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also the length of the stroke. Twenty strokes per minute are made in each of the three cylinders, corresponding to an expulsion of nearly 5,000 cubic feet of air per minute. The fourth cylinder is used to regulate the pressure, as will be explained presently. The piston-rods arc worked so that while one is at the highest, anotner is half-way down or up, and the third is quite down. A large iron wind-chest, 22 feet 5 inches long, is situated in the cellar below: on this the four cylinders are fixed. The bottom of the fourth cylinder is open to the chest; the others are closed at bottom. From this chest, under the third cylinder, proceeds the main eduction-pipe, from which branch-pipes proceed to the several forges, each pipe being furnished with a cock for turning the blast on or off. Behind the eduction-pipe is a short cylinder, containing a valve, shown in the section, Fig. 129, which passes through the axis both of the valve cylinder and the blowing cylinder.

On the principal axis arc three eccentric wheels, with iron straps, connected with a lever under the

wind-chest, and these wheels arc so arranged in respect to the corresponding crank that when the piston of any cylinder is either above or below, the lever is horizontal, and the valve v exactly closes the hole h. When the piston in this figure begins to ascend, the end E of the lever continues to ascend also, and the other end p descends, and being connected with the valve-rod at o, this also descends, and opens a communication between the interior of the cylinder and the external air, which rushes in with a fresh supply. This valve continues to descend until the piston is half-way up; it then begins to ascend until the piston is at the highest point, when the valve has the position shown in the figure. The piston now descends, but the valverod continues to ascend, and opens a communication between the cylinder and the wind-chest, into which the air is forced by the piston. When the piston is half-way down, the valve-rod has reached the highest point, and then continues to descend with the piston until the latter is down, when the hole A is again covered with the valve. In this way the three cylinders arc successively opened to the atmosphere and to the wind-chest, and a constant influx of air is produced. To preserve a steady action in the valve-rods, they are made to pass through guards level with the floor v. The fourth cylinder has no bottom, but is open to the wind-chest, and its piston, which weighs 700lbs., serves only to regulate the pressure, which amounts to about \ lb. on the square inch. When the pressure exceeds this, the piston rises, and opens a safety-valve

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at the back of the cylinder. The form of the bottom of the cylinder in the section belongs only to that part of the cylinder: the other part is perfectly fiat, its purpose being to open a communication with the valve-cylinder.

BENZOIC ACID. When bitter almonds arc subjected to great pressure, a fixed oil is obtained. By distilling with water the almond-paste which remains, a volatile oil is obtained, which is prepared in large quantities, chiefly for the use of the perfumer. This oil does not pre-exist in the almonds, but appears to be formed by the action of water upon a peculiar crystallizable substance called amygdaline, aided by the presence of the pulpy albuminous matter of the seed. The crnde oil has a yellow colour, and contains a quantity of hydrochloric acid, which is formed at the same time as the oil. By agitating it with a solution of protochloride of iron, containing an excess of hydrate of lime, and then distilling the whole, the essential oil is obtained in a purified form. It is freed from the water which passes over with it by means ot fused cldoride of caleinm.

This oil is supposed to be the hydruret of a basic substance named benzoyle, from its relation to benzoic acid, containing Cu H5 0«. Pure hydruret of benzoyle, or bitter-almond oil (Cu H5 08 + H), is a thin colourless fluid, of great refractive power, and of a peculiar and agreeable odour; its density is 1.043, and its boiling-point 356°. Its vapour is inflammable, and burns with a bright smoky flame. It is soluble in about 30 parts of water, but aleohol and ether dissolve it indefinitely. It absorbs oxygen rapidly from the air, and forms a mass of crystallized benzoic acid. It is doubtful whether the pure oil is poisonous, but the crnde product is highly so, and yet this is sold for flavouring pnddings, custards, &c.

Benzoic acid, or oxide of benzoyle, BzO (Ci,H;,Os -I- O), is not usually obtained by the oxidation of bitter-almond oil. Several of the balsams, especially gum-benzoin, yield benzoic acid in abundance. By exposing this substance to a gentle heat in a subliming vessel, the benzoic acid is volatilized, and condensed in the upper part of the apparatus. The best contrivance for this purpose is a shallow iron pan, containing the substance to be sublimed, in a thin layer: a sheet of bibulous paper, pierced with a number of pin-holes, is stretehed over the pan, and a cap of stout cartridge-paper, secured by a string or hoop, is drawn over the whole, as in Fig. 130. The pan is slowly heated on a sand-bath; the vapour Fig lMof the acid condenses in the cap, and the crystals are prevented from f falling back into the pan by the | porous paper. The acid thus obtained is in the form of snow-white,. light, feathery crystals, with a fragrant odour, which is due to the presence of a small quantity of volatile oil. A more abundant product may be obtained by mixing the powdered gum-benzoin with an equal weight of hydrate of lime, boiling the mixture with water, filtering, and evaporating, and then decomposing it with an excess of hydrochloric acid. The benzoic acid crystallizes out on cooling, in thin plates, which may be drained upon a cloth filter, and dried in the air. By sublimation the acid may be obtained perfectly white. The crystals obtained in this way contain an equivalent of water, so that the formula for the hydrous acid is C,4 H3 0, + HO.

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Benzoic acid is inodorous when cold, but has a faint smell when gently heated; it fuses just below 212°, and sublimes a little above that point: it boils at 462°, and emits a dense vapour, which is very irritating to the throat and eyes. It dissolves in about 200 parts cf cold, and 25 of boding water. It dissolves in about twice its weight of aleohol; it also dissolves in ether, and in fat and volatile oils. It combines with bases, and forms salts, which are called benzoates.

Benzoic acid is an ingredient in some kinds of perfumery, and in fumigating powders and pastiles. It was formerly used as an expectorant in asthma and dry cough. When taken internally, it is rejected trom the system in the state of hippuric acid, which occurs in large quantity, in combination with potash or soda, in the urine of horses, cows, and other graminivorous animals. If the urine be slightly putrid, it yields benzoic instead of hippuric acid. Much of the cheap benzoic acid of commerce is prepared in this way, the perfume being superadded by subliming with a little gum-benzoin. Benzoic acid is a principal ingredient in friars'-balsam, useful for stimulating languid wounds, but mischievous when applied to recent wonnds. A cosmetic, under the name of virgin's-milk, is prepared by mixing two drachms of the aleoholic solution of benzoin with a pint of rose-water.

The other benzoyle compounds, such as the chloride, bromide, iodide, and sulphuret of benzoyle, possess great chemical interest, but are not of importance in a manufacturing point of view.

BILE. A secretion separated from venous blood by the largest internal organ of the body, the liver. It was regarded by the old chemists as a saponaceous compound, in which an organic acid was combined with soda. Modern chemists nave re-adopted this view, regarding bile as a soda-soap, and, as such, the bile of the ox, or ox-gall, as it is called, is used in the arts, by painters in water-colours, scourers of ctothes, and many others; but, from its green colour, it requires for many purposes to be clarified. This is done by allowing the fresh gall to settle for a day in a basin; the liquor is then poured off from the sediment into an evaporating-dish, and exposed to a boiling heat in a water-bath until it is somewhat thick. It is then spread upon a dish, and dried before the fire, in which state it may be kept for years in jelly-pots covered with paper. When required for use, a piece of the size of a pea may be dissolved in a table-spoonful of water. The gall may be made perfectly colourless by the following process: A pint of gall is to be boiled and skimmed, and an ounce of alum, in fine powder, or an ounce of common salt, added; the mixture to be kept on the fire until

the alum is dissolved. The mixture, when cool, is to be poured into a bottle, and loosely corked. In about three months it deposits a thick sediment, and becomes clearer. The clearer portion of the gall prepared with alum is then to be mixed with the clear portion of the gall prepared with salt, when the colouring matter will be coagulated and precipitated, leaving the ox-gall perfectly colourless. It may, if necessary, be further purified by passing it through filtering-paper. This gall becomes purer by keeping, and never loses its good qualities, nor contracts a disagreeable smell.

Prepared gall combines with colouring matters and pigments, and gives them solidity either by being mixed with or passed over them upon paper. It adds to the brilliancy of ultramarine, carmine, green, and most delicate colours, and makes them spread more evenly upon paper, ivory, &c. Mixed with gum arabic, it thickens the colours without giving a glistening appearance; it prevents the gum from craking, and fixes the colours so well, that others may be applied over them without running into them. Mixed with lamp-black and gum, it forms a good imitation of China ink. A coat of ox-gall upon black-lead or crayon drawings prevents the lines from being effaced, and such drawings may be safely coloured by first mixing the colours with ox-gall. Miniature painters use it for removing the unctuous matter from the surface of ivory, and when ground with the colours it enables them to be spread easily and renders them fast. It is also useful for transparencies, by passing it first over the varnished or oiled paper and allowing it to dry. The colour ismixed with the gall and then applied, and cannot afterwards be removed.

It takes out spots of grease and oil, and is useful to the laundress in washing dresses, the colours of which would run or be removed by the ordinary process of washing. A small portion dropped into ink renders it fluid.

BINNACLE, or BITTACLE (from the French, habitacle, a small habitation). The box in which the compass is placed for steering a ship. The form is not of much importance by day, provided the man at the helm can get a good view of the compass-card; but at night it is of great consequence to throw the strong light of a lamp on the card, to preserve the lamp from the action of wind and weather, and to prevent its light from being seen out of the ship.

Sir Home Popham's binnacle is in general use in the navy. It consists of a square box about 2 feet high and 18 inches in the side, with a top in the form of the frustum of a square pyramid. The four sides are glazed with plate-glass, and the compass-card, which is about level with the upper part of the square box, is distinctly seen. By night thin copper screens shut up those sides which are not necessary for the steersman's purpose, and the inner surfaces of these screens assist in reflecting the light of the lamp strongly upon the card. The lamp is attached to one of these screens, a hole being cut in it to admit the necessary light. To prevent the fracture of the glass surfaces, the four edges of the frustum are defended by a strong wooden frame with projecting edges, and at the top by a flat piece of wood also projecting considerably beyond the glass.

A good arrangement of a ship's binnacle is that by Mr. Grant Preston, of Wapping, described in the Transactions of the Society of Arts. The defects of the ordinary binnacle and compass-box are first pointed out by him. The compass-box is generally of wood, aud square, containing within it a cireular brass box suspended on gimbals; within this is the compasscard, the points of which are read against a mark within the brass box, called the lubber's point or mark. A line drawn from this to the centre of the compasseard should be exactly parallel to the line of the ship's keel, or her course by the compass will not be correct. The mode of fitting the compass-box into the binnacle is by driving wedges all round to make it fast, but nothing is done to make it truly parallel with the ship's keel. The binnacle is sometimes made with three divisions instead of two, in which case a compass is placed in the two outer divisions, and the light between them; but this method is objectionable, because the needles are liable to act upon each other. The light is often thrown upon the compass-card very imperfectly, and may also be seen at a distance from the ship, which is an objection.

Mr. Preston's binnacle has a cylindrical top for enclosing the lamp in a case, so that it can be lighted below in bad weather. The light is powerful and steady, and is thrown vertically upon the compass-card, and the expenditure of oil is small. No direct light is seen, to dazzle the eye of the steersman, nor is any light shown which can be seen by the enemy at sea. Fig. 131 represents this binnacle as it standsupontbe

deck of a vessel, opposite to the steering-wheel. Fig.132 is a section of the box containing the lamp and reflector. A A is a square box closed by a door in front, but omitted in the figure in order to show the interior. This box is fixed down, with the two sides parallel with the ship's keel. B is a shelf in the box, to support a board c, which exactly fits the box, but has its angles taken off, to allow it to slide in and out freely: it has a stem a, of brass wire, standing up from the centre, and terminating in a sharp point, on which

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the compass-card is freely suspended to turn round; being then included within a cireular opening made through the top of the box, and its divisions reading against the lubber s point, drawn on a piece of white paper, and seen plainly in the figure. The opening in the top of the box is surrounded by an octagonal lantern, which has glass panes in all its sides, which are clos:;d at night by sliding shutters a a. The compass is seen through the glass b, placed at a proper inclmation to commaud the view of the card. The lamp is situated in a cireular box, fitted with a ring P at the top of the lantern-frame, and as a dome G, with a chimney d to carry oft' the smoke. The section, Fig. 132, will explain the interior parts, n Ii are the sides of the cylindrical box which fits into the ring/, Fig. 133. ee ff are the sections of two brass cireles or gimbals, shown separately in Fig. 133. The external one has two projecting points, which are received in pieces of copper, soldered to the inside of the box; the internal ring has similar pivots, but these are received into holes in the outer ring, the direction of the two lines of pivots being at right angles to each other, so that the interior ring, and all that it supports, hasauniversal motion, and, if properly balanced, will preserve its horizontal position in any inclination of the box. i K is a brass box, shown separately, fitting the ring f, and in the bottom is a large planoconvex lens, K K, which concentrates the light of the lamp, and throws it' down upon the card. The lamp L is just within the box: it consists of a deep hollow hoop of copper, l, Fig. 133, for containing the oil, whien is poured in by two tubes, g h. The wick »' is contained in a narrow spout proceeding from the interior lo the centre of the hoop, and the flame projects over the end of the spout. The conical chimney M mcludes a reflector of tinned iron, well polished, which reflects the light downwards. By these means the card is well illuminated, and if the shutters a a be put down, no light escapes except at the aperture b, and this directs the light upwards in a direction in which it will not fall upon any part of the ship.

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BIRD-LIME. This substance is now in great part imported into England from Turkey, but was formerly manufactured here to a considerable extent, and exported to India for the purpose of destroying insects. It is a green substance, viscid and tenacious, made from the bark of various shrubs, but chiefly from that of the common holly. It may also be made from mistletoe and other parasites. It contains a resin (which has been called tiscine), mucilage, colouring and extractive matter, and a little free acid. The middle bark of the holly contains a large amount of viscid matter, and from this, and the bark stripped from the young shoots, the best birdlime is made. The bark is boiled six or eight hours in water, until tender; it is then drained from the water, and laid in pits, for two or three weeks, to ferment, being occasionally moistened with water, if necessary. After this it is taken out, and reduced to a paste by pounding in mortars, then washed and kneaded, and packed in earthen vessels. After three or four days, during which it ferments and purifies itself, it is fit for use.

BISCUIT (Latin, bis coctm, twice baked). An unfermented bread, which, if properly prepared, can be kept for a great length of time, and hence its use as a common form of bread at sea. At present the ships of the Royal Navy are supplied with biscuits made by machinery, before the introduction of which they were made by hand in the following manner. A gang of five men were employed, who were severally named, thefurner, the mate, the driver, the breakman, and the idleman. The driver made the dough, by mixing the flour and water together in a trough with his naked arms, until, by a laborious operation, a proper consistency was obtained. The rough dough was then deposited on a break, or wooden platform, to be worked by the breakman, who kneaded it by riding or jumping upon it by means of a breakstaff. When sufficiently kneaded, it was taken to a strong table, called the moulding-board, where it was first cut into slips, then divided into lumps of the size of the biscuit, then moulded by hand into the circular shape, and lastly docked, or pierced full of holes, by means of a docker, the whole of the gang assisting in this operation. The oven being properly heated, the biscuits were pitehed in by the joint labours of the furner, the mate, and the idleman. The gang thus produced 100 lbs. weight of biscuit in 36 minutes, inclnding 15 minutes, the time allowed for baking. Hence the nine ovens in the Royal Clarence Victualling Yard at Gosport required the lalwur of 45 men to keep them in full operation, and the produce was about 14 cwt. of biscuit per hour, at a cost for labour and utensils of 19rf. per cwt.

The good quality of biscuit chiefly depends on the thorough kneading of the dough, and its subsequent division into portions of equal size and thickness. If

the meal be not equally mixed with the water, some portions of the biscuit will be wetter than others, and will require more baking than the dry parts: these will be overbaked or burnt up, or the moist parts will remain unbaked; the biscuit thus becomes hard or flinty. So also if the biscuits are of unequal thickness, if the thin ones are not overbaked, the thicker must be underbaked; and the thin parts of a badly moulded biscuit will perish from the action of the fire, while its thick part is converted into flint.

About the year 1833 this method was superseded by machinery contrived for the purpose by Mr. Grant, of Gosport. In the first process, the meal is conveyed into a cylinder 4£ feet long, 3 feet 2 inches in diameter, and the water is let in from a cistern at the back of the cylinder, regulated by a gauge to the exact quantity required for mixing the meal. Through the centre of the cylinder is fitted a shaft armed with knives, and working horizontally. The shaft being set in motion, the knives revolve through the meal and water. During the first half-minute the meal and water do not appear to unite; but after this the dough begins to assume a consistency, and in two minutes 5 cwt. of well mixed dough is produced. The cylinder is formed so that its lower half is easily separated by means of a wheel and pinion from the upper sides, thereby forming a trough containing the dough, from which it is removed, and placed under the breakingrollers to be kneaded. These rollers, two in number, weigh 1,500 pounds each, and are propelled from off a two-throw crank-shaft by means of connecting rods and pendulums; they pass backwards and forwards over the dough during five minutes, when the 5 cwt. of dough is brought into a solid, perfect, and equal consistency. From the breaking-rollers the dough is cut into pieces 18 inches square, and placed on boards 6 feet long by 3 feet wide, which are conveyed by means of a line of friction-rollers connected by an endless chain unde'r a second set of rollers, to be rolled to the required thickness of the biscuit. The square of dough being thus pressed out, so as to cover the surface of the board, on which it is transferred under the cutting and stamping-plate, is at the same moment cut and stamped, or docked, into 42 hexagonal biscuits, which, being now complete, are at once conveyed to the oven on carriages constructed for the purpose. The hexagonal shape is preferred in order that there may be no waste, the sides of each biscuit by this contrivance fitting accurately into those of the adjoining biscuits, as seen in Fig. 134. Each biscuit Pig- IM.

is stamped with the broad arrow, the number of the oven, and also docked by the same movement which cuts it out of the piece of dough. The hexagonal cutters do not completely separate the biscuits, so that a whole sheet of them can be put into the oven at once, and after being withdrawn, they are broken asunder by hand.

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The corn for the biscuits is prepared at the Government mills: it is a mixture of tine flour and middlings. [See Bread.] The ovens are of wrought-iron, with an area of about 160 square feet. About 112 lbs. weight of biscuits is put into the oven at one time: this is called a suit, and is reduced to about 100 lbs. by the baking. The men engaged in this work wear clean check shirts, and white linen trousers, apron, and cap; and the most scrupulous attention to cleanliness is observed.

The bakehouse at Gosport was provided with one mixing-machine, two breaking-rollers, four sheetrollers, and four stampers; and it was caleulated that this machinery would require eight men and eight boys, to supply the nine ovens; that the produce per hour would be 10,000 biscuits, or one ton of bread, at a cost for labour and other incidental expenses of b$d. per cwt. It was found, however, in practice, that the machinery could easily supply eighteen ovens, should it ever be advisable to enlarge the bakehouse to that extent. With the exception of the men employed in heating and managing the ovens, no professional bakers are required, ordinary labourers and boys being fully competent to every other part of the work. This is a great advantage, since, in time of war, it has hitherto been found very difficult to supply the navy with biscuit, and the men employed as biscuit-bakers required very high wages. In the late war, double gangs of workmen were constantly employed; but the supply of biscuit was so inadequate that the Government was compelled to have recourse to contractors, who supplied,bad biscuit at a high price. It has been caleulated that the three bakehouses at Deptford, Gosport, and Plymouth, could, by working eight hours per day, produce annually 7,351 tons of biscuit. If this quantity had to be made by hand, the price paid for labour and utensils, at 19rf. per cwt., would amount to 11,643/. The machinery manufactures at h\d, per cwt., inclnding 10 per cent. for wear and tear, and all other expenses; so that this same quantity of biscuit would be produced for 3,217/., showing a net saving of 8.426/.1

The term biscuit is also applied to porcelain, when baked and not glazed. [See Pottery and Porcelain.]

BISMUTH. A metal of no great importance in the arts. It was first distinguished from lead by Agricola, in the 16th century. It is found native, and also in combination with oxygen, with arsenic and sulphur. It is found in very limited quantities in Cornwall, Germany, France, and Sweden. In the smelting works of the Saxon Erzegebirge, at Schnceberg, the metal is separated from its gangue by a very simple process. The ore is enclosed in tubes of iron plate, (Fig. 135), placed in an inclined position. The mineral is introduced by the opening at p, which is then shut. The other extremity is closed by a plate with a small aperture near the lower edge, through which the metal flows out as it is melted by the action of the heat. It is received into clay pots c on the outside, which are kept hot by a fire beneath them. From these pots the motal is ladled into (1) Nautical Magazine, vol. I. Now Scries. 1837.

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Bismuth (Bi 213) is a brittle white metal, with a slight red tint, which is very evident in holding a specimen by the side of a lump of antimony or zinc. Its specific gravity is 9.822. It fuses at 476°, or according to another authority 507°, and always crystallizes in cooling. It expands at the moment when it solidifies, so that it is lighter in the solid than in the liquid state. Good crystals may be obtained by carefully melting the purified metal, and then pouring it into a heated mould, and allowing it to cool very slowly and quietly. When a solid crust has formed on the surface, it is pierced in two opposite places near the edge, and the liquid metal is poured out at one hole, while the air enters at the other. The mould is then suffered to cool, and on removing the crust the cavity will be found lined with beautiful cubical crystals (Fig. 136), highly iridescent from the formation of a thin pellicle of oxide on the surface, at the moment when the hot metal comes in contact with the air. Bismuth transmits heat more slowly than mostothermetals, probably on account of its highly crystalline texture. It is volatile at a high temperature, and may be distilled in close vessels, but with difficulty. A cast bar of bismuth Tvui inch in diameter supports a weight of 48 lbs.

There are three oxides of bismuth, the sub-oxide, (he oxide, and the superoxide. The oxide may be obtained by dissolving bismuth in nitric acid, and fusing the precipitate of subnitrate thrown down by water. This subnitrate, also called pearl-white, is used by some ladies as a cosmetic. It is more usefully employed as a flux for certain enamels, increasing their fusibility without imparting colour. It is hence used as a vehicle for the colours of other metallic oxides. When well washed it is employed in gilding processes, an addition of yjth being made to the gold. It is also used in medicine.

Some of the alloys of bismuth were noticed under Alloy. In this article it was stated that

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