626 CREATIVE CHEMISTRY to sulfur trioxide, which then reacts with water to produce sulfuric acid. 2SO2 + O2 —>- 2SO3 sulfur dioxide oxygen sulfur trioxide SO3 + H2O >- H2SO4 sulfur trioxide water sulfuric acid When sulfur is burned in air, only sulfur dioxide is produced. A catalyst (see Section 5 of this Unit), i.e., an added material which, by its mere presence, changes the rate of a chemical reaction, must be employed to add an extra oxygen to sulfur dioxide to form sulfur trioxide. the "lead chamber" process the catalyst consists of oxides of nitrogen; in the contact process the catalyst consists of finely divided platinum or other materials. Because sulfuric acid is a heavy, oily liquid and was formerly prepared from vitriol, it is called "oil of vitriol," and its salts are called "vitriols"; for example, copper sulfate is called "blue vitriol." Sulfuric acid is so important in modern industry that its production is one of the best indexes of industrial prosperity in general. The annual production of sulfuric acid is about 7,000,000 tons. Sulfuric acid is the cheapest and most satisfactory acid for many purposes. Large quantities of sulfuric acid are used in the treatment of phosphate rock, which is insoluble in water, to produce calcium superphosphate, which is soluble in w^ater, for use in fertilizers. Its reactivity with unsaturated compounds is applied in the refining of petroleum; and its great affinity for water makes it useful in reactions in which nitric acid is used to nitrate such material as cellulose or toluene, because these reactions will not go to completion unless the water is removed as rapidly as it is produced. CeHsCHs + 3HNO3 —> C6H2(N02)3CH3 + 3 H2O toluene nitric acid T.N.T. water In Sulfuric acid has such a great affinity for water that it will extract water from carbohydrates, leaving carbon as a residue. Because of this property, clothing and the skin of laboratory workers must be protected against sulfuric acid. The low volatility of sulfuric acid makes possible its use in the preparation of the other, more volatile acids. For example: 2NaN03 + H2SO4 —>- 2HNO3 + Na2S04 sodium nitrate sulfuric acid nitric acid sodium sulfate 2NaCl + H2SO4 —>- 2HC1 + Na2S04 sodium chloride sulfuric acid hydrochloric acid sodium sulfate
OXYGEN AND SULFUR, CARBON AND SILICON 627 The acid properties of sulfuric acid find wide application in cleaning scale from iron and steel. This process is called "pickling." Everyone is familiar with the use of sulfuric acid in lead storage batteries. Old-fashioned gunpowder was a mixture of sulfur, charcoal, and saltpeter. Sulfur, dissolved in lime and water to form lime-sulfur spray or in the powdered form, is in agriculture. used to check scale and fungus enemies Sulfur is used in the manufacture of fireworks, matches, paints, rubber, plastics, and hundreds of other materials. The Utilization of Waste Sulfur Dioxide Constitutes an Important Conservation Problem. About one fifth of the sulfuric acid is manufactured from the waste gases of smelters in which metallic sulfides are roasted, i.e., heated in the presence of air to change them into oxides. Pyrite, FeS2, may be burned to produce sulfur dioxide, and it is used for the manufacture of sulfuric acid where it can be obtained more cheaply than sulfur. Over one half of the production of sulfuric acid in the United States could be taken care of by the gases which are still wasted in the western smelters. This loss is a crime from the point of view of conservation, but our present economic system is so organized that it is not financially advantageous to conserve these gases. Here is another challenge to the ability of a democracy to conserve its resources. Is this a job for the government or can it be handled by private initiative and research ? Coal is produced from plant materials, the protein of which contains sulfur. Some coals contain as high as 5 per cent sulfur. Large cities which use coal as a fuel are deluged by large quantities of sulfur dioxide, which acts on stone, metals, wood, and textiles. Wearing apparel quickly wears out in these regions because of their daily acid bath produced by the reaction of sulfur dioxide with moisture. How can these sulfurous fumes be kept out of the air of our large cities? This is now an economic problem that remains to be solved. Carbon, in Its Several Forms, Is Another Important Industrial Raw Material. The utilization of coal, petroleum, and natural gas as sources of important organic compounds is discussed in Sections 8 and 9 of this Unit. The discussion of carbon in this Unit will be restricted to elemental carbon and its inorganic compounds. Carbon occurs in nature in the two crystalline allotropic forms, graphite and diamond, and as amorphous carbon.