C6H5NH·NH·SO3K + HCl + H2O = C6H5·NH·NH2·HCl + KHSO4.
Phenylhydrazine is a colourless oily liquid which turns brown on
exposure. It boils at 241° C., and melts at 17.5° C. It is slightly
soluble in water, and is strongly basic, forming well-defined salts
with acids. For the detection of substances containing the carbonyl
group (such for example as aldehydes and ketones) phenylhydrazine is a
very important reagent, since it combines with them with elimination
of water and the formation of well-defined hydrazones (see ALDEHYDES,
KETONES and SUGARS). It is a strong reducing agent; it precipitates
cuprous oxide when heated with Fehling's solution, nitrogen and
benzene being formed at the same time--C6H5·NH·NH2 + 2CuO = Cu2O + N2
+ H2O + C6H5. By energetic reduction of phenylhydrazine (e.g. by use
of zinc dust and hydrochloric acid), ammonia and aniline are
produced--C6H5NH·NH2 + 2H = C6H5NH2 + NH3. It is also a most important
synthetic reagent. It combines with aceto-acetic ester to form
phenylmethylpyrazolone, from which antipyrine (q.v.) may be obtained.
Indoles (q.v.) are formed by heating certain hydrazones with anhydrous
zinc chloride; while semicarbazides, pyrrols (q.v.) and many other
types of organic compounds may be synthesized by the use of suitable
phenylhydrazine derivatives.
HYDRAZONE, in chemistry, a compound formed by the condensation of a
hydrazine with a carbonyl group (see ALDEHYDES; KETONES).
HYDROCARBON, in chemistry, a compound of carbon and hydrogen. Many occur
in nature in the free state: for example, natural gas, petroleum and
paraffin are entirely composed of such bodies; other natural sources are
india-rubber, turpentine and certain essential oils. They are also
revealed by the spectroscope in stars, comets and the sun. Of artificial
productions the most fruitful and important is provided by the
destructive or dry distillation of many organic substances; familiar
examples are the distillation of coal, which yields ordinary lighting
gas, composed of gaseous hydrocarbons, and also coal tar, which, on
subsequent fractional distillations, yields many liquid and solid
hydrocarbons, all of high industrial value. For details reference should
be made to the articles wherein the above subjects are treated. From the
chemical point of view the hydrocarbons are of fundamental importance,
and, on account of their great number, and still greater number of
derivatives, they are studied as a separate branch of the science,
namely, organic chemistry.
See CHEMISTRY for an account of their classification, &c.
HYDROCELE (Gr. [Greek: hydôr], water, and [Greek: kêlê], tumour), the
medical term for any collection of fluid other than pus or blood in the
neighbourhood of the testis or cord. The fluid is usually serous.
Hydrocele may be congenital or arise in the middle-aged without apparent
cause, but it is usually associated with chronic orchitis or with
tertiary syphilitic enlargements. The hydrocele appears as a rounded,
fluctuating translucent swelling in the scrotum, and when greatly
distended causes a dragging pain. Palliative treatment consists in
tapping aseptically and removing the fluid, the patient afterwards
wearing a suspender. The condition frequently recurs and necessitates
radical treatment. Various substances may be injected; or the hydrocele
is incised, the tunica partly removed and the cavity drained.
HYDROCEPHALUS (Gr. [Greek: hydôr], water, and [Greek: kephalê], head), a
term applied to disease of the brain which is attended with excessive
effusion of fluid into its cavities. It exists in two forms--_acute_ and
_chronic hydrocephalus_. Acute hydrocephalus is another name for
tuberculous meningitis (see MENINGITIS).
_Chronic hydrocephalus_, or "water on the brain," consists in an
effusion of fluid into the lateral ventricles of the brain. It is not
preceded by tuberculous deposit or acute inflammation, but depends upon
congenital malformation or upon chronic inflammatory changes affecting
the membranes. When the disease is congenital, its presence in the
foetus is apt to be a source of difficulty in parturition. It is however
more commonly developed in the first six months of life; but it
occasionally arises in older children, or even in adults. The chief
symptom is the gradual increase in size of the upper part of the head
out of all proportion to the face or the rest of the body. Occurring at
an age when as yet the bones of the skull have not become welded
together, the enlargement may go on to an enormous extent, the Spaces
between the bones becoming more and more expanded. In a well-marked case
the deformity is very striking; the upper part of the forehead projects
abnormally, and the orbital plates of the frontal bone being inclined
forwards give a downward tilt to the eyes, which have also peculiar
rolling movements. The face is small, and this, with the enlarged head,
gives a remarkable aged expression to the child. The body is
ill-nourished, the bones are thin, the hair is scanty and fine and the
teeth carious or absent.
The average circumference of the adult head is 22 in., and in the normal
child it is of course much less. In chronic hydrocephalus the head of an
infant three months old has measured 29 in.; and in the case of the man
Cardinal, who died in Guy's Hospital, the head measured 33 in. In such
cases the head cannot be supported by the neck, and the patient has to
keep mostly in the recumbent posture. The expansibility of the skull
prevents destructive pressure on the brain, yet this organ is materially
affected by the presence of the fluid. The cerebral ventricles are
distended, and the convolutions are flattened. Occasionally the fluid
escapes into the cavity of the cranium, which it fills, pressing down
the brain to the base of the skull. As a consequence, the functions of
the brain are interfered with, and the mental condition is impaired. The
child is dull, listless and irritable, and sometimes imbecile. The
special senses become affected as the disease advances; sight is often
lost, as is also hearing. Hydrocephalic children generally sink in a few
years; nevertheless there have been instances of persons with this
disease living to old age. There are, of course, grades of the
affection, and children may present many of the symptoms of it in a
slight degree, and yet recover, the head ceasing to expand, and becoming
in due course firmly ossified.
Various methods of treatment have been employed, but the results are
unsatisfactory. Compression of the head by bandages, and the
administration of mercury with the view of promoting absorption of the
fluid, are now little resorted to. Tapping the fluid from time to time
through one of the spaces between the bones, drawing off a little, and
thereafter employing gentle pressure, has been tried, but rarely with
benefit. Attempts have also been made to establish a permanent drainage
between the interior of the lateral ventricle and the sub-dural space,
and between the lumbar region of the spine and the abdomen, but without
satisfactory results. On the whole, the plan of treatment which aims at
maintaining the patient's nutrition by appropriate food and tonics is
the most rational and successful. (E. O.*)
HYDROCHARIDEAE, in botany, a natural order of Monocotyledons, belonging
to the series Helobieae. They are water-plants, represented in Britain
by frog-bit (_Hydrocharis Morsusranae_) and water-soldier (_Stratiotes
aloïdes_). The order contains about fifty species in fifteen genera,
twelve of which occur in fresh water while three are marine: and
includes both floating and submerged forms. _Hydrocharis_ floats on the
surface of still water, and has rosettes of kidney-shaped leaves, from
among which spring the flower-stalks; stolons bearing new leaf-rosettes
are sent out on all sides, the plant thus propagating itself on the same
way as the strawberry. _Stratiotes aloïdes_ has a rosette of stiff
sword-like leaves, which when the plant is in flower project above the
surface; it is also stoloniferous, the young rosettes sinking to the
bottom at the beginning of winter and rising again to the surface in the
spring. _Vallisneria_ (eel-grass) contains two species, one native of
tropical Asia, the other inhabiting the warmer parts of both hemispheres
and reaching as far north as south Europe. It grows in the mud at the
bottom of fresh water, and the short stem bears a cluster of long,
narrow grass-like leaves; new plants are formed at the end of horizontal
runners. Another type is represented by _Elodea canadensis_ or
water-thyme, which has been introduced into the British Isles from North
America. It is a small, submerged plant with long, slender branching
stems bearing whorls of narrow toothed leaves; the flowers appear at the
surface when mature. _Halophila_, _Enhalus_ and _Thalassia_ are
submerged maritime plants found on tropical coasts, mainly in the Indian
and Pacific oceans; _Halophila_ has an elongated stem rooting at the
nodes; _Enhalus_ a short, thick rhizome, clothed with black threads
resembling horse-hair, the persistent hard-bast strands of the leaves;
_Thalassia_ has a creeping rooting stem with upright branches bearing
crowded strap-shaped leaves in two rows. The flowers spring from, or are
enclosed in, a spathe, and are unisexual and regular, with generally a
calyx and corolla, each of three members; the stamens are in whorls of
three, the inner whorls are often barren; the two to fifteen carpels
form an inferior ovary containing generally numerous ovules on often
large, produced, parietal placentas. The fruit is leathery or fleshy,
opening irregularly. The seeds contain a large embryo and no endosperm.
In _Hydrocharis_ (fig. 1), which is dioecious, the flowers are borne
above the surface of the water, have conspicuous white petals, contain
honey and are pollinated by insects. _Stratiotes_ has similar flowers
which come above the surface only for pollination, becoming submerged
again during ripening of the fruit. In _Vallisneria_ (fig. 2), which is
also dioecious, the small male flowers are borne in large numbers in
short-stalked spathes; the petals are minute and scale-like, and only
two of the three stamens are fertile; the flowers become detached before
opening and rise to the surface, where the sepals expand and form a
float bearing the two projecting semi-erect stamens. The female flowers
are solitary and are raised to the surface on a long, spiral stalk; the
ovary bears three broad styles, on which some of the large, sticky
pollen-grains from the floating male flowers get deposited, (fig. 3).
After pollination the female flower becomes drawn below the surface by
the spiral contraction of the long stalk, and the fruit ripens near the
bottom. _Elodea_ has polygamous flowers (that is, male, female and
hermaphrodite), solitary, in slender, tubular spathes; the male flowers
become detached and rise to the surface; the females are raised to the
surface when mature, and receive the floating pollen from the male. The
flowers of _Halophila_ are submerged and apetalous.
[Illustration: FIG. 1.--_Hydrocharis Morsusranae_--Frog-bit--male plant.
1, Female flower.
2, Stamens, enlarged.
3, Barren pistil of male flower, enlarged.
4, Pistil of female flower.
5, Fruit.
6, Fruit cut transversely.
7, Seed.
8, 9, Floral diagrams of male and female flowers respectively.
s, Rudimentary stamens.]
[Illustration: FIG. 2.--_Vallisneria spiralis_--Eel grass--about ¼
natural size. A, Female plant; B, Male plant.]
[Illustration: FIG. 3.]
The order is a widely distributed one; the marine forms are tropical or
subtropical, but the fresh-water genera occur also in the temperate
zones.
HYDROCHLORIC ACID, also known in commerce as "spirits of salts" and
"muriatic acid," a compound of hydrogen and chlorine. Its chemistry is
discussed under CHLORINE, and its manufacture under ALKALI MANUFACTURE.
HYDRODYNAMICS (Gr. [Greek: hydôr], water, [Greek: dynamis], strength),
the branch of hydromechanics which discusses the motion of fluids (see
HYDROMECHANICS).
HYDROGEN [symbol H, atomic weight 1.008 (o = 16)], one of the chemical
elements. Its name is derived from Gr. [Greek: hydôr], water, and
[Greek: gennaein], to produce, in allusion to the fact that water is
produced when the gas burns in air. Hydrogen appears to have been
recognized by Paracelsus in the 16th century; the combustibility of the
gas was noticed by Turquet de Mayenne in the 17th century, whilst in
1700 N. Lémery showed that a mixture of hydrogen and air detonated on
the application of a light. The first definite experiments concerning
the nature of hydrogen were made in 1766 by H. Cavendish, who showed
that it was formed when various metals were acted upon by dilute
sulphuric or hydrochloric acids. Cavendish called it "inflammable air,"
and for some time it was confused with other inflammable gases, all of
which were supposed to contain the same inflammable principle,
"phlogiston," in combination with varying amounts of other substances.
In 1781 Cavendish showed that water was the only substance produced when
hydrogen was burned in air or oxygen, it having been thought previously
to this date that other substances were formed during the reaction, A.
L. Lavoisier making many experiments with the object of finding an acid
among the products of combustion.
Hydrogen is found in the free state in some volcanic gases, in
fumaroles, in the carnallite of the Stassfurt potash mines (H. Precht,
_Ber._, 1886, 19, p. 2326), in some meteorites, in certain stars and
nebulae, and also in the envelopes of the sun. In combination it is
found as a constituent of water, of the gases from certain mineral
springs, in many minerals, and in most animal and vegetable tissues. It
may be prepared by the electrolysis of acidulated water, by the
decomposition of water by various metals or metallic hydrides, and by
the action of many metals on acids or on bases. The alkali metals and
alkaline earth metals decompose water at ordinary temperatures;
magnesium begins to react above 70° C., and zinc at a dull red heat. The
decomposition of steam by red hot iron has been studied by H.
Sainte-Claire Deville (_Comptes rendus_, 1870, 70, p. 1105) and by H.
Debray (ibid., 1879, 88, p. 1341), who found that at about 1500° C. a
condition of equilibrium is reached. H. Moissan (_Bull. soc. chim._,
1902, 27, p. 1141) has shown that potassium hydride decomposes cold
water, with evolution of hydrogen, KH + H2O = KOH + H2. Calcium hydride
or hydrolite, prepared by passing hydrogen over heated calcium,
decomposes water similarly, 1 gram giving 1 litre of gas; it has been
proposed as a commercial source (Prats Aymerich, _Abst. J.C.S._, 1907,
ii. p. 543), as has also aluminium turnings moistened with potassium
cyanide and mercuric chloride, which decomposes water regularly at 70°,
1 gram giving 1.3 litres of gas (Mauricheau-Beaupré, _Comptes rendus_,
1908, 147, p. 310). Strontium hydride behaves similarly. In preparing
the gas by the action of metals on acids, dilute sulphuric or
hydrochloric acid is taken, and the metals commonly used are zinc or
iron. So obtained, it contains many impurities, such as carbon dioxide,
nitrogen, oxides of nitrogen, phosphoretted hydrogen, arseniuretted
hydrogen, &c., the removal of which is a matter of great difficulty (see
E. W. Morley, _Amer. Chem. Journ._, 1890, 12, p. 460). When prepared by
the action of metals on bases, zinc or aluminium and caustic soda or
caustic potash are used. Hydrogen may also be obtained by the action of
zinc on ammonium salts (the nitrate excepted) (Lorin, _Comptes rendus_,
1865, 60, p. 745) and by heating the alkali formates or oxalates with
caustic potash or soda, Na2C2O4 + 2NaOH = H2 + 2Na2CO3. Technically it
is prepared by the action of superheated steam on incandescent coke (see
F. Hembert and Henry, _Comptes rendus_, 1885, 101, p. 797; A. Naumann
and C. Pistor, _Ber._, 1885, 18, p. 1647), or by the electrolysis of a
dilute solution of caustic soda (C. Winssinger, _Chem. Zeit._, 1898,
22, p. 609; "Die Elektrizitäts-Aktiengesellschaft," _Zeit. f.
Elektrochem._, 1901, 7, p. 857). In the latter method a 15% solution of
caustic soda is used, and the electrodes are made of iron; the cell is
packed in a wooden box, surrounded with sand, so that the temperature is
kept at about 70° C.; the solution is replenished, when necessary, with
distilled water. The purity of the gas obtained is about 97%.
Pure hydrogen is a tasteless, colourless and odourless gas of specific
gravity 0.06947 (air = 1) (Lord Rayleigh, _Proc. Roy. Soc._, 1893, p.
319). It may be liquefied, the liquid boiling at -252.68° C. to -252.84°
C., and it has also been solidified, the solid melting at -264° C. (J.
Dewar, _Comptes rendus_, 1899, 129, p. 451; _Chem. News_, 1901, 84, p.
49; see also LIQUID GASES). The specific heat of gaseous hydrogen (at
constant pressure) is 3.4041 (water = 1), and the ratio of the specific
heat at constant pressure to the specific heat at constant volume is
1.3852 (W. C. Röntgen, _Pogg. Ann._, 1873, 148, p. 580). On the spectrum
see SPECTROSCOPY. Hydrogen is only very slightly soluble in water. It
diffuses very rapidly through a porous membrane, and through some metals
at a red heat (T. Graham, _Proc. Roy. Soc._, 1867, 15, p. 223; H.
Sainte-Claire Deville and L. Troost, _Comptes rendus_, 1863, 56, p.
977). Palladium and some other metals are capable of absorbing large
volumes of hydrogen (especially when the metal is used as a cathode in a
water electrolysis apparatus). L. Troost and P. Hautefeuille (_Ann.
chim. phys._, 1874, (5) 2, p. 279) considered that a palladium hydride
of composition Pd2H was formed, but the investigations of C. Hoitsema
(_Zeit. phys. Chem._, 1895, 17, p. 1), from the standpoint of the phase
rule, do not favour this view, Hoitsema being of the opinion that the
occlusion of hydrogen by palladium is a process of continuous
absorption. Hydrogen burns with a pale blue non-luminous flame, but will
not support the combustion of ordinary combustibles. It forms a highly
explosive mixture with air or oxygen, especially when in the proportion
of two volumes of hydrogen to one volume of oxygen. H. B. Baker (_Proc.
Chem. Soc._, 1902, 18, p. 40) has shown that perfectly dry hydrogen will
not unite with perfectly dry oxygen. Hydrogen combines with fluorine,
even at very low temperatures, with great violence; it also combines
with carbon, at the temperature of the electric arc. The alkali metals
when warmed in a current of hydrogen, at about 360° C., form hydrides of
composition RH (R = Na, K, Rb, Cs), (H. Moissan, _Bull. soc. chim._,
1902, 27, p. 1141); calcium and strontium similarly form hydrides CaH2,
SrH2 at a dull red heat (A. Guntz, _Comptes rendus_, 1901, 133, p.
1209). Hydrogen is a very powerful reducing agent; the gas occluded by
palladium being very active in this respect, readily reducing ferric
salts to ferrous salts, nitrates to nitrites and ammonia, chlorates to
chlorides, &c.
For determinations of the volume ratio with which hydrogen and oxygen
combine, see J. B. Dumas, _Ann. chim. phys._, 1843 (3), 8, p. 189; O.
Erdmann and R. F. Marchand, ibid., p. 212; E. H. Keiser, _Ber._, 1887,
20, p. 2323; J. P. Cooke and T. W. Richards, _Amer. Chem. Journ._,
1888, 10, p. 191; Lord Rayleigh, _Chem. News_, 1889, 59, p. 147; E. W.
Morley, _Zeit. phys. Chem._, 1890, 20, p. 417; and S. A. Leduc,
_Comptes rendus_, 1899, 128, p. 1158.
Hydrogen combines with oxygen to form two definite compounds, namely,
water (q.v.), H2O, and hydrogen peroxide, H2O2, whilst the existence of
a third oxide, ozonic acid, has been indicated.
_Hydrogen peroxide_, H2O2, was discovered by L. J. Thénard in 1818
(_Ann. chim. phys._, 8, p. 306). It occurs in small quantities in the
atmosphere. It may be prepared by passing a current of carbon dioxide
through ice-cold water, to which small quantities of barium peroxide are
added from time to time (F. Duprey, _Comptes rendus_, 1862, 55, p. 736;
A. J. Balard, ibid., p. 758), BaO2 + CO2 + H2O = H2O2 + BaCO3. E. Merck
(_Abst. J.C.S._, 1907, ii., p. 859) showed that barium percarbonate,
BaCO4, is formed when the gas is in excess; this substance readily
yields the peroxide with an acid. Or barium peroxide may be decomposed
by hydrochloric, hydrofluoric, sulphuric or silicofluoric acids (L.
Crismer, _Bull. soc. chim._, 1891 (3), 6, p. 24; Hanriot, _Comptes
rendus_, 1885, 100, pp. 56, 172), the peroxide being added in
small quantities to a cold dilute solution of the acid. It is necessary
that it should be as pure as possible since the commercial product
usually contains traces of ferric, manganic and aluminium oxides,
together with some silica. To purify the oxide, it is dissolved in
dilute hydrochloric acid until the acid is neatly neutralized, the
solution is cooled, filtered, and baryta water is added until a faint
permanent white precipitate of hydrated barium peroxide appears; the
solution is now filtered, and a concentrated solution of baryta water is
added to the filtrate, when a crystalline precipitate of hydrated barium
peroxide, BaO2·H2O, is thrown down. This is filtered off and well washed
with water. The above methods give a dilute aqueous solution of hydrogen
peroxide, which may be concentrated somewhat by evaporation over
sulphuric acid in vacuo. H. P. Talbot and H. R. Moody (_Jour. Anal.
Chem._, 1892, 6, p. 650) prepared a more concentrated solution from the
commercial product, by the addition of a 10% solution of alcohol and
baryta water. The solution is filtered, and the barium precipitated by
sulphuric acid. The alcohol is removed by distillation _in vacuo_, and
by further concentration _in vacuo_ a solution may be obtained which
evolves 580 volumes of oxygen. R. Wolffenstein (_Ber._, 1894, 27, p.
2307) prepared practically anhydrous hydrogen peroxide (containing 99.1%
H2O2) by first removing all traces of dust, heavy metals and alkali from
the commercial 3% solution. The solution is then concentrated in an open
basis on the water-bath until it contains 48% H2O2. The liquid so
obtained is extracted with ether and the ethereal solution distilled
under diminished pressure, and finally purified by repeated
distillations. W. Staedel (_Zeit. f. angew. Chem._, 1902, 15, p. 642)
has described solid hydrogen peroxide, obtained by freezing concentrated
solutions.
Hydrogen peroxide is also found as a product in many chemical actions,
being formed when carbon monoxide and cyanogen burn in air (H. B.
Dixon); by passing air through solutions of strong bases in the presence
of such metals as do not react with the bases to liberate hydrogen; by
shaking zinc amalgam with alcoholic sulphuric acid and air (M. Traube,
_Ber._, 1882, 15, p. 659); in the oxidation of zinc, lead and copper in
presence of water, and in the electrolysis of sulphuric acid of such
strength that it contains two molecules of water to one molecule of
sulphuric acid (M. Berthelot, _Comptes rendus_, 1878, 86, p. 71).
The anhydrous hydrogen peroxide obtained by Wolffenstein boils at
84-85°C. (68 mm.); its specific gravity is 1.4996 (1.5° C.). It is very
explosive (W. Spring, _Zeit. anorg. Chem._, 1895, 8, p. 424). The
explosion risk seems to be most marked in the preparations which have
been extracted with ether previous to distillation, and J. W. Brühl
(_Ber._, 1895, 28, p. 2847) is of opinion that a very unstable, more
highly oxidized product is produced in small quantity in the process.
The solid variety prepared by Staedel forms colourless, prismatic
crystals which melt at -2° C.; it is decomposed with explosive violence
by platinum sponge, and traces of manganese dioxide. The dilute aqueous
solution is very unstable, giving up oxygen readily, and decomposing
with explosive violence at 100° C. An aqueous solution containing more
than 1.5% hydrogen peroxide reacts slightly acid. Towards lupetidin [aa'
dimethyl piperidine, C5H9N(CH3)2] hydrogen peroxide acts as a dibasic
acid (A. Marcuse and R. Wolffenstein, _Ber._, 1901, 34, p. 2430; see
also G. Bredig, _Zeit. Electrochem._, 1901, 7, p. 622). Cryoscopic
determinations of its molecular weight show that it is H2O2. [G.
Carrara, _Rend. della Accad. dei Lincei_, 1892 (5), 1, ii. p. 19; W. R.
Orndorff and J. White, _Amer. Chem. Journ._, 1893, 15, p. 347.] Hydrogen
peroxide behaves very frequently as a powerful oxidizing agent; thus
lead sulphide is converted into lead sulphate in presence of a dilute
aqueous solution of the peroxide, the hydroxides of the alkaline earth
metals are converted into peroxides of the type MO2·8H2O, titanium
dioxide is converted into the trioxide, iodine is liberated from
potassium iodide, and nitrites (in alkaline solution) are converted into
acid-amides (B. Radziszewski, _Ber._, 1884, 17, p. 355). In many cases
it is found that hydrogen peroxide will only act as an oxidant when in
the presence of a catalyst; for example, formic, glycollic, lactic,
tartaric, malic, benzoic and other organic acids are readily oxidized in
the presence of ferrous sulphate (H. J. H. Fenton, _Jour. Chem. Soc._,
1900, 77, p. 69), and sugars are readily oxidized in the presence of
ferric chloride (O. Fischer and M. Busch, _Ber._, 1891, 24, p. 1871). It
is sought to explain these oxidation processes by assuming that the
hydrogen peroxide unites with the compound undergoing oxidation to form
an addition compound, which subsequently decomposes (J. H. Kastle and A.
S. Loevenhart, _Amer. Chem. Journ._, 1903, 29, pp. 397, 517). Hydrogen
peroxide can also react as a reducing agent, thus silver oxide is
reduced with a rapid evolution of oxygen. The course of this reaction
can scarcely be considered as definitely settled; M. Berthelot considers
that a higher oxide of silver is formed, whilst A. Baeyer and V.
Villiger are of opinion that reduced silver is obtained [see _Comptes
rendus_, 1901, 133, p. 555; _Ann. Chim. Phys._, 1897 (7), 11, p. 217,
and Ber., 1901, 34, p. 2769]. Potassium permanganate, in the presence of
dilute sulphuric acid, is rapidly reduced by hydrogen peroxide, oxygen
being given off, 2KMnO4 + 3H2SO4 + 5H2O2 = K2SO4 + 2MnSO4 + 8H2O + 5O2.
Lead peroxide is reduced to the monoxide. Hypochlorous acid and its
salts, together with the corresponding bromine and iodine compounds,
liberate oxygen violently from hydrogen peroxide, giving hydrochloric,
hydrobromic and hydriodic acids (S. Tanatar, _Ber._, 1899, 32, p. 1013).
On the constitution of hydrogen peroxide see C. F. Schönbein, _Jour.
prak. Chem._, 1858-1868; M. Traube, _Ber._, 1882-1889; J. W. Brühl,
_Ber._, 1895, 28, p. 2847; 1900, 33, p. 1709; S. Tanatar, _Ber._,
1903, 36, p. 1893.
Hydrogen peroxide finds application as a bleaching agent, as an
antiseptic, for the removal of the last traces of chlorine and sulphur
dioxide employed in bleaching, and for various quantitative
separations in analytical chemistry (P. Jannasch, _Ber._, 1893, 26, p.
2908). It may be estimated by titration with potassium permanganate in
acid solution; with potassium ferricyanide in alkaline solution,
2K3Fe(CN)6 + 2KOH + H2O2 = 2K4Fe(CN)6 + 2H2O + O2; or by oxidizing
arsenious acid in alkaline solution with the peroxide and back
titration of the excess of arsenious acid with standard iodine (B.
Grützner, _Arch. der Pharm._, 1899, 237, p. 705). It may be recognized
by the violet coloration it gives when added to a very dilute solution
of potassium bichromate in the presence of hydrochloric acid; by the
orange-red colour it gives with a solution of titanium dioxide in
concentrated sulphuric acid; and by the precipitate of Prussian blue
formed when it is added to a solution containing ferric chloride and
potassium ferricyanide.
_Ozonic Acid_, H2O4. By the action of ozone on a 40% solution of
potassium hydroxide, placed in a freezing mixture, an orange-brown
substance is obtained, probably K2O4, which A. Baeyer and V. Villiger
(_Ber._, 1902, 35, p. 3038) think is derived from ozonic acid,
produced according to the reaction O3 + H2O = H2O4.
HYDROGRAPHY (Gr. [Greek: hydôr], water, and [Greek: graphein], to
write), the science dealing with all the waters of the earth's surface,
including the description of their physical features and conditions; the
preparation of charts and maps showing the position of lakes, rivers,
seas and oceans, the contour of the sea-bottom, the position of
shallows, deeps, reefs and the direction and volume of currents; a
scientific description of the position, volume, configuration, motion
and condition of all the waters of the earth. See also SURVEYING
(Nautical) and OCEAN AND OCEANOGRAPHY. The Hydrographic Department of
the British Admiralty, established in 1795, undertakes the making of
charts for the admiralty, and is under the charge of the hydrographer to
the admiralty (see CHART).
HYDROLYSIS (Gr. [Greek: hydôr], water, [Greek: luein], to loosen), in
chemistry, a decomposition brought about by water after the manner shown
in the equation R·X + H·OH = R·H + X·OH. Modern research has proved that
such reactions are not occasioned by water acting as H2O, but really by
its ions (hydrions and hydroxidions), for the velocity is proportional
(in accordance with the law of chemical mass action) to the
concentration of these ions. This fact explains the so-called
"catalytic" action of acids and bases in decomposing such compounds as
the esters. The term "saponification" (Lat. _sapo_, soap) has the same
meaning, but it is more properly restricted to the hydrolysis of the
fats, i.e. glyceryl esters of organic acids, into glycerin and a soap
(see CHEMICAL ACTION).