Chapter M: F. Capitaine, who, acting upon a suggestion made by Liebig, some twenty (6)

=Hydrogen, Antimo''niuretted.= (SbH_{3}.) _Syn._ ANTIMONETTED HYDROGEN, HYDRIDE OF ANTIMONY, STIBAMINE; HYDROGENIUM ANTIMONIATUM, L. A gaseous compound of antimony and hydrogen, prepared by dissolving an alloy of antimony with a large excess of zinc in hydrochloric or dilute sulphuric acid. It has never been obtained pure, a variable proportion of free hydrogen being always present. It burns with a bluish-white flame, giving rise to dense fumes of teroxide of antimony, and when conducted through a red-hot tube, or the flame is thrown on a cold surface, as a porcelain plate, metallic antimony is deposited. This gas is a deadly poison when inhaled. See ARSENIOUS ACID.

=Hydrogen, Arsen''iuretted.= (AsH_{3}.) _Syn._ ARSENETTED HYDROGEN, HYDRIDE OF ARSENIC, ARSENAMINE; HYDROGENIUM ARSENIURATUM, L. A gaseous compound of arsenic and hydrogen.

_Prep._ Arsenide of zinc (made by fusing together equal weights of zinc and arsenic) is acted upon by strong hydrochloric acid or by sulphuric acid diluted with three parts of water.

_Obs._ This gas is produced whenever arsenious or arsenic acid, or any of their salts, is in presence of nascent hydrogen. The properties of arsenetted hydrogen are fully described in the tests for ARSENIOUS 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 passing the gas through a solution of caustic potassa or milk of lime.

_Prep._ (Dumas.) A mixture of acetate of soda (cryst.) and hydrate of potassa (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. Thénard in 1818.

_Prep._ (Odling.) A known quantity of pure hydrochloric acid, diluted with 8 or 10 times its volume of distilled water, is placed in a glass beaker surrounded with ice or a freezing mixture. A quantity 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 quantity 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. 1·452. 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 circumstances, however, it plays the part of a reducing agent. To the chemist, peroxide of hydrogen and its analogue, 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 refreshing and slightly laxative drink; in fevers, hoarseness, 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, BAUMÉ'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:--

BAUMÉ'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 space 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 Baumé was 12·5° Centigrade (54·5° 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 Baumé 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 Baumé's, but its degrees are rather smaller, 30° Baumé 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 quantities. Those of Fahrenheit, Nicholson, and Sykes are the most accurate, both in principle and application. They are all employed with a tall glass cylinder termed a sample, test, or hydrometer glass, in the way already noticed; but the thermometer for ascertaining the temperature must be covered with a glass 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 principal 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 practitioner, 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 constitutional effects arising, the use of lemon juice, or arsenical 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 accomplishing this end are Daniel's dew-point hygrometer; and the wet bulb hygrometer.

By the first, the quantity of moisture in the atmosphere, is determined by noting with a sensitive thermometer, the temperature at which a film of dew mass, 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 mass, 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.).

=HYPOCHLO'RIC ACID.= See CHLORINE.

=HYPOCHONDRI'ASIS.= _Syn._ HYPOCHONDRIACISM. The 'hip' or 'hyp,' the 'vapours,' depression of spirits, 'blue devils.' This disease chiefly affects persons of the melancholic temperament, and is commonly induced by hard study, irregular habits of life, want of proper social intercourse, living in close apartments, and insufficient out-of-door exercise. The treatment may, in most cases be similar to that recommended for DYSPEPSIA, observing, however, that success depends more on amusing and engaging the mind, and in gradually weaning it from old conceits, than in the mere administration of medicine. When the patient is tormented with a visionary or exaggerated sense of pain, or of some concealed disease, or a whimsical dislike of certain persons, places, or things, or groundless apprehensions of personal danger or poverty, or the conviction of having experienced some dreadful accident or misfortune, the better way is to avoid any direct attempts to alter his opinions, but to endeavour to inspire confidence in some method of relief. Greding mentions the case of a medical man who conceived that his stomach was full of frogs, which had been successively spawning ever since he had bathed, when a boy, in a pool in which he had perceived some tadpoles; and he had spent his life in endeavouring to get them removed. One patient, perhaps, fancies himself a giant; another as heavy as lead; a third a feather, in continual danger of being blown away by the wind; and a fourth a piece of glass, and is hourly fearful of being broken. Marcellus Dentatus mentions a baker of Ferrara who thought himself a lump of butter, and durst not sit in the sun, or come near the fire, for fear of being melted. The writer of this article once knew a man who always put on his coat the wrong side in front, because he conceived his face looked behind him. In such cases it is useless to argue with the patient, as it only causes irritation, and increases the malady. The restoration of the bodily health, and a sudden surprise or change of scene, will often effect a cure.

=HYPONI'TRIC ACID.= See NITROGEN.

=HYPONI'TROUS ACID.= See NITROGEN.

=HYPOPHOS'PHITES.= See PHOSPHORUS.

=HYPOPHOS'PHITE.= A salt of hypophosphorous acid.

=HYPOSUL'PHATE.= _Syn._ DITHIONATE; HYPOSULPHAS, L. A salt of hyposulphuric acid.

=HYPOSUL'PHITE.= _Syn._ THIOSULPHATE; HYPOSULPHIS, L. A salt of hyposulphurous acid.

=HYPOSUL'PHUROUS ACID.= See SULPHUROUS ACID.

=HYRA'CEUM.= A substance produced by the Cape badger (_Hyrax Capensis_), and proposed as a substitute for CASTOREUM. Pereira considered it to be inert and useless.

=HYSTERICS.= _Syn._ HYSTERIA, PASSIO HYSTERICA, L. In _pathology_, a nervous affection peculiar to women, attacking in paroxysms or fits, preceded by dejection; tears, difficult breathing, sickness, and palpitation of the heart. The treatment of this disease varies with the causes and the symptoms. Bleeding, cupping, and depletives, are generally had recourse to in robust and plethoric habits, and stimulants and tonics in those of a weakly or relaxed constitution. Affusion of cold water and nasal stimulants will frequently remove the fit in mild cases. Exercise, proper amusements and regular hours and diet, are the best preventives. See DRAUGHT (Antihysteric and Hydrocyanic), &c.

=ICE.= _Syn._ GLACIES, L. Water in the solid state. On being cooled, water gradually contracts until the temperature has fallen to 39·9° Fahr., when it begins to expand. At the freezing-point, 32° Fahr., under ordinary conditions, water crystallises or freezes, and in consequence of the continued expansion, the sp. gr. of ice, as compared with that of water at 39·9°, is as ·94 to 1·00. Ice has the peculiar property of reuniting by the contact of adjoining surfaces after having been broken into fragments (REGELATION). Coloured water and salt water, by freezing, produce colourless and fresh ice; and clean solid ice, when thawed, furnishes water equal in purity to that which has been distilled.

The use of ice in the preparation of ICE-CREAMS, ICED-LIQUORS, &c., is noticed elsewhere. The confectioner collects his ice as early as possible during the winter, and stores it in a well-drained well or excavation, somewhat of the form of an inverted sugar-loaf, contained in a small shed or building called an ICE-HOUSE. This building should always be situated on a dry sandy soil, and, if possible, on an eminence. The door should be on the north side, and the roof should be conical and thickly thatched with straw.

In _medicine_, ice is frequently employed externally in inflammation of the brain, to resolve inflammation, to stop hæmorrhage, to constringe relaxed parts, and an anodyne, to deaden pain. For these purposes it is pounded small, in a cloth, and placed in a bladder or bag of gauze (ICE-CAP, ICE-POULTICE) before applying it. Internally, ice or ice-cold water has been given with advantage in heartburn, typhus, inflammation and spasms of the stomach, to check the vomiting in cholera, and to arrest hæmorrhage, whether bronchial, gastric, nasal, or uterine. Very recently, ice has been proposed as a remedy in the treatment of diphtheria. Small lumps of ice, or a small glassful of pounded ice-and-water, will often temporarily restore the tone of the stomach and nervous system during hot weather, when all other means fail. Ice-creams, taken in moderation, act in the same way.

In the warmer climates of Europe an ICE-HOUSE or an ICE-SAFE (a REFRIGERATOR) is a necessary appendage to every respectable dwelling, not merely for the purpose of pleasing the palate with iced beverages, but to enable the residents to preserve their provisions (fish, meat, game, milk, butter, &c.) in a wholesome state from day to day. In addition to large cargoes of ice imported yearly from Norway, and principally consumed in England, Germany and France, ice is now manufactured to no inconsiderable amount, in these three countries artificially, the principal consumption of the factitious article being by brewers, who use it for the cooling of their worts. The artificial manufacture of ice is effected by the means of the condensation of elastic vapours in machines expressly made for the purpose. In Siebe's ice-making machine the vapour of ether is made to traverse metallic tubes surrounded with a concentrated solution of common salt, by which it becomes recondensed to the liquid state, to be again utilised in the production of the vapour; the solution of salt becoming at the same time so reduced in temperature, as to convert into ice, water, contained in proper vessels, placed in it. In Carré's machine the same end is accomplished by means of ammoniacal gas, a solution of calcic chloride being used for absorbing the cold instead of common salt. Reece's is a modification, (he states an improvement) of Carré's. Ice machines are also made, in which ice is produced, by bringing water into contact with air, which has been greatly reduced in temperature by cooling it when in the compressed state, and subsequently allowing it to expand. Liquid carbonic and sulphurous acids have likewise been used in the preparation of artificial ice, but not when it has been required in any considerable quantity. See REFRIGERATION.

=Ice, Medicated.= Mr Martin, of Weston-super-Mare, writing to the 'Lancet,' says:--"Every practitioner has at times to face the difficulties of the scarlatinal throat in young children. It may sadly want topical medication; but how is he to apply it? Young children cannot gargle, and to attempt the brush or the spray fills them with terror. In many cases neither sternness nor coaxing avails. Yet these little ones in almost every case will greedily suck bits of ice. This has long been my chief resource where I could not persuade the child to submit to the sulphurous acid spray. Lately, I have been trying an ice formed of the frozen solution of the acid (or some other antiseptic). Though, of course, not so tasteless as pure ice, the flavour is so much lessened by the low temperature, and probably also through the parched tongue, very little appreciating any flavour, that I find scarcely any complaint on that score from the little sufferers; they generally take to it very readily. The process of making it is very simple. A large test-tube immersed in a mixture of ice and salt is the only apparatus required, and in this the solution is easily frozen. When quite solid a momentary dip of the tube in hot water enables one to turn out the cylinder of ice, as the cook turns out her mould of jelly. I have tried the three following formulæ, all of which answer, although I think I prefer the first.

"1. Sulphurous acid, 1/2 dr.; water, 7-1/2 dr.; mix and freeze.

"2. Chlorate of potass, 1 scruple; water, 1 oz.; dissolve, and freeze.

"3. Solution of chlorinated soda, 1/2 dr.; water, 1 oz.; mix and freeze.

"However, the form is of secondary importance, as each practitioner can construct his own. Boracic acid, salicylic acid, or any other harmless antiseptic with not too much taste, would doubtless be as useful as those indicated."

=ICE'LAND MOSS.= _Syn._ CETRARIA (B. P.), LICHEN ISLANDICUS, L. The lichen termed _Cetraria Islandicus_. It is much employed, both as a nutritious food and as a mild mucilaginous tonic, in catarrh and consumption. It may be purified from its bitter principle by a little cold solution of potassa.

=Iceland Moss, Saccharated.= _Syn._ (P. C.), SACCHARUM LICHENIS. Iceland moss, 1 lb.; refined sugar 1 lb.; macerate the moss in water to extract the bitterness, express, boil in water for an hour, strain, let settle, decant, add the sugar, evaporate to dryness with a gentle heat, constantly stirring, and finally reduce to powder.

=ICES.= (In _confectionery_.) These are commonly composed of cream or sweetened water, variously flavoured, and congealed by ice or a freezing mixture. Sometimes, instead of cream, the materials of a custard are used. The mixed ingredients are placed in a tin furnished with a handle at top, called a 'freezer,' or 'freezing-pot,' which is then plunged into a bucket containing ice broken small, and mixed with about half its weight of common salt, and is kept in rapid motion, backwards and forwards, until its contents are frozen. As the cream congeals and adheres to the sides, it is broken down with the ice-spoon, so that the whole may be equally exposed to the cold. As the salt and ice in the tub melt, more is added, until the process is finished. The 'ice-pot,' with the cream in it, is next placed in a leaden 'ice-stand,' is at once surrounded with a mixture of ice and salt, and closely covered over. In this state it is carried into the shop. The glasses are filled as required for immediate use, and should have been previously made as cold as possible.

PLAIN ICE-CREAM, or CREAM FOR ICING, is commonly made by one or other of the following formulæ:--

1. New milk, 2 pints; yolks of 6 eggs; white sugar, 4 oz.; mix, strain, heat gently and cool gradually.

2. Cream 1 pint; sugar, 4 oz.; mix as above.

3. Cream and milk, of each 1 pint; white sugar, 1/2 lb.

FLAVOURED ICE-CREAMS are made by mixing cream for icing with half its weight of mashed or preserved fruit, previously rubbed through a clean hair sieve; or, when the flavour depends on the juice of fruit or on essential oil, by adding a sufficient quantity of such substances. RASPBERRY and STRAWBERRY ICES are made according to the former method; LEMON, ORANGE, NOYEAU, and ALMOND ICES, by the latter method. In the same way any other article besides cream may be frozen.

CHOCOLATE FOR ICING is made by rubbing 1 oz. of chocolate to a paste with a tablespoonful of hot milk, and then adding 'cream for icing,' 1 pint.

COFFEE FOR ICING is made of cream for icing, 1 quart, to which a small teacupful of the strongest possible clarified coffee has been added together with 2 oz. of sugar and the yolks of 3 or 4 eggs. See ICING (_below_).

=I'CING.= (For cakes.) _Syn._ SUGAR ICE. The covering of concreted sugar with which the confectioners adorn their cakes. _Prep._ Beat the white of eggs to a full froth, with a little rose or orange-flower water; then add gradually, as much finely powdered sugar as will make it thick enough, beating it well all the time. For use, dust the cakes over with flour, then gently rub it off, lay on the icing with a flat knife, stick on the ornaments while it is wet, and place it in the oven for a few minutes to harden, but not long enough to discolour it. It may be tinged of various shades by the addition of the proper 'stains.'

=ID'RIALIN.= A fusible, inflammable substance, found associated with the native cinnabar of the mines of Idria, in Carniola. It is extracted from the ore by means of oil of turpentine. It is only slightly soluble in alcohol and ether. When pure, it is white and crystalline.

=ID'RYL.= A hydrocarbon generally found associated with idrialin.

=IGASU'RIC ACID.= _Syn._ ACIDUM IGASURICUM, L. An acid associated with strychnine in the St. Ignatius' bean and in nux vomica. It may be obtained by digesting the rasped or ground beans first in ether and then in boiling alcohol, evaporating the latter decoction to dryness, diffusing the residuum through water, adding a little carbonate of magnesium, again boiling for some minutes, filtering, washing the powder with cold water, and digesting it in alcohol, and filtering. The igasurate of magnesium thus obtained is dissolved in boiling water, the solution decomposed by acetate of lead, and the precipitate (igasurate of lead), after being washed and diffused through distilled water, is decomposed by sulphuretted hydrogen. The solution thus obtained yields crystals (igasuric acid) on being evaporated. It is soluble in both water and alcohol.

=IGNI''TION.= In the laboratory this term is commonly applied to the act of heating to redness or luminousness. See CALCINATION.

=ILLICIN.= Boil a clear decoction of holly with animal charcoal; let it settle, collect the deposited charcoal, wash it with cold water, dry it, and treat it with boiling alcohol; let the filtered liquid be evaporated to dryness. Febrifuge.--_Dose_, 6 to 24 gr.

=ILLUMINA'TION.= The act of illuminating or making luminous. For supplying artificial light to streets and the interiors of houses coal gas and oils and fats are generally employed. These illuminating agents are compounds rich in carbon, upon the presence of which the brightness of their flames depends. Flame is gas or vapour heated to incandescence during the process of combustion. A flame containing no solid particles emits but a feeble light, even if its temperature is the highest possible. Pure hydrogen, for instance, burns with a pale, smokeless flame, though with the production of considerable heat. On the other hand, wax, paraffin, coal-gas, &c., while undergoing combustion, give out considerable light, because their flames contain innumerable solid particles of carbon, which act as radiant points. To give the greatest degree of luminosity to flame, the supply of air must be proportioned to the character of the burning substance, and be insufficient for the instantaneous combustion of the evolved gases; in which case the hydrogen takes all the oxygen, and the larger portion of the carbon is precipitated, and burnt in the solid form, at some little distance within the outer surface of the flame. When the supply of air is sufficient for the immediate and complete combustion of the whole of the combustible matter, no such precipitation takes place, and the flame is neither white nor brilliant. The richest coal-gas, mixed with sufficient air to convert all its hydrogen and carbon into water and carbonic acid, explodes with a pale blue flash; yet the same gas, when consumed in the ordinary way, burns with a rich white flame. Every one must have noticed the effect of a gust of wind upon the flaring gas-jets of a butcher's shop; the plentiful supply of air causes complete combustion, and so converts the bright white flames into dull blue streaks of fire. When the supply of air is insufficient to cause the combustion of the newly formed solid carbon at the instant of its development, and whilst it is in an incandescent state, the flame becomes red and smoky, and unburnt sooty particles are thrown off. The same occurs when the temperature of any portion of the hydrogen is reduced below that intensity required for the combustion of the newly separated charcoal. Solid bodies, as tallow, oils, and fats, which burn with flame, are converted into the state of gas by the heat required to kindle them, and it is this gaseous matter which suffers combustion, and not the substance which produces it.

The relative value of the ordinary illuminating agents has been accurately determined by Dr Frankland. According to his experiments, the quantities of various substances required to give the same amount of light as would be obtained from 1 gallon of Young's Paraffin oil are as follows:--

Young's Paraffin oil 1·00 gall.
American rock oil[352] 1·26 "
Paraffin candles 18·6 lbs.
Sperm 22·9 "
Wax 26·4 "
Stearic 27·6 "
Composite 29·5 "
Tallow 39·0 "

[Footnote 352: Acknowledged to be an inferior sample.]

The following table exhibits the comparative cost of the light of 20 sperm candles, each burning 10 hours at the rate of 120 gr. per hour; also the amount of carbonic acid produced and heat evolved per hour, in obtaining this quantity of light:--

Carb. acid Units of
Cost. per hour in heat
_s._ _d._ cub. feet per hour.

Wax 7 2-1/2 }
Spermaceti 6 8 } 8·3 82
Paraffin candles 3 10 6·7 66
Tallow 2 8 10·1 100
Rock oil 0 7-1/2 }
Paraffin oil 0 6 } 3·0 29
Coal gas 0 4-1/2 5·0 47
Cannel gas 0 3 4·0 32

These figures prove that coal-gas and the mineral oils are the cheapest and best illuminating agents, producing the largest amount of light with the least development of heat.

The light emitted by incandescent lime (DRUMMOND LIGHT, HYDRO-OXYGEN LIGHT, LIME LIGHT, OXYHYDROGEN LIGHT) is intensely brilliant, and is often made use of to enable workmen to continue operations at night. It is obtained by directing the flame produced by the combustion of a mixture of hydrogen (or coal-gas) and oxygen upon a small cylinder of lime. In the improved form of this light the lime is protected from crumbling by a cage of platinum wire, and is caused to rotate slowly by means of clockwork, so as constantly to expose a fresh surface to the flame. When reflected from a 'parabolic mirror' in a pencil of parallel rays, the Drummond light has been recognised during daylight at a distance of 108 miles. The lime light produced with coal-gas and oxygen is used for the MAGIC LANTERN and GAS MICROSCOPE.

The most powerful illuminator is the ELECTRIC LIGHT, which is now being subjected to trial in many cities for street illuminations, &c., in place of coal-gas. It is usually produced by the passage of a strong current of electricity between two pencils of hard carbon. The electric light has been successfully applied to lighthouse illumination. Hitherto it has been found too intense and too costly for application to domestic purposes. See CANDLES, FLAME, GAS, PHOTOMETRY, &c.

=ILLU'TATION.= See BATH (Mud).

=IMAGINA'TION.= The influence of the imagination, both in the production and cure of disease, has been long admitted by medical practitioners. It is probably the most powerful therapeutic agent known. "Extraordinary cures have been ascribed to inert and useless means, when, in fact, they were referable to the influence of the imagination." (Dr Pereira.)

=IMPE'RIAL.= _Syn._ POTUS IMPERIALIS, PTISANA I., L. _Prep._ 1. Cream of tartar, 1/4 oz.; 1 lemon, sliced; lump sugar, 2 oz.; boiling water, 1 quart; infuse, with occasional stirring until cold, then pour off the clear portion for use.

2. A lemon, sliced; sugar, 1 oz.; boiling water, 1 pint.

3. Yellow rind and juice of lemon; citric acid, 1 dr.; sugar, 2-1/2 oz.; hot water (which has been boiled), 1 quart; as No. 1. Refrigerant and slightly diuretic. Used as a common drink in fevers, dropsy, &c., and as a summer beverage.

=IM'PLEMENTS (Agricultural).= "Almost all the operations of agriculture may be performed by the plough, the harrow, the scythe, and the flail; and these are the sole implements in the primitive agriculture of all countries. With the progress of improvement, many other implements (and machines) have been introduced, the more remarkable of which are the DRILL PLOUGH, the HORSE HOE, the WINNOWING MACHINE, the THRESHING MACHINE, the HAY-MAKING MACHINE, and the REAPING MACHINE. The object of all these implements and machines is to abridge human labour, and to perform the different operations to which they are applied with a greater degree of rapidity, and in a more perfect manner than before." (Loudon.) On the perfection of agricultural implements and machines depends much of the improvement of which this art is susceptible. See AGRICULTURE, &c.

=IMPROV'ING.= The trade name for 'doctoring,' 'adulterating,' or 'lowering,' the quality of any substance, with the view of cheapening it or increasing its bulk. See WINE, &c.

=IN'CENSE.= _Prep._ 1. Olibanum, 2 or 3 parts; gum benzoin, 1 part.

2. Olibanum, 7 parts; gum benzoin, 2 parts; cascarilla, 1 part. Placed on a hot plate or burned, it exhales an agreeable perfume. Used in some of the rituals of the Roman Catholic church.

3. Benzoin and storax, of each 4 oz.; labdanum and myrrh, of each 6 oz.; cascarilla 3 oz.; oil cinnamon, 8 minims; oils bergamot and lavender, of each 20 minims; oil cloves, 10 minims; mix, and pass through a coarse sieve.

=INCINERA'TION.= The reduction of organic substances to ashes by combustion. See CALCINATION.

=INCOMBUSTIBIL'ITY.= The property of being incapable of being kindled, or of being consumed by fire. Substances possessing this property are said to be 'incombustible' or 'fire-proof.'

=INCOMBUST'IBLE FAB'RICS.= _Syn._ NON-INFLAMMABLE FABRICS. The fashion of wearing light gauzy dresses extended by hoops or crinoline has made death from fire a common casualty. With a view of diminishing the danger to which women expose themselves, chemists have lately devoted considerable attention to the problem of rendering muslin and other light fabrics non-inflammable. This object may be attained by steeping the fabric in almost any saline solution. Thus, cotton or linen stuffs prepared with a solution of borax, phosphate of soda, phosphate of ammonia, alum, or sal ammoniac, may be placed in contact with ignited bodies without their suffering active combustion or bursting into flame. The salts act by forming a crust of incombustible matter on the surface of the fibres. They do not, however, prevent carbonisation taking place, when the temperature is sufficiently high. It is by a knowledge of this property of culinary salt that jugglers are enabled to perform the common trick of burning a thread of cotton while supporting a ring or a small key, without the latter falling to the ground. The cotton is reduced to a cinder, but from the action of the salt its fibres still retain sufficient tenacity to support a light weight.

The addition of about 1 oz. of alum or sal ammoniac to the last water used to rinse a lady's dress, or a set of bed furniture, or a less quantity added to the starch used to stiffen them, renders them uninflammable, or at least so little combustible that they will not readily take fire; and if kindled, are slowly consumed without flame. None of the above-named salts are adapted for fine soft muslins, which mostly require chemical treatment, because they injure the texture, rendering the fabric harsh and destroying all its beauty. The salt which is found to answer most completely all the required conditions is TUNGSTATE OF SODA. "Muslin steeped in a solution containing 20% of this salt is perfectly non-inflammable when dry, and the saline film left on the surface is smooth and of a fatty appearance like talc, and therefore does not interfere with the process of ironing, but allows the hot iron to pass smoothly over the surface. The non-fulfilment of this latter condition completely prevents the use of many other salts--such as sulphate or phosphate of ammonia, which are otherwise efficacious in destroying inflammability--for all fabrics which have to be washed and ironed." (Watts.)

The addition of a little phosphoric acid or phosphate of soda to the tungstate is recommended, for without this addition a portion of the tungstate is apt to undergo a chemical change and become comparatively insoluble. Messrs Versmann and Oppenheim, the introducers of tungstate of soda, give the following formula for a solution of minimum strength:--

Dilute a concentrated solution of neutral tungstate of soda with water to 28° Twaddell (sp. gr. 1·14), and then add 3% of phosphate of soda. This solution is found to keep and to answer its purpose very well; it is now constantly used in the Royal Laundry.

PAPER, WOOD, &c., may be also rendered comparatively incombustible by soaking them in saline solutions. See ASBESTOS, FIRE, &c.

=INCOMPAT'IBLES.= In _medicine_ and _pharmacy_, substances which exert a chemical action on each other, and cannot, therefore, with propriety, be prescribed together in the same formula or prescription. The principles on which we should act to avoid prescribing or dispensing incompatibles, are briefly developed under the heads AFFINITY and DECOMPOSITION. To this we may add that, if a substance is endowed with well-marked therapeutical or poisonous properties, independent of those which may exert a chemical effect upon the tissues, its mode of action will neither be changed nor destroyed by the combinations which it forms, provided always that the new compounds are not insoluble in water.

"It is not necessary to give two incompatible medicines at the same time, in order to produce decomposition; it is sufficient if they are given within a very short interval of each other. Thus, a sick person, who has been treated with lead externally, or even internally, will present a discoloration of the skin, if he takes a sulphur bath four or five days after the lead treatment has been discontinued. If a person is rubbed with iodide of potassium shortly after having applied Vigo's plaster (plaster of ammoniacum with mercury), or the Neapolitan ointment (mercurial ointment), iodide of mercury and caustic potash will be formed, which will cause vesication. So also vomiting occurs if lemonade made with tartaric acid is taken five or 6 days after the administration of white oxide of antimony." (Trousseau and Reveil.)

Lists of incompatibles are published in many pharmaceutical and medical works, but are, in reality, of little use beyond illustrating rules and principles which are familiar to every chemist, and which every prescriber should also be intimately acquainted with.

=INCRUSTATION, Prevention of, in Steam Boilers.= With all qualities of water commonly used for feeding steam boilers there is a tendency to the production of hard calcareous deposits or layers of incrustation within the boilers, due to the separation of lime salts (particularly the carbonate and sulphate, or mixtures of these with a certain amount of carbonate of magnesia) as the direct consequence of the accumulation of these impurities from large quantities of water evaporated. The sparing solubility of the sulphate of lime (gypsum) in hot water fully accounts for its deposition in the boiler, and the carbonate of lime (chalk) is thrown down, not only as the result of direct evaporation, but by the ebullition expelling free carbonic acid, which holds this body to some extent in solution. Rain water, which of itself is too pure to give rise to these incrustations, cannot be used _alone_ for boiler purposes, for it has been found to exert a highly corrosive action upon the iron plates and fittings. It can, however, be advantageously employed in conjunction with 'hard' spring or river waters, and has the effect of diminishing the incrustation merely as the result of dilution. The drain pipes leading from the roof of the factory may be placed in connection with the tank or well from which the supply of water is drawn for the boilers. It will be seen hereafter that the self-same remedy is efficient both as a means of preventing incrustation and obviating corrosion, and that by using one of the alkaline substances about to be specified this twofold advantage may be secured. Iron will not rust when immersed in water containing a mere trace of caustic alkali, and it is a common observation that the iron vessels used in the preparation of potash and soda remain for any length of time free from all appearance of rust. This singular property is, no doubt, susceptible of important applications, amongst them may be mentioned the better protection of iron ships from the attack of bilge water, of hydraulic rams, moulding boxes, smith's tools, and other objects liable to be placed at times under the influence of water. Some forms of surface condensers become quickly corroded in consequence of the purity of the water accumulating in them by the process of distillation, and a small dose of caustic alkali is then useful as a means of protection; the engine-cylinders also to some extent are preserved when alkaline anti-incrustation fluids are introduced into the boilers, for the minute quantity which is carried forward mechanically in the form of spray mixed with the steam, suffices to preserve the iron. Whilst a tendency to 'priming' undoubtedly results from a too liberal use of soda or other alkali in the boiler, it will in practice be found easy to adjust the proportion of this ingredient, so as to secure immunity from corrosion and incrustation, and at the same time, avoid the tumultuous kind of ebullition known as 'priming.' In all cases it is advisable to carry out a rigid system of inspection, and it is only in the way of saving fuel and labour that the application of boiler fluids is to be recommended.

Much benefit has often resulted from a coating of coal-tar or 'dead oil' applied to the interior surfaces below the water line, when the boiler is opened for cleaning and inspection. These will tend very considerably to lessen the adhesion of calcareous crusts, and are not in any way affected by the boiler fluids in common use. Soda crystals and caustic soda may be used with great success in boilers to effect the immediate precipitation of the lime salts, and they act by throwing down a finely divided form of carbonate of lime, which in time furnishes nuclei for the deposition of subsequent accretions both of the carbonate and sulphate, so that they are prevented from crystallising upon the walls of the boiler. A granular mud is thus formed, which subsides quickly and may be for the most part got rid of through the 'blow-off cock,' which should be opened for this purpose two or three times every day, and run out with as little water as possible.

The use of caustic soda has undergone a thorough trial at the hands of Mr J. Spiller, F.C.S., in the boilers of the Royal Arsenal, Woolwich, and we are favoured with the following general instructions regarding its use, which are based upon an experience of upwards of ten years. The caustic soda should be dissolved in water so as to make a concentrated solution of specific gravity 1·300. This, being perfectly miscible with water, may be introduced into the boiler with the feed-water at any time when, from the pressure of steam, it may not be convenient to pour it through the safety valve or other openings in the boiler. But when the steam is down there is no difficulty in introducing the prescribed dose by using a tin funnel with flattened aperture to pass it through the safety valve; or a tubular arrangement with double cocks will answer at all times. Half a gallon per diem is the average quantity found sufficient for a 20-horse stationary boiler, working with Thames water for ten hours daily. If the water should happen to be unusually hard a larger dose may be employed, but it would not be expedient to add in one charge more than the amount required for the day's consumption. Locomotive and multitubular boilers have been worked successfully with caustic soda, and it is here that the importance of using anti-incrustation fluids makes itself most apparent.

Many other methods have at various times been proposed to prevent the formation of deposits in steam boilers. Dr Ritterband's method consists in simply throwing a little sal ammoniac into the boiler, by which carbonate of ammonia is formed, which passes off with the steam, and chloride of calcium, which remains in solution. In Holland this plan has been used with satisfaction for locomotive boilers. About 2 oz. of the salt may be placed in the boiler twice a week. The chloride of tin is equal to sal ammoniac, and is similar in its action. Carbonate of soda has been recommended by Kuhlmann and Fresenius of Germany, and by Crace Calvert of England. It is now employed generally in the boilers of engines in Manchester. The common plan adopted by working engineers to prevent incrustations from either variety of water is, on each occasion of cleaning out the boiler, to introduce some substance which, by its mechanical action, shall prevent the precipitated earthy matter caking together, or adhering to the boiler plates. Some common tar, bitumen, or pitch, appears to answer well under most circumstances. Mr Ira Hill recommends the use of 3 or 4 shovelfuls of course sawdust. He states that, after adopting the use of this article, he never had any difficulty from lime, although using water strongly impregnated with it, and has always found the inside of his boilers as smooth as if just oiled. Mr De Haen recommends the sulphate and bicarbonate of calcium to be decomposed by adding barium chloride and milk of lime in the proper proportion; when the water is at a temperature of 35°-45° C. the whole becomes clear in about ten minutes, a precipitate consisting of a mixture of barium sulphate and calcium carbonate deposits; if the water be cold, the greater part separates in ten minutes, but a little turbidity is noticeable for some hours due to suspended matter.

Protzen recommends the introduction of a piece of zinc into the boiler, this determines a galvanic current, which protects the iron against oxidation and corrosion, and causes the mineral ingredients of the water to be deposited as a fine loose mud, entirely preventing the formation of incrustation.

Slippery elm bark, and spent bark from the tan works have also been suggested. We (A. J. Cooley) have worked a powerful boiler daily for months without opening the 'man-hole,' after throwing a few pounds of potatoes into it. In all cases, when the earthy matter can be kept in a state of solution, or precipitated in a pulverulent form, it is easily removed from the boiler by what engineers term 'priming,' which is allowing the hot water to be blown over with the steam, so that, after a sufficient time, the whole original contents of the boiler are removed, and replaced by fresh water. Before doing so, however, it is of consequence to cut off the communication with the cylinders, and to open the waste-steam cock. Consult a pamphlet on 'Boiler Incrustation and Corrosion' by F. J. Rowan, published by Spon, London.

=INCUBA'TION (Artificial).= The hatching of eggs by artificial heat. This has been practised by the Egyptians from a very remote period. M. Bonnemain has the honour of having introduced this art to Western Europe, in 1775, and having been the first to pursue it successfully on the commercial scale. The source of heat employed by him was a circulatory hot-water apparatus, and the temperature maintained by it 100° Fahr. His plan was to introduce, daily, 1-20th only of the eggs the apparatus was capable of receiving, so that on the 21st day the first chickens were hatched, and a like number every day afterwards as long as the supply of eggs was kept up. Among the trays containing the eggs he placed saucers of water, to compensate for the absence of moisture derived in natural incubation by transpiration from the body of the hen. The chickens, as soon as hatched, were transferred to a 'nursery' or 'chick-room,' also artificially heated, and were fed with crushed millet seed. Several attempts have been made of late years to introduce artificial incubation into this country, with variable success.

=IN'CUBUS.= See NIGHTMARE.

=IN'DIA RUB'BER.= See CAOUTCHOUC.

=INDIGES'TION.= See DYSPEPSIA.

=IN'DIGO.= _Syn._ INDICUM, PIGMENTUM INDICUM, L. A blue dyestuff extracted from several plants growing in India and America, especially from the leguminous species _Indigofera tinctoria_ and _I. c[oe]rulea_. It exists in the plant as a colourless juice. The method of manufacture consists in steeping the plant in water until fermentation sets in; the colouring matter dissolves in the water, forming a yellow solution, which is drawn off from the rest of the vegetable matter, and agitated and beaten to bring it freely into contact with the air for about 2 hours; this treatment causes the indigo to form and settle down as a blue precipitate; this is cut, while soft, into cubical cakes, and dried by artificial heat. To hasten the formation of the indigo, a little lime water is sometimes added to the yellow solution. The indigo of commerce contains INDIGO-BLUE or INDIGOTIN, its most important constituent, INDIGO-RED, and many other substances, some of which must be regarded as accidental impurities or adulterations.

_Prop._ Tasteless; scentless; of an intense blue colour, passing into purple; when rubbed with a smooth hard body, it assumes a coppery hue; insoluble in water, cold alcohol, ether, alkalies, hydrochloric acid, dilute sulphuric acid, and the cold fixed and volatile oils; slightly soluble in boiling alcohol and oils; freely soluble in concentrated sulphuric acid, and, when decoloured or reduced by contact with deoxidising substances, in alkaline lyes; soluble in creasote; its colour is destroyed by chromic acid, nitric acid and chlorine; when suddenly heated, it gives off rich purple fumes, which condense into brilliant copper-coloured needles.