An index of the ability of a substance to attenuate the transmission of an electrostatic force from one charged body to another, as in a condenser. The lower the value, the greater the attenuation. The standard measurement apparatus utilizes a vacuum whose dielectric constant is 1. In reference to this, various materials interposed between the charged terminal have the following values at 20C: air 1.00058, glass 3, benzene 2.3, acetic acid 6.2, ammonia 15.5, ethanol 25, glycerol 56, and water 81. The exceptionally high value for water accounts for its unique behavior as a solvent and in electrolytic solutions. Most hydrocarbons have high resistance (low conductivity). Dielectric-constant values decrease as the temperature rises.