Chapter VII: Part 7

In the manufacture of fire-arms the chief parts consist of the metal tube from which the projectiles are to be expelled, the stock of the musket and the carriages of great guns or cannon being only varieties of the same thing, namely a convenient platform from which to fire the tube, which is the real instrument. In the manufacture of muskets, pistols, and cheap fowling-pieces, the barrel is made from a sheet of soft iron rolled up lengthwise round a rod or “mandril,” the edges overlapping each other, which are then welded together; but in the best guns the barrels are twisted, that is, a slip or fillet of iron half-an-inch broad and of sufficient length is twisted in a spiral round the mandril, and then the whole is welded together. The barrel is “bored” by means of a square-headed drill of steel turned in a kind of lathe (fig. 1), and the interior afterwards polished with oil and emery-powder until it is perfectly bright and even; the breech is then made separately, and screwed in. The best iron for gun-barrels is called “stubb iron,” consisting of old horse-shoe nails welded together, and is very soft and even in its grain. The barrel is made red-hot and suffered to cool very slowly; this is called “annealing,” and it prevents any part being brittle, and therefore liable to burst with the charge in firing. Rifled barrels are those which have one or more grooves cut in the inside of the barrel from the muzzle to the breech in a spiral direction, each making one turn before it completes the length of the barrel (fig. 2).

Illustration: FIG. 3. (‡ PERCUSSION CAP BREECH.)

Illustration: FIG. 4. (‡ HAMMER MECHANISM.)

Illustration: FIG. 5. (‡ RIFLE WITH BAYONET.)

The old “flint” lock has now quite gone out of use, having been superseded by the “percussion.” This is a contrivance to cause that part of the lock called the cock or hammer to strike the percussion cap with great force, and so discharge it (figs. 3 and 4). The cap is put on to a small projection called the “nipple,” which has a hole at the top communicating with the barrel, and down which the spark from the percussion cap passes.

In rifled guns, of late, the use of conical balls has been introduced, for the effect of the charge in propelling a ball rapidly out of a barrel with spiral grooves is to turn it as it passes out of the barrel, and consequently to “spin” it with great velocity in one direction, like a top; the effect of this is to balance every part of the ball in the air and so cause it to take a true direction, for if the merest notch or hollow existed in a spherical ball, that part being lightest and having the least momentum would not maintain its rate so long, and by lagging behind cause the ball to describe a part of a circle in its course. It is thus that the balls from common muskets, although rightly directed, often fall extremely wide of the mark. Military muskets and rifles are fitted with bayonets, that they may act both as lances and fire-arms (fig. 5).

Illustration: GUN-MOULD.

Illustration: GUN-BORING MACHINE.

“Ordnance,” or great guns are made of cast-iron or of gun-metal (a mixture of copper and tin), but experiments have lately been made with wrought-iron and cast-steel, with the view of obtaining a tougher and more durable material. They are cast solid, and afterwards bored with a machine. The following account of gun-casting at Woolwich Arsenal appeared in the “Times” of January 22, 1858:--“As the plug was drawn the glowing mass leapt out like a stream of silver, filling up the moulds for two twelve-pounder howitzers that were to be cast, and leaving a bright, hungry-looking flame playing over them, making everything red-hot which it approached. In this workshop about twenty men and boys produce twelve brass guns per week, as well as tangent-scales for ships’ guns, lock-covers, brass fittings for machinery, &c., and iron castings. Each gun cast requires two days to cool, when it is removed to the turnery to be bored; and it was to this workshop that the royal party next proceeded, and saw the guns in all their stages of trimming, finishing, and boring. Three-quarters of an hour suffice to cut a gun to its proper length and remove the rough sand which adheres to it after casting. It is then turned over to another man and another machine, and the whole of its outside shaping and marking is completely finished in two days, when it is again turned over to a fresh machine, and bored and drilled ready for service in a day-and-a-half more. With the present machinery the turnery at Woolwich could finish thirty brass guns in a week, though at this time it never completes more than ten or twelve.”

Illustration: FIG. 6. (‡ FIELD GUN).

The ordinary form of “gun” is shown by fig. 6. The knob at the right-hand side of the cut is called the “button,” the next division the “vent field,” beyond this to the rim the “first reinforce,” further on, the “second reinforce,” from which a cylindrical bar projects on each side for attaching the gun to the carriage, called “trunnions.” Beyond this to the next rim is called the “chace,” and beyond this again to the end the “muzzle.” Guns are chiefly used to throw solid round shot of cast-iron, accurately turned to a sphere, and the weight of these determines the character of the gun, as a thirty-two pounder, &c., the words “heavy” and “light” designating the thickness and consequent weight of the metal composing it. There is a smaller and shorter kind of gun, called a “carronade,” which is held to the carriage by a projection underneath, having a hole for a bolt to secure it, instead of trunnions. Another kind of gun, called a “howitzer,” is of shorter proportions than the ordinary gun and larger in the bore; it is chiefly intended to throw shells at a slight elevation. The mortar is still shorter, and of much thicker metal; it is held to a sort of platform by trunnions at its extreme end, and is intended to throw shells to great distances, and at a great elevation.

Illustration: FIG. 7. SHELL CASTING.

Illustration: BULLET-CASTING, WOOLWICH ARSENAL.

Illustration: FIG. 8. (‡ BULLET MOULD.)

Illustration: FIG. 9. (‡ BULLETS.)

Illustration: FIG. 10. (‡ NIPPERS.)

Illustration: PREPARING LEAD FOR BULLETS.

The sizes of howitzers and mortars are expressed by the diameter of the shell they are intended to throw; the largest of which at present in general use is the “thirteen-inch.” This immense shell when charged weighs nearly 200 pounds. These shells or “bombs” as they were formerly called, are cast hollow (fig. 7), with a small opening into which a “fuze” or wooden tube filled with combustible matter is inserted; they are charged with gunpowder, which on being ignited by the fuze burning down to it, explodes and bursts the shell into fragments, which fly about with terrible force. What are called “shrapnel-shells,” are those shells which are filled with both gunpowder and leaden bullets, to be scattered about by the explosion. Case-shot is a name given to a packet of bullets inclosed in a tin canister and used as a projectile, the case bursts and the bullets are scattered. Grape-shot is the name given to a collection of nine iron balls packed up so as to be used as one. Hand-grenades are small shells of about three pounds’ weight, to be cast by hand. Bullets for the ordinary musket are simple balls of lead, in some cases cast six at a time in moulds (fig. 8), and coming out in one piece as seen at fig. 9, which are afterwards separated and finished off by a sort of nippers as seen in fig. 10; but for the most part musket and rifle bullets are formed by compression. The bullets for the Minié rifle are made by machinery; they are of a conical form, with a hollow at the base into which a small plug of box wood is fitted, this end being towards the powder receives the whole force of the explosion, the effect of which is to drive in the plug and open out the bullet, thus fitting it tightly into the grooves of the rifle and preventing any loss of power by the escape of the gases resulting from the combustion of the powder. The machine for making these bullets is shown at fig. 11. The following is an account of it, taken from the “Times”:--

“Like all the machines here, these are perfectly automatic. Coils of solid leaden piping are hung in it, which it unwinds, cuts to the required length, stamps with steel dies into the form of a Minié bullet, and then conveys away into boxes. Each machine has four dies, which cut, stamp, and pass into boxes thirty-six bullets per minute, giving for each machine an average of 7,000 per hour. There are four of such machines, which thus each day turn out 300,000 Minié bullets; but, of course, as they never tire, the number produced can at any time be doubled by leaving them to work all night. They are so simple in their construction that one man could easily attend to them all. It was a curious contrast to the silent rapidity with which these deadly messengers were formed, to watch a number of men and boys working near them casting round musket-balls for Shrapnel shells, in the old style of hand work. By this method two persons can only rough-cast seven cwt. of bullets per day, or about 12,500, which it takes two persons another day to trim. Thus, four hands, with a great consumption of fuel to keep the lead always melted can only produce 6,000 bullets per day or 1,000 less than each machine produces in one hour.”

The machines for making the box wood plugs are also described:--

“Each of these was managed by a child, who kept it properly fed with small sticks of box, which the machine converted into plugs at the rate of 15,000 in nine hours, or nearly 300,000 per day for them all.”

Rockets, as used for projectiles, are similar to those in ordinary use, but that they have iron cases and are made to start from an iron tube, down which the stick passes, and which directs the course of their flight. They are made of various weights, the largest being thirty-two pounds. These enormous rockets pass to a very great distance and are made either to explode like shells, or burn fiercely for several minutes, like what are called “carcases,” thus setting fire to houses, &c., against which they may be directed; but hitherto their course has been but little under control, and therefore not much to be depended on. They cause great confusion in masses of troops, when directed against them.

PERCUSSION CAPS.

Illustration: PERCUSSION CAP MACHINE, WOOLWICH ARSENAL.

Illustration: FIG. 1. (‡ PERFORATED COPPER.)

Illustration: FIG. 2. (‡ CAP.)

Illustration: FIG. 3. (‡ PERFORATED PLATE.)

Illustration: FIG. 4. (‡ SPREADING FULMINATING POWDER.)

Illustration: FIG. 5. (‡ TAMPING MACHINE.)

Illustration: FIG. 6. (‡ VARNISHING MACHINE.)

These are little hollow cups of copper having a fulminating substance at the bottom, so that when put on to the “nipple” of the gun and struck by the “hammer,” the fulminating powder explodes, and the spark passing down the hole in the nipple discharges the gun. To prepare the fulminating powder for these caps, let 100 grains of mercury be dissolved in a measured ounce-and-a-half of nitric acid, and when cold let two ounces of spirits of wine be added, and the whole put into a Florence-oil flask made perfectly clean, and let it be placed in the open air; copious fumes will pass off and a violent action take place, during which a white crystalline powder will be deposited; as soon as all action has ceased and the liquid cooled, pour the whole on a filter of blotting paper, and let the fluid pass through, wash the powder which remains on the filter with a little water, and let it dry, without heat. This is fulminating mercury, which is a highly dangerous compound, and should be kept in a bottle with a cork, and not a stopper, as the friction of this against the neck of the bottle might cause an explosion. At the Arsenal at Woolwich is a machine (shown at the head of this article) which makes the caps complete. It is fed by a band of thin copper about two inches wide, out of which pieces are punched in the form of a thick cross, leaving the perforated copper as shown in fig. 1; these pieces are punched or “struck up,” and expelled as perfect caps of the form of fig. 2, at the rate of about 1000 per minute. The caps have next to receive their charge of fulminating powder, which is done by dropping them into a perforated plate (fig. 3), capable of receiving many hundreds; this is covered over by two other plates, each perforated to correspond, but the upper one made to shift, so that in one position the holes correspond, and in the other they do not, but remain as small shallow dints. A portion of the fulminating powder is put on this plate and scraped all over it by means of a piece of paste-board (fig. 4), so as to fill all the little dints; the plate is then shifted and the holes made to correspond, when the powder falls through into the percussion caps, each one of which thus receives a definite charge. The next process is to press it down into the cap, so as to prevent it falling out. For this purpose the plate full of caps is removed to a machine (fig. 5), having a row of little stoppers, which are moved rapidly up and down, the pressure being exactly regulated by flat leaden weights, suspended so as to give only so much pressure as will consolidate the powder, without exploding it. They are next removed to a third machine called the “varnishing machine” (fig. 6). This has a trough of varnish, made by dissolving shellac in spirits of wine, into which a row of wires dip, and by a turn of the hand convey the minute portion of varnish on their points into the caps, row after row. This varnish dries in a few minutes, and causes the fulminating powder to adhere; the caps are now complete. The old form of caps was a simple short cylinder, but it is found better to allow the four little flaps to remain on, that the right end may be distinguished and instantly placed on the nipple the proper side downwards, which cannot otherwise so readily be done in the dark, and when the hands are benumbed with cold.

PUMPS AND FIRE ENGINES.

Illustration: FIG. 1. (‡ COMMON LIFTING PUMP.)

Pumps are used for lifting fluids above their level into some higher situation, such as from the hold of a ship or from a well. Fig. 1 shows the different parts of a common “lifting pump;” _a a_ is a cylinder, _b_ a piston rod or “plunge,” _c_ the sucker made of leather to fit nicely the cylinder, _d_ a valve in the sucker to open upwards, _e_ a valve fixed to the cylinder, also to open upwards, _f_ a box with a spout.

Illustration: FIG. 2. (‡ AIR PUMP.)

The piston being raised by lowering the handle of the pump, a partial vacuum is formed below the upper valve, which shuts down directly the piston is raised by the pressure of the air; this vacuum causes the external air to force the water some way up the tube _g_. On the piston descending, the lower valve is forced down and the upper one opened, this keeps the water where it is and allows the piston to descend without forcing the water down again, and on its being raised a second time the upper valve shuts and the lower one opens, the water being drawn up still higher, and this takes place till the box at the top is full to the spout, when it runs out. The air-pump is on the same principle, and is generally made with two cylinders worked by means of a “rack” and wheel (fig. 2); this is only to save time, instead of pumping water it pumps out air from any vessel called a “receiver,” because it receives any object to be placed in a “vacuum,” that is to say a partial vacuum, for the air-pump cannot produce a vacuum, as the air is only partly removed by each stroke of the piston, leaving the air more rarefied inside; and although each stroke of the piston increases the rarefaction, yet it cannot get all, as it merely takes part, and always leaves part.

Illustration: (‡ FIRE ENGINE.)

Illustration: FIG. 3. (‡ AIR CHAMBER.)

Fire and garden engines are only applications of the pump to different purposes. The fire-engine has generally two cylinders and pistons, and has moreover an air-chamber for the purpose of making the stream of water continuous. It acts in this way:--The water is forced by the power of those who are pumping the engine into a vessel air-tight and full of air, having an opening which joins the “hose” at its lower part; the result is, that as the water is forced in faster than it can well escape, the air above it--becoming greatly compressed, and by its expansion between each stroke of the pistons--forces the water out, and so continues the stream or jet. Fig. 3 shows this air-chamber; _a_ joins to the hose _c_, and _b_ is in union with the forcing-pumps of the engine. The air is represented as it would be compressed to about half its bulk, for it at first filled all the air-chamber down to the openings.

VALVES.

Illustration: FIG. 1. (‡ FLAPPER VALVE.)

Illustration: FIG. 2. (‡ BALL VALVE.)

Illustration: FIG. 3. (‡ PLUG VALVE.)

Illustration: FIG. 4. (‡ CLOSED PISTON VALVE.)

Illustration: FIG. 5. (‡ OPEN PISTON VALVE.)

Valves are contrivances to admit the passage of fluids or gases by their own pressure in one direction, and in such a manner that the same pressure shall of itself prevent their return or passage in the opposite direction, as in fig. 1, which is the piston of a common pump. There are almost innumerable varieties of valves, one consists of a ball of metal fitting into a cup which has a hole at the bottom (fig. 2). Another (fig. 3), is a plug of a conical shape fitting in the same way, and having a rod affixed to the top which passes through a hole in a piece of metal so as to guide it in its ascent and descent; this is the kind of valve used as a “safety-valve” in steam boilers, but having the pressure regulated by a spring or weights. Figs. 4 and 5 are representations of a kind of valve which forms the piston itself, and is very useful as a piston for a square wooden tube for temporary purposes, as on board ship, where any number may be fitted up at little trouble, time, or expense. There are many other valves besides these, as the sliding valves of steam-engines, &c.

WHEELS.

Illustration: FIG. 1. (‡ FLY-WHEEL.)

Illustration: FIG. 2. (‡ POWER GEARS.)

Illustration: FIG. 3. (‡ BEVELED GEARS.)

Illustration: FIG. 4. (‡ SIDE-COGGED GEAR.)

Illustration: FIG. 5. (‡ RATCHET GEAR.)

Illustration: FIG. 6. (‡ CAPSTAN.)

Illustration: FIG. 7. (‡ PULLEYS.)

Illustration: FIG. 8. (‡ ENDLESS BAND PULLEYS.)

Scarcely any kind of machinery can be constructed without wheels of some kind--they serve almost numberless purposes. The fly-wheel (fig. 1) serves to produce a continuous motion, from its size and weight giving it a tendency to go on, and in this way causing it to fill up the intervals of unequal action, as in the ascent and descent of the piston in a steam-engine. The toothed-wheel serves to give motion to other wheels, and this at a certain rate either greater or less than its own, according to its size, and consequently the number of its teeth; thus a wheel with a hundred “cogs” or teeth united to one with but fifty, causes this to go round twice while the larger one passes round but once; but a large wheel turned round by a small one, although it moves more slowly yet does so with increased power just in proportion to its slowness (fig. 2). The bevel-wheel (fig. 3) is used to change the direction of a shaft, and for all the other purposes of a toothed-wheel, from which it differs only in the position of the teeth or cogs. Wheels are sometimes made to answer the purposes of bevel wheels, by having the cogs on the surface of the one wheel, and the other as an ordinary toothed-wheel (fig. 4). The ratchet-wheel (fig. 5) is a wheel with its teeth pointing in one direction like the teeth of a saw, and into which a tongue of iron is made to fall, so that the wheel can only be turned in one direction. These wheels are used where the machinery is liable to run back if left, as in the “crane,” &c. The capstan (fig. 6) is a kind of ratchet wheel, and is so made that long spokes may be placed in the holes, to be moved round by men, and taken away when out of use; it is a very powerful piece of machinery, and is used for “weighing anchor” (see “Anchors”). The pulley (fig. 7) is a series of wheels used to increase power by diminishing the rate of movement; they are much used in the rigging of ships, and are then called “blocks.” There are different ways of connecting wheels so as to communicate the motion of one to another; they may be toothed as before described, or a “lathe-band” may be passed over them. This may be either round or cord-like, and made of cat-gut, or flat and made of leather or gutta-percha. This mode of producing motion is very useful where evenness and smoothness of action are required, or where the wheels are at a considerable distance apart; they have their ends united so as to form a ring, or endless band, and are sometimes used to communicate motion to a great many wheels, as seen in fig. 8. The eccentric-wheel has its axis out of the centre; it is used for the same purpose as a crank, but the action is more continuous and even. While the crank is most frequently used to produce a circular or rotatory motion from an up-and-down motion, the eccentric-wheel is more commonly used to produce an up-and-down motion from a rotatory one (fig. 9). Wheels take almost every variety of form, and are not, in some cases, even round; in winding yarn on to bobbins, where a motion is required of a constantly varying rate, two elliptical wheels are made to act on each other, the end of one being approximated to the centre of the long axis of the other, (fig. 10).

Illustration: FIG. 9. (‡ ECCENTRIC-WHEEL.)

Illustration: FIG. 10. (‡ TWO ECCENTRIC-WHEEL GEARS.)

Wheels for carriages are used to diminish friction, by causing the “tire” or smooth outer edge to roll upon the surface instead of being rubbed; all the friction in wheels is in the centre or axle, which being turned smooth, and greased or oiled, works very easily. Carriage wheels are made to revolve upon a fixed axle, and each wheel revolves independently of the other, but in railway-carriages and engines, the wheels are united in pairs, and the axle revolves with them, the weight being borne outside of the wheel on a small part of the axle which projects. The various parts of a wheel are the box or “nave” which is the centre part, the “spokes” or those bars which connect it with the centre edge or felloes, and the “tire,” an iron band binding the whole together. Wheels for gun-carriages are made at Woolwich Arsenal by machinery. The following is a description of them, taken from the “Times” newspaper:--

“Here a few unskilled labourers superintending the machines produce forty complete gun-carriage wheels a day, though all their component parts are made of the hardest woods--viz., elm for the naves, oak for the spokes, and ash for the felloes. The novelty here was the new mode in which a wheel is fitted together. Instead of by hand, as formerly, the pieces are all laid together on the ground, and of course in a circle, around the outside of which are six small hydraulic rams, with the head of the piston of each curved so as to form a segment of a circle touching the outside portion of the wheel. One small steam-engine pumps the water into all these with an equal pressure, which, as it increases, forces the felloes into the spokes and the spokes into the nave of the wheel, with such force as to compress the whole, by a strain of 250 tons, into the solidity of one piece.”

Paddle-wheels are made to revolve with their lower part in water, and are furnished with a series of short boards fixed to the tire of the wheel, which is generally double, that they may be better held on; these boards or paddles take a great hold on the water and cause the resistance which is necessary to move the vessel. The wheel of a watermill is constructed in the same way.

WATERMILLS.

Illustration: (‡ WATERMILL.)

Watermills are those kind of mills, the motion of which is derived from the flow of a stream of water against the lower part of a large wheel, provided with paddle-boards similarly to the paddle-wheels of steam-vessels; or else by the weight of a stream of water falling against the upper part of the wheel from a spout or trough; the former of these is called the under-shot, and the latter the over-shot mill. The former is used where there is a large body of water flowing at a sufficiently rapid rate, and the latter kind where there is but a small supply, the whole of which is often used for driving the mill; but other circumstances, of position, &c., may determine which shall be used. The large wheel being thus driven round, any kind of machinery may of course be attached, according to the nature of the work to be done. Like windmills these watermills are for the greater part superseded by steam power; the locality, &c., must determine which can be used with most advantage.

WINDMILLS.

Illustration: (‡ WINDMILLS.)

These picturesque objects are buildings containing machinery, to be driven by the wind, for grinding corn, sawing wood, and any other purpose that may be required. They consist of a basement, generally of stone or brick, and a superstructure surmounted by a sort of dome capable of being turned round. From this dome projects the shaft of a wheel, and on this is fastened four fans or sails made of long bars of wood crossed by shorter ones; these being covered with canvass, form a surface to catch the wind. These sails are placed obliquely to the front of the cross, so that when the wind blows upon them right in front, they are at an angle with it, they are therefore turned round; for the wind which pushes them from the front, as they are oblique, tends also to push them on one side; when once in motion, being heavy, they form a sort of fly-wheel to the machinery. The dome has several small wheels attached to its lower border, to act as friction rollers and cause it to be easily turned round (which is often required), that the sails may be made to face the wind in whatever direction it may blow; this is sometimes done by ropes attached to the dome, but is more frequently effected by means of a small set of sails, shown in the cut, which are placed at right angles to the large set, so that when the wind acts on the large sails the small ones are not affected; but should the wind shift, these small ones begin to move, and they are connected with a toothed wheel acting upon a band which surrounds the dome; this is therefore caused to turn round whenever the small sails are turned, and as the dome turns, it brings with it the large sails until they are in the right position. These sails are generally fixed not quite upright, but inclined with their fronts looking a little upwards, which is found to be the best position to catch the wind.

SYPHONS.

Illustration: FIG. 1. (‡ SUCKING SYPHON.)

Illustration: FIG. 2. (‡ GLASS BALL ON SUCKING TUBE.)

Syphons are bent tubes for drawing off liquids from cisterns, butts, &c., where there is no tap, and where it would be inconvenient to make any second opening. Fig. 1 gives the outline of the most usual form of syphon; these are only used for liquids that may be drawn into the mouth without injury, such as spirits from casks. The mode of using the syphon is this--the bottom of the longest leg _a_ is stopped with the palm of the hand, the tap is then turned on and the mouth applied to the small tube _c_, the air is then drawn out by sucking; the liquid rises and fills both legs of the instrument, the tap is turned off, and the syphon is full. Now as the leg _a_ is longer than the leg _b_, the fluid in it weighs more than that in _b_, and sinking down draws the fluid in _b_ up, and so on till all is drawn from the cask. Syphons are generally made of copper, but gutta-percha would answer exceedingly well. Fig. 2 represents a contrivance for drawing off acids, &c., which would injure the mouth; the ball prevents the acid rising into it, as the mouth is removed directly it begins to fill, which as the instrument is of glass, can easily be seen.

STOP-COCKS OR TAPS.

Illustration: FIG. 1. (‡ OPEN TAP.)

Illustration: FIG. 2. (‡ CLOSED PLUG.)

Illustration: FIG. 3. (‡ OPEN PLUG.)

Illustration: FIG. 4. (‡ CLOSED TAP.)

Illustration: FIG. 5. (‡ SPOUTED TAP.)

Taps are used for the purpose of letting off or stopping at pleasure the flow of liquids from vessels or through pipes. The forms of stop-cocks are very various, but the form shown at fig. 1 is by far the most general; it consists of a short curved tube, having an upright cylinder in the centre in which a plug with a handle turns; this plug is perforated in the direction of the length of the handle, so that when this is turned crosswise the communication is shut off (figs. 2, 3, and 4). The “nose” or end of the tap is sometimes prolonged into a spout, for filling bottles, &c., as in fig. 5.

Illustration: FIG. 6. (‡ OPEN SAFETY TAP.)

Illustration: FIG. 7. (‡ CLOSED SAFETY TAP.)

Illustration: FIG. 8. (‡ AMERICAN WOODEN TAP.)

Illustration: FIG. 9. (‡ SAFETY TAP KEY.)

Illustration: FIG. 10. (‡ 4-WAY TAP (a-b, c-d).)

Illustration: FIG. 11. (‡ 4-WAY TAP (a-c, b-d).)

The safety tap differs somewhat from the ordinary tap, a section is seen in figs. 6 and 7; the plug is hollow and forms the nose or spout itself, this plug is only perforated on one side, so that it has to be turned round half-way instead of quarter-way as in the common tap. The upper part of the cylinder has an opening (of different shapes) leading to the top of the plug, &c., a key being made to fit it (fig. 9). The American wooden taps (fig. 8), are just like it, but have the handle united instead of a key. The four-way tap is a clever contrivance for uniting four passages in alternate pairs; figs. 10 and 11 indicate the different positions of the plug. This kind of tap was formerly an important part of the steam-engine, and allowed the steam alternately to enter above and below the piston.

FILTERS.

Illustration: FIG. 1. (‡ BLOTTING-PAPER FILTER.)

Illustration: FIG. 2. (‡ FILTERING STONE.)

Filters are contrivances for separating substances from liquids which are not dissolved in them; but in the most common acceptation of the term, filters are vessels used for separating the impurities from water. Filters on the very large scale required by the water companies consist of sand or gravel so contrived that the water shall drain through them. This, indeed, is the natural way in which well or spring water is filtered; for the rain falling on the surface of the earth sinks down through such substances as gravel and sand, and lies in beds at the bottom, when it meets with stone or clay, through which it cannot sink (see “Artesian Wells”). This water when drawn up is in most cases very bright, as it has been strained through the sand or gravel in passing downwards. The best substance through which to filter water for household use is sponge pressed together with some force, and this is the usual plan adopted in all the earthenware filtering vessels sold; but there is usually a layer of sand or some other substance placed below, which is useless or worse, as it often becomes foul and taints the water. If the water has a bad odour, a few pieces of newly-burned charcoal placed in it above the sponge will purify it (see “Charcoal”). Filters for other purposes, and for any small quantity of liquid, may be made by cutting a piece of white blotting paper round, and then folding it into quarters and partially opening it (fig. 1); this if put into a funnel forms a convenient filter for any substance to be brightened, as water, vinegar, or wine. A particular kind of porous sandstone used to be hollowed out and used as a filter, but these filtering-stones are now but seldom used, except in the case of self-filtering cisterns, which are made by enclosing the inner opening for the tap in slabs of porous stone, so as to form a box within the cistern (fig. 2); by this contrivance, when the tap is turned, only that water escapes which has been filtered. It is necessary to have an air-tube to let the air in as the filtered water runs out, and to let the air out as the water filters in from the cistern. Even in these cisterns a box of slate or other substance having several holes with sponges pressed into them would answer much better, as these could be removed from time to time, washed, and returned. Filters, of course, can only separate mechanical impurities, such as dust, insects, &c., for if sugar or salt were put into the water, all the filtering that could be used would not separate them when dissolved, and thus it is that well and spring water, although perfectly bright, are still very impure, containing much lime and carbonic acid dissolved in them, together with other matters, as iron, &c., which are not separable by filtration; if it be desirable to separate them, distillation must be had recourse to (see “Distillation”). Some of these, however, as lime, may be separated by boiling the water for some time, which causes the lime to fall down in the form of chalk, and adhere to the bottom of the vessel--hence the “fur,” as it is called, in kettles. Water containing lime, although quite “hard” and unfit for washing purposes, is made sufficiently “soft” for use by boiling.

PRESSES.

Presses are contrivances for compressing or squeezing together substances that may require to be so treated, as in the case of extracting the oil from seeds, &c. The earliest presses were simply heavy stones or pieces of metal, put on one after the other; but the great inconvenience and loss of time incurred in putting on and taking off these, soon led to the screw and lever, which form the usual screw press. The screw is fixed at one end in a socket and is turned round by a long bar of iron or wood, and as the “worm” works in a corresponding hollow screw which is fixed, it ascends or descends slowly but with great power. But by far the most powerful contrivance of this kind is the “hydraulic” press; this machine is not only used as a press, but also to raise great weights, and for many other purposes. The hydraulic press consists of a strong iron cylinder having a solid piston exactly fitting to it, this piston is raised by forcing water under it by means of a pump; the principle depends upon the peculiar property which water and every other fluid has, of exerting, when confined in a given space, an equal pressure upon every part of that space; thus if one pound pressure be made upon one square inch, the water will press with one pound power upon every square inch of surface that it comes into contact with; for example, suppose a cylinder, the piston of which is one foot measurement on the face--this foot contains 144 square inches--and from the bottom of the cylinder a tube should be made to rise a few feet above the piston, and that this tube should have an area of one inch; then one pound weight of water poured in at the top of this tube would raise 144 pounds weight placed on the piston, for these 144 pounds would press but one pound on each inch, and the pound of water would have the whole of its weight on the one inch of the tube, they would therefore balance each other. But instead of pouring in the water, let a piston be fitted to the tube; a man with his hand can easily exert 100 pounds pressure on this, and the result would be that he would raise 14,400 pounds or nearly six-and-a-half tons, and if to this small piston a handle and valves be fixed so as to make a pump of it he can easily pump in water at a pressure of two or three hundred pounds to the square inch; and if instead of the large piston containing one foot area it has three or four feet, then the weight raised would be very great; indeed there is no limit to the power of this instrument but the strength of the material used. It must however be observed that when the piston descends, say six inches, it does not raise the six-and-a-half tons six inches, but only a hundred-and-forty-fourth part of that distance, so that the piston would have to be raised and depressed six inches 144 times in order to raise the six-and-a-half tons six inches. But this is such a saving and concentration of labour that the application of the hydraulic press is becoming more in demand every day.

STILLS.

Illustration: FIG. 1. (‡ RETORT.)

Illustration: FIG. 2. (‡ COMMON STILL.)

Illustration: FIG. 3. (‡ SMALL PORTABLE CONDENSER.)

These are vessels of different kinds used in distilling, that is, when any volatile product has to be converted into vapour and afterwards condensed, for the purpose of separating it from various matters not otherwise separable. One of the oldest forms of still is that even yet used in most chemical operations, called the “retort” (fig. 1). It is blown out of glass in one piece, is easily made of all sizes, not exceeding a few gallons; it is chiefly used for distilling small quantities of fluids, and those which act on metals, as the acids. For some purposes, chiefly those requiring a very high temperature, earthenware retorts are used, and in other cases retorts made of platinum; the retort is often “tubulated,” a name given to those with an orifice in the upper part having a stopper fitted to it, this opening is useful to introduce any substance while the body of the retort is already partly filled with its contents, or to add more of anything from time to time as it distils over. An indispensable adjunct to the retort is a “receiver” for condensing the liquid distilled; this is generally of a globular form, with an opening to receive the spout of the retort, which is also frequently “tubulated” that it may be attached by a bent tube to a second or third receiver. The receiver is to be kept cool, and this is generally done by a stream of cold water being poured on it, or a cloth dipped in cold water being spread over it, &c. The stills properly so called, such as are used in the manufacture of large quantities of liquids, as, for example, in the distillation of spirit, are generally made of copper tinned inside to prevent the formation of verdigris, and consist of a body, a head, and a condenser, the common form of which is seen at fig. 2. The condenser consists of a long tube coiled up into a spiral and placed in a large tub of water, having a supply tube to let in cold water at the bottom, and one for the exit of the hot water at the top, for hot water being lighter than cold, rises up to the top of the tub. A very good form for a small portable condenser may be seen at fig. 3, in which a constant current of cold water is made to pass through the outer tube, and so keep the inner one cold.

Illustration: FIG. 4. (‡ FLASKS AND BENT TUBE.)

Illustration: FIG. 5. (‡ TWO TUBES.)

A distilling apparatus for experiments in chemistry can easily be made with flasks and bent glass tubes, fig. 4, or even by means of pieces of tube alone as in fig. 5, one being bent and the other straight; the tubes and flasks can be united by means of corks perforated by a round or keyhole file. Empty oil-flasks serve well for this purpose, they can readily be cleansed by putting a little oil of vitriol into them, shaking it well about, and then washing them out with clean water.

BLOWPIPES.

Illustration: _a._ (‡ COMMON BLOWPIPE.)

Illustration: _b._ (‡ RESERVOIR BLOWPIPE.)

Illustration: _c._ (‡ RESERVOIR BLOWPIPE.)

Illustration: _d._ (‡ HOME-MADE BLOWPIPE.)

Blowpipes may be considered as miniature blast-furnaces. They are little instruments used to force--by means of air blown from the mouth--the flame of a lamp or candle into a jet of flame so fierce that the very highest heat can be produced by it. Various forms of blowpipes are shown in the figures; the common blowpipe, used by gas-fitters, tinmen, &c., is shown at _a_; better blowpipes have generally some reservoir to contain the condensed breath and so prevent it issuing into the jet; the bulb shown at _b_ is for this purpose and also the conical part of _c_. Very good and cheap blowpipes may be made by bending a piece of glass tube into the form shown at _d_, adding a perforated cork and a small piece of bent glass tube fixed as in the figure. The end of the small tube, intended to produce the jet, should be held in the flame of a lamp or gas till it is red hot and turned round all the while; in this way the hole will gradually become smaller as the melted sides collapse, forming a neat round hole about the size to admit a fine needle; with this blowpipe a very great heat can be produced, and it can be easily repaired. The oxy-hydrogen blowpipe is a contrivance for forcing a jet of oxygen and hydrogen gases--mixed together in the proportions in which they form water--through a small orifice and setting fire to it; this produces the very highest heat. Almost any substance can be fused by it, but the experiment should not be made unless with a proper apparatus, as the flame will be sure to run down the tube and explode the mixed gases with dangerous violence. A common flame is merely a cone of vapour burning on the surface where it comes into contact with the air, and therefore gives out but little heat, but when air is forced into it, a small blue cone of solid flame is projected, which gives off more heat than the hollow cone.

THERMOMETERS.

Illustration: FIG. 1. (‡ BULB AND STALK WITH MERCURY.)

Illustration: FIG. 2. (‡ SCALED THERMOMETER.)

Illustration: FIG. 3. (‡ REGISTER THERMOMETERS.)

The thermometer is an instrument for determining the temperature of the air or any other fluid into which it may be introduced. The thermometers in general use contain mercury, but some contain colored spirit; yet, as mercury is most generally used, it will be only necessary to say of spirit thermometers, that they act on the same principle. A thermometer consists of a glass ball having a long thin hollow tube rising out of it and attached to a graduated scale--the bore or hollow of the tube is very small, scarcely sufficient to admit a piece of sewing cotton. The ball or bulb and part of the stalk are filled with mercury by holding a lamp to the ball till the air is nearly all expelled by its expansion--for heat expands air very greatly--and putting the end of the stalk into a vessel of the fluid. When the lamp is removed the air in the bulb cools and therefore contracts, by which means the mercury is forced up the fine tube, very nearly filling the bulb. The bulb is then held downwards and the mercury so heated that it expands, as did the air, till it fills the whole of the bulb and stalk up to the very top; the top is then melted with the blow-pipe (see “Blowpipes”), and the glass, running together, closes up the bore at the end. As the mercury cools it contracts, and consequently, occupying less space, falls down in the stalk pretty close to the bulb, the space above it is therefore empty, and forms a “vacuum.” Now, therefore, we have an instrument, consisting of a bulb and stalk half-filled with mercury (fig. 1). Upon any amount of heat being applied to the bulb, the mercury in it expands, and rises in the stalk in proportion to the amount of heat applied, or shrinks and sinks down again as it cools. The next thing to be done is to form a “scale” by which the height of the mercury in the stalk may indicate some known or recognised temperature. There are three scales in use, “Fahrenheit’s,” “Reaumur’s,” and the “centigrade.” The scale universally used in England is Fahrenheit’s, although both this and Reaumur’s are sometimes marked on the same thermometer (fig. 2). Fahrenheit’s scale is formed thus:--The bulb of the thermometer is placed in boiling water, and the height to which the mercury rises is marked by a scratch on the stalk; it is then put into snow or ice in the act of melting, and another scratch is made where the mercury has descended to. The space between these two marks is divided into 180 equal parts called degrees, and these divisions are carried upwards to nearly the end of the stalk and downwards to near the bulb; the upper scratch, indicating the heat of boiling water, is marked 212, and the lower one, which marks the freezing point of water, being 180 divisions lower, will be 32; and of course, 32 degrees lower will be 0, and is called “zero.” On the scale of Reaumur’s thermometer the zero or point marked 0, is at the freezing point of water, and the boiling point is marked 80 (fig. 2). The centigrade differs from Reaumur’s only in having the space between the boiling and freezing point of water divided into 100 parts instead of 80. What are called “register thermometers” have two bulbs, stalks, and scales, on the same instrument (fig. 3); one bulb is filled with mercury, and the other with colored spirit. In each stalk a piece of enamel, about half-an-inch long and fitting the cavity, is introduced; the one in the mercury is to register the highest, and that in the spirit to register the lowest degree of heat. They act in the following manner:--The spirit, being very liquid or thin in its nature, wets the enamel and passes by it when it rises in the stalk, so that the elevation of temperature does not affect its position, but when the spirit sinks down it drags the enamel with it, thus registering the lowest temperature, so that the distance the enamel is found down the stalk indicates how low the spirit may have descended in any particular time, say a night. With respect to the mercury, it is not of a nature to adhere to the enamel, and therefore instead of passing it pushes it up in the stalk as it rises, but on descending leaves it behind, the height at which the enamel is found up the stalk indicating the highest point to which the mercury had risen, and consequently the highest temperature. To adjust the instrument, a slight tap or shake will make the index in the spirit tube fall to the surface of the spirit, where it is held by the adhesive quality of the liquid, and by the same process that in the mercurial stalk will fall to the surface of the mercury, but will not penetrate it, owing to its great density.

BAROMETERS.

Illustration: FIG. 1. (‡ BENT GLASS TUBE.)

Illustration: FIG. 2. (‡ TUBE IMMERSED IN MERCURY.)

Illustration: FIG. 3. (‡ WEATHER GLASSES.)

The barometer is designed to indicate the weight or pressure of the air on any surface, at any particular time or place; for the air, although invisible, is still of considerable weight, as there are many miles of it pressing from above downwards on all parts of everything upon the earth, and the barometer is for the purpose of ascertaining how much this pressure amounts to. It is formed as follows: a piece of glass tubing, about three feet long, is first closed at one end, then turned up at the other and expanded (fig. 1); when this tube is filled with mercury and held with the bulb downwards, the mercury sinks in the stalk to a certain height (say twenty-nine inches), and that height shows the weight or pressure of the air. The reason of this will be understood by supposing a piece of straight glass tubing, three feet long, to be closed at one end and then filled with mercury; if the finger be placed on the end not closed, and that end turned downwards and put into a basin of mercury (fig. 2) before the finger is withdrawn, the fluid, if the air exerted no pressure, would all sink down from the inside of the tube into that in the basin, leaving a “vacuum” or empty space in the hollow of the tube, but it is evident if the air exerted any pressure on the surface of the mercury in the basin, this pressure would force the mercury up the tube (for there is no opposing pressure in an empty space), and that the mercury would rise higher and higher the greater the the pressure. Well, then, the air really exerts this pressure, and to such an extent as to raise the mercury somewhere about thirty inches in height, and the pressure necessary to do this is found by calculation to be about fifteen pounds upon every square inch of surface. The barometer tube is divided into a scale of inches and fractions of inches. What are called weather glasses, are barometers having the lower part brought up by a curve, and a small weight resting on the mercury in it, which being attached to a corresponding weight by means of a cord running over a little wheel or pulley fixed to hands moving round a sort of dial, turns them as the mercury rises or sinks (fig. 3), for as the mercury falls in the stalk it must of course rise in the short stalk of the curve; the hands by these means are turned round, and the rise or fall of the fluid will cause them to point to “fair,” “rain,” &c., as the case may be, for these names are marked where a corresponding change of the weather may so influence the weight of the air, as to raise or depress the mercury, and so bring the hands in a position to point to them.

PENDULUMS.

Illustration: FIG. 1. (‡ GRIDIRON PENDULUM.)

Illustration: FIG. 2. (‡ MERCURIAL PENDULUM.)