Part 15

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.)