Tar (thing)

Tar

Tar seems to be such a simple and ordinary thing, yet few products have matched it's importance and impact on manufacturing evolution.

When people first began to heat coal to get coke for furnaces, the stiff black liquid that came from it was thought to be valueless. It was called "coal tar," and was thrown away. Now, more than 200,000 by-products are made from this tar that are used everyday.

The first use of coal tar was as a fuel. Later on, it was used as a protective coating on wood and ropes. Tar is waterproof, as well as wear-resistant. Finally, it was discovered that other useful substances could be made from the tar. When tar was heated and distilled, different oils were obtained. One of these was used for a long time as a substitute for turpentine.

Then, in 1856, a 17-year old chemistry assistant in England, William Henry Perkin, accidentally discovered that certain dyes, called aniline, could be made from coal tar. This opened a whole new world of industry.

After that point, chemists began to take a closer look at tar, and noticed just how useful it could be.

How are various products obtained from tar? The process is called distillation. The tar is boiled in big ovens that have bent tubes leading from them. The released gasses are separated and collected, as are the liquids. (for a thorough description of distillation, visit the node) Coal tar itself contains a little of everything(2.com). As it is distilled again, different substances are drawn off. The "pitch" that remains is the tar we are familiar with in tar shingles, tar-paper roofing, and asphalt on the streets.

Most of the colors now used for dyes and printing inks are made from coal tar. Carbolic acid, used as antiseptic in hospitals, comes from tar. Aspirin, saccharin (which is 550 times as sweet as cane sugar), and nylon all come from tar in some form. (Note- today, most of the chemicals for aspirin that came from tar are synthesized in a lab) Also, the entire modern plastics industry is based on tar! Mothballs, artificial food flavorings, asphalt, carbon paper, etc. all come from tar in some form. So you see that in a lump of coal, and the tar inside, we have the source of thousands of products we use every day.