hydrodynamometer 
An instrument for measuring the pressure ex- 
erted by a flowing liquid, and hence for deter- 
mining its velocity. 
Hydrcecia 1 (hi-dre'si-a), n. [NL. (Guon<V, 
1841), < Gr. Map (Mp-), water, + okof, a house. J 
A genus of noctuid moths, of the family AJXI- 
midie, having the male antennae not pectinate, 
the proboscis moderately long, and the legs 
Stout. There are many species, confined to Europe and 
North America. //. immani* is a hop-pest in the United 
States. H. micacea Is known as the rosy-rustic. 
hydroecia 2 , n. Plural of hydrcecium. 
hydroecial (hl-dre'si-al), a. [< hydrcecium + 
-al.] Having the character of a hydroacium. 
hydrOBCium (hi-dre'si-um), .; pi. hydrcecia 
(-a). [NL., < Gr. iitiap (v6p-), water, + O'IKOC, a 
house.] A sac attached to the swimming-bell 
or nectocalyx of certain oceanic hydrozoans, 
as calycophorans, into which the coenosarc may 
be retracted. See cut under Diphyidee. 
hydroelectric (hl'dro-e-lek'trik), a. [< Gr. 
vdup (viSp-), water, + E. electric.] Effecting the 
development of electricity by a certain use of 
steam: as, a tiydro-electric machine. Hydro- 
electric machine, a machine for generating electricity 
by the escape of steam under high pressure from a series of 
jets connected with a strong boiler, in which the steam is 
2936 
Hydrogastrum (hi-dro-gas'trum), n. [NL. 
(I)esvaux, 1810) (so called in allusion to the 
sack-like shape of the plants), < Gr. if up (Mp-), 
water, + ynariip, stomach.] A genus of fresh- 
It. idrogeno, < NL. lii/ilmi/i iiinm, hydrogen (so 
called because it is one of the elements of water, 
H 2 O), < Gr. iidup (i>op-), water, + -ft w/c, produ- 
cing: see -gen.'] Chemical symbol, H. Oneofthe 
elementary substances, existing as a colorless, 
tasteless, and inodorous gas. It is the lightest sub- 
stance known, and for that reason its specific gravity has 
been taken as the unit for comparing the specific gravity of 
gases, though air is the more commonly accepted standard. 
Under like conditions of temperature and pressure, hydro- 
gen is approximately 14. 4 times as light as an equal volume 
of air. Its combining weight is also less than that of any 
other element, and is therefore called unity, all the other 
atomic weights being expressed as multiples of it. It is 
but slightly soluble in water or any other liquid. Hydro- 
gen refracts light strongly, is extremely diffusible, and is 
absorbed or occluded in a remarkable manner by certain 
metals when they are heated, as though It formed a kind 
of alloy with them. Hydrogen burns in air with a very 
pale blue flame and intense heat, the sole product of com- 
bustion being water, BgO, which is the protoxid of hydro- 
gen. A mixture of two volumes of hydrogen and six of 
ah- or one of oxygen explodes violently when brought in 
contact with a flame or the electric spark. Hydrogen is 
not specifically poisonous when inhaled, but is fatal to 
life by preventing or hindering access of oxygen to the 
bluod. It is prepared by the action of dilute sulphuric 
acid on zinc or iron, by passing steam through a red-hot 
tube filled with iron turnings, by the electrolysis of water, 
and in a variety of other ways. Hydrogen occurs free in 
nature in small quantity in the emanations of volcanoes 
and of some oil-wells, but generally it is found only in 
its combinations, which are universally distributed. One 
ninth of the weight of water consists of hydrogen, and 
it is an indispensable element of every animal or vegeta- 
ble structure. It is a component of all acids, and its 
replacement in them by bases produces salts. In De- 
cember, 1877, and January, 1878, the French chemists 
Cailletet and Pictt succeeded in liquefying hydrogen, 
and the latter in solidifying it, by means of extreme pres- 
sure and cold produced in special forms of apparatus in- 
dependently invented by them. Arsenlureted hydro- 
gen. See arseniureied. Bicarbureted or heavy car- 
bureted hydrogen. Same as ethyUne. Hydrogen 
eWorld, Iodide, bromide, etc. Same as hydrochloric 
Artnstrong's Hydro-electric Machine. 
produced. The Jets of steam (which have to 
a cooling-box) are electrified by friction. 
through 
itive elec- 
tricity is collected by directing the steam upon a metal 
comb communicating with an Insulated conductor. 
hydroferricyanic (hl*dro-fer*i-si-an'ik), a. [< 
hydro(gen) + ferricyanic.] Compounded of 
hydrogen and ferricyanogen. Hydroferricyanic 
acid, HRFe2(CN)ij>, a strong hexavalent acid produced by 
the action of sulphuric acid and potassium ferricyanide. 
It forms brown deliquescent crystals. 
hydroferrocyanic (ui'dro-fer'o-si-an'ik), a. [< 
hydro(gen) + ferrocyanicj q. v.] Compounded of 
hydrogenandferrocyanogen Hydroferrocyanic 
acid, HiFefCJOe, a strong tetrabasic acid formed by the 
action of dilute acid on potassium ferrocyanide. 
hydrofluoboric (hi-dro-flo-o-bo'rik), a. [< hy- 
drogen) + Jlitoboric.] Same as fluoboric. 
hydrofluoric (hi"dr6-flij-or'ik), a. [< hydro(gen) 
+ _fluor(in) + -ic.] Consisting of fluorin and 
hydrogen. Alsofluohydric, fluorliydric Hydro- 
fluoric add, HF, an acid obtained by distilling a mix- 
ture of fluor-spar with sulphuric acid. It has an intense- 
ly irritating, suffocating odor, and a very strong affinity for 
water, acts energetically on glass, and is most destructive 
to animal matter. Also called fluoric acid. 
hydrofluosilicate (hi-dro-flo-o-sil'i-kat), . 
[< hydrojtnosilic(ic) + -ate.] A salt formed 
by the union of hydrofluosilicic acid with a 
base. 
hydrofluosilicic (hMrp-fl6''9-si-lis'ik), [< 
hydro(gen) + fluonilicic.] Consisting of hy- 
drofluoric and fluosilicic acid Hydrofluoslllcic 
acid, a compound acid (HgSiFfi) which is formed when 
silicon tetrafluoride is led into water. The saturated so- 
lution is a very acid, fuming, colorless liquid. 
hydrofuge (hi'dro-fuj), a. [< Gr. iiiup (i'Sp-), 
water, -F ii.fugare, put to flight, (fugere, flee: 
see fugitive."] In zool., shedding water; im- 
pervious to water, as the plumage of ducks, the 
pubescence of many insects, etc. 
hydrogalvanic (hi"dro-gal-van'ik), a. [< Gr. 
vSup (vdp-), water, + E. galvanic.] Pertaining 
to, consisting of, or produced by electricity 
evolved by the action or use of fluids: as, a 
lii/flrogalranie current. 
Hydrogastreae (hi-dro-gas'tre-e), TO. pi. [NL. 
(Endlicher and Unger, 1843), < Hydrogastrum 
+ -ere.'] A family of fresh-water alga?, allied 
closely to the F r auchcriacea>. The plants are small, 
terrestrial, and unicellular, in the form of an expanded 
sack or bag at the top, with the lower portion excessively 
and finely branched, but with the cavity continuous. It 
contains the single genus Hydrogaitrum. Also written 
Hydrogastridece (Lindley). 
, , , . 
acid, hydriotiic acid, etc. Hydrogen sulphid, or BUl- 
phureted hydrogen, HoS, a colorless inflammable gas 
having a sweetish taste and an exceedingly fetid smell 
resembling rotten eggs. It is extremely poisonous when 
inhaled. It has feeble acid properties, and its compounds 
with bases are called sulphuls. It occurs in the emana- 
tions of volcanoes, and is evolved when animal or vegeta- 
ble tissue containing sulphur decays. It also occurs in 
mineral springs, being liberated by the reduction of gyp- 
sum or other sulphates through the action of a microbe. 
Light carbureted hydrogen. See carbureted. Se- 
leniureted hydrogen. Same as hydroselenic acid (which 
see, under ttyarosflrnic). 
hydrogenate (hi'dro-jen-at), r. t. ; pret. and pp. 
hydrogenated, ppr. hydrogenating. [< hydrogen 
+ -ate 2 .] To cause to combine with hydrogen ; 
hydrogenize. 
hydrogenation (hi'dro-je-na'shpn), . [< hy- 
drogenate + -ion.] Tlie act of fiydrogenating, 
or the state of being hydrogenated. 
This hydrogetiation is easily effected by treating cuprous 
acetylene with hydrogen. 
W. n. BowdUch, Coal Gas, p. 284. 
hydrogeniferous (hi'dro-je-nif'e-rus), a. [< 
Hydrogen + L. ferre = E. bear 1 .] Containing 
hydrogen. 
hydrogenise, r. t. See hydrogenize. 
hydrogenium (hi-dro-je'ni-um), n. [NL. : see 
hydrogen.] 1. Hydrogen regarded as a metal; 
solidified hydrogen. 
Water is the rust of hydrogenimn, a true metal. 
J. R. Nichols, Fireside Science, p. 182. 
2. Hydrogen occluded by palladium. See oc- 
clusion. Graham. 
hydrogenize (hi'dro-jen-iz), v. t. ; pret. and pp. 
hydrogenized, ppr. hydrogenizing. [< hydrogen 
+ -ize.] To combine with hydrogen ; form a 
hydrogenous compound of. Also spelled hy- 
drogenise. 
Chlorine readily enters into reaction with a large num- 
ber of hydrogenized carbon compounds, and displaces the 
hydrogen more or less completely. Ki\cyc. Brit., V. 493. 
hydrogenous (hi-drpj'e-nus), a. [< hydrogen 
+ -ous.] 1. Pertaining to or containing hy- 
drogen. 2. Formed or produced by water: ap- 
plied to rocks formed by the action of water, 
in contradistinction to pyrogenous rocks, or 
those formed by the action of fire. 
hydrogeology (hi'dro-je-ol'o-ji), n. [< Gr. 
i'dup (vdp-), water, + E. geology.] The geology 
of water ; that part of geological science which 
has to do with the relations of water standing 
or flowing beneath the surface of the earth. 
The term is but little used, and rarely, if ever, with refer- 
ence to chemical changes brought about at depth by the 
agency of water, or in which water plays a part. 
Hydroidea 
hydrogiobertite (hi'dro-jo-biTt'it), . [< Gr. 
iifup (vfip-), water, -f- giolicrtite, q. v.] A hydrous 
carbonate of magnesium occurring in small 
spherical forms of a light-gray color at Vesuvi us. 
hydrognosy (hi-drog no-si), n. [= 8p. hidro- 
iinoxin, < Gr. vAup (iiup-), water, + } i'uaif. know- 
ledge.] A treatise on, or a history and descrip- 
tion of, the waters of the earth. 
hydrographer (hi-drog'ra-fer), n. [As liydroi/- 
raph-y + -cr 1 .] One who is versed in the sci- 
ence or engaged in the practice of hydrography ; 
specifically, one who has charge of hydrograpli- 
ic surveys and of other operations belonging to 
hydrography. 
In all coasts, what moon maketh full sea, and what way 
the tides and ebbes come and go, the hydrographer ought 
to record. D{, Pref. to Euclid (1570). 
He [Dr. Halley] likewise corrected the position of the 
coast of ISrazil. which had been very erroneously laid down 
by all former hydrographers. Atitton, Voyage, 1. 8. 
hydrographic (hi-dro-graf ' ik), a. [Anhydrogra- 
pli-y + -ic.] Of, pertaining to, or treating of 
hydrography: as, a hydrographic survey or 
treatise Hydrographic Office, an office of the Xavy 
Department of the United States, connected with the 
Bureau of Navigation. Its duties are to provide nautical 
charts, sailing directions, etc., for United States vessels 
and others. Its head is called the hydrographer. Other 
governments have similar bureaus. 
hydrographical (hi-dro-graf'i-kal), a. [< hy- 
drographtc + -al.] Same as hydrographic. 
The artificer must in the framing of his little engine 
have had due regard to all these, and consequently have 
had a comprehension of divers celestial and hydrographi- 
cal truths. Boyle, Works, VI. 724. 
hydrography (hi-drog'ra-fi), . [= F. hydro- 
graphic = sp. hidrografia = Pg. hydrographia 
= It. idrografia, < Gr. i>Sup (t'op-), water, -f 
-ypa^ia, < jyxtye/v, write.] 1. The science of the 
measurement and description of the sea, lakes, 
rivers, and other waters, with especial reference 
to their use for the purposes of navigation and 
commerce. It embraces pilotage and marine survey- 
ing, the determination of winds, currents, etc., as well as 
the art of forming charts exhibiting not only the sea- 
coast, gulfs, bays, Islands, promontories, channels, and their 
configuration and geographical position, but also the con- 
tour of the bottom of the sea and of harbors. It also 
embraces the study of the relation of changes in depth to 
their causes. 
Hydrographie requireth a perticular register of certain 
landmarks (where marks may be had) from the sea well 
able to be skried, in what points of the sea-compasse they 
appear, and what apparent form, situation, or bigness 
they have in respect of any dangerous place in the sea or 
tieer unto it assigned. Dee, Pref. to Euclid (1570). 
Setting downe alwayes with great care and diligence 
tnie obseruations & notes of al those countreys, islands, 
coasts of the sea. and other things requisite to the artes 
of nanigation and hydrographie. 
Hakluyt'l Voyages, I. 417. 
2. The distribution, character, and relations of 
bodies of water ; the condition of the earth or 
any part of it with respect to its seas, rivers, 
etc.: as, the hydrography of North America. 
hydroguret (ni-drog'u-ret), n. [< hydroy(cn) 
+ -wet.] A compound of hydrogen with a 
base. 
hydrogureted. hydroguretted (hi-drog'u-ret- 
ed),. [< hydrogiiret-r- -cd 2 .] Combined with 
hydrogen, as a metal or other base. 
hydrohematite, hydrohaematite (hi-dro- 
hem'a-tit), n. [< Gr. iioup (vip-), water, + E. 
hematite.] A hydrated iron sesquioxid, resem- 
bling the anhydrous iron sesquioxid hematite, 
particularly in its red streak. See titrgite. 
hydrohemdstat, hydrohaemostat (hi-dro- 
hem'o-stat), n. [< Gr. i<$up (vop-), water, + 
ai/ta, blood, + ararof, verbal adj. of iariivat, 
cause to stand: see static. Cf. hemostatic.] 
A device to arrest a hemorrhage, consisting 
of a bag through which cold water is passed, 
while it is pressed against the surface. 
hydroid (M'droid), a. and n. [< Gr. ii&poetifc, 
like water, < vSup (vdp-), water, + eliof, form. 
In defs. 2 and 3, as Hydra + -aid.] I. a. 1 . Like 
water; living in the water. 2. Resembling 
the hydra, or an animal of the genus Hydra. 
3. Pertaining to the Hydroida or Hydroidea, 
or having their characters : as, a hydroid hydro- 
zoan Hydroid stock, a stolon ; a hydrorhiza. 
II. w. One of the Hydroidea. 
In the Gulf of Mexico are communities of hydroids so 
organized that they seem to constitute but one animal. 
Pop. Set. Mo., XIII. 318. 
Calyptoblastic hydroids. See calyptoblastic. Tubu- 
lariau hydroids. See Gymnoblaetea. 
Hydroidea (hi-droi'de-a), n.pl. [NL. : see hy- 
droid.] An order or subclass of the class Hy- 
drozoa, approximately equivalent to Sydro- 
phora, and consisting of the eleutheroblastic, 
gymnoblastic, and calyptoblastic hydrozoans. 
