Mechanical equivalent of heat
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. [1913 Webster]

He owned that, if the Test Act were repealed, the Protestants were entitled to some equivalent.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. [1913 Webster]

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. [1913 Webster]

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. [1913 Webster]

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. [1913 Webster]

{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. [1913 Webster +PJC]


The Collaborative International Dictionary of English. 2000.

Look at other dictionaries:

  • Mechanical equivalent of heat — Heat Heat (h[=e]t), n. [OE. hete, h[ae]te, AS. h[=ae]tu, h[=ae]to, fr. h[=a]t hot; akin to OHG. heizi heat, Dan. hede, Sw. hetta. See {Hot}.] 1. A force in nature which is recognized in various effects, but especially in the phenomena of fusion… …   The Collaborative International Dictionary of English

  • mechanical equivalent of heat — n the value of a unit quantity of heat in terms of mechanical work units with its most probable value in cgs measure being 4.1855 × 107 ergs per calorie symbol J called also Joule s equivalent …   Medical dictionary

  • Mechanical equivalent of heat — For other uses, see Conservation of energy. In the history of science, the mechanical equivalent of heat was a concept that had an important part in the development and acceptance of the conservation of energy and the establishment of the science …   Wikipedia

  • mechanical equivalent of heat — the value of a unit quantity of heat in terms of mechanical work units with its most probable value in cgs measure being 4.1855 × 107 ergs per calorie symbol J; called also Joule s equivalent * * * (in any system of physical units) the number of… …   Useful english dictionary

  • mechanical equivalent of heat — noun Obsolete the relation of heat units to mechanical units of work or energy, thus if 1 calorie = 4.186 joules, 4.186 was called the mechanical equivalent of heat. In SI all forms of energy are measured in the same units (joules) …   Australian English dictionary

  • mechanical equivalent of heat — mechaninis šilumos ekvivalentas statusas T sritis fizika atitikmenys: angl. Joule’s equivalent; mechanical equivalent of heat vok. mechanisches Wärmeäquivalent, n rus. механический эквивалент теплоты, m pranc. équivalent mécanique de la calorie,… …   Fizikos terminų žodynas

  • mechanical equivalent of heat — (in any system of physical units) the number of units of work or energy equal to one unit of heat, as 4.1858 joules, which equals one small calorie. [1835 45] * * * …   Universalium

  • mechanical equivalent of heat — Смотри механический эквивалент теплоты …   Энциклопедический словарь по металлургии

  • Dynamical theory of heat — Heat Heat (h[=e]t), n. [OE. hete, h[ae]te, AS. h[=ae]tu, h[=ae]to, fr. h[=a]t hot; akin to OHG. heizi heat, Dan. hede, Sw. hetta. See {Hot}.] 1. A force in nature which is recognized in various effects, but especially in the phenomena of fusion… …   The Collaborative International Dictionary of English

  • Unit of heat — Heat Heat (h[=e]t), n. [OE. hete, h[ae]te, AS. h[=ae]tu, h[=ae]to, fr. h[=a]t hot; akin to OHG. heizi heat, Dan. hede, Sw. hetta. See {Hot}.] 1. A force in nature which is recognized in various effects, but especially in the phenomena of fusion… …   The Collaborative International Dictionary of English

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”