any of a group of intensely black, finely divided forms of amorphous carbon, usually obtained as soot from partial combustion of hydrocarbons, used principally as reinforcing agents in automobile tires and other rubber products but also as extremely black pigments of high hiding power in printing ink, paint, and carbon paper. Carbon black is also used in protective coatings, plastics, and resistors for electronic circuits. As a reinforcing filler it greatly increases resistance to wear and abrasion. About one fourth of the weight of a standard automobile tire is carbon black. For tires on vehicles on which it is necessary to avoid building up an electrostatic charge, such as oil trucks and hospital operating carts, even more carbon black is added to make the rubber electrically conducting.