The carbon-arc furnace, which dates from 1845 when it was battery operated, was of no practical value until after the development in 1867 of the electrical dynamo for converting water or steam power into electricity. Not until the work in Spray did the arc furnace become an industrial reality.

Improved Lighting
Over the half century following its discovery in 1836 by Edmund Davy, a cousin of Humphry Davy, acetylene was only a laboratory curiosity. After Thomas L. Willson's discovery of a cheap commercial process for making acetylene in 1892, massive quantities of the gas were in demand for lighting.

A newly developed acetylene burner, designed to bring adequate air to the flame to eliminate smoke and soot, gave a brilliant white light, 10 to 12 times brighter than that of any commercial fuel then in use. By 1897, acetylene generators and compressed acetylene were successfully competing with the fledgling electric light industry to provide excellent lighting, particularly in country homes and those not accessible to gas utilities.

Portable acetylene generators, which worked simply by dropping water on calcium carbide, provided a practical way for lighting railways, mines, bicycles, and automobiles. Acetylene lighting was used in transportation for a decade or more until electrical generation systems and shock-resistant light bulbs were developed. Miners continued to use carbide lights on their caps until long-lasting, dry-cell electric batteries were perfected in the 1920s.

Acetylene also replaced oil in marine buoys because it provided a far brighter light. The automatic carbide acetylene generators used at first were not very reliable and were replaced by compressed acetylene. Swedish engineer Gustaf Dal¸n received the 1912 Nobel prize in physics for his discovery of techniques that allowed safe compression of acetylene. A few of the acetylene buoys were still in operation in the 1960s.

High-Quality Alloy Steels
In 1894, Thomas Willson began experiments at Spray with smelting metals in the carbon-arc furnace. After 1895, this work was carried on by Guillaume de Chalmot. The high temperature of the arc furnace provided a more efficient means for alloying iron with chromium, manganese, and other metals.

As a group, these low-iron alloys, called ferro-alloys, can be readily dissolved in steel to impart predictable properties according to the type and amount of metal added. For the first time, steels could be tailor-made for such properties as toughness, impact strength, high strength at high temperatures, and corrosion resistance. Improved armor plate for battle ships, high-speed tool steels, and stainless steels are just three of the hundreds of specialized steel products now in use.

Rapid Welding and Cutting of Metals
During the 19th century, the only means of continuously joining two pieces of iron or steel was to heat them in a forge and hammer them together. In 1886, electric welding was introduced, but it was of no practical value because the electric power industry was not sufficiently developed to sustain it. Oxyhydrogen and thermite welding were known but had not been perfected.

When burned with oxygen instead of air, acetylene gave a flame temperature of 3000 ¯C compared with 1900 ¯C for the Bunsen burner flame. This high flame temperature was reported in 1895 but not exploited until about 1901, when a commercial oxyacetylene welding apparatus was developed in France. The first oxyacetylene welding shop in the United States was set up in 1906, and in 1907 the technique was adopted at the Brooklyn Navy Yard. There, oxyacetylene torches could cut a porthole in 3-inch armor plate in 30 minutes, a task that formerly had required five men working for two weeks to complete. The sudden, great demand for oxygen for welding launched oxygen as a commodity product.

Nitrogen Fixation and Fertilizer Manufacture
Henri Moissan observed in 1893 that calcium carbide absorbed atmospheric nitrogen. In 1898, Fritz Rothe of Germany found that the compound formed by this absorption was calcium cyanamide. In the soil, calcium cyanamide decomposes to yield urea and ammonium carbonate, both potent fertilizers. A commercial process patented by Adolf Frank and Nikodem Caro for making calcium cyanamide from carbide was perfected in Germany in 1903 and was widely adopted almost immediately. This was the first commercial process that was used worldwide to fix atmospheric nitrogen. World output of calcium cyanamide increased from 1,700 tons in 1907 to an estimated peak production of 1.5 million tons in 1945.

Organic Chemicals and Macromolecules
Following Willson's synthesis of chloroform and aldehydes from acetylene in 1894, acetylene soon became the starting material in the synthesis of a host of organic substances, particularly for the solvent, plastics, and synthetic rubber and fiber industries. By 1896, work in Germany led to chlorinated solvents by partial or complete chlorination of acetylene, and in 1908 to a full-scale plant producing 1,1,2-trichloroethene. These solvents were used extensively after 1920 for degreasing metals in preparation for electroplating or painting. By 1912, Germany was producing polyvinyl acetate for use in varnishes. Subsequently, polyvinyl acetate was used in adhesives, paints, paper, textiles, glue, and flooring materials.

During World War I, commercial processes for the production of acetaldehyde, acetic acid, and acetone (by passing acetic acid over a hot catalyst) were installed in Canada; acetone in particular was needed for making explosives. Similar processes in the United States in the 1920s served the cellulose acetate industry for the production of fibers and film. In the same decade, the synthesis of vinyl acetylene by Julius Nieuwland led to the development in 1932 of the synthetic rubber, neoprene, by DuPont. Its annual output reached 120,000 tons by 1960.

In Germany after World War I, butadiene made from acetylene was the basis of a rubber substitute that made the country self-sufficient in rubber. Also in Germany, beginning in 1925, J. Walter Reppe pioneered the study of acetylene chemistry at pressures as high as 200 atmospheres. This opened up a vast new field, often known as "Reppe chemistry." Reppe even managed to form cyclooctatetraene by linking four acetylene molecules in a ring, thereby confirming Richard Willstïtter's much contested claim that he had made the same compound in 1911.

With hydrocyanic acid, acetylene forms acrylonitrile, which can then be polymerized and spun into acrylic fibers. World production of acrylic fibers in 1988 was 2,523,000 tons.

In the past 40 years or so, acetylene has increasingly been derived from petroleum, but if petroleum reserves dwindle sufficiently to raise the price above that of coal, industry might return to coal, and calcium carbide would again become a main path to organic chemicals.