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SURAXICS_XIX.

right angles to the motion of the body, no velocity is destroyed,

the only alteration being in its direction. VIEW XORCE—THE PENDULUM-CENTRE We constantly meet with illustrations of the action of this * OSCILLATION.

force. A can filled with water may be swung round the head * Auk strike one another, they touch first in some

without a drop being spilt. When the can is at its highest x and the motion of these is usually com.

point, and therefore month downwards, the water is attracted my moment to whole body. Thus, when a carpenter strikes towards the earth ; but this attraction is more than overcome mwaka mot L Laser, it only touches part of the head, but by the centrifugal force, and hence it remains in the can as if it

* * ***** *quired by this part is shared by the whole. were a solid. So, too, when rapidly turning a corner or running 1, ** Fold blow be not true, the head alone may receive round the inside of a ring, we lean inwards. The body has :

ANA nitly off by itself, leaving the rest unmoved. tendency to move onwards in its previous direction, the feet Vivaras especially if the body struck be soft or brittle, are, however, compelled to move in another, and thus the head Ama kwa wodity of the other be great, there is no time for the and body are thrown outward; to obviate this we lean in the

to be thus shared, and then the shape of the mass is contrary way. For the same reason, in a curve on a railway * or the part struck flies off as a chip. A homely illus- the inner rails are lower than the outer, so that the carriage Se of this is afforded by a simple experiment which all inclines inwards, and thus removes the danger of its opsetting

or tearing up the rails. A carriage is not unfrequently upset in Wytry.

Melanoe a small piece of card on one of the fingers of the left this way while rapidly turning a corner. band, and lay & shilling on the top of it. By a sudden blow

If a glass of water be placed on a small whirling table so with the finger and thumb of the other hand the card may be that it can be rapidly turned, the water will leave the centre jorked away without moving the shilling. Care must, however,

and rise towards the edges; it may even be scattered over the be taken to strike the card exactly in the direction of its surface, sides if the rotation be rapid enough. The same effect is seen as if it be tilted up or down the shilling will, of course, be jerked if we rapidly stir a cup of tea, the level at the sides being above oft. After a few trials, however, you may be pretty certain of that at the centre. The explanation is, that the motion of the card is so

A practical applioation of these principles is seen in the rapid that it has moved quite away before it has had time to centrifugal drying machine. This consists of a large hollow communicate its motion to the shilling.

cylinder, the bottom of which is perforated by a number of There are many other familiar examples of this, some of which holes. The linen is put into this, and it is then made to rotate verge on the marvellous.

rapidly. In this way it is closely pressed against the sides, If a bullet be fired at a door set half open, it will pass through and the water is given off and runs away through the holes is the panel without shutting the door or moving it on its hinges. the cylinder. Linen can thus be rendered almost dry in a very We may even go further, and, instead of a bullet, put a tallow short space of time. Another useful application of this foros is candle into the gun and fire it at the door, it will be found to

seen in the "governors" of a steam-engine. These consist of pass through instead of being smashed against it, as we should two heavy balls susnaturally expect. The velocity of the particles of tallow is so

pended by rods, and great that they have passed through the door before they have when the speed of the time to alter their relative position. So, if we fire a bal at å engine is increased be

belky window, it will pass through the pane without cracking it, yond the proper degree merely making a clean round hole. If, however, the bullet be they fly apart, and in nearly spent, or its velocity be not sufficiently great, the glass so doing raise a loose will be shivered to pieces.

collar below them, and This, coo, explains why a good skater will glide swiftly over

by a series of levers ico far too thin to sustain his weight. His motion is so rapid, partly close the throttle that before the ice has time to yield he has passed on to another valve, and thus di. portion of it. We see, then, that a certain amount of time is minish the supply of required for any motion to be imparted from one body to another.

steam.

In Fig. 105 a, a re

present the balls susIf a lump of metal or other heavy substance be fastened to a pended by rods, which piece of string, and then swung round and round, we shall find are hinged at b to the

Fig. 105. that the string is stretched with a strain which varies in pro- vertical shaft g. Moportion to the speed with which the body revolves. This strain tion is imparted to this by means of a strap, which passer

is called centrifugal force, and is round the shaft of the fly-wheel, or some other convenient part merely one of the results of the first of the engine, and then round the driving-palley, d. When the law of motion.

engine is moving too rapidly the balls fly further apart, and Let B (Fig. 104) represent a body re- ' by so doing raise the runner, e. This, by means of the best volving round a centre A, and confined lever, k, works the rods, f, and thus partly closes the valve. by the string AB; its tendency at every Were it not for some such arrangement as this, there would instant is to continue in the same lino be great danger of the

engine at times moving so rapidly, that in which it is travelling at that instant, the fly-wheel would from the momentum of its particles be that is, to fly off at a tangent, as shivered to pieces. These balls keep the speed nearly mni

. along BC. We can easily prove that form; for if it diminishes much they fall, and thus open the Fig. 104. this is the case, for if, when whirling throttle-valve to a greater extent and allow more steam to pak

å sling, we suddenly cut the cord or The laws of centrifugal force are important, because they leave the end free, the stone will fly off in a straight line. help to explain the motions of the heavenly bodies. The planets

, Suppose D to be the point which the stone has reached at when first made, were started from the hand of their Creator the end of one second, then B D will represent the space passed with a certain velocity. This produces a constant tendene over, and therefore the velocity of B. This we can resolve into to fly off at a tangent from their orbits. They are, however, two parts, BF acting along the tangent bc, and BG acting restrained by another force, and that is the universal attraction along the direction of the cord. The former represents the of all bodies for each other. Gravity is but one manifestation velocity the stone has acquired, the latter is the force exerted of this: the earth draws the small bodies to it merely on account by the string to keep it moving in a circle; this, therefore, re- of its superior weight, and for the same reason the sun attracte presents the centrifugal force. We can thus easily see that all the planets ; or, to speak more accurately, all are attracted the greater the velocity with which В moves, the greater will to the common centre of gravity of our own solar syster, be the strain on the cord. If, for example, the velocity be so which is situated very near to the sun. much increased that at the end of one second B is at E instead of D, the tension of the cord will be represented by Bh instead line in which they would otherwise move, and as a result os

This attraction, then, constantly deflects the planets from the As, however, this tension always acts in a direction at these two forces they describe ellipses, in one focus of which

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THE PENDULUM.

the sun is situated. As this motion is through space, and not sent the portion of gravity which produces motion in the through a resisting mediun like the air, the retarding forces pendulum, and a Y that which produces tension in the cord; which diminish the motion of bodies near the earth do not and it is clear that the smaller the aro AC, the less will yx affeot them, and hence they move with undiminished speed. be, and therefore the less the velocity of the pendulum. This This speed, however, varies with their distance from the sun, velocity is found to decrease in the same proportion of the and the following rule, discovered by Kepler, shows the rela- length of the arc, and this accounts for the vibrations occupying tion that exists between the speed and the distance:-The straight equal times. line drawn from the planet to the sun always describes equal Now as the force which moves the pendulum is the resolved areas in equal times. This law partly depends on another, part of gravity, it clearly increases or decreases with that force, which teaches us that the attraction of any body for another and thus the vibrations afford us a means of measuring the force diminishes with the square of the distance. If, for instance, we of gravity and comparing its power at different parts of the remove a body to double the distance, the attraction is , if to earth. At the equator it is least, the diameter there being three times the distance, it is only $, and so on. This is an greatest, and a part of the force, which is reckoned at ašo, being experimental law, though by analogy with light we can easily overcome by the centrifugal force produced by the earth's see why it should be so. If we take a piece of board, and rotation. A pendulum will, therefore, make fewer vibrations having cut out of it a piece a foot square, hold the board at any there than it will as we move towards the poles. The times distance from a bright light, and place a screen behind it at twice of oscillation vary, then, at different parts of the earth's surface. the distance from the light, the illuminated space on the screen We find, too, that the time of oscillation depends upon the will measure 2 feet each way, or 4 feet in all. The light is thus length of the pendulum, a longer pendulum making less vibraspread over four times the area, and therefore the illumination tions in any given time than a short one. The rule about this at any point is only one-fourth as great.

is as follows :Similarly, if the distance of the screen from the light be three The time of oscillation increases in the same ratio as the square times as great as that of the board, a space of 9 square feet will root of the length of the pendulum. be illuminated, and each part will have one-ninth of the If we take three pendulums whose lengths are in the probrilliancy.

portion of 1, 4, and 9-say, for example, 6 inches, 2 feet, and From this we see that when a planet is in the part of its 4 feet 6 inches, respectively--we shall find that while the long one orbit most remote from the sun, it is attracted less powerfully, makes one vibration, that two feet long will make two, and the and therefore its velocity must be less than when nearer the shortest, three. In the latitude of London, a pendulum to beat sun, or else it would fly out of its path.

seconds must have a length of 39:13 inches; at the equator, the length must only be 39.01 inches.

In the compound pendulum all parts must swing at exactly We must now notice this very important instrument, so the same rate; but by what we have seen, those nearer the point valuable to us, not only as a regulating power for clocks, but of suspension have a tendency to swing more rapidly, and thus also for calculating the force of gravity and its variations in to accelerate the motion of those below, while those at the different places.

extreme end exert just the contrary influence. Now there is A simple pendulum is one all the weight of which is collected evidently some point where the particles are as much retarded at a single point. Such a one can, of course, only exist by those below as accelerated by those above, and this point theoretically; but we may obtain a near approach to it by sus- must move at the same rate as if it were free. We might, in pending a small ball of some heavy substance, as lead or fact, have all the weight collected at this spot without altering platinum, by a very fine string.

in any degree the rate of oscillation. A common pendulum is called compound, for the weight is This point is called the “centre of oscillation,” and when divided throughout it, and it may therefore be considered as a we speak of a pendulum of any length-as e.g., 39.13 inchesnumber of simple pendulums connected together, so that all we measure from this point to that of suspension. This centre swing at the same rate. All are familiar with its action, but of oscillation is always below the centre of gravity. However many do not know why it is used as a regulator.

much we alter the weight of the pendulum, provided we make When a pendulum hangs freely, all its oscillatrons, if not of no difference in the position of this point, the time of oscillation wide extent, occupy exactly the same time. If the pendulum be remains exactly the same. The rate of vibration, then, is not made to swing in a cycloidal curve, instead of an arc of a circle, at all affected by the nature or weight of the pendulum, but then from whatever part of the aro it falls it always takes depends alone upon its length. We see, thus, the way in which exactly the same time. This remarkable property is called the we can regulate the speed; we can either raise the bob by means isochronism of the pendulum, this term being derived from two of a small nut, as is usually done, or we can have a smaller Greek words, meaning "equal” and “time.” Galileo was the weight sliding on the rod, and raise or lower this. In either first to discover this law, and it is said his attention was called | case, the effect produced is the same—the position of the centre to it by observing a chandelier in a cathedral. By some cause of oscillation is moved, and thus the length altered. When the it had been set swinging, and he noticed that however long the pendulum rod is made of metal, as it usually is, it varies in arc, it appeared to swing in exactly the same time. He ac. length with the alterations of temperature, being lengthened by cordingly tried some experiments on his return home, and found heat and contracted by cold, and thus a source of irregularity that such was the case.

is introduced which would be very objectionable. This difIn Fig. 106 let o represent the point of suspension. When ficulty is met by what is called the compensation pendulum.

oc is vertical the force of gravity is exactly In one form of this the bob consists of a cup of mercury. When
overcome by the tension of the cord, and thus the rod lengthens by the heat and lowers the centre of oscilla-
the pendulum serves as a plumb-line, for if c be tion, the mercury expands and rises, and its bulk is so arranged
raised above the lowest point it will swing back that this expansion raises the centre in exactly the same
wards and forwards till it settles at that point. degree as the expansion of the rod depresses it. In large
Now raise c to A. The same two forces act church clocks the pendulum rod is frequently made of wood,
upon it, namely, tension along A 0 and the force of and thus this difficulty is avoided.
gravity acting vertically downwards along A X. Another compensating pendulum is composed of parallel bars
Produce o A to y, and draw A za tangent to the of brass and zinc, so arranged that by their joint alterations in

We can now resolve the force of gravity length the position of the bob remains unaltered.
into two, acting along A Y and a Z. The former The balance wheel of a watch acts on the same principle as
of these will be overcome by the tension of the the pendulum, its vibrations being isochronous.

string, the other part acting along a Z will cause When a pendulum is made to swing by itself it soon comes to c the pendulum to move towards c. On arriving rest; and even if every care be taken to remove the air and re

there it will have acquired a velocity which duce the friction, it will not continue in motion more than about Fig. 106. will carry it on over an arc nearly equal to ca, twenty-four hours. A maintaining force is therefore needed,

and thus it will continue to oscillate till its when it is employed as a measurer of time. This is supplied by motion is stopped by the resistance it meets with. If we the spring or weight of the clock. The pendulum rod works in now draw a line through y parallel to AZ, YX will repre- a fork which is attached to the anchor and pallets. Those

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catch in the teeth of the escapement wheel, and allow it at each Thomas. No, it would be wrong; "the fleet has sailed” is oscillation to move forward half a tooth, and then again stop it. correct English. The true rule in this matter is this : Nouns of The motion of the escapement wheel is thus at each stoppage multitude require their verb to be in the plural when the mind transferred to the pendulum, and keeps it in vibration. A train dwells on the individual objects which they comprise; but when of wheels, connects this escapement with the hands.

those objects are presented or contemplated as a whole, then the We have thus acquired a general acquaintance with the more verb must be in the singular. In the phrase " the majority of important facts of Mechanics. The subject is far from ex- us," the idea of plurality is made prominent, you of necessity hausted, but we must leave you to follow it up in works think of several persons, therefore your verb must be in the specially devoted to it. Our attention will now be turned plural; but in the phrase “the fleet has sailed," you conceive to the other branches of Natural Philosophy, all of which are cf the component parts as forming a whole, several elemente of great interest and importance. The next branch we shall coalesce into one, unity is the predominant feeling, and conse. take up is Hydrostatics, a scienco which has been claimed as a quently you must employ a singular verb. I give you another branch of mechanics, but is more accurately considered as a instance : “ The imprisonment of us is wrong.” What say you separate science.

to that?

William. It is correct.

Thomas. Yes, it is correct. Now do you not see the words LESSONS IN ENGLISH.-XXIV.

“of us” hold in this sentence precisely the same relation or CONVERSATIONS ON ENGLISH GRAMMAR.--IIL

position that is held in the first sentence by the words " of ou

conversation ?” Look at this arrangementWilliam. The substance of our two conversations are pretty clear to me now. Thomas. I am glad you have carefully studied them, but

Verb. Attribute. you have just committed a grammatical error.

The imprisonment of us

wrong William. You do not say so? I fear I shall never geu | Usyou see, is not the nominative case (or, as I prefer right. Thomas. Yes, you will get right by perseverance. The error putting it, is not the subject), for we, you know, is the nomina

You would not sy into which you have fallen is a very common one; I have heard tive, and us is in the objective case. it even from the lips of persons who do not think themselves ignorant of grammar.

William. Oh, no, that wonld be ridiculous. William. Wherein does it lie ?

Thomas. And yet I heard a man, the other day, say we is ; Thomas. You have used a plural verb where you should have nay, I am not sure that you yourself-speaking, for example

, of used a singular one.

the potatoes you might have had to-day for dinner-did not say, William. But “conversations " is in the plural.

"they is good.” What think you ? Thomas. It is. That word, however, is not the subject to

William. It is not impossible; these things are very per the verb of the sentence; it comes immediately before the verb,

plexing. and so has led you to put the verb into the plural, by a kind of

Thomas. Yes, at first they are troublesome; but stads and latent attraction, against the influence of which I must put you practice will remove all difficulties. They have done so in mj on your guard.

case, why not in yours ? William, What, then, is the subject ?

William. Well, I am not going to yield. Thomas. Substance is the subject, or what in common

Thomas. Certainly not. Bonaparte is reported to have said grammars is called the nominative case, and the sentence that the French had not such a word as impossible" in their should have stood thus: “The substance of our two conversa

language. However this may be, you, as an Englishman, will tions is pretty clear to me now." “ Substance,” I repeat, is not, I am sure, oasily admit the idea into your mind, or the the subject. What is clear? You do not mean that the “

thing itself into your conduct. “Impossible ?" No, nothing versations” are clear ?

that is good and honest is impossible. What man has done

, William. No; for there are some things in them that I do

man may do. Now I must put you to rights in regard to this not quite comprehend; but they are clear on the whole.

verb w and are; it is a word against which many, very mans, Thomas. Yes, your language expressed your meaning cor

persons sin grievously. Study this form :rectly, although your grammar is at fault. This I have often

THE VERB to be. observed in persons of defective education. Right in their logic, and having a good command of words, they are unable to

Person. put them together correctly, and so lose a large part of the

1. I am.

i. advantage they ought to derive from their efforts at self-culture.

Singular 2. Thou art. ii. Thou wast. Observe, now, conversations is dependent on the preposition

3. He is. iii,

He wns. "of.” In the ordinary phraseology, it is governed by that pre

1. We are.

We were. position; and being governed by it, is in what is called the

Plural 2. You are. ii. You were. objective case--it cannot be the nominative, or the subject to

3. They are.

iii. They were. the ensuing verb. In fact, the word " conversations” is a part This surely is not very complicated, yet it contains all you need of the compound subject of the sentence, as you may see exhi- know in order to speak and write correctly, so far as this point bited thus :

is concerned. Take care, then, not to separate the propong from the proper forms of the verb. Take care not to mix

together verbs and pronouns that should be kept apart. Do Verb. Altribute.

not take the first person I, and put it before the third person The substance of our conversations is clear

to me now

is. In other terms, 1 and i. must go together; 1 and iï. must Take another instance: “The majority of us are stonemasons." | not be combined. You must say we were (1 and 1.), and not they Is that correct?

was (iii. and 1). Before I conclude, let me impress it on your William. No.

mind that you will never speak grammatically, or, at any rate

, Thomas. I beg your pardon, it is quite correct.

never be sure that you speak grammatically, unless you take William. How so?

the trouble to mako yourself familiar with the terms and the Thomas. Becanse the word “majority” is what is called a laws of grammar. Many, finding the study somewhat difficult noun of multitude-a noun, that is, which being singular in after a little while give it up in a sort of confident spirit form, is plural in signification. In a majority, you know, there thinking such drudgery beneath them, and fancying they can must be more than one. Now nouns of this kind, as they do all that is necessary by a sort of nondescript grammatical imply more than one, are constructed according to their sense, feeling. This is silly. "Accurate knowledge is not obtained by and not according to their form. Consequently, “ majority" genius, or inspiration, or any other fancied short cut to science

. requires its verb to be in the plural.

If you would know, you must condescend to learn, and all trua William. Then it would be right to say, "The feet have learning demands, as it well rewards, diligent and constant nailed,” for a fleet consists of many ships.

labour.

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William. Well, I do not know that I am in that danger; I 2. Graphite or Plumbago, erroneously called blacklead, is all never thought myself a “genius,” and as for "inspiration,” that but pure carbon, slight traces of iron generally being present. belongs to a subject too sacred for me to venture on-a subject It is a crystallised body, belonging to the third or Rhomboheon which I had rather worship than speculate, much less be dral system. The distinction between this and the first or over-confident.

regular system, in which the diamond crystallises, will be Thomas. Those are wise words; the man who is without explained in a future lesson on crystallisation. It occurs in reverence will be a small man to the end of his days.

veins, always in rocks of the earliest formations. The most celebrated mine is that of Borrowdalo, in Cumberland. Here it is found in "nests in trap traversing clay slates. It is an

good conductor of electricity, and is as difficult to burn as the LESSONS IN CHEMISTRY.-XI.

diamond. It is chiefly used for manufacturing lead pencils. CARBON AND ITS OXIDES.

Being very friable, it leaves its particles on paper when passed

across it. The particles themselves, however, are extremely CarBox.--SIMBOL, C; ATOMIC WEIGHT, 12.

hard, and soon wear out the saws with which the graphite No solid plays a more prominent part in the economy of nature is cut. than carbon, as it forms well nigh the whole of the wood of vege- Formerly good pencils could only be made from lumps suffi. tation. It is a very remarkable substance, for it appears in three ciently largé to permit of long pieces being cut. The small perfectly distinct states—the diamond, graphite, and charcoal.

masses and dust were cemented together with sulphur, but by 1. The diamond is found in alluvial débris—that is, in this the “ marking" quality of the graphite was so injured that water-worn deposits of gravel. It is presumed that the gem only the coarsest pencils could be made of it. But it has been was formed by crystallisation when the rock was in & fluid discovered that by submitting this dust to crormous pressure state, and when in after ages it became broken in pieces by tho it will cohere, forming plates fit for the manufacture of the action of water and other geological forces, the hard diamond best pencils. was delivered from its matrix, and mixed with the débris. The

Graphite is used for lubricating machinery, and also for chief diamond mines are those of Golconda and Bundelçund, making crucibles. For this purpose it is mixed with fire-clay. in India, Borneo, and Brazil.

These crucibles are not so liable to crack as those made of clay When found, the stone has the appearance of a piece of only. white glass ; oocasionally there is an approach to the crystal 3. The third form of carbon has no appearance of crystallisaform of the octahedron.

tion. It is therefore said to be “amorphous," or without form. It is the hardest of all known bodies, and is capable of This state is shown in cocl, charcoal, soot, etc. Of the composition dispersing light-that is, of breaking up white light into its of coal we shall treat in the next lesson. Charcoal is got coloured component rays-in a greater degree than any other from the "destructive distillation" of wood—that is, the wood body except chromate of lead. To exhibit this property to its is heated in vessels of iron, closed so that no air can cause the full advantage, the gem must be cut. This was once an opera- carbon in the wood to burn. Of course there is a pipe to carry tion of the greatest difficulty, and could only be executed by off the gases liberated by the heat. If blood or bones be subthe Dutch diamond-cutters, who fastened two stones in cement, mitted to this process, the result is animal charcoal. and then rubbed them against each other until a facet was pro- Wood charcoal is also made by cutting the wood into logs, duced. Now, diamond-cutting is much less laborious. The and arranging them on end, then covering the whole with sods, stone is fixed, as before, in a metallic cement, and pressed upon and setting fire to the heap at some central point. A portion a disc of steel about eight inches in diameter, which revolves of the wood is consumed, but the heat thus produced converts horizontally with a great velocity. As with all crystals, there the remainder into charcoal. Charcoal is a bad conductor of are certain directions in which the diamond is more readily cut. heat and electricity. It is very porous, in virtue of which, It is the skill of the cutter to place the stone upon the disc in like spongy platinam, it absorbs gases, the quantity varying the right position. The steel, were this not done, would itself with the nature of the gas. Thus, boxwood charcoal.absorbs of be cut, instead of making any impression on the diamond. The secret of the disc being enabled to wear down the hard

Hydrochloric acid gas mineral is, that the minute interstices of the metal become filled

Sulphuretted hydrogen with dust from the diamond. This is in many instances applied

Carbonic acid gas

35.00 to the plate mixed with olive oil; but when a disc has been

Oxygen

9:25. some time in work, it is sufficiently impregnated with the dust

When heated or placed in vacuo, these gases are again given not to need this addition.

off. Whilst in this state of condensation their powers of In the Brazil mines is fonnd a dark brown carbonaceous affinity are greatly increased. Thus sulphuretted hydrogen at matter, in small pieces, which is as hard, if not harder, than

common temperature is not altered by contact with oxygen ; the diamond itself; and it commands as high a price on account but if a piece of charcoal which has absorbed the former gas be of its use in forwarding the cutting of the stones.

plunged into a jar of the latter, a detonation ensues from The most important use of the diamond is the cutting of glass. the violence of the combustion, water and sulphuric acid being This is effected by a natural face of the crystal. If the edge be

formed :formed by the intersection of two artificial faces, the cut produced

SH, + S0 =1,0 + SO,. on the glass is not a true cut, but only a scratch with rugged edges. The natural faces of the diamond are frequently curved. This power is also shown in what are termed the antiseptic The diamond may be heated intensely in an atmosphere of any properties of charcoal-that is, the power it has of removing gas except oxygen, but if it be suspended in a cage of platinum offensive smells. If putrefying meat or fish be packed in chatwire, and hcated to a bright redness, and then plunged in a jarcoal, all smell is removed; for the gases which cause the of that gas, it burns with a steady red light, producing carbonic unpleasant effluvia are absorbed by the charcoal ; and while acid gas (CO2).

in this state the oxygen, previously in its pores, attacks and It was reserved for Sir H. Davy to show that this gas was changes the various gases, or oxidises the volatile organic the sole product of the combustion of the diamond, though the matter. The process of putrefaction, however, is not arrested, fact that it was combustible was known in 1694 to the philo- but rather increased. This is often resorted to by unprincipled sophers at Florence. The combustion, however, is not complete, butchers and fishmongers who present tainted meat or fish for as there always remains an ash, which is generally in the form sale, which escapes detection for the moment by its inodoronsof a cellular network—the skeleton, as it were, of the gem, and ness. Yet it possesses all the deleterious properties of unwholewhich consists of silica and the oxide of iron. With this excep- some food. Charcoal, especially animal charcoal, clears coloured tion the diamond is pure carbon. When submitted to the most liquids which are passed through it. This may be well illusintense of heats, that of the voltaic arch, the diamond loses its trated by shaking a little of it with a few ounces of port wine transparency, begins to swell, and is converted into a black in a bottle, and then filtering the mixture; the liquid which mass resembling coke, the amorphous form of carbon. In this passes the filter will be colourless. state it is a good conductor of electricity, a property it does not Sugar is clarified by means of charred bullock's blood. After possess in its transparent condition.

being in use for some time the charcoal is found to lose its

Volumes.

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55.00

The oxy

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decolorising power; but this it regains upon being calcined at a | is better not to use sulphuric acid, as the fragments of marble low red heat.

are then coated with calcium sulphate, which is insoluble, and These properties render charcoal invaluable in the construc- thus the action is retarded. The gas is unable to support life, tion of filters ; not only does it “aörate” and decolorise the and when breathed, spasm of the glottis prevents its entrance water, but by oxidising any animal matter it may contain, into the lungs. If its presence in air exceed four per cent., it does much to render it innoxious.

acts as a narcotic poison. Lampblack is prepared by burning turpentine or resin with a It is exhaled from the lungs, which are organs composed of limited supply of air, and condensing the smoke; when mixed a membrane some 160 square with linseed oil and soap, it forms "printers' ink.”

yards in surface, which has The oxides of carbon are :

the property of absorbing the Carbonic oxide

CO

oxygen from the air inhaled, Carbonic acid

CO,

and thus bringing it in conBesides these there are some vegetable acids-one of the simplest, tact with the venous blood oxalic acid (C,02), is the sour principle in sorrel.

beneath. This blue blood Carbonic Oxide (symbol, co; atomic weight, 28; density, owes its colour to the pre14).---This gas is best prepared either by

sence of carbon. 1. Depriving carbonic acid of an atom of oxygen, or

gen combines with this car2. By adding to it an atom of carbon.

bon, forming carbonic acid, (1) C0, -0 =CO;

which is exhaled. (2) CO, + C=2CO.

This may easily be proved To perform the first experiment, neat in the iron retort used to by blowing through a glass

Fig. 37.

tube into some lime water, prepare oxygen from manganese dioxide, a mixture of zinc or iron filings and well-dried cha!'s, thus

or barytic water. The calcium, or barium carbonate, is formed,

which renders the water milky. This chemical action is not Caoco, + Zn = CaO + ZnO + CO.

only carried on in the lungs, but over the whole body through For the other method, for zinc substitute carbon, thus- the pores of the skin. If the hand be introduced into a jar Caoco, + C=CaO + 2CO.

of oxygen standing over water, in a short time that gas will

be found to be converted into carbonic acid. Hence from this The heat drives off carbonic acid from the chalk, and in the simple experiment will be seen the imperative necessity of

first case the zinc is oxidised at cleanliness.
the expense of this CO,, and in the

This chemical action is the source of animal heat, and is second case the CO takes another exactly that which goes on more vigorously in a coal fire. I atom of carbon.

this case the oxygen entering in at the bottom of the gaste In each instance the gas con combines with the coal, forming carbonic acid. As this partes tains a little carbonic acid, and upward through the fire, it takes another atom of carbon

, therefore to obtain it pure, it must forming, as we have seen, carbonio oxide, which burns again be collected over water containing into carbonic acid when it reaches the top of the fire. The potash, which retains the carbonic blue, flickering Aame seen over a cinder fire is carbonic oxide acid to form potassium carbonate. burning into the higher oxide. Another method of preparing it is

To exhibit the presence of carbon in carbonic acid, it is only to digest pulverised ferrocyanide of necessary to pass the gas over a piece of heated potassium. potassium with seven or eight times The arrangement is shown in Fig. 37. The metal deprives the

its weight of sulphuric acid. Fig. 36.

gas of its oxygen, and the liberated carbon is deposited on the Properties.—The gas is colour- interior of the bulb.

less, tasteless, inodorous, poisonA taper introduced into it is extinguished; but the becomes a liquid. This is the means by which it is accom.

When submitted to a pressure of 35.4 atmospheres, the gas gas burns where it meets the oxygen with a blue flame, forming plished. A and c (Fig. 38) are two wrought-iron vessels. A carbonic acid, thus

mixture of water and sodium bicarbonate is introduced into a, CO + O=CO,

and the tube 6, filled with sulphuric acid, is placed upright in the 2 + 1 = 2.

generator," A. The top is now fixed, and the tap, s, turned. The numerals refer to the volumes that is, the carbonic acid The vessel is inverted, being placed on stands for that purpose, formed is of the same volume as the carbonic oxide burnt. This and the acid is emptied into the solution of sodium bicarbonate. may be proved by mixing in the eudiometer carbonic oxide, and Sodium sulphate is half its volume of oxygen; after the spark has passed, nothing formed, and a vast but carbonic acid will remain, whose volume is that of the quantity of carbonic acid

HS MHS

d carbonic oxide. This gas has a great affinity for oxygen, and gas is liberated. By therefore is a powerful reducing agent; in iron-smelting fur. means of the pipe, d, naces the reduction of the ore is chiefly due to its action. the generator is con

6 A solution of cuprous chloride (Cu,C1,), in hydrochloric nected with the “ acid absorbs carbonic oxide, as also does melted potassium. denser," C, which is

с Carbonic Acid (symbol, CO,; atomic weight, 44; density, 22).- packed in ice. So great When limestone or chalk, which are both carbonates of lime is the pressure of the (Ca000,), are heated in a kiln, the heat drives off the gas (CO,), gas, that when both the leaving the lime (Cao). The gas, being half as heavy again as taps are turned the air, collects in the fire-pit, and in any hollows close by the liquid carbonic acid diskiln; and here many a wanderer has slept his last sleep, poisoned tils over. When the by the gas. It is also the chief product of fermentation, and operation is complete, collects at the bottom of vats; its presence is ascertained by the two vessels are dis

Fig. 38. lowering a lighted candle, which will be extinguished if the gas connected. A little of be present. The escape of this gas causes the effervescence of the liquid can be received on a piece of wool by turning wines, the froths of porter, ale, etc., and makes bread "rise.” M, the pressure of the gas in c forcing the liquid up the tube.

It is best prepared by pouring dilute hydrochloric acid on So rapid is the evaporation, that the liquid on the wool is chalk, or, what is better, on pieces of marble (Fig. 36). On frozen. When mixed with ether, a paste is formed, which account of its density it may be collected by displacement, and possesses an extremely low temperature, by which merours is even may be poured from one jar into another. The reaction is at once solidified. thus expressed :

Carbonic acid, though a very weak acid, forms a numerous CaOco, + 2HCl = Caci, + H,O + Co,,

class of “carbonates." All these effervesce with dilute nitrio calcium chloride, water, and carbonic acid being the result. It acid.

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