In the United States most galvanized products, such as telegraph wire, garbage cans, and roofing and siding for buildings, are galvanized by the hot dipping method. In this process, iron or steel sheets are dipped into molten zinc. The zinc combines with the iron or steel to produce a protective layer of zinc-iron alloy overlaid by a layer of zinc. The entire coating is usually from 0.0002 inch to 0.004 inch thick.
Electrogalvanizing, a less costly process, produces a thinner, less durable zinc coating. Here the iron or steel is placed in a solution of zinc or zinc salts. A strong electric current is passed through the solution to deposit a layer of 99.99 percent pure zinc on the surface of the steel or iron.
Sherardizing is a process used to galvanize small items, such as nails or bolts. These are placed in a rotating drum containing fine zinc dust. The drum is heated to a temperature from 350 °C to 370 °C. (660 °F to 700 °F.), well below the melting point of zinc. As in hot dipping, a layer of zinc-iron alloy forms on the surface of the iron or steel.
Large objects are often zinc-coated by being sprayed with molten zinc. This does not result in true galvanizing, since an alloy is not formed with the zinc.
Galvanizing is named for Luigi Galvani, an 18th- century Italian physician who performed early experiments in electricity.
The compounds of fluorine are called fluorides, and many are useful to man. For example, hydrogen fluoride, a colorless gas with an irritating odor, is used to etch glass, and sodium fluoride is used as an insecticide. To prevent enamel decay in teeth, many dentists apply fluorides to the teeth; many communities add fluorine compounds to their drinking water.
Fluorine is commercially produced by the electrolysis of mixtures of hydrogen fluoride, HF, and molten potassium fluoride,
Born in Schivelbein, Pomerania (Germany), Rudolf Virchow was the only child of a small merchant. He was educated at the Gymnasium of Coslin and Friedrich Wilhelm Institute in Berlin. A gifted student, Virchow was able to work long hours without tiring and his interests were many. In 1843, a few months after graduation from Wilhelm Institute, Virchow became assistant surgeon at Charite Hospital at the age of 21 and prorector three years later. In spite of a heavy schedule, Virchow continued his research and started the leading medical publications of Europe of his day.
In 1847 Virchow was sent by his government to Silesia, Poland, to take measures in the control of an outbreak of typhus fever among the Silesians suffering from famine.
Angered by the conditions he found, Virchow actively joined the German revolution of 1848 and when the monarchy was restored he was asked to resign his post at Charite. He accepted an invitation to become Professor of Pathological Anatomy at Wursburg, where he served for several years, and published Cellular Pathology and Thrombosis and Embolism.
What is a depressant?
A depressant is a drug that reduces the activity of various body functions. Some depressants such as anesthetics, sedatives, antiepileptics, narcotics analgesics, and some muscle relaxants, slow nervous and muscular activity by acting on the central nervous system. Tranquilizers are depressants that affect only part of the nervous system. They induce relaxation without causing total depression.