Hydraspididae 
the family ia limited to pleurodirous tortoises with threa 
phalanges to most of the digits, and no zygomatio but a 
parietomastoid arch. 
Hydraspis (hl-dras'pis), n. [NL. (Bell), < Gr. 
vaup (V>-)i water, + dcrmf, a shield.] The typi- 
cal genus of Hydraspididw, containing such tur- 
tles as the Brazilian H. maximiliani. 
hydrastine (hi-dvas'tin), . [< Hydrastis + 
-iHi a .j 1. An alkaloid found in the root of 
goldeuseal, Hydrastis Canadcnsis. It is crys- 
talline, odorless, and, on account of its insolu- 
bility, nearly tasteless. Alsohydr/istia. 2. A 
medicine used by eclectic physicians, which is 
a mixture of hydrastine, berberine, and resin. 
It is not to be confounded with the alkaloid hy- 
drastine. U. S. Dispensatory, 
Eydrastis (hl-dras'tis), n. [NL. (said to allude 
to the active properties of the juice), irreg. < 
Gr. vSup (tip-), water, + Spav, act: see drastic.] 
A genus of North American plants, of the natu- 
ral order Rammcnlacece. The only known species is 
H. Canaiensis, a small perennial herb, with a thick knot- 
ted rootstock, a single radical leaf, and a simple 2-leafed 
hairy stem which bears a solitary greenish-white flower. 
It is sometimes used in dyeing, and gives a beautiful yel- 
low color; hence the common names yellowroot, orange- 
root, goldenseal, and yellow pitccoon. 
hydratation (hi-dra-ta'shon), . [< hydrate + 
-atwn.~\ Same as hydration. 
hydrate (hi'drat), . [= P. hydrate; as Gr. i'Sap 
(vdp-), water, + -afei.J In chem., a compound 
of a class which may be regarded as formed 
upon the same type as water, or by the substi- 
tution of a metallic atom, or a basic radical, 
for one of the atoms of hydrogen in water: for 
example, HOH, water; KOH, potassium hy- 
drate; NH^OH, ammonium hydrate Croton- 
chloral hydrate. See crotan, 
hydrate (hi'drat), v. t. ; pret. and pp. hydrated, 
ppr. hydrating. [= F. hydratcr; as Gr. vSup 
(v6p-), water, + -ate 2 .] 1. To combine or im- 
pregnate with water. 2. To form into a hy- 
drate. 
To hydrate the milk and cane-sugar. 
Hueppe, Bacteriological Investigations (trans.), p. 90. 
Hydrated copper oxid. See copper. 
hydration (hi-dra'shon), n. [< hydrate + -ion.] 
The process of combining or impregnating with 
water, or the resulting condition. Also hydra- 
tation. 
The truths he [Prof. Graham] established respecting the 
hydration of compounds, the transpiration and the diffu- 
sion of liquids, . . . are all of them cardinal truths. 
H. Spencer, Study of Sociol., p. 226. 
- The solidity of the crust of the earth is limited by tem- 
perature and pressure under conditions of chemical con- 
stitution and hydration. Science, III. fill. 
hydraulic (hi-dra'lik), a. [< F. hydraulique = 
Sp. hidrdulico = Pg. hydraulico = It. idraulico 
(cf. D. G. hydranlisch = Dan. Sw. hydraulisJc), < 
L. hydraulicus, < Gr. v6pavMK6s, pertaining to the 
water-organ, < WpavXis, also vopai&oft & water- 
organ invented by an Egyptian named Ctesibius, 
lit. a water-pipe, < Map (vdp-), water, + aiAo?, a 
tube, pipe : see auletic.] Pertaining or relating 
to fluids in motion, or to hydraulics. See hydrau- 
lics. Hydraulic balance, a regulator or governor for a 
water-wheel. Hydraulic bear, a form of hydraulic press 
especially designed for punching rivet-holes or shearing 
iron. Hydraulic belt, a water-lifting device consisting 
of an endless belt fitted with caps or buckets, like the 
lifter of a grain-elevator. The lower part works on a 
wheel submerged in the water, and the buckets discharge 
their loads as they turn over an upper wheel. Hydrau- 
lic block, in a repairing-dock, a hydraulic lifting-press 
used as a substitute for a building-block under the keel 
of a vessel. It is adjustable as to height, and is used 
in straightening hogged or sagged vessels. Hydraulic 
blower, a form of bellows operated by a hydraulic motor. 
Hydraulic brush, a brush at the end of a long handle, 
the handle serving as a pipe to convey water to the brush 
from a hose, or acting as an aquapult or syringe. Hy- 
draulic buffer, a device for checking the recoil of a can- 
non. A piston-rod working in a cylinder filled with liquid 
is fastened to the top carriage. The liquid escapes through 
holes in the piston-head, but so slowly that it hinders the 
motion of the piston, thus acting as a buffer. Hydraulic 
cane, a rude form of pump, consisting of a tube having a 
valve opening inward at the lower end. By plunging the 
lower end in water and moving it rapidly up and down, the 
water can be made to rise in the tube. Hydraulic ce- 
ment. See cetnent. Hydraulic compressor, in a gun- 
carriage, a device to prevent the recoil of the piece, by 
receiving the impact upon a piston which forces liquid 
through holes i a diaphragm contained in a chamber. 
Hydraulic condenser, in gas- mtmvf., achamberin which 
gas from the retorts is cooled. Hydraulic crane, an ap- 
paratus for the raising or hoisting of loads on the princi- 
ple of the hydraulic press. Hydraulic dock, a float- 
ing dock. See cut under dock. Hydraulic elevator. 
See elevator. Hydraulic engine, a motor employing 
water under pressure as the source of power. Hydrau- 
lic engineering, a special branch of civil engineering 
concerned with the construction of water-works and 
hydraulic machinery, and the improvement and control 
of streams, navigable waters, and canals. Hydraulic 
gage, a kind of manometer used to record the pressure 
to a hydraulic press, pump, or engine. Hydraulic in- 
2933 
dicator, n gage to indicate the pressure of water. 
Hydraulic jack, a jack or lifting-apparatus operated 
by means of some liquid, 
usually oil, acting against a 
piston or plunger, the pres- 
sure on the liquid being pro- 
duced by a force-pump. 
Hydraulic lime, a species 
of lime that hardens in water, 
or which can be used for mak- 
ing hydraulic cement. Hy- 
draulic main, in gas-works, 
a large iron pipe partly filled 
with water, into which all the 
pipes bringing the raw gas 
from the retorts enter, dipping 
below the water to form a seal. 
The main serves as the first 
purifier of the gas for use, and 
also to convey the crude gas to 
the condenser. Hydraulic 
mill, a form of crushing-mill 
in which sugar-cane is steam- 
ed and pressed. Hydraulic 
Hydraulic jack. mining, a method of attacking 
J, cylinder; fi.s, ram; c, the gravel or auriferous de- 
space beneath the ram ; D. tritUS and bringing it into the 
plunger ; L, lever. sluices, invented and until re- 
cently extensively employed 
in California. It has also been introduced into other gold 
regions, notably those of Australia. The essential feature 
of the method is that the gravel is broken up and washed 
down into the head of the sluice by one or more powerful 
jets of water, thrown upon the bank and used in such a way 
as to furnish a current of sufficient velocity to carry the 
hydrencephalon 
motion of the column. The simplest form is shown in the 
figure. A is the supply-pipe ; E, the source of supply ; 
B, a hollow hall-valve seating upwardly, of less diameter 
than the inside diameter of A, and having a specific grav- 
ity enough greater than that of the water to enable it to 
overcome the pres- 
sure of the water 
in A, and fall away 
from its seat when 
the water is at rest. 
Hydraulic Mining. 
debris down into the sluice. The volume of water used is 
often very large, and the delivery from the pipe takes place 
with great velocity, the water being under a heavy head. 
The diameter of the stream as it issues from the pipe is 
sometimes as much as 6 or 8 inches, and the pressure 
from 100 to 200 feet. Hydraulic mortar. See mortar. 
Hydraulic motor, a motor driven by water-power. 
Hydraulic organ, an old form of organ in which water 
was used to regulate the pres- 
sure of the air. Also called 
hydrauluxm. Hydraulic 
pivot, in mach., a device by 
which a film of water is in- 
troduced below the end of a 
vertical axis to receive its 
weight, and relieve friction. 
Also called liquid bearing. 
E. H. Knight.- Hydraulic 
press, a press operated by 
the pressure of a liquid, under 
the action either of gravity 
or of some mechanical device, 
as a force-pump. It depends 
on the law of hydrostatics that 
any pressure upon a body of 
water is distributed equally 
in all directions throughout 
the whole mass, whatever its 
shape. In the more common 
forms the pressure of a piston 
upon a body of water in a cyl- 
inder of small area is distrib- 
uted through pipes or openings to a piston of larger area, 
the statical force being thus multiplied in the direct ratio 
of the areas of the pistons. Thus, if the diameter of the 
small piston A is one inch and of the larger piston C in 
cylinder B is one foot, 
the area of C will be 144 
times that of A ; and if 
a load of one ton is ap- 
plied to A, C will exert 
an upward statical 
force of 144 tons. The 
press properly so called 
is simply aframeplaced 
over the large plunger 
so that its upward 
thrust can be exerted 
against any material 
held in the frame. 
Section of Force-pump, Plunger, etc., 
of Hydraulic Press. 
Since the power of a hydraulic press can be exerted in any 
direction, it is used as the basis of a great number of ma- 
chines, as the hydraulic block, crane, jack, dock, hoist, lift, 
punch, rail-bender, and shears, and for the pressing of paper 
and other materials. The pressure is applied to the water 
in the smaller cylinder by the simple weight of a column of 
water, as in the hydrostatic bellows, or by a weight placed 
on the piston by means of a lever or a screw, etc. Also called 
hydrostatic prcs* and Dramah's prest. Hydraulic ram. 
(a) A self-contained and automatic pump operated partly 
by the pressure of a column of water in a pipe, and partly 
by the vis viva or living force acquired by intermittent 
D is an air-cham- 
ber connected at 
tlie bottom with A, 
and near the bot- 
tom with a much 
smaller discharge- Hydraulic Ram. 
pipe, F. C is a 
clack-valve. Water at first flows freely through A, by the 
ball-valve, and out at K. The column in A soon acquires 
velocity and consequent living force competent to lift 
the ball-valve to its seatj abruptly stopping the flow at B; 
but the living force of the column in A is now sufficient 
to overcome the back pressure upon, and lift, the valve C, 
and to force a part of the water from A into the chamber 
D. The discharge-pipe, F, being much smaller than A. 
the flow into D is temporarily much larger than the dis- 
charge from F. The confined air in D is therefore com- 
pressed. This pressure soon becomes sufficient to bring 
the liquid column in A to rest. The valve C then closes, 
but the pressure of the air in D still acts with diminishing 
force to expel water from D through F. The valve B now 
drops away from its seat, which again begins the series of 
operations, and so the action is indefinitely repeated. The 
water escaping from B is wasted. The machine can be 
used to raise water to a height many times greater than 
the available head. In another form this machine is 
adapted to draw water from a source independent of that 
which supplies the power for operating it. (6) The larger 
or lifting piston of a hydraulic press. Hydraulic valve, 
an inverted cup which is lowered over the upturned open 
end of a pipe, the edge of the cup being submerged in wa- 
ter, forming a water-seal, and closing the pipe against the 
passage of air or gases. E. H. Knight. 
hydraulical (hi-dra'li-kal), a. [< hydraulic + 
-al.~\ Same as hydraulic. [Bare.] 
I look not on a human body as on a watch or a hand- 
mill, . . . but as an hydraulical, or rather hydraulo-pneu- 
matical engine, that consists not only of solid and stable 
parts, but of fluids, and those in organical motion. 
Boyle, Works, p. 232. 
hydraulically (hl-dra'li-kal-i), adv. By hy- 
draulic means; according to hydraulic prin- 
ciples. 
hydraulician (hi-dra-lish'an), n. [< hydraulic 
+ -tan.] One who is skilled in hydraulics. 
hydraulicity (hi-dra-lis'i-ti), . [<t hydraulic + 
-ity.] The qualities necessary for making hy- 
draulic cement, or that kind of mortar which 
will harden under water; the property of set- 
ting under water. 
hydraulicking (hi-dra'li-king), . [< l/ydrau- 
lic(k) + -</!.] Hydraulic mining. See hy- 
draulic. 
hydraulicon (hi-dra'li-kon), )(. [< Gr. vdpavAiitov 
(so. opyavov), the hydraulic organ : see hydrau- 
lic.] Same as hydraulic organ (which see, under 
hydraulic). 
hydraulics (hi-dra'liks), n. [PI. of hydraulic: 
see -ics.~\ That branch of engineering science 
which treats of the motion of liquids, the laws 
by which it is regulated, and the application of 
these principles to machinery, marine engineer- 
ing, etc. 
hydraulist (hi-dra'list), n. [< hydraul(ic) + 
-*<.] One who is skilled in hydraulics. 
Meton (the astronomer and hydraulist). 
C. 0. Mutter, Manual of Archieol. (trans.), 111. 
hydrazine (hi'dra-zin), n. [< hydr(ogen) + 
<iz(ote) (?) + -ine 2 .] 1. Diamide, H 4 N 2 , a col- 
orless stable gas, soluble in water, having a pe- 
culiar odor and a strongly alkaline reaction. 
2. The general name of a class of bodies de- 
rived from this gas by replacing one or more 
of its hydrogen atoms by a compound radical : 
as, ethyl hydrazine, C2H B N 2 H3. 
hydremia. hydrsemia (hi-dre'mi-a), n. [NL., < 
Gr. vdup (vilp-), water, + a\fia, blood.] A watery- 
state of the blood ; an excess of plasma in the 
blood. 
hydremic, hydrsemic (hi-drem'ik), a. [< hydre- 
mia, hydr(emia, + -!>.] Pertaining to or of the 
nature of hydremia; affected with hydremia: 
as, a hydremic state of the blood. 
hydrencephal (hi-dren'se-fal), n. [< hydren- 
cephalus.] Same as liydrencepMlon. 
hydrencephalocele (hi-dren-sef 'a-lo-sel), . [< 
Gr. Map (vSp-), water, + f}'Kf^/.ci'brain, + KT/?.!/, 
tumor.] 1. A cephalocele in which the sac con- 
tains serous liquid and brain-substance. 2. A 
monster having this deformity. Dunalison. 
hydrencephaloid (hi-dren-sef 'a-loid), a. [< Gr. 
bftup (Mp-), water, + f/Kf^a/lof, brain, + tldof, 
form.] Same as h i/drocephaloid. 
hydrencephalon (iii-dren-sef'a-lon), n. A hy- 
drocephalous brain ; a case of hydroeephalus. 
Also hydrencephal. 
