It is usual to reckon the difference of pressure at the inlet and outlet of a fan in inches of water-column. One inch of water-column = 64.4 ft. of air at average atmospheric pressure = 5.2℔ per sq. ft.Roughly the pressure-head produced in a fan without means of utilizing the kinetic energy of discharge would be v2/2g ft. of air, or 0.00024 v2in. of water, where v is the velocity of the tips of the fan blades in feet per second. If d is the diameter of the fan and t the width at the external circumference, then πdt is the discharge area of the fan disk. If Q is the discharge in cub. ft. per sec., u = Q/π dt is the radial velocity of discharge which is numerically equal to the discharge per square foot of outlet in cubic feet per second. As both the losses in the fan and the work done are roughly proportional to u2in fans of the same type, and are also proportional to the gauge pressure p, then if the losses are to be a constant percentage of the work done u may be taken proportional to √p. In ordinary cases u = about 22 √p. The width t of the fan is generally from 0.35 to 0.45d. Hence if Q is given, the diameter of the fan should be:—For t = 0.35d, d = 0.20 √ (Q / √p)For t = 0.45d, d = 0.18 √ (Q / √p)If p is the pressure difference in the fan in inches of water, and N the revolutions of fan,v = πdN/60ft. per sec.N = 1230 √ p/drevs. per min.As the pressure difference is small, the work done in compressing the air is almost exactly 5.2pQ foot-pounds per second. Usually, however, the kinetic energy of the air in the discharge pipe is not inconsiderable compared with the work done in compression. If w is the velocity of the air where the discharge pressure is measured, the air carries away w2/2g foot-pounds per ℔ of air as kinetic energy. In Q cubic feet or 0.0807Q ℔ the kinetic energy is 0.00125 Qw2foot-pounds per second.The efficiency of fans is reckoned in two ways. If B.H.P. is the effective horse-power applied at the fan shaft, then the efficiency reckoned on the work of compression isη = 5.2pQ / 550 B.H.P.On the other hand, if the kinetic energy in the delivery pipe is taken as part of the useful work the efficiency isη2= (5.2 pQ + 0.00125 Qw2) / 550 B.H.P.Although the theory above is a rough one it agrees sufficiently with experiment, with some merely numerical modifications.An extremely interesting experimental investigation of the action of centrifugal fans has been made by H. Heenan and W. Gilbert (Proc. Inst. Civ. Eng.vol. 123, p. 272). The fans delivered through an air trunk in which different resistances could be obtained by introducing diaphragms with circular apertures of different sizes. Suppose a fan run at constant speed with different resistances and the compression pressure, discharge and brake horse-power measured. The results plot in such a diagram as is shown in fig. 213. The less the resistance to discharge, that is the larger the opening in the air trunk, the greater the quantity of air discharged at the given speed of the fan. On the other hand the compression pressure diminishes. The curve marked total gauge is the compression pressure + the velocity head in the discharge pipe, both in inches of water. This curve falls, but not nearly so much as the compression curve, when the resistance in the air trunk is diminished. The brake horse-power increases as the resistance is diminished because the volume of discharge increases very much. The curve marked efficiency is the efficiency calculated on the work of compression only. It is zero for no discharge, and zero also when there is no resistance and all the energy given to the air is carried away as kinetic energy. There is a discharge for which this efficiency is a maximum; it is about half the discharge which there is when there is no resistance and the delivery pipe is full open. The conditions of speed and discharge corresponding to the greatest efficiency of compression are those ordinarily taken as the best normal conditions of working. The curve marked total efficiency gives the efficiency calculated on the work of compression and kinetic energy of discharge. Messrs Gilbert and Heenan found the efficiencies of ordinary fans calculated on the compression to be 40 to 60% when working at about normal conditions.Fig. 213.Taking some of Messrs Heenan and Gilbert’s results for ordinary fans in normal conditions, they have been found to agree fairly with the following approximate rules. Let pcbe the compression pressure and q the volume discharged per second per square foot of outlet area of fan. Then the total gauge pressure due to pressure of compression and velocity of discharge is approximately: p = pc+ 0.0004q2in. of water, so that if pcis given, p can be found approximately. The pressure p depends on the circumferential speed v of the fan disk—p = 0.00025 v2in. of waterv = 63 √p ft. per sec.The discharge per square foot of outlet of fan is—q = 15 to 18 √p cub. ft. per sec.The total discharge isQ = π dt q = 47 to 56 dt √pFort = .35d, d = 0.22 to 0.25 √(Q / √p) ft.t = .45d, d = 0.20 to 0.22 √(Q / √p) ft.N = 1203 √ p/d.These approximate equations, which are derived purely from experiment, do not differ greatly from those obtained by the rough theory given above. The theory helps to explain the reason for the form of the empirical results.
It is usual to reckon the difference of pressure at the inlet and outlet of a fan in inches of water-column. One inch of water-column = 64.4 ft. of air at average atmospheric pressure = 5.2℔ per sq. ft.
Roughly the pressure-head produced in a fan without means of utilizing the kinetic energy of discharge would be v2/2g ft. of air, or 0.00024 v2in. of water, where v is the velocity of the tips of the fan blades in feet per second. If d is the diameter of the fan and t the width at the external circumference, then πdt is the discharge area of the fan disk. If Q is the discharge in cub. ft. per sec., u = Q/π dt is the radial velocity of discharge which is numerically equal to the discharge per square foot of outlet in cubic feet per second. As both the losses in the fan and the work done are roughly proportional to u2in fans of the same type, and are also proportional to the gauge pressure p, then if the losses are to be a constant percentage of the work done u may be taken proportional to √p. In ordinary cases u = about 22 √p. The width t of the fan is generally from 0.35 to 0.45d. Hence if Q is given, the diameter of the fan should be:—
For t = 0.35d, d = 0.20 √ (Q / √p)For t = 0.45d, d = 0.18 √ (Q / √p)
If p is the pressure difference in the fan in inches of water, and N the revolutions of fan,
As the pressure difference is small, the work done in compressing the air is almost exactly 5.2pQ foot-pounds per second. Usually, however, the kinetic energy of the air in the discharge pipe is not inconsiderable compared with the work done in compression. If w is the velocity of the air where the discharge pressure is measured, the air carries away w2/2g foot-pounds per ℔ of air as kinetic energy. In Q cubic feet or 0.0807Q ℔ the kinetic energy is 0.00125 Qw2foot-pounds per second.
The efficiency of fans is reckoned in two ways. If B.H.P. is the effective horse-power applied at the fan shaft, then the efficiency reckoned on the work of compression is
η = 5.2pQ / 550 B.H.P.
On the other hand, if the kinetic energy in the delivery pipe is taken as part of the useful work the efficiency is
η2= (5.2 pQ + 0.00125 Qw2) / 550 B.H.P.
Although the theory above is a rough one it agrees sufficiently with experiment, with some merely numerical modifications.
An extremely interesting experimental investigation of the action of centrifugal fans has been made by H. Heenan and W. Gilbert (Proc. Inst. Civ. Eng.vol. 123, p. 272). The fans delivered through an air trunk in which different resistances could be obtained by introducing diaphragms with circular apertures of different sizes. Suppose a fan run at constant speed with different resistances and the compression pressure, discharge and brake horse-power measured. The results plot in such a diagram as is shown in fig. 213. The less the resistance to discharge, that is the larger the opening in the air trunk, the greater the quantity of air discharged at the given speed of the fan. On the other hand the compression pressure diminishes. The curve marked total gauge is the compression pressure + the velocity head in the discharge pipe, both in inches of water. This curve falls, but not nearly so much as the compression curve, when the resistance in the air trunk is diminished. The brake horse-power increases as the resistance is diminished because the volume of discharge increases very much. The curve marked efficiency is the efficiency calculated on the work of compression only. It is zero for no discharge, and zero also when there is no resistance and all the energy given to the air is carried away as kinetic energy. There is a discharge for which this efficiency is a maximum; it is about half the discharge which there is when there is no resistance and the delivery pipe is full open. The conditions of speed and discharge corresponding to the greatest efficiency of compression are those ordinarily taken as the best normal conditions of working. The curve marked total efficiency gives the efficiency calculated on the work of compression and kinetic energy of discharge. Messrs Gilbert and Heenan found the efficiencies of ordinary fans calculated on the compression to be 40 to 60% when working at about normal conditions.
Taking some of Messrs Heenan and Gilbert’s results for ordinary fans in normal conditions, they have been found to agree fairly with the following approximate rules. Let pcbe the compression pressure and q the volume discharged per second per square foot of outlet area of fan. Then the total gauge pressure due to pressure of compression and velocity of discharge is approximately: p = pc+ 0.0004q2in. of water, so that if pcis given, p can be found approximately. The pressure p depends on the circumferential speed v of the fan disk—
p = 0.00025 v2in. of waterv = 63 √p ft. per sec.
p = 0.00025 v2in. of water
v = 63 √p ft. per sec.
The discharge per square foot of outlet of fan is—
q = 15 to 18 √p cub. ft. per sec.
The total discharge is
Q = π dt q = 47 to 56 dt √p
For
t = .35d, d = 0.22 to 0.25 √(Q / √p) ft.t = .45d, d = 0.20 to 0.22 √(Q / √p) ft.
N = 1203 √ p/d.
These approximate equations, which are derived purely from experiment, do not differ greatly from those obtained by the rough theory given above. The theory helps to explain the reason for the form of the empirical results.
(W. C. U.)
1Except where other units are given, the units throughout this article are feet, pounds, pounds per sq. ft., feet per second.2Journal de M. Liouville, t. xiii. (1868);Mémoires de l’Académie, des Sciences de l’Institut de France, t. xxiii., xxiv. (1877).3The following theorem is taken from a paper by J. H. Cotterill, “On the Distribution of Energy in a Mass of Fluid in Steady Motion,”Phil. Mag., February 1876.4The discharge per second varied from .461 to .665 cub. ft. in two experiments. The coefficient .435 is derived from the mean value.5“Formulae for the Flow of Water in Pipes,”Industries(Manchester, 1886).6Boussinesq has shown that this mode of determining the corrective factor α is not satisfactory.7In general, because when the water leaves the turbine wheel it ceases to act on the machine. If deflecting vanes or a whirlpool are added to a turbine at the discharging side, then v1may in part depend on v2, and the statement above is no longer true.
1Except where other units are given, the units throughout this article are feet, pounds, pounds per sq. ft., feet per second.
2Journal de M. Liouville, t. xiii. (1868);Mémoires de l’Académie, des Sciences de l’Institut de France, t. xxiii., xxiv. (1877).
3The following theorem is taken from a paper by J. H. Cotterill, “On the Distribution of Energy in a Mass of Fluid in Steady Motion,”Phil. Mag., February 1876.
4The discharge per second varied from .461 to .665 cub. ft. in two experiments. The coefficient .435 is derived from the mean value.
5“Formulae for the Flow of Water in Pipes,”Industries(Manchester, 1886).
6Boussinesq has shown that this mode of determining the corrective factor α is not satisfactory.
7In general, because when the water leaves the turbine wheel it ceases to act on the machine. If deflecting vanes or a whirlpool are added to a turbine at the discharging side, then v1may in part depend on v2, and the statement above is no longer true.
HYDRAZINE(Diamidogen), N2H4or H2N·NH2, a compound of hydrogen and nitrogen, first prepared by Th. Curtius in 1887 from diazo-acetic ester, N2CH·CO2C2H5. This ester, which is obtained by the action of potassium nitrate on the hydrochloride of amidoacetic ester, yields on hydrolysis with hot concentrated potassium hydroxide an acid, which Curtius regarded as C3H3N6(CO2H)3, but which A. Hantzsch and O. Silberrad (Ber., 1900, 33, p. 58) showed to be C2H2N4(CO2H)2, bisdiazoacetic acid. On digestion of its warm aqueous solution with warm dilute sulphuric acid, hydrazine sulphate and oxalic acid are obtained. C. A. Lobry de Bruyn (Ber., 1895, 28, p. 3085) prepared free hydrazine by dissolving its hydrochloride in methyl alcohol and adding sodium methylate; sodium chloride was precipitated and the residual liquid afterwards fractionated under reduced pressure. It can also be prepared by reducing potassium dinitrososulphonate in ice cold water by means of sodium amalgam:—
P. J. Schestakov (J. Russ. Phys. Chem. Soc., 1905, 37, p. 1) obtained hydrazine by oxidizing urea with sodium hypochlorite in the presence of benzaldehyde, which, by combining with the hydrazine, protected it from oxidation. F. Raschig (German Patent 198307, 1908) obtained good yields by oxidizing ammonia with sodium hypochlorite in solutions made viscous with glue. Free hydrazine is a colourless liquid which boils at 113.5° C., and solidifies about 0° C. to colourless crystals; it is heavier than water, in which it dissolves with rise of temperature. It is rapidly oxidized on exposure, is a strong reducing agent, and reacts vigorously with the halogens. Under certain conditions it may be oxidized to azoimide (A. W. Browne and F. F. Shetterly,J. Amer. C.S., 1908, p. 53). By fractional distillation of its aqueous solution hydrazine hydrate N2H4·H2O (or perhaps H2N·NH3OH), a strong base, is obtained, which precipitates the metals from solutions of copper and silver salts at ordinary temperatures. It dissociates completely in a vacuum at 143°, and when heated under atmospheric pressure to 183° it decomposes into ammonia and nitrogen (A. Scott,J. Chem. Soc., 1904, 85, p. 913). The sulphate N2H4·H2SO4, crystallizes in tables which are slightly soluble in cold water and readily soluble in hot water; it is decomposed by heating above 250° C. with explosive evolution of gas and liberation of sulphur. By the addition of barium chloride to the sulphate, a solution of the hydrochloride is obtained, from which the crystallized salt may be obtained on evaporation.
Many organic derivatives of hydrazine are known, the most important being phenylhydrazine, which was discovered by Emil Fischer in 1877. It can be best prepared by V. Meyer and Lecco’s method (Ber., 1883, 16, p. 2976), which consists in reducing phenyldiazonium chloride in concentrated hydrochloric acid solution with stannous chloride also dissolved in concentrated hydrochloric acid. Phenylhydrazine is liberated from the hydrochloride so obtained by adding sodium hydroxide, the solution being then extracted with ether, the ether distilled off, and the residual oil purified by distillation under reduced pressure. Another method is due to E. Bamberger. The diazonium chloride, by the addition of an alkaline sulphite, is converted into a diazosulphonate, which is then reduced by zinc dust and acetic acid to phenylhydrazine potassium sulphite. This salt is then hydrolysed by heating it with hydrochloric acid—C6H5N2Cl + K2SO3= KCl + C6H5N2·SO3K,C6H5N2·SO3K + 2H = C6H5·NH·NH·SO3K,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 (seeAldehydes,KetonesandSugars). 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.
Many organic derivatives of hydrazine are known, the most important being phenylhydrazine, which was discovered by Emil Fischer in 1877. It can be best prepared by V. Meyer and Lecco’s method (Ber., 1883, 16, p. 2976), which consists in reducing phenyldiazonium chloride in concentrated hydrochloric acid solution with stannous chloride also dissolved in concentrated hydrochloric acid. Phenylhydrazine is liberated from the hydrochloride so obtained by adding sodium hydroxide, the solution being then extracted with ether, the ether distilled off, and the residual oil purified by distillation under reduced pressure. Another method is due to E. Bamberger. The diazonium chloride, by the addition of an alkaline sulphite, is converted into a diazosulphonate, which is then reduced by zinc dust and acetic acid to phenylhydrazine potassium sulphite. This salt is then hydrolysed by heating it with hydrochloric acid—
C6H5N2Cl + K2SO3= KCl + C6H5N2·SO3K,C6H5N2·SO3K + 2H = C6H5·NH·NH·SO3K,C6H5NH·NH·SO3K + HCl + H2O = C6H5·NH·NH2·HCl + KHSO4.
C6H5N2Cl + K2SO3= KCl + C6H5N2·SO3K,
C6H5N2·SO3K + 2H = C6H5·NH·NH·SO3K,
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 (seeAldehydes,KetonesandSugars). 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 (seeAldehydes;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.
SeeChemistryfor an account of their classification, &c.
SeeChemistryfor an account of their classification, &c.
HYDROCELE(Gr.ὕδωρ, water, andκήλη, 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.ὕδωρ, water, andκεφαλὴ, 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—acuteandchronic hydrocephalus. Acute hydrocephalus is another name for tuberculous meningitis (seeMeningitis).
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.*)
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.
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.Hydrocharisfloats 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 aloïdeshas 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 byElodea canadensisor 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,EnhalusandThalassiaare submerged maritime plants found on tropical coasts, mainly in the Indian and Pacific oceans;Halophilahas an elongated stem rooting at the nodes;Enhalusa short, thick rhizome, clothed with black threads resembling horse-hair, the persistent hard-bast strands of the leaves;Thalassiahas 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. InHydrocharis(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.Stratioteshas similar flowers which come above the surface only for pollination, becoming submerged again during ripening of the fruit. InVallisneria(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.Elodeahas 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 ofHalophilaare submerged and apetalous.
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 underChlorine, and its manufacture underAlkali Manufacture.
HYDRODYNAMICS(Gr.ὕδωρ, water,δύναμις, strength), the branch of hydromechanics which discusses the motion of fluids (seeHydromechanics).
HYDROGEN[symbol H, atomic weight 1.008 (o = 16)], one of the chemical elements. Its name is derived from Gr.ὕδωρ, water, andγεννάειν, 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 alsoLiquid 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 seeSpectroscopy. 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, SrH2at 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.
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 addedin 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 distillationin vacuo, and by further concentrationin vacuoa 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 [seeComptes 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.
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.ὕδωρ, water, andγράφειν, 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 alsoSurveying(Nautical) andOcean 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 (seeChart).
HYDROLYSIS(Gr.ὕδωρ, water,λύειν, 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 (seeChemical Action).