becoming jealous of his abilities, formed an alliance with the Mahrattas and the nizam of the Deccan against him; but Hyder not only gained over the nizam to his side, but for two years waged vehement war on the British. By a series of skilful manœuvres he managed to draw their force to a distance from Madras, and then at the head of 6,000 horsemen rode 120 m. in 3 days and appeared before the city. The outlying country being at his mercy, the government of the presidency was disposed to come to terms, and Hyder agreed to a treaty of which the principal feature was that the British should form an offensive alliance with him in his defensive wars. In 1770, the Mahrattas having invaded his dominions, he applied to the British for their promised aid, but could obtain from them nothing more than neutrality. By the year 1778 he had recovered from the disadvantages their defection had caused him. Being once more threatened by the same warlike people, he again invited British assistance, but with a like result. Incensed by this conduct, he formed an alliance with the Mahrattas and the nizam, and in 1780 invaded the British territory of the Carnatic, which he ravaged with fire and sword, capturing many of the strong places, but avoiding battle in the open field. The desolation he brought on the country during the two years' war was such that the British force, and even the city of Madras, were in danger from famine. This war elicited a remarkable display of military talent by the British general Sir Eyre Coote on the one side, and by Hyder and the French officers, of whom he had many in his service, on the other. The Mysore leader had already rejected terms of adjustment offered by Lord Macartney, the governor of Madras, when he died, and was succeeded by his son Tippoo Sultan.

HYDERABAD, or the NIZAM'S TERRITORY, a country of the Deccan, in Hindostan, bounded N. E. by Nagpoor, S. E. by the Madras presidency, W. and N. W. by the Bombay presidency, and N. W. by Gwalior and the British districts of Saugor and Nerbudda; area, 95,337 sq. m.; pop. estimated at 10,000,000. The surface consists chiefly of a high table-land watered by the Godavery, Wurda, Kistnah, and several other rivers, fertile but not well cultivated. Wheat and cotton are the principal productions. The climate, owing to the elevated position of the country, is colder than is usual in this latitude. The territory is crossed by several good military roads. The government is Mohammedan, but the majority of the people are Hindoos. Hyderabad was anciently subject to the rajahs of Telingana and Bijanagur. It was erected into a separate kingdom in 1512 by a Turkish adventurer, and in 1687 became a province of the Mogul empire. Azof Jah, an officer of the court of Delhi, who in 1719 governed this and the 5 other provinces of the Deccan with the title of Nizam-ul-mulk (" regulator of the state"), made himself independent. On his death in 1748 the succession was disputed by his

son Nazir Jung, whose cause was espoused by the English, and his grandson Mirzapha Jung, who was favored by the French. The latter finally triumphed, and governed under the direction of the French commander Dupleix until he was put to death by some Patan chiefs. During a period of anarchy which followed, the French and English supported rival claimants for the sovereignty. Nizam Ali, who came to the throne in 1761, ravaged the Carnatic, but was overpowered by a British force, and induced to sign a treaty in 1766 which gave to the East India company the Northern Circars. The English bound themselves to maintain a military force for the nizam's protection. In the war between the British and Hyder Ali, however, the nizam sided with the sultan of Mysore, but in that with Tippoo Sultan he formed an alliance with the company and the peishwa, and received a share of the spoils of victory. The accession of territory which he then obtained he subsequently ceded to the British in lieu of payment for the support of the British contingent. On the conclusion of the first Mahratta war in 1804 his dominions were again enlarged. The misgovernment of the country under the successors of Nizam Ali plunged Hyderabad deeply in debt. The East India company was at one time creditor to the amount of £500,000 or £600,000, and in liquidation they accepted a cession of territory, part of the revenues of which were to be devoted to the support of the subsidiary native force known as the nizam's contingent. The nizam remained true to the British during the mutiny of 1857-'8, and his dominions were little disturbed except by marauders. The present nizam, Afzul-ud-Dowlah, succeeded to the throne on the death of his father, May 19, 1857.— HYDERABAD, the capital of the above territory, is situated on the river Miessi, 389 m. N. W. from Madras, 314 S. from Nagpoor, and 962 S. W. from Calcutta; pop. about 200,000, a large majority of whom are Mohammedans. It is a weakly fortified town, crowded with buildings, some of which are large and imposing, having numerous mosques, and surrounded by gardens of remarkable beauty. The British residency is a magnificent edifice on the opposite side of the river, connected with the town by a stone bridge. In the neighborhood there are large water tanks, one of which is 20 m. in circuit. There is a large British military cantonment at Secunderabad, a few miles N. from the town. HYDRA. See HERCULES.

HYDRA, an island in the Grecian archipelago, off the E. coast of the Morea; greatest length N. E. to S. W. about 12 m., greatest breadth 3 m.; pop. about 20,000. Its surface is rocky, sterile, and mountainous. The inhabitants are esteemed the best sailors of Greece, and rendered important services during the war of independence.-HYDRA, the capital of the island, is situated on a barren rugged height on the N. W. shore; pop. about 12,000. The streets are steep and uneven, and the houses

substantially built. The manufactures are silk and cotton stuffs, soap and leather. The harbor is formed by a deep bay, but is neither spacious nor well sheltered. While the war of the revolution raged Hydra was a place of general refuge for people from all parts of Greece.

HYDRABAD, a town of British India, in the province of Sinde, situated on an eminence belonging to the Gunjah hills, 4 m. E. from the E. bank of the Indus; pop. about 24,000. Part of it is built on an island 15 m. long, which is formed by the Indus and an offset of that stream called the Fulailee. It is defended by a fortress of imposing appearance but no great strength, and has manufactures of matchlocks, swords, spears, and shields, and of ornamental silks and cottons. The town is to be connected with Kurrachee on the Arabian sea by a railway 120 m. long, which was begun in April, 1858. Hydrabad was formerly the residence of the chief ameers of Sinde, who governed the S. and principal part of the country. A victory was gained over a Sindian force near here by Sir C. Napier, Feb. 24, 1843.

HYDRANGEA (Gr. vdwp, water, and ayyos, a vase), a genus of shrubby plants, so called from their predilection for water, and from the calyx of some species resembling a cup, belonging to the natural order saxifragaceæ, and natives of Asia and of North America. The species best known by this naine (H. Hortensis) received the generic name of Hortensia from Commerson, and this name it still bears in France. The common hydrangea was brought to England from China in the year 1790. Cuttings of the wood or of the growing stems will root without difficulty; those of the latter make roots soonest, and if they are then potted in rich soil, they will grow rapidly. The hydrangea delights in an unlimited supply of water, fading at once on its being withheld. There has lately been introduced into cultivation a variety with variegated foliage, nearly all silvery white. In some parts of England the common hydrangea stands the winter, very severe weather only killing the stems to the roots. Specimens there are mentioned of 30 feet circumference, and producing on a single plant more than 1,000 heads or corymbs of flowers. In the United States, even so far north as Boston, it will survive the winter, if slightly protected by the stems being covered. The Japan hydrangea (H. Japonica, Siebold), introduced into this country about 15 years ago, and into England a short time previous, is considered inferior in both leaf and blossom. The wild hydrangea (H. arborescens, Linn.) is a shrub having a stem 4 to 6 feet high with opposite branches, leaves 3 to 6 inches long, ovate, pointed, serrate, and green on both sides; its flowers, which are borne on flat cymes, are white or yellowish, and usually all fertile. The species ranges from Pennsylvania and Ohio southward to the mountains of Carolina. The oak-leaved hydrangea (H. quercifolia) was first discovered by Bartram in his travels through the southern states,

and is attributed by Elliott to Georgia. It was carried to England in 1803, and is considered the finest of the North American species. It has deeply lobed, sinuate leaves, and fine large corymbs of nearly white flowers, which change afterward to purple. In the gardens at the north is often seen the snowy-leaved hydrangea (H. nivea, Mx.), a shrub from 6 to 8 feet high, with large leaves of a silvery whiteness beneath, and flowers in terminal cymes, having a few showy, white sterile florets enclosing many small green fertile ones. It grows naturally in the upper part of Georgia and the Carolinas.

HYDRATES (Gr. vowp, water), compounds in which water is an ingredient in definite proportion. Thus lime (oxide of calcium) slaked with water forms a chemical combination with a portion of this, and falls to a white powder, which is a hydrate of lime (CaO, HO). Hydrate of potassa is a combination of one equivalent of potassa and one of water, and is permanent even when exposed to high temperature. Common oil of vitriol is also a chemical combination of one equivalent of water and one of pure concentrated sulphuric acid.

HYDRAULIC RAM, or WATER RAM, & machine first erected by John Whitehurst in Cheshire in 1772, and improved by Montgolfier, the object of which is to raise a small stream of water to a considerable height by the power afforded by a larger stream with little fall. The main current is made to flow through a pipe from the reservoir which feeds it, and which by its elevation above the lower end of the pipe furnishes the required power. An opening on the upper side of the pipe at the lower end allows the water to escape; but this opening is supplied with a valve, in the form of a hollow metallic ball, held within the pipe in a sort of claw directly under the opening. As the current acquires velocity this ball, twice as heavy as the water it displaces, is lifted up and shuts the orifice of escape. Another similar but smaller valve is placed on a short upright length of pipe a little above the lower valve, and works in the opposite direction, closing the orifice by its descent, and opening it as it is lifted up. This short pipe opens above into a strong metallic chamber, which serves as a reservoir of water in its lower part, and of air above. A tube, called the ascension tube, leads from the water through the wall of the chamber to any place required. The recoil of the water throws up the valve and opens the passage into the chamber, the action being facilitated by the spring produced by the pressure upon a body of air contained in an annular space surrounding the valve box, which is let a little way down into the short upright pipe to give room for this annular chamber. As the impulse fails which opens the upper valve, the lower one is relieved of the pressure which lifted it and falls down, opening the outlet, and the other also falls, closing the orifice into the chamber, when the force again accumulates, repeating the operation. With each stroke a quantity of water is inject

ed into the large chamber. The air in the upper part of this is each time compressed, and by its elasticity drives the water up the ascension tube, equalizing the effect of the strokes. Montgolfier was thus able with a head of 73 feet to raise to the height of 50 feet a quantity of water compared with the whole that flowed as 2 to 21, making the useful effect as 64 to 100 of that expended; but it is more commonly about of that expended. A uniform flow may be obtained without the air chamber by using two or more rams, and connecting their ascension tubes into one. Water has thus been raised at Marly in France to the height of 187 feet. The younger Montgolfier improved the ram so as to obtain for it a useful effect of 60 per cent. The changes introduced were in the form of the valves, the lower one, of dish shape, being attached to a guide stem, which kept it in place as it worked up and down, and was so contrived as to give longer or shorter play to the valve as circumstances required. For the annular air space was substituted an air chamber of similar form to the large one, within which it was contained, and into which it opened by two valves. Under it a capillary open tube connected with the air without, and with each stroke a jet of water was forced out and air returned, the latter serving to keep up the supply required by the air chambers. Its entrance was caused by the reduced pressure within the smaller air chamber immediately after the elastic force had expended itself, this pressure for an instant becoming less than that of the air without. When the water is propelled by the ram to considerable height, its workings are so violent that the ground is shaken, and the tremor is felt through the whole length of the pipe. This destructive action is partially corrected by the improvements introduced in the rams constructed by Mr. Birkinbine of Philadelphia. In these the force of the blow of the larger valve as it rises is received by a portion of water caught be tween the valve and its seat, which serves as a water cushion. Some of the larger rams are worked by driving pipes of 6 inches diameter, and one of these with a fall of 6 feet is capable of raising 20,000 gallons per day 60 feet high.

HYDRAULICS. See HYDROMECHANICS. HYDROCEPHALUS (Gr. vdwp, water, and Kepaλn, the head), dropsy of the brain. Chronic hydrocephalus is commonly the result of either a malformation of the brain, or a chronic inflammation of the lining membrane of the ventricles. It is for the most part congenital, or shows itself within a few weeks after birth, though it sometimes seems to have been caused by injuries received on the head in early childhood. Congenital hydrocephalus is occasionally an obstacle to childbirth, the head requiring to be lessened before it can be delivered with safety to the mother. When it occurs after birth, the head gradually enlarges, assuming a globular form, the sutures and fontanelle becoming more and more open. As the nutrition of the remainder of the body is imperfect and its growth

dwarfed, the contrast between the immense head, the weight of which the child is unable to sustain, and the small and infantile face, gives the patient a strange and characteristic aspect. More or less squinting or a constant rolling motion of the eyes is an attendant upon the disease. The intellect is weak, and the child is subject to spasmodic attacks and convulsions; exhaustion, diarrhoea, or convulsions generally terminate the patient's existence at an early age; in one instance, however, an extreme case, the patient reached the age of 29 years. A variety of remedial means have been recommended, but their effects are very uncertain, and the complaint when once fairly established may be looked upon as hopeless.-Acute Hydrocephalus. Dr. Whytt in 1768 was the first to call the attention of the medical profession to the fact that in a large class of cases in young children, evidently involving the brain and rapidly terminating in death, the ventricles of the brain were apt to be more or less distended by a serous effusion; to this effusion the symptoms during life were attributed, and the disease was classed as a dropsy. Toward the commencement of the present century the inflammatory origin of the disease began to be recognized, and about the year 1830 the observations of MM. Rufz and Gherard, at the hôpital des enfants, proved the tubercular nature of by far the greater number of cases. In consonance with more correct views of its pathology, the disease has accordingly been termed tubercular meningitis. As would be anticipated, it is most apt to attack feeble and delicate children, especially those who have inherited a tendency to tubercular complaints; yet it often occurs in those who until its invasion have appeared to be in good health. In the beginning the child is fretful and irritable, it loses its appetite, and its movements are sluggish; the bowels are apt to be constipated, the evacuations scanty and offensive, the skin dry, and the pulse accelerated. If old enough, the child complains of headache, or it carries its hands to its head; it is unusually sensitive to light and noise; it seems drowsy, but sleeps badly, starting and grinding its teeth. Occasionally it appears for a few moments to lose its consciousness, gazing fixedly with its eyes wide open, and then suddenly resuming its former manner. It is often attacked with vomiting, which continues, without apparent cause. After more or fewer of these symptoms of nervous disturbance have continued for a variable number of days, the complaint becomes fully formed. The child remains in a drowsy condition, the eyes closed, the brow contracted, and the countenance expressive of suffering. It is averse to being disturbed, answers shortly and quickly, and if old enough complains only of its head and of weariness. The skin remains hot and dry; the pulse, at first more frequent, often suddenly becomes comparatively slow. At night there is an exacerbation of fever attended with restlessness, and often with delirium. Sometimes

the child continues to utter at intervals a short piercing cry characteristic of the disease. The bowels remain confined, and the evacuations are scanty and unnatural, though the abdomen is neither hard nor full; on the contrary, it is commonly retracted. The pupils are sometimes natural, and sometimes one is dilated while the other is contracted; they are apt to be sluggish to the influence of light, and squinting often occurs. Toward the close of the disease, the child sometimes falls into a state of stupor, from which it cannot be roused; frequently convulsions ensue, followed by paralysis of one side, with automatic movements of the other. The child often picks at its nose, lips, or head, drawing blood and leaving frightful-looking ulcerations. The eyes remain constantly half open, filmy, insensible to light, and commonly squinting; the cheeks are now flushed, now pale; the head is often retracted; the pulse becomes feeble and exceedingly frequent, and the child is more and more emaciated, until finally death after a variable interval closes the scene. The appearance after death to which for a long time the attention of observers was confined is the increased quantity of fluid in the ventricles; this varies greatly in different cases, and is in general perfectly transparent. The pia mater, and more especially the arachnoid membrane, particularly at the base of the brain, present a milky or opaline appearance; often more or less yellow lymph is found underneath the latter membrane. Beside these appearances, a number of minute granular bodies are found scattered within the membranes, the largest of them being of the size of a small pin's head; some of these bodies are yellowish and friable, others grayish, semi-transparent, and resistant. These bodies are always associated with the presence of tubercles in other organs of the body, and the general opinion of pathologists is that they are tubercular. When the disease is recognized as tubercular meningitis, the prognosis is exceedingly unfavorable, the cases of cure on record being few and doubtful. More can be done to ward off the attack of the disease than to cure it after its development. To this end, all efforts must be directed toward strengthening the system of the child, and repressing undue activity of the brain or nervous system. In the commencement, and when the diagnosis is still uncertain, the employment of mild but efficient purgatives seems to be indicated; calomel with rhubarb and soda are among the most useful. Occasionally the application of a few leeches to the head may be advisable, but the disease occurs mostly in children who bear depletion badly. When the complaint is thoroughly established, all measures seem to be of no avail; still a few cures are reported which appear to have been obtained by the employment of large doses of iodide of potassium.-In rare instances meningitis appears independently of a tubercular origin. Here the disease occurs in children who have been previously healthy. It is more violent in its invasions, being commonly ushered in by

convulsions, which often recur until the death of the patient; and its course is shorter, rarely lasting beyond a week. After death none of the granulations characteristic of tubercular meningitis are found, but the serum effused in the ventricles is apt to be turbid, and pus is sometimes found on the surface of the brain. The treatment must be prompt; leeches and cold to the head, active purgatives, and stimulating foot baths are recommended.

HYDROCHLORIC ACID, or CHLOROHYDRIC ACID, a gaseous compound of one equivalent of chlorine and one of hydrogen (HCl), of combining proportion 36.5, long known in its aqueous solution by the names of muriatic acid, marine salt, and spirit of salt, in reference to its being prepared from sea salt (murias). Priestley first obtained it as a gas in 1772, and Gay-Lussac, Thénard, and Davy long afterward showed that it consists of equal volumes of chlorine and hydrogen, and occupies the same space as the gases which produce it. Its elements mixed together slowly combine by the action of the light, but instantly with explosion if exposed to the direct rays of the sun, or if an electric spark is passed through the mixture, or a lighted taper is brought in contact with it. The gas is obtained by adding concentrated sulphuric acid to common salt placed in a retort, and collecting over mercury, The chlorine of the salt (chloride of sodium) unites with the hydrogen of the water of the sulphuric acid, and the sodium, taking the oxygen of the water, forms with the sulphuric acid sulphate of soda; or, by symbols, NaCl+SO, HO yields NaO, SO3+HCl. The gas is colorless, but escaping in the air it instantly unites with moisture present, and forms a white cloud. It has a strongly acid taste and a pungent odor. Taken into the lungs it is irrespirable, but when diluted with air is not so irritating as chlorine. It neither supports combustion nor is itself inflammable. Under a pressure of 40 atmospheres, at 50° F., it is condensed into a liquid of specific gravity 1.27. The density of the gas is 1269.5, air being 1000. Its affinity for water is such that it can be kept only in jars over mercury. If a piece of ice be introduced into a jar containing the gas, the ice is instantly liquefied, and the gas disappears. If the jar be opened under water, the water rushes up as into a vacuum. A cubic inch of water absorbs 418 cubic inches of gas at 69°, and becomes 1.34 cubic inches. The aqueous solution is the form in which the acid is commonly known. It is of various degrees of strength, the strongest readily obtained having 6 equivalents of water to one of acid, 40.66 per cent. of real acid, and being of specific gravity 1.203. This loses acid by evaporation, coming, according to Prof. Graham, to 12 equivalents of water to one of acid, this containing 25.52 of real acid, and being of specific gravity 1.1197. When reduced by distillation till it changes no more, it contains 16.4 equivalents of water and 20 per cent. of real acid, and is of specific gravity 1.0947. The following table by Mr. Ed. Davy gives its strength at different densities:

An approximate result is obtained by multiply ing the decimal of the specific gravity by 200.The pure concentrated acid is colorless, and fuming when exposed to the air. It is conveniently used for most purposes diluted to a specific gravity of about 1.1, at which it does not fume. Though powerfully acid, it is not so corrosive as sulphuric acid. It is decomposed by substances which yield oxygen freely, as the peroxide of manganese, and is thus made to furnish chlorine gas, its hydrogen combining with the oxygen of the metallic oxide. Nitrate of silver detects its presence by a white curdy precipitate (chloride of silver), soluble in ammonia, but not in nitric acid, which forms on the addition of a drop or two of its solution.—The ingredients used for preparing hydrochloric acid, either upon a large or small scale, are common salt, sulphuric acid, and water. Different proportions are adopted, the most usual being equal weights of concentrated acid and of salt, or in the large way 6 parts of salt to 5 of acid, being an equivalent of each. In the small way, by distilling in a glass retort, may be used 3 parts or 1 equivalent of chloride of sodium, 5 parts or 2 equivalents of oil of vitriol, and parts of water. The acid mixed with 2 of water is poured when cool upon the salt contained in a large retort, and the remaining 3 parts of water are placed in the vessel serving as a condenser to receive the gas. Heat is applied to the retort, and the acid gas distils over; the water in the condenser allows none of it to escape, so long as it is kept cool and is not saturated. The aqueous solution obtained is of specific gravity about 1.17, and contains 34 per cent. of dry acid. The residuum is bisulphate of soda. The acid is so cheaply prepared in large chemical works, that it is seldom made in the laboratory. It is an incidental product in the manufacture of carbonate of soda, and was formerly allowed to go to waste. The commercial article is often contaminated with iron, which gives it a yellow color, though this is sometimes owing to organic matter, as cork or wood. Sulphuric acid is almost always present in it, and sometimes free chlorine and nitrous acid. Sulphurous acid has also been found to the amount of 7 to nearly 11 per cent. Sulphuric acid is detected by the white precipitate of sulphate of baryta produced when chloride of barium is added to a diluted portion of acid. Protochloride of tin decomposes sulphurous acid, and causes after a time a brown precipitate to appear. Arsenic and chloride of lead may sometimes be detected by a current

of sulphuretted hydrogen. The common meth od of purifying is to dilute, add chloride of barium, and distil.-The acid is largely employed in the arts, especially as a solvent for mineral substances. In combination with nitric acid it makes the aqua regia, used for dissolving gold and platinum. It is used to furnish chlorine in the preparation of bleaching and disinfectant salts, and in the production of sal ammoniac; and is employed to extract gelatine from bones. When neutralized with basic oxides, it does not combine as an acid with these, but gives its hydrogen to their oxygen, and its chlorine unites with the metallic base of the oxide. In medicine the acid is employed as a tonic, refrigerant, and antiseptic. The latter quality recommends it as an adjunct to gargles in ulcerated sore throat and scarlet fever.

HYDROCYANIC ACID, or PRUSSIC ACID (HCy; chemical equivalent 27), was first obtained in its aqueous solution by Scheele in 1782, who described it correctly as consisting of hydrogen, carbon, and nitrogen; but the true nature of the compound was determined by Gay-Lussac 30 years later, who first obtained the anhydrous acid. This is a colorless, inflammable liquid, possessing a strong odor, which is recognized in peach blossoms; but when exhaled from the pure acid it is so powerful as to cause immediate headache and giddiness, involving the most serious consequences to life itself. The vapor is so remarkably volatile, that a drop of the acid congeals upon a piece of glass by the rapid evaporation of a portion of the liquid. It boils at 80°, and freezes at 5° into a fibrous mass. At 64° its specific gravity is .6969. Its taste (a hazardous test) is acrid and bitter like that of bitter almonds. Its acid properties are feeble; the faint red tinge it imparts to litmus paper soon disappears; and it fails to decompose salts of carbonic acid. It exists in parts of many plants, as the kernels of peaches, almonds, plums, &c., and in the leaves of the peach, laurel, &c. It is also generated in the processes contrived for extracting it from various vegetable matters. The chief source of the acid, however, is the animal kingdom, the blood, hoofs, horns, and tissues of the animal body being made to furnish cyanogen to potassium on being ignited with carbonate of potash, and the cyanide thus obtained and other cyanides of the same derivation are employed to furnish the cyanogen for the acid. Its detection in the cyanide salt, Prussian blue, gave it the name of Prussic acid. Many methods have been devised for preparing the anhydrous acid. The cyanide of mercury has been decomposed together with hydrochlo ric acid, thus producing chloride of mercury and hydrocyanic acid; and sulphuretted hydrogen and also diluted sulphuric acid have by suitable processes been substituted for the hydrochloric acid. But the aqueous solution or medicinal acid is commonly prepared direct by some one of the numerous processes of the pharmacopoeias. The following, adopted in the United