Cooley's Cyclopaedia of Practical Receipts Volume I Part 281

_Prep._ a.r.s.enide of zinc (made by fusing together equal weights of zinc and a.r.s.enic) is acted upon by strong hydrochloric acid or by sulphuric acid diluted with three parts of water.

_Obs._ This gas is produced whenever a.r.s.enious or a.r.s.enic acid, or any of their salts, is in presence of nascent hydrogen. The properties of a.r.s.enetted hydrogen are fully described in the tests for a.r.s.eNIOUS ACID.

This gas is a deadly poison when inhaled.

=Hydrogen, Car'buretted.= _Syn._ CARBONETTED HYDROGEN. This term is specially applied to two of the numerous compounds of carbon and hydrogen (CARBIDES OF HYDROGEN, HYDROCARBONS):--

1. =Light Carburetted Hydrogen.= (CH_{4}.) _Syn._ MARSH GAS, FIRE-DAMP, GAS OF THE ACETATES. This is often abundantly disengaged in coal mines, and its combustion occasions those fearful explosions which are so destructive to human life. The mud at the bottom of stagnant pools, on being stirred, suffers bubbles of gas to escape, which, when collected and examined, are found to be a mixture of light carburetted hydrogen and carbonic acid. The latter is easily removed by pa.s.sing the gas through a solution of caustic pota.s.sa or milk of lime.

_Prep._ (Dumas.) A mixture of acetate of soda (cryst.) and hydrate of pota.s.sa (dry), of each 2 parts, and quicklime (in powder), 3 parts, is strongly heated in a flask or retort. The gas in a state of absolute purity is disengaged in great abundance, and may be collected over water.

_Prop._ Colourless; neutral; nearly inodorous; burns with a yellow flame, producing pure water and carbonic acid; explodes when kindled in contact with air or oxygen.

2. =Heavy Carburetted Hydrogen.= (C_{2}H_{4}.) See OLEFIANT GAS.

_Obs._ COAL GAS, OIL GAS, and RESIN GAS, consist, for the most part, of mixtures of these two gaseous hydrocarbons in uncertain proportions, obtained respectively from coal, oil, and resin, by the action of heat, and used for the purposes of illumination. See GAS.

=Hydrogen, Oxides of.= There are two well-defined compounds of hydrogen and oxygen:--

1. =Subox'ide of Hydrogen.= (H_{2}O.) Water (which _see_).

2. =Perox'ide of Hydrogen.= (HO.) _Syn._ HYDROXYL, BINOXIDE OF HYDROGEN, DEUTOXIDE OF H., OXYGENATED WATER; HYDROGENIIBINOXYDUM, L. This singular fluid was discovered by M. Thenard in 1818.

_Prep._ (Odling.) A known quant.i.ty of pure hydrochloric acid, diluted with 8 or 10 times its volume of distilled water, is placed in a gla.s.s beaker surrounded with ice or a freezing mixture. A quant.i.ty of binoxide of barium rather less than sufficient to neutralise the acid is then ground to a fine paste with distilled water, and added gradually to the acid in which it should dissolve without effervescence. Diluted sulphuric acid is next added cautiously, to precipitate the barium, and reproduce hydrochloric acid to act upon a fresh quant.i.ty of peroxide. The liquid having been filtered from the insoluble sulphate of baryta, a second proportion of binoxide of barium paste is added gradually, as before. The treatment with sulphuric acid, filtration and addition of binoxide, is repeated 6 or 7 times. Sulphate of silver is then very carefully added, so as exactly to precipitate in the form of chloride of silver the whole of the chlorine. After filtration, pure baryta, first as a paste and then in solution, is cautiously added, to precipitate exactly the sulphuric acid set free from the sulphate of silver. Filtration is again resorted to, and the clear liquid (aqueous solution of peroxide of hydrogen) is placed in a dish over oil of vitriol in vacuo, in order that the water mixed with it may evaporate.

_Prop., &c._ A colourless, transparent, somewhat syrupy liquid, of sp. gr.

1452. It has a metallic taste, and corrodes the skin. It is easily resolved into oxygen and water. It mixes freely with water, and becomes more permanent by the dilution. It bleaches organic substances, and acts as a powerful oxidating agent. Under certain circ.u.mstances, however, it plays the part of a reducing agent. To the chemist, peroxide of hydrogen and its a.n.a.logue, binoxide of barium, have been of great service as instruments of research. Binoxide of hydrogen has been applied in the arts to restore the blackened lights of paintings which have become darkened by sulphuretted hydrogen; it is also sold by hair-dressers for bleaching human hair.

=Hydrogen, Phosphuret'ted.= See PHOSPHORUS.

=Hydrogen, Sulphides of.= See SULPHUR.

=HYDROMEL.= _Syn._ HYDROMELI, L. An aqueous solution of honey. _Prep._ (P.

Cod.) Honey, 2 oz.; boiling water, 32 oz.; dissolve, and strain. A refres.h.i.+ng and slightly laxative drink; in fevers, hoa.r.s.eness, sore throats, &c.

=HYDROM'ETER.= _Syn._ AREOMETER, GRAVIMETER; HYDROMETRUM, L. An instrument for ascertaining the specific gravities of liquids, and hence their strength, the latter being either in inverse or direct proportion to the former. Hydrometers are of two kinds:--1. Those which are always immersed to the same depth in distilled water, and the liquid to be tried, small weights being used for the purpose, as in FAHRENHEIT'S and NICHOLSON'S hydrometers; and 2nd, those which are suffered to rise or sink freely in the liquid, until they come to a state of rest, as in SYKE'S, BAUMe'S, &c.

In both cases a correction must be made for any variation in temperature.

Of the two kinds, the first give the most accurate results, and have the great advantage of being applicable to liquids either lighter or heavier than water, but the second are the readier in practice, requiring less time and less skill to use them. The following are those best known:--

BAUMe'S HYDROMETER or AREOMETER, which is very generally employed on the Continent, consists of two distinct instruments, the one for liquids heavier than water, the other for liquids lighter than that fluid. The first floats at the 0, or 'zero,' of the scale, in distilled wafer, at the temperature of 58 Fahr., and each degree, marked downwards, indicates a density corresponding to one per cent. of common salt. The hydrometer for liquids lighter than water is poised so that the 0 of the scale is at the bottom of the stem, when it is floating in a solution of 1 oz. of common salt in 9 oz. of water, and the depth to which it sinks in distilled water shows 10; the s.p.a.ce between these fixed points being equally divided, and the graduation continued upwards to the top of the scale.

The temperature at which these instruments were originally adjusted by Baume was 125 Centigrade (545 Fahr.). They are now commonly adjusted in this country at 58 or 60 Fahr. Hence arise the discrepancies observable in the published tables of the "correspondence between degrees of Baume and real specific gravities."

CARTIER'S HYDROMETER, which is much used in France for light liquids, has the same point for the zero of its scale as Baume's, but its degrees are rather smaller, 30 Baume being equal to 32 Cartier.

FAHRENHEIT'S HYDROMETER consists of a hollow ball, with a counterpoise below, and a very slender stem above, terminating in a small dish. The middle, or half-length of the stem, is distinguished by a fine line across it. In this instrument every division of the stem is rejected, and it is immersed in all experiments to the middle of the stem, by placing proper weights in the little dish above. Then, as the part immersed is constantly of the same magnitude, and the whole weight of the hydrometer is known, this last weight, added to the weights in the dish, will be equal to the weight of fluid displaced by the instrument, as all writers on hydrostatics prove. And accordingly, the specific gravities for the common form of the tables will be had by the proportion--

_As the whole weight of the hydrometer and its load, when adjusted in distilled water_, is to the _number_ 1000, so is the _whole weight when adjusted in any other fluid, to the number expressing its specific gravity._

GAY-LUSSAC'S ALCOHOLOMETER is used to determine the strength of spirituous liquors. It, at once, indicates on the stem, the per-centage of absolute alcohol in the liquid examined. The original experiments of Gay-Lussac having been made on liquids at a temperature of 59 Fahr., all examples examined by the alcoholometer, must either be brought to that temperature previous to being tested, or a correction made in the strength found.

NICHOLSON'S HYDROMETER is constructed on the same principle as Fahrenheit's. It has in addition to the small dish for weights above, a little cup attached below, for holding any solid body whose weight in water is required. It is chiefly intended for taking the sp. gr. of minerals.

RICHTER'S HYDROMETER resembles, for the most part, Gay-Lussac's.

SYKE'S HYDROMETER is that adopted by the Revenue authorities in England for ascertaining the strength of spirits, and has been already fully noticed.

TRALLES'S HYDROMETER resembles Gay-Lussac's (nearly).

TWADDELL'S HYDROMETER is much used in the bleaching establishments of Scotland, and in some part of England. According to this scale, 0 is equal to 1000 or the sp. gr. of distilled water, and each degree is equal to 005; so that, by multiplying this number by the number of degrees marked on the scale, and adding 1, the real specific gravity is obtained.

_Obs._ Hydrometers, unless manufactured with great care and skill, merely afford approximate results; but which are nevertheless sufficiently correct for all ordinary purposes. They also require several ounces of liquid to float them, and hence cannot be used for very small quant.i.ties.

Those of Fahrenheit, Nicholson, and Sykes are the most accurate, both in principle and application. They are all employed with a tall gla.s.s cylinder termed a sample, test, or hydrometer gla.s.s, in the way already noticed; but the thermometer for ascertaining the temperature must be covered with a gla.s.s case, or arranged with a folding scale to allow of its immersion in corrosive liquids.

ALCOHOLOMETERS, ELAIOMETERS, SACCHAROMETERS, URINOMETERS, &c., are simply hydrometers so weighted and graduated as to adapt them for testing spirits, syrups, urine, &c. See ALCOHOLOMETRY, ALONHOLMETRY, AREOMETER, SPECIFIC GRAVITY, &c.

=HYDROM'ETRY.= _Syn._ AREOMETRY. The art of determining the specific gravity of liquids, and hence their strength and commercial value. The instruments used are noticed above; their action depends upon the fact that a floating body displaces a bulk, equal to itself in weight, of the fluid in which it floats, and consequently that a body of a given weight sinks deeper in a lighter than in a heavier fluid. In hydrometric determinations the temperature of the samples must be carefully attended to, for fluids expand as their temperature is increased. The hydrometers used in England are generally adjusted to the standard temperature of 60 Fahr., and when 'Hydrometer Tables,' giving the corrections for the variations of the thermometer, are not accessible, the fluids to be examined should be brought to this standard temperature by applying heat directly to the vessel, when the temperature is below the standard, or by surrounding the vessel, with cold water, when it is above the standard.

The princ.i.p.al applications of hydrometry are described in different parts of this work. See ACETIMETRY, ALCOHOLOMETRY, CHLOROMETRY, SPECIFIC GRAVITY, &c.

=HYDROP'ATHY.= _Syn._ WATER CURE; HYDROPATHIA, L. A mode of curing diseases by the copious use of pure cold water, both internally and externally, together with dry sweating, and the due regulation of diet, exercise, and clothing. This "treatment of diseases undoubtedly includes powerful therapeutic agents, which, in the hands of the educated and honourable pract.i.tioner, might be most beneficially resorted to as remedial agents." (Pereira.)

=HYDROPHO'BIA.= _Syn._ CANINE MADNESS; RABIES CANINA, L. A disease which is generally considered as the result of a morbid poison being introduced into the system by the bite of a rabid animal. A clear case of idiopathic or spontaneous hydrophobia has never yet been known to occur in the human subject.

The common symptoms of hydrophobia are great excitability and horror at the sight of water, or the attempt to drink, fever, vomiting, excessive thirst, spitting of viscid saliva, difficult respiration, irregular pulse, convulsions, syncope, delirium, and death.

The whole materia medica has been, unfortunately, unsuccessfully sought without the discovery of a single remedy for this disease, or even a palliative of its severer symptoms. See CURARINE.

The treatment of recent bites of venomous animals has been fully explained, and need not be repeated here. To prevent secondary or const.i.tutional effects arising, the use of lemon juice, or a.r.s.enical solution, has long been popular. (Graham, and others.) Dr Buchan remarks that "vinegar is of considerable use, and should be taken freely."

=HYDROSULPHU'RIC ACID.= See SULPHUR.

=HYGIENE'.= _Syn._ HYGIENE, Fr. Health; its preservation, promotion, and restoration. That department of medicine and civil government which relates to health. See AIR, BATH, EXERCISE, FLANNEL, FOOD, NUTRITION, SLEEP, VENTILATION, &c.

=HYGROMETER.= An instrument for measuring the amount of moisture in the atmosphere.

Amongst the various contrivances for accomplis.h.i.+ng this end are Daniel's dew-point hygrometer; and the wet bulb hygrometer.

By the first, the quant.i.ty of moisture in the atmosphere, is determined by noting with a sensitive thermometer, the temperature at which a film of dew ma.s.s, to deposit on one of the bulbs of a species of cryophorus, disappears; the tension of the aqueous vapour present in the air at that period, being readily ascertained from tables constructed for the purpose, the corresponding proportion of moisture can thus be readily ascertained.

The wet bulb hygrometer consists of two small thermometers placed side by side, the bulb of them being surrounded by cotton films kept constantly damp by a simple contrivance. According to the rate of evaporation of the bulb so moistened, with the fall of the thermometer to which the moistened bulb belongs, the depression, of course, being greater the further the surrounding atmosphere is from the saturation point, and tables are furnished for determining the degree of saturation for all differences of temperature within the ordinary atmospheric range.

=HYOCHO'LIC ACID.= C_{25}H_{40}O_{4}. _Syn._ GLYCOHYOCHOLALIC ACID. A compound peculiar to the gall of pigs, discovered by Strecker and Gundelach.

_Prep._ The fresh gall of pigs is mixed with a solution of sulphate of sodium; the precipitate is dissolved in absolute alcohol, and decolourised by animal charcoal. From this solution ether throws down hyocholate of sodium, which, on the addition of sulphuric acid, yields hyocholic acid as a resinous ma.s.s, which is dissolved in alcohol, re-precipitated by water, and dried. When heated with alkaline solutions, glycocine and a new crystalline acid (hyocholalic acid) are formed. When boiled with acids, it yields glycocine and hyodyslysin.

=HYOSCY'AMINE.= _Syn._ HYOSCYAMIA, HYOSCYAMINA, DATURINE, DATURIA. An alkaloid obtained from common henbane (_Hyoscyamus niger_), and also from the thorn apple (_Datura stramonium_). See DATURA.

=HYPNOT'ICS.= _Syn._ HYPNOTICA, L. Agents or medicines which induce sleep, as opium, morphia, henbane, Indian hemp, lactucarium, &c. Agents which prevent sleep are called agrypnotics (_Agrypnotica_, L.), or anthypnotics (_Anthypnotica_, L.).