COLORIMETER, an instrument for determining the inten sity of a colour (q.v.) relative to a standard colour intensity. The two are viewed simultaneously and the standard is modified by definite degrees until the intensities appear equal. This modifica tion may be effected (a) for liquids, by altering the length of the column or the concentration of the standard liquid, (b) for solids or liquids, by interposing in front of or behind the standard a movable transparent, coloured wedge or some such device. Colori metric methods may be used to determine hydrogen ion concen tration. (See HYDROGEN ION CONCENTRATION; Determination of Hydrogen, etc.) (See CHEMISTRY: Analytical.) (See also