British military and the general public.
Thomas Hancock contributed his knowledge of rubber technology beginning in 1830 (for which he was made a partner in 1934). He contributed the use of vulcanized rubber, which solved the problems of stickiness or stiffness with temperature changes.
Macintosh’s business grew and expanded into the manufacture of other india-rubber goods, including rubber shoes and cushions.
Macintosh was honored for his contributions to chemistry by his election in 1823 as a fellow of the Royal Society.
He died still close to his native hometown, at Dunchattan, near Glasgow, Scotland.
R. Baker, New & Improved (1976), British Library Board.
Patrick Robertson, The Shell Book of Firsts (1974), Ebury Press.
Hazel Muir (ed.), Larousse Dictionary of Scientists (1994).