Io moth
I"o moth ( 115). (Zoöl.) A large and handsome American moth ( Hyperchiria Io), having a large, bright-colored spot on each hind wing, resembling the spots on the tail of a peacock. The larva is covered with prickly hairs, which sting like nettles.

Iod-
I´od- (Chem.) See Iodo- .

Iodate
I´o•date (i"o•dat), n. (Chem.) A salt of iodic acid.

Iodhydrin
I•od•hy´drin, n. [ Iod- + chlor hydrin.] (Chem.) One of a series of compounds containing iodine, and analogous to the chlorhydrins.

Iodic
I•od´ic, a. [Cf. F. iodique. See Iodine.] (Chem.) Pertaining to, or containing, iodine; specif., denoting those compounds in which it has a relatively high valence; as iodic acid. Iodic acid, a monobasic acid, consisting of iodine with three parts of oxygen and one of hydrogen.

Iodine
I´o•dine (i"o•din or -den; 104), n. [Gr. ’iw•dhs violetlike; ’i•on a violet + e’i^dos form: cf. F. iode, iodine. The name was given from the violet color of its vapor. See Violet, Idyl.] (Chem.) A nonmetallic element, of the halogen group, occurring always in combination, as in the iodides. When isolated it is in the form of dark gray metallic scales, resembling plumbago, soft but brittle, and emitting a chlorinelike odor. Symbol I. Atomic weight 126.5. If heated, iodine volatilizes in beautiful violet vapors. Iodine was formerly obtained from the ashes of seaweed ( kelp or varec), but is now also extracted from certain natural brines. In the free state, iodine, even in very minute quantities, colors starch blue. Iodine and its compounds are largely used in medicine (as in liniments, antisyphilitics, etc.), in photography, in the preparation of aniline dyes, and as an indicator in titration. Iodine green, an artificial green dyestuff, consisting of an iodine derivative of rosaniline; — called also night green. — Iodine scarlet, a pigment of an intense scarlet color, consisting of mercuric iodide. — Iodine yellow, a brilliant yellow pigment, consisting of plumbic iodide.

Iodize
I´o•dize, v. t. [ imp. & p. p. Iodized p. pr. & vb. n. Iodizing ] To treat or impregnate with iodine or its compounds; as to iodize a plate for photography. R. Hunt.

Iodocresol
I•o•do•cre´sol, n. [ Iodo- + cresol.] (Org. Chem.) Any of several isomeric iodine derivatives of the cresols, C₆H₃I(CH₃)OH, esp. one, an odorless amorphous powder, used in medicine as a substitute for iodoform.

Iodoform
I•od´o•form, n. [ Iodo- + formyl. See Formyl, and cf. Chloroform.] (Chem.) A yellow, crystalline, volatile substance, CI₃H, having an offensive odor and sweetish taste, and analogous to chloroform. It is used in medicine as a healing and antiseptic dressing for wounds and sores.

Iodol
I´o•dol, n. [ Iodo- + pyrr ol.] (Chem.) A crystallized substance of the composition C₄I₄NH, technically tetra-iodo- pyrrol, used like iodoform.

Iodoquinine
I•o•do•qui´nine, n. [ Iodo- + quinine.] (Chem.) A iodide of quinine obtained as a brown substance. It is the base of herapathite. See Herapathite.

Iodous
I´o•dous, a. (Chem.) Pertaining to, or containing, iodine. See -ous (chemical suffix). Iodous acid, a hypothetical acid, analogous to chlorous acid.

Iodyrite
I•od´y•rite, n. [From Iodine.] (Min.) Silver iodide, a mineral of a yellowish color.

Ion
I´on (i"on), n. [Gr. ’io•n, neut, of ’iw•n, p. pr. of ’ie•nai to go.] (Elec. Chem.) One of the elements which appear at the respective poles when a body is subjected to electro-chemical decomposition. Cf. Anion, Cation.

Ion
I´on, n.
1. One of the electrified particles into which, according to the electrolytic dissociation theory, the molecules of electrolytes are divided by water and other solvents. An ion consists of one or more atoms and carries a unit charge of electricity, 3.4 x 10^-10 electrostatic units, or a multiple of this. Those which are positively electrified (hydrogen and the metals) are called cations; negative ions (hydroxyl and acidic atoms or groups) are called anions. Thus, hydrochloric acid (HCl) dissociates, in aqueous solution, into the hydrogen ion, H+, and the chlorine ion, Cl-; ferric nitrate, Fe(NO₃)₃, yields the ferric ion, Fe+++, and nitrate ions, NO3-, NO3-, NO3-. When a solution containing ions is made part of an electric circuit, the cations move toward the cathode, the anions toward the anode. This movement is called migration, and the velocity of it differs for different kinds of ions. If the electromotive force is sufficient, electrolysis ensues: cations give up their charge at the cathode and separate in metallic form or decompose water, forming hydrogen and alkali; similarly, at the anode the element of the anion separates, or the metal of the anode is dissolved, or decomposition occurs.
2. One of the small electrified particles into which the molecules of a gas are broken up under the action of the electric current, of ultraviolet and certain other rays, and of high temperatures. To the properties and behavior of ions the phenomena of the electric discharge through rarefied gases and many other important effects are ascribed. At low pressures the negative ions appear to be electrons; the positive ions, atoms minus an electron. At ordinary pressures each ion seems to include also a number of attached molecules. Ions may be formed in a gas in various ways.

Ionian
I•o´ni•an, a. [L. Ionius. See Ionic.] Of or pertaining to Ionia or the Ionians; Ionic. — n. A native or citizen of Ionia.

Ionidium
I•o•nid´i•um, n. [NL. Cf. Iodine.] (Bot.) A genus of violaceous plants, chiefly found in tropical America, some species of which are used as substitutes for ipecacuanha.

Iota
I•o´ta, n. [L., fr. Gr. ’iw^ta. See Jot.]
1. The ninth letter of the Greek alphabet (ι) corresponding with the English i.
2. A very small quantity or degree; a jot; a particle.
"They never depart an iota from the authentic formulas of tyranny and usurpation." Burke. Iota subscript (Gr. Gram.), iota written beneath a preceding vowel, as a,, h,, w,, — done when iota is silent.