TABLE OF CONTENTS When light passes from one medium into another, its velocity is changed. The ratio of the velocity of light in a vacuum to that in a substance is known as the index of refraction or refractive index of that substance. The index of refraction varies with the wavelength of light employed, with temperature, and with pressure (for gases).
A variety of instruments, called refractometers, permits the measurement of indices of refraction of gases, liquids, and solids. Refractometry is the term applied to the group of optical methods for the analysis of either relatively pure substances or complex mixtures, based on refractive-index measurements. It, usually, is applied to identify pure substances.
Some substances, called isotropic materials, transmit light with equal velocity in all directions and have only one index of refraction. Gases, liquids, glasses, and most solids of the isometric system belong to the isotropic group of materials. Other solids, which do not transmit light with equal velocity in all directions, are called anisotropic materials.
The refractive index of a liquid is the ratio of the velocity of light in a vacuum to the velocity of light in the liquid. The angle of refraction varies with the wavelength of the light used. Usually the yellow sodium doublet lines are used; they have a weighted mean of 589.26 nm and are symbolized by D. A typical refractive index ( ?) would be expressed as
where the superscript indicates the temperature and the subscript indicates...
