hollow, opening opposite the mouth of one of the trumpets, and communicating with a large case placed in an adjoining room, and containing the confederate.

Upon this principle also is constructed the oracular bust, which is thus made :-Place a bust on a pedestal in the corner of a room, and let there be two tin tubes, one going from the mouth and the other from the ear of the bust, through the pedestal and floor, to an under apartment; there may likewise be wires that go from the under jaw and the eyes of the bust, by which they may be easily moved. A person being placed in the under room, and at a given signal applying his ear to one of the tubes, will hear any question that is asked by another person above who speaks into the ear of the bust, and he may immediately reply; the sound will move through the tube, and seem to come from the mouth of the bust.

INVOICE; an account, in writing, of the particulars of merchandise, with their value, custom, charges, &c., transmitted by one merchant to another in a distant country.

INVOLUTION, in mathematics; the raising of a quantity from its root to any power assigned. Thus 2x2x2=8. Here 8, the third power of 2, is found | by involution. By continuing the process, we can obtain any power of 2, and so with other numbers.

somewhat analogous to that of chlorine. It is a non-conductor of electricity, and possesses in an eminent degree the electrical properties of oxygen and chlorine.

Iodine enters into fusion at 225° Fahr., and boils at 347°; but, when moisture is present, it sublimes rapidly at a temperature considerably below 212°, and gives rise to a dense vapour of the usual violet hue. It is scarcely at all soluble in water, but is readily taken up by alcohol and ether, to which it imparts a reddish-brown colour. It extinguishes vegetable colours, but with less energy than chlorine. It is not inflammable. Its range of affinity for other bodies is very extensive; the most important compounds it forms with these we shall describe after alluding to its natural state and preparation. It exists most abundantly in the various species of fucus, which form the greatest part of the sea-weeds of our coast; it also occurs in the sponge, and in the coverings of many molluscous animals, and has been found in a great number of mineral waters, as those of Salz in Piedmont, Saratoga in New York, &c., and more recently has been detected in some silver ores from Mexico, and in an ore of zinc from upper Silesia. But it is from the incinerated sea-weed, or kelp, that the iodine in large quantities is obtained.

As the soap-manufacturers are in the habit of obtaining their soda from kelp, iodine may be procured, very economically, from the residuums of their opera. tion, according to the process invented by Dr. Ure, which is as follows:-The brown iodic liquor of the

IODINE is the name of an undecompounded principle or element in chemistry. It had escaped the observation of chemists until 1812, when a manufacturer of saltpetre, at Paris, detected it in the ashes of sea-soap-boiler, or the solution of kelp from which all weeds, in the following manner. In evaporating the the crystallizable ingredients have been separated by ley from these ashes, to procure the carbonate of concentration, is heated to about 230° Fahr., poured soda which they contain, he noticed that the metallic into a large stone-ware, basin, and saturated with vessels with which he operated were powerfully cor- diluted sulphuric acid. When cold, the liquor is filroded, and that the corrosion was increased as the tered through woollen cloth; and to every 12 oz. liquor became more concentrated. Having at hand, | (apothecaries' measure) of it are added 1000 grains of one day, a bottle of sulphuric acid, he added some black oxide of manganese in powder. The mixture of it to a portion of water, and was surprised to see is put into a glass globe, or large matrass with a wide a rich violet vapour disengaged; this vapour was the neck, over which a glass globe is inverted, and heat iodine. He at once communicated the observation is applied, which causes the iodine to sublime coto M. Clément Desormes, who set about collect- piously, and to condense in the upper vessel. As ing some of the vapour, and, after examining its soon as the balloon becomes warm, another is subleading properties, announced it to the Royal Insti- stituted for it; and, when the second becomes heated, tute of France as a new body. Its real nature was the first is again applied. The iodine is withdrawn soon after unfolded through the accurate researches from the globes by a little warm water, which disof Gay-Lussac and Sir H. Davy. Its history proved solves it very sparingly; and it is purified by undersingularly interesting in modifying the then prevail- going a second sublimation. The test made use of ing theory of chemistry. Sir H. Davy had, a few for the detection of iodine in any solution, when it years previously, promulgated the new theory of is suspected to be present, is starch, with which chlorine, which was still received with suspicion iodine has the property of uniting, and of forming among chemists. The strong analogies, however, with it a compound, insoluble in cold water, which between this substance and chlorine, in their relations is recognized with certainty by its deep blue colour. to combustibles,-both bodies forming compounds The solution should be cool at the time of adding the by uniting with them, similar to acids containing starch; and, if the colour does not become apparent oxygen, or oxides,-were conceived to give great simply on the addition of the starch, a few drops of weight to the views of Sir H. Davy, and operated sulphuric acid should be cautiously added, when, if completely to overthrow the erroneous hypothesis of any iodine be present, the blue colour will make its oxygenation invented by Lavoisier. Its investiga-appearance. This test is so exceedingly delicate tion, therefore, may be said to form a new era in that a liquid, containing of its weight of iodine, chemistry. receives a blue tinge from a solution of starch. The physical properties of iodine are as follow:- Iodine has a powerful affinity for hydrogen, which It is a soft, friable, opaque solid, of a bluish-black it takes from animal and vegetable substances, in the colour, with a metallic lustre, usually in scales, but same manner as chlorine, and, uniting with it, forms sometimes in distinct crystals of the form of rhom-hydriodic acid. The following are the methods for boids or rhomboidal tables, referrible to an octaheJron, with a rhombic base as their primary form; its specific gravity is 4.046. It possesses an odour

obtaining this acid in the gaseous and in the liquid state:-Into a flask, to which a recurved tube is fitted, dipping under a jar of mercury, are introduced eight

parts of iodine and one of phosphorus, and to the | acid, which is also formed by simply immersing dry mixture a few drops of water are added; the water iodine in chlorine gas, deliquesces in the open air, and is immediately decomposed; the phosphorus, seizing dissolves very freely in water. Its solution is very its oxygen, forms phosphoric acid, while the hydro- sour to the taste; and it reddens vegetable blues, but gen combines with the iodine. As there is not wa-afterwards destroys them. It does not unite with alter present in sufficient quantity to dissolve the hy-kaline bases; in which respect it wants one of the chadriodic acid, it passes over in the gaseous state, and racteristics of an acid, and has hence been called by is collected over the mercury. In contact with air, Gay-Lussac a chloride of iodine. Iodine unites with it smokes, or fumes, like muriatic acid, and, like it, nitrogen, forming a dark powder, which is characreddens vegetable blues. It is distinguished, how-terized, like chloride of nitrogen, by its explosive proever, from that acid, by the superior affinity pos-perty. In order to form it, iodine is put into a sosessed by chlorine for hydrogen, in consequence of lution of ammonia; the alkali is decomposed; its which, if chlorine and hydriodic gases are mingled elements unite with different portions of iodine, and together, the yellow colour of the former disappears, thus cause the formation of hydriodic acid and iodide and the violet vapour of iodine makes its appearance, of nitrogen. Iodine forms, with sulphur, a feeble which proves the decomposition of the hydriodic acid compound, of a grayish-black colour. With phosby the chlorine. If the decomposition be complete, phorus, also, it combines with great rapidity at comthe vessel will be wholly occupied by muriatic acid mon temperatures, attended with the emergence of gas, heat. It manifests little disposition to combine with metallic oxides; but it has a strong attraction for the pure metals, producing compounds which are called iodurets, or iodides.

less than in the preceding instance. Silver forms with | ney. The entire furnace is built in a very solid manit a perfectly malleable compound, the surface of ner, and strengthened by bands and cross bars of iron. which is merely tarnished by cupellation; yet the The bellows are usually cylindrical, and their pistons iridium appears to be diffused through it in fine pow-worked either by water or a steam-engine. The blastder only. Gold remains malleable, and little altered holes, which are situated in the upper part of the in colour, though alloyed with a considerable propor- crucible, are two in number, and frequently placed tion; nor is it separable by cupellation. Dr. Wollas-on opposite sides, but so angled that the currents of ton observed that, among the grains of crude pla-air do not impinge on each other. At the lower part tinum, there are some scarcely distinguishable from of the crucible are openings for the discharge of the the rest but by their insolubility in nitro-muriatic metal and scoria. These openings are kept stopped acid. They are harder, however, when tried by the by accumulations of clay and sand upon the exterior file, not in the least malleable, and of the specific gra- when the furnace is in operation. The process of vity of 19.5. These he concluded to be an ore con- reduction commences by first gradually heating up sisting entirely of iridium and osmium. the furnace, until it will bear to be filled entirely with fuel, after which, as the contents of the furnace begin to sink, alternate charges of ore mingled with flux, and of charcoal or coke, are added: the blast is let on, and the metal in the ore, parting with its oxygen, flows by degrees, and subsides to the bottom of the crucible, covered with a melted slag. The slag is occasionally allowed to flow off by re

IRON. This metal is extremely diffused. It exists in the mineral kingdom in large quantities, and under numerous forms; it is a constituent principle of vegetable matter, and is obtained from the ashes of almost every plant; it exists in the blood, and other animal products; it is even an atmospheric or meteoric production, those stony masses which at different times, and in different countries, have fallen from the at-moving the clay from some one of the apertures in mosphere, containing iron as their principal ingredient.

the crucible; and when the bottom of the furnace becomes filled with the metal, which it ordinarily does after a space of nine or twelve hours, the iron itself is discharged by one of these openings, into a fosse of sand mingled with clay. As soon as the iron has flowed out, the aperture is closed again; and thus the furnace is kept in incessant activity.

The ores from which iron is extracted are those in which it is mineralized by oxygen, of which there are many varieties, consisting of the oxide intermixed with argillaceous, calcareous, and silicious earths. It is principally from the argillaceous ore, or clay iron-stone, that iron is extracted in this The flux employed to assist the fusion of the ore, country. After raising, the ores are picked, to sepa- by vitrifying the earths associated in it with the oxide rate, as far as possible, the considerable pieces of of iron, is limestone of the best quality. The iron earthy or otherwise refractory matters, with which which has run out from the blast-furnace is in the they may be associated. They are next submitted condition of cast-iron, or iron with a considerable to a roasting, in large heaps, in the open air, to expel portion of carbonaceous matter intermingled with the sulphur and arsenic which they may contain, as its particles, and a small proportion of oxygen, from well as to render them more friable and easy of fur- which causes it has a coarse grain, and is brittle. In ther reduction to powder. The roasting is performed converting it into bar-iron, it undergoes one or the generally by bituminous coal. The result of the other of the following processes, according as charoperation is, that it becomes full of fissures, friable, coal or coke is employed. In the former case, a furand loses altogether its vitreous lustre. It is now nace is made use of resembling a smith's hearth, transferred to the crushing-mill, where it undergoes a with a sloping cavity sunk from ten to twelve inches further pulverization, after which it is transported to below the blast-pipe. This cavity is filled with charthe smelting furnace, to be converted into iron. Here coal and scoria, and on the side opposite to the blastit passes through two distinct operations-1. the re-pipe is laid a pig of cast-iron, well covered with hot duction of the oxide to the metallic state; 2. the fuel. The blast is then let in, and the pig of iron, separation of the earthy matters in the form of scoria. being placed in the very focus of the heat, soon These processes consist in exposing the ore, ordi- begins to melt, and, as it liquefies, runs down into the narily mixed with certain fluxes, to the action of car- cavity below. Here, being out of the direct influence bon at an elevated temperature, in furnaces urged by of the blast, it becomes solid, and is then taken out bellows, hence called blast-furnaces, or sometimes high- and replaced in its former position, the cavity being furnaces. These furnaces vary in height from twelve again filled with charcoal. It is thus fused a second to sixty feet, and have, externally, the shape of a four-time, and after that a third time, the whole of these sided pyramid, truncated at top, and terminating in a cylindrical chimney, whose internal diameter is from four to six feet. The interior body of these furnaces is usually in the circular form, except the laboratory at its bottom, where the liquid metal gathers. This, called sometimes the crucible or hearth, is a rightrectangular prism, oblong in the direction perpendicular to the blast orifices, or tuyeres of the bellows. The sides of the crucible are commonly made of a fine gritstone.

Above the crucible the boshes are placed, in the form of an inverted quadrangular pyramid, approaching to the prismastic shape; and above these stone boshes rises the conical body of the furnace, lined with fire-bricks, contracting as it ascends, like the narrow end of an egg, until it terminates in the chim

three processes being usually effected in between three and four hours. As soon as the iron is become solid, it is taken out and very slightly hammered, to free it from the adhering scoria. It is then returned to the furnace, and is placed in a corner, out of the way of the blast, and well covered with charcoal, where it remains till, by further gradual cooling, it becomes sufficiently compact to bear the tilt, or triphammer, whose weight varies from 600 to 1200 lbs., and which is moved by water. Here it is well beaten, till the scoria are forced out, and is then divided into several pieces, which, by a repetition of heating and hammering, are drawn into bars, and in this state it is ready for sale.

The stream of air employed in a blast-furnace is procured by various processes. The first and most

IRON MANUFACTURE.