James Orr.

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done by the injection of tincture of iodine into the fbc, or by ibe passage of a fine
setoii or an iron wire (as proposed by Dr Simpson) tlirougb it.

IIYDROCETHALUS. Under this t«*rm, which literally means water in the head,
are included three distinct diseases— via., aonte hyd roueph'i las, cb runic hydroot-pb-
alus, and spurious hydrocephalus, or us Dr Mar»lmll UaU termed it, liydrocepbaloid

ll lUPlfcW Pii

By AeuU Uydroeephaltta is signified i'lflammatlon of the brain as it usually occurs
in scrofulous children. The name i;* not m good one. because it merely refers to a
* freqneut effect of tlie disease, aud not to it-^ cause or easeuco ; ai>d because, furtlier,
aBimilar effect may result from other morbid conditions: it ia, however, so nnl-
veraally adopted, tliat it would ho inexpedient to change it. Tiie direase is one of
M) datigcrons a nature, that It is of the greatest importance to detect it in its earii<-st
stage, and oven to look oat for iudicatioiis of its approach. The iMremooitory ? ymp-



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HjrdrocharidM» 'T Q 9

Hfdrochlorio * ^^



toras (trhicta, however, do not occur In all cams) consist chlefl j in % morbid ststo of the
Dnrrilivo tuiictious. Tbe appetite is capriclons, the tongne foul, the hmUi oCeuslTe,
t'.itt bcliy eiilariRMi, iuid ■omeiimes tender, oud the evucantious nnuatoml; aud the
child is lieavir, uiDguid, uud deitscted, aud becomes either fretful aiid irritable, or
drowsy aud lislles!^ Kestluss sleep, attended by ffriudiu^ of the teeth or moaning, a
f requeut suddeu screain, clenchiut; of the flsts, and a turning in of the thumb towards
the palm of the iiaud, are alou important premonitory warnings.

After these symptoms hnve lusted for some days, severe pain in the head come*
on ; it is generally of a sharp shooting clMiracter, recurring at Intervals, aud often
during sleep, aud causing the child to shriek in a very characteristic manner. Coma
or morbid arowsiness uow supervenes, aud the shrieking is replaced by moaniog.
Vomiting is a frequent coucomitaut of this stage of the disease. In this first



of hydrocephalas, which most commonly lasts two or three days, the pulse is rapM .
and the symptoms generally are those of excitement. In the second stage the pulse
becomes irr^^iar, variable, and often slow. General heaviness and stupor come ou.
The light, which auuoyed the child in the first stage» is no louser a source of annoy-
ance; the pupils become dilated, the power of sight becomes nnperfect or lost, aud
squinting is almost always to l>e obsorved. The little patient uow lies on bis t>ack
in a drowsy condition, and at this period spasmodic twitchings, oonmlsions or
paralysis may come on. I'he czcretious are passed unconscioosly. lliis second stace
may last a week or two, and is often attended by deceptive appearenceri of ameiiH-
meiit, the child not nufreqnently rt^ainiiig the ose of its senses for a day or two,
but then rela|ising hito a deci>er stupor than before. The symptoms In ttie third or
last stage, which may last only a few hours or may extend to a fbrtnight, are very
similar to those i:i the second, except that the pulse again becomes ferv rapid, beat-
ing sometimes so quickly that it can sparcely be counted, 'and gradually sets moro
and more weak till the patient expires. The Ciiaraclcristlc appearances after deatli
are softening of the central patt of the brain, wiih the effusion of serous fluid, usu-
ally to the extent of several oaucos, into the ventricles ; and a tnbercnhir deposit, in
the shupe of small gr:inuli*s, upon or between the membranes of the brain.

The only disorder with which acute hydrocephalus can easily be confounded Is
infantile remittent fever; but we have not space to uotice the various pomts which
enable us to diffcriiulnate between these two complaints. Acute hydrocephalus is
essentially a disease of childhood: it scarcely ever occurs after the twelfth year.
Half the cases that occur are In children between three aud six years of age.

As the treatment shoulil be left entirely to the physician, it is unnecessary to
notice it further, than to state that strong antiphlogistic remedies— such as cold to
the head, iei>ching, and active purging— ap,>lied in the tlr^t stage of th3 disease, yield
the most satisfactory results; yet under this treatment, three cases out of four are
lost

Chnmic Hifdroeephaltu is a perfectly distinct disease from acute hydrocephalus ;
while the latter is an inflammation, the former is a drop^^y. In chronic hydrocepha-
lus, a watery fluid collects withio the skull, before tlie bones have united to form tlio
soUd brain-case, and by pressure outwards causes the bones to separate, and in-
creases the size of the head sometimes to an enormous extent Thus Dr D^vid
Monro relates the case of aglrl six yean old whose head measured two feet four
In :he8 in circunifereuco. While the skull Is rapidly enlarging, the bones of the faces
grow no faster than usual, aud the great disproportion of size between the h<^ and
the face is at once diagnostic of the disease. This disorder sometimes commences
before birth, and almost always in early childhood, bi'fore the fontauelles tmd sutures
of the skull have closed. In some rare cas.^, it has occurred later, as, for example,
at seven or nine years old, and tlie closed sutures have opened under the augmenting
pre«sortt. When tlio sutures will not yield, death from pressure on the brain
speedily ensues. Most children with chronic hydrocephalus either recover or die in
infancy ; but a few survive, bearing their complaint to adult life, or even to old age.
Blindness, di^fness, palsy, and idiocy— one or more— are commonly associated witti
this disease, but oec:isionally the intellect aud senses are sufllcieutiy perfect for the
ordinary reqnirements of social life.

The tre«itmtnt may be attempted bv Internal remedies or by surgical appllsncea.
The medical treatment most worthy of trial consists in the administration of dlurw
sties, pui^tives, and uspedaily mercory, which may be given in the form of catomel



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It O Q Bf drocbarldM»

iVO Bydrochlorlo

hi miavte doees, and spplted as otetment eztemany. " The anrstcml expedients are
bandaging and pnncturitig the bead. The former has iu some case effected a per-
muneut care; the latter lias iu many cases certainly prolonged life, although the db^
taso hnf floally conanered. Neither of these means Is applicable after the bones of
the f^kiiU hare nuited.

This dii^ense occasionally occurs in adalt or in adrauced life, after enlargement
t>f the head has become Imposiable. Stapor, paralysis, and au inability or anwlll-
iiigness to opcak, are iu these cases the most prominent pymptoms. Dean Swift's
ileath was due to this disease, and It Is recorded that daring the last three years of
his life he remained In a state of silence, with few and slight exceptions.

Spuriont Hydrocephalus— ^tUe hjfdrccephaloid diaeam of Dr Marsholl Hall— re-
sembles acute hydrocephalus in many of Its symptoms, and bos often been mistaken
for it. Instead, however, of being an infliunmatory diseaae^it is a disease of de>
bllitv, and Is due to a deficient supply of blood to the brain. The following are, ao-
ccrdiugto Watson, the distinctive characters of this spurious hydrooephalos : the
pale, cool clieek; the half-shut, r^ardless eve; the iusensible pupil; tlie inter-
mptt-d, sighing respiration : and the state of tiie unclosed foutauelle. If the symp-
toms are those of acute hydrocephalus, the surface of the fontanelle will bo convex
and prominent ; while if they are due to spurious hydrocephalas^ and originate In
empthiess aud want of support, the fontanelle will be concave ana depressed. The
rcmeoles In this disease, which readily yields to treatment, are nourishing diet,
small doses of wine or even of brandy in arrow-root, decoction of bark, ammonia,
Ac

HTDROCHARI'DBiE, or Hydrocharlda'cen. See Axaohabis and Yalub-

KBBXA.

UTDKOCHLO'RIC ACID (symbol, JICl ; equivalent, 86 6) is one of the most
Important compounds in inorganic chemistry. If the two ga»es which enter into its
composition (liydrogen and chlorine) be mixed in eaual volumes, they will remain
without action upon each other, if kept iu the dark ; out as soon as ibej^are brought
Into direct sunlight, they unite with a loud explosion, and bvdrochtoric acid gas is
the result. The principal characters of tliis gas are that it is colorless. Intensely
acid, Irresplrable, and even when largely diluted, is very irritating to the lungs and
eyes, and very injurious to vegetation ; that it la heavier than air (its specific gravity
being 1*M74, air being taken at IDOO) ; that it can be condensed into a colorless
liquid ; that it is very soluble in water, and that it is neither combustible nor a sup-
porter of combustion. When altowed toeacape Into the air, it produces white fames,
by condensing tlie atmospheric moiatvre. If the air be previously dried, no soch
fumes are apparent.

The solutions of ttiis gas h& water form Ibe acid which was first known as Spirit
^SaUf then as Muriatic Addy^ and wbtoh is now termed Hydroehlorie or Chlorhydric
Add, A saturated watery soimtion of this gas at 4<P has a specific gravity of 1*21,
aud consists of t equivalent of the gas dissolved in 6 equivalents of water. It forms
a colorless, fuming liquid, which acts as a caustic. On nesting it, the gas Is evolved
abundantly until the temperature slightly exceeds Sit", when there distils over a
diluted selution having a speoiflc gra>aty of 1*1, and consisting of 1 equivalent of the
gas, and 14 equivalents of water. It Is to these solutions of nydrochloric acid that
tlie term hydrochloric add is far more commonly applied tban to the gas itself.
They possess the ordinary characters of an energetic acid, and neutralise the
strongest bases. The neutralisation is, however, not in consequence of the acid
combining with the oxide, bat is due to the simultaneous decomposition of the acid
and of tlie oxide, water and a metallio chloride being formed. If M represents the
metal, the reaction is expressed by the eqnotlou MO + HCl r= HOI -i- HO. All
metals wliich, at a red heat, decompose water, also decompose this acid, and cause
au evolution of hydrogen, the reaction being expressed as follows: M + HCi =
MCI + H.

Hydrochloric acid gas Is a common gaseoos volcanic product. Free hydrochloric
acid, in a very dilute form, Is aiso a constituent of the gastric juice of man and ani-
mals, and plays an essential part in the digestive process.

Commercial mitriaUe act»— to use the name employed br manufacturing chcm-
frts— is niade by heating, in iron cylinders, common salt (chloride of sodlnm) and
oil of vitrol (liydrated sulphuric acid), aud condensing the evolved gas iu water con-



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Bv?^^*^*f 794



Bfdrocyaaio

tnlaed iu a seriM of itonoware Woife*a Bottles (q. t.), the raactioo being ffipiamHI
by the eqaadoa :

iSa^m. OIlofVltroL ^J^XSdl^ Sulphate of Sodiu
CINa + HO.SOf = HCI + XaO,SO,

Tbia coramercial acfd may contain vnrfons imparities— 4is, for example, iron
(which given )t a brfgbt deep yellow color), the cliiorides of sodiam and a»euic —
tlie bitter beinr deri^ from the oil of viirl )1— sulphnric and salpimroos actdai,
chkniucL ^. : from which it can he parifled lo a ^rrcat extent by dilution and re-
di8ti.]atiou. **If pure,** says Professor Mil lor, •'the acid sliould leave no residue
wlieu 9miM>rated; on saturating it with ammouLa, it should give no precipitate of
pxide of iron ; sulphuretted hydroj^n should produce no turpidity In it, which
would be tlie caw if arrtenic. frv« chlorine, or sulphurous acid were presoui ,
and on dilallon with three or four times Its bulk of watur, no white cloud of sul-
phate of baryta should be produced hy the additiou of chloride of barinuu"

The presence of hydrochloric acid, or of the soluble chloride* in solution, mar
be detected by tlie addition of a few drops of a solution of nitrate of silver, which
occasions the formation of a white curdy precipitate oC cbloridj of silver, which is
iusolable In nitric acid, but dissolves in a solution of ammouia.

Liquid hydrochloric add (under the name of spirit of salt) was known to tho
alchemists. Hydrochloric acid gas was discovered by Priestley in 1772 ; and Davy,
iu 1810, ascertained that it was composed of chlorine and hydrogen.

In many of their properties, the analogous acids, hydrobronuc, hydrofluoric, and
bydriodic acids rasemble hydrochloric ucid.

HTDROCO'TTLE, a genus of umbelliferous plants, having simple nmbles, en.
tiro acste petals, and fruft of two flat orbicular carpel.% with flVe mare or less dis-
tinct threadlike ribs, and no vithe. The species are nnmi'ronf>, generally more or
loss sqnatic, widely distributed. One only is u native of Britain, £f. vuZ^om, which
grows in marshyplaces, and is called Marsh Penntwort from the orbicohir leavesi.
and sometimes White-rot, Sheeps-bane, Plowk-wort, &c., from a notion that It is
Injurious to sheep which eat It, causing foot-rot or flake- worm— effects rather to ba
ascribed to the marshy situations in which it grows.

HYDROCYA'NIC ACID (CsN.H or Cy, H), known also as Pmsslc Acid, from
its having been llrst obtained by Scheelo, in 1782. from the substance known as
Prussian or Beriln Blue, is of almost equal interest to the chemist, the physician, and
the loxicologirtt. We shall notice a) lis chemistry, (2) its medical value, and (S) its
action ns a poison, and its antidotes. •

1. It* ChenU^try.-^Fnve anhydrous hydrocyanic ackf is a limpid volatile fluid, with
a specific Kravity of 0-6»7 at 64P F. It boils at 80®, and solidiflea into a crystaniue
mass at 6° F. Its volaUliiy is so great, that if a drop be allowed 1 1 fall on a piece of

flass, part of the acid becomes froxsn by the cold produced by its own evaporation,
t possesses a vvv penetrating odor, resembling that of peach-blossoms or oil of
bitter almonds. It bums with a whitisli flame, reddens litmus paper slightly (its
acid properties ^ng feeble), and is very soluble in water and alcohol. Fwre hydro-
cyanic acid may be kepi unchanged If oxdnded from lleht, which occasions its
decomposition, and the formation of a brown substance known as paracyanoffcn.

Hydrocyanic acid is readily obtained by distillation from the kernels ofWtler
almouds, and many kinds of stone-fruit, from the leaves and flowere of various
plants, and from the juice of the tapioca plant {Jatropha manihoO- Anhydrous liy-
drocyaoic add is obtained by the reaction of concentrated hydrochloric acid on
cyanide of mercury.

The preparation of the dilute add is, however, of much greater practical ira-
portaucc. The London, Edinburgh, Dublin, and United Sfates pharmacopoeias
aeree in recommending that it should be obtained by the distillation of a mlxrure of
dilute sulphuric acid and ferrocyanlde of potassium (known also as ]>nissiate of
potash). The distillate should contain nothing but hydrocyanic acid and water, so
that, by the addition of more water, we can obtain an acid of any strength wo

? lease. Sometimes, however, a second, or even a third dlsiiUation is neci^sary.
'Ue dilate acid of the " Ph. Lond.*' conUins 2 per cent. ; that of the "Ph. Dub."



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*7Qf\ HydTocotfl*

* ^^ Hydrocyanic

rnthcr more ; that of the '*Ph. Edtn." contains 8*8 per cent ; while what In knoAvu
B9 SchceleV acid is very variable, bnt averagee 4 per cent, of the anhydrous acid.

The oi-dinary testa for hydrocyanic add are 1, the peculiar odor: 2, the nitrate of
silver test— there l>eing formed a white precipitate of cyanide ot silver, which is
polnble in boiling nitric acid ; S^ tlie formiition of Pmsslau blue, by adding to the
fluid under exaiiiiuotion n solution oCforoe proto- and per-salt of iron, by then satn-
rii^Dg with caustic pota»b, and finally adding an excess of hydrochloric acid ; when,
if hydrocyanic acid is present, we have a cimracteristic blue precipitate ; 4, the sul-
plint tc^t, which is tlie best, and most accurate that has yet oecu discovered. Let
tlie suspected liquid be acidulated wiih ii few drops of hydrochloric acid; place it in
a watch-glass, and let a .second watch-glass, moistened with a drop of a solution of
hvdrosulphate of ammonia, be inverted over it ; after a few minutes, let the upper

J^hiss be removed, and the moistened spot be gently dried. The whitish film which is
eft may consist merely of sulphur ; when hydrocyanic acid is present. It consists
of snipuocyauate of ammonia. Let this residue l>e treated with a drop of a weak
solution of perchloride of iron, when, if hydrocyanic acid was present, a blood-red
tint is developed, which disiiupears o\\ the addition of one or two drops of a solntiou
of corrosive sublimate. Q'his is known as Liebig's test

2. Its Medxchial (Tses.— We are Indebted to the Italians for the introduction of
hydrocyanic acid in the materia medicu ; and it was first employed at the beginniirg
of the present century. There are no cases in whicli it is so serviceable as iii those
affections of the stomach in which pain is a leadlns symptom, as in gastrodyuia,
water-brash, and in aises of intense vomiting. Uence it is often ufeful in English
clioleni, when opium has completely failed. In pulmonary diseases, it does not pro>
ducc tlie good effects Uiat were foi-merly ascribed to it ; but it is sometimes useful in
allaying spasmodic congh. It has been employed with advantage in chronic skin«
diseases, to allay pain and irritntiou. A mixture of two drachms of the dilute acid
(of 2 per CfUt. strength) with half a pint of rose-water, and half an ounce of rectified
spirit, forms a pood lotion. When given internally, the avcnige dose Is from 8 to 6
minims of tlie 2 pf^r cent, dilute acid, three or four times a day ; it must be admin-
istered in some mild vehicle, such as simple water, or orange-flower water.

8. Ab a PoMon.— Hydrocyanic acid isoneof our most energetic poisons, and is
fi-equently employed both in murder and suicide. When Vktmall poisonous dose
(about half a drachm of the 2 per cent, acid) has been taken, the first symptoms are.
weight and ])ain in the head, with confusion of thought giddiness, nausea (and
sometimes vomiting), a quick pulse, &ud loss of muscular power. If death result^
this is preceded by tetanic spasms and involuntary evacuations. When a large dose
has been taken (as from tialf an ounce to an ounce of the 2 per cent acid), the
symptoms may commence instantaneously, and it Is seldom that their appearance
is delayed beyond one or two minutes. " when," says Dr A. S. Taylor, ** the pa-
tient has been seen at tills perio<l, he has been perfectly insensible, the eyes fixed
and glistening, the pupils dilated and unaffected by light^ the limbs flaccid, the skin
cold and covered with a clammy perspiration ; tlicre la convulsive respiration at
long intervals, and the patient appears dead In the Intermediate time ; tne pulse Is
im})erceptible, and the respiration is slow, deep, gasping, and sometimes heaving or
sobbing." The patient survives for a longer or shorter period, according to the
dose. According to Dr Lonsdale, death lias occurred as early as the second^ and as
late as the/<?rfy-;I<iC/imiunte.

The parts ppecifically affected are, the brain and the spinal system. The affection
of tlie respiratory system seems to be due to the influence of the acid on those parts
of the nervous systs m from which the respiratory organs derive their nervous power.
The immediate cause of death is, In most cases, the obstruction of the respiration ;
bnt in some cjtses, the stoppage of the heart's action.

Where the fatal .".ctlon Is so rapid, antidotes are of comparatively little value.
Chlorine, ammonia, rxjld affusion, and artificial respiration arc the most important
agents ill the treatment. The first two should l>e used with great caution, and only
by the medical practitioner. Cold affusion on the head, neck, and down the spine
is a valuable remedy, and It is asserted that its efficacy Is almost certain, when it Is
employed before the convnlslve etflge of poisoning is over, and that it is often puc-
cessfnl even in the Ptiges of Instnsibility and paralysis. Artificial respiration (8<«e
Hespiration, Artificial) should never be omitted. Dr Pereira states, that he



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Hjdrodvnamios 'iT 9 6

once rccoTerod a rabbit by this mMoa only, after the coDTalMons had oeaaed, aud the
auiinal wan apparently dead.

HTDRODYNA'MICS treats of the laws of the motion of liquids ; the flow of
water from orifices and in pipes, canals, and rivers ; its oscillations or wave^ ; and its
resistance to bodies roovin^ through iL The tenn hydranlics is sotneliines apiriied
lo the same salijects, from the Greek word aWos, a pipe. The appilcatiou of water
Rs a moving power forms the practical port of the snbject. — In what f jIIows, tne
lllnstrations are mostly taken from the case ot water, hot the principles established
are tme of liqnids in general

jE^ux.— It three apertnres, D, C, B, are made at different heights in the side of a
vessel (fig. 1) filled with water, the liqald will poor ont with greater impetoosity from
C than from D, and from E than from C. The velocity does not increase in the sim-
ple ratio of the depth. The exact law of dependence is known as the theorem of
Torricelli ; the demonstration is too abstnise for introduction here, but the law il>
self is as follows : ** Particles of fluids <m isauitig from an aperture^ po saas the game
degree of velocity aa if thev had fallen freely^ in vacuo^ frmn a height equal to the dia-
tatiee of the ewrface of the fluid above the centre of the aperture.^ The jet from
C, for instance, has the same velocity as if the particles conipoi^ing it had fallen in
vacno from the level of the liqoid to C Now, the velocity acquired by a body in
failing is as the time of the fail ; but the space fallen through being as the equare
of the time, it follows that the velocity acquired is as the square root of the ppace
fallen througli. In the first second, a body falls 16 feet, and acquires a velocifjr of
BS feet If E, then, is 14 feet below the level, a jet from B flows at the rate of 9i
feet; and If D is at a depth of 4 feet, the velocity of tlie jet al J> will be half the ve-
locity of that at B, or 14 feet. In general, to find the velocity for any given height,
multiply the height by 8 x Si, and extract the square root of the product, lliis rule
may be expressed by the formula v = \/—fig/i^ in which r signifies the velocity of
the issue, g the velocity given by gravity in a second, or 38 feet, and h the height of
the water in the reflervoir above the orifice. This last qnantitx is technically called
the head or charge.



That this theory of the efflux of liqnids is correct, may be proved by experiment.
Let the vessel, MB (fig. 1), have an orifice situated as at o ; the water ought to issne
with the velocity that a body would acquire in fulling from M to thclevefof o. Now,
it is established in the doctrine of Projectiles (q. v.), that when a body Ia projeciea
vertically upwards with a certain velocity, it ascends to the same height from which
it would require to full in order to acquire that velocity. If the theory then, is cor-
rect, the jet onirlit to rise to the level uf the wiiter In the vessel at M. It ii# found
in reality to full short of this; but not more thuu can be accounted for by friction,
the resistance of the air, and the water that rests on tlie top in eudeavorijig to de-
scend. When the jet receives a very slight inclination, so that the returning



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HdrodTiiamlos



water f«l^ down br the side of the asoendlDe, ten hicheB of bead of water may be
made to give a jet of nine iuchea. A vtream oT water apootluff out horisontaltv, or
in any (n>iiqao direction. olwyK the laws of projecUleSt ana moves in a parabola ;
and the ranire of the jet lor any (riven velocity and angle of direction may bo calcu-
lated precisely as in projectiles. The range of horizontal jets la readily determined
by pmcticAl geometry. Ou AB describe a semicircle ; from B, the orifice of the jet,
draw DF perpendicnlar to AB, and make BK eqaul to twice DF ; then It can be
proved by the laws of falliuff bodies and the properties of the circle, that the jet
mQf>t meet BL in the point K. If BE is equal to AD, the perpendicnlar EH is equal



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