Glass

Do not try to sunbathe at the closed windows. Its a wasted effort! Ordinary glass does not pass ultraviolet rays, which give our skin a healthy tan.
Doctors called the ultraviolet rays " rays of life," because they kill bacteria, heal wounds and strengthen health. Before revolution kids of poor peasants were huddled in basements and dark hovels, where it was damp and little light. The lack of  ultraviolet rays and bad food caused severe disease - rickets. The matter is that the window glass is brewed from sand, which contains impurities of iron, lead, and antimony. These impurities detain required for our health ultraviolet rays.
Technologists glass manufacturers have created special glasses, which passes ultraviolet rays. They were called uviol glasses - " glasses of life". For the manufacture of such glasses are used crushed quartz, chalk and soda. In order glasses pass more ultraviolet rays, boric acid is also added to the charging material. But the best uviol glasses still are quartz glasses. They are also very durable and by heating almost unchanged their volume. If the quartz test tube heat up to red and throw in the ice water, it will not burst. However, the production of quartz glass is expensive. For it, you need a special, pure quartz, which melts at high temperatures and requires a lot of energy. Glassmakers have found substitutes of quartz glass. If to the usual glass you will add lanthanum or zirconium, it becomes similar to quartz glass. It can be heated up to 400 °, and then rapidly cooled: and it will not crack.
Ultraviolet rays are not always useful. If the paper is lying in the sun - it turns yellow, ink fade, dyeing collapses. That's why in the shop windows, libraries, and in rooms, where the manuscripts are stored, are inserted glasses which delay ultraviolet rays.
When surgeons perform operations over them hangs a powerful electric lamp. A lot of heat comes from it, and it becomes hot in the operating room. The surgeon sweating profusely, and patient feels himself uncomfortably. Glassmakers formed thermal protective "cold" glasses, which absorb heat rays. There are glasses which protect from X- rays. There are those, which protect the eyes from the sun. Protective glasses which are used by steelworkers, contain cobalt and iron oxide.
Just recently glassmakers learned to make photosensitive glass, which is very similar to a photographic plate. These glasses include oxides of gold, silver, copper and cesium. These substances decompose under the action of ultraviolet rays and "hidden image" occurs in the glass.  Glasses processing is carried out on heating to 600 ° C. "Light damaged" areas of photosensitive glasses are more soluble in acid, than "not light damaged". Therefore, on the glass can be received most varied and complex in its shape image.
Glass is a good insulator of electric current, but if it includes chromium or nickel, then "heating" glasses will be obtained from it. These glasses well conduct electric current and and when connected to network they become a source of heat.
Glass has found, seemingly, the most unusual applications. It is known that plants need molybdenum, copper, manganese, zinc, boron, and other so-called trace elements in soil. They are added into the glass and eceive the glass fertilizers. Glass containing these elements are crushed and applied to the soil. Glass fertilizers increase the yield of wheat, tomatoes, sugar beets.
Modern manufacture making many diverse things from glass: glass wool and glass starch, fibers and fabrics, glass concrete and grease for machines, glass paper and wallpapers, giant lenses for telescopes, having a diameter of several meters, and light bulbs, which can pass through the eye of a needle.