In"di*ca`tor (&ibreve;n"d&ibreve;*kā`t&etilde;r),
n. [L.: cf. F. indicateur.]
1. One who, or that which, shows or points
out; as, a fare indicator in a street car.
2. (Mach.) A pressure gauge; a water
gauge, as for a steam boiler; an apparatus or instrument for showing
the working of a machine or moving part; as:
(a) (Steam Engine) An instrument which
draws a diagram showing the varying pressure in the cylinder of an
engine or pump at every point of the stroke. It consists of a small
cylinder communicating with the engine cylinder and fitted with a
piston which the varying pressure drives upward more or less against
the resistance of a spring. A lever imparts motion to a pencil which
traces the diagram on a card wrapped around a vertical drum which is
turned back and forth by a string connected with the piston rod of
the engine. See Indicator card (below).
(b) A telltale connected with a hoisting
machine, to show, at the surface, the position of the cage in the
shaft of a mine, etc.
3. (Mech.) The part of an instrument
by which an effect is indicated, as an index or pointer.
4. (Zoöl.) Any bird of the genus
Indicator and allied genera. See Honey guide, under
Honey.
5. (Chem.) That which indicates the
condition of acidity, alkalinity, or the deficiency, excess, or
sufficiency of a standard reagent, by causing an appearance,
disappearance, or change of color, as in titration or volumetric
analysis.
&fist; The common indicators are litmus, tropæolin, phenol
phthalein, potassic permanganate, etc.
Indicator card, the figure drawn by an
engine indicator, by means of which the working of the engine can be
investigated and its power calculated. The Illustration shows one
form of indicator card, from a steam engine, together with scales by
which the pressure of the steam above or below that of the
atmosphere, corresponding to any position of the engine piston in its
stroke, can be measured. Called also indicator diagram. -
- Indicator telegraph, a telegraph in which the
signals are the deflections of a magnetic needle, as in the trans-
Atlantic system.
