Carbon

Carbon occurs in three forms: amorphous (non-crystalline, lampblack), graphite, and diamond.   Amorphous carbon, a fine powder, is used as a rubber filler, fuel, and black pigment.   Graphite is used as a lubricant, electrical conductor (e.g., carbon-arc lamps), and heat-resistance material.   Natural and synthetic diamonds are used as gems and the best of the abrasives.   Radioactive carbon-14, with a half-life of 5,715 years, is used to date ancient objects that once contained organic compounds ("carbon dating").   Activated carbon, made from coal by subjecting it to high-temperaure steam, thus becoming almost pure carbon with an immense porous surface, is used to filter out undesirable chemicals from water (e.g., water treatment plants, tap water, swimming pools, food and chemical processing plants) and air (e.g., refrigerator odors).   Hydrocarbons (molecules made of long chains of carbon and hydrogen atoms), such as, coke, made from coal, and charcoal, made from wood, are important fuels.

Carbon forms a huge number of useful compounds, some of which are listed below:

Carbon dioxide, CO₂, a major consituent of air, is essential to plant photosynthesis and animal respiration.   Large quantities of solid carbon dioxide ("dry ice") are used in processes requiring large amounts of refrigeration.   It is used in fire extinguishers in preference to water for most types of fires.   It is a constituent of medical gases that require exhalation.   Carbon dioxide is dissolved under pressure to produce many highly popular carbonated beverages.   Some alcoholic beverages develop carbon dioxide during the fermentation process

Around 1624, Jan Baptista van Helmont, a Flemish physician, isolated and studied the gas produced by burning wood.   He called it "sylvestre".   In 1754, Joseph Black, a Scottish chemist, determined that carbon dioxide was a product of burning limestone to produce lime.   He also found that he could reverse the process, i.e., combine carbon dioxide with lime to produce limestone.   He called the gas "fixed air" at the time.   Later, "sylvestre" and "fixed air" came to be called carbon dioxide. ^{Asimov 154,228}

Although deadly to animals, carbon monoxide, CO, is widely used as a fuel and also as a reducing agent in the chemical industry.

Carbon-hydrogen compounds, called hydrocarbons, are the main constituents of coal, petroleum, plastics, and natural gas, thereby making it extremely important in producing energy and power for all industries.   Some of the better known hydrocarbons are methane, CH₄, ethylene, C₂H₄, acetylene, C₂H₂, and benzene, C₆H₆.

Carbon disulfide, CS₂, is used in the manufacturing of rayon, cellophane, carbon tetrachloride, dyes, rubber, solvents, waxes, cleaners and insecticides.

Chloroform, CHCl₃, is used mainly to produce fluorocarbon-22, an important refrigerant and ingredient in fluoropolymer production.   It is also used as a solvent used in pesticide and pharmaceutical manufacturing.   On the negative side, chloroform is a carcinogen, so it must be used with caution.

Ethyl alcohol, C₂H₅OH, (ethanol, grain alcohol), is used primarily to produce alcoholic beverages.   When "denatured" by adding compounds to make it distasteful as a drink, it is used in antifreeze products, as a good solvent for perfumes, paints and tinctures, and as a disinfectant.

Acetic acid, CH₃COOH, is used mainly in the form of vinegar, which is used as a food condiment, and in the pickling of vegetables and other foods.   Acetic acid is also sprayed onto silage as a preservative against bacterial and fungal growth.

Carbon is not only essential to life, being a part of plant photosynthesis and animal respiration, it defines life itself, since all carbon compounds, except arguably carbon dioxide and carbon monoxide, are considered "organic".   Carbon dioxide, CO₂, is a component of plant photosynthesis and animal respiration.   Carbon is found in carbohydrates, proteins, lipids, and nucleic acids, e.g., DNA.   On the negative side, excess amounts of carbon dioxide are toxic and the large amounts accumulating in the atmosphere as a result of respiration, vehicle exhaust and industrial effluents, coupled with the fewer amounts being taken up by plants because of continued logging and farming, are causing the earth's atmosphere to rise gradually in temperature.   A rise in atmospheric temperature will cause polar ice melting and flooding of low land areas, and faster evaporation and land desertification.

Carbon was known to the ancients.   Rock formations of carbonates of calcium (calcite), magnesium (dolomite), and iron are abundantly distributed in nature.

In 1874, Jacobus Hendricus van't Hoff, a Dutch physical chemist, discovered through light polarization experiments that carbon compounds were three-dimensional, with different shapes for the same chemical formula, what are now called isomers, the shape determining chemical reaction.   This discovery led to the new branch of chemistry, called stereochemistry. ^{Asimov 408}