: 652 CREATIVE CHEMISTRY Portland cement is high in Hme, whereas in glass silica predominates. Ceramic products, such as pottery, earthenware, and porcelain, occupy, generally, a position between these two extremes. The ceramic products are of three types (1) Unglazed, porous materials such as bricks, pottery, and terra cotta. (2) Partially glazed, porous materials such as earthenware and sanitary ware. (3) Nonporous materials such as stoneware, chinaware, and porcelain. The type of product produced depends to a large extent on the very careful selection and analysis of raw materials, although the great improvements made in these products in recent years have been paid for only by Fig. 285. Left, old juice bottle. Right, new juice bottle, equal in capacity but lighter in weight. Changes in the design of glass bottles to stronger bottles containing less glass accounted for an increased production capacity of 2,500,000 gross of glass containers in 1939. (Courtesy of Industrial and Engineering Chemistry, News Edition, published by the American Chemical ^*^^^^"^ very extensive research. Glass Is One of the Most Important Industrial Products of Today. Ordinary "soft glass" such as used in window panes and bottles is "lime-soda" glass; that is, it is a sodium calcium silicate, produced by melting together calcium carbonate, sodium carbonate, and quartz (sand, or Si02). When these materials are heated, carbon dioxide is evolved, and the resulting products consist of about 1 part sodium oxide, Na20, 1 part calcium oxide, CaO, and 6 to 8 parts silica, Si02. The Na20 and CaO may be partially or entirely replaced by other oxides such as BaO, K2O, ZnO, or PbO. Thus lead glass used in cutglass ware contains PbO. The Si02 may also be replaced by B2O3, P2O5, and other oxides. Heat-resisting glasses, for example, are often borosilicate glasses, which are high in boron oxide, B2O3, content. Highly stable borosilicate glasses were first developed in America some thirty years ago. Their resistance to mechanical shock and sudden temperature changes has brought them into wide use for cooking utensils, while their resistance to chemical reagents, along with
COMBUSTION 653 their other properties, has resulted in their almost universal adoption for chemical laboratory glassware. Colored glass is obtained by adding small traces of the oxides of heavy metals; thus cobalt oxide imparts a blue color; selenium oxide, a ruby red; chromium trioxide, a green; manganese dioxide, a violet; and iron oxide, an amber color. One of the latest developments in building is the use of glass blocks. These blocks can be improved as to their insulating and light-diffusing properties by sealing sheets of Fiberglas into them. Melted glass can be passed through tiny holes or pulled out to produce threads that are less than one tenth of the diameter of a human hair. These fibers can be spun into moistureproof, verminproof, rotand mildewproof, fireproof cloth. Because of their electrical insulating properties glass fabrics are used in the electrical industry for such applications as battery-plate separators. At present glass fabrics are too harsh for wearing apparel in direct contact with the skin and have limited utility in uses involving much wear or flexing. Glass wool is widely used in air conditioning as a filtering medium and an insulating material. Mineral wool, a product similar to glass wool, is likewise widely used for heat and sound insulation. The raw materials for mineral wool are slags, formerly the waste products from the refining of metals, to which certain rock materials are sometimes added to impart the desired properties to the final product. The mineral wool is usually produced by melting the slag or slag-rock mixture and then blowing air or steam under high pressure into a small stream of the molten material. STUDY QUESTIONS 1. Differentiate between quicklime and hydrated lime. 2. What is the composition of mortar, and what reaction takes place when it sets? 3. Why is it desirable to keep concrete wet while it is setting? 4. Discuss mineral wool as to (a) its preparation, and (b) its uses. 5. Discuss Portland cement as to (c) composition, (b) raw materials, and (c) method of manufacture. 6. Discuss glass as to (o) composition, (b) raw materials, (c) types of glass, and (d) modern uses. 7. Discuss the progress that man has made in duplicating the materials produced in nature. 8. Discuss plaster of Paris as to (a) its preparation, (b) its uses, and (c) what happens when it sets. 9. Discuss the nature of incendiary bombs.