Isologous
(I*sol"o*gous) a. [Iso- + Gr. lo`gos proportion.] (Chem.) Having similar proportions, similar
relations, or similar differences of composition; — said specifically of groups or series which differ by a
constant difference; as, ethane, ethylene, and acetylene, or their analogous compounds, form an isologous
series.
Isomer
(I"so*mer) n. [See Isomeric.] (Chem.) A body or compound which is isomeric with another
body or compound; a member of an isomeric series.
Isomeric
(I`so*mer"ic) a. [Iso- + Gr. me`ros part: cf. F. isomérique.] (Chem.) Having the same percentage
composition; — said of two or more different substances which contain the same ingredients in the same
proportions by weight, often used with with. Specif.: (a) Polymeric; i. e., having the same elements
united in the same proportion by weight, but with different molecular weights; as, acetylene and benzine
are isomeric (polymeric) with each other in this sense. See Polymeric. (b) Metameric; i. e., having
the same elements united in the same proportions by weight, and with the same molecular weight, but
with a different structure or arrangement of the ultimate parts; as, ethyl alcohol and methyl ether are
isomeric (metameric) with each other in this sense. See Metameric.
Isomeride
(I*som"er*ide) n. (Chem.) An isomer. [R.]
Isomerism
(I*som"er*ism) n. (Chem.) The state, quality, or relation, of two or more isomeric substances.
Physical isomerism (Chem.), the condition or relation of certain (metameric) substances, which, while
chemically identical (in that they have the same composition, the same molecular weights, and the same
ultimate constitution), are yet physically different, as in their action on polarized light, as dextro- and
lævo-tartaric acids. In such compounds there is usually at least one unsymmetrical carbon atom. See
Unsymmetrical.
Isomeromorphism
(I`so*mer`o*mor"phism) n. [Isomer + Gr. form + -ism.] (Crystallog.) Isomorphism
between substances that are isomeric.
Isometric
(I`so*met"ric I`so*met"ric*al) a. [Iso- + Gr. me`tron measure.]
1. Pertaining to, or characterized by, equality of measure.
2. (Crystallog.) Noting, or conforming to, that system of crystallization in which the three axes are of
equal length and at right angles to each other; monometric; regular; cubic. Cf. Crystallization.
Isometric lines (Thermodynamics), lines representing in a diagram the relations of pressure and temperature
in a gas, when the volume remains constant. — Isometrical perspective. See under Perspective.
— Isometrical projection, a species of orthographic projection, in which but a single plane of projection
is used. It is so named from the fact that the projections of three equal lines, parallel respectively to
three rectangular axes, are equal to one another. This kind of projection is principally used in delineating
buildings or machinery, in which the principal lines are parallel to three rectangular axes, and the principal
planes are parallel to three rectangular planes passing through the three axes.
Isomorph
(I"so*morph) n. [See Isomorphous.] A substance which is similar to another in crystalline
form and composition.
Isomorphic
(I`so*mor"phic) a. Isomorphous.
Isomorphism
(I`so*mor"phism) n. [Cf. F. isomorphisme.] (Crystallog.) A similarity of crystalline form
between substances of similar composition, as between the sulphates of barium (BaSO4) and strontium
It is sometimes extended to include similarity of form between substances of unlike composition, which
is more properly called homœomorphism.
Isomorphous
(I`so*mor"phous) a. [Iso- + -morphous.] Having the quality of isomorphism.
