Chapter VI: Part 6

When a solution of “chloride of gold” is mixed with ether, the ether takes the gold away from the solution, and may be poured off the top charged with it. This solution, if applied to polished steel by means of a camel-hair pencil, rapidly evaporates, leaving a film of gold adhering to the steel, which, when burnished with any hard substance, has a very elegant appearance. In this way any ornamental design in gold may be produced, but it is not very durable. The gilt ornaments, scrolls, and mottoes on sword-blades, &c., are sometimes done in this way.

“Gilding refined gold” would appear a great absurdity, but something very like it is often practised in the process called “coloring,” used by jewellers. This is however never applied to “refined gold” but to gold that is not quite so good in color as it should be. It is boiled in a liquid containing chemical substances capable of dissolving the alloy from the surface of the article and depositing a thin coating of pure gold, giving it the appearance of being made of better gold than it really is. This is in truth a species of electro-plating, but was in use very many years before the electro-depositing process had been discovered.

SILVERING LOOKING-GLASSES.

Although this process is called “silvering,” yet no silver is used; the substance at the back of the glass is a mixture of tin and mercury, called an “amalgam,”--indeed, the term “amalgam” applies to all mixtures of mercury with other metals. The process is as follows:--A sheet of “tin-foil” (tin rolled out to about the thickness of paper) the size of the glass to be silvered is placed on a perfectly level table, covered with cloth; upon the tin-foil some mercury is poured, and spread evenly and quickly over the surface with a hare’s foot. The plate of glass is in the meanwhile to be made perfectly clean and dry--not the slightest speck or smear must remain. A sheet of tissue paper, also clean and dry, is laid over the surface of the mercury, the plate of glass is placed on the paper and made to correspond with the mercurialised tin-foil beneath. Weights are now placed on the plate of glass to keep it firmly down, and the sheet of paper is drawn out steadily and slowly; as it passes over the surface of the mercury it brings away all film or dust, and the surface being left perfectly bright, adheres so firmly to the dry glass that it is not easily removed. A great difficulty is to prevent air-bubbles from finding their way between the glass and mercury. The table is now raised slightly at one end, and the superfluous mercury allowed to drain off. After a few hours the tin-foil will be found to be completely united all through with the mercury, and will be so brittle that it can be scraped off in powder from the glass. Great care and practice are required to silver large plates, but any one by a few trials may succeed perfectly with a piece of glass a few inches square. Glass globes are silvered inside by shaking in them a mixture of mercury and tin filings until it adheres to the surface of the glass, which must first be made perfectly dry and warm.

SILVER PLATING.

Plated goods consist of metallic articles coated with a thin plate of silver; the metal is made of a mixture of brass and copper, which is cast into flat slabs or ingots about an inch-and-a-half thick, the surface on one or both sides is filed flat and smooth, and a plate of silver of about the thirtieth part of an inch thick, but a little smaller than the metal, is applied smoothly to it, the edges are covered all round with borax ground fine with water and the plates tied tightly together with wire. The whole is then put into a furnace and closely watched till the silver begins to melt, when it is at once taken out and allowed to cool; by this mode of treatment the silver adheres so firmly to the metal that they become as one piece. It is then passed between steel rollers and rolled out to the required substance, the silver and metal both becoming thinner in about the same proportion, so that on a plate of metal, of whatever thickness, the silver is somewhere about a fortieth or forty-fifth part of its thickness; these plates of metal coated with silver are worked by stamping, punching, or passing between rollers the edges of which have mouldings, curves, &c., cut on them, and the parts of each article when moulded are afterwards soldered together so as to form what is intended. Wires of various forms are plated in the same way and afterwards drawn out by means of draw-plates (see “Wire-drawing”). Electro-plating has to a great extent superseded this process (see “Electro-plating”).

ELECTRO-PLATING AND DEPOSITION OF METALS.

Illustration: (‡ ELECTRO-PLATING PROCESS.)

This art has for its objects the coating of metallic articles with other metals of more value, beauty, or durability, such as gold, silver, or copper, by means of electricity, and the formation (by the same means) of other articles by the deposition of metals, from liquids containing them, upon moulds or engraved surfaces capable of modelling them. When the deposit forms a coating intended to be permanent, and which adheres to the article so as to be incapable of removal, it is called “electro-plating,” but when a fac-simile of any surface is required, or a cast of a mould which may be removed, forms the object to be produced, it is called “electrotyping” or “electro-depositing.”

Illustration: FIG. 1. (‡ ELECTRO-PLATING EXPERIMENT.)

Illustration: GILDING RINGS.

By way of experiment, procure two vessels, A and B, fig. 1, in one of them, A, put some dilute sulphuric acid and two plates, one of zinc, Z, the other of copper, _c_, these must not touch each other, but may be separated about half an inch by two or three pieces of wood or cork, and bound round with string; each of these plates must have a piece of wire fastened by soldering to their upper parts. In the vessel B put some solution of sulphate of copper and a small quantity of dilute sulphuric acid, and attach another copper plate to the wire which comes from the copper plate in the acid; this second copper plate is to be immersed in the solution of sulphate of copper, and to the wire from the zinc plate is to be fixed the object to be coated with copper. If a medallion or other object is plaster, it should be soaked in very hot wax and then brushed over with blacklead until the surface is perfectly blackened and bright; the wire should be bound all round the margin and soldered (as it were) with melted wax to the medallion, taking care that this wax also is well coated with blacklead. If the object be now immersed in the sulphate of copper solution and kept at a short distance from the plate (it must not touch it), a coating of copper will soon cover the surface and form a perfect cast, which when of sufficient thickness may be removed by filing the edge all round (if instead of the plaster cast a copper coin or other copper object be used, the blackleading is not required, but the surface must be first made clean and bright). With the same arrangement, but using instead of the sulphate of copper a solution made by dissolving cyanide of silver in a solution of cyanide of potassium, a coating of silver will be deposited, and the same of gold (if cyanide of gold be used), but these coatings will not adhere. If it be intended that the coatings shall adhere, to plate the article with silver or gold, it should be first thoroughly cleaned, then brushed over with a solution of nitrate of mercury, washed in clean water, and put into the gold or silver solution; the nitrate of mercury will cover the copper article with a thin coating of mercury, which will be taken up as the gold or silver is deposited, and this coating will adhere, the article being thus “electro plated.” As in using the solution of sulphate of copper, a copper plate was immersed in the solution and united by the wire to the copper plate in the vessel A, so in using the solution of cyanide of silver, a silver plate must be used, and in the gold solution a gold plate, these plates being dissolved as the metal is deposited, the liquid remaining pretty much the same and serving for future operations. The gold and silver thus deposited are dull, but may be burnished with a steel burnisher, all over or in parts as the design may require. In manufacturing, these processes are much modified, and powerful galvanic batteries or electro-magnets used; in the latter case the electro-magnetic machine is often driven by a steam-engine and the troughs of depositing liquids contain often many dozens of articles, which are all receiving a coating at once.

SOLDERING AND BRAZING.

The art of uniting metals by another metal or alloy, is called soldering (which includes “hard and soft soldering,” and “brazing”). If any metal be applied in a melted state to the surface of a piece of cold metal, under ordinary circumstances it will not adhere, but runs off in globules, this is owing to the surface being covered with “oxide” or rust, but if the surface be scraped or filed bright and some substance applied which will defend it from the air, and at the same time become fluid at the heat of the melted metal, then it will adhere. For this purpose borax is used in hard soldering and brazing, that is in soldering with metals which require a considerable amount of heat to melt them; and sal ammoniac, rosin, oil, &c., in cases of soldering with “soft solder,” or solder that will readily melt. This soft solder is made of a mixture of lead and tin, and if required to melt very easily (as in soldering pewter), then some “bismuth” is added. Bismuth itself does not melt more readily than lead, but it has the property of causing other metals to melt more readily.

If the edges of two pieces of tin, for example, have to be soldered together, an iron with a wooden handle and a piece of copper joined to the other end is used. This is made red-hot, and the pieces of tin being placed smoothly together and their edges sprinkled with rosin or sal ammoniac, the hot iron (first touched on a piece of rosin to clean it) is then applied to the joint, a piece of soft solder being applied at the same time, and as this melts it is drawn in a melted state by means of the hot iron (to which it adheres) down the joint. An excellent substance for soldering: all sorts of small work, such as pieces of brass, copper, or tin, is chloride of zinc-this may easily be made by putting pieces of zinc into spirit of salt, (hydrochloric acid), and allowing them to remain as long as any effervescence continues; this solution may be kept in a bottle and applied to any edge to be soldered, by means of a small brush or feather. When iron and copper have to be “brazed,” the joints are made bright, and then coated with borax ground into a paste with water. A mixture of brass and zinc (called spelter) in small grains is sprinkled on the joint and it is then put into the hollow of a bright fire which is urged by bellows till the spelter melts. Silver is joined by hard or “silver” solder, which is a mixture of silver, zinc, and copper, and the fusion is generally effected by a blow-pipe, (see “Blow-pipe”); gold is soldered by a mixture of gold and copper. Leaden pipes are joined by having the ends to be united scraped bright and introduced a short way one within the other, some melted solder is then poured from a small iron ladle on the joint at the same time that it is rubbed round with a piece of folded cloth greased on the surface. Joints in cisterns, etc., are generally made by scraping the edges clean with a steel scraper, and applying some lamp-black and size by means of a brush to the parts beyond, leaving a bright space of an inch or so on each side of the joint, a ladle of melted solder is then gradually poured on the joint and rubbed down with a piece of greased cloth, the lamp-black and size preventing the solder adhering to any part but that left bright, and in this way a straight neat joint is produced.

THE SMELTING OF METALS.

All metals are got from the earth where they exist in the form of “ores” (in reality metals combined with other matters), and “smelting” is the process of getting rid of these other matters, the chief of which are sulphur and oxygen. The ores when dug from the mine are generally stamped into powder, then “roasted,” that is, made hot and kept so for some time to drive off water, sulphur, or arsenic, which would prevent the “fluxes” acting properly. The fluxes are substances which will mix with, melt, and separate the matters to be got rid of, the chief being charcoal, coke, and limestone. The ore is then mixed with the flux and the whole raised to a great heat; as the metal is separated it melts, runs to the bottom of the “smelting furnace” and is drawn off into moulds made of sand; it is thus cast into short thick bars called “pigs,” so we hear of pig-iron, pig-lead, &c. Iron is smelted from “ironstone,” which is mixed with coke and limestone. The heat required to smelt iron is so very great, that a steam-engine is now always employed to blow the furnace (before the invention of the steam-engine, water-mills were used for the same purpose). The smelting is conducted in what is called a blast furnace. When the metal has all been “reduced” or smelted, and run down to the bottom of the furnace, a hole is made, out of which it runs into the moulds; this is called “tapping the furnace.”

Smelting is often confounded with melting, as the names are somewhat alike, but the processes are entirely different; in melting, the metal is simply liquified, in smelting the metal has to be produced from ores which often have no appearance of containing any, as in the case of iron-stone, which looks like brown clay. By way of experiment let the reader take a small portion of “litharge,” which is a reddish powder, mix it with a drop of oil into a thick paste and place it on the end of a flat piece of charcoal or wood, and direct the flame of a candle upon it by means of a blow-pipe; a slight hissing noise will be heard, and in a moment or two a small, bright globule of lead will make its appearance.

FOUNDING.

Illustration: GENERAL FOUNDRY, WOOLWICH ARSENAL.

Founding is the art of casting metals into various forms by means of moulds. The products of smelting are of a coarse kind, and have to be remelted before the process of casting or founding begins. Before any article can be cast in metal, a pattern must be formed in wood, clay, or other suitable substance. The floor of the foundry is made up of sand and powdered charcoal to the depth of several feet, serving to imbed the moulds which are used, and in several places deep pits full of the same material are formed for large castings; an iron frame, corresponding to another like it, and capable of being united to it by pins and sockets, is used to contain the moulding sand and pattern.

Illustration: GUN FOUNDRY, WOOLWICH ARSENAL.

Let it be supposed, for simplicity, that a cannon ball has to be cast, one of the frames is filled with moulding sand moist enough to bear a good impression, and a cannon ball pressed half-way in; the surface is now dusted over with red ochre (to keep the upper half from sticking to it), and the other frame applied and united with the lower one, this is now filled with the sand and beaten or trodden down firmly. On separating the two and removing the pattern, there is an impression of half a ball in each half of the mould, and when these are again put together there is a hollow corresponding to the pattern used. There are, however, two things more to be attended to, one is to have an opening for the melted metal to be poured in, the other an opening for the air to escape, and this is effected by attaching to the pattern two pieces of wood or iron which project upwards through the upper half of the mould, and when this is carefully lifted up two holes appear which on being united to the lower half lead into the round hollow. When the moulds are ready they are put into a room heated by means of stoves, and thoroughly dried. They are then buried in the floor of the foundry, leaving the holes for pouring the metal exposed, channels being formed in the sand, so that when the furnace is “tapped” the melted metal may flow down these and fill the moulds. Some forms are so complicated that the moulds have to be made in several pieces, and the ingenuity of the founder is taxed to the utmost to produce those required.

GLASS BLOWING AND CASTING.

Illustration: CASTING PLATE GLASS.

Illustration: FIG. 1. (‡ COLLECTING GLASS WITH A PUNTIL.)

Illustration: FIG. 2. (‡ BLOWING ON THE PUNTIL.)

Illustration: FIG. 3. (‡ BEGINNING GLASS FORM.)

Illustration: FIG. 4. (‡ GLASS GLOBE WITH HOLE AT END.)

Glass-blowing requires great practice and manual dexterity, for the material used being red-hot cannot be touched with the hands, and has to be very rapidly worked, or it becomes cooled and hard; to any one unused to work with it, it is the most unmanageable material conceivable, but by practice the glass-blower contrives to produce almost any form required, and of a size quite astonishing--as, for instance, the globular bottles seen in druggists’ windows, which often hold twelve gallons, also glass shades, which are of an uniform thickness, and two or three feet high. This is all done by means of a hollow rod of iron called a “puntil,” on the one end of which a mass of molten glass is collected (fig. 1), and the workman blows into the other, at the same time turning the tube rapidly round in his hands (fig. 2). When the kind of glass called “crown-glass” has to be made, the end of the iron tube is put into the pot of melted glass, and turned round till a ball of it is collected about the size of one’s head, the workman then blows in at the other end, still turning the rod in his hands; it has now the appearance presented at fig. 3. An iron rod is stuck on to the side of the globe opposite to the “puntil,” which is then pulled suddenly away, leaving a round hole. The globe of glass is again made red-hot, and spun round rapidly, the hole increasing in size until it resembles fig. 4. By continuing the rapid twirling of the rod, the hole opens wider and wider till at last one broad sheet is produced; it is then separated from the rod by putting a drop of cold water at its junction with the glass, which causes it to crack across at that part. It is now about six feet in diameter, perfectly round and flat, and when cold it is cut into halves and packed with straw in a “crate” for carriage. The knot of glass often seen in kitchen or stable windows, is the part in the centre of the glass where the iron rod has joined it, and is called the “punty.”

Illustration: FIG. 5. (‡ ELONGATED BLOW GLASS.)

Sheet-glass is commenced in the same way as crown, but instead of a hole being made the blowing is continued till a great round ball is formed, the rod and this ball are then swung round at arm’s length--a hole being sunk in the ground for the purpose--which causes the globe to become elongated, as in fig. 5. It is then laid upon an iron table, and rapidly slit up, the compressed air escaping from within opening it out into a broad sheet, which is instantly cut square while yet soft.

Illustration: PLATE GLASS CASTING. BRINGING OUT THE POT.

Illustration: FIG. 6. (‡ GRINDING THE PLATE GLASS.)

Plate glass is cast by pouring it from a large pot on to a flat iron table with a ridge all round it, and on which an iron roller is so placed that when the molten glass flows on the table it passes over and flattens it out to the required thinness, which is regulated by elevating or depressing the ridges at the sides of the table, made moveable for that purpose (the process is illustrated by the cut at the head of this article). When cold, the surface of the plate is ground perfectly flat and even by means of emery-powder (fig. 6), and then polished with a cloth rubber charged with a fine red oxide of iron called “crocus” (fig. 7). The grinding and polishing are both performed by steam machinery.

Illustration: FIG. 7. (‡ POLISHING THE PLATE GLASS.)

Illustration: FIG. 8. (‡ BLOWING GLASS INTO FORM.)

Bottles, and such like articles are either simply blown into the form required, or into moulds made to close upon the ball of soft glass, and again open when the required form has been given (fig. 8).

Many articles of glass are cast, or “struck-up” by compression in a mould, and are often made to resemble cut-glass articles, but they are much inferior in appearance. The best articles of glass are first blown, and afterwards cut and polished (see “Glass-cutting”). Of whatever kind the article of glass may be, it is so brittle that the slightest blow would break it, a bad quality which is got rid of by a process called “annealing.” This consists in placing it while quite hot on the floor of an oven, which is allowed to cool very gradually indeed. This slow cooling takes off the brittleness; and articles of glass well annealed, will scarcely break with boiling water, and are very much tougher than others.

GLASS-CUTTING.

Illustration: GLASS-CUTTING.

The kind of glass generally used for ornamental cutting is flint-glass. Decanters, wine-glasses, &c., are also made of it; it is very bright, white, and easily cut. Glass is cut by means of wheels of different sizes and materials, turned by a treadle, as in a common lathe; some are made of fine sandstone, some of iron, others of tin or copper; the edges of some are square, some round, and some are sharp. They are used with sand and water, or emery and water, but stone wheels are used with water only. The glass-cutter also uses rods of copper with knobs at their ends, for making round indentations; these turn on their axis, so that the end cuts a round hollow in the glass. The work is at first cut roughly, afterwards smoothed off with the sandstone or tin wheel (the latter has to be smeared with emery and water), and finally polished by a wooden wheel with finely-powdered pumice-stone applied to its edge, and moistened with water. The glasses for spectacles and optical instruments are cut by concave or convex moulds of brass moistened with emery and water, and polished by means of a mould of pitch wetted with crocus and water. Great art and accuracy are required to grind the glasses for optical instruments, especially very large or very small ones, as for microscopes, the various “powers” of which constitute their chief expense--one of the sixteenth of an inch in diameter costing about twelve pounds.

BRICKLAYING.

Illustration: BRICKLAYING.

Illustration: FIG. 1. (‡ UNSTABLE STACKING OF BRICKS.)

Illustration: FIG. 2. (‡ ENGLISH BOND.)

Illustration: FIG. 3. (‡ FLEMISH BOND.)

Illustration: FIG. 4. (‡ PLUMB.)

Illustration: FIG. 5. (‡ TROWEL.)

Illustration: FIG. 6. (‡ HOD.)

Nearly all houses are built of bricks, as they are less expensive than stone, and more durable than wood, besides being less liable to be burnt. Walls of brick may be formed of any required thickness, and as the length of a brick is twice its breadth, they admit of being so laid that the wall shall not part in pieces, which would be the case if laid as in fig. 1, as the seams of mortar run continuously through the wall, which in bricklaying is always avoided, by different methods. Formerly bricks were laid in what was called “English bond” (fig. 2), but this is not now used, “Flemish bond” (fig. 3) having superseded it. The mortar with which bricks are laid is made of lime and sand, mixed with water to a convenient consistence; it sets quickly, hardens with age, and resists the action of rain and time. The ordinary mode of laying bricks is to stretch a line from end to end of the course on which they are to be laid; the surface of the under course is spread for a short distance with mortar, and the bricks intended to form the outer surface of the wall are laid first, in an exact line with the cord, the “plumb” (fig. 4) being frequently used to ascertain if they are perpendicular. The “plumb” is a piece of board with a notch at the centre of the top, and a hole, also in the centre, near the bottom; a piece of cord is passed through the notch, with a leaden ball attached, which swings in the hole as the plumb is placed at the side of the wall. The ball of lead just falls in the hole if the wall is upright, and in this way a wall may be built to any height, exactly perpendicular. The corner of brickwork where windows occur, is called the “arris,” and has to be made upright both in front and at the side. When very thick walls are to be made (as in railway cuttings), the outer surface and back of the walls are laid in the usual way, the space between is filled with a layer of bricks, and thin liquid mortar is poured on and scraped about with a sort of hoe till the spaces between the bricks are all filled up and the surface left level, when another course is laid in the same manner. Fig. 5 is a trowel, or instrument used to take up and spread out the mortar, and fig. 6 is the hod, in which the labourer carries supplies of bricks or mortar to the spot where the bricklayer is working.

STONE CUTTING.

Illustration: STONE-CUTTING.

Illustration: FIG. 1. (‡ IRON PICK.)

Illustration: FIG. 2. (‡ CHISEL AND SCRAPER.)

Some stones, as “Bath stone” can be cut with a common toothed saw, and are but little harder than chalk; others, as marble, Portland stone, &c., require to be cut with a flat blade of iron stretched in a frame and having a supply of sand and water. A man sits in a shed having this heavy saw suspended from two poles, and balanced by a piece of stone swung over a pulley; he alternately pushes and pulls the frame, allowing the water to trickle into the seam as it forms, the sand being rubbed between the edge of the saw and the stone as the saw is moved backwards and forwards, slowly cutting the stone (see illustration). By this slow and tedious process building stones are cut into squares, slices, slabs, or any other form required. Granite is too hard for even this slow process, and after the pieces are chosen as nearly as can be got of the size and shape required, they are worked with a heavy iron pick (fig. 1), which at each blow strikes off a little piece not bigger than a pea, by which method the stone is shaped into the form required. Smaller cuttings of stone for building purposes, such as carvings, &c., are formed by the mallet and chisel (fig. 2), the work being finished with a rasp or steel scraper.

APPARATUS AND MACHINERY.

STEAM-ENGINES.

Illustration: BEAM OF STEAM ENGINE, WOOLWICH ARSENAL.

The great improvements in machinery--whether for looms, locomotive engines, or steam-ships, for forging anchors, boring cannon, rolling out and rivetting iron plates together for tubular bridges and boilers, or any other kind of work--are chiefly owing to the wonderful ease with which these machines can be driven by the power of steam. It matters not whether the object to be wrought is the head of a pin, or the crank of a steam-ship, it is done with both delicacy of touch and power of arm, a hundredfold beyond what could be effected by hand in the same time. The motive power of steam is derived from the property which water has of being expanded into vapour when heated to a certain degree, and of again resuming the form of water when cooled; this moreover takes place in the most easily manageable manner, and either by degrees or suddenly, according as the heat and pressure balance each other; moreover water, being easily obtained, and in sufficient quantity for the purpose, in all places where machinery is required, can always be applied. Before the use of steam, wind, water, horse, and hand power were chiefly in use; water-mills were, of course, only erected in those situations where a good supply of water could be obtained, and this even often failed in dry weather; windmills also depended on that uncertain element. Horse and hand powers are limited in their extent, and are moreover very expensive. The first attempts at a steam-engine were those in which the steam was only used that by its condensation a vacuum might be formed in a cylinder under a piston, so that the weight of the air should cause this to descend with considerable force--15 lbs. on the square inch. The piston was balanced by a weight, so that the steam might raise it with scarcely any pressure; the steam beneath the piston being condensed by a stream of cold water, the weight of the air again forced down the piston into the vacuum. This therefore was not a steam but an air-engine, as all the power exerted was derived from the weight of the air, and the steam merely used to procure a vacuum. After this came the low-pressure or condensing engine, and then the high-pressure or non-condensing engine, both of which are now used, the former in marine engines and the latter in locomotives.

Illustration: FLY-WHEEL, WOOLWICH ARSENAL.

Illustration: FIG. 1. BOILERS, WOOLWICH ARSENAL.

Illustration: FIG. 2. BOILERS, WOOLWICH ARSENAL.

The steam-engine consists essentially of a boiler or steam-generator, with a furnace adapted to it, connected by a steam-pipe to a cylinder having a piston working accurately in it, and valves so contrived that the steam shall enter alternately above and below the piston. In the condensing engine, each compartment, above and below the piston, communicates with the condenser--the vessel in which the steam is suddenly condensed by cold water--and the valves are so arranged that when the steam enters above the piston, the space below is opened to the condenser, and is therefore a partial vacuum; by the time the piston is driven down by the force of the steam above it, the space is shut off from the condenser and opened to the steam-pipe, while the space above is shut off from the steam-pipe and opened to the condenser. In this way one side of the piston is alternately pressed by the steam while there is a vacuum on the other side. In the non-condensing engine the space above and below the piston is alternately pressed by steam at a great degree of tension; while at the opposite side of the piston, the space is opened to the air by a valve. These valves are what are called “sliding valves,” being both in connection with the same action, which shuts one while it opens the other; that is, when the piston has nearly descended, it slides the valve which shuts off the steam from the space above and opens it to the air, the same action opening the steam-valve below the piston and shutting it from the air. In this kind of engine the piston is moved simply by the power of the steam, which first presses it down and then presses it up again, and as the steam escapes at each stroke of the piston, and has to be at a great tension or pressure, a large and rapidly-formed supply of steam is required. In the locomotive and other high-pressure engines this is effected by having a great number of tubes passing through the boiler leading from the fire-place to the flue, so that the fire and heated air shall pass through them before reaching the flue, and consequently, as these all pass through the water in the boiler, producing a very rapid generation of steam. Of the various forms of boilers, the most simple was that in which the heat was merely applied to the lower part (fig. 1); next may be named the wagon-head boiler, in which the flue passed all round; some were made with a cylindrical flue passing though the whole length, and some with two (fig. 2). Of whatever form the boiler may be, it should be strong enough to well resist the pressure of the steam, but to make this sure, a contrivance called a safety-valve is always used; this consists of a valve held down by a weight, which would be raised by the steam if it should press so hard as to endanger the boiler in the least degree; when the safety-valve is forced up, the steam escapes and the pressure is taken off. Most steam engines require the up-and-down motion of the piston to be converted into a circular motion, and this is effected by means of a “crank,” (see “Cranks”); but this circular motion needs in most cases to be regulated by a fly-wheel which is so heavy, that upon being set in motion it continues to revolve for a time by its own weight, so that the intermitting pulls exerted by the piston-rod on the crank are blended into one continuous action (see cut); but in steam-ships, and locomotive engines, fly-wheels cannot be used. In these cases there are two cylinders and pistons, each fixed to a crank formed in one axle united to the two wheels, and these cranks are so arranged that the greatest power is exerted on one when the least is exerted on the other, and for this purpose they are placed so that when one crank is upright the other is horizontal. The stroke of the piston-rod is not always made to act directly on the crank, but has a “beam” interposed working on bearings in its centre, hence the term beam-engine (see cut). This beam moves the crank at the opposite end to that which is moved by the piston and at the same time works the air-pump, feed-pump, and cold-water-pump, by means of jointed rods.

Illustration: FIG. 3. (‡ GOVERNOR.)

In those engines which have to perform unequal work, and in which sometimes a great drag is suddenly removed from the engine, some contrivance is necessary to prevent the too rapid motion which would ensue, to the great risk of damaging the engine; this is effected by what is called the “governor;” a contrivance by which a part of the steam is struck off when the action is too rapid, and again let on when it has diminished. This arrangement is shown in fig. 3; the two heavy iron balls swing round as the engine works, and the faster they revolve the more they tend to separate, from the natural tendency to fly off called “centrifugal force,” and in separating they bring the other ends of the rods to which they are attached nearer together, and so push up a collar, A, attached to the levers which turn off the steam-tap; and as the action subsides the balls sink down together and the collar also, the steam being thus turned on again. In order that the pressure of the steam in the boiler may be known, a “gauge” is used, which acts on the principle of the barometer, consisting of a column of mercury which is pressed up by the force of the steam, the height to which it rises indicating the pressure. With respect to the details of the steam-engine, they are too various and complicated to be enumerated or described here; but the motion--being regular, continuous, and powerful--can be applied to almost any sort of work by being adapted to the machine suitable for such work, and which receives its motion from the steam-engine, the same as though it were worked by water or by hand.

BOILERS.

Boilers are vessels in which fluids are boiled or heated, and are almost of every form and size. Some boilers, such as those attached to steam-engines, are more strictly called “steam generators,” as they are constructed solely for the production of steam at the lowest possible expense of time and fuel, and also to resist the pressure which the steam exerts at high temperatures; these boilers are not only used to produce the steam for the motion of engines, but are extensively used in its production for heating evaporating-pans and boilers (in the strict sense of the word), and also for warming and ventilating buildings. They are more particularly noticed under the head “Steam Engines.”

Boilers for all purposes were formerly made of metal (usually copper or iron), and were exposed directly to the fire intended to heat their contents, but since the properties of steam have been more fully recognised, it is now very frequently employed for heating boilers--especially where a heat at or below the boiling point of water is required. There are great advantages arising from this plan, one of which consists in doing away with the risk of the materials in the boiler being burnt. Some boilers are now made of wood, having steam-pipes running through them, and in those cases in which the admixture of water is no detriment steam--in the form of jets--is thrown directly into the fluid to be heated, which very quickly raises it to the boiling point. Boilers of cast-iron, lined with platinum or enamel, are also used for various purposes, as the condensation of acid substances, &c., which would act on most metals. Glass and glazed pans, too, can be used with a steam apparatus, without any danger arising from breakage, which would frequently occur if they were directly applied to the fire.

FURNACES.

Illustration: FIG. 1. (‡ REVERBERATORY FURNACE.)

Illustration: FIG. 2. (‡ BLAST FURNACE.)

Illustration: FIG. 3. (‡ CUTAWAY DIAGRAM OF BLAST FURNACE.)

Furnaces are fire-places constructed to serve particular purposes, and are chiefly of two kinds, “Wind furnaces” and “Blast furnaces.” Of the first kind the common house grate is an instance, of the second the blacksmith’s forge. The fire in a wind furnace is more or less shut up, so that the draught of air entering it shall pass from the ash-pit right up into the fire, and through it into the flue or chimney--the latter being tall, and of certain proportions, so as to ensure the requisite draught. These furnaces are used where heat of the very highest degree is not required, as in glass-houses, pottery-kilns, &c. The “Reverberatory furnace” is a modification of the wind furnace, and is used to throw heat on to the surface of substances, as in roasting ores of metals, to drive off the sulphur, arsenic, &c., or in the making of soda, litharge, and other processes where the admission of hot air with the flame is either beneficial, or at least not detrimental; fig. 1 shows the construction of this kind of furnace. Blast furnaces are for the production of the very highest degrees of temperature, and in these the air is forced into the fire by blowing machines or bellows, often worked by steam-engines; such furnaces are used for the smelting and casting of iron, &c. (fig. 2). A good blast furnace for small purposes may be made by two crucibles--those made of coarse blacklead and clay, and called “Blue pots,” are the best--one placed inside the other, the outer one having a hole at the lower part for the nose of the bellows, the inner one having the bottom cut off and a grating of iron put in to lodge just above the lowest part; the space between the two should be filled with powdered fire-brick or broken-up crucibles (fig. 3).

BELLOWS AND BLOWING MACHINES.

Illustration: FIG. 1. (‡ BLACKSMITH BELLOW.)

Illustration: FIG. 2. (‡ DOUBLE-BELLOW.)

Illustration: FIG. 3. (‡ FAN WHEEL.)

Illustration: FIG. 4. (‡ FAN WHEEL HOUSING.)

The common bellows is the most familiar form of blowing machine. It consists of two boards bound together with leather, having folds so arranged that the upper board may be raised or depressed, and the whole is made air-tight; in the lower board is a hole with a leather flap-valve opening inwards. When the upper board is raised, the air rushes in at the hole, pushing up the valve, and when the board is lowered the air presses the valve down, and so shuts it close, it has therefore no exit but at the nose of the bellows, from which it passes out. Blacksmiths’ bellows (fig. 1) are made double, for the purpose of keeping up a continuous stream of air, instead of the separate puffs produced by the common single bellows. The arrangement of the double bellows is as follows:--There are three boards bound together with leather folded as in the common house bellows; the board in the middle is fixed, and to this the nose is fastened, but it opens only into the space above; the upper and lower boards are united to the middle one by a hinge, and are capable of being moved up and down; the middle and lower ones have each holes and valves opening upwards as in the common bellows, and when the lower board is raised it presses the air in the space between it and the middle board through the hole in the latter, into the space between it and the upper one, and so raises it; this has a heavy iron weight placed on it which makes it sink down and force the air out through the nose. While this weight is sinking the lower board is pushed down, and is ready to force a fresh quantity of air into the upper space, so that one continuous stream of air issues at the nose of the bellows. The handle is fixed to the lower board, and generally has a cord uniting it to a wooden handle, which is worked like a pump-handle (fig. 2). For large furnaces, blowing machines of various kinds are used, generally consisting of a pair of large cylinders having pistons worked in them by steam power, and pumping air into a large air-chamber, from which it proceeds in three or four pipes to the furnace, or sometimes to numerous furnaces, each having a tube and stop-cock by which the “blast” may be turned on, similarly to gas or water, the air-chamber being always kept filled at a great pressure by the cylinders, and furnished with a safety-valve to prevent the pressure bursting it. There is another kind of blowing-machine, consisting of a fan wheel turning very rapidly in a round box (figs. 3 and 4), from which a tube proceeds, and having holes in the sides to admit the air, which is thrown forwards by the fans of the wheel.

SCREW PROPELLERS.

Illustration: SCREW STEAM-VESSEL.

Illustration: FIG. 1. SCREW STEAM-VESSEL, SHOWING THE FAN.

Illustration: FIG. 2. (‡ PROPELLER.)

These are instruments placed at the back part of steam-vessels for the purpose of propelling them through the water. Fig. 1 will show the position they occupy, and fig. 2 the shape of the propeller. When first used, they had one or two entire turns round the axis, but are now made with two blades, each forming about one-sixth part only of one turn, and this is found to give more power with less friction. The propeller is turned rapidly round in the water, from which it meets with resistance in a direction perpendicular to the surface of its blades, but as this is oblique to the direction of rotation the force is exerted in two directions, one directly opposes this rotation, and is overcome by the power of the steam-engine, the other is in a direction towards the ship, overcoming the inertia of the vessel and the friction and resistance of the water, so that the ship is moved along, and the propeller winds its way through the water in a spiral direction as an ordinary screw does through the hollow screw made to fit it, the vessel travelling at a speed proportionate to the screw’s revolutions.

ANCHORS.

Illustration: FIG. 1. (‡ ANCHOR WITH WOOD STOCK.)

Illustration: FIG. 2. (‡ ANCHOR WITH IRON STOCK.)

Illustration: FIG. 3. (‡ SPACE-SAVING ANCHOR.)

Illustration: FIG. 4. (‡ ANCHOR AT REST.)

Illustration: FIG. 5. (‡ “WEIGHING” ANCHOR.)

These ponderous instruments are used for the purpose of securing ships and other vessels, that they may not be driven onwards by the wind or tide. They are attached to a strong rope or chain, called the “cable,” and when not in use are kept swung at the fore-part or bow of a ship, the cable being wound round an apparatus called the capstan, which serves to let it out or draw it in. Anchors are made of iron, and are of the form delineated in fig. 1. The straight part from the ring to the bend is called the “shank,” the curved part is made up of the two “arms,” and the centre where it joins the shank is called the “crown.” At the end of each arm is a plate of iron of triangular form, called a “fluke,” and crossing the shank close to the ring is the “stock,” which is made of two pieces of oak bound together with iron bands; sometimes it is made wholly of iron, as in fig. 2, in which case it runs through a hole in the shank, and has one of its ends curved for the purpose of packing more closely and saving space (fig. 3). The anchor, when let fall from the ship, carries the cable with it, and generally falls on the crown, then tilts over so that the stock lies flat on the bottom and one of the flukes sinks in to a considerable depth by its great weight; when the ship drags at the cable it lifts up the stock and throws the whole weight of the anchor on the fluke, and makes it sink completely; any further pull must bring up a large piece of the earth before it can be moved. In “weighing” anchor, that is in pulling it up from the bottom to bring it on board again, the cable is slowly wound up by the capstan, and as the cable is shortened the ship is drawn along to a point nearly over where the anchor rests, when--the pull at the cable continuing--the shank is raised into an upright position, and the fluke and arm, instead of dragging up a great piece of earth, remove but a small portion, as may be seen by the dotted lines in figs. 4 and 5, which show the earth to be removed before the anchor can be drawn from its hold.

Large vessels carry four anchors, the “best bower,” the “small bower,” the “sheet,” and the “spare” anchors, their size depending on the size of the ship, the rule in the Royal Navy being a hundred-weight for each gun; so that an eighty-gun ship carries anchors of four tons each, or eighty hundredweight. Anchors are made of the best and toughest wrought iron, and the greatest care is necessary in forging them in order that there may be no flaw in the welding, for a ship may be lost by an anchor breaking.

CHAINS.

Illustration: FIG. 1. (‡ LINK CHAIN.)

Illustration: FIG. 2. (‡ WHEEL CHAIN.)

Illustration: FIG. 3. (‡ CHAIN WITH STAY.)

Illustration: FIG. 4. (‡ CHAIN WITH EXTENDED STAY.)

Chains are made up of separate links of rigid metal which having no flexibility in themselves are yet so united that each shall move freely on the next links to it, and thus produce a flexible whole. For ornamental purposes there is almost an endless variety of patterns, as may be seen in jewellery-work--but for the purposes of business and machinery there are chiefly but two, the ordinary, as fig. 1, and that which will only bend in one plane, as in fig. 2--this is chiefly made use of in passing round wheels, as in clocks. Chains are used where rough wear is required, in which case rope would be rapidly worn through. Cables of chain are now much more generally used than hempen ones, as they are more to be depended on, take up less room, and are not so liable to be cut or worn by rough rocks at the bottom. In chain cables a “stay” is placed in every link (fig. 3), which greatly increases its strength, but the best form of chain cable is shown at fig. 4; in this the links are somewhat angular, and the stays longer. Chains are chiefly made by machinery; the rods are first drawn out of the proper size, pieces of the required length are then cut off and bent to the right form, and the stay and this link are then both made white hot, placed in their right position, and welded together by pressure.

CRANES.

Illustration: (‡ YARD CRANE.)

Illustration: FIG. 1. (‡ WHEEL ASSEMBLY.)

Illustration: FIG. 2. (‡ FLOOR CRANE.)

Illustration: FIG. 3. (‡ LANDING CRANE.)

Illustration: FIG. 4. (‡ LANDING CRANE.)

Illustration: FIG. 5. (‡ JIB CRANE.)

Illustration: FIG. 6. (‡ SWING CRANE.)

These machines are used for raising heavy bodies in a perpendicular direction. They are of various forms suitable for almost every purpose, and to most of them are adapted two or more wheels with teeth, one small and one large, for the purpose of obtaining power at the expense of time (fig. 1); the small wheel is turned by a windlass, and turns the larger one very slowly but with great power. The common warehouse or cellar crane is generally an iron frame with two pulleys, and the arrangement shown at fig. 1. which is usually inside the warehouse, while the crane is outside to raise goods from carts, &c., into the floors above (fig. 2). Cranes at the sides of canals or rivers for landing goods are sometimes made as figs. 3 and 4; in the last there is a heavy stone placed to balance the weight at the end of the crane. What is called the “jib crane” is often “rigged” up on shipboard for shipping and unshipping goods (fig. 5). Cranes for very heavy purposes have been made upon the tubular principle and consist of iron plates rivetted together so as to form a hollow curved crane, similar to the hollow girders used in bridges. Where goods have to be brought from one particular spot to another, as in fig. 6, the swing crane is used. Amongst cranes may be named the hydraulic lift; this is exactly similar to the hydraulic press, only applied in a different manner, and is used to lift very heavy weights but short distances, as for raising heavy goods on to railway trucks, &c.

CRANKS.

Illustration: (‡ KNIFE-GRINDER.)

Illustration: (‡ PISTON CRANK.)

Cranks are bends in the axle of any part of a machine by which an up-and-down motion is converted into a circular or rotatory one, as in the common knife grinder’s machine; in this arrangement a fly-wheel is necessary to continue by its momentum (tendency to go on) the motion begun by the upward and downward action of the treadle, piston-rod, &c., as the case may be. The cranks of steam-vessels are among the heaviest pieces of forging that are wrought by Nasmyth’s steam hammer, cast-iron being too brittle to be used for the purpose.

FIRE-ARMS AND PROJECTILES.

Illustration: FIG. 11. MACHINE FOR MAKING MINIÉ RIFLE BULLETS.

Illustration: FIG. 1. MUSKET BORING.

Illustration: FIG. 2. RIFLING PROCESS.