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The Collaborative International Dictionary of English v.0.48 (gcide)

Equivalent \E*quiv"a*lent\ ([-e]*kw[i^]v"[.a]*lent), a. [L.
aequivalens, -entis, p. pr. of aequivalere to have equal
power; aequus equal valere to be strong, be worth: cf. F.
['e]quivalent. See {Equal}, and {Valiant}.]
1. Equal in worth or value, force, power, effect, import, and
the like; alike in significance and value; of the same
import or meaning.
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For now to serve and to minister, servile and
ministerial, are terms equivalent. --South.
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2. (Geom.) Equal in measure but not admitting of
superposition; -- applied to magnitudes; as, a square may
be equivalent to a triangle.
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3. (Geol.) Contemporaneous in origin; as, the equivalent
strata of different countries.
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Equivalent \E*quiv"a*lent\ ([-e]*kw[i^]v"[.a]*lent), n.
1. Something equivalent; that which is equal in value, worth,
weight, or force; as, to offer an equivalent for damage
done.
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He owned that, if the Test Act were repealed, the
Protestants were entitled to some equivalent. . . .
During some weeks the word equivalent, then lately
imported from France, was in the mouths of all the
coffeehouse orators. --Macaulay.
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2. (Chem.) That comparative quantity by weight of an element
which possesses the same chemical value as other elements,
as determined by actual experiment and reference to the
same standard. Specifically:
(a) The comparative proportions by which one element
replaces another in any particular compound; thus, as
zinc replaces hydrogen in hydrochloric acid, their
equivalents are 32.5 and 1.
(b) The combining proportion by weight of a substance, or
the number expressing this proportion, in any
particular compound; as, the equivalents of hydrogen
and oxygen in water are respectively 1 and 8, and in
hydric dioxide 1 and 16.
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Note: This term was adopted by Wollaston to avoid using the
conjectural expression atomic weight, with which,
however, for a time it was practically synonymous. The
attempt to limit the term to the meaning of a
universally comparative combining weight failed,
because of the possibility of several compounds of the
substances by reason of the variation in combining
power which most elements exhibit. The equivalent was
really identical with, or a multiple of submultiple of,
the atomic weight.
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3. (Chem.) A combining unit, whether an atom, a radical, or a
molecule; as, in acid salt two or more equivalents of acid
unite with one or more equivalents of base.
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{Mechanical equivalent of heat} (Physics), originally defined
as the number of units of work which the unit of heat can
perform, equivalent to the mechanical energy which must be
expended to raise the temperature of a pound of water one
degree Fahrenheit; later this value was defined as one
{British thermal unit} (B.t.u). Its value was found by
Joule to be 772 foot pounds; later measurements give the
value as 777.65 foot-pounds, equivalent to 107.5
kg-meters. This value was originally called Joule's
equivalent, but the modern Joule is defined differently,
being 10^{7} ergs. The B.t.u. is now given as 1,054.35
absolute Joules, and therefore 1 calorie (the amount of
heat needed to raise one gram of water one degree
centigrade) is equivalent to 4.186 Joules.
[1913 Webster PJC]

Note: The original definition of the Mechanical equivalent of
heat in the 1913 Webster was as below. The difference
between foot pounds and kilogram-meters ("on the
centigrade scale") is puzzling as it should be a factor
of 7.23, and the figure given for kilogram-meters may
be a mistaken misinterpretation of the report. -- PJC:
The number of units of work which the unit of heat can
perform; the mechanical energy which must be expended
to raise the temperature of a unit weight of water from
0[deg] C. to 1[deg] C., or from 32[deg] F. to 33[deg]
F. The term was introduced by Dr. Mayer of Heilbronn.
Its value was found by Joule to be 1390 foot pounds
upon the Centigrade, or 772 foot pounds upon the
Fahrenheit, thermometric scale, whence it is often
called {Joule's equivalent}, and represented by the
symbol J. This is equal to 424 kilogram meters
(Centigrade scale). A more recent determination by
Professor Rowland gives the value 426.9 kilogram
meters, for the latitude of Baltimore.
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Equivalent \E*quiv"a*lent\, v. t.
To make the equivalent to; to equal; equivalence. [R.]
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