Part 147

Robert's wind-blown head and tall form wrapped in an Inverness cape.

Mrs. Humphry Ward.

In*vert"ase (?), n. (Chem.) (a) An enzyme capable of effecting the inversion of cane suger, producing invert sugar. It is found in many plants and in the intestines of animals. (b) By extension, any enzyme which splits cane sugar, milk sugar, lactose, etc., into monosaccharides.

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.

I`o*do*for"mo*gen (?), n. [Iodoform + -gen root of gi`gnesqai to be born.] (Pharm.) A light powder used as a substitute for iodoform. It is a compound of iodoform and albumin.

I"o*dol (?), n. [Iodo- + pyrrol.] (Chem.) A crystallized substance of the composition C4I4NH, technically tetra-iodo- pyrrol, used like iodoform.

I`o*do*thy"rin (?), n. [Iodo- + thyro- + -in.] (Physiol. Chem.) A peculiar substance obtained from the thyroid gland, containing from nine to ten per cent of iodine.

It is a very stable compound, and is believed to be active principle in thyroid extracts and in the internal secretion of the thyroid gland. It was originally called thyroiodin.

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.

I"on*ize (?), v. t. [imp. & p. p. Ionized (?); p. pr. & vb. n. Ionizing (?).] (Elec. Chem.) To separate (a compound) into ions, esp. by dissolving in water. -- I`on*i*za"tion (#), n.

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I"ris, n. (Zoöl.) Inner circle of an oscillated color spot.

I"ris di"a*phragm. An adjustable diaphragm, suggesting the iris of the eye in its action, for regulating the aperture of a lens, consisting of a number of thin pieces fastened to a ring. It is used in cameras and microscopes.

I"rish A*mer"i*can. A native of Ireland who has become an American citizen; also, a child or descendant of such a person.

I"ron ("rn), n. (Golf) An iron-headed club with a deep face, chiefly used in making approaches, lifting a ball over hazards, etc.

Ir`o*quoi"an (r`*kwoi"an), a. Of, pertaining to, or designating, one of the principal linguistic stocks of the North American Indians. The territory of the northern Iroquoian tribes, of whom the Five Nations, or Iroquois proper, were the chief, extended from the shores of the St. Lawrence and of Lakes Huron, Ontario, and Erie south, through eastern Pennsylvania, to Maryland; that of the southern tribes, of whom the Cherokees were chief, formed part of Virginia, the Carolinas, Georgia, Tennessee, and Kentucky. All of the tribes were agricultural, and they were noted for large, communal houses, palisaded towns, and ability to organize, as well as for skill in war. -- n. An Indian of an Iroquoian tribe.

Ir`re*vers"i*ble steering gear. (Mach.) A steering gear, esp. for an automobile, not affected by the road wheels, as when they strike an obstacle side ways, but easily controlled by the hand wheel or steering lever.

I"so*bront ("s*brnt), n. [Iso- + Gr. bronth` thunder.] (Meteor.) An imaginary line, or a line on a chart, marking the simultaneous development of a thunderstorm, as noted by observing the time when the thunder is heard at different places.

I"so*chor (?), n. [Iso- + Gr. xhw`ra space.] (Physics) A line upon a thermodynamic diagram so drawn as to represent the pressures corresponding to changes of temperature when the volume of the gas operated on is constant. -- I`so*chor"ic (#), a.

I*soch"ro*nize (?), v. t. [imp. & p. p. -nized; p. pr. & vb. n. -nizing.] [See Isochronous.] To make, or tend to make (the motion of a moving body), uniform in rate of rotation, or in frequency of vibration.

I"so*drome (?), n. [Iso- + Gr. &?; course.] (Nav.) A method of moving a fleet from one formation to another, the direction usually being changed eight points (90°), by means of paths of equal length for each ship. It is prohibited in the United States navy.

I"so*mere (?), n. [Iso- + - mere.] (Zoöl.) 1. A homologous or corresponding part or segment.

2. (Chem.) = Isomer.

I"so*morph (?), n. (Biol.) An animal, plant, or group having superficial similarity to another, although phylogenetically different.

I`so*mor"phic (?), a. (Biol.) Alike in form; exhibiting isomorphism.

I"so*spore (?), n. (Biol.) (a) One of the spores produced by an isosporous organism. (b) A zygospore.

I*sos"po*rous (?), a. [Iso- + Gr. &?; fruit.] (Biol.) Producing but one kind of spore, as the ferns.