Hydrobranchiata Hy`dro·bran`chi·a"ta noun plural [ New Latin , from Greek "y`dwr water + ... gills.] (Zoology) An extensive artificial division of gastropod mollusks, including those that breathe by gills, as contrasted with the Pulmonifera. -- Hy`dro*bran"chi*ate adjective

Hydrobromate Hy`dro·bro"mate noun (Chemistry) Same as Hydrobromide .

Hydrobromic Hy`dro·bro"mic adjective [ Hydro- , 2 + bromic .] (Chemistry) Composed of hydrogen and bromine; as, hydrobromic acid. Hydrobromic acid (Chemistry) , a colorless, pungent, corrosive gas, HBr, usually collected as a solution in water. It resembles hydrochloric acid, but is weaker and less stable. Called also hydrogen bromide .

Hydrobromide Hy`dro·bro"mide noun (Chemistry) A compound of hydrobromic acid with a base; -- distinguished from a bromide , in which only the bromine unites with the base.

Hydrocarbon Hy`dro·car"bon noun [ Hydro- , 2 + carbon .] (Chemistry) A compound containing only hydrogen and carbon, as methane, benzene, etc.; also, by extension, any of their derivatives. Hydrocarbon burner , furnace , stove , a burner, furnace, or stove with which liquid fuel, as petroleum, is used.

Hydrocarbonaceous Hy`dro·car`bo·na"ceous adjective Of the nature, or containing, hydrocarbons.

Hydrocarbonate Hy`dro·car"bon·ate noun (a) (Old Chem.) A hydrocarbon. [ Obsolete] (b) (Chemistry) A hydrous carbonate, as malachite.

Hydrocarbostyril Hy`dro·car`bo·sty"ril noun [ Hydro- , 2 + carbostyril .] (Chemistry) A white, crystalline, nitrogenous hydrocarbon, C ₉ H ₉ NO, obtained from certain derivatives of cinnamic acid and closely related to quinoline and carbostyril.

Hydrocarburet Hy`dro·car"bu·ret noun [ Hydro- , 2 + carburet .] (Chemistry) Carbureted hydrogen; also, a hydrocarbon. [ Obsolete]

Hydrocaulus Hy`dro·cau"lus noun ; plural Hydrocauli . [ New Latin , from Greek "y`dwr water + ... a stalk.] (Zoology) The hollow stem of a hydroid, either simple or branched. See Illust. of Gymnoblastea and Hydroidea .

Hydrocele Hy`dro·cele noun [ Latin , from Greek ...; "y`dwr water + ... tumor.] (Medicine) A collection of serous fluid in the areolar texture of the scrotum or in the coverings, especially in the serous sac, investing the testicle or the spermatic cord; dropsy of the testicle.

Hydrocephalic Hy`dro·ce·phal"ic adjective Relating to, or connected with, hydrocephalus, or dropsy of the brain.

Hydrocephaloid Hy`dro·ceph"a·loid adjective [ Hydrocephalus + -oid .] (Medicine) Resembling hydrocephalus. Hydrocephaloid affection (Medicine) , the group of symptoms which follow exhausting diarrhea in young children, resembling those of acute hydrocephalus, or tubercular meningitis.

Hydrocephalous Hy`dro·ceph"a·lous adjective Having hydrocephalus. " Hydrocephalous offspring." G. Eliot.

Hydrocephalus Hy`dro·ceph"a·lus noun [ New Latin , from Greek ... hydrocephalus; "y`dwr water + ... head.] (Medicine) An accumulation of liquid within the cavity of the cranium, especially within the ventricles of the brain; dropsy of the brain. It is due usually to tubercular meningitis. When it occurs in infancy, it often enlarges the head enormously.

Hydrochlorate Hy`dro·chlo"rate noun (Chemistry) Same as Hydrochloride .

Hydrochloric Hy`dro·chlo"ric adjective [ Hydro- , 2 + chloric : confer French hydrochlorique .] (Chemistry) Pertaining to, or compounded of, chlorine and hydrogen gas; as, hydrochloric acid; chlorhydric. Hydrochloric acid (Chemistry) , hydrogen chloride; a colorless, corrosive gas, HCl, of pungent, suffocating odor. It is made in great quantities in the soda process, by the action of sulphuric acid on common salt. It has a great affinity for water, and the commercial article is a strong solution of the gas in water. It is a typical acid, and is an indispensable agent in commercial and general chemical work. Called also muriatic, & chlorhydric, acid .

Hydrochloride Hy`dro·chlo"ride noun (Chemistry) A compound of hydrochloric acid with a base; -- distinguished from a chloride , where only chlorine unites with the base.

Hydrocorallia Hy`dro·co·ral"li·a noun plural [ New Latin See Hydra , and Coral .] (Zoology) A division of Hydroidea, including those genera that secrete a stony coral, as Millepora and Stylaster . Two forms of zooids in life project from small pores in the coral and resemble those of other hydroids. See Millepora .

Hydrocyanate Hy`dro·cy"a·nate noun (Chemistry) See Hydrocyanide .

Hydrocyanic Hy`dro·cy·an"ic adjective [ Hydro- , 2 + anic : confer French hydrocyanique .] (Chemistry) Pertaining to, or derived from the combination of, hydrogen and cyanogen. Hydrocyanic acid (Chemistry) , a colorless, mobile, volatile liquid, HCN, having a characteristic peach-blossom odor. It is one of the most deadly poisons. It is made by the action of sulphuric acid on yellow prussiate of potassium (potassium ferrocyanide), and chemically resembles hydrochloric and hydrobromic acids. Called also prussic acid , hydrogen cyanide , etc.

Hydrocyanide Hy`dro·cy"a·nide noun (Chemistry) A compound of hydrocyanic acid with a base; -- distinguished from a cyanide , in which only the cyanogen so combines.

Hydrodynamic, Hydrodynamical Hy`dro·dy·nam"ic, Hy`dro·dy·nam"ic·al adjective [ Hydro- , 1 + dynamic , - ical : confer French hydrodynamique .] Pertaining to, or derived from, the dynamical action of water of a liquid; of or pertaining to water power. Hydrodynamic friction , friction produced by the viscosity of a liquid in motion.

Hydrodynamics Hy`dro·dy·nam"ics noun [ Hydro- , 1 + dynamics : confer French hydrodynamique .] That branch of the science of mechanics which relates to fluids, or, as usually limited, which treats of the laws of motion and action of nonelastic fluids, whether as investigated mathematically, or by observation and experiment; the principles of dynamics, as applied to water and other fluids. » The word is sometimes used as a general term, including both hydrostatics and hydraulics, together with pneumatics and acoustics. See Hydraulics .

Hydrodynamometer Hy`dro·dy`na·mom"e·ter noun [ Hydro- , 1 + dynamometer .] An instrument to measure the velocity of a liquid current by the force of its impact.

Hydroferricyanic Hy`dro·fer`ri·cy·an"ic noun [ Hydro- , 2 + ferricyanic .] (Chemistry) Pertaining to, or containing, or obtained from, hydrogen, ferric iron, and cyanogen; as, hydroferricyanic acid. See Ferricyanic .

Hydroferrocyanic Hy`dro·fer`ro·cy·an"ic adjective [ Hydro- , 2 + ferrocyanic .] (Chemistry) Pertaining to, or containing, or obtained from, hydrogen, ferrous iron, and cyanogen; as, hydroferrocyanic acid. See Ferrocyanic .

Hydrofluate Hy`dro·flu"ate noun (Chemistry) A supposed compound of hydrofluoris acid and a base; a fluoride. [ Archaic]

Hydrofluoric Hy`dro·flu·or"ic adjective [ Hydro- , 2 + fluoric .] (Chemistry) Pertaining to, or containing, hydrogen and fluorine; fluohydric; as, hydrofluoric acid. Hydrofluoric acid (Chemistry) , a colorless, mobile, volatile liquid, HF, very corrosive in its action, and having a strong, pungent, suffocating odor. It is produced by the action of sulphuric acid on fluorite, and is usually collected as a solution in water. It attacks all silicates, as glass or porcelain, is the agent employed in etching glass, and is preserved only in vessels of platinum, lead, caoutchouc, or gutta-percha.

Hydrofluosilicate Hy`dro·flu`o·sil"i·cate noun (Chemistry) A salt of hydrofluosilic acid; a silicofluoride. See Silicofluoride .

Hydrofluosilicic Hy`dro·flu`o·si·lic"ic adjective [ Hydro- , 2 + fluo rine + silicic .] (Chemistry) Pertaining to, or denoting, a compound consisting of a double fluoride of hydrogen and silicon; silicofluoric. See Silicofluoric .

Hydrogalvanic Hy`dro·gal·van"ic adjective [ Hydro- , 1 + galvanic .] Pertaining to, produced by, or consisting of, electricity evolved by the action or use of fluids; as, hydrogalvanic currents. [ R.]

Hydrogen Hy"dro·gen noun [ Hydro- , 1 + -gen : confer French hydrogène . So called because water is generated by its combustion. See Hydra .] (Chemistry) A gaseous element, colorless, tasteless, and odorless, the lightest known substance, being fourteen and a half times lighter than air (hence its use in filling balloons), and over eleven thousand times lighter than water. It is very abundant, being an ingredient of water and of many other substances, especially those of animal or vegetable origin. It may by produced in many ways, but is chiefly obtained by the action of acids (as sulphuric) on metals, as zinc, iron, etc. It is very inflammable, and is an ingredient of coal gas and water gas. It is standard of chemical equivalents or combining weights, and also of valence, being the typical monad. Symbol H. Atomic weight 1. » Although a gas, hydrogen is chemically similar to the metals in its nature, having the properties of a weak base. It is, in all acids, the base which is replaced by metals and basic radicals to form salts. Like all other gases, it is condensed by great cold and pressure to a liquid which freezes and solidifies by its own evaporation. It is absorbed in large quantities by certain metals (esp. palladium), forming alloy-like compounds; hence, in view of quasi-metallic nature, it is sometimes called hydrogenium . It is the typical reducing agent, as opposed to oxidizers, as oxygen, chlorine, etc. Bicarbureted hydrogen , an old name for ethylene. -- Carbureted hydrogen gas . See under Carbureted . -- Hydrogen dioxide , a thick, colorless liquid, H ₂ O ₂ , resembling water, but having a bitter, sour taste, produced by the action of acids on barium peroxide. It decomposes into water and oxygen, and is manufactured in large quantities for an oxidizing and bleaching agent. Called also oxygenated water . -- Hydrogen oxide , a chemical name for water, H...O. -- Hydrogen sulphide , a colorless inflammable gas, H ₂ S, having the characteristic odor of bad eggs, and found in many mineral springs. It is produced by the action of acids on metallic sulphides, and is an important chemical reagent. Called also sulphureted hydrogen .

Hydrogenate Hy"dro·gen·ate transitive verb [ imperfect & past participle Hydrogenated ; present participle & verbal noun Hydrogenating .] (Chemistry) To hydrogenize.

Hydrogenation Hy`dro·gen·a"tion noun (Chemistry) The act of combining with hydrogen, or the state of being so combined.

Hydrogenide Hy"dro·gen·ide noun (Chemistry) A binary compound containing hydrogen; a hydride. [ R.] See Hydride .

Hydrogenium Hy`dro·ge"ni·um noun [ New Latin See Hydrogen .] (Chemistry) Hydrogen; -- called also in view of its supposed metallic nature. Graham.

Hydrogenize Hy"dro·gen·ize transitive verb [ imperfect & past participle Hydrogenized ; present participle & verbal noun Hydrogenizing .] (Chemistry) To combine with hydrogen; to treat with, or subject to the action of, hydrogen; to reduce; -- contrasted with oxidize .

Hydrogenous Hy·drog"e·nous adjective Of or pertaining to hydrogen; containing hydrogen.

Hydrognosy Hy·drog"no·sy noun [ Hydro- , 1 + Greek ... knowledge.] A treatise upon, or a history and description of, the water of the earth.

Hydrogode Hy"drog·ode noun [ Hydrog en + Greek ... way. path.] (Electricity) The negative pole or cathode. [ R.]

Hydrographer Hy·drog"ra·pher noun One skilled in the hydrography; one who surveys, or draws maps or charts of, the sea, lakes, or other waters, with the adjacent shores; one who describes the sea or other waters. Boyle.

Hydrographic, Hydrographical Hy`dro·graph"ic, Hy`dro·graph"ic·al adjective Of or relating to hydrography.

Hydrography Hy·drog"ra·phy noun [ Hydro- , 1 + -graphy : confer French hydrographie .] 1. The art of measuring and describing the sea, lakes, rivers, and other waters, with their phenomena. 2. That branch of surveying which embraces the determination of the contour of the bottom of a harbor or other sheet of water, the depth of soundings, the position of channels and shoals, with the construction of charts exhibiting these particulars.

Hydroguret Hy·drog"u·ret noun [ From Hydrogen .] (Chemistry) A hydride. [ Obsolete]

Hydroid Hy"droid adjective [ Hydra + - oid .] (Zoology) Related to, or resembling, the hydra; of or pertaining to the Hydroidea. -- noun One of the Hydroideas.

Hydroidea Hy·droi"de·a noun plural [ New Latin See Hydra , and -oid .] (Zoology) An extensive order of Hydrozoa or Acalephæ. [ Written also Hydroida .] » This order includes the hydras and the free-swimming hydromedusæ, together with a great variety of marine attached hydroids, many of which grow up into large, elegantly branched forms, consisting of a vast number of zooids (hydranths, gonophores, etc.), united by hollow stems. All the zooids of a colony are produced from one primary zooid, by successive buddings. The Siphonophora have also been included in this order by some writers. See Gymnoblastea , Hydromedusa , Gonosome , Gonotheca .

Hydrokinetic Hy`dro·ki·net"ic adjective [ Hydro- , 1 + kinetic .] Of or pertaining to the motions of fluids, or the forces which produce or affect such motions; -- opposed to hydrostatic . Sir W. Thomson.

Hydrological Hy`dro·log"ic·al adjective Of or pertaining to hydrology.

Hydrologist Hy·drol"o·gist noun One skilled in hydrology.