Cornell University Library arV17317 Scientific amusements ,. 3 1924 031 296 126 olin.anx Cornell University Library The original of this book is in the Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31 924031 2961 26 SCIENTIFIC AMUSEMENTS. SCIENTIFIC AMUSEMENTS Translated from the French of GASTON TISSANDIER. By henry frith. ffullB jllustcateO. LONDON : WARD, LOCK & CO., LIMITED, NEW YORK & MELBOURNE. K HALF-HOURS OF SCIENTIFIC AMUSEMENT. PREFACE. jQUNG people of both sexes, and persons ol all ages who have leisure and a taste for that which is ingenious as well as instructive and amusing, may be commended to this remark- ably interesting collection of experiments, nearly all of which can be readily performed by an iinskilled person who will carefully follow out the directions given. It is surprising how near we are to the most fundamental principles of science when we perform some of the simplest operations. The act of balancing oneself on one foot may be made to illustrate most instructively the principle of gravitation and the centre of gravity. The musical (or unmusical, as ^ the case may be) performance of whistling illustrates the power of air in motion, and the effects of vibrating cords^ (the vocal cords) in a limited space. The toasting of a piece of bread is an example of evaporation of water change of structure owing to heat, and the appearance of a black substance out of a white one by a change' in chemical combination. It is so in a multitude of the common occupations of life, and especially in the amuse- ments in which children take so great a delight. The schoolboy's sucker exemplifies the effect of the external pressure of the atmosphere ; his top, coerced to move vi PREFACE. circularly by the effect of a string wound round it in a spiral fashion, illustrates the effect of a spinning turn long after the force has been applied. A large number of experiments with coins— piercing a halfpenny with a needle, revolving a penny in a lampshade, catching coins held on the elbow in the hand, rotating a coin between two pins, and the like, show to how many amusing incidents these may give rise. Inertia, the bane of too many boys and men, is seen to prevail in the physical world in the experiment of projecting one or two draughts from a heap of them (page 1 8), and in removing a domino, as on page 20. The strange effects which can be produced by virtue of the principle of the centre of gravity are seen in the pencil and knife balanced on the point of the former, the match puzzle (page 30), the poising of a tumbler upon three sticks, each having one end in the air, the suspension of a bucket of water from a stick resting on a table, etc. Hydrostatics, the study of the effects of fluids, supplies many interesting facts and illustrations to this little book. The ascent of wine in an inverted glass of water, the floating of a needle, and the lobster syphon, are among these. The maintenance of various bodies in the air by currents of air, and the phenomena of vortex rings of smoke, are equally striking and instructive. Various experiments on the pressure of the air and with com- pressed air, and the properties of air and gas balloons, complete the section dealing with pneumatics. The conduction of heat by metals, and their dilatation by heat, furr>ish several striking phenomena of which PREFACE. vii the placing of a red-hot coal on a muslin handkerchief encircling a copper globe,' without setting fire to the handkerchief, is one of the most notable. Even more remarkable, perhaps, are the optical illusions, effects of refraction, etc., explained in Chapter VI. How to make a florin appear like five shillings and sixpence appeals strongly to the cupidity of mankind ; but it must not be imagined that this book will enable any one to buy five shillings and sixpence worth of goods for a florin. It is astonishing how many optical illusions may be produced by the varied arrangements of lines, points, and squares, and these are here duly set forth. The "imp on the ceiling" illustrates the persistence of impressions on the retina. Eleqtricity and magnetism, as is only to be expected in these days of the electric light, supply us with some most interesting subjects. The "dance of the paper puppets," and the " magnetised magician," are examples of these. Chemistry without a laboratory introduces us to the air and its elements, the formation of salts, instantaneous crystallisation, the "Tree of Saturn," the produ^;tion of gas, and the graven eggs. Mathematical games, as here expounded, are capable of affording no small amusement. Marjy of the best mechanical toys invented in recent years are described in Chapter XL, such as the acrobatic ape, the magic glass, the fantoccini top, the mechanical paper bird, the magic picture with three faces, and the mechanical fly. Every one may take his friend's portrait by the silhouette process given on pages 85, 86, while the formation of typica/ Vlll PREFACE. portrait sketches by the combination of implements used in any given craft is amusingly shown on pages 139-141-. Thus it will be evident that a vast amount of amusement, combined with instruction, is to be got out of the attentive perusal of the following pages. CONTENTS. Chapter i.— properties of bodies. PAGE STRENGTH — ELASTICITY — POROSITY — PERMEABILITY — RE- SISTANCE OF SUBSTANCES — HARDNESS— CENTRIFUGAL FORCE— THE PRINCIPLE OF INERTIA .... I CHAPTER II.- EQUILIBRIUM OF BODIES. THE CENTRE OF GRAVITY 28 CHAPTER III.— DENSITY, HYDROSTATICS, ETC. HYDROSTATICS — THE MOVEMENTS OF GASES — RESISTANCE OF THE AIR • 38 CtlAPTER IV.— PRESSURE OF THE AIR. PRESSURE OF THE AIR — EXPERIMENTS WITH COMPRE.SSED AIR— ASRONAUTICS 56 CHAPTER v.— HEAT. THE CONDUCTIBILITY OF METALS — DILATATION OF BODIES BY HEAT .... 66 X CONTENTS. CHAPTER VI.— LIGHT, OPTICAL ILLUSIONS, ETC. PAGV REFRACTION— VISIONAND OPTICAL ILLUSIONS— PERSISTENCE OF IMPRESSIONS ON THE RETINA CHAPTER XI. MECHANICAL TOYS, ETC. . 73' r\ CHAPTER VII. ELEpTRICITY AND MAGNETISM. . . . , , . .88 CHAPTER VIII. CHEMISTRY WITHOUT A LABORATORY . „ . >q2 CHAPTER IX.— MATHEMATICAL GAMES. THE DICE TRICK , .... 104 CHAPTER X. NATURAL SCIENCE IN THE COUNTRY . . , , . U3 »I7 HALF HOURS OF SCIENTIFIC AMUSEMENT. CHAPTER I.— PROPERTIES OF BODIES. strength elasticity — porositv — permeability — resistance of substances— hardness — centri- fugal force — the principle of inertiai Strength. .VERYONE who practises experimental science knows how useful it is to unite with his theories the manual dexterity which practice in experiments gives. Chemists and physicists, should in every way be stimulated to construct their own apparatus. In numerous cases it will be found possible to put together even delicate apparatus at a very small cost ; and these will be found quite' as useful as the most expensive ones. Is it not then even more useful to lay down the elements of a course of experimental physics without apparatus? This is just what we are about to do in a recreative guise. Our first experiment will be on falling bodies. THE HALFPENNY AND THE PIECE OF PAPER. Take a sou — a halfpenny^ — and a piece of paper cut into the same shape as the coin. Let these two bodies fall at the same moment side by side, aj shown in the 2 I'kOrERTIES OF BODIES. illustration (Fig. i). You will find that the coin will reach the ground a long while before the disc of paper. But now place the piece of paper upon the upper surface of the halfpenny and permit thenn to fall together in a horizontal position, as in illustration (Fig. 2). You will find that the two bodies will reach the ground at the same time ! Why .? Because the piece of paper is protected Irom the action of the air by the halfpenny ! The weight of the bodies counts for nothing in their fall. It is the air only which prevents them from falling :■*..."; '■ "■- -^ ^^^^^ w ,.;:; ;■;■ E.liiul:nlll I'ig. I.- Fall of a Halfpenny and a Piece of Fig Paper cut to same Shape. ?. — Fall of the ?ame Bodies. The Paper placed upon the Coin. with the same velocity. Under the receiver of an air- pump both bodies would fall with the same speed. T//E TWO PIECES OF PAPER. Take a sheet of paper, fold it in half, and cut it so that you obtain two pieces of exactly the same size and weight. Rub one into the shape of a ball, and leave the other in its former condition. Then let both fall together. The rolled-up paper will reach the ground before the other piece ! /.■ STRENGTH. 3 TO BREAK A NUT WITH A FALLING KNIFE. Attach, lightly, a penknife to the upper framework of a wooden door by inserting its point in the wood as shown in the illustration (Fig.' 3) herewith. The knife must be suspended so that it can be detached by a blow of the^fist on the frame of the door. If a nut be placed Fig. 3.— Experiment with Falling Bodies. beneath, at the ej^act spot on which the handle of the penknife will strike the floor, the nut will be cracked immediately. "Yes; but how are we to determine the exact spot .' " you will say. I will tell you. , 4 FROPERTIES OF BODIES. Moisten the end of the knife-handle with water in a glass in the manner shown in the illustration (Fig. 3). A drop of water will adhere to the handle and fall to the floor. On the spot thus indicated the nut must be placed.' The illustration indicates the manner in which this experiment should be made. On the left is seen the knife suspended above the nut. On the right is the glass by which the positions of the two bodies can be ascer-' tained. Elasticity. the unalterable pellet of bread. Knead between your fingers, a piece of the crumb of Fig. 4.— Pellet of Crumb of Bread modelled for the Demonstration of the Elasticity of Bodies. a fresh loaf in such a manner as to impart to it the spiny appearance of the figure in illustration (Fig. 4). Place this moulded pellet on a wooden table and strike the pellet on top with your hand. You will find that you caftnot alter its shape! No matter how violent your^ blows, the elastic material, for an instant flattened, will a:lways return to its formation again. Again, take the pellet and throw it violently on the ground. The shock will not permanently deform it any^ POROSITY. PERMEABILITY. 5 more than your blows did, and it will resume its shape again, because its elasticity has preserved it from injury ! The experiment will hot succeed unless the bread be perfectly fresh. A band of india-rubber gives a very striking illustration of the elasticity of bodies. If all bodies are not elastic to the same extent, they are, nevertheless, all capable of some degree of expansion. If force be applied, they can be more or less extended ; they will return again, when released, almost to their normal shape. Porosity. Permeability, a blotting-paper filter. Place a piece of blotting-paper on the mouth of a tumbler ; pour upon it some water darkened with charcoal or other such' substance. The water will filter into the tumbler in a perfectly clear condition ; the blotting-paper will retain all the solid impurities of the charcoal or coal. This experiment -is illustrate;d in Fig. 5. TO PASS STEAM THROUGH CARDBOARD, lake two tumblers or goblets of equal capacity.; placp one of them on the table, and pour into it a small quantity of hot, almost boiling, water. Then cover the tumbler with a piece of cardboard, and place over the cardboard the other tumbler, as in the illustration (Fig. 6). Care must be taken that the upper glass, is perfectly clean and free from moisture. Now wait a while, and you will perceive that the steam from the boiling water in the lower vessel will penetrate the cardboard, the porosity and permeability of which will thus be clearly demonstrated, and the vapour will in time fill the upper glass. Wood, cloth, or woollen substances PROPERTIES OF BODIES. may be experimented upon in succession, and will givej the same result. But there are other textures which are impermeable, and will not permit the transmission of the vapour; such, for instance, as vulcanized india-rubber, of which waterproofs are made. 1] 1 1 1 III ..1 1,1 , 'ik <^^B> ^ ■'' '|''!I, ^ ^ rsic " ^. j' 1 ' 1 ,1 1 Fig. 5.— The Blotting-paper Filler. , This experiment tends to explain w^y fog is, as it is well said, " so penetrating." It passe? through the tissue! of our cloth coats and our flannels, and thus comes; into contact with our bodies. A waterproof will protect us from its action. resistance of substances. 'j Resistance of Substances. AT WtilCH SIDE WILL THE MATCH CATCH FIRE? Take four " safety " matches from a box, and insert two of them in the spaces which are apparent when the Fig. 6. — Steam passing thipugh Cardboard. box is partly opened ; the third match should be placed between the two former, when the whole will appear' as in the annexed figure (Fig. 7). Care must be taken that the third match is firmly gripped between the other two, PROPERTIES OF BODIES. which will be bent outwards, but must not be broken, by the contact. The fourth match should then be struck, and the third (the horizontal) match lighted by it in the cetitre. The question for the spectators to solve now is : — Which of Fig. 7- The Match Problem. the two supporting side matches will be fired first.? That on the right or that on the left >. Will it be that side at which we have two ends tipped with phos-'^ phorus, or the side at which there is only one phosphoric ' end .? The reply must be— At neither of them. The' HARDNESS. side matches will not ignite at all, because immediately the centre of the horizontal, match is burned, the two side matches will spring back and throw off the third match, which will fall to the ground and be extinguished. Hardness, to pierce a halfpenny with a needle, Everyone knows that if of two bodies one is harder than the other the former will scratch the latter. A piece of glass will scratch marble ; a diamond will cut glass. The glass is harder than the marble, the diamond harder than the glass. A bit of steel — a knife, for instance — will scratch copper. It is not impossible to pierce a halfpenny with a needle, because it is harder than the coin. The problem may appear impossible of solution, for if we endeavour to drive a needle through a halfpenny as we would drive a nail through a board we shall fail every time, because we shall break the needle; which, though it possesses great durability, is also very brittle. But if by some method we can manage to maintain the needle in a rigid and upright< position above the halfpenny, we can drive it into the coin with a hammer ! In order to perform this experiment successfully we must have a cork which is of the same height, as the needle, and into which the latter must be driven. Thus the needle is maintained in a perfectly rigid condition, and may be struck violently in the direction of its axis without being broken. Now place the needle (buried in the cork) above a halfpenny, which may rest either upon , a " bolt-washer," or even on a wooden table, which will not be injured lO PROPERTIES OF BODIES. by the experiment. Then with a somewhat heavy (lock- smith's) hammer strike the cork decidedly. If the blow be delivered straight and strong the needle will pass right through the halfpenny. The experiment can be made equally well with any Fig. 8.— How to pierce a Halfpenny with a Needle. other piece of money. We must, however, add that the experiment may not succeed at the first attempt ; it may be necessary to repeat the trial many times ; but - it is capable of accomplishment, and we have beside. us some coins which have been pierced by needles in the manner above described. Centrifugal force. II It will be a very difficult matter to withdraw the needle from the coin after the experiment. The adhesion is very great. Centrifugal Force., to keep a penny revolving in a lamp-shade. Grasp a lamp-shade in the right hand, as shown in the illustration (Fig. 9), Now, with the left hand, tw'iri Fig. 9. — Twirling a Penny in a Lamp-shade. a coin on its edge into the shade, and at the same I moment cause the sha!de to rotate in the right hand in the opposite direction. The coin will roll round without falling. i If the movement of the shade be gradually slackened, the coin will by degrees rotate towards the lower part of tlje lamp-shade ; if the speed be augmented, the coin will 12 PROPERTIES OF BODIES. by degrees ascend the cone towards the upper circum- ference. The movement of the coin will continue just as long as the twirling motion of the shade is kept up. The money is maintained by the action of centrifugal force, and moves in an inclined position similar to that of a rider in the circus. With practice one can roll two pieces of money in the lamp-shade at the same time. The experiment we have described is very easy to perform ; only a slight movement of the hand is needed. Although some dexterity is required in launching the penny into the lamp-shade at first, still no particiilar skill on the part of the performer is required. We ourselves have done the trick with ease, and have taught many persons inexperienced in sleight of hand to perform it. If a lamp-shade be not available, we may use a basin, or pan, or a salad-bowl ; but the cardboard la np-shade is lightest and most handy, and should be diosen in preference to all other articles. A Japanese umbrella will also suit. EFFECTS OF CENTRIFUGAL FORCE. \ The effects of centrifugal force are manifested under a great variety of circumstances, and we may filequently observe them. | When a railway is run round a sharp curve, tie outer rail is always raised above the inner, so that tne train when passing round the curve may retain its position on the metals. f If you run rapidly round a small circular track you will find it necessary to incline your body towards the centre, so that your, course may thus become the more rapid. The effects of centrifugal force are otherwise frequently observable, as, for instance, when a carriage-wfieel is CENTRIFUGAL FORCE. 13 revolving rapidly the mud which adheres to the tire is flung away from the wheel by the action of centrifugal force. It is centrifugal force which sometimes causes mill- stones to split when revolving at a high speed. It is the same force which causes the tiny drops of water to Fig. 10. — The Cane-sling. fly out of the wicker basket in which -lettuce is being washed, dried, and shaken. TffE SLING. When one launches a stone from a sling, the stone 14 PEOPERTIES OF BODIES. escapes from the circle which it has been made to describe as soon as one string of the sling has been let go, and it flies off at a tangent with the same velocity that has been imparted to it at the moment it was released. TO THROW A POTATO TO A GREAT HEIGHT. When the writer was a schoolboy and used to walk in the country, he substituted an ordinary walking-stick for the sling, and for the stone a potato, and in the following manner he succeeded in his experiment. He fixed a potato at the end of his cane in a firm way, and then, whirling the stick as he would whirl a sling, he suddenly stopped the motion when the end of the stick pointed upwards. The potato .was thus hurled to an immense height in the air. The Principle of Inertia. In treatises on mechanics and physics, " inertia " is defined as a property of matter by which bodies tend to preserve a condition of repose, and by which a body,' in motion is prevented from modifying of itself the movement which has been imparted to it. ' A PIECE OF MONEY ROLLING ON AN UMBRELLA. ' We will first give an illustration of the feat performed by some jugglers — viz., the circling of a half-crown upon a Japanese umbrella, as shown in the engraving. The umbrella is turned rapidly round, and, to all appearance, the half-crown is running along the surface ; but it is really the umbrella that is moving beneath the piece of THE PRINCIPLE OF INERTIA. IS money. This is an example. of the principle of inertia.- The experiment is performed very cleverly by the Japanese jugglers. to cut A PEACH, WITH ITS STONE, RIGHT THROUGH. Take an almost ripe peach, of medium size, and insert in it a table-knife so that the blade may be in contact with ths edge of the stone. If the peach be too ripe Fig. II. — Half-crown rolling over an Umbrella. to remain suspended on the blade it can be fastened by a thread, but only on the condition that the knife-blade remains in contact with the edge of the stone. ^ The knife with the peach attached is then grasped in the left hand tightly and firmly, and with another table- knife a blow is struck by the right hand — a smart, violent i6 PROPERTIES OF BODIES. blow — on the knife, close to the fruit. If the knife has been properly inserted into the fruit, so that the shock is transmitted in the direction of the centre of gravity of the peach, the stone will be cut normally to its axis, as well as the tissue which encloses it, and moreover in a very neat manner indeed. Fig. 12. — How to cut through a Peach. In performing this experiment it will be well to suspend the peach over a table, and to use common knives, which are not likely to be damaged. Many games based upon " inertia " are practised. One of therh consists in placing in the midst of a certain THE PRINCIPLE OF INERTIA. 1 7 circumference a pipe, at the upper end of which some pieces of money are placed. The pipe, when thrown at with quoits or a stick, lets the coin fall to the ground ■within the circle ; but if the pieces must be struck beyond the circle, it is necessary to avoid hitting the pipe. (On this principle the " cocoa-nut throwing " is practised at fairs.) It is by virtue of the inertia of matter that the par- ticles of dust are beaten out of our clothes, every particle being in a condition of repose. When the shock of the sudden stroke puts in motion the stuff in which the particles are resting, they remain behind, and at once fall down released from the clothes. When a piece of cord is vigorously flourished and then suddenly checked in the moment of its greatest impulse, the extreme end, which has the greatest velocity, has a tendency to escape from the other sections, and in its attempt a noise is produced. This is the cracking of the whip. It is on the same principle that the drops of water will run from the lettuce-leaves when forcibly shaken in a wicker basket. In this there is also an illustf-ation of ceritrifugal force, as already mentioned. Facts of this nature may be multiplied exceedingly. A bullet shot from a rifle will go through a pane of glass and leave a round hole in it ; but if the ball be thrown by the hand, at a much less speed, the glass will be shivered into fragments. The flexible stem of a plant may be severed by a switch horizontally thro-vt^n at it with great force. The velocity in this case is very high, and the molecules directly struck attain also a speed so great that they separate themselves from the surrounding molecules before they have ,had time to communicate their velocity to the latter. PROPERTIES OF BODIES. TO PRPJECT ONE OR 2'WO "DRAUGHTSMEN" FROM A HEAP OF THEM. This experiment is a variation of one which we hav^ explained in another place. It is performed by means of draughts or backgammon " men," but instead of a piece of wbod, another disc is used as a projectile. Build up a column of ten or twelve pieces, as in Fig. I3-— The Draughtsmen. the illustration, and with the thumb and forefinger propel the single disc violently against the pile, causing the disc to strike the column (Fig. 13). The piece thus launched out will strike tangentially the pile in one of two ways either it will hit it at the point of contact of two discs,- in which case two will be projected from the column- or it will strike a single disc, as shown in the illustration' THE PRINCIPLE OF INERTIA. ig in which the black piece only will be projected from the pile, without disturbing the stability of the other pieces. THE CARD AND THE COIN. Place on the forefinger of your left hand, held upright, a card ; on the card place a halfcrown or other good- Fig. 14.— The Card and the Coin. sized coin, and offer to remove the card without disturbing the coin. To do this you must " fillip " the card forcibly with the middle finger of the right hand ; the pasteboard will be propelled across the room, and the coin will remain upon the finger. In performing this trick, care must be taken to flip the card in a plane perfectly horizontal to the coin — as shown in the illustration (Fig. 14). io TROPERTIES OF BODIES. EXPERIMENT OF INERTrA MADE WITH DOMINOES., Place two dominoes upright at their highest elevation: with their faces towards each other, and then another. piece horizontally across them, forming a door. Upon this third — the horizontal — domino place a fourth, the black B'ig. I5-— Experiment of Inertia. surfaces bemg in contact. Finally upon this fourth domino set two others in the same manner as the first pair, face to face, then a seventh piece over all • as in illustration (Fig. 15). ' - The experiment consists in detaching rapidly the lowest THE PRINCIPLE OF INERTIA. 21 horizontal domino from the building, without disturbing the remainder of the erection. To do this you must place another domino in front of the building lengthwise (A-B), at such a distance that it can be conveniently reached by the forefinger passing beneath the first storey. The epd E of this domino is then sharply pulled down Fig. i6.— The Plate and the Coins Experiment. backwards, by which movement the corner D describes a curve in the direction of the dotted line to C. ' If this movement be properly accomplished, the angle D will suddenly strike the lower horizontal domino and project it in the direction of the arrow F. This displace- 2 2 PROPERTIES OF BODIES. ment will be followed by the instantaneous descent of the upper horizontal domino upon the two lower perpen- dicular pieces, in place of the domino removed, and the structure will remain otherwise undisturbed. THE PLATE AND THE PILE OF COPPERS. Put a dozen coins in a plate and propose to deposit them at one movement in the same order upon the table. People who have never tried this experiment will essay it in vain. To accomplish it you must raise the plate about a foot above the table, suddenly depress it, as shown in the illustration, and draw it towards you. The coins, not finding any support, will fall to the table in the same position as they left the plate. It is by no means an easy task to let the pile of money fall as here described without separating them. With practice and skill you will surely accomplish the task, in performing which it is best to let the coins fall or slide off the plate upon a cloth, which i^ more elastic than a bare table. The cloth will lessen the shock of propulsion. THE MONEY ON THE ELBOW. This is another experiment which the writer has fre- quently performed. It is managed by holding the arm back upwards, the elbow being almost flat and the hand open, palm upwards, as in the illustration . (Fig. 17), On the arm, close to the joint, place the coin or coins. Perhaps one at first will be sufficient, in case of failure and possible loss. If the hand be suddenly brought down with a circular sweep, the pile of money— or the single coin — will be left for an instant in space, and be at once clasped in the palm coming down upon it. THE PRINCIPLE OF INERTIA. 23 It will be found easy and possible to catch a pile of a dozen pence or halfcrowns in this way, after a little pre- liminary practice, without letting one coin escape. Care must nevertheless be taken that no breakable articles are in front of you when you are practising this m \^\ Fig. 17. — Catching the Pile of Money. experiment, for, if you do not succeed in catching the coins, they will be struck by the hand with very con- siderable force, and may do damage to the surroundings ; they also may roll out of sight ! 24 PROPERTIES OF BODIES. TO CUT AN APPLE IN A HANDKERCHIEF WITHOUT INJURING THE LATTER. In this instance the apple is wrapped up in the hand- kerchief and suspended by a cord, as indicated in the Fig. i8.— The Apple in the Handkerchief. illustration (Fig. i8). Take a sabre or a strong knife the plan of which is indicated in the right-hand upper corner. The edge of the blade should be very sharp, the more polished and the sharper the blade the more THE PRINCl'PLE OF INERTIA. 2 5 likely is the experiment to succeed. The cut must be given without sawing, and perpendicularly to the point of suspension. If the blade be rather thick, the apple will jump up slightly and then the handkerchief will enter with the blade and be uncut. In 1887 there were some clowns at the circus in Paris who used to perform this trick very neatly indeed, and with great dexterity. THE ST0NE'BBE4ICEIi. By great acquired force, or inertia in repose, one is enabled to break stones with the fist: This feat is performed by men at fairs in the manner following : — The right hand is carefully wrapped in a bandage, and in the left is held a piece of flint of rounded form, which the operator places upon a larger stone or upon an anvil ; then with the right hand he strikes the flint some very powerful blows, always taking care to raise it a little from the anvil when he is about to strike. Thus the object struck acquires the force of the fist that has struck it, and, as it comes , in violent contact with the anvil it is quickly broken. Simple as the feat is it never fails to evoke great astonishment from the spec- tators (Fig. 19). II© UNCORK A BOTTLE WITHOUT A CORKSCREW. Take a bottle of wine or beer, or any other liquid, and having folded a dinner napkin into a pad, strike the bottom of the bottle violently against it,, as in the illus- Fig. 19. — Experiment of Acquired Force. THE PRINCIPLE OF INERTIA. 27 tration (Fig, 20), on the wall. By virtue of the principle of inertia the liquid in the bottle will force out the cork. If the contents be beer or gaseous water, it will come out with considerable force, and carry some of the liquid _ ncorking a Bottle. with it over the spectators. This fact will enchance the success of the experiment, with which we will end our chapter on the inertia of matter. CHAPTER 11.— EQUILIBRIUM OF BODIES. THE CENTRE OF GRAVITY. 5dEAS relative to the centre of gravity and to the equilibrium of bodies can be demonstrated by means of a number of every-day objects. When we find a box of soldiers in w^hich each warrior is gifted with a small piece of lead at his feet, we have an illustration of the centre of gravity. We know that the cylinders, roughly representing soldiers, will always resume their .upright position when one endeavours to overturn them. It has been stated that it is possible, with patience and lightness of hand, to make an egg stand on one end. To accomplish this the egg must be placed upon a perfectly plane surface — a marble chimney-piece, for instance. The egg must be shaken to mingle the yolk with the white, and then if one succeed in making the egg stand upright, one of the most elementary principles, of physjics is illus- trated thereby ; for the centre of gravity is at the point of contact at the end of the egg, and the plane surface on which it rests. We will give some illustrations of this. TO BALANCE A PENCIL ON ITS POINT. The arrangement of the pencil and the knife, the blade of which is buried in the wood, is held in equilibrium at the point of the finger, becai*se the centre of gravity of THE CENTRE OF GRAVJTY. 29 the. arrangement is situated in the vertical, beneath the point of contact (Fig. 21). THE MATCH PUZZLE. Slit a match at one end, and insert into the groove ''/'', "/""'t'J't Fig. 21. —A Pencil balanced on its Point another, so that the pair shall form a certain angle. Place them on a table, angle upwards, tent fashion ; and let a third match rest against them as in Fig. 22. Now all is ready for the experiment, Take a fourth match, and 30 EQUILIBRIUM OF BODIES. handing It to one of )-our audience, request him to lift the three others with it. If the Seeker, the interesting paper from which we borrow this pleasing problem, be correct, the solution of the puzzle will test the patience of many an architect or jrr, .-^-M.,^..- . .TTT — -■■,■:.- . r ^ ^1 / Iv:. ^^ ^ ■ \ * i 1^ i ' ^ ^ :■ j \ k i 1 i k ^^^ S r 1 ^rjr'i- ^ 1 'J&A $ w Fig. 22. — Problem of the Four TVfatclies. builder who is not previously acquainted with the experi- ment. The upper diagram in the illustration explains the mode of proceeding. The way the trick is performed is to allow the third match to fall lightly against the match you hold, and then lower the hand until this third THE CENTRE OF GRAVITY. 31 match enters within the angle formed by the first pair ; then lift your fourth match and you wpl find that the other matches will rest crosswise on your match, No. i and 2 on one side, and No. 3 on the other. Fig, 23.— The Tumbler and the Sticks. TO POISE A TUMBLER UPON THREE STICKS, EACH ONE OF WHICH HAS ONE END IN THE AIR. Ozanam, in his "Mathematical and Physical Recrea- tions in the 1 6th Century," laid down the following problem : " Place three sticks on a horizontal plane, so that each one shall have one end resting on the plane and the other end ^unsupported." 32 EQUILIBRIUM OF BODIES. To perform this experiment, and even to place a weight on the sticks thus poised, you must carefully proceed as follows : — Place in a sloping position one stick with one end resting on the table and the other elevated. Put another in a similar fashion above, and resting on the first. Then form a triangle by means of the third stick poised in the same way but passing under one and above the other of the two sticks already laid down. The three sticks will in this manner prove o\ mutual support to each other, and will not .give way even if a tumbler or other weight be placed upon them over the points of contact, as in Fig. 2 3. THE WATER-BOTTLE AND THE THREE KNIVES. In almost the same manner as above illustrated, we can place three Itnives upon three wine-glasses as represented in Fig. 24. The knives not only support each other blade to blade, but they will sustain as heavy an object as a filled water,-carafe upon the triangle at their inter- sections. TO SUSPEND A BUCKET OF WATER FROM A STICK RESTING ON A TABLE. Here is another very old-fashioned experiment oh the " centre of gravity," which consists in suspending by the handle a bucket filled with water passed over the stick A B, which is laid on the table. To succeed in this experiment, which appears almost impossible \o perform. THE CENTRE OF GRAVITY. 33 we must fix a switch C D oi convenient length between the point B of suspension and the bottom of the pail. The arrangement thus consolidated forms, virtually, one object — a whole, and the pail or bucket is easily main- ^. »•., Fig. 24.— The Glasses and the Knives Trick. tained in the position shown in the illustration, because the centre of gravity of the whole mass is beneath the point of suspension situated almost at the centre of the stick A B (Fig. 25). f , 34 EQUILIBRIUM OF BODIES. THE FORKS AND THE COIN. Place two forks with their prongs one set over the other, and slip a coin — a five-franc piece or a halfcrown" — between the middle prongs of the forks. Then place the coin flat on the rim of a wineglass or tumbler, 25— Pail of Water suspended from a Stick. pushing it outwards until the two circumferences shall be touching externally. In this position, as shown in the accompanying engraving, the forks will remain in eqiiilibKio,' and the water may be poured steadily from THE CENTRE OF GRAVITY. 35 the glass into another without disturbing the coin or the two forks. (See Fig. 26.) We have now indicated almost all the recreative experi- ments connected with the centre of gravity and the laws of equilibrium. We will, however, explain another problem requiring skill, which can be worked out with a box of dominoes. Fig. 26. — Experiment of Equilibrium on the Centre of Gravity, EXPERIMENT WITH DOMINOES. The illustration shows how the contents of a box of dominoes can be supported upon one of their number. We must begin by placing three of the pieces on the table so as to form a solid base,; the first domino being laid upon three supports. When the edifice is finikhed, 36 EQUILIBRIUM OF BODIES. as in the illustration, the two outside dominoes must' be withdrawn and very gently placed upon the top of the construction. The" erection will remain in equilibrio provided that the perpendicular drawn from the centre of gravity of the system passes through the base of Experiment of the Centre of Gravity witli Dominoes. ^ sustentation of the lowest domino (Fig. 27). This experiment should only be attempted upon a perfectly firm and level table. In our next section we shall deal with Density and the Movements of Gases. THE CENTRE OF GRAVITY. 37 ffOl'F TO SIT WITHOUT CHAIRS. I This amusing feat can be perforqied by a number of persons arranging themselves as ybu see them in the illustration, the last in the ring sitting on the knees of the first. While the circle is being formed it would be advisable for the first to be seated on a chair, which can *-."•->•» ^jLi ft- Hs- J-^' '*'*' - / I'lg. 28.— S.ttlng withoi t Clla rs be slipped away when the ring is completed. This plan^ was adopted by French soldiers in Algeria, when they found themselves in any place where the soil was marshy, and where it would have been unwise for them to sit down on the ground. CHAPTER III.-^DENSITY, HYDRO- STATICS, ETC. hydrostatics — the movements of gases — re- sistance of the air. Hydrostatics. HERE is no necessity to dwell upon the density of bodies here : it is well known that, con- sidered as possessing the same volume, bodies have different weights. We shall consider this subject at greater length in the subsequent part of the work, when dealing with the prope;rties of metals. The principles of hydrostatics, which we intend to consider now, can be easily explained. It is very easy to understand the principle of Archimedes^ Take any body of irregular form, — a. stone will do, — and having attached to it a thread, let it dip into a vessel filled to the brim with water. The water will overflow in volume equivalent to the bulk of the stone ; as can readily be proved by weighing the glass partly emptied of water and the stone against another similar glass full of water. ASCENT OF WINE IN AN INVERTED GLASS OF WATER. Dip two wineglasses into a basin of water, and before taking them out, place the brims together, so that they may remain full, but one over the other. Then move ilVUKUbTAllCb. 39 them slightly, so that a very small space may intervene between the rims. Take a third glass and drip from it some wine in such a manner as it may spread slowly over the surface of the inverted glass, as shown in the Fig. 29. — Experiment on the Density of Liquids. illustration (Fig, 29). When the wine has trickled down to the line of separation, you will perceive the ruddy dfops filtering into the glasses and ascending into the upper one, in consequence of the difference in the densities of wine and water., 40 DENSITY, HYDROSTATICS, ETC. THE GRAPE-SEED IN THE CLASS OF CHAMPAGNE. If we place a grape-seed, quite dry, at the bottom of a glass, and fill it with champagne, we shall see the bubbles attaching themselves to the seed, and it will rise to the Fig. 30.^The Grape-seed in the Glass of Champagne. ^ surface of the wine, where the bubbles burst/and disappear. Then the seed will fall to the bottom of the glass again. The seed in this instance has been raised to' the surface by the aid of the air-bubbles, which play the part 'of little balloons in bringing it to the top of the liquid (Fig. 30). HOW TO MAKE A SYPHON WITH A COMMON BOILED LOBSTER. Take a glass filled with water, and attach a lobster to it, plunge the tail as far as possible into the liquid, letting HYDROSTATICS. 41 the body and head hang over the side of the glass ; it is necessary also to cut the antennae, so that they shall not touch the vessel on which the glass of water stands. The moment that the lobster is hooked on to the edge of the glass, small globules of water will be seen to form at the Fig.' 31. — The Ldbster Syphon. end of the antennae, which eventually form themselves into a trickling stream, which lasts as long as the tail of the lobster remains immersed in the water. TO MAKE A NEEDLE FLOAT. Take an ordinary needle and put it upon a fork, and 42 DENSITY, HYDROSTATICS, ETC. slowly lower the fork into a tumbler of water ; the needle will then float just like a piece of straw. The reason of this is that a meniscus, or bed, convex on one side, and concave on the other, is formed upon the surface of the water ; and the surface of this meniscus being large in Fig. 32.— The Floa.ing Needle. comparison with that of the needle, the latter is supported by it, so that scarcely any part of the needle is touching the water ; of course, if the water penetrated the needle's eye, the weight of the fluid would cause the thing to sink immediately. Another method is to put a leaf of cigarette or tissue paper on the surface of a tumbler of water, lay THE MOVEMENTS OF GASES. 43 a needle very gently upon the paper, which will soon become soaked and sink to the bottom of the glass leaving the needle floating on the top of the water. Fig- 33'— Direction of Candle-flames under the influence of Air-( The MOVEMENTS of Gases. AERIAL CURRENTS. Hot air is much lighter than cold air, and the differ- ences in density of the air-strata play a very important part in the movements of the atmosphere. Air is warmed in the Equatorial, and cooled in the Polar, Regions. It is easy to understand the differences in density of 44 DENSITY, HYDROSTATICS, ETC. the aerial currents if we open the door of a ^ warm room which is entered from a cold hall. A candle held to the upper part of the open door will show the direction of the warm current, while the course of the cold air will be demonstrated by the flaring flame of a candle placed on the floor. The currents pass in opposite directions, out and in (Fig. 33). M^^^^ Fig. 34. — Extinguisbing a Candle placed behind a Bottle, , BLOWING OUT A CANDLE BEHIND A BOTTLE. Put a lighted candle on the table, and in front of it, about 10 inches removed, a bottle like the one in the engraving (Fig. 34). Then blow on the bottle at a THE MOX'KMENTS OF GASES. 45 distance of 8 or 9 inches, and the light will be extinguished just as though there was nothing between it and your breath. The breath divides into two currents on the smooth surface of the bottle, one going right, the other left, 'which join each other just at the flame of the candle. Fig. 35* — Rotation of Coin between Two Pins., TO REVOLVE A COIN BETWEEN TWO PINS.^ It is not necessary to have recourse to the action of warm air to produce aerial motion. We have in our- selves an apparatus which is capable of producing ■ gaseous currents, and which will assist us in Our Scientific Amusements — viz., our ittouths ! Place a halfcrown flat on the table, then, seize it between two pins held at the extremities of the same diameter. You may raise it thus with,out any trouble. Blow against the upper surface, and you will see the- coin revolving with considerable speeid between the pins. The illustration (Fig. 3 5) shows the 46 DENSITY, HYDROSTATICS, ETC. manner in which this feat can be accomplished. The coin can be made to revolve (by blowing on its upper surface) with such rapidity as to make it appear a metallic sphere. In this we have an illustration of the persistence of impres- sions on the retina, of which we shall speak hereafter. ; TO KEEP A PEA IN EQUILIBRIUM BY MEANS OF A CURRENT OF AIR. Choose as rounded a pea as you can find, . and soften it, if dry, in water. Then skilfully impale it on a pin, so as not to damage its exterior surface and shape. Then get a pipe, of very small bore, and place the pea Fig. 36.— Pea sustained in the Air by blowing through a Tube. on one of its extremities, where it is maintained by the pin which has been inserted in the tube. Throw your head back until the pipe is in a vertical position, and then blow gradually and slowly through it. The pea will rise up ; then blow more forcibly, and it will be, sustained by the current of air turning on itself when the breath strikes the pin (Fig. 36). THE MOVEMENTS OF GASES. 47 Here is another experiment of the same kind : — Take a metallic penholder which is closed at one of its ends. At a little distance from the closed extremity drill a tiny hole. Then blow up through the aperture, thus formed, regularly and steadily. A small bread pellet, perfectly round, can then be kept up, as shown in the illustration (Fig. 37). The pellet should be as spherical as possible, its size varying with the density of the material of which it is Fig.'37. — Bread Pellet sustained by a Current qf Air. composed and the size of the aperture in the tube. Many other experiments can be maae by any means which will ensure a constant, even, supply of air, or gas, or steam from the extremity of a pipe. By analogous means an egg-shell can be maintained at the upper extremity of a jet of water, on which it will revolve without falling off. [A wooden ball can also be kept up in revolution in the same manner.] 48 DENSITY, HYDROSTATICS, ETC. rb MA/CE A PLANK ADHERE TO A TABLE BY MEANS OF A NEWSPAPER. Take a thin plank; about a quarter of an inch thick, and eight inches wide, and twenty-eight in length. Place this plank on a table slightly out of the horizontal, and it Fig. 38, — Kxperiment in Equilibrium. will be evident that the least touch will bring it to the ground. On the plank thus balanced place a newspaper sheet ; and then if you strike the portion of the plank which extends beyond the table you will be surprised to find that the plank will resist the blow absolutely, as if it had been nailed to the table. If you strike hard you will perhaps hurt your hand or break the plank, but you will not raise the sheet of newspaper which holds it. The quick compression of the air which is exercised on a considerable surface is" sufficient to explain this phenomenon (Fig. 38),: resistance of the air. 49 Resistance of the Air. the australian boomerang. Everyone has heard of the Australian boomerang. It is a weapon formed in the shape of an arc of hard wood, which^ the Aborigines and , inhabitants of Australia throw with unerring skill at some object — an enemy or quarry. When the boomerang strikes the object aimed at, it ■'■ ~.\ V ^ \ Fig. 39. — The Boonieraii'j. \ returns to the hand which launched it. One may quickly learn to throw_this weiapon after a few trials. Fifteen years ago M. Marcy, of the Paris Institute, published an interesting paper on this subject in the A'e'ronaut, in which journal were discussed questions relative to the resistance of the air. The learned professor then prepared^uncpnsciously— -a little chapter for Scientific 50 DENSITY, HYDROSTATICS, ETC. Amusements, and we will reproduce the gist of his remarks. A piece of cardboard shaped into a crescent, the corners of which are rounded off, should be placed on the, tip of the finger, or, still better, supported between the nail and the finger tip, so that the cardboard be inclined at an angle of 43°, or so. Then, with a vigorous flip of the finger of the right hand at the extremity of the toy, it is impelled into the air with a rotatory motion. The cardboard crescent then appears as a wheel, and moves in an oblique ascending direction, stops, and without^ turning a somersault, returns in the same trajectory, if the experiment be successful, but more frequently it, will come back in front or beside the point of departure, and always retrograding. The illustration (Fig. 39) will ex- plain the method of procedure. We may add that it is preferable to place the crescent with its horns tozvards the experimentalist, not as in the illustration. Now why does the boomerang return thus in the same direction with reference to the plane of the horizon .' Here come in the notions which Foucault has alreaxily given us respecting the preservation of the plane of oscillation by the pendulum, and by the plane of gyration of the gyroscope. "The boomerang receives from the thrower a double movement — viz., rapid rotation and a general impulse. The rotation given to the implement obliges it to retain its plane : it whirls obliquely in the air until its impulse is exhausted. At a given moment the weapon turns without advancing in space, and then its weight causes it to fall. But as the projectile continues to turn, still maintaining its inclined plane, the resista,nce of the air causes it to fall back in a direction parallel to this plane — that is to say, towards its point of departure." RESISTANCE OF THE AIR. SI WHIRLING RINGS. If you bore a hole in a box made of playing cards, and fill this box from your mouth with tobacco smoke, and then tap at the bottom of the box you will cause the smoke to -rise in rings from the orifice with remarkable regularity (Fig. 40). Fig. 40. — Mode of making Smoke-rings. Every one has seen smokers making pretty white diadems which they watch turning in the air with great satisfaction. It is a matter of daily observation that a drop of soapy water escaped from the tip of the finger enlarges itself in the basin in the form of a perfect ring, which slowly grows larger as it reaches the bottom. 5 2 DENSITY, I-IYDROSTATICS, ETC. These observations are applicable to the phenomena of whirling rings ; they are not futile, and can be made interesting. There is nothing corhmonplace for him who can use his eyes,, nothing different to him who is able to observe. We can also project the rings or diadems of smoke by Fig. 41. — Crowns of Tobacco Smoke (after picture by Branwer in the LouVre). projecting puffs from a cigarette through a tube. But some precautions are necessary to assure the success of the experiment. Any draught must be avoided, and to prevent the action even of the air currents, which ascend in the proximity of the body, we should operate at a table as shown in Fig. 44. The rings which float beyond RESISTANCE OF THE AIR. 53 the table will not be sensibly influenced by the warm '^'S; 42. Fig. 43. Aspects of Smoke-rings (42, genlly emitted ; 43, tmitted with some force). Fig. 44. — With a little Smoke some Distance from the Tube. air-currents. A tube formed from a sheet of ordinary S 54 DENSITY, HYDROSTATICS, ETC, note-paper will suffice to produce some elegant rings (Fig. 44). Fig. 45 Dissipation of SmoKe-rings (genera! aspect). The better to watch these rings they should be Fig. 46.— Dissipation of Smoke-rings (magnified ring). propelled to the darker side of the room, towards a dark RESISTANCE OF THE AIR. 55 picture, for instance. The first puffs will not produce a ring if the tube has not been previously filled with smoke. The rotatory movement will be plainly visible at the end of the tube, and even beyond it. The next illustration (Fig. 45) gives a clear idea of the more or less rapid movements of the smoke-rings. The last illustration of all (Fig. 46) shows the way in which th6 rings are dissi- pated in a calm atmosphere. The filaments of smoke fall, preceded by a kind of skull-cap. These capricious forms of smoke in a calm atmosphere are always more readily observed when the sun is shining into the'room. CHAPTER IV.— PRESSURE OF THE AH^. pressure of the air — experiments with com- pressed air — aeronautics. Pressure of the Air. the magdeburg hemispheres. Jake two tumblers of the same size. Be careful that they fit closely when one is placed on top of the other. Light a piece of wax candle, and place it within the tumbler on the I''ic, 47. — The Adhesive Tumblers. table. Place on top of it a piece of rather thick paper ^ PRESSURE OF THE ATR. 5 7 saturated with water. Then place upon it the other tumbler, as in the illustration (Fig. 47). The tumblers will then be found to adhere closely. The candle will be extinguished ; but while burning it has dilated the air contained in the lower tumbler, and this air has, therefore, ^^ Fig. 48, — The " Sucker.'" become rarefied. The exterior pressure of the atmosphere will fix the tumblers as closely together as the classical Magdeburg hemispheres are united. It is possible to" raise the undermost tumbler by holding up the upper one. The paper may be scorched on the under side, but the success of the experiment is not thereby imperilled. 58 !=RESSURE OF THE AIR THE •■' sucker:' This is a plaything familiai: to all schoolboys, and has, no doubt, served as the text for many a dissertation on the pressure of the air. Readers are aware that the " sucker " is formed of a piece of leather, in the centre jH)^ Fig. 49. — The Schoolboy Inventor of the Air-pump. \ of which a cord is fixed. This piece of leather pressed upon the pavement forms a kind of " cupping-glass '' arrangement, and considerable force must be exercised to draw it away from the pavement. Large stones may be lifted by these means. The piece of leather should EXPERIMENTS WITH COMPRESSED AIR. $g be first wetted, and the cord attached to it, so that no air may penetrate through the aperture in which the string is inserted. A circular piece of leather seems to act best. Tff£ PENHOLDER AND A VACUUM. The schoolboy who first exhausted the air from a tube penholder and made it cling to his lip, by reason of the exterior pressure of the air, was perhaps the first to discover the air-pump. Tq perform this little experi- ment, you must have a penholdei" with one closed end. Put the open end in the mouth, exhaust the air by aspiring it, and then permit the end in the mouth to slide on to the lip, which seals it hermetically. Experiments with Compressed Air. to extinguish a gamble by means of a bottle. Take an ordinary bottle, the neck of whicl^ is about three-quarters of an inch wide. Hold the bottle in the right hand, and cover the neck with the ball of the thumb of the left hand, leaving only a small aperture (see A, FiS- So)- Care must be taken to leave only a small aperture. Then applj' your mouth to the opening, so as to cover it completely, and breathe into the bottle gradually but forcibly, so as to compress the air in it. Under these circumstances it is evident that, in con- sequence of the communication which exists between the interior of the bottle and the lungs, an equilibrium of 6o Plif.SSURE OF THE AIR. pressure will be established. Three or four seconds will suffice for the action. At that moment, by a rapid movement, close the bottle completely, by applying the ball of the thumb to the orifice, displacing, the lips. Then place the bottle in an inclined position, as in Fig. 50.- -Posilion of the Hartd', before the Compression of the Air by the ^foiith. Fig. 5 I , mouth downwards, and bring it within about an inch and a half of a lighted candle. Loose the thu'mb, and permit the compressed air to escape from the bottle through an aperture as nearly the same size as possible to the opening through which the bottle was filled. The EXrERlMENTS- WITH COMPRESSED AIR. 6l flame of the candle will be blown aside and perhaps extinguished. THE PAPER BAG FILLED WITH AIR. After the experiments with a vacuum, we may next Fi^ 5t.--MocIe of holdin^; the Bottle in order to extinguish, or hlow aside, the Flame. speak of those which refer to the compression of gases. Let us recall the experiment of the bag, full of air, which is broken by a blow of the hand. The com.pressed air bursts the bag, and produces an explosion. 62 PRESSURE OF THE AIR Aeronautics. a montgolfier balloon. Make a hollow cylinder, about the size of an ordinary cork, with a sheet of silver-paper or cigarette-paper. The edges of the cylinder must be somewhat bent over, so as to make it retain its form. With a lighted match set f re 'ig. 52.— Cuniprts.sed A to the cylinder at its upper part. The paper will burn, and be converted into a thin layer of ashes. This residue enclosing rarefied air suddenly rises, and mounts rapidly for several feet like a Montgolfier balloon (Fig. 1:3). AERONAUTICS. 63 AIR AND GAS BALLOONS. Take a glass tube, about three-quarters of an inch in diameter, and about eight inches long, or, in default of it, a roll of ordinary notepaper, which will enable you to .^^* \ J ' -ft i Fig.'53.— Demonstration of the Principle of the Ascent of Bfilloons by means of Heated Air. blow bubbles as big as a man's head'. Dip the end of the tube in a solution of soap, and blow rapidly and strongly through the tube. The bubble, filled with the warm air from your lungs, will soon ascend. Without 64 PRESSURE OF THE AIR. letting it go, follow it in its ascending movement, turning the end of the tube gradually upwards until you can touch off the drop suspended at the bottom of the bubble. Your balloon, fully inflated, will only want to be released, if it has not already freed itself. If the temperature is low, the bubble will break against the ceiling ; in the contrary case, it will descend slowly, as soon as it becomes somewhat chilled. l'''S- 54-— Soap-bubble lifting a Paper Aeronaut. Let a small, thin paper-figure be cut out, and fastened by a thread to a disc of paper ; it can be made to adhere- to the bubble, as shown in Fig. 54. If the bubble then be released, it will carry the figure up with it (Fig. 55). If smaller tubes be used, bubbles of smaller size will be produced. The paper tubes must be replaced by others when wet and soddened, but glass tubes are preferable. AERONAUTICS. 65 By inflating soap-bubbles with hydrogen gas we can ^"io- 55-— Soap-bubble iuJiated with warm Air. Mode of fixing an Aeronaut. represent the ascents of gas balloons, which differ from warm air balloons. CHAPTER v.— HEAT. THE CONDUCTIBILITY OF METALS DILATATION OF' BODIES BY HEAT. >HE art of producing fire or of procuring heat artificially is one of the most profitable of human industries, since it has given us the means of moving machinery in manufactures;, locomotives, and steamboats. The impression which produces the sensation of heat in our organism is a subjective phenomenon, and the impression which we convey when we say that a body is hot or cold is relative. ,When we enter a cellar in the summer when, the exterior air is warm, we find the cellar cold ; if we enter during the wintry weather, we find the temperature rather warm. Nevertheless it remains about the same heat all the while. Suppose that we hold the right hand in a vessel con- taining hot water, and the left hand in a vessel containing cold water ; if we then withdraw our hands at the same moment and plunge them together into a third vessel full of tepid water, we shall then experience two different sensations, heat and cold, proceeding from water of a certain temperature. The study of heat and caloric can be immediately undertaken without any apparatus, as we have seen when dealing with other branches of physics. THE CONDUCtlBILlTY OF METALS. 67 The Conductibility of Metals. a burning coal on a muslin hand kerchief. Take a globe of copper, about as large as the globular ornaments which one sees at the bottom of a staircase, and wrap it in muslin or, in a cambric handkerchief. Fig. 56. — A Burning Coal placed on a Handkerchief wrapped round a Copper Globe. Tne Handkerchief is not scorched. Place on this metallic bowl, thus enveloped, a red'hot coal, and it will continue to glqw, without in any way damaging the muslin wrapper. The reason is this : the metal being an excellent conductor absorbs all the heat 68 HEAT. developed by the combustion of the coal, and as the handkerchief has not absorbed any of the heat, it remains at a, lower temperatmre to that at which it would be injured (Fig. 56). ^ f'"'o- 57.— Gas Jet (Metal) wrapped in a Cambric Handkerchief, tightly stretcheijl. The Flame will burn above the Handkerchief without injuring it. TO MAKE GAS BURN UNDER A HANDKERCHIEF. Take a batiste handkerchief, and wrap it round a copper gas jet. The jet must be of metal. This is in- dispensable. Turn on and light the gas, which will burn above the handkerchief without injuring it (Fig. 57). To^ THE CONDUCTIBILITY OF METALS. 69 succeed in this experiment it is necessary that the hand- kerchief should fit I quite closely to the metal without any crease whatever. It will be found advantageous to tie the batiste with a thin copper wire. There THE METAL IN THE PENHOLDER. „ „.,„fi,=, ,,=.-,, easy way of evidencing the F.g. 58. —Carbonization of Paper on llie WooJen Portion of a Penholder, conductibility of metals for heat. Take a wooden pen- holder with a metallic end, and fix a piece of paper partly on the wood and partly on the metal. Heat the paper above the flame of a lamp. The paper will carbonize at the side on which it adheres to. the wood - — a bad conductor of heat — but it will remain un- changed, and preserve its whiteness on the side which is in contact with the metal. g 70 HEAT. Metals strike cold when wc place them in our palms ; by their conductibility they draw the heat from our hands. We do not- experience the same effect when we touch wood or cloth. A silver spoon will be burning hot after being dipped in a cup of boiling coffee, but an ivory or wooden spoon will not be so heated. tig. 59.— 'ihe CapLivti Imp, Dilatation of Bodies by Heat. tbe captive imp. This consists of a tube of thin glass, like a shade, as in illustration, the lower extremity being rendered opaque by a coat of black varnish. The iQwer portion being held in the hand, the liquid with which the receptacle is filled DILATATION OF BODIES BY ^EAT. 71 will immediately tise and sustain the small image of blown glass which is contained in the tube. AH gases expand under the' influence of heat. No>v » e perceive in the section of the apparatus (Fig. 59) that the upper tube terminates in a caplillary tube which is ii ig. 00. — K-xpcrim jnt in Linear Dilatation. immersedln the bulb underneath. A certain quantity of air is enclosed in the portion A A in the bulb. If this supply of air be warmed by the hand it expands, presses upon the water in the tube, and it rises with the floating imp. 73 HEAT. LINEAR DILATATION. Cut a cork in the manner shown in the illustration (Fig. 60), so as to form a plane surface, and " scolloped " out in a semi-cylindrical form. In one of these hollowed spaces at A place a needle A B, the head of which is supported at B, and at a slightly less elevation at that end. Through the eye of this needle pass another, and insert its point lightly in the cork. Parallel to it, and behind it, place another needle of the same length. If we hold a lighted candle beneath the horizontal needle, we shall see the needle B C incline sideways, as in the illustration. CHAPTER VI.— LIGHT, OPTICAL ILLUSIONS, ETC. refraction — vision and optical illusions — persistence of impressions on the retina. Refraction. 'O illustrate refraction we have only to plunge a stick into water and it will appear broken. We can also place a piece of money at the , bottom of a basin and stoop until the coin is no longer visible. If then some one pours water into the basin the coin will appear, as if the bottom of the, basin had been raised. THE MIRAGE. Amongst the optical experiments easy to make we may instance those relating to the curious phenomenon of the mirage. If we warm an iron plate, and look beyond the column of heated air which arises from the plate, we shall see the object we are gazing at deformed, or its image will appear in a different place from the true object. These effects are due to the difference in the density of the air-strata through which the visual rays pass. This is the effect whereby the traveller in the desert is deceived when the sun is very hot. HOW TO MAKE A FLORIN APPEAR LIKE FIVE SHILLINGS AND SIXPENCE. This experiment requires for its performance a tum- 74 LIGHT, bier, a plate, a little water, a florin, and a match. With these appliances we can solve the astonishing problem of how to make a two-shilling-piece appear like iive shillings and sixpence. Take the florin and place it in the centre of a plate containing water just sufficient to cover the money. Then Fig. 6i. —Experiment of Refraction and Divergent Lens obtained wiih a Tumbler take an ordinary tumbler, and holding it upside-down, warm the interior with a lighted match. When the air within the tumbler has been well warmed — which will be when the tumbler looks steamy — place it over the florin in the plate. ^ VISION AND OPTICAL ILLUSIONS. 75 The water in the plate will ascend then into the tumbler in consequence of the contraction of the cooling air in the "glass, and because of the exterior atrnospheric pressure. Look at the surface of the water, and you will see that the florin is doubled in size by refraction. You will distinguish the florin, and a little below it will appear the image of a coin as large as a five-shilliiig-piece. Again look at the tumbler from the top. The bottom of it forms a lens, which gives you the reduced image of the florin so that it resembles a sixpence in size. Thus the problem is solved, and we have five shillings and sixpence for our florin (Fig. 6i); Vision AND Optical Illusions. The eye is an optical instrument of the greatest delicacy, and the phenomena of vision maybe regarded as amongst the most complicated and the most worthy of the attention of physicists. We cannot here enter upon the great theoretical developments of the subject, biit will confine ourselvfes specially to the consideration of some curious illusions which will be ; fotind , adapted to sfmple experiments. Let us, in the first place, notice that nature on all sides offers to us opportunities to observe these phenomena. In the morning we see the sun rise in the east, we notice . it on its course across the sky during the day, and watch it setting in the west in the evening. This movement is an optical illusion ; the sun is immovable as regards the earth : it is our globe which turns around the orb in the twenty-four hours. A somewhat similar phenomenon may be observed in a train in motion. The telegraph poles appear to fly past with great rapidity, and give the traveller an impres- sion of immobility, which is a sensation contrary to fact. 76 LIGHT. These optical illusions are numerous, and present to usmany opportunities for amusement; as follows: — • THE WHITE AAD BLACK SQUARES. The illustration herewith presents to us (Fig. 62) a white square on a black ground, and a black square on a w'.iite ground. Although the squares are precisely of the same dimensions, the white one appears to be the larger. Fig 62. — The White appears larger Ihan the Bhick. Fig. 63. — The Angles of the White Squares seem to Unite. For designs formed of white and black squares, like those of the draught-board (Fig. 63), the angles of the white squares unite by irradiation, and separate the black squares. If we look at a draught-board in its entirety the effect will be more fully appreciated. THE DIVIDED f.TNES. We will now show an experiment of another kind which gives rise to some comment. A divided space appears larger than when it is not I I M 1 I I I I I 10 Fig. 64.— a i appears equal to i c. divided. So thus in the cut (Fig. 64) one would say that the length a b is equal to b c, while in reality a b is longer than be. VISION AND OPTICAL ILLUSIONS. 17 The reader may satisfy himself of the exactitude of the measurement ; when the lines are drawn on a larger scale the illusion is more striking. We recommend our readers to try the effect for themselves. LINES AND ANGLES. The illusions relative to parallel lines are appreciable when the distances to be compared take different direc- tions. If we look at A and B (Fig. 65), which are both Fig. -A and B are perfect Squares. perfect squares, A appears higher than it is wide, and B appears wider than it is high. It is the same with angles. Look at Fig. 66. The angles i, 2, 3, 4, are right angles, and ought to appear so when examined with both eyes. But i and 2 seem to Fig. 66;— ^The Angles 1—4 are equal. be acute, and 3 and 4 obtuse angles. The illusion will be intensified if the diagram be looked at with the right eye. Certain analogous illusions are daily presented to us.^ 78 LIGHT, For instance, an empty room appears smaller than when furnished, a papered wall appears larger than a naked wall, a dress striped crossways makes the wearer appear bigger than when the dress is striped downwards — lengthway. Fig 67.— The Height o( the Hat. THE HAT EXPERIMENT. A simple amusement consists in requesting some one to measure the height of your hat on the wall from the floor. Generally the person addressed will indicate one and a half times the actual height if unacquainted with the trick. In drawing the illustration (Fig. 67) for this VISION AND OPTICAL ILLUSIONS. 79 experiment we were astonished to find that the design reproduced the same illusion. The plinth in the illustra- tion is exactly the same height as the hat, but one would scarcely think so when looking at the two objects. The measurement can be verified with a compass.' THE THREE GREAT MEN. Which is the tallest of the three figures in the annexed illustration ? (Fig. 68.) If you trust only to your eyes you will certainly .reply, " Number 3." Well, then, take a graduated scale and measure the figures, and you will ascertain that your vision has been playing you a trick, and that Number i is the tallest of all. M. Viallard, Professor of Physics at Dieppe, who brought this curious effect to our notice, gave us at the same time the explanation of it, which is as follows : — Placed in the midst of carefully calculated vanishing lines the three silhouettes are not in perspective. Our eyes:, accustomed to perceive objects diminish in propor- tion to their distance from us, and believing that Number 3 is elevated, come therefore to the conclusion that the third figure must be the tallest of the three. It is an optical delusion. There is in this illustration, then, a fault in drawing, purposely committed, which deceives the spectator, and produce^ in his vision an inverse effect from that which would be obtained with a correctly-dr^wn sketch. The origin of the design is not less curious than the drawing itself. It did not emanate from the portfolio of a scientist, but from the warehouse of a firm of Soap- makers who printed their name in perspective between the vanishing lines, and published the drawing in a number of newspapers in Great Britain and America. So LIGHT, OPTICAL ILLUSIONS, ETC. Fig. 68.— Optical Illusion— Which is the tallest of the Three ? {By pcnnisstoji ofRIcssrs. A. ajid F, Pears.) VISION AND OPTICAL ILLUSIONS. 8l The Soap-merchants completed this telling advertise- ment by giving the three figures the " counterfeit pre- sentiments " of Lord Randolph Churchill (i), Lord Salisbury (2), and Mr.- Gladstone (3). We have repro- duced the illustration by permission of the proprietors of the picture. THE MAGIC RINGS. Fig. 6p. — The Magic Rings. The rings, virhich we reproduce from a photo- graph, give birth to a curious illusion, which may be included in the class of phenomena which we have been studying. These rings are made of metallic coils, each alternate "strand " being of a golden and silvern hue, and brilliantly polished. The rings are of equal diameters, the coils of equal thickness, and absolutely parallel. Now when we look 82 LIGHT. at one of the rings sideways, the coils seem to come closer near the bottom, and the ring appears thinner there than at the top, and when the ring is turned round the finger the illusion is produced at the same point. The ring at the left of the illustration gives some notion of the illusion, but the effect is much greater in the real ring. In the three-coiled ring shown in the centre of the illustration the middle coil appears to lean aside, but the design does not reproduce the illusion as it is in actual practice. The right-hand ring merely shows the arrange- ment of the coils. It is not very easy to give an explanation to these facts. The phenomenon is in great measure due to the re- flection of the light on the rounded threads of the metallic coils. The light is reflected on the exterior border of the upper part, and in the middle of the coil in the lower part of the ring. The left-hand ring shows this plainly. Other objects probably would facilitate the study of this illusion. Skeins of silk of various colours rolled round a hoop or ring would afford the same effect. It would be necessary to be careful in the blending of the colours so as to produce the proper result. By adoptingt this suggestion many amusing experiments may be at- tempted. But in any case, the ring represented can be obtained at most jewellers' shops at a small cost, and the experiment may be tried. Persistence of Impressions on the Retina. the imp on the ceiling. This experiment, which can be performed with the aid of the next illustration, is one appertaining to the principle of persistence of impressions on the retina, to which must be added that of complementary colours. ' PERSISTENCE OF IMPRESSIONS ON THE RETINA, 83 Look Steadily wjth both eyes at the white figure in the illustration, on a black ground, particularly keeping yoUr gaze ^xed on the band in the centre ; then, just when your eyes are beginning to feel tired- — say in half a minute — look up to the ceiling, and in a few seconds you will perceive the outline of the imp, in grey, on the ceiling, repeatedly. This experiment will gain by being made in a strong Fig. 70. —Figure for Experiment of Persistence of Impressions on the Retina. light. I If the imp be red m the silhmette the impression will come out in green, which is the complementary colour of red. It is rather comical when a nuniber of people try the experiment simultaneously, all with heads in the air waiting for the irtip to appear. A card, such as the ace of hearts, may replace the design, and instead of the ceiling, a sheet of white paper may be looked at 84 LIGHT. after the figure has been studied. This experiment can be varied to any extent — a white, black, or green image will be reproduced in the complementary blue, white, or red. If painted green on a red ground the result will appear as red on green. The annexed illustration coloured will suffice for any experiments. Fig. 7i.— The Mule Rigolo. THE MULE RIGOLO. We have seen on the boulevards a very simple zoo- troptic apparatus represented in the cut above (Fig. 71). It is composed of four panels of cardboard, mounted at a right angle around a hollow axis. This cardboard' PERSISTENCE OF IMPRESSIONS ON THE RETINA. 85 arrangement can be put on a vertical stem, fixed on a pedestal, on which it turns >vith ease. Each panel con- tains a zpotroptic design, and the impression of each figure on the retina gives the spectator the idea of a single figure with different action ; at the different periods of a movement comprised between its extreme limits. Fig. 72. — The Silhouette Portraits. THE SILHOUETTE PORTRAITS. Take a large sheet of paper, black on one side and white on the other. Fix it by means of pins to the wall so that the white surface is outermost. On a table close by place a good lamp, and let the person whose portrait 7 86 LIGHT. you wish to take stand between the lamp and the sheet of white paper. You can then outline the proiile with a pencil. Cut out the design, and, turning the paper, gum the drawing black side outwards on another sheet of (white) paper. Your portrait will then be mounted, and the sillwttette will show very well in black. TO VARY THE SIZE OF A HALFPENNl, Take a rectangular box of white wood, and in one side Fig 73.- Mode of EquaHzing llie size ot larger and smaller Coins. of it fix a nail or bodkin, to which attach, with wax or other substance, a halfpenny. Beside this halfpenny, but on the surface of the box; fasten a farthing.; If you gaze at these two pieces of money through- a small , circular hole in a piece of cardboard (as in Fig. 73), you will not be able to distinguish one coin from the other. They will both appear the same size. l'JlK&lSi^lSJ^^CE OF IMPRESSIONS OF THE RETINA. 87 Of course the distance at which the coin^ must be placed will depend upon the powers of vision of the spectator. It is as well to fix the cardboard screen, and then move the box farther or nearer, as may be desirable. A time will come when the two coins will appear of equal size ; but by gradually lessening , the distance the "farthing will actually appear larger than the halfpenny. This experiment demonstrates that the eye under the conditions indicated is unable to appreciate the distance between two objects. By a similar phenomenon the moon, when viewed thi^ough an astronomical telescope, appears smaller than it looks to the unaided eye, while as a matter of fact it is magnified by the telescope. CHAPTER VII.— ELECTRICITY AND MAGNETISM. E will now reproduce a few experiments in electricity, and commence with THE ELECTRIFIED PIPE. Fig. 74. — Pipe attracted by an EiectriHed Glass. Place a clay pipe in equilibrium on the edge of a ELECTRICITY AND MAGNETISM. 89 glass in such a manner that it may oscillate freely. The problem now is to make the pipe fall without touching it, blowing upon it, or agitating the air, and without moving the table. Take another glass, similar to that which supports the pipe, and rub it rapidly on the sleeve of your coat. The glass will % -^^^ectrified by the friction, and when you have rubbed, it»Avell bring it close to the pipe with- out touching it. You will then see it turn after the glass and follow it till it falls from its support. • THE PAPER PUPPETS. We will now explain the means of obtaining some electrical manifestations of great simplicity in performance, such as the " dance of the paper puppets." Procure a square of glass and two volumes sufficiently, large to support the plate of glass in the manner shown in the picture (Fig. 75), about an inch from the table. Then cut out of rice-paper or silver paper any figures you choose — frogs, men, women, children, or any animals. These little figures should not exceed three-quarters of an inch In height We give some specimens of larger size in the upper part of the illustration. They can be . cut out of different coloured papers, which will improve the experiment. 1 Place these little people in their ball-room — that is to say, beneath the glass which you have supported above the table, lying side by side on it. Then rub the plate of glass vigorously with a silk rubber (silk is best), and after a while you will see the paper figures jump up to the celling of their "ball-room,"' attracted by the electricity which you have developed in the glass by rubbing. They fall again and are again atttacted, impelled to an extravagant dance. Even when the rubbing ceases the 90 ELECTRICITY AND MAGNETISM. dancing will continue for a certain time, and the contact of your hand with the glass will be sufficient to animate the little dancers. To ensure the success of this experiment the glass must be perfectly dry, as well as the handkerchief or Fig. 75. — The Dance of Dolli. rubber with which you operate ; and if the table be warmed the manifestation will be ' more successful. Silk is better than cloth for rubbing purposes. THE MAGICIAN. The little toy depicted in the Illustration is based on ELECTRICITY AND MAGNETISM. 91 the property of repulsion possessed by the opposite poles of magnets. It consists of a magician, or " diviner," fixed on a pivot upon which he turns easily. A series of questions are written on the pieces of cardboard, which are introduced into the pedestal on which the magician stands. These cards contain magnets properly placeci, Fig. 76.— The Magnetized IMagician. and when a card is put into the pediment of the figure the magician turns the magnet in the form of a horse- shoe (U) hidden in his dress, obeys the influence of the other magnet in the card, and with his magic wand he indicates a number in the circle which surrounds him. The number corresponds to those on a list of answers supplied with the apparatus. , CHAPTER VIII.— CHEMISTRY WITHOUT A LABORATORY. ^E have in foregoing pages shown the possibility of practising a course of physics without ap- paratus ; we now propose to perform some experiments in chemistry without the aid of a laboratory, and only with the assistance of a number of simple and inexpensive articles. The preparation of gases, such as oxygen, hydrogen, and carbonic acid gas, is very easy and very inexpensive. We have merely to procure some glass tubes, a few phials, and a number of sound corks, which we can pierce with a round file called a rats tail. For " furnace " we can easily make a spirit lamp from an ordinary penny glass ink-bottle, which we fill with spirits of wine, and fit with a metal top, in which we punch a hole to permit the wick to ascend through a metallic pen-holden Our heating-apparatus is then complete. OXYGEN AND HYDROGEN The ancients believed that earth, air, fire, and water were the four elements ; but they were mistaken, for each of these so-called elements is composed of other bodies. Thus — water is composed of two gases, oxygen and hydrogen, which we may now proceed to prepare. To make oxygen it is only necessary to warm in a glass tube a mixture of chlorate of potash and the bi-oxide of manganese. Oxygen is contained in water, but it is also CHEMISTRY WITHOUT A LAEORATORV. 93 contained in air; it supports the respiration of animals and the combustion of burning substances. After we have warmed our glass tube for a while we may perceive the escape of the oxygen from it by putting the incan- descent point of an extinguished match in the tube : the niatch will at once be re-lighted, and burn under the influence of the oxygen. Fis- 77- — Preparation of Oxygen, To prepare hydrogen gas — another of the constitutional elements of water^we must decompose the water by a metal, such as zinc or iron, under the action of sulphuric acid. \Procure a glass vessel with three tubes, which can be closed with corks. One of these is furnished with a funnel, into which we may pour sulphuric acid and water ; another tube is furnished with a removable tube with a fine point, through which the hydrogen gas 94 CHEMISTRY WITHOUT A LABORATORY. escapes. The glass vessel is half filled with zinc filings. When the sulphuric acid and water come in contact with the zinc filings an effervescence due to the disengagement of the gas is produced. ' Care must be taken that the air in the glass receptacle for' the hydrogen gas is expelled, else there will be an explosion, for air and hydrogen gas form an explosive Fig. 78. — Iron Filings burning in a Jet of Air. mixture. When the air has been withdrawn the hydrogen.' gas can be lighted at the extremity of the tube. Hydrogen is a combustible gas ; oxygen is a supporter of combustion. The latter is the active constituent of the air, and by its aid iron filings can be burned in the flame of a candle driven by the action of a blow-pipej formed by a common clay pipe, as in the foregoing illustration (Fig 78). CHEMISTRY WITHOUT A LABORATORY. 95 AIR AND ITS ELEMENTS— CARBOMC ACID. Air contains oxygen and azote (nitrogen), a heavy gas which extinguishes bodies in combustion ; the air also contains a small quantity of carbonic acid, which we Fig. /, -ting on the Surface of a Layer of Carbonic Acid Gas, can ascertain by a very pleasing experiment, at the same time proving the density of gas and the equilibrium of floating bodies. Take a large glass — a soda-water glass or some wider tumbler—and support it on a tripod or in some other secure way. At the bottom of the glass vessel put a g6 CHEMISTRY WITHOUT A LABORATORY. thin layer of bi-carbonate pf soda and tartaric acid, mixed in equal quantities. The quantity of the powder em- ployed will depend upon the thickness of the carbonic acid atmosphere which you wish to produce. One must proceed on the basis that the bi-carbonate of soda con- tains half its weight of carbonic acid, and consequently we must dissolve four grammes of the bi-carbonate to produce a litre of carbonic acid gas. Over the glass vessel place a cardboard covering so as to fit it closely. The centre of this covering should be perforated so as to admit a small glass tube long enough to reach to the bottom of the vase and rise above the cardboard. By this tube and a small funnel we can pour in the small quantities of water, which must be successively introduced in order that the effervescence may not become too violent, and so that the powder may be quite covered with water. When the carbonic has ceased to disengage itself the glass tube may be with- drawn. It must be supposed that a good lather of soap has been prepared beforehand, and with this mixture a bubble some two inches in diameter may be blown ; then cdrefully let the bubble fall into the glass vessel perpendicularly. If this fall be from a certain height the bubble will rebound as if it had been repelled by a spring ; then it re-descends and again ascends many times, and executes many vertical oscillations before it becomes motionless. At that moment the covering should be replaced, so that no agitation is produced within the vessel. The soap bubble floats upon the stratum of carbonic acid gas, which is invisible. CHEMISTRY WITHOUT A LABORATORY. 97 FORMATION OF SALTS—INSTANTANEOUS CRYSTALLIZATION. We are aware that caustic soda or oxide of sodium is an alkaline , production endowed with very energetic properties ; it blisters the skin and destroys organic matter. Sulphuric acid is endowed with not less destructive properties : a drop falling on the hand will produce intense pain, and cause a terrible burn ; a piece of wood plunged into this acijd is carbonised iriimediately. If we mix forty-nine grammes of sqlphuric acid and p? 1 / /"^Sv^ Fig. 80. — Bottle containing a Saturated Solution of Sulphate of Soda. Crystallization is shown in the Decanter to the left of the. Illustration. thirty-one grammes of caustic ' soda a most intense re- action will set in, accompanied by a considerable increase of tehiperature ; after the mass has co9led we find la substance which may be hand led with impunity ; the acid and the alkali have combined and their properties have been reciprocally destroyed. The combination has given birth to a salt which is sidphaie of soda. The result of 98 CHEMISTRY WITHOUT A LABORATORY. the union exercises no action on litmus paper ; it in no respect resembles its parents. In cliemistry there is an almost infinite number' of salts, which result from the combination of an acid with an alkali, or base. Some, like the sulphate of copper, or : As " blown " eggs are generally experipiented upon it will be necessary to close up the ends with yellow or ■white wax ; aild as these eggs are necessarily very light they must be weighted to keep them in the acid bath, or Fig. 84. — Manner of engraving an Egg. 1 held down with a glass rod. If the acid be very much diluted the operation, although it will occupy more time, will be more complete. Two or three hours will be sufficient to bring ont th6 tracing. Thus the, miracle of the sorcerer has become an amusing and easy experiment in chemistry. CHAPTER IX.— MATHEMATICAL GAMES. The Dice Trick. jHIS trick, which always astonishes people who have not previously witnessed it, is based upon a very simple calculation. Few people know that dice are made and " printed " on a cer- tain plan, which is that every face with the number of dots on the side immediately opposite shall, added to- gether, make seven. This is the whole point of the trick. If there are two dice the total of the points on the opposed faces will be fourteen. This ascertained, we may proceed and throw the dice. We find six, for instance, and we seize the cubes between the thumb and index finger (Fig. 85, No. i)." , The performer knows at once that the total of the under faces is nine, but he takes good care not to show them. He "quickly turns his hand to reach the position shown in Fig. 85, No. 2, but during the movement he has taken a "quarter turn" of the dice in his fingers, by slightly raising the thumb and lowering his fore-finger (as in No. 2). He then exhibits to his audience the points, eight, for instance, which the spectators think was the total underneath, but which is, in truth, the total of one of the lateral faces. This point established the operator quickly resumes position No. i, and replaces the dice in their first position by manipulation which is easily acquired by practice- Then he says, " I have just shown you that the points MATHEMATICAL GAMES. 105 underneath are number eight, now I am going to add a point." Requesting a spectator to touch the dice so as to ensure the addition of the required unit, the operator takes his fingers from them to show that he will not alter their position (No. s),when the dice are taken up. The sub-total is found to be nine instead of eight as before. It is evident that in some cases points must be sub- tracted and not added. If one has begun with twelve, for instance, and that the false total is shown as nine, though Fig. 85.— A Trick with Dice by a Turn of tlie Hand. the true total is two, the performer must request an assistant to efface s6ven points instead of adding any. Again,, there are circumstances in which the true and false points are equal. - Thus, when the upper total is ten the lateral face against the thumb is double ^ve. ; and the false total will be four by the double two, while the true total will also be four, by three and one. So no addition I06 MATHEMATICAL GAMES. or subtraction can be requested. In such a case one of the thousand deceptions practised by prestidigitators must be employed, and by simply letting the dice fall, " by accident," you may begin ' over again, and with another total. THE TOWER OF HANOI AND THE QUESTION OF TONQUIN. This game, which has attained great success, is in the form of a small pasteboard box, on which is inscribed the Tower of Hanoi, a real Chinese puzzle, brought from Tonquin by Professor Claus of Siam, Mandarin of the College of Li-Sou-Stiaq. A real puzzle truly, but in- teresting. ]V[. H. de Parville was the first, to introduce it. We borrow his lively description of it. It is related tha:t, in the great temple at Benares, beneath the dome which marks the centre of the world, one may see fixed in a brass-plate three diamond needles, a cubit high and as thick round as the body of a bee. On one of these needles God at the creation placed sixty-four discs of pure gold, the largest disc resting on the brass slab, and the others smaller and smaller to the top one. This is the Tower of Bramah. Night and day the priests are continually occupied in transferring the discs from the first diamond needle to the third, without infringing any of the fixed and immutable laws of Bramah. The priest must not move more than one disc at a time, he must only place this disc on an unoccupied needle, and then only on a disc larger than it.. When according to these rules the sixty-four discs shall have been transferred from the needle on which the Creator placed them to the third needle, the tower and the Brahmins will all crumble into dust, and that will be the end of the world. , It was, this legend evidently that inspired the Mandarin of Li-Sou-Stian. The Tower of Hanoi is the Tower of MATHEMATICAL , GAMES. 107 Bramab, only the diamond needles are replaced by nails, and round blocks of wood substituted for the golden Fig. 86. — The Tower of Hanoi". ^ , I. Beginning ot'the Game : the Tower complete. Tl.Procefs of TrAnsposition : the Discs are placed Successively on the Sticks A, B, C. III. End of the Game : the Tower is rebuilt at B. discs. The blocks of wood, of decreasing circumferences, are only eight in tivimber, and that is quite sufficient. If io8 MATHEMATICAL GAMES. the trick were to be attempted in thC' manner of the Brahmins, with sixty-four discs, it would be necessary ^ Fig. 87.— The Question of Tonquin. I. Cardboai-d Pyramids i^8 with their Supports A, B. C. II. Course of Proceeding, showing the Superposition of the Pyramids, which must take place in (Transit. III. End of the Game : the Pyramid is rebuilt at C. to move them as many times as expressed in the bewildering row of figures following — viz.:-; MATHEMATICAL GAMES. 109 18,446,744,075,709,65 1,615 — a task which would occupy more than five thousand millions of centuries in accom- plishment. ' With eight discs it is necessary to make two hundred and five transpositions, and allowing for each movement one second of time, four minutes will be required to transport the " tower." Let us put this into practice. It will be conceded that in order to transfer two discs three movements must be made, for three discs seven move- ments, that is to say double each number of discs moved plus i. For four discs fifteen movements^ — double plus i, and so on. So to move all the eight blocks we must make two hundred and fifty-five moves. This ingenious game is founded upon the elementary problem of combinations. Newton gave the world a general and now well-known formula^the Binomial Theorem. But the ancients long before his time knew how to find the correct expression for the number of combinations which they could obtain TXrith eleven letters of the alphabet^ The number of combinations possible with four letters is equal to i* minus i ; with five letters, it is equal to 2^ diminished by a unit, and so on. With eight letters, or eight discs, the same rule holds ; 2* di- minished by one unit is equal to/2X4v A tower of nine discs would necessitate the samedouble number of dis- placements //mj I, or what is the same thing — 2' — i., that is 5 1 3 moves, and so on. The Tower of Hanoi brings to our recollection the ring puzzle, which appears in a volume which we have already mentioned, entitled Mathematical Recreations, by Mr. Edward Lucas, Professor at the College of St. Louis. This reminiscence comes to me very opportunely, as I think I have discovered the name of the Mandarin, the inventor of, the Tower of Hanoi. One is only betrayed by himself. A Mandarin who conceives a game founded I 10 MATHEMATICAL GAMES. on combinations would be perpetually thinking of and seeing combinations everywhere. Now, in examining the letters inscribed on the box containing the Tqwer of Hanoi, it seems to me that without much difficulty we Fig. 88.— A Mathematical Game— The Packer's Secret. ' can transpose St. Claus (of Siam) Mandarin of the College of Li-Sou-Stian, into Lucas d'A miens, Professor of the College of Saint Louis ! Have I also solved my problem, I wonder ? MATHEM-ATICAL. GAMES. I I I Since the conception of the Tower ot Hanof we have found another analogous game, called the Question of Tonquin, a game of Chinese hats., This puzzle is com- posed of pasteboard pyramids of decreasing sizes (as in Fig. 87 on page io8)j which must be manipulated in the manner already related with references to the discs and the foregoing illustrations. Fig. 8g. — Explanation of Method of Packing. THE PACKER'S SECRET. This ingenious game consists of a cardboard box con- taining twelve wooden discs, which lie loosely in their receptacle as on the upper portion of the foregoing illus- tration (see Fig. 88, page 1 10). The problem to be solved is this. Place the twelve pieces in the box in such a manner that, they will remain immovable, and will not fall out even when the box is turned upside down without the lid. The solution consists in placing th^ discs tangentially, and the puzzle can be performed by arranging them as |shown in the cut above (Fig. 89). All the " men ", thus [isustain each other by gentle pressure, and the' box may f'be shaken without any one of them falling out. To perform this puzzle one must understand, in some mea- I 12 MATHEMATICAL GAMES. sure, the packer's secret (see Fig. 89). We place one disc (No. i) in the centre, and dispose around it six other discs, 2, 3, 4, 5, 6, 7. Steady these with the left hand, so that they will not move except en bloc, and then insert the remaining pieces 8, 9, 10, 11, 12 around them, next the circumference of the box. Then remove the disc No. I from the central place, and put it where i''"' is resting. The twelve discs will then remain firm in their places. The puzzle is solved ! CHAPTER X.— NATURAL SCIENCE IN THE COUNTRY. >HE manner of constructing an aquarium has already been described, but we will here show a charming apparatus which will be' both aviary and aquarium combined. Procure a large melon-glass, as shown in Fig. 91, page 114; and into it introduce a cylindrical glass vase, in which you have Fig. 90; — Aviary Aquarium previously placed some pieces of lead or pther metal ^painted, green, etc., so as to suggest the bed of a fountain or a clear stream. Upon the bottom of this vase rest a movable " perch " with a foot: — a metal one will serve. Over the mouth of the melon-glass place a wfre-work 114 NATURAL SCIENCE IN THE COUNTRY / / Fig. Qi. — Birds in an Aquarium. NATURAL SCIENCE IN THE COUNTRY. I '5 screen, with meshes wide enough to adniit ^ir to the birds, and finally place, pots of flowers around the grill to em- bellish it. Place the aquarium glass thus prepared on a pedestal or rest suitable to your apartment, and when all is ready introduce gold and silver fish - into the melon- glass and a pair of birds into the cylindrical vase within it. The flowers will close the mouth of the glasses, so you will possess an aquarium, aviary, and garden in one ; Npcklace of Nuts suspended by Hairs. and also produce a curious effect, as the birds will be seen living apparently in the water with the fishes. We can also produce a still more surprising effect as shown in Fig. 90. A balloon -glass is reversed ihto an ordinary glass aquariunl vase. The neck of the inner vase, sufficient to admit air, is concealed at the foot of the aquarium by plants and by the opaque base, which Il6 NATURAL SCIENCE IN THE COUNTRV. seems to support the globe. When the water and the glass are clear the illusion is perfect. A COLLAR OF NUTS. If we closely examine a nut we shall perceive clearly some inequalities on its surface which look like little cavities. Not only are they cavities, but they also cor- respond to small excavations which traverse the nut within — little tunnels, in fact. If you scratch the super- ficial cavity with a penknife you will open up the entrance to the little tunnel, and you will be able to pass a hair through it, fastening it by its root, which will not penetrate the nut. To pass a hair through a nut, and even to pass many hairs through nuts, were problems which we confess we at one time regarded as visionary : but we have seen them performed by skilful hands. With dexterity and patience, with some lady' s hair, we can make collars and necklaces like those shown in the illustration. This proves that nuts are full of perforations, and whether the fact be known or not to botanists, amateurs may derive some amusement from the exercise of their dexterity on the fruit CHAPTER XL— MECHANICAL TOYS, ETC. ACROBATIC APE. *MONGST the most amusing of modern me- chanical toys this takes a foremost place. The inventor has succeeded in reproducing very effectively all the movements of a >man climbing up a rope. Hitherto the puppet has always been more or less stiff in his movements, but in the, toy under ' notice it is completely independent and free. Just suspend the cord or hold it in the left hand and pull it with the right hand — the puppet will then ascend. Notwithstanding the complicated nature of the movements produced the system is ver)' simple : it requires only a single articulation at D to permit the motions of the limbs. A kind of catch or Spring V, in which the cord fixes at certain times, simul,ates the grasp- ing of the hands. The movement of the legs towards the body is effected by the india-rubber band R (No. 2), fixed in the chest and thigh of the figiire. We must now proceed to explain the mechanism which produces the ascending movement of the puppet. Suppose the cord suspended, the figure is at the lower end : we can describe the cycle "of ascent in three phases. First Phase. — The figu^-e is in the position indicated in No. I in the illustration; his limbs are drawn up by the tension of the india-rubber band. You will see that when the string is pulled the limbs will pivot round the points A and B, and the puppets will assume the position represented in No. 2, the body having slid along the cord, 9 ii8 MECHANICAL TOYS, ETC. which it cannot get away from because of the peg C, which only permits a movement along the string.^ It is the movement of a climber moving upright on his legs. The fork V stops the cord at the end of the climb imitat- ing the prehensile movement of hands. -Fig., 93- — A Mechanical Toy. The Acrobatic Ape. 1. Position at starting : pull the Cord and the Puppet will assume Position 2. 2. End of Ascension Motion. The String is caught at V. The India-rubber pulls up the Legs (3). 3. Puppet suspended by V. Pull the Cord, and the Figure resumes Attitude No. I. Second Phase. — When we loose the cord the puppet remains suspended by V, the limbs being again drawn up by the india-rubber, and it assumes the po.sition as in No. 3. This is the climber suspended by his hands, and gathering up his legs. MECHANICAL TOYS, ETC. 119 Third Phase. — If we pull the cord again it escapes from V and reassumes the position as in No. i , as already described. By pulling the string the various motions are continued until the puppet has reached the end of his tether. It is important that the cord should in the first phase be pulled until it is finished in V. If not the puppet will slide down again as soon as the pull is intermitted, because it will have to be in the position of a man who has not gripped the rope with his hands. THE ROAD LOCOMOTIVE. r Every one is aware that to impart a certain velocity to a given mass a certain amount of energy must be deve- loped — an energy in proportion to the mass and to the square of the velocity which is imparted to it. We also I20 MECHANICAL TOYS, ETC. know that bodies thus animated do not return to a con- dition of repose until thpy have exhausted the power or force imparted to them, and in the cases of bodies whose friction is reduced to a minimum the energy will be slowly exhausted ; the motion will continue for a long time. We can utilize this force by putting in motion a wheel by a system of impulse by pulling, finally producing progression, as evidenced in the little apparatus illustrated (Fig. 94). It is composed of a fly-wheel V, to which a rapid rotatory movement is imparted by a thread or string wound round it. The wheel acts on the two trailing wheels of the engine, furnished with adhering tires. The axle which acts on the wheels is about wth of an inch in diameter, and the wheel about two inches, so it results that the velocity of the small wheel is much greater than the larger, and the latter moves only Tuth as fast as the former. The initial velocity of the small wheel is, how- ever, very great, and the machine moves with considerable speed until its impetus dies away. On a level floor it will run rapidly and for a long while. The same principle has been applied to many other toys popular in England and France. The hind wheels are the motive power, the others are only supporters. TO LIFT A MAN WITH FIVE FINGERS. This is a school-boy pastime, and consists in one indi- vidual being lifted and sustained by the fingers. Two operators put their index fingers under the person's boots, two others place their fingers under each elbow, and a fifth under the chin of the subject. At a given signal each person lifts his hand and the person is easily lifted up (Fig. 95 )• The result may seem very surprising, but it is only a question of the equal sub-division of weight. The MECHANICAL TOYS, ETC. 121 average human being weighs about 70 kilogrammes, or say eleven stone ; so each finger has only to sustain about 30 lbs. weight (10 kilogrammes) which is nothing extra- ordinary. GiLBEf\T. , Fig. 95.— A Man held up by Five Fingers. ATTJ^ACT/OJV. Take a cork and fix in it three hairpins, so as to form a species of tripod. In the centre fix a knitting-needle, and on this fasten a sheet of paper cut as shown in the illustration Fig. 96. We have now two surfaces of paper A and B, sus- 122 MECHANICAL TOYS, ETC. iseptible of turning, at the least wind which blows, around the needle which serves as an axis. Well, if we fan one of these surfaces with a piece of cardboard or a wooden plate .directed normally to the surface, we shall preceive that the surface thus fanned, instead of being repelled as one would anticipate, is actually attracted. In certain A B - -:~-^- m Ll_,- — ^zj: Fig. g6, — A Curious Experiment in Rotatory Movement-Attraction. cases when a flexible fan is employed there is repulsion. We have performed this really curious experiment in the presence of many savants, and have arrived at the con- clusion that the disc of paper is attracted by the fan-plate, Which in its sudden fall creates a vacuum, and the surface of the paper is attracted towards the operator. MECHANICAL T0Y3, ETC. THE MAGIC GLASS. 123 A skilful chemist, M. Wideman, has supplied a curiosity. It is a square of glass perfectly plain, on which no drawing or any lines can be distinguished even after minute investi- gation. But if any one breathes on the surface of the glass a figure such as in the engraving appears. The figure will disappear immediately the breath has evaporated Fig. 97.— The Magic Glass. On the Left the Transparent glass ; on the Right the Sanie after being breathed on. from the glass. You may wash and rub the glass, but the image will again appear if the plate be breathed upon. The explanation is simple. Prepare the, piece of looking-glass, and let the operator draw upon it any design he , chooses with some fluor-hydric acid, which is, obtained by dissolving some powdered fluor spar in the 124 MECHANICAL TOYS, ETC ordinary sulphuric acid of commerce. When it is su ciently liquefied the figure should be traced on the glass with a quill-pen. Leave it for a few minutes— five to ten at the most. Wash the glass and dry it well. Then when it is breathed upon the figure or design will appear. Fig. gS. — Fantoccini Top. A little experience will decide the length of time requisite for the proper production of the figure ; the acid if left too long will eat into the glass, and the design will remain visible even on tiie dry surface. MECHANICAL TOYS, ETC. 12 5 A FANTOCCINI TOP. This apparatus is composed of foiir small triangular mirrors, whose surfaces form a square-based pyramid. The sides of this base are precisely double the height of the pyramid. The mirrors are set at an inclination of 45°; At the apex of the pyramid, which is somewhat trun- cated, are placed successive discs of cardboard, on which are painted divers figures in various attitudes. Rotation at a moderate speed, by means of the handle at the upper extrernity, will bring the reflections of the figures in succession before the eyes of the spectators, and every figure will appear to be moving. So a girl skipping, a dancer, or a gymnast on a trapeze, a ■ horse leaping a bar, etc., may all be seen in rapid succession. A SMALL LOOM MADE WITH CARDBOARD. When we see a weaving-machine at work we admire the ingenious mechanism, but we are unable at first to seize the fundamental principles of its working. We will now endeavour to show the working of the loom by the very best method that can be imagined, viz., that which consists in making the apparatus for oneself, and weaving a piece of tissue with it. Two pencils, a visiting-card or playing-card, some thread, a good knife, and, if you please, a wooden paper- knife, — that is the whole of the material for our ap- paratus. Our loom consists of two pencils, which serve for beams ; a comb (or " heddles ") cut out of the card by the penknife into a kind of grating, on which longitu- dinal openings alternate, with small circular holes. The apparatus is completed by two shuttles cut from the same cardboard, on which are wound the cotton for the weft which is destined to pass across the warp-threads. 126 MKCHANICAL TOYS, ETC. ' Place the pencils at the edge of a table, and, supported by some books, as shown in the illustration herewith (Fig. lOo). Then you may commence by attaching to one of the pencils one end of the thread of the warp, and by means of a needle pass it through the first slit in the "comb," then turn it around the second pencil, returning below it and passing it through the first circular hole in the comb. Then around the first pencil and Fig. 99. — Shuttles and Comb cut from Card ; above is a Specimen of the Material woven. through the second longitudinal opening, and so on, until tke last hole in the comb is reached, as represented in the illustration (Fig. 100). Now, to proceed to our weaving, we have only to raise and lower the comb alternately ; and we shall perceive that the only threads engaged will be those which are drawn through the holes. It now remains for us to pass, be- tween each movement, the shuttle full of the thread of the weft between the two lines of the warp threads placed MECHANICAL TOYS, F.TC. 127 at different elevations. We may use the paper-cutter as a " batten " to drive home the shot. This little apparatus will enable you to comprehend the mechanism of the ■loom, and may be regarded as at once a medium of amusement and of information. With patience we may weave some material' by its aid. Fig. 100. — The Loo^ ready : showing the " Comb " between the renciis. Ihe' Warp is ex- tended between the Pencils : the Thread of the Weft passes transversely by the Aid of the Shuttle. THE- PAPER RINGS. This little arrangement, whichwe are abo ut to explain wiir creJate some astonishment amongst those who have not been initiated in the manner of performance ; it gives rise to' some very interesting geometrical questions. We will show how it is done. 'Look at the illustration (Fig. loi). Here are three paper rings. They ought to be in reality of much greater 128 MECHANICAL TOYS, ETC. diameter in proportion to their length, but in the cut we have reduced the circumference so as not to insert such a large picture as would be necessary if the true dimensions N. \ \ Fjg. loi. — The Papsr Rings. Firstly, I give you ring No. i with a pair of scissors, and request you to cut it as indicated by the dotted line. You will then obtain two rings, as shown under- MECHANICAL TOYS, ETC. 129 neath — No. i'. The dotted line will not be in the paper bands in practice. Then I request you to cut ring No. 2 in the same manner ; but this time you will be surprised to find in your hands, when you have finished cutting round the ring, not two rings, as at first, but one long ring — No. 2'^twice as large as either of the former rings. Now for No. 3'. There is another surprise in store. As you cut the third ring you will be astonished with the result. You will again obtain two rings, but one will be^ looped inside the other, as in No. 3'. Let us explain this trick. You must prepare paper bands 0.05 metre in width, and I or li metres in length. Take the first strip, cut and join its ends directly in the ordinary manner, as shown in fig. i, so that the same side of the paper forms the exterior of the ring all round. The second band is united after it has been twisted on itself, so that one of the ends is united with the opposite surface of the other extremity; as for the third band, you must, give it two turns before you unite the ends. Let the gum dry, and then ydur appa!ratus will be ready. The larger the rings are the less apparent will be the turns in them. A MECHANICAL PAPER BIRD. The art of making paper articles would necessitate a long study on our part, and we do not intend to enter on the various phases of it here. , We know that many things can be made in paper, but the particular object which we are about to explain is a mechanical bird introduced by the Japanese jugglers — a bird which will flap its wings when manipulated. The illustration shows the action of the hands, which, approaching arid separating I30 MECHANICAL TOYS, ETC. alternately, make the bird flap its wings. The other designs indicate the progress of construction as follows : — Take a sheet of ordinary writing paper and cut it so that it will form a perfect square. Fold this, as indicated in No. I, by the middle and the angles, and then turn down the angles as in 2, emphasizing the fold strongly, following a b only, and operating in this way on both sides of the four angles. You will then have turned down eight folds like a b, and your paper will have assumed the Fig. 102. — The Paper Bird. appearance of No. 3 diagram. Then fold the paper as No. 4, so as to accentuate the folds, which can be pressed with the nail ; it will then be easy by fastening the folds around the centre c to obtain fig. 5 from 4. Then turn the paper upside down, and bring up the two opposite folds as in diagram 6, and proceed to raise the points right and left, thus forming diagram 7. By extending the points d and / to right and left you will produce the appearance of the bird as in diagram 8. The head of MECHANICAL TOYS, ETC, r ', 1 the bird can be supplied by turning down the point d. If now you hold the figure tenderly by the extremities, ■m and /«, you may produce the flapping of the wings. The 2 J \/.. .^ / /^\ Fig. 103. — Mechanical Paper Bird— Manner of Construction. same movement may be made by holding the bird at ;//, and pulling its tail^ This toy requires little application to perfect — anyone hiay succeed in making it. 132 MECHANICAL TOYS, tie. TO CUT A CORD WITH THE HANDS. We have often seen grocers' assistants and others breaking the twine which they have tied round parcels Fig. 104. — Manner of cutting a Cord with the Hands. by a sudden pull, and you may have fancied this jerk sufficient to break the' string. Well, try ; you will injure or cut your hands and will not break the end. To succeed you must get the cord into a certain position, which we will tell you. MECHANICAL TOYS, ETC. ' 1 33 Place in the left hand the cord you want to break, and pass one end of it over the other in the form of a cross, and wind round the fingers the end forming the small arm of the cross — you must leave it sufficiently long to make several turns. The other end is then wound round the, right hand, with some distance between the two hands. If your arrangement be correct the string ought to form a Y in the centre of the hand, as seen in the lower part of the illustration. Then grasping the end tightly in the right hand as in the upper part of the cut, bring the, hands close and jerk them quickly apart, and the cord will be cut at the point of intersection of the arms forming the Y, which act as a knife. If the cord be quickly jerked, the shock will not have time to communicate itself to the hands ; this is an interesting demonstration of the principle of inertia. ' Cords of considerable thickness can be thus severed without any ill effects. The most delicate hands may succeed in this experiment, provided the jerk be sudden and the twine properly^ arranged. With a little practice it can be done , rapidly, and the shop-assistants, who are very expert at it, never use knife or scissors. THE MAGIC PICTURE WITH THREE FACES. The following is the most simple method of making the toy. Cut three chromo-lithographs, which we will call A B C, on thin paper and of the same size, into strips. These strips being numbered right to left, we paste them down side by side upon a large sheet of this, paper, which is of the same height as one of the chromon but as long as all three together. We thus obtain a very extraordinary picture, in which are mixed up people lO 134 MECHANICAL TOYS, ETC. landscapes, flowers, and every other detail. The bands or strips only appear distinct in this uniform order — a\ h\ c\ 3?, b^, c^ and so on (Fig. 105). The gum being dry, we fold our picture accordion-fashion as in Fig. 105 ; fastening each to each behind, a b, etc., by the edges, the dihedral angle also appears, and we have then a series of small plans perpendicular to the ground plan. Seen full-face this picture presents the plan C, which seems to mark somewhat a grille formed by the edges of the two other plans. We then step a pace to the left of - Fig. 105. — The Magic Picture witli Tliree F^ces. the picture, and our eye passes in succession from the exterior edge of the facet a^ to the interior edge of the other facet a^, from 0? to a^, and so on, and perceive then the plan A without dissection, but lightly covered with a series of lines which in no wise detracts from its clear- One pace to the right and we see in the same ness. manner the section B — (See Frontispiece). IMITATION THUNDER. Ask some one to place his hands over his ears and pass above the hands around his head a cord in the manner MECHANICAL TOYS, ETC. 1 35 shown in the illustration below (Fig. 106). If you rub the string lightly between the finger and thumb, drawing the hand along the cord, the subject will hear a loud rolling as of thunder. To properly produce the desired effect some precautions are necessary. We will mention them. Before reaching the end of the string you must seize it with the other hand at the point of departure • ' Fig. loS.— The Rolling of Thunder Imitated. by so doing it will be possible to prolong the experiment for some time. If you grasp the string with the nails and draw the hand back by jerks you will produce short sharp peals of thunder, which can be changed into rolling peals at will by continuous rubbing. 136 MECHANICAL TOYS, ETC. THE MECHANICAL FLY. This fly, made of. polished metal some three inches ,long, is suspended from the ceihng or chandelier by a -long thread. The "animal" contains a band of india- rubber, which is twisted round by a kind of handle. The untwisting of the india-rubber sets in motion a screw at Fig. 107. — The Mechanical Fly. the other end, by means of the cogged wheel delineated in the lower part of the illustration herewith (Fig. 107). A catch permits the release of the machinery at the desired moment. The screw imparts a rapid movement to the fly, and makes it fly in a circle around the point of suspension. "v MECHANICAL TOYS, ETC. 137 THE DOUBLE MARBLE. Place the middle finger of the hand under the index, and touch a marble with them in the manner shown below (Fig. 108). You will then experience the sensa- tion of touching two marbles. In normal conditions the Fig. 108.— The Dduble' Marble. ball cannot be touched at the same time by the exteriors" of two fingers of the same hand. When we cross our fingers, however, the normal conditions are changed, but the instinctive interpretation remains the same, so much sp that the frequent repetition of the experiment does not 138 MECHANICAL TOYS, ETC. confirm the first impressions. In fact, if the experiment be frequently repeated the illusion will become less and less marked. EXPERIMENT IN SOUND— ACOUSTICS. Sound is a sensation which affects our ears ; it is pro- duced by a cause exterior to the organ itself — generally by vibration of a body. This vibration is transmitted by the medium serving as a means of communication between nerves of hearing and the object vibrating. There are three different ways of producing sound, — by percussion, when objects strike each other ; by rubbing, 109. — Wooden Whistle, which a Lad may make for Himself. as when a bow of a violin is drawn across the strings ; and by twanging the strings of an instrument. It is easy to prove that sound is transmitted in a perceptible space of time from one place to another. When at a distance we see a man hammering a nail, we perceive that the noise occasioned by the striking of the object does not reach our ears until some seconds after the moment of contact. We see the flash of a cannon before we hear the sound of the discharge, and lightning before thunder. We need not give any particular experiments here save MECHANICAL TOYS, ETC. 139 6ne — the Wooden Whistle, a toy much in vogue amongst school-boys. Take a piece of lilac or willow-wood, and cut the bark round it with a penknife in a circle. Moisten the bark, and then beat it on your knee with the handle of the knife. Then hollow out the pith, and you will have an ordinary whistle, as in a key. A, or by cutting the Fig. no. — The Fruiterer. Fig. III.— The Cobbler. wood (as shown in B and C) a true whistle can be fashioned (Fig. 109). An excellent whistle can be produced with the cowl of an acorn, which forms a small cup. Place this cup between the first and middle fingers, and close the fingers so that only a very small orifice is left. If you blow into this opening a whistle will result. I40 MECHANICAL TOYS, ETC. PORTRAITS UNDER TWO ASPECTS. Drawings from two points of view, so to speak, have already had considerable success ; and chance has recently put in our possession a work by an artist named Galliot, published in Berlin. The author, under the title Arts and Professions, has drawn very amusing figures, which are really the result of a combination of the tools and utensils belonging to the trades or professions of the Fig. 112. — The Alchemist. Fig. 113.— The Brewer. people they represent.' We reproduce some of these essentially original compositions. The Fruiterer (Fig. 1 1 o) is composed of a melon, which forms the head ; an arti- choke, the stem of which forms the nose in profile ; a basket makes the .bust, while some vegetables form a collarette, etc. The Cobbler (Fig. in) is likewise repre- sented by the tools of his trade, notably the nose and chin ; the Alchemist (Fig. 112) is obtained by means MECHANICAL TOYS, ETC. 141 of a furnace and retorts ; the Brewer (Fig. 1 1 3) with a jug, a tub, a cask, and a funnel; the Artist (Fig. 114) with the palette and box of colours ; the Sportsman (Fig. 1 15) is composed of a gun, a powder-flask, and a hunting-horn ; and so on. We have here some amusing pictures, with which we may fitly conclude our recreations. Fig. 114.— The Artist. Fig. 115. — The Sportsman. The talented reader can exercise his pencil in other compositions. ' With these illustrations we bid our friends Farewell, We have endeavoured to indicate to them how they can occupy their leisure profitably, and with amusement to themselves at the same time. MARVELS OF TFIE ELEMENTS. PREFACE. To the child and the savage everything is equally strange and unknown. They do not even imagine that there are such things as elements and compounds. They see certain things, and they perceive or feel certain effects. Water boils and steam rises. Fire burns, and if a hot thing is touched pain is felt. Heat is the first thing the effects of which are noticed, in addition to such things as down- pour of rain and brightness of light followed by darkness. And from the study of the effects of heat many of our most important discoveries have arisen. It is very difficult to realise what an enormous step in advance was made when mankind first began to have some real knowledge about the various substances we see around us, to find out their differences, and to learn that they can be made to change in some regular ways by heat or by letting them mix with each other. The high position to which man had advanced before he began to find out these things may serve as one measure of the difficulty he had experienced in getting at nature's secrets. It was not till after the middle of the last century that Joseph Black, a professor at Edinburgh, arrived at the idea that heat positively disappears in melting ice, leaving vi PREFACE. the water produced from it no hotter thai; the ice, although much heat is needed to melt the ice. The same he found to be the case in changing water into steam. From this discovery came many others which have revealed new worlds to us in the substances which surround us, and not only so, but have given us the power of making a vast number of new substances previously unknown, some of which have proved of the utmost benefit, such as chloroform, while others are of much more doubtful value, such as dynamite. When it was discovered that in the heating of lime- stone to make quicklime a particular kind of air was given off, which we now call carbonic acid gas, and which was found to be poisonous, and that this gas was identical with a gas given off in the breath of animals, and which will render the air of any room poisonous if the ventila- tion is bad, a most important means of advance was put in the chemist's hand. What did it mean, that a gas could be locked up, as it were, in a solid stone and then given out again by heating it, and that the same gas should come out of the bodies of men and animals } Till those questions were answered there could be no rest for the mind anxious to know something of the secrets of nature, and the chemist and natural philosopher have gone on and on until they have conquered those secrets and a multitude more beside. By the light of modern chemistry we find a remarkable interest attaching to the commonest substances. Our table salt is found to be so universally diffused that it is scarcely absent anywhere in nature. Its salt taste appears PREFACE. vii to be far removed from sourness ; yet from it can be got one of the sourest of acids, once known as spirit of salt, now called muriatic or hydrochloric acid. From the tasteless gypsum or alabaster, and also from the un- pleasant Epsom salts, can be extracted the terribly corrosive oil of vitriol. The purgative calomel and the poisonous corrosive sublimate are found to be near neigh- bours in composition, simply differing in the proportions of their elements. A dull stone yields a bright metal, and a light or a heavy gas. The resplendent diamond is nothing but a morsel of charcoal in a different condition. Water can be split up into two gases, one of which we can breathe and the other not. The air is a mixture princi- pally of two gases, one of which by itself would hurry our life too fast, the other of which is quite inactive upon us. This is but a sample of the marvels of chemistry, and the list might be indefinitely prolonged. And. all these strange phenomena have been brought under laws which can be understood as well as we under- stand anything. They have their appropriate places in the scheme of the universe, and furnish us with endless sources of pleasure and profit. Surely even those who have least leisure may afford time to enter into conversa- tion, as it were, with the Maker of the universe as to the laws which it has pleased Him to impose upon ft, and by which all things are ordered, a.nd subsist even to this day. No more worthy object can be set before the intelligent mind than an acquaintance with his Maker's works, which in all their forms show, if but partially, and through a veil, the impression of ^ marvellous mind and energy, if w? vni PREFACE. may apply such terms to Him Who " rolls the stars along." The very fact that man has been gifted with a mind capable of discovering these laws of his Maker proves unmistakably that he is intended to know them and to make use of them. The youth who reads such a work as this should reflect that he is here gathering up the knowledge acquired by the slow and painful toil and thought of generations of the wisest and most patient men who have ever lived. Often in poverty, frequently persecuted, thought silly or over-presumptuous by their contemporaries, they per- severed in spite of all, and found in nature and nature's God a rich reward for all their toil. We in the present generation reap where we have not sowed ; other men have studied, and we derive the profit. The least we can do is to endeavour to understand what they so laboriously acquired, and in our degree to carry on the work they began, not living as if blind in the midst of light, not resting content in the material advantages which the labours of our predecessors have gained for us, not resigning ourselves to disastrous indolence, but rousing our manhood, developing our thoughts, raising our ideas to the regions which still remain beyond our thought, feeding the highest parts of our nature with the thought of the marvels which eye hath not seen, ear hath not heard, nor hath it yet entered into the heart of man to conceive. CONTENTS. PAGE CHAPTER I. INTRODUCTION I CHAPTER II. CHEMISTRY WITHOUT A LABORATORY 10 CHAPTER III. CHEMISTRY AND ALCHEMY 46 CHAPTER IV. NON-METALLIC ELEMENTS 65 CHAPTER V. NON-METALLIC ELEMENTS {continued) 9^ CHAPTER VI. THE METALS '^4 CHAPTER VII. pRGAfTIC CPEMIST^Y 1 6° THE MARVELS OF THE ELEMENTS. CHAPTER I.— INTRODUCTION. WHAT CHEMISTRY IS — THE ELEMENTS — METALLIC AND NON-METALLIC ATOMIC WEIGHT ACIDS — ALKALIS — BASES — SALTS — CHEMICAL COMBINATION AND STUDY. [KEMISTRY is the science of phenomena which are attended by a change of the objects which produce them. We know that when a candle burns, or when wood is burned, or even a piece of metal becomes what we term " rusty," that certain chemical changes take place. There is a change by what is termed chemical action. Rust on iron is not iron ; it is oxide of iron. The oxygen of the air causes it. So we endeavour, by Chemistry, to find out the nature of various bodies, their changes, and the results. In nature we have simple and compound bodies. The former are called ELEMENTS. We must not confuse these elements with the so-called elements — earth, air, fire, and water. Those are really compound bodies. An element is a substance or a gas which is not composed of more than one constituent ; it is itself — a compound of perfectly identical particles. Every " compound " body, therefore, must be made up of some of the elements, of which there are sixty-five. These bodies are divided into non-metallic and metallic elements, and all bodies are composed of CHEMISTRY. them, or are these bodies themselves. The list is as follows. The ^on-metallic elements are " metalloids." We have omitted fractions from the weights, on which chemists differ. TABLE OF ELEMENTS WITH THEIR CHEMICAL SYMBOLS AND COMBINING WEIGHTS. Non-Metallic Elements. Oxygen Hydrogen Nitrogen Chlorine Iodine Fluorine Carbon Sulphur Phosphorus Arsenic* Silicon Boron Silenium Tellurium Bromine . Symbols. o Gaseous < N (ci /I F C , S , P , As. Si , B , Se, .Te, Fluid , >• Solid ■{ Atomic or Combining Derivation of Name. Weights. . i6 . Gr. Oxus, acid ; gennao, to make. I . Gr. Udor, water ; gennao, to make. . 14 . Gr. Natron, nitre ; gennao, to make. . 35 . Gr. Chloros, green. . 127 . Gr. loeides, violet. . 19 . Fluor spar, the mineral. . 12 . Lat. Carbo, coal. , 32 . Lat. Sulphurium. 31 . Gr. Phos, light ; pherein, to carry. 75 . Gr. Arsenicon, potent. , 23 . Gr. Silex, flint. 1 1 . Gr. Borax, Arab., baraga, to shine. , 79 . Gr. Selene, the moon. .129 . Lat. Tellus, the earth. . 80 . Gr. Bromos, offensive smell. METALS. Name. Aluminium Antimony (Stibium) [Arsenic] Barium Bismuth Cadmium Caesium Calcium Cerium Chromium Cobalt Atomic or Symbols. Combining Weights. Al Sb As Ba Bi Cd Cs Ca Ce Cr Co 27 122 75 137 210 112 133 40 141 52 58 Derivation. Lat. Alumen, alum. Gr. Anti, against ; minos, one. Gr. Barsu, heavy. Ger. Weissmuth, white matter. Gr. Cadmeia, calamite. Lat. Caesius, sky-blue. Lat. Calx, lime. The planet Ceres. Gr. Chroma, colour. Ger. Kobald, a sprite. * Arsenic is sometimes considered a non-melallic and sometimes a metallic substance. THE ELEMENTS. METALS (continued). Atomic or Naiae. ! Symbols, Combining Deriyation. Weight" Copper • . Cu . 63 . Lat. Cuprum (Cyprium), Cyprus. Didymium . D . 147 . Gr. Didumos, twins. Erbium . E . — . Ytterby in Sweden. Gallium . Ga . 70 . (Not known.) Glucinum . . Gl . 9 • Gr. Glukos, sweet. Gold Au , 197 . From Hebrew, to shine (doubtful). Indium . . In . "3 . Indigo colour. Iridium . • Ir . 198 . Gr. Iris, rainbow. Iron Fe . 56 . Hebrew, to meet (doubtful). Lanthanum . La . 139 • Gr. Lanthanein, to lie hid. Lead . . Pb . 207 , (Plumbum) malubodos (galena). Lithium . • Li . 7 ■ Gr. Lithos, stone. Magnesium • Mg. 24 . Magnesia, Asia Minor. Manganese i Mn. 55 • Mangana, E. I. (or Magnesia). Mercury . . Hg- 200 . Heathen deity (quick). Molybdenum . Mo . 96 . Gr. Molybdena, lead ore, like lead. Nickel . Ni . 58 . Ger. Kupfer nikel, false copper. Niobium(Columbium) Nb . 94 . Columbite. Osmium . Os . 199 . Osme, an odour. Palladium . PI . 106 . Pallas, Minerva. Platinum , Pt . 197 . Spanish, platina, little silver. Potassium (Kalium) K . 39 • Potash. Rhodium Rh . 104 . Gr. Roda, rose. Rubidium Rb 85 . Lat. Rubidus, red. Ruthenium Ru . 104 . (Not known.) Silver (Argentum) Ag 108 Hebrew, money. Sodium (Natrum) Na • 23 Salsoda plant. Strontium Sr . 87 Strontian, N.B. Tantalum Ta . 182 Tantalite mineral Terbium • Tr . — (Not known.) Thallium Tl . 204 Gr. Thallos, green twig. Thorium . Th . 230 . Thor, deity. Tin (Stannum) . Sn . 118 . (Not known.) Titanium Ti . so . Titans. Tungsten (Walpam) W . 184 . Swedish. Uranium . " . U . 240 . Urania. Vanadium . V • SI . Vanadis, a goddess in Sweden, etc. Yttrium . • Y • 93 . (Not known.) Zinc • • Zn . 6s . Ger. Zinken, nails. Zirconium . • Zr . 89 . Ger.Zircon,four-cornered(Ceylon) 4 CHEMISTRY. The term " combining weight" requires a little explana- tion. We are aware that water, for instance, is made up of oxygen and hydrogen in certain proportions. This we will prove by-and-by. The proportions are in eighteen grains or parts of water, sixteen parts (by weight) of oxygen, and two parts (by weight) of hydrogen. These are the weights or proportions in which oxygen and hydrogen combine to form water, and such weights are always the same in these proportions. Chemical com- li. Liwii '<«■;>, w'lpu^^f HI It EM i; RK., '' J i "^' 1 ^**^'^4?* t i^ 1' Xil II The Laboratory. bination always occurs for certain substances in certain proportions which never vary in those compounds, and if we wish to extract oxygen from an oxide we must take the aggregate amount of the combining weights of the oxide, and we shall find the proportion of oxygen ; for the compound always weighs the same as the sum of the elements that compose it. To return to the illustration of water. The molecule of water is made up of one atom of oxygen and two atoms of hydrogen. One atom ATOMS AND MOLECULES. 5 of the former weighs sixteen times the atom of the latter. The weights given in the foregoing table are atomic weights, and the law of their proportions is called the Atomic Theory. An atom in chemistry is usually considered the smallest quantity of matter that exists, and is indivisible. A molecule is supposed to contain two or more atoms, and is the smallest portion of a compound body. The standard atom is hydrogen, which is put down as i, because we find that when one part by weight of hydrogen is put in combination, it must have many more parts by weight of others to form a compound. Two grains of hydrogen, combining with sixteen of oxygen, make eighteen of water, as we have already seen. Take an example so plainly given by Professor Roscoe, remembering that the numbers" in our table represent the fixed weight or proportion by weight in which the simple body combines. The red oxide of mercury contains six- teen parts by weight of oxygen to two hundred parts by weight of mercury (we see the same numbers in the table) ; these combined make two hundred and sixteen parts of oxide. So to obtain i6 lbs. of oxygen we must get 216 lbs. of the powder. It is the same all through, and it will be found by experiment that if any more parts than these fixed proportions be taken to form a compound, some of that element used in excess will remain free. Lime is made up of calcium and oxygen. We find calcium combining weight is forty, oxygen sixteen. Lime is oxide of calcium in these proportions (by weight). When we wish to express the number of atoms in a compound we write the number underneath when more than one; thus water is Hp. Sulphuric acid H^SO^. As we proceed we will give the various formula when con- sidering the chief elements. In chemistry we have acids, alkalis, and salts, with 6 CHEMISTRY. metallic oxides, termed bases, or bodies, that when com- bined with acids form salts. Alkalis are bases. Acids are compounds which possess an acid taste, im- part red colour to vegetable blues, but lose their qualities when combined with bases. Hydrogen is present in all acids. There are insoluble acids. Silicic acid, for instance, is not soluble in water, has no sour taste, and will not redden the test litmus paper. On the other hand, there are substances (not acids) which possess the characteristics of acids, and most acids have only one or two of these characteristics. Thus it has come to pass that the term " acid" has in a measure dropped out from scientiiic nomenclature, and salt of hydrogen has been substituted by chemists. For popular exposition, however, the term is retained. Alkalis are bases distinguished by an alkaline taste. The derivation is from Arabic, al-kali. They are charac- terized by certain properties, and they change vegetable blues to green, and will restore the blue to a substance which has been reddened by acid. They are soluble in water, and the solutions are caustic in their effects. Potash, soda, and ammonia are alkalis, or chemically, the oxides of potassium ; sodium, ammonium, lithium, and caesium are all alkalis. Potash is sometimes called "caustic" potash. There are alkaline earths, such as oxides of barium, stron- tium, etc. Bases may be defined as the converse of acids. Acids and alkalis are then evidently opposite in char- acter, and yet they readily combine, and in chemistry we shall find that unlike bodies are very fond of combining (just as opposite electricities attract each other), and the body made by this combination differs in its properties from those of its constituents. Salts are composed of acids and bases, and are con- sidered neutral compounds, but there are other bodies not salts, which likewise come under that definition — sugar^ for PliEPARAtlOlSfS. 7 « instance. As a rule, when acids and alkalis combine salts are found. Chemical phenomena are divided into two groups, called inorganic and organic, comprising the simple and com- pound aspects of the subject, the elementary substances being in the first, and the chemistry of animals or vege- tables, or organic substances, in the latter. In the inorganic section we shall become acquainted with the elements and IHTj. ■[_ I . Laboratory furnace. their combinations so often seen as minerals in nature. Chemical preparations are artificially prepared. To con- sider these elements we must have certain appliances, and indeed a laboratory is needed. Heat, as we very commonly see, plays a great part in developing substances, and by means of heat we can do a great deal in the way of chemical decomposition. It expands, and thus diminishes cohesion ; it counteracts the chemical attraction. Light 8 CHEMISTRY. and electricity also decompose chemical combinations. But before proceeding it will be as well to notice a few facts showing how Nature has balanced all things. The earth, and its surrounding envelope, the atmo- sphere, consist of a number of elements, which in myriad combinations give us everything we possess, — the air we breathe, the water we drink, the fire that warms us, are all made up of certain elements or gases. Water, hydrogen and oxygen ; air, oxygen and nitrogen. Fire is combus- tion evolving light and heat. Chemical union always evolves heat, and when such union proceeds very rapidly fire is the result. In all these combinations we shall find when we study chemistry that not a'particle or atom of matter is ever lost. It may change or combine or be " given' off," but the matter in some shape or way exists still. We may burn things, and rid ourselves, as we think, of them. We do rid ourselves of the compounds, the elements remain some- where. We only alter the condition. During combustion, as in a candle or a fire, the simple bodies assume gaseous or other forms, such as carbon, but they do not escape far. True they pass beyond our ken, but nature is so nicely balanced that there is a place for everything, and every- thing is in its place under certain conditions which never alter. We cannot destroy and we cannot create. We may prepare a combination, and science has even suc- ceeded in producing a form like the diamond — a crystal of carbon which looks like that beautiful of all crystals, but we cannot make a diamond after all. ' We can only separate the chemical compounds. We can turn diamonds into charcoal it is true, but we cannot create " natural " products. We can take a particle of an element and hide it, or let it pass beyond our ken, and remain incapable of detection, but the particle is there all the time, and when we retrace our steps we shall find it as it was before. A PASTIME. 9 This view of chemistry carries it as a science beyond the mere holiday amusement we frequently take it to be. It is a grand study, a study for a lifetime. Nature is always willing, like a kind, good mother as she is, to render us up her secrets if we inquire respectfully and lovingly. The more we inquire the more we shall find we have to learn. In these and the following pages we can only tell you a few things, but no one need be turned away because he does not find all he wants. We never do get all we want in life, and there are many first-rate men — scientists — who would give " half their kingdom " for a certain bit of knowledge concerning some natural phenomena. There are numerous excellent treatises on chemistry, and exhaus- tive as the}' are, at present they do not tell us all. Let these popular pages lead us to the study of nature, and we shall find our labour far from onerous and full of interest, daily increasing to the end, when we shall know no more of earth, or chemistry. As a preliminary we will put our workshop aside, and show you something of Chemistry ivithout a Laboratory. CHAPTER II.— CHEMISTRY WITHOUT A LABORATORY. AMMONIUM — PHARAOH'S SERPENTS SALTS AND ACIDS VARIOUS EXPERIMENTS. fE have elsewhere shown the possibility of going through a course of physics without any special apparatus ; we shall now endeavour to show our readers the method of performing some experiments in chemistry without a laboratory, or at any rate with only a few simple and inexpensive appliances. The preparation of gases, such as hydrogen, carbonic acid, and oxygen, is very easily accomplished, but we shall here point out principally a series of experiments that are not so much known. We will commence by describing an in- teresting and rather dangerous experiment which often occurs in a course of chemistry. Ammoniacal gas combined with the elements of water is analogous to a certain metallic oxide which includes a metallic root, ammonium. This hypothetically composed metal may be in a manner per- ceived, since it is possible to amalgamate it with mercury by operating in the following manner : — We take a porcelain mortar, in which we pour a quantity of mercury, and then cut some thin strips of sodium, which are thrown into the mercury. By stirring it about with the pestle a "loud cracking is produced, accompanied by a flame, which bears evidence to the union of the mercury and the sodium, and the formation of an amalgam of sodium. If this amalgam of sodium is put into a slender glass tube containing a concentrated solution of hydrochlorate of ammonia in AMMONIUM. I I water, we see the ammonia expand in an extraordinary- manner, and spout out from the end of the tube, which is now too small to contain it, in the form of a metallic substance (see below). In this case, the ammonium, the radical which exists in the ammoniacal salts, becomes amalgamated with the mercury, driving out the sodium with which it had previously been combined ; the am- monium thus united with the mercury becomes decomposed in ammoniacal gas and hydrogen, the mercury assuming Experiment with ammonium. its ordinary form. Phosphate of ammonia is very valuable from its property of rendering the lightest materials, such as gauze or muslin, incombustible. Dip a piece of muslin in a solution of phosphate of ammonia, and dry it in con- tact with the air ; that done, you will find it is impossible to set fire to the material ; it will get charred, but you cannot make it burn. It is to be wished that this useful precaution were oftener taken in the matter of ball-dresses, 1 2 CHEMISTRY. which have so frequently been the cause of serious acci- dents. There is no danger whatever with a dress that has been soaked in phosphate of ammonia, which is very inexpensive, and easily procured. For preparing cool drinks in the summer ammoniacal salts are very useful ; some'nitrate of ammonia mixed with its weight in water, produces a considerable lowering of the temperature, and is very useful for making ice. Volatile alkali, which is so useful an application for stings from insects, is a solution of ammoniacal gas in water, and sal- volatile, which has such a refreshing and reanimating odour, is a carbonate of ammonia. We often see in chemists' shops large glass jars, the insides of which are covered with beautiful transparent white crystals, which are formed over a red powder placed at the bottom of the vase. These crystals are the result of a combination of cyanogen and iodine. Nothing is easier than the prepara- tion of iodide of cyanogen, a very volatile body, which possesses a strong tendency to assume a definite crystalline form. We bruise in a mortar a mixture of fifty grams of cyanide of mercury, and one hundred grams of iodine ; under the pestle, the powder, which was at first a brownish colour, assumes a shade of bright vermilion red. The cyanogen combines with the iodine, and transforms itself into fumes with great rapidity. If the powder is placed at the bottom of a stoppered glass jar, the fumes of the iodide of cyanogen immediately condense, thereby producing beautiful white crystals which often attain a large size (page 1 3). Cyanogen forms with sulphur a remarkable substance, sulpho-ryanogen, the properties of which we can- not describe without exceeding the limits of our present treatise ; we shall therefore confine ourselves to pointing out one of its combinations, which is well known at the present day, owing to its singular properties. This is sulpho-cyanide of mercury, with which small combustible PHARAOH'S SERPENTS. 13 cones are made, generally designated by the pompous title of Pliaraolis serpents. For making these, some sulpho- cyanide of potassium is mixed into a solution of nitric acid on mercury, which forms a precipitate of sulpho- cyanide of mercury. This is a white, combustible powder, which after passing through a filter, should be trapsformed into a stiff paste by means of water containing a solution of gum. The paste is afterwards mixed with a small quantit}- of nitrate of potash, and fashioned into cones or cylinders ^5: ■ ' ^ iCn^ Iodide of cyanogen. of about an inch and a quarter in length, which should be thoroughly dried. The "egg" thus obtained can be hatched by the simple application of a lighted match, and gives rise to the phenomenon. The sulpho-'cyanide slowly ex- pands, the cylinder increases in length, and changes to a yellowish substance, which dilates and extends to a length of twenty* or five-and-twenty inches. It has the appear- ance of a genuine serpent, which has jiist started into 14 CHEMISTRY. existence, and stretches out its tortuous coils, endeavour- ing to escape from its narrow prison (see below). Ihe residue— which all readers should be careful about where Pharaoh's serpent. children are — constitutes a very poisonous substance, which should be immediately thrown away or burned. It can be easily powdered into dust in the fingers. During SALT. IS the decomposition of the sulpho-cyanide of mercury, quantities of sulphurous acid are thrown off, and it is to be regretted that Pharaoh's serpent should herald his appear- ance by such a disagreeable, suffocating odour. After these few preliminary experiments, we will en- deavour to show the interest afforded by the study of chemistry in relation to the commonest substances of every-day life. We will first consider the nature of a few pinches of salt. We know that kitchen salt, or sea salt, is white or greyish, according to its degree of purity ; that it has a peculiar flavour, is soluble in water, and makes a peculiar crackling when thrown in the fire. But though its principal physical properties may be familiar enough, many people are entirely ignorant of its chemical nature and elementary composition. . Kitchen salt contains a metal, combined with a gas possessing a very suffocating odour ; the metal is sodium, the gas is cJilorine. The scientific name for the substance is chloride of sodium (salt).* The metal contained in common salt in no way resembles ordinary metals ; it is white like silver, but tar- nishes immediately in contact with air, and unites with oxygen, thus transforming itself into oxide of sodium. To preserve this singular metal it is necessary to protect it from the action of the atmosphere, and to keep it in a bottle containing oil of naphtha. Sodium is soft, and it is possible with a pair of scissors to cut it like a ball of soft bread that has been kneaded in the hand. It is lighter than water, and when placed in a basin of water floats on * It is the same with a number of other common products, such as clay, sandstone, etc., the composition of which chemistry has revealed. Argil, or clay, slate, and schist all contain a metal — aluminium, which has become most valuable for industrial purposes. Stones for building are composed of a metal combined with carbon and oxygen — calcium s sandstone is composed of silicium, a metallic body united with oxygen ; and sulphate of magnesia, which enters into the composition of a pur- gative drink, also contains a m^tA— magnesium. i6 CHEMISTRY. the top like a piece of cork ; only it is disturbed, and takes the form of a small brilliant sphere ; great effervescence is also produced as it floats along, for it reduces the water to a common temperature by its contact. By degrees the small metallic ball disappears from view, after blazing into flame (see below). This remarkable experiment is very easy to carry out, and sodium is now easily procured at any shop where chemicals are sold. The combustion of sodium in water can be explained in a very simple manner. Water, as we know, is composed of hydrogen and oxygen. Sodium, by reason of its great affinity for the latter gas, combines with it, and forms a very soluble oxide ; the hydrogen is released and thrown off, as we shall perceive by placing a lighted match in the jar, when the combus- tible gas ignites. Oxide of sodium has a great affinity for water ; it combines with it, and absorbs it in great quantities. It is a solid, white substance, which burns and cauterizes the skin ; it is also alkaline, and brings back the blue colour to litmus paper that has been reddened by acids. Sodium combines easily also with chlorine. If plunged into a jar containing this gas it is transformed into a sub- stance, which is sea salt. If the chlorine is in excess a part of the gas remains free, for simple substances do not mingle in undetermined ratios ; they combine, on the con- trary, in very definite proportions, and 35-5 gr. of dry chlorine always unites with the same quantity of soda equal to 23 grams. A gram of kitchen salt is formed, therefore, of o'6o6 gr. of chlorine, and 0*394 gr. of sodium. Combustion of sodium in water. GLAUBER'S SALTS. 1 7 Besides sea salt, there are a number of different salts which may be made the object of curious experiments. We know that caustic soda, or oxide of sodium, is an alkaline product possessing very powerful properties ; it burns the skin, and destroys organic substances. Sulphuric acid is endowed with no less powerful pro- perties ; if a little is dropped on the hand it produces great pain and a sense of burning ; a piece of wood plunged into this acid is almost immediately carbonized. If we mix forty-nine grams of sulphuric acid and thirty-one grams of caustic soda a very intense reaction is produced, accom- panied by a considerable elevation of temperature ; after it has cooled we have a substance which can be handled with impunity ; the acid and alkali have combined, and their properties have been reciprocally destroyed. They have now originated a salt which is sulphate of soda. This substance e3?ercises no influence on litmus paper, and re- sembles in no way the substances from which it originated. There are an infinite number of salts which result in like manner from the combination of an acid with an alkali or base. Some, such as sulphate of copper, or chromate of potash, are coloured ; others, like sulphate of soda, are colourless. The last-mentioned salt, with a number of others, will take a crystalline form ; if dissolved in boiling water, and the solution left to stand, we shall perceive a deposit of transparent prisms of very remark- able appearance. This was discovered by Glauber, and was formerly called Glauber's salts. Sulphate of soda is very soluble in water, and at a tem- perature of thirty-three (Centigr.) water can dissolve it in the greatest degree. If we pour a layer of oil on a solution saturated with Glauber's salts, and let it stand, it will not produce crystals ; but if we thrust a glass rod through the oil into contact with the solution, crystallization will be instantaneous. This singular phenomenon becomes even i8 CHEMISTRY. more striking when we put the warm concentrated solution into a slender glass tube, A B, which we close after having driven out the air by the bubbling of the liquid (see below). When the tube has been closed, the crystals of sulphate of soda will not form, even with the temperature at zero ; nevertheless the salts, being less soluble cold than hot, are found in the fluid in a proportion ten times larger than they would contain under ordinary conditions. If the end Pveparation of a solution saturated with sulphate of soda. of the tube be broken the salt will crystallize immediately We will describe another experiment, but little known and very remarkable, which exhibits in a striking manner the process of instantaneous crystallizations. Let one hundred and fifty parts of hyposulphite of soda be dissolved in fifteen parts of water, and the solution slowly poured into a te.st-glass, previously warmed by means of boiling wa^er until the vessel is about half-full. One hundred parts of acetate of soda is then dissolved in fifteen parts of water CRYSTALLIZATION. 19 and poured slowly into the first solution, so that they form two layers perfectly distinct from each other. The two solutions are then covered with a little boiling water, which, however, is not represented in our illustration. After it has been left to stand and cool slowly, we have two solutions of hyposulphite of soda and acetate of soda Expenment of instantaneous crystallization. superposed on each other. A thread, at the end of which is fixed a small crystal of hyposulphite of soda, is then lowered into the test-glass ; the crystal passes through the solution of acetate without disturbing it, but it has scarcely reached the lower solution of hyposulphite when the salt crystallizes instantaneously. {See the test-glass on the left 20 CHEMISTRY. of page 1 9.) , We then lower into the upper solution a crystal of acetate of soda, suspended from another thread. This salt then crystallizes also. {See experiment glass on the right of page 19.) This very successful experiment is one of the most remarkable belonging to the subject of instantaneous crystals. The successive appearance of crystals of hyposulphite of soda, which take the form of large, rhomboidal prisms, terminating at the two extremi- ties with an oblique surface, and the crystals of acetate of soda, which have the appearance of rhomboidal, oblique prisms, cannot fail to strike the attention and excite the interest of those who are not initiated into these kinds of experiments. Another remarkable instantaneous crystallization is that of alum. If we leave standing a solution of this salt it gradually cools, at -the same time becoming limpid and clear. When it is perfectly cold, if we plunge into it a small octahedral crystal of alum suspended from a thread, we perceive that crystallization instantly commences on the surface of the small crystal ; it rapidly and perceptibly increases in size, until it nearly fills the whole jar. Common Metals and Precious Metals, How many invalids have swallowed magnesia without suspecting that this powder contains a metal nearly as white as silver, and as malleable, and capable of burning with so intense a light that it rivals even the electric light in brilliancy ! If any of our readers desire to prepare magnesium themselves it can be done in the following manner : — Some white magnesia must be obtained frbm the chemist, and after having been calcined, must be sub- mitted to the influence of hydrochloric acid and hydro- chlorate of ammonia. A clear solution will thus be obtained, which by means of evaporation under the in- fluence of heat, furnishes a double chloride, hydrated and MAGNESIA. 2 1 crystallised. This chloride, if heated to redness in an earthenware crucible, leaves as a residue a nacreous pro- duct, composed of micaceous, white scales, chloride of anhydrous magnesium. If six hundred grams of this chloride of magnesium are mixed with one hundred grams of chloride of sodium, or kitchen salt, and the same quantity of fluoride of calcium and metallic sodium in small fragments, and the mixture Group of alum crystals. is put into an earthenware crucible made red-hot, and heated for a quarter of an hour under a closed lid, we shall find on pouring out the fluid on to a handful of earth, that we have obtained instead of scoria, forty-five grams of metallic magnesium. The metal thus obtained is impure, and to remove all foreign substances it must be heated in a charcoal tube, through which passes a current of hydrogen. Magnesium is now produced in great abundance, and is very inexpensive. It is a metal endowed with a great 2 2 CHEMISTRY. affinity for oxygen, and it is only necessary to thrust it into the flame of a candle to produce combustion ; it burns with a brightness that the eye can scarcely tolerate, and is transformed into a white powder — oxide of magnesium, or magnesia. Combustion is still more active in oxygen, and powder of magnesium placed in a jar filled with this gas produces a perfect shower of fire of very beautiful effect. To give an idea of the lighting power of mag- nesium, we may add that a wire of this metal, which is ^^Q of a millimetre in diameter, produces by combustion a light equal to that of seventy-four candles. The humble earth of the fields — the clay which is used ^,.,,, in our potteries,alsocontains aluminium, f^'""' Ia that brilliant metal which is as malle- \ \ able as silver, and unspoilable as gold. When clay is submitted to the influence of sulphuric acid and chloride of pota- sium, we obtain alum, which is a sul- phate of alumina and potash. Alum is a colourless salt, which crystallizes on the surface of water in beautiful octahedrons of striking regularity. The Calcined alum. |^g_ ^^ page 21 represents a group of alum crystals. This salt is much used in the colouring of fabrics ; it is also used for the sizing of papers, and the clarification of tallow. Doctors also use it as an astrin- gent and caustic substance. When alum is submitted to the action of heat in an earthenware crucible, it loses the water of crystallization which it contains, and expands in a singular manner, overflowing from the jar in which it is calcined (see above). Iron, the most important of common metals, rapidly unites with oxygen, and, as we know, when a piece of this metal is exposed to the influence of damp air, it becomes covered with a reddish substance. In the well-known experiment of the formation of rust, the iron IRON. 23 gradually oxidises without its temperature rising, but this combination of iron with oxygen is effected much more rapidly under the influence of heat. If, for example, we redden at the fire a nail attached to a wire, and give it a movement of rotation as of a sling, we see flashing out from the metal a thousand bright sparks due to the com- bination of iron with oxygen, and the formation of an oxide. Particles of iron burn spontaneously in contact with air, and this property for many centuries has been utilized in striking a tinder-box ; that is to say, in sepa- Preparation of metallic iron. rating, by striking a flint, small particles of iron, which ignite under the influence of the heat produced by the friction. We can prepare iron in such atoms that it ignites at an ordinary temperature by simple contact with the^air. To bring it to this state of extreme tenuity, we reduce its oxalate by hydrogen. We prepare an apparatus for hydrogen as shown above, and the gas produced at A is passed through a desiccative tube, B, and finally reaches a glass receptacle, c, in which some oxalate of iron is placed. The latter salt, under the combined influence of hydrogen and heat, is reduced to metallic iron, which assumes the 24 CHEMISTRY. appearance of a fine black powder. When the experiment is completed the glass vessel is closed, and the iron, thus protected from contact with the air, can be preserved in- definitely ; but if it is exposed to the air by breaking off the end of the receptacle (see below), it ignites immediately, producing a shower of fire of very beautiful effect. Iron thus prepared is known under the name oi pyrophoric iron. Iron is acted upon in a very powerful manner by most Pyrophoric iron. acids. If some nitric acid is poured on iron nails, a stream of red, nitrous vapour is let loose, and the oxidised iron is dissolved in the liquid to the condition of nitrate of iron. This experiment is very easy to perform, and it gives an idea of the energy of certain chemical actions. We have endeavoured to represent its appearance on page 25. Fuming nitric acid does not act on iron, and prevents it being attacked by Ot-dinary nitHb acid. This property has NITRIC ACID. 25 given rise to a very remarkable experiment on passive iron. It consists in placing some nails in a glass, into which some fuming nitric acid is poured, which produces no result ; the fuming acid is then taken out, and is re- placed by ordinary nitric acid, which no longer acts on Iron and nitric acid. the iron rendered passive by the smoking acid. After this, if the nails are touched by a piece of iron, which has not undergone the action of nitric acid, they are immediately acted upon, and a giving off of nitrous vapour is manifested with great energy. ' Lead is a verj'- soft metal, and can even be scratched by the nails. It is also extremely 26 CHEMISTRY. pliable, and so entirely devoid of elasticity that when bent it has no tendency whatever to return to its primitive form. Lead is heavy, and has a density represented by 11-4; that is to say, the weight of a quart of water being one kilogram, that of the same volume of lead is 1 1 -400 k. The figure below represents cylindrical bars of the best known metals, all weighing the Platinum Density 21 '50 same, showing their -omparative density. 1 GoldD. 19-25 ^^^^^ j.j^^ ^.^^ .^ ^^p^j^jg ^f ^^^j^g a Mercury D. 13-66 a beautiful crystalline form when placed in solution by a metal that is less oxydisable. The crystalliza- siiverD. 10-47 tion of lead, represented on page 27, is designated by the name of the Tree oj Saturn. This is how the experi- ment is produced : Thirty grams of acetate of lead are dissolved in a quart of water, and the solution is poured into a vase of a spherical shape. A stopper for this vase is made out of a piece of zinc, to which five or six separate brass wires are attached ; these Aluminium D. 2-56 are plunged into ) Lead D. 11'35 S Bismuth D. 9-82 I Copper D. 8-78 t Nickel D. 8-27 STinD. 7 29 I Iron D. 7'20 I Zinc D 6*86 Uaeneeium D. 1*43 Sodiom D. ( Representation of bars of metal, all of the same weight. the fluid, and we see the wires become immediately covered with brilliant crystallized spangles of lead, which continue increasing in size. The alchemists, who were familiar with this experiment, believed that it consisted in a transformation of copper TREE OF SATURN. 27 into lead, while in reality it only consists in the substitu- tion of one metal for another. The copper is dissolved in the liquid, and is replaced by the lead, but no meta- morphosis is brought about. We may vary at will the form of the vase or the arrangement of the wire ; thus it is easy to form letters, numbers, or figures, by the crystal- lization of brilliant spangles. Copper, when it is pure, has a characteristic red colour, which prevents it being confounded with any other metal ; it dissolves easily in nitric acid, and with considerable effervescence, giving off vapour very abundantly. This property has been put to good use in engraving with aqua fortis. A copper plate is covered with a layer of varnish, and when it is dry some strokes are made on it by means of a graver ; if nitric acid is poured on the plate when thus prepared, the copper is only acted on in the parts that have been exposed by the point of steel. By afterwards removing the varnish, we have an engraved plate, which will serve for printing purposes. Among experiments that may be attempted with com- mon metals, we may mention that in which salts of tin are employed. Tin has a great tendency to assume a crystal- line form, and it will be easy to show this property by an interesting experiment A concentrated solution of proto- chloride of tin, prepared by dissolving some metallic tin in hydrochloric acid, is placed in a test glass ; then a rod of tin is introduced, as shown on page 28. Some water is next slowly poured on the I'od, so that it gradually trickles Tree of Saturn, 28 CHEMISTRY. down, and prevents the mingling of the proto-chloride of tin. The vessel is then left to stand, and we soon see brilliant crystals starting out from the rod. This crystal- lization is not effected in the water ; it is explained by an electric influence, into the details of which we cannot enter Jupiter's Tree. without overstepping our limits ; it is known as " Jupiter's Tree." It is well known that alchemists, with their strange system of nomenclature, believed there was a certain mys- terious relation between the seven metals then known and the seven planets ; each metal was dedicated to a planet ; METALS. ig tin was called Jupiter ; silver, Luna ; gold, Sol ; lead, Saturn ; iron, Mars ; quicksilver. Mercury ; and copper, Venus. The crystallization of tin may be recognised also by rubbing a piece of this metal with hydrochloric acid ; the fragments thus rubbed off exhibit specimens of branch- ing crystals similar to the hoar-frost which we see in severe winter weather. If we bend a rod of tin in our hands the crystals break, with a peculiar rustling sound. When speaking of precious metals, we may call to mind that the alchemists considered gold as the king of metals, and the other valuable ones as noble metals. This defini- tion is erroneous, if we look upon the useful as the most precious ; for, in that case, iron and copper would be placed in the first rank. If gold were found abundantly on the surface of the soil, and iron was extremely rare, we should seek most eagerly for this useful metal, and should despise the former, with which we can neither make a ploughshare nor any other implement of industry. Nevertheless, the scarcity of gold, its beautiful yellow colour, and its unalterability when in contact with air, combine to place it in the first rank in the list of precious metals. Gold is very heavy ; its density is represented by the figure I9'S. It is the most malleable and the most ductile of metals, and can be reduced by beating to such thin sheets that ten thousand can be laid, one over the other, to obtain the thickness of a millimetre. With a grain of gold a thread may be manufactured extending a league in length, and so fine that it resembles a spider's web. When gold is beaten into thin sheets it is no longer opaque ; if it is fastened, by means of a solution of gum, on to a sheet of glass, the light passes right through it, and presents a very perceptible green shade. Gold is some- times found scattered in sand, in a condition of impalpable dust, and, in certain localities, in irregular lumps of varying size, called nuggets. Gold is the least alterable of the 30 CHEMISTRY. metals, and can be exposed, indefinitely, to the contact of humid atmosphere without oxidizing. It is not acted on by the most powerful acids, and only dissolves in a mixture of nitric acid and hydrochloric acid. We can prove that gold resists the influence of acids by the following operation : — Some gold-leaf is placed in two small phials, the first containing hydrochloric acid, and the second nitric acid. The two vessels are warmed on the stove, and whatever the duration of the ebullition .of the acids, the gold-leaf remains intact, and completely resists their action. If we then empty the contents of one phial into the other, the hydrochloric and nitric acids are mixed, and we see the gold-leaf immediately disappear, easily dissolved by the action of the liquid {aqua regid). Gold also changes when in contact with mercury; this is proved by suspending some gold-leaf above the surface of this liquid (page 31); it quickly changes, and unites with the fumes of the mer- cury, becoming of a greyish colour. Silver is more easily affected than gold, and though so white when fused, tarnishes rapidly in contact with air. It does not oxidize, but sulphurizes under the influence of hydro-sulphuric emanations. Silver does not combine directly with the oxygen of the atmosphere ; but under certain conditions it can dissolve great quantities of this gas. If it is fused in a small bone cupel, in contact with the air, and left to cool quickly, it expands in a remark- able manner, and gives off oxygen. Nitric acid dissolves silver very easily, by causing the formation of abundant fumes. When the solution evapo- rates, we perceive white crystals forming, which are nitrate of silver. This fused nitrate of silver takes the name of lunar caustic, and is employed in medicine. Nitrate of silver is very poisonous ; it possesses the singular property of turning black under the action of the sun's rays, and is LUNAR CAUSTIC. 3.1 used in many curious operations in photography. It is also employed in the manufacture of dyes for the hair ; it is applied to white hair with gall-nut, and under the in- fluence of the light it turns black, and gives the hair a very dark shade. Salts of silver in solution with water have the property of forming a precipitate under the in- fluence of chlorides, such as sea salt. If a few grains of common salt are thrown into a solution of nitrate of silver, Gold-leaf exposed to the fumes of mercury. it forms an abundant precipitate of chloride of silver, which blackens in the light. This precipitate, insoluble in nitric acid, dissolves very easily in ammonia. Platinum, which is the last of the precious metals that we have to consider, is a greyish-white colour, and like gold is only affected by a mixture of nitric acid and hydro- chloric acid. It is the heaviest of all the ordinary metals; its density is 21 '50. It is very malleable and ductile, 32 CHEMISTRY. and can be beaten into very thin sheets, and into wires as slender as wires of gold. Platinum wires have even been made so fine that the eye can scarcely perceive them ; these are known as Wollaston's invisible wires. Platinum resists- the action of the most intense fire, and we can only luse it by means of a blow-pipe and hydro-oxide gas. Its unalterability and the resistance it opposes to fire render it very valuable for use in the laboratory. Small crucibles are made of it, which are used by chemists to calcine their precipitates in analytical operations, or to bring about reactions under the infl.uence of a high temperature. Platinum may be reduced to very small particles ; it then takes the form of a black powder. In this pulverulent condition it absorbs gases with great rapidity, to such an extent that a cubic centimetre can condense seven hundred and fifty times its own volume of hydrogen gas. It also condenses oxygen, and in a number of cases acts as a powerful agent. Platinum is also obtained in porous masses ("spongy platinum"), which produce phenomena of oxidation. A very ingenious little lamp may be constructed which lights of itself without the help of a flame. It contains a bell of glass, which is filled with hydrogen gas, produced by the action exercised by a foundation of zinc on acidu- lated water. If the knob on the upper part of the apparatus is pressed, the hydrogen escapes, and comes in contact with. a piece of spongy platinum, which, acting by oxidation, becomes ignited. The flame produced sets fire to a small oil lamp, which is opposite the jet of gas. This very ingenious lamp is known under the name of Gay-Lussac's lamp. Platinum can also produce, by mere contact, a great number of chemical reactions. Place in a test glass an explosive mixture formed of two volumes of hydrogen and one volume of oxygen ; in this gas plunge a small piece of spongy platinum, and the combination of the FLAMELESS LAMP. 33 two bodies will be instantly brought about, making a violent explosion. Make a small spiral of platinum red-hot in the flame of a lamp, having suspended it to a card ; then plunge it quickly into a glass containing ether, and you will see the metallic spiral remain red for some time, while Discolouration of periwinkles by sulphuric acia. in the air it would cool immediately. This phenomenon is due to the action of oxidation which the platinum exercises over the fumes of ether. This curious experi- ment is known under the name of the lamp without a flame. This remarkable oxidizing power of platinum, which has not yet been explained, was formerly designated by 34 CHEMISTRY. the title of catalytic action. But a phrase is not a theory, and it is always preferable to avow one's ignorance than to simulate an apparent knowledge. Science is powerful enough to be able to express her doubts and uncertainties boldly. In observing nature we find an experience of this, Experiment for turning columbines a green colour with ammoniacal ether and often meet with facts which may be put to profit, and become useful in application ; nevertheless it is often the case that the why and the wherefore will for a long time escape the most penetrating eye and lucid intelligence. It is true the admirable applications of science strike us with the importance of their results, and the wonderful COLOURING OF FLOWERS. 35 inventions they originate ; but if they turn to account the observed facts of nature, what do they teach us as to the first cause of all things, the wherefore of nature ? — Almost nothing. We must humbly confess our powerlessness, and say with d'Alembert: "The encyclopaedia is very abun- dant, but what of that if it discourses of what we do not understand 1 " Artificial Colouring of Flowers. In a course of chemistry, the action exercised by sul- phurous acid on coloured vegetable matter is proved by exposing violets to the influence of this gas, which whitens them instantaneously. Sulphurous acid, by its disoxi- dating properties, destroys the colour of many flowers, such as roses, periwinkles, etc. The experiment succeeds very readily by means of the little apparatus which we give on 'page 33. We dissolve in a small vessel some sulphur, which ignites in contact with air, and gives rise, by its combination with oxygen, to sulphurous acid ; the capsule is covered with a conical chimney, made out of a thin sheet of copper, and at the opening at the top the flowers that are to be discoloured are placed. The action is very rapid, and a few seconds only are necessary to render roses, periwinkles, and violets absolutely white. M. Filpol, a distinguished savant, has exhibited to the members of the Scientific Association, Paris, the results which he obtained by subjecting flowers to the influence of a mixture of sulphuric ether and some drops of ammonia ; he has shown that, under the influence of this liquid, a great number of violets or roses turn a deep green. We have recently made on this subject a series of experiments which we will here describe, and which may be easily attempted by those of our readers who are interested in the question. Some common ether is poured into a glass, and to it is added a small quantity of liquid ammonia 36 CHEMISTRY. (about one-tenth of the volume). The flowers with which it is desired to experiment are then plunged into the fluid (page 34). A number of flowers, whose natural colour is red or violet, take instantaneously a bright green tint ; these are red geranium, violet, periwinkle, lilac, red and pink roses, wall-flower, thyme, small blue campanula, fumeter, myosotis, and heliotrope. Other flowers, whose colours are not of the same shade, take difierent tints when in contact with ammoniacal ether. The upper petal of the violet sweet-pea becomes dark blue, whilst the lower petal turns a bright green colour. The streaked carnation becomes brown and bright green. White flowers gener- ally turn yellow, such as the white poppy, the variegated snow-dragon, which becomes yellow and dark violet, the white rose, which takes a straw colour, white columbine, camomile, syringa, white daisy, potato blossom, white Julian, honeysuckle, and white foxglove, which in contact with ammoniocal ether assume more or less deep shades of yellow. White snap-dragon becomes yellow and dark orange. Red geranium turns blue in a very remarkable fashion ; with the monkey-flower the ammoniacal ether only affects the red spots, which turn a brownish green ; red sna-p-dragon turns a beautiful brown ; valerian takes a shade of grey ; and the red corn-poppy assumes a dark violet. Yellow flowers are not changed by ammoniacal ether ; buttercups, marigolds, and yellow snap-dragon pre- serve their natural colour. Leaves of a red colour are instantly turned green when placed in contact with am- moniacal ether. The action of this liquid is so rapid that it is easy to procure green spots by pouring here and there a drop of the solution. In like manner violet flowers, such as periwinkles, can be spotted with white, even with- out gathering them. We will complete our remarks on this subject with a description of experiments performed by M. Gabba in Italy by means of ammonia actintj on PHOSPHORESCENCE. 37 flowers. M. Gabba simply used a plate, in which he poured a certain quantity of solution of ammonia. He placed on the plate a funnel turned upside down, in the tube of which he arranged the flowers on which he wished to experiment. He then found that under the influence of the ammonia the blue, violet, and purple flowers became a beautiful green, red flowers black, and white yellow, etc. The most singular changes of colour are shown by flowers which are composed of different tints, their red streaks turning green, the white yellow, etc. Another curious example is that of red and white fuchsias, which, through the action of ammonia, turn yellow, blue, and green. When flowers have been subjected to these changes of colour, and afterwards plunged into pure water, they preserve their new tint for several hours, after which they gradually return to their natural colour. Another interesting observation, due to M. Gabba, is that asters, which are naturally inodorous, acquire an agreeable aro- matic odour under the influence of ammonia. Asters of a violet colour become red when wetted with nitric acid mixed with water. On the other hand, if these same flowers are enclosed in a wooden box, where the)- are ex- posed to the fumes of hydrochloric acid, they become, in six hours' time, a beautiful red colour, which they preserve when placed in a dry, shady place, after having been pro- perly dried. Hydrochloric acid has the effect of making flowers red that have been rendered green by the action of ammonia, and also alters their appearance very sensibly. We may also mention, in conclusion, that ammonia, com- bined with ether, acts much more promptly than when employed alone. Phosphorescence. Artificial flowers are frequently to be seen prepared in a particular manner, which have the property of be- 38 CHEMISTRY. coming phosphorescent in darkness, when they have been exposed to the action of a ray of light, solar or electric. These curious chemical objects are connected with some very interesting phenomena and remarkable experiments but little known at the present time, to which we will now ' draw the reader's attention. The faculty possessed by certain bodies of emitting light when placed in certain conditions, is much more general than is usually supposed. M. Edmond Becquerel, to whom we owe a remarkable work on this subject, divides the phenomena of phos- phorescence into five distinct classes : — 1. Phosplwrescence through elevation of temperature. Among the substances which exhibit this phenomenon in a high degree we may mention certain diamonds, coloured varieties of fluoride of calcium, some minerals ; and sulphur, known under the name of artificial phosphorus, when it has previously been exposed to the action of the light. 2. Phosphorescence through mecJianical action. This is to be observed when we rub certain bodies together, or against a hard' substance. If we rub together two quartz crystals in the dark, we perceive red sparks ; and when pounding chalk or sugar, there is also an emission of sparks. 3. Phosphorescence through electricity. This is mani- fested by the light accompanying disengagement of elec- tricity, and when gases and rarefied vapours transmit electric discharges. 4. Spontaneous Phosphorescence is observed, as every one knows, in connection with several kinds of living creatures, — glow-worms, noctilucids, etc., and similar phosphorescent efiTects are produced also with organic substances, animal or vegetable, before putrefaction sets in. It is manifested also at the flowering time of certain plants, etc. 5. Phosphorescence through insolation and the action of PHOSPHORESCENCE. 39 light. "It consists," says M. Edmond Becquerel, "in ex- posing for some instants to the action of the sun, or to that of rays emanating from a powerful luminous source, certain mineral or organic substances, which immediately Artificial flower coated with phosphorescent powder, exposed to the light of magnesium wire. become luminous, and shine in the dark with a light, the colour and brilliancy of which depend on their nature and physical character ; the light gradually diminishes in intensity during a period varying from some seconds to 4 40 CHEMISTRY. several hours. When these substances are exposed anew to the action of light, the same effect is reproduced. The intensity of the light emitted after insolation is always much less than that of the incidental hght." These phenomena appear to have been first observed with pre- cious stones ; then, in 1604, in calcined Bologna stone, and later, in a diamond by Boyle, in 1663; in 1675 it was noticed in Baudoin phosphorus (residuum of the cal- cination of nitrate of lime), and more recently still in con- nection with other substances which we will mention. The substances most powerfully influenced by the action of light are sulphates of calcium and barium, sulphate of strontium, certain kinds of diamonds, and that variety of fluoride of calcium, which^ has received the name of chloropkane. Phosphorescent sulphate of calcium is prepared by calcining in an earthenware crucible a mixture of flowers of sulphur and carbonate of lime. But the preparation only succeeds with carbonate of lime of a particular cha- racter. That obtained from the calcination of oyster shells produces very good results. Three parts of this substance is mixed with one part of flowers of sulphur, and is made red-hot in a crucible covered in from contact with the air. The substance thus obtained gives, after its insolation, a yellow light in the dark. The shells of oysters, however, are not always pure, and the result is sometimes not very satisfactory ; it is therefore better to make use of some substance whose composition is more to be relied on. " When we desire to prepare a phosphorescent sulphate with lime, or carbonate of lime," says M. E. Becquerel, " the most suitable proportions are those which in a hundred parts of the substance are composed of eighty to a hundred of flowers of sulphur in the first case, and forty- eight to a hundred in the second, that is, when we employ the quantity of sulphur which will be necessary for burning SULPHATES. 4 r with carbonate of lime to produce a monosulphate.* It is necessary to have regard to the elevation of the tem- perature in the preparation. By using lime procured from arragonite, and reducing the temperature below five hundred degrees for a sufficient time for the reaction between the sulphur and lime to take place, the excess of sulphur is eliminated, and we have a feebly luminous mass, of a bluish tint ; if this mass is raised to a temperature of eight hundred or nine hundred degrees, it will exhibit a very bright light." Sulphate of calcium possesses different phosphorescent properties according to the nature of the salt which has served to produce the carbonate of lime employed. If we transform marble into nitrate of lime, by dissolving it in water and nitric acid, and form a precipitate with carbonate of ammonium, and use the carbonate of lime thus obtained in the preparation of sulphate of calcium, we have a pro- duct which gives a phosphorescence of a violet-red colour. If the carbonate of lime used is obtained from chloride of calcium precipitated by carbonate of ammonia, the phos- phorescence is yellow. If we submit carbonate of lime, prepared with lime water and carbonic acid, to the in- fluence of sulphur, we obtain a sulphur giving a phos- phorescent light of very pure violet. Carbonate of lime obtained by forming a precipitate of crystallized chloride of calcium with different alkaline carbonates also gives satisfactory results. Luminous sulphates of strontium may be obtained, like those of calcium, by the action of sulphur on strontia or the carbonate of this base, by the reduction of sulphates of strontia with charcoal. Blue and green shades are the most common. Sulphates of barium also present very remarkable phenomena of phosphorescence ; but to obtain very luminous intensity a higher temperature is needed * These substances must be finely powdered and thoroughly mixed. 42 CHEMISTRY. than with the other substances mentioned, and we have the same result when we reduce native sulphate of baryta with charcoal ; that is to say, when the reaction takes place which produces the phosphorus formerly known as phos- phorus of Bologna. Preparations obtained from baryta have a phosphorescence varying from orange-red to green. Phosphorescent flower emitting hght in a daric rooui. The preparation of such substances as we have just enumerated afford an easy explanation of the method of manufacturing the luminous flowers which we describdd LUMINOUS fLOWEllS. 43 at the commencement of this chapter. We obtain some artificial flowers, cover them with some liquid gum, sprinkle with phosphorescent sulphur, and let them dry. The pul- verulent matter then adheres to them securely, and it is only necessary to expose the flowers thus prepared to the light of the sun, or the rays emanating from magnesium wire in a state of combustion (page 39), to produce im- mediate phosphorescent effects. If taken into a dark room page 42) they shine with great brilliancy, and give off very exquisite coloured rays. Phosphorescent sulphates are used also in tracing names or designs on a paper surface, etc., and it can easily be conceived that such experiments may be infinitely varied according to the pleasure of the ex- perimenter. But let us ask ourselves if these substances are not capable of being put to more serious uses, and of being classed among useful products. To this we can reply very decidedly in the affirmative. With phosphorescent matter we can obtain luminous faces for clocks placed in dark, obscure spots, and it is not impossible to use it for making sign-boards for shops, or numbers of houses, which can be lit up at night. Professor Norton even goes so far as to propose in the "Journal of the Franklin Institute," not only coating the walls of rooms with these phosphorescent substances, but also the fronts of houses, when he considers it would be possible to do away entirely with street lights, the house-fronts absorbing sufficient light during the day to remain luminous the whole of the night. Chemistry Applied to Sleight of Hand. While physics has provided the species of entertainment called "sleight of hand " with a number of interesting effects, chemistry has only offered it very feeble contribu- tions. Robert Houdin formerly made use of electricity to move the hands of his magic clock, and the electric 44 CHEMISTRY. magnet in making an iron box so heavy instantaneously that no one could lift it. Robin has made use of optics to produce the curious spectacle of the decapitated man, spectres, etc. Those persons who are fopd of this kind of amusement may, however, borrow from chemistry some original experiments, which can be easily undertaken, and I will conclude this chapter by describing a juggling feat Amusing experiment in chemistry. which I have seen recently executed before a numerous audience by a very clever conjurer. The operator took a glass that was perfectly trans- parent, and placed it on a table, announcing that he should cover the glass with a saucer, and then, retiring to some distance, would fill it with the smoke from a cigarette. And this he carried out exactly, standing smoking his SLEIGHT OF HAND. 45 cigarette in the background, while the glass, as though by enchantment, slowly filled with the fumes of the smoke. This trick is easily accomplished. It is only necessary to pour previously into the glass two or three drops of hydro- chloric acid, and to moisten the bottom of the saucer with a few drops of ammonia. These two liquids are unper- ceived by the spectators, but as soon as the saucer is placed over the glass, they unite in forming white fumes of hydrochlorate of ammonia, which bear a complete re- semblance to the smoke of tobacco. This experiment excited the greatest astonishment among the spectators present on the occasion, but under- standing something of chemistry myself, I easily guessed at the solution of the mystery. The same result is obtained in a course of chemistry in a more simple manner, and without any attempt at trickery, by placing the open- ing of a bottle of ammonia against the opening of another bottle containing hydrochloric acid. CHAPTER III. CHEMISTRY AND ALCHEMY CHEMICAL COMBINATION.! THE ATMOSPHERIC AIR. , E have in the foregoing pages given some experiments, and considered several of the metals, but there are numerous very interest- ing subjects still remaining ; indeed, the num- ber is so great that we can only pick and choose. All people are desirous to hear something of the atmosphere, of water, and the earth ; and as we proceed to speak of crystals and minerals, and so on to rocks, we shall learn a good deal respecting our globe — its conformation and constituents. But the atmospheric air must be treated of first. This will lead us to speak of oxygen and nitrogen. Water will serve to introduce hydrogen with a few experi- ments, and thus we shall have covered a good deal of ground on our way towards various other elements in daily use and appreciation. Now let us begin with a few words concerning Chemistry itself At the very outset we are obliged to grope in the dark after the origin of this fascinating science. Shem, or " Chem," the son of Noah, has been credited with its in- troduction, and, at any rate, magicians were in Egypt in the time of Moses, and the lawgiver is stated by ancient writers to have gained his knowledge from the Egyptians. But we need not pursue that line of argument. In more modern times the search for the Philosopher's Stone and ..he Elixir of Life, which respectively turned everything to ALCHEMY. 47 gold, and bestowed long life upon the fortunate finder, occupied many people, who in their researches no doubt discovered the germs of the popular science of Chemistry in Alchemy, while the pursuit took a firm hold of the popular imagination for centuries; and even now chemistry is the most favoured science, because of its adaptability to all minds, for it holds plain and simple truths for our every-day experience to confirm, while it leads us step by step into the infinite, pleasing us with experiments as we proceed. Alchemy was practised by numerous quacks in ancient times and the Middle Ages, but all its professors were not quacks. Astrology and alchemy were associated by the Arabians. Geber was a philosopher who devoted himself entirely to alchemy, and who lived in the year 730 A.u. He fancied gold would cure all disease, and he did actually discover corrosive sublimate, nitric acid, and nitrate of silver. To give even a list of the noted alchemists and magicians would fill too much space. Raymond Sully, Paracelsus, Friar Bacon, Albertus Magnus, Thomas Aquinas, Flamel, Bernard of Treves, Doctor Dee, with his assistant Kelly, and in later times Jean Delisle, and Joseph Balsamo (Cagliostro), who was one of the most notorious persons in Europe about one hundred years ago (1765-1789), are names taken at random ; and with the older philosophers chemistry was an all-absorbing occupa- tion — not for gold, but knowledge. The revelation was slow. On the temperature of bodies the old arts of healing were based — for chemistry and medicine were allies. The elements, we read, existed on the supposition "that bodies were hot or cold, dry or moist " ; and on this distinction for a long time " was .based the practice of medicine." The doctrine of the " three principles" of existence superseded this, — the prin- ciples being salt, mercury, and sulphur. Metals had been 48 CHEMISTRY. regarded as living bodies, gases as souls or spirits. The idea remained that the form of the substance gave it its character. Acid was pointed ; sweet things were round. Chemistry, then, has had a great deal to contend against. From the time of the Egyptians and Chinese, who were evidently acquainted with various processes, — dyeing, etc., — the science filtered through the alchemists to Beecher and Stahl, and then the principle of affinity — a disposi- tion to combine — was promulgated, supplemented in 1 674 by Mayow, by the theory of divorce or analysis. He con- cluded that where union could be effected, separation was equally possible. In 171 8 the first " Table of Affinities " was produced. Affinity had been shown to be elective, for Mayow pointed out that fixed salts chose one acid rather than another. Richter and Dalton made great advances. Before them Hales, Black, Priestley, Scheele, Lavoisier, and numerous others penetrated- the mysteries of the science whose history has been pleasantly written by more than one author whom we have not been able to consult, and have no space to do more than indicate. In later days Faraday, De la Rive, Roscoe, and many others have rendered chemistry much more popular, while they have added to its treasures.. The story of the progress of chemistry would fill a large volume, and we have regret- fully to put aside the introduction and pass on. Before proceeding to investigate the elements, a few words concerning the general terms used in chemistry will be beneficial to the reader. If we look at the list of the elements, pp. 2-3, we shall see various termina- tions. Some are apparently named from places, some from their characteristics. Metals lately discovered by the spectroscope (and recently) end in iuni ; some end in "ine," some in " on." As far as possible in late years a certain system of nomenclature has been adhered to, but the old popular names have not been interfered with. COMPOUNDS. 49 When elements combine together in certain proportions of each they receive certain names. The following table will explain the terms used ; for instance, we find that — Compounds of Oxygen are termed Oxides, as oxide of copper. Hydrogen „ Hydrides,as hydride of potassium. Chlorine „ ' Chlorides, as chloride of sodium. Nitrogen „ Nitrides, as nitride of boron. Bromine „ Bromides, asbromide of potassium. Iodine „ Iodides, as iodide of potassium. Sulphur „ iSjSs."} laf '''""* °' Selenium „ Selenides, as selenide of mercury. P , Carbides, or i as carbide of nitro- " Carburets, I gen, and so on. The above examples refer to the union in single pro- portion of each and are called Binary Compounds. When more than one atom of each element exists in different proportions we have different terms to express such union. If one atom of oxygen be in the compound it is called a "monoxide," or "protoxide"; two atoms of oxygen in combination is termed " dioxide," or " binoxide " ; three, " trioxide," or " tritoxide " ; four is the " tetroxide," or " per-oxide," etc. When more than one atom, but not two atoms is involved, we speak of the sesgui-oxide (one- and-a-half), — "oxide" being interchangeable for "sulphide" or " chloride," according to the element. There are other distinctions adopted when metals form two series of combinations, such as ons and zc, which apply, as will be seen, to acids. Sulphur«V and sulphurous acids, mtric and nitrous acid are familiar examples. In these cases we shall find that in the acids ending in " ous " oxygen is present in less quantity than in the acids ending in ic. The symbolic form will prove this directly, the number of atoms of oxygen being written below, Sulphurous Acid = HoSOj. Nitrous Acid = HNOj. Sulphuric Acid = H2SO4. Nitric Acid = HNO3. Whenever a stronger compound of oxygen is discovered than that denominated by ic, chemists adopt the plan of so CHEMISTRY. dubbing it the per {vtrep, over), as per-chloric acid, which possesses four atoms of oxygen (HCIO4), chloric acid being HCIO3. The opposite Greek term, vtto {/mp9, below), is used for an acid with less than two atoms of oxygen, and in books is written "hypo "-chlorous (for instance). Care has been taken to distinguish between the higher and lower; for "hyper" is used in English to denote excess, as hyper-critical ; and hypo might to a reader unacquainted with the derivation convey just the opposite meaning to what is intended. While speaking of these terminations we may show how these distinctive endings are carried out. We shall find; if we pursue the subject, that when we have a salt of any acid ending in ic the salt terminates in " ate." Similarly the salts of acids ending in otis, end in " ite." To continue the same example we have — Sulphuro«j- Acid, which forms salts called SulphzV«. Sulphur/c Acid, „ „ Sulphates. Besides these are s\i\^\iides, which are results of the o© Combinations of elements. unions or compounds of elementary bodies. SulphzV^j are more complicated unions of the compounds. Sulphates are the salts formed by the union of sulphuric acid with bases. Sulphides or sulphurets are compounds in which sulphur forms the electro- negative element, and sulphites are salts formed by the union of sulphur^wj acids with bases, or by their action upon them. The symbolical nomenclature of the chemist is worse than Greek to the uninitiated. We frequently see in so- called popular chemical books a number of hieroglyphics and combinations of letters with figures very difficult to CHEMICAL UNION. 5 i decipher, much less to interpret. These symbols take the place of the names of the chemical compounds. Thus water is made up of oxygen and hydrogen in certain pro- portions ; that is, two of hydrogen to one of oxygen. The symbolic reading is simple, H2O, = the oxide of hydrogen. Potassium again mingles with oxygen. Potassium is K in our list ; KO is oxide of potassium (potash). Let us look into this a little closer. The union of one particle of a simple body with a par- ticle of another simple body can be easily understood ; but, as we have seen, it is possible to have substances con- sisting of four or five different particles, though the greater number of chemical combinations consist of two or three dissimila'r ones. In the diagram (page 50) we have some possible combinations. 0) (=) (3) ©0 (2& ®So) (i) Hydrosulphurous Acid. (2) Sulphurous Acid. (3) Sulphuric Acid. In these combinations we may have one particle of a in combination with one, two, three, four, or five of b, and many particles of a can unite with various molecules of b. Suppose we have oxygen and sulphur compounds as follows : — Thus there are three different compounds of these two elements — SO, SO2, SO3 (without water). A compound body may combine with another com- pound body, and this makes a complicated compound. Suppose we have a mixture of sulphuric acid and potash. We have a sulphate of potassium (K2S0^ and combinations of these combinations may likewise be formed. We must read these symbols by the light of the combining weights given in the table, and then we shall find the weight of 5 2 CHEMISTRY. oxygen or other elements in combination. Thus when we see a certain symbol (Hg.S for instance), we understand that they form a compound including so many parts of mercury and so many of sulphur, which is known as ver- milion. Hg.O is oxide of mercury, and by reference to the table of Atomic Weights, we find mercury is Hg., and its combining weight is 200 ; while oxygen is O, and its weight is i6. Thus we see at once how much of each element is contained in oxide of mercury, and this propor- tion never varies ; there must be 200 of one and 16 of the other, by weight, to produce the oxide. So if the oxygen has to be separated from it, the sum of 2 1 6 parts must be taken to procure the 1 6 parts of oxygen. When we see, as above, O2 or O3, we know that the weight must be calculated twice or three times, O being 16 ; O3 is therefore 32 parts by weight. So when we have found what the compounds consist of, we can write them sym- bolically with ease. Composition of the Atmospheric Air. We have elsewhere communicated a variety of facts concerning the air.* We have seen that it possesses pressure and weight. We call the gaseous envelope of the earth the atmosphere, and we are justified in con- cluding that other planets possess an atmosphere also, though of a different nature to ours. We have seen how easy it is to weigh the air, but we may repeat the experiment. We shall find that a perfectly empty glass globe will balance the weights in the scalepan ; admit the air, and the glass globe will sink. So air possesses weight. We have mentioned the Magdeburg hemi- spheres, the barometer, the air-pump, and the height and the pressure of the atmosphere have been indicated. The density of the atmosphere decreases as we ascend " * See " Marvels of Earih, Air, and Water." THE AIRv 53 for the first seven miles the density diminishes one-fourth that of the air at the sea-level, and so on for every suc- ceeding seven. In consequence of the equal, if enormous, pressure exercised in every direction, we do not perceive the incon- venience, but if the air were removed from inside of a drum, the parchment would quickly collapse. We feel the air when we move rapidly. We breathe the air, and that statement brings us to consider the composition of the atmosphere, which, chemically speaking, may vary a little (as compared with the whole mass) in consequence of changes which are continually taking place, but to all intents and purposes the air is composed as follows, in loo parts : Nitrogen . . .79 parts. Oxygen . . . 20 „ Carbonic Acid. . . '04 „ with minute quantities of other ingredients, such as ammonia, iodine, carbonetted hydrogen, hydrochloric acid, sulphuretted hydrogen, nitric acid, carbonic oxide, and dust particles, as visible in the sunbeams, added. The true composition of the atmosphere was not known till Lavoisier demonstrated that it consisted of two gases, one of which was the vital fluid, or oxygen, discovered by Priestley. To the other gas Lavoisier gave the name of Azote, — an enemy of life, — because it caused death if in- haled alone. The carbonic acid in the air varies very much, and in close, heated, and crowded rooms increases to a large quantity, which causes lassitude and headache. We can easily prove the existence of carbonic acid gas as exhaled from the lungs. Suppose we take a glass and fill it partly with clear lime-water; breathe through a glass tube into the water in the glass, and very quickly you will perceive that the lime-water is becoming cloudy and turbid. This cloudiness is due to the presence of chalk, which has been produced by the action of the carbonic 54 CHEMISTRY. acid gas in the lime-water. This is a well known and always interesting experiment, because it leads up to the vital question of our existence, and the functions of breath- ing and living. ,u ^ A popular writer once wrote a bo&J< entitled, " Is Life Worth Living ?" and a witty coraime|itator replied to the implied question by saying, '''rt"aepends*'upon,the liver" This was felt to be true by many people who^siiffer, but the scientific man will go farther, and tell you it depends upon the air you breathe, and on the carbonic acid you can raise to create heat, — animal heat, — which is so essen- tial to our wfcll-being. We are always burning ; a furnace is within us, never ceasing to burn without visible combus- tion.' We are generating heat by means of the blood. We know that we inhale air into the lungs, and probably are aware that the air so received parts with the oxygen to renew the blood. The nitrogen dilutes the oxygen, fpr if we inhaled a less-mixed air we should either be burnt up or become lunatics, as light-headed as when inhaling "laughing-gas." This beautifully graduated mixture is taken into our bodies, the oxygen renews the blood and gives it its bright red colour ; the carbon which exists in all our bodies is cold and dead when not so vivified by oxygen. The carbonic acid giren off produces heat, and our bodies are warm. But when the action ceases we become cold, we die away, and cease to live. Man's life exemplifies a taper burning ; the carbon waste is con- sumed as the wax is, and when the candle burns away — it dies ! It is a beautiful study, full of suggestiveness to all who care to study the great facts of Nature, which works by the same means in all matter. We will refer to plants presently, after having proved by experiment the existence of nitrogen in the air. Rutherford experimented very cruelly upon a bird which he placed beneath a glass shade, and there let it CARBONIC ACID. 55 remain in the carbonic acid exhaled from its lungs, till the oxygen being at length all consumed by the bird, it died. When the atmosphere had been chemically purified by a solution of caustic potash, another bird was introduced, but though it lived for some time, it did not exist so long as the first. Again the. air was deprived of the carbonic acid, and a third bird was introduced. The experiment was thus repeated-, till at length a bird was placed beneath the Rutherford's experiment. receiver, and it perished at once. This is at once a cruel and clumsy method of making an experiment, which can be more pleasantly and satisfactorily practised by burning some substance in the air beneath the glass. Phosphorus, having a great affinity for oxygen, is usually chosen. The experiment can be performed as follows with a taper, but the phosphorus is a better exponent. Let us take a shallow basin with some water in it, a 56 CHEMISTRY. cork or small plate floating upon the water, and in the plate a piece of phosphorus.. We must be careful how we handle phosphorus, for it has a habit, well known, but sometimes forgotten by amateur chemists, of suddenly taking fire. Light this piece of phosphorus, — a small piece will do if the jar be of average " shade " size,^ — and place the glass over it, as in the illustration (page 57). The smoke will quickly spread in the jar, and the entry of air being prevented, because the jar is resting under water, phosphoric acid will be formed, and the oxygen thereby consumed. The water, meanwhile, will rise in the jar, the pressure of the air being removed. The burning phosphorus will soon go out, and when the glass is cool, you will be able to ascertain what is inside the jar. Put a lighted taper underneath, and it will go out. The taper would not go out before the phosphorus was burnt in the glass, and so now we perceive we have azote in the receptacle — that is, nitrogen. The other, the constituent of our atmosphere, carbonic acid, as we have seen, is very injurious to the life of animals, and as every animal breathes it out into the air, what becomes of it ? Where does all this enormous volume of carbonic acid, the quantities of this poison which are daily and nightly exhaled, where do they all go to .' We may be sure nature has provided for the safe disposal of it all. Not only because we live and move about still, — and of course that is a proof, — but because nature always has a compensating law. Remem- ber nothing is wasted ; not even the refuse, poisonous air we get rid of from our lungs. Where does it go .? It goes to nourish the plants and trees and vegetables that we delight to look upon and to eat the fruit of. Thus the vegetable world forms a link between the animals and the minerals. Vegetables obtain food, so to speak, and nourishment from water, ammonia, and carbonic acid, all compound bodies, but inorganic. WATER. 57 Water consists of oxygen and hydrogen, carbonic acid of carbon and oxygen, and ammonia of hydrogen and nitrogen. Water and ammonia are present in the air ; so are oxygen and nitrogen. Water falls in the form of rain, dew, etc. So in the atmosphere around us we find nearly every necessary for plant-life ; and in the ground, which supplies some metallic oxides for their use, we find the remainder. From the air, then, the plant derives its life. Drawing the oxygen from air by combustion. The vegetable kingdom in turn gives all animals their food. This you will see at a glance is true. Certainly animals live on animals. Man and wilder animals live on the beasts of the field in a measure, but those beasts derive their nourishment from vegetables — the vegetable kingdom. So we live on the vegetable kingdom, and it separates the carbonic acid from the air, and absorbs it. What we do not want it takes. What we want it gives. 5 8 CHEMISTRY. Vegetables give out oxygen, and we consume it gladly. We throw away carbonic acid, and the plants take it greedily ; and thus the atmosphere is retained pure for our use. We can, if desirable, prove that plants absorb carbonic acid and give out oxygen by placing leaves of a plant in water, holding the acid in solution, and let the sun shine upon them. Before long we shall find that the carbonic acid has disappeared, and that oxygen has come into the water. Carbonic acid is sufficiently heavy to be poured from one vessel to another ; and if we have obtained some in a glass, we can extinguish a taper by pouring the invisible gas on to the lighted taper, when it will be immediately extinguished. From the foregoing observations it will be perceived how very desirable it is that ventilation should be attended to. People close up windows ami doors and fireplaces, and go to bed and sleep. In the morning they complain of head- ache and lassitude ; they wonder what is the matter, and why the children are not well. Simply because they have been rebreathing the carbonic acid. Go into a closed railway carriage which is nearly filled (and it is astonishing to us how people can be so foolish as to close every out- let), and you will recoil in disgust. These travellers shut the ventilators and windows " because of the cold." A very small aperture will ventilate a railway carriage ; but a close carriage is sickening and enervating, as these kind of travellers find out by the time they reach their journey's end. Air was given us to breathe at night as well as by day ; and though from man's acts or omissions there may be circumstances in which "night" air may affect the health, we maintain that air is no more injurious naturally than ■' day " air. Colder it may be, but any air at night is " night " air, in or out of doors at night ; and we are '-crtain that night air in itself never hurt any healthy OZONE. 59 person. It is not nature's plan to destroy, but to save If a person delicate in constitution gets hot, and comes out into a colder atmosphere, and defy nature in that way, he (or she) must take the consequences. But air and ventilation (not draught) are necessaries of health, and to say they injure is to accuse nature falsely. There are many impurities in the air in cities, and in country places sometimes, but such impurities are owing to man's acts and omissions. With average sanitary arrangements and ap- pliances in a neighbourhood no one need be afraid to breathe fresh air night or day ; and while many invalids have, we believe, been retarded in recovery from being kept in a close room, hundreds will be benefited by plenty of fresh air. We should not so insist upon these plain and simple truths were there not so many individuals who think it beneficial to close up every avenue by which air can enter, and who then feel ill and out of spirits, blam- ing everything but their own short-sightedness for the effect of their own acts. An inch or two of a window may be open at night in a room, as the chimney register should be always fully up in bedrooms. When there are fires the draught supplies fresh air to the room with sufficient rapidity. But many seaside journeys might be avoided if fresh air were insisted on at home. There is another and an important constituent of the atmosphere called OzONE, which is very superior oxygen, or oxygen in what is termed the " AUotropic " state, and is distantly related to electricity, inasmuch as it can be pro- duced by an electrical discharge. This partly accounts for the freshness in the air after a thunderstorm, for we are all conscious that the storm has " cleared the air." The fresh, crisp ozone in the atmosphere is evident. Ozone differs from oxygen in possessing taste and smell, and it is heavier by one-half than the oxygen gas. There is a good deal of ozone in the sea breeze, and we can, though not infal- 6o CHEMISTRY. llbly, detect its presence by test-paper prepared with iodide of potassium, which, when ozone is present, will turn blue. We have still something to learn about ozone, which may be considered as "condensed oxygen." Development of gas by combustion. We have frequently mentioned " combustion," and as under ordinary circumstances siich effects cannot take place without atmospheric. air, we will consider it. Com- bustion is chemical action accompanied by light and heat. COMBUSTION. 6l Chemical union is always attended by the development of heat, not always by light, because the union varies in inten- sity and quickness. But when a candle is burning we can study all the interesting phenomena of combustion. We have elsewhere spoken of Heat and Light, so we need only refer the readers to those subjects in the former parts of this series. Heat is referable to chemical action, and varies according to the energy of union. Heat is always present, remember, in a greater or less degree ; and when Gas evolved from flame. visible combustion takes place we see light. Invisible combustion goes on in our bodies, and we feel heat ; when we get cold we feed the fire by eating, or blow it by exercise and air in our lungs. We shall speak, however, of combustion now as it affects us in daily life ; our fires, our candles, gas, etc., and under these ordinary circumstances hydrogen and carbon are present. (We shall hear' rnore' about carbon presently.) These unite with the oxygen to form water and carbonic acid ; the water being visible as we first put the cold shade 62 CHEMISTRY. upon the lighted lamp, and the carbonic acid renders the air impure. In the case of a common candle, or lamp, combustion takes place in the same way. The wick is the inter- mediary. The oil mounts in the lamp wick, where it is Davy's safety lamp. Davy lamp (section). converted into a gas by heat; it then "takes fire," and gives us light and heat. The candle-flame is just the same with one exception : the burning material is solid, not liquid, though the difference is only apparent, for the wax is melted and goes up as gas. The burning part FLAME. 63 of the wick has a centre where there is no combustion, and contains carbon. We can prove this by placing a bent tube, as in the illustration (page 60), one end in the un- burning part of the flame. We shall soon see a dark vapour, come over into the receiver. This is combustible, for if we raise the tube without the glass we can light the gas. If we insert the end of the tube into the brilliant portion of the flame we shall perceive a black vapour, which will extinguish the combustion, for it is a mixture of carbonic acid gas and aqueous vapour, in which (page 61) particles of carbon are floating. When we proceed to light our lamps to read or to write by, we find some difficulty in making the wick burn at first. We present to it a lighted taper, and it has no immediate effect. Here we have oil and cotton, two things which would speedily set a warehouse in flanies from top to bottom, but we cannot even ignite them, try all we can. Why ? — Because we must first obtain a gas, oil will not bui^i liquid ; it must be heated to a gaseous point before it will burn, as all combustion depends upon that, — so flames mount high in air. Now in a candle-flame, as ^Sr/flamef will be seen in the accompanying diagram, there are three portions, — the inner dark core, which consists of unburnt gas ; the outer flame, which gives light ; and the outside rim of perfect combustion non-luminous. In the centre. A, there is no heat. If we place a piece of- gauze wire over the flame at a little distance the flame will not penetrate it. It will remain underneath, because the wire, being of metal, quickly absorbs the heat, and consequently there is no flame. This idea led to the invention of the " safety " lamp by Sir Humphrey Davy, which, although it is not infallible, is the only lamp in general use in mines (page 62). 64 CHEMISTRY. Mines must have light, but there is a gas in mines, a "marsh'' gas, which becomes very explosive when it mixes with oxygen. Of course the gas will be harmless till it meets oxygen, but, in its efforts to meet, it explodes the moment the union takes place ; instead of burning slowly like a candle it goes off all at once. This gas, called "fire damp," is carburetted hydrogen, and when it explodes it develops into carbonic acid gas, which suffocates the miners. CHAPTER IV.— NON-METALLIC ELEMENTS. OXYGEN— SYMBOL ; ATOMIC WEIGHT 16. I XYGEN is certainly the most abundant element in nature. It exists all around us, and the animal and vegetable worlds are dependent upon it. It constitutes in combination about one-half of the crust of the earth, and composes eight- Oxygen from oxide of mercury. ninths of its weight of water. It is a gas without taste or colour. Oxygen was discovered by Priestley and Scheele, in 1774, independently of each other. Oxygen can be procured from the oxides of the metals, particularly from gold, silver, and platinum. The noble metals are reducible from their oxides by heat, and this fact assists us at once. If we heat chlorate of potash, mixed with binoxide of manganese, in a retort in a furnace, 66 CHEMISTRY. the gas will be given off. There are many other ways of obtaining oxygen, and we illustrate two (pages 65, 67). The red oxide of mercury will very readily evolve oxygen, and if we heat a small quantity of the compound in a retort as per illustration (page 65) we shall get the gas. In a basin of water we place a tube test-glass, and the gas from the retort will pass over and collect in the test-tube, driving out the water. The other method mentioned above, — viz., by heating chlorate of potash, etc., in a furnace, is shown in the follow- ing illustration. Oxygen, as we have said, is a colourless and inodorous gas, and for a long time it could not be obtained in any other form ; but lately both oxygen and ..^ hydrogen have been liqui- ^^^~s fied under tremendous :^^f^ pressure at a very low S^^ I temperature. Oxygen '' - '' " *- causes any red-hot sub- stance plunged into it to ^ burn brightly ; a match will readily inflame if a Showing retort placed in furnace. spark be remaining, while phosphorus is exceedingly brilliant, and these appearances, with many others equally striking, are caused by the affinity for those substances possessed by the gas. Com- bustion is merely oxidation, just as the process of rusting is, only in the latter case the action is so slow that no sensible heat is produced. But when an aggregate of slowly oxidising masses are heaped together, heat is gene- rated, and at length bursts into flame. This phenomenon is called " spontaneous combustion." Cases have been known in which the gases developed in the human body by the abuse of alcoholic drinks have ended fatalh' in like manner, the body being completely charred. (Combustion must not be confounded with ignition, as in the electric OXYGEN. 67. light.) Oxygen then, we see, is a great supporter of com- bustion, though not a combustible itself as coal is. When the chemical union of oxygen with another substance is very rapid an explosion takes place. Oxidation occurs in various ways. Besides those already mentioned, all verdigris produced on copper, all decays of whatever kind, disintegration, and respiration, are the effects of oxygen. The following experiment for the extraction of oxygen directly from the air was made by The generation of oxygen from oxide of manganese and potash. M. Boussingault, who passed the gas upon a substance at a certain temperature, and released it at a higher. The illustration on page 69 will show the way in which the experiment was performed. Boussingault permitted a thin stream of water to flow into a large empty flask, and by this water the air was gradually driven out into a flask containing chloride of calcium and sulphuric acid, which effectually dried it This dry air then passed into a large tube inside the 68 CHEMISTRY. revcrberatory furnace, in which tube were pieces of caustic baryta. Heated to a dull redness this absorbs oxygen, and when the heat is increased to a bright red the superabun- dant gas is given off. Thus the oxygen was permitted to pass from the furnace-tube into the receiving glass, and so pure oxygen was obtained from the air which had been in the glass bottle at first (page 69). HYDROGEN— SYMBOL H; ATOMIC WEIGHT I. Phosphorus burning- in oxygen. HYDROGEN is abundaOt iu nature, but never free. United with oxygen it forms water, hence its name, "water-former." It is to Parcelcus that its discovery is due, for he found that oil of vitriol in contact with iron disengaged a gas which was a constituent of | water. This gas was subse- quently found to be inflam- mable, but it is to Cavendish that the real explanation of I hydrogen is owing. He ex- plained his views in 1766. Hydrogen is obtained in the manner illustrated in the cut, by means of a furnace, as on page 70, or by the bottle method, as per page 71. The I first method is less convenient ' than the second. A gun- barrel or fire-proof tube is passed through the furnace, and filled with iron nails or filings ; a delivery tube is at the 1 1 F^^ Kwi^fti 1 1 |B W»m ^^^^ S^^H^^siw! '' ^^M JISi'JM ^^^S ■ 1 1 Magnesium wire burning in oxygen. HYDROGEN. 69 farther end, and a flask of water boiling at the other. The oxygen combines with the iron in the tube, and the hydrogen passes over. The second method is easily arranged. A flask, as in the cut, is provided, and in it some zinc shavings are put. Diluted sulpuric acid is then poured upon the metal. Sulphate of zinc is formed in the flask, and the hydrogen passes off". Extraction of oxygen from air. Hydrogen being the lightest of all known bodies, its weight is put as i, and thus we are relatively with it enabled to write down the weights of all the other elements. Hydrogen is fourteen-and-a-half times lighter than atmospheric air, and would do admirably for the in- flation of balloons were it not so expensive to procure in 70 CHEMISTRY. such large quantities as would be necessary. Ordinary coal gas, however, contains a great deal of hydrogen, and answers the same purpose. A very pretty experiment may be made with a bladder full of hydrogen gas. If a tube be fitted to the bladder already provided with a stop-cock, and a basin of ordinary soap-suds be at hand, by dipping the end of the tube in Preparation of hydrogen with furnace. the solution and gently expressing the gas, bubbles will be formed which are of exceeding lightness (page 72). They • can also be fired with a taper. Another experiment may be made with hydrogen as follows : — If we permit the gas to escape from the flask, and light it, as in the illustration, and put a glass over it, we shall obtain a musical note, higher or lower, according to the length, breadth, and thickness of the open glass- WATER. 71 \ tube (page 73). If a number of different tubes be t employed, we can obtain a musical instrument — a gas harmonium. Hydrogen burns with a blue flame, and is very inflam- mable. Even wa:ter sprinkled upon a fire will increase its fierceness, because the hydrogen burns with great heat, and the oxygen is liberated. Being very light, H can be transferred from one vessel to ' another if both be held upside down. Some mixtures of H and O are very explo- sive. The oxyhydrogen blow-pipe is used with a mixture of O and H, which is forcibly blown through a tube and then ignited. The flame thus produced has a most intense heating-power. Apparatus for generating hydrogen by flask. A very easy method of producing hydrogen is to put a piece of sodium into an inverted cylinder full of water, ^standing in a basin of water. The sodium liberates the hydrogen by removing the oxygen from the liquid. WATER-SYMBOL HoO ; ATOMIC WEIGHT 18. At page 4 of this volume we said something about water, and remarked (as we have since perceived by ex- periment) that "water is composed of oxygen and hydrogen in proportions, by weight, of eight of the former to one of the latter gas ; in volume, hydrogen is two to one " ; 72 CHEMISTRY. and we saw that " volume and weight were very different things.'' This we will do well to bear in mind, and that, to quote Professor Roscoe, "Water is always made up of sixteen parts of oxygen to two parts of hydrogen by weight " ; sixteen and two being eighteen, the combining weight of water is eighteen. We can prove by the Eudiometer that hydrogen when burnt with oxygen forms water ; and here we must Blowing bubbles with hydrogen gas. remark that water is not a mere mechanical mixture of gases, as air, is. Water is the product of chemical com- bination, and as we have before said, is really an oxide of hydrogen, and therefore combustion, or electricity, must be called to our assistance before we can form water, which is the result of an explosion, the mixture meeting with an ignited body — the aqueous vapour being expanded by heat. The ancients supposed water to be a simple body, but Lavoisier and Cavendish demonstrated its true character. WATER. 73 Pure water, at ordinary temperatures, is devoid of taste and smell, and is a transparent, nearly colourless, liquid. When viewed in masses it is blue, as visible in a marked degree in the Rhone and Rhine, at Geneva and Bale respectively. Its specific gravity is i, and it is taken as the standard for Sp. Gravity, as hydrogen is taken as the standard for Atomic Weight. The uses of water and the very important part it plays in the arrangements of nature as a mechanical agent, geology can attest, and me- teorology confirm. It com- poses the greater portions of animals and plants ; without water the world would be a desert — a dead planet. We sometimes speak of " pure " spping water, but such a fluid absolutely pure can scarcely he obtained ; and though we can filter water, there will always re- | main some foreign substance ^ or substances in solution. It ^ is well known that the action of water wears away and rounds off hard rocks, and this power of disintegration is supplemented by its strength as a solvent, which is very great. Rain-water is purest in the country as it falls from the clouds. In smoky towns it becomes sooty and dirty. It is owing to the solvent properties of water, therefore, that we have such difficulty in obtaining a pure supply. There is hard water and soft water. The former is derived from the calcareous formations, and contains lime, like the Kent Experiment with hydrogen. 74 CHEMISTRY. water. This can be ascertained by noticing the incrusta- tions of the vesselj wherein the water is boiled. But water rising from hard rocks, such as granite, can do little to disintegrate them at the moment, and therefore the water rises purer. Springs from a great depth are. warm, and are known as "thermal springs"; and when they come in contact with carbonic acid and some salts in their passage to the surface, they are known as "mineral waters." These The composition of water. waters hold in solution salts of lime and magnesia, or car- bonates of soda with those of lime and magnesia; salts of iron, and compounds of iodine and bromine are found in the natural mineral waters also, as well as sulphurous impregnations, instances of which will occur to every reader. We mentioned the Eudiometer just now, and we give an illustration of it. This instrument is used to ascertain the proportions in which the elements of water are com- THE EUDIOMETER. 75 posed by synthesis, or a putting together of the constituents of a body to make it up. This is distinguished from analysis, which means separating the compound body into its elements, as we do when we pass the electric current through water. The Eudiometer consists of a stout glass tube sealed hermetically at one end ; two platinum wires are pushed in through the glass just before the end is sealed. The tube is now filled with mercury, and inverted in a bowl of The Eudiometer. the same metal. Hydrogen, and then oxygen, are admitted through the mercury in the recognised proportion of two to one. By the time the mercury is somewhat more than half displaced, the tube should be held upon a sheet of india-rubber at the bottom of the vessel to keep the metal in the tube,, for when the necessary explosion takes place the mercury might also be driven out. A spark from the electrophorus or from a Leyden ,jar may now be passed ^6 CHEMISTRY. through the gases in the tube. The explosion occurs, and water is formed inside. If the mercury be again admitted it will rise nearly to the very top of the tube, driving the bubble up. Thus we find we have formed water from the two gases. The decomposition of water is easily affected by elec- tricity, and if a little sulphuric acid be added to the water, the experiment will be thereby facilitated. Two wires from a battery should be inserted through a glass filled with the water, and into two test tubes also filled. The wires Decomposition of water. terminate in platinum . strips, and are fastened at- the other end to the positive and negative poles of the galvanic battery. The gases will collect in the test tubes, and will be found in proper proportions when the current passes. So much for water in its liquid stSte. The solid con- dition of water (ice) is equally interesting. When we apply heat to water, we get a vapour called "steam"; when we cool water to 32° Fahr., we get a solid mass which weighs just the same as the liquid we have congealed, or the steam we have raised from an equal amount of water. But water expands while in the process of solidification ICE CRYSTALS. -jy just as it does when it bfecomes gaseous, and as we have i-etnarked before, our water-pipes bear full testimony to this scientific fact. When ice forms it has a tendency to crystallize, and some of these ice crystals are, as we see, very beautiful. Snow is only water in a nearly solid form, and the crystals are extremely elegant, appearing more Snow crystals. like flowers than congealed water, in tiny six-pointed ice crystals. Many philosophers of late years have written concerning these tiny crystals, which, in common with all crystals, have their own certain form, from which they never depart. Snowflakes are regular six-sided prisms grouped around a centre forming angles of 60° and 120°. There are a number of forms, as will be seen from the 78 CHEMISTRY. accompanying illustrations, and at least ninety-six varieties have been observed. One snowflake, apparently so like all other flakes that fall, can thus be viewed with much interest, and yet, while so very various, snowflakes never get away from their proper hexagonal structure. It has been, remarked that snowflakes falling at the same time have generally the sanje form. Of the latent heat of ice, etc., we have already spoken in our article upon Heat, and therefore it will be sufficient to state that the latent heat of water is 79 thermal units, because when passing from the liquid to the solid state a j^istilling water. certain amount of water absorbs sufficient heat to raise an equal quantity of the liquid 79°. This can be proved by taking a measured quantity (say a pint) of water at 79° and adding ice of the same weight to the water. The mixture will be found to be at zero. Therefore the ice has absorbed or rendered latent 79" of heat which the water possessed. If we melt ice until only a trace of it is left, we shall still find the water as cold as the ice was ; all the latent heat is employed in melting the ice. So it will take as much heat to bring a pound of ice at zero to a pound of water at zero, as it would to raise 79 pounds of water 1°. The same law applies to steam. Water can be distilled in small quantities by an ap- DISTILLATION. 79 paratus, as figured in the illustration, and by these means we get rid, of all impurities which are: inseparable from the liquid otherwise. When it is desirable to distil large quantities of water a larger apparatus is used, called an " Alembic." The principle is simply to convert the liquid by , heat into vapour, then cool it, by condensation, in another vessel. The evaporation .of water, with its effects upon our globe, belong more to the study of Meteorology. Rain-water is the purest, as we have said, because it goes through the process of distillation by nature. The sua takes it up, by evaporation, into the air, where it is condensed, and falls as rain-water. Water containing carbonate of lime will petrify or harden, as in stalactite 8o CHEMISTRY. caverns. The carbonic acid escapes from the dripping Water, the carbonate in solution is deposited as a stalactite, and finally forms pillars in the cave. Sea-water contains StalacuLe Cavern. many salts; its composition is as follows, according to Dr. Schwertzer, of Brighton : — Water . . 96474372 grs Chloride of sodium (salt) . 2805948 , Chloride of potassium 076552 , Chloride of magnesium 3-66658 , Brorriide of magnesium 0-02929 Sulphate of magnesia 229578 . Sulphate of lime o'4o662 , Carbonate of lime 0-03301 , (With traces of iodine and arr imon a). jooo'ooooo grains. NITROGEN. 8i There fs much more oxygen in water than in air, as can be ascertained by analysis of these compounds. This great proportion in favour of water enables fish to breathe by passing the water through the gills. Marine animals (not fishes), like the whale, — which is a warm-blooded creature, and therefore not suited to exist without air, — are obliged to come to the surface to breathe. The density of salt water is much greater than that of fresh water, and there- fore swimming and flotation arc easier in the sea than in a river. We shall have more to say of water by-and-by. NITROGEN— SYMBOL- N ; ATOMIC WEIGHT 14. We have already made some reference to this gas when Obtaining nitrogen. speaking of the atmospherfe and its constituents, of which nitrogeh is the principal. From its life-destroying pro- perties it is called "azote" by French chemists, and when we wish to obtain a supply of nitrogen all we, have to do is to take away the oxygen from the air by burning phos- phorus on water under a glass. Nitrogen is not found frequently in solid portions of the globe. It is abundant in ahimals. It is without colour or smell, and can be bi-eathed in air without danger. It is heavy and sluggish ; 82 CHEMISTRY. but if we put a taper into a jar of nitrogen it will go out, and animals die in the gas for want of oxygen, as nitrogen alone cannot support life. The affinity of nitrogen for other substances is not great, but it gives rise to five compounds, which are as below, in the order they are combined with oxygen : — Nitrous oxide (" laughing gas ") (Monoxide; NjO. Nitric oxide. • ■ • Dioxide N,0,. Nitrous acid . • • • Trioxide N,0,. Nitric peroxide * • ■ Tetroxide N^O^. Nitric acid • ■ . Pentoxide NjOs. These compounds are usually taken as representative examples of combining weight, and as explanatory of the symbolic nomenclature of chemistry, as they advance in such regular proportions of oxygen with nitrogen. The combining weight of nitrogen is 14, and when two parts combine with five of oxygen it makes nitric acid, and we put it down as NjOg ; on adding water, 'HNOg, as we can see by eliminating the constituents and putting in the pro- portions. Actually it is HgNgOo, or, by division, HNO3. Nitrogen plays a very important part in nature, par- ticularly in the vegetable kingdom. Nitric acid has been known for centuries. Geber, the alchemist, was acquainted with a substance called " nitric," which he found would yield a dissolvent under certain circumstances. He called it " dissolving fluid." At the end of the twelfth century Albert Magnus investigated the properties of this acid, and in 1235 Raymond Lully prepared nitre with clay, and gave the liquid the name of " aqua-fortis." But till 1 849 nitric acid was only known as a hydrate, — that is, in com- bination with water, — but now we have the anhydrous acid. Oxygen and nitrogen combine under the influence of electricity, as shown by Cavendish, who passed a current through an atmospheric mixture of oxygen and nitrogen, in a tube terminating in a solution of potash, lime, and NITROGEN. 83 soda. Every time the spark passed, the volume of ga.-, diminished, and nitric acid was formed, as it is in thunder- storms, when it does not remain free, but unites with ammonia, and forms a highly useful salt, which promotes vegetable growth. Here is another instance of the useful- Apparatus for obtaining nitrogen by using metal to absorb the oxygen of the air ne=s of thunderstorms, and of the grand provisions of nature for our benefit. Nitric acid is obtained by distilling nitre with sulphuric acid. The liquid is, when pure, colourless, and is a powerful oxidizer. : It dissolves most metals, and destroys vegetable and animal substances. 84 CHEMISTRY. By an addition of a little sulphuric acid the water is taken from the nitric acid, and a very powerful form of it is the resijlt. The acid is of great use in medicine, and as an application to bites of rabid animals or serpents. It con- verts cotton waste into " gun-cotton " by a very simple process of steeping, washing, and pressing. From the hydraulic press it comes in discs like " quoits," which will burn harmlessly and smoulder away, but if detonated they lllljTHFf' ^"WuifcliCTli I 1 1 I I Nitric apid obtained from nitric and sulphuric acid. explode with great violence. As a rule, when damp, it is not dangerous, but it can be fired even when wet. It will explode at a less temperature than gunpowder, and, moreover, yields, no smoke, nor does it foul a gun. Gun- cotton, when dissolved in ether, gives us collodion for photographic purposes. In speaking farther of the compounds of nitrogen with oxygen, we will limit ourselves to the monoxide, or laugh- nl.1 jtvlVj At^lJJ. 85 ing gas. This is now used as an anaesthetic in dentistry, etc., and is quite successful, as a rule. People afflicted Cavendish's experiment. with heart disease should not use it without advice, how- ever. When inhaled into the lungs it makes the subject very hilarious, and the effect is rather nojsy, It is obtained Experiment to obtain nitric aqid. from the nitrate of ammonia, which, on the application of heftt, decomposes into nitrous oxide and vapour. Warm 86 CHEMISTRY. water should be used for the trough. The gas is a powerful supporter of combustion. Binoxide of nitrogen is of importance in the manufac- ture of sulphuric acid. Nitrogen combines with hydrogen, forming various compounds. These are the " amines," also ammonia, and ammonium. Ammonia possesses the properties of a base. Its name is derived from Jupiter Ammon, near whose temple it was prepared, from camels' dung. But bodies containing nitrogen give off ammonia in course of dis- tilling, and hartshorn is the term applied to horn-cuttings, Apparatus for obtaining laugiiing-gas. which yield ammonia, which is a colourless gas of strong odour and taste now obtained from gas-works. To obtain AMMONIA heat equal parts of chloride of ammonia (sal ammoniac) and quick-lime powdered (see page 87). The gas must be collected over mercury, be- cause it is very soluble in water. Ammonia is useful to restore tipsy people and fainting ladies. A solution of ammonia is used for cauteries. Ammoniacal gas is re- markable for its solubility in water. To prepare the solution the gas is forced thmugh a series of flasks. The tubes carrying the gas should be continued to the bottoms of the flasks, else Ae solution, being lighter than water LAUGHING GAS. 87 the upper portion alone would be saturated. The tubes carrying away the solution are raised a little, so that the Inhaling laughing gas. renewal is continually proceeding. The gas liquifies under a pressure of six atmospheres, at a temperature of 10^ Cieneration of ammonia. Cent. This experiment can be artificially performed by 88 CHEMISTRY. heating chloride of silver saturated with ammonia, and the silver will part with the gas at a temperature of 40° C. The gas will then condense in a liquid form in the tube. The experiment may be facilitated by placing the other extremity of the tube in snow and salt, and by the liquid we can obtain intense cold. This experiment has been made use of by M. Carre in his refrigerator (which was described in the Physics' section), by which he freezes Liquefaction of ammania. water. We may however, just refer to the process. Whenever the condition of a body is changed from that of liquid to a -gas, the temperature is greatly lowered, because the heat becomes "latent." The latest freezing machine consists of an apparatus as shown in the illustra- tions on pages 89 and 90. The machine is of- wrought iron, and contains, when ready for action, a saturated solu- tion of ammonia at zero. This is in communication with another and an air-tight vessel, of which the centre is REFRIGERATION. 89 hollow. The first process is to heat the solution, and the gas escapes into the second " vase," which is surrounded by cold water, and quite unable to escape. A tremendous pressure is soon obtained, and this, added to the cold water, before long liquifies the ammonia, and when the temperature indicates 130' the hot vessel is suddenly cooled by being put into the water. The gas is thus sud- denly converted into a liquid, the water in the second hollow vase is taken out, and the bottle to be frozen is put into Carre's refrigerator (first action). the cavity. The cold is so great, in consequence of the transformation of the liquid ammonia into a gas, that it freezes the water in any vessel put into the receiver. The ammonia can be reconverted into liquid and back again, so no loss is occasioned by the process, which is rapid and simple. This is how great blocks of ice are produced in water-bottles. The one important point upon which care is necessary is the raising of the temperature. If it be elevated beyond 90 CHEMISTRY. 130° C, the pressure will be too great, and an explosion will occur. The abundant formation of ammonia from decaying animal matter is evident to everyone, and depends upon the presence of moisture to a great extent. Chloride of ammonia is called sal-ammoniac, and the carbonate of ammonia crystallizes from the alkaline liquid produced by the distillation of certain animal matter. The compounds of ammonia are easily recognized by a certain sharp taste. Carre's refrigerator (second action). They are highly valuable remedial agents, acting particu- larly upon the cutaneous system, and when taken internally,, produce the effect of powerful sudorifics. Their volatility,. and the facility with which they are expelled from other substances, render them of great importance in chemistry,, and peculiarly fit them for the purposes of many chemical analyses. The ammonia compounds display a remarkable analogy to the corresponding combinations of potash and' soda. The compounds of ammonia are highly important in their relation to the vegetable kingdom. It may be- AMINES. 91 assumed that all the nitrogen of plants is derived from the ammonia which they absorb from the soil, and from the surrounding atmosphere. The similarity of ammonia to the metallic oxides has led to the conjecture that all its combinations contain a compound metallic body, which has received the name ammoninm (NH_j) ; but no one has yet succeeded in its preparation, although by peculiar processes it may be obtained in the form of an amalgam. Ammonias, in which one or more atoms of hydrogen are replaced by basic radicals, are termed Amides, or A mines. CHAPTER v.— NON-METALLIC ELEMENTS. {Continued^ (..HLORXNE— BROMINE — IODINE — FLUORINE — CAR150N — SULPHUR — PHOSPHORUS — SILICON — BORON — TELLU- RIUM ARSENIC. HLORINE (CI.) is usually found with sodium in the mineral kingdom, and this chloride of sodium is our common salt. Chlorine can be obtained by heating hydrochloric acid with binoxide of manganese. (Atomic weight 3 5'5.) Chlorine possesses a greenish-yellow colour, hence its name " Chloros," green. " It should be handled carefully, for it is highly injurious and suffocating. It possesses a great affinity for other substances, and attacks the metals. For hydrogen it has a great affection, and when hydrogen is combined with any other substances chlorine imme- diately attacks them, and in time destroys them. But even this destructive and apparently objectionable quality makes chlorine very valuable ; for if we carry the idea to its conclusion, we shall find that it also destroys offensive and putrid matter, and purifies the atmosphere very much. Most colouring matters include hydrogen, and therefore they are destroyed by chlorine, which is a great " bleacher " as well as a purifier. If we dip any vegetable dyes into a jar of chlorine, they will become white if the dyed sub- stances are damp. Hydrochloric acid is known as muriatic acid and spirits CHLORINE. 93 of salt. It is obtained when salt' is treated with sulphuric acid and the gas comes off into water. Equal parts of the acid and the salt are put into a flask as in the cut on page 94, and diluted with water. The mixture is then heated. The gas is condensed in the bottles half-full of •water. The result gives sulphate of soda and hydrochloric L -i-^lL _ T i?J«»'^ -" ■*-*■*" "■"= I J. ''Sj t < A" _ f (^ '«>ij *?^ a> ^^> g f ip^^"'^- 1^ Generation of chlorine. acid. This acid is procured in soda manufactories, and with nitric acid is called "aqua regia," a solvent for gold. When chlorine and hydrogen are mixed in equal propor- tions they explode in sunlight. In the dark or by candle- light they are harmless. Dry chlorine gas can be obtained by interpo.sing a glass filled with some chloride of calcium. 94 CHEMISTRY. The gas being heavier than air (about 2i times), displaces it in the flask, and when it is filled another can be placed in position. This mode causes a little waste of gas, which should not be breathed. Chlorine possesses a great affinity for certain bodies. If the gas be thrown upon phosphorus, the latter will burn brilliantly. Arsenic, tin, and antimony when powdered and poured from a shoot into a vase of chlorine will burst into briUiant sparks, and other metals will glow when in- troduced to this gas. Chlorine forms many unstable com- Productioii cf hytlrcjcliloric acid, _ -^ binations with oxygen. Its combination with hydrogen has already been referred to. Bromine is a rare element. (Symbol Br. Atomic weight 80.) It is deep brownish red, very volatile, and of a peculiar odour. Bromine unites with the elementary bodies, and forms some oxygen compounds. It resembles chlorine- in its properties, and is used in medicine and in photo- graphy. It is found in saline springs and in salt water, combined with soda and magnesium. The presence of lODINK. 95 bromine may easily be detected in tlie strong smell of sea weed. Its combinations with metals are termed bromides. It is a powerful poison. Iodine is another relative of chlorine. It is found in seaweed, which by burning is reduced to kelp. When iodine is heated a beautiful violet vapour comes off, and this characteristic has given it its name ("iodes," violet). Apparatus for obtaining dry chlorine gas. Iodine was discovered by Courtojs, of Paris, and in 1813 Gay^Lussac made it a special study. It is solid at ordinary temperatures, and assumes crystallized forms in plates of metallic lustre. It is an excellent remedy in "goitre" and such afifections. (Symbol I. Atomic weight 127.) Fluorine is very difficult to prepare. Fluor spar is a compound of fluorine and calcium. This element is gaseous, and combines so rapidly that it is very difficult 96 , CHEMISTRY. to obtain in a free state. Etching on glass is accomplished by means of hydrofluoric acid, for fluorine has a great affinity for silicic, acid, which is contained in glass. The glass is covered with wax, and the design is traced with a needle. The acid attacks the glass and leaves the wax, so the design is eaten in. (Symbol F. Atomic "weight 19.) Chlorine, fluorine, bromine, and iodine are termed " Halogens " (producers of salts). They appear, as we have seen, in a gaseous, liquid, and solid form respectively. Carbon is the most, or one of the most, largely dif- Facets of a brilliant. fused elements in nature, and claims more than a passing notice at our hands, though even that must be brief. We may put down carbon next to oxygen as the most im- portant element in the world. The forms assumed by carbon are very variable, and pervade nature in all its phases. We have carbon in crystals, in the animal and vegetable kingdoms, and amongst the chief minerals a solid, odourless, tasteless, infusible, and almost insoluble body. In various combinations carbon meets us at every turn ; united with oxygen it forms carbonic acid, which we exhale for the plants to imbibe. We have it in coal, CARBON. 97 with hydrogen and oxygen. We have it building up animal tissues, and it is never absent in two out of the three great divisions of nature — the plants and the animals (Symbol C ; Atomic W. 1 2). We have carbon in three different and well-known con- ditions ; as the diamond, as graphite, or black-lead, and as charcoal. The properties of the diamond are well known, and we shall, when we get to Crystallography, learn the forms of diamond or crystals of carbon. At pre- sent we give an illustration or two, reserving- all explana- tion for the present.. Diamond cutting is a matter of some Facets of a rose diamond. difficulty, and it requires, skill to cut in the' proper direction. Diamonds are found in India, Brazil, and at the Cape of Good Hope, in alluvial soil. The identity of diamond and char(!oal was discovered accidentally. An experiment to fuse at few small diamonds resulted in their disappearance, and when the residue was examined it was found that the diamonds had been burned, that they had combined with oxygen and formed carbonic acid, just as when coal burns. The diamond is the hardest of all substances, the most valuable of gems, and the purest condition in which carbon appears. 9- CHEMISTRY. ' black-lead," and is It crystallizes and In Cumberland it is Graphite (Plumbago) is termed the next purest form of carbon, belongs to the primitive formations, dug up and used to make pencils; the operations can be seen at Keswick. It has other uses of a domestic character. Charcoal is the third form of carbon, and as it possesses no definite form, is said to be amorphous. Charcoal is Coke ovens. prepared in air-tight ovens, so that no oxygen can enter and burn the wood thus treated. Coke is the result of the same process applied to coal. The gas manufactories are the chief depots for this article, and it is used in locomotive engines. The various smokeless coals and prepared fuels, however, are frequently substituted. Coke ovens were formerly much resorted to by the rail- way companies, who found the ordinary coal too smoky CHARCOAL. 99 for locomotive purposes, and apt to give rise to complaints by passengers and residents near^the line. The origin of wood charcoal we have seen. All vege- table substances contain carbon. When we burn wood, in the absence of air as far as possible, oxygen and hydrogen are expelled. The wood is piled in layers as in the illus- tration below, covered over with turf and mould, with occasional apertures for air. This mass is ignited, the oxygen and hydrogen are driven off, and carbon remains. (Animal charcoal is obtained from calcining bones). Wood charcoal attracts vapours, and water, if impure, can be purified by charcoal, and any impure or tainted animal matter can be rendered inoffensive by reason of charcoal absorbing the gases, while the process oFdecay goes on just the same. Housekeepers should therefore not always decide that meat is good because it is not offensive to the olfactory nerves. Char- coal will, remove the aroina, but the,- meat may be never- charcoai burning. theless bad. The use of charcoal in filters is acknowledged universally, and as a constituent of gunpowder it is im- portant. Carbon is not easily affected by the atmospheric air, or in the earth; so in many instances wood is charred before being driven into the ground ; and casks for water are prepared so. Soot is carbon in a pulverised condition, and Indian ink is manufactured with its assistance. The preparation of wood charcoal gives occupation to men who are frequently wild and untutored, but the results of their labour are very beneficial. Care should be taken not to sleep in a room with a charcoal stove burning, unless there is ample vent for the carbonic acid gas, for it lOO chemistrv will cause suffocation. Lampblack is obtained by holding a plate over the flame of some resinous substance, which deposits the black upon it. There is a special apparatus for this purpose. Carbon combines with oxygen to make carbonic acid gas, as we hav.e already mentioned, and in other propor- tions to form a more deadly compound than the other. The former is the dioxide (COJ, the latter the monoxide, or carbonic oxide (CO). The dioxide is the more im- =--.,?Sa^s "^3 Wood piles of charcoal burners. portant, being held in the atmosphere, and combined with lime in chalk. All sparkling beverages contain carbonic, acid, to which their effervescence is due. The soda and other mineral waters owe their sparkle to this gas. Soda- water consists of a weak solution of carbonate of soda and the acid. There is a vessel holding chalk and water, and another containing some sulphuric acid. When the sul ■ phuric acid is permitted to unite with the chalk and water,, carbonic acid is liberated. A boy turning a wheel forces SODA WATER. roi the gas into the water in the bottles, or the water and carbonate of soda is drawn off thus impregnated into fc:-^s^ Seltzer-water manufactory. bottles and corked down, in the manner so familiar to all. I02 CHEMISTRY. The bottles are made of the shape depicted, so that the bubble of air shall be at the top when the bottle lies down. If it be not kept so, the air will eventually escape, no matter how tightly the cork be put in. The ordinary " soda-water " contains scarcely any soda. It is merely water, chalk, and carbonic acid. The " Gazogene " is made useful for small quantities of soda-water, and is arranged in the following manner. The appearance of it is familiar to all. It consists of a double vessel, into the upper part of which a solution of any kind — wine and water, or even plain water— ^is put, to be saturated with carbonic acid, or "aerated," and into the lower one some carbonate of soda and tartaric acid. A tube leads from this lower to the top of the upper vessel, which screws on and off. By shaking the apparatus when thus charged and screwed together, some of the liquid descends through the tube into the lower vessel and moistens the soda and acid, which therefore act on each other, and cause carbonic acid to be disengaged ; this, rising up through Gazogene. ^^6 tubc (which is perforated with small holes at the upper part), disperses itself through the liquid in small bubbles, and causes sufficient pressure to enable the liquid to absorb it, which therefore effervesces when drawn off by the tap. Carbonic acid can be liquified, and then it is colour- less. In a solid form it resembles snow, and if pressed with the fingers it will blister them. Being very heavy the gas can be poured into a vase, and if there be a light in the receptacle the flame will be immediately extinguished. That even the gas introduced into seltzer-water is CARBONIC ACID GAS. 103 capable of destroying life, the following experiment will prove. Let us place a bird within a glass case as in the Soda-water apparatus. illustration (page 104), and connect the glass with a bottle of seltzer-water or a siphon. As soon as the liquid enters the carbonic acid will ascend, and this, if continued for a long time, would suffocate the bird, which soon begins to develop an appearance of restless- ness, We have already remarked upon the important part taken by this gas in nature, so we need only mention its existence in pits and caves. There are many places in which the vapour is so strong as to render the localities uninhabitable. In the Middle Ages the vapours were attributed to the presence of evil spirits, who were supposed to extinguish miners' lamps, and suffocate people who ventured into the Pouring out the carbonic acid gas. I04 CHEMISTRY, caves. In the Grotto Del Cane there is still an example, and certain caves of Montronge are often filled with the gas. A lighted taper held in the hand will, by its ex- tinction, give the necessary warning. Oxygen and carbon are condensed in carbonic acid, for the gas contains a volume of oxygen equal to its own. If we fill a glass globe, as per illustration (page los), with pure oxygen, and in the globe insert two carbon points, through which we pass a current of electricity, we shall find, after the ex- Experiment with carbonic acid. periment, that if the stop-cock be opened, there is no escape of gas, and yet the mercury does not rise in the tube, so the oxygen absorbed has been replaced by an equal volume of carbonic acid. The other combination of carbon with oxygen is the carbonic oxide (CO), and when a small quantity of oxygen is burnt with it, it gives a blue flame, as on the top of the fire in our ordinary grates. This gas is present in lime kilns, and is a very deadly one. We must now pass rapidly COAL. 105 through the compounds of carbon with hydrogen, merely referring to coal for a moment as we go on. Coal, of which we shall learn more in Mineralogy and Geology, is a combination, mechanical or otherwise, and is the result of the decomposition of vegetable matter in re- ■ mote ages, — the so-called " forests," which were more like the jungles than the woods of the present day. Moss and fern played prominent parts in this great transformation, Experiment showing that carbonic acid contains oxygen and carbon. as we can see in the Irish peat-bogs, where the first steps to the coal measures are taken. The compounds of carbon with hydrogen are important. There is the " light " carburetted hydrogen (CH^), which is usually known as fire-damp in coal mines. It is highly inflammable and dangerous. The safety-lamp invented by Davy is a great protection against it, for as the gas neters it is cooled by the wire, and burns within harmlessly. io6 CHEMISTRY. The explosion warns the miner. " Heavy " carburetted hydrogen possesses double the quantity of carbon (C^H^). It is also explosive vifhen mixed with oxygen. The most useful compound is coal-gas, and though its Temperature reduced by contact with wire. principal function appears to be in some manner super- seded by electricity, " gas " is still too important to be put aside. It can easily be obtained by putting small frag- ments of coal into the bowl of a tobacco-pipe, closing the bowl with clay, and putting it in the fire. Before long the gas will issue from the stem of the pipe, and may either be lighted or col- lected in a bladder. For the use of the " million," however, gas is prepared upon a very large scale, and is divided into three processes — its " forma- tion," " purification," and its " collection " for dis- tribution to consumers. The first process is carried on by means of retorts shown in the illustration above. The first portion of the next figure is a section of a furnace, the other part shows two furnaces from the front. The following is the nr.ode em- Retorts. COAL-GAS. 10/ ployed. The coal is put into retorts fitted to the furnace, so that they are surrounded by the flames, and terminating in a horizontal tube called the hydraulic main, E, which is in its turn connected with a pit or opening for the recep- tion of the tar and ammoniacal liquor, etc., which con- Sectioa. front vie denses from the gas. It then passes up and down a series of tubes in water, called a " condenser," and in this are reservoirs or receptacles for any tar and ammonia that remain. But sulphur is still present, so the gas is carried to the purifying apparatus (D in fig. below), which consists Condens of a large cylindrical vessel air-tight, with an inverted funnel, nearly filled with a mixture of lime and water. The gas bubbles in, and the sulphur unites with the lime, while the gas rises to the top (trays of lime are used when the gas enters from the bottom). The Gasometer, a large io8 CHEMISTRY. vessel closed at the top and open below, dips into a large trough of circular shape. The gasometer is balanced by weights and chains, and may be raised {see illustration). When quite empty the top rests upon the ground, and when the gas enters it is raised to the top of the frame which supports it. We have now our Gasometer full. When the time comes to fill the pipes for lighting purposes, some of the weights are removed, the Gasometer falls down slowly, and forces the gas through the tubes ■ into the main supply to be dis- tributed. About four cubic feet of gas is obtained from every pound of coal. When gas and air become mixed; the mixture is very explosive. In a house where an escape of gas is detected let the windows Gasometer. be opened at the top, and no light introduced for several minutes. Coal-gas 109 It has been calculated that one ton of good coal pro- duces the following : — I Chaldron of coke . . . 12 Gallons of tar . . . . 12 Gallons of ammoniacal liquor 5,900 Cubic feet of gas Loss (water) . , . , weighing 1,494 lbs. „ 135 lbs. „ 100 lbs. „ 291 lbs. I, 220 lbs. Total 2,240 lbs. We can thus estimate the profits of our gas companies at leisure. The analysis of gas made by Professor Bunsen is as under, iri 100 parts. Hydrogen . . Marsh gas . , Carbonic oxide . defiant gas . Bufyline Sulphide of hydrogen Nitrogen Carbonic acid . 45-58 34-90 6-64 4-08 2-38 0'29 2 '46 3-67 Gas, therefore, is very injurious, for it rapidly vitiates the atmosphere it burns in, and is very trying to the eyes, as well as destructive to gilt ornaments. Tar is familiar to all readers, and though unpleasant to handle or to smell, it produces the beautiful aniline dyes. Tar pills are very efficacious for some blood disorders, and will remove pimples, etc., from the face, and cure " boils " eff( ctually. If a dose of five be taken first, in a day or two four, and so on, no second remedy need be applied. We have known cases finally cured, and no recurrence of boils ever ensued after this simple remedy. Tar is one of the results left in the distillation both of wood and coal : in places where wood is plentiful and tar in request, it is produced by burning the wood for that no CHEMISTRY. purpose ; and in some of the pits in which charcoal is produced,' an arrangement is made to collect the tar also. Coal-tar and wood-tar are different in some respects, and are both distilled to procure the naphthas which bear their respective names. From wood-tar creosote is also ex- tracted, and it is this substance which gives the peculiar tarry flavours to provisions, such as ham, bacon, or herrings, cured or preserved by being smoked over wood fires. Tar is used as a sort of paint for covering wood-work and Tar manufactory. cordage when much exposed to wet, v;hich it resists better than anything else at the same price ; but the tar chiefly used for these purposes is that produced by burning fir or deal wood and condensing the tar in a pit below the stack of wood ; it is called Stockholm tar, as it comes chiefly from that place. Carbon only combines with nitrogen under peculiar cir- cumstances. This indirect combination is tei-med cyanogen (CN). It was discovered by Gay-Lussac, and is used for SULPHUR. II I the production of Prussian blue. Hydrocyanide of potas- sium (Prussia acid) is prepared by heating cyanide of potassium with sulphuric acid. It is a deadly poison, and found in peach- stones. Free cyanogen is a gas. The bisulphide of carbon is a colourless, transparent liquid. It will easily dissolve sulphur and phosphorus and several resins. When phosphorus is dissolved in it, it makes a Sulphur furnace. very dangerous " fire," and one difficult to extinguish. We must now leave carbon and its combinations, and come to sulphur. Sulphur is found in a native state in Sicily and many other localities which are volcanic. It is a yellow, solid body, and as it is "f>ver perfectly free from earthy matter. I I 2 CHEMISTRY. it must be purified before it can be used. It possesses neither taste nor smell, and is insoluble in water. Sulphur is purified in a retort, C D, which communicates with- a brick chamber, A. The retort is placed over a furnace, K, and the vapour passes into the chimney through the tube, D, where it condenses into fine powder called "flowers of sulphur'' (brimstone). A valve permits the heated air to pass off, while no exterior air can pass in, for explosions would take place were the heated vapour to meet the atmospheric air. The danger is avoided by putting an air reservoir outside the chimney which is heated by the furnace. The sulphur is drawn out through the aperture, r, when deposited on the floor of the chamber. The sulphur is cast into cylinders and sold. Sulphur is soluble in bisulphide of carbon, and is used as a medical agent. The compounds of sulphur with oxygen form an interesting series. There are two anhydrous oxides (anhydrides), — viz., sulphurous and sulphuric anhydride (SOj and SO3). There are two notable acids formed by the combination with water, sulphurous and sulphuric, and some others, which, as in the case of nitrogen, form a series of multiple proportions, the oxygen being present in an increasing regularity of progression, as follows : — Name of Acid. Chemical Formula. Hypo-sulphurous acid H2SO2 Sulphurous acid HjSO, Sulphuric acid H2S04 Thio-sulphuric, or hypo- sulphuric acid . . H2S2O3 Dithionic acid . . .... HjSsOs Trithionic acid HvSsOs Tetrathionic acid HjSiOe Pcntathionic acid H2S5O5 The last four are termed " polythionic," because the pro- portions of sulphur vary with constant proportions of the other constituents. The sulphurous anhydride mentioned above is produced SULPHURIC ACID. 113 when we burn sulphur in the air, or in oxygen ; it may be obtained in other ways. It is a colourless gas, and when subjected to pressure may be liquified, and crystallized at very low temperature. It was formerly called sulphuric Liquefaction of sulphuric acid. acid. It is a powerful "reducing agent," and a good anti- septic. It dissolves in water, and forms the H^SO now known as sulphurous acid. Sulphuric acid is a most dangerous agent in wicked or inexperienced hands, and ama- teurs should be very careful when dealing with it. It takes the water from the moist air, and from vegetable and animal substances. It carbonizes and destroys all animal tissues. Its discovery is due to Basil Valen- tine, in 1440. He distilled sulphate of iron, or green vitriol, and the result was " oil of vitriol." It is still manufactured in this way in the Hartz district, and the acid passes by retorts into receivers. The earthen retorts, A, are arranged in the furnace as in Retorts and receivers for acid. 114 CHEMISTRY. the illustration, and the receivers, B, containing a little sulphuric acid, are firmly fixed to them. The oily brown product fumes in the air, and is called " fuming sulphuric acid," or Nordhausen acid. Sulphuric acid is very much used in chemical manufactures, and the prices of many necessaries, such as soap, soda, calico, stearin, paper, etc., are in close relationship with the cost and production of sulphur, which also plays an important part in the making „ ,(|l!l]klfMrJJJrfl.im ii-tperimcnt to show the existence of gases in solution. of gunpowder. The manufacture of the acid is carried on in platinum stills. Sulphuretted hydrogen, or the hydric sulphide (HjS), is a colourless and horribly-smelling gas, and arises from putrefying vegetable and animal matter which contains sulphur. The odour of rotten eggs is due to this gas, which is very dangerous when breathed in a pure state in drains, etc. It can be made by treating a sulphide with PHOSPHORUS. 1 I 5 sulphuric acid. It is. capable of precipitating the metals when in solution, and so by its aid we can discover the metallic ingredient if it be present. The gas is soluble in water, and makes its presence known in certain sulphur- springs. The colour imparted to egg-spoons and fish- knives and forks sometimes is due to the presence of metallic sulphides. The solution is called hydro- sulphuric acid. Phosphorus occurs in very small quantities, though in the form of phosphates we are acquainted with it pretty generally, and as such it is absorbed by plants, and is useful in agricultural operations. In our organization — in the brain, the nerves, flesh, and particularly in bones — phosphorus is present, and likewise in all animals. Never- theless it is highly poisonous. It is usually obtained from the calcined bones of mammalia by obtaining phosphoric acid by means of acting upon the bone-ash with sulphuric acid. Phosphorus when pure is colourless, nearly trans- parent, soft, and easily cut. It has a strong affinity for oxygen. It evolves white vapour in atmospheric air, and is luminous ; to this element is attributable the luminosity of bones of decaying animal matter. It should be kept in water, and handled — or indeed not handled but grasped with a proper instrument — carefully. Phosphorus is much used in the manufacture of lucifer matches, and we are all aware of the ghastly appearance and ghostly presentment it gives when rubbed upon the face and hands in the dark. In the ripples of the waves and under the counter of ships at sea, the phosphorescence of the ocean is very marked. In Calais harbour we have frequently noticed it of a very brilliant appearance a.s the mail steamer slowly came to her moorings. This appear- ance is due to the presence of phosphorus in the tiny animalculse of the sea. It is also observable in the female glow-worm, and the " fire-fly." Phosphorus was discovered by Brandt in 1669. Ii6 CHEMISTRY. It forms two compounds with oxygen — phosphorous acid, H,PO^, and phosphoric acid, H PO,. The com- 3 4 pound with hydrogen is well marked as phosphuretted hydro- gen, and is a product of animal and veget- able decomposition. It may frequently be observed in stagnant pools, for when emit- ted it becomes lumi- nous by contact with atmospheric air. There is a very pretty but not altogether safe experiment to be performed when phos- phuretted hydrogen has been prepared in the following manner. Heat small pieces of phosphorus with milk of lime or a solution of caustic potash ; or make a paste of quick- lime and phosphorus, and put into the flask with some quick-lime powdered. Fix a tube to the neck, and let the other end be inserted in a basin of water. (^See illustration, page i i8.) " WILL-O'-THE-WISP. 117 Apply heat; the phosphuretted hydrogen will be given off, and will emerge from the water in the basin in luminous rings of a very beautiful appearance. The greatest care Should be taken in the performance of this very simple ii8 CHEMISTRY. experiment. No water must on any account come in con- tact ivith the mixture in the flask. If even a drop or two find its way in through the bent tube a tremendous explo- sion will result, and then the fire generated will surely prove disastrous. The experiment can be performed in a cheaper and less dangerous fashion by dropping phosphate of lime into the basin. We strongly recommend the latter course to the student unless he has had some practice in the handling of these inflammable substances, and learnt caution by experience. The effect, when the experiment is properly performed is very good, the smoke rising in a succession of coloured rings. Experiment with phospiiuretted hydrogen. Silicon is not found in a free state m nature, but, combined with oxygen, as Silica it constitutes the major portion of our earth, and even occurs in wheat stalks and bones of animals. As flint or quartz (see Mineralogy), it is very plentiful, and in its purest form is known as rock crystal, and approaches the form of carbon known as diamond. When separated from oxygen, silicon is a powder of greyish^brown appearance, and when heated in an atmosphere- of oxygen forms silicic " acid " again, which, however, is not acid to the taste, and is also termed "silica," or "silex." It is fused with great difificulty, but GLASS. 1 1 9 enters into the manufacture of glass in the form of sand. The chemical composition of glass is mixed silicate of potassium or sodium, with silicates of calcium, lead, etc. Ordinary window glass is a mixture of silicates of sodium and calcium ; crown glass contains calcium and silicate of potassium.. Crystal glass is a mixture of the same silicate and lead. Flint glass is of a heavier composition. Glass can be coloured by copper to a gold tinge, blue by cobalt, green by chromium, etc. Glass made on a large scale is composed of the following materials, according to the kind of glass that is required. Flint glass (" crystal ") is very heavy and moderately soft, very white and bright. It is essentially a table-glass, and was used in the construction of the Crystal Palace. Its composition is — pure white sea-sand, 52 parts, potash 14 parts, oxide of lead, 34 parts = 100. Plate Glass. Crown Glass. Green (Botlle) Glass. Parts. Parts.- Parts. Pure white sand. . 55 Fine sand . . . 63 Sea sand . . . 80 Soda 35 Chalk .... 7 Salt 10 Nitre 8 Soda .... 30 Lime .... 10 Lime 2 loo 100 100 The ingredients to be made into glass (of whatever kind it may be) are thoroughly mixed together and thrown from time to time into large crucibles placed in a circle, A A (page 120), in a furnace resting on buttresses, BB, and heated to whiteness by means of a fire in the centre, c, blown by a blowing machine, the tube of which is seen at D. This furnace is shown in perspective in page 120. The ingredients melt and sink down into a clear fluid, throwing up a scum, which is removed. This clear glass in the fused state is kept at a white heat till all air- bubbles have disappeared ; the heat is then lowered to a bright redness, when the glass assumes a consistence and ductility suitable to the purposes of the " blower." 9 I20 CHEMISTRY. Crucibles. Glass blowing requires great care and dexterity, and is done by twirling a hollow rod of iron on one end of which is a globe of melted glass, the workman blowing into the other end all the time. By reheating and twirling a sheet of glass is produced. Plate glass is formed by pouring the molten glass upon a table with raised edges. When cold it is ground with emery powder, and *B then polished by machinery. Many glass articles are cast, or " struck-up," by compression in moulds, and are made to resemble cut-glass, but they are much inferior in appearance. The best are first blown, and afterwards cut and polished. Of whatever kind of glass the article may be, it is so brittle that the slightest blow would break it, a bad quality which is got rid of by a process called " annealing," that is, placing it while quite hot on the floor of an oven, which is allowed to cool very gradually. This slow cooling takes off the brittleness, consequently articles of glass well annealed are very much tougher than others, and will scarcely break in boiling water. The kind generally used for ornamental cutting is flint-glass. Decanters and wine-glasses are therefore made of it ; it is very bright, white, and easily cut. The cutting is performed by means of wheels of different sizes and materials, turned by a treadle as m a common lathe, or by steam power ; some wheels are made of fine sandstone, some of iron, others of tin or copper; the edges of some are square, or round, or sharp. Plate-glass casting -bringing out the pot. SELENIUM. 121 They are used with sand and water, or emery and water, stone wheels with water only. In a soluble form silicic acid is found in springs, and thus enters into the composi- tion of most plants and grasses, while the shells and scales of " infusoria " consist of silica. As silicate of alu- mina, — i.e., clay, — it plays a very important role in our porcelain and pottery works. Boron is found in volcanic districts, in lakes as boracic acid, in combination with Glass flimace (see also page 120 for detail). oxygen. It is a brownish-green, insoluble powder, in a free state, but as boracic acid it is white. It is used to colour fireworks with the beautiful green tints we see. Soda and boracic acid combine to make borax (or biborate of soda). Another and inferior quality of this combination is tinkal, found in Thibet. Borax is much used in art and manufactures, and in glazing porcelain. (Symbol B, Atomic Weight 1 1.) Selenium is a very rare ele- ment. It was found by Berzelius in a sulphuric-acid factory. It is [not found in a free state in nature.. It closely resembles sulphur in its properties. Its union with hydro- Giass-cutting. ggjj produccs a gas, seleniuretted hydrogen, which is even more offensive than sulphuretted hydrogen. (Symbol Se, Atomic Weight 79.) Tellurium is also a rare substance generally found 122 CHEMISTRY. in combination with gold and silver. It is like bismuth, and is lustrous in appearance. Telluretted hydrogen is horrible as a gas. Tellurium, like selenium, sulphur, and oxygen, combines with two atoms of hydrogen. (Symbol Te, Atomic Weight 129.) Arsenic, like tellurium, possesses many attributes of a metal, and on the other hand has some resemblance to phosphorus. Arsenic is sometimes found free, but usually combined with metals, and is reduced from the ores by Casting plate-glass. roasting ; and uniting with oxygen in the air, is known as •' white arsenic." The brilliant greens on papers, etc., contain arsenic, and are poisonous on that account. Arsenic and hydrogen unite (as do sulphur and hydrogen, etc.), and produce a foetid gas of a most deadly quality. This element also unites with sulphur. If poured into a glass containing chlorine it will sparkle and scintillate. (Symbol As, Atomic Weight 75.) Before closing this division, and passing on to a brief METALLOIDS. 123 review of the Metals, we would call attention to a few facts connected with the metalloids we have been consider- ing. Some, we have seen, unite with hydrogen only, as chlorine ; some with two atoms of hydrogen, as oxygen, sulphur, etc., and some with three, as nitrogen and phos- phorus ; some again with four, as carbon and silicon. It The manufacture qt porcelain in China. has been impossible in the pages we have been able to devote to the Metalloids to do more than mention each briefly and incompletely, but the student will find sufficient, we trust, to interest him, and to induce him to search farther, while the general reader will have gathered some few facts to add to his store of interesting knowledge. We now pass on to the Metals. CHAPTER VI.— THE METALS. WHAT METALS ARE CHARACTERISTICS AND GENERAL ■PROPERTIES OF METALS CLASSIFICATION SPECIFIC GRAVITY DESCRIPTIONS. [E have learnt that the elements are divided into metalloids and metals, but the line of demarca- tion is very faint. It is very difficult to define what a metal is, though we can say what it is not. It is indeed impossible to give any absolute defini- tion of a metal, except as " an element which does not unite with hydrogen, or with another metal to form a chemical compound." This definition has been lately given by Mr. Spencer, and we may accept it as the nearest affirmative definition of a metal, though obviously not quite accurate. A metal is usually supposed to be solid, heavy, opaque, ductile, malleable, and tenacious ; to possess good con- ducting powers for heat and electricity, and to exhibit a certain shiny appearance known as " metallic lustre." These are all the conditions, but they are by no means necessary, for very few metals possess them all, and many non-metallic elements possess several. The " alkali " metals are lighter than water ; mercury is a fluid. The opacity of a mass is only in relation to its thickness, for Faraday beat out metals into plates so thin that they became transparent. All metals are not malleable, nor are they ductile. Tin and lead, for example, have veiy THE METALS. 125 little ductility or tenacity, while bismuth and antimony have none at all. Carbon is a much better conductor of electricity than many metals in which such power is ex- tremely varied. Lustre, again, though possessed by metals, is a characteristic of some non-metals. So we see that while we can easily say what is not a metal, we can scarcely define an actual metal, nor depend upon unvary^ ing properties to guide us in our determination. The affinity of metals for oxygen is in an inverse ratio to their specific gravity, as can be ascertained by experi- ment, when the heaviest metal will be the least ready to oxidise. Metals differ in other respects, and thus classification and division become easier. The fusi- bility of metals is of a very wide range, rising from a temperature below zero to the highest heat obtainable in the blow-pipe, and even then in the case of osmium there is a difficulty. While there can be no question that certain elements, iron, copper, gold, silver, etc., are Laminate, metals proper, there are many which border upon the line of demarcation very closely, and as in the case of arsenic even occupy the debatable land. Specific Gravity is the relation which the weight of substance bears to the weight of an equal volume of water, as already pointed out in Phvsics. The specific gravities of the metals vary very much, as will be seen from the table following — water being, as usual, taken as i : — 126 CHEMISTRY. Aluminium , 2"S6 Antimony Arsenic 67 6- Bismuth . 97 Cadmium 8-6 Calcium . I'S Chromium 6'8 Cobalt . 8-9 Copper , 8-9 Gold 19-3 Indium . Ti Iridium . 2I'I Iron 7-8 Lead 113 Lithium . •593 Magnesium 174 Manganese 8- Mercury 13-5 Molybdenum 8-6 Nickel . Osmium . Palladium Platinum Potassium Rhodium Rubidium Ruthenium Silver Sodium . Strontium Thallium . Tin. Titanium Tungsten Uranium Zinc Zircon 8-8 21'4 11-8 21-5 •86s 12'I "■4 lo-s •972 2-5 11-8 7-2 5'3 17-6 18-4 7'i 4'3 Some metals are therefore lighter and some heavier than water. The table underneath gives the approximate fusing points of some of the metals (Centigrade Scale) — (Ice melts at o°.) Platinum* . about isoo° Zinc . . about 400 Gold . „ 1200° Lead . „ 330° Silver . „ 1000° Bismuth „ 26s^ Cast iron 1000-1200° Tin . « 23s' Wrought iron , „ isoo° Sodium » 97= Copper „ I loo" Potassium . „ 6o' Antimony . >, 432° Mercury „ 40= There are some metals which, instead of fusing, — that is, passing from the solid to the liquid state, — go away in vapour. These are volatile metals. Mercury, potassium, and sodium, can be thus distilled. Some — antimony and bismuth for instance, — do not expand with heat, but con- tract (like ice) ; while air pressure has a considerable effect Reauires oxy-liydrogen blow-pipe. ALLOYS. 127 upon the fusing point. Some vaporise at once without hquefying ; others, such as iron, become soft before melting. Alloys are combinations of metals which are used for many purposes, and become harder in union. Amalgams are alloys in which mercury is one constituent. Some of the most useful alloys are under-stated : — Name of Alloy. Aluminium bronze Bell metal . Bronze . . Gun metal . Brass . Dutch metal. Mosaic gold. Ormolu Tombac German silver Britannia metal Solder . Pewter . Type metal . Shot . Gold currency Silver currency Stereotype metal Metals combine Metals „ Metals „ Composition. Copper and aluminium. Copper and tin. Copper and zinc Copper, nickel, and zinc. Antimony and tin. Tin and lead. Lead and antimony (also copper at times). Lead and arsenic. Gold and copper. Silver and copper. Lead, antimony, and bismuth, with chlorine, and produce chlorides, „ sulphur „ „ sulphides, „ oxygen „ „ oxides, and so on. The metals may be classed as follows in divisions : — ., , ^^. „ ,. > Potassium, Sodium, Lithium, Am- Metals of the alkalies . as ^ ^.^„„-,^. ) MONIUM. Metals of the alkaline ) Barium, Calcium, Magnesium, Stron- earths as j tium. •i Aluminium, Cerium, Didymium, Erbium, Metals of the earths . as [ Glucinium, Lanthanum, Terbium, Tho- ) rium, Yttrium, Zirconium. 128 CHEMISTRY. Metals proper — y Iron, Manganese, Cobalt, Nickel, Common Metals . . as | Copper, Bismuth, Lead, Tin, Zinc, ' Chromium, Antimony. 1 Mercury, Silver, Gold, Platinum, Noble Metals ... as [ Palladium, Rhodium, Ruthenium, ) Osmium, Iridium. We cannot attempt an elaborate description of all the metals, but we will endeavour to give a few particulars concerning the important ones, leaving many parts for Mineralogy to supplement and enlarge upon. We .shall therefore mention only the most useful of the metals in this place. We will commence with POTASSIUM. Metals of the Alkalies. Potassium has a bright, almost silvery, appearance, and is so greatly attracted by oxygen that it cannot be kept anywhere if that element be present — not even in water, for combustion will immediately ensue on water ; and in air it is rapidly tarnished. It burns with a beautiful violet colour, and a very pretty experiment may easily be performed by throwing a piece upon a basin of water. The fragment combines with the oxygen of the water, the hydrogen is evolved, and burns, and the potassium vapour gives the gas its purple or violet colour. The metal can be procured by pulverizing carbonate of potas- sium and charcoal, and heating them in an iron retort. The vapour condenses into globules in the receiver, which is surrounded by ice in a wire basket. It must be collected and kept in naphtha, or it would be oxidised. Potassium was first obtained by Sir Humphrey Davy in 1807. Potash is the oxide of potassium, and comes from the " ashes " of wood. The compounds of potassium are numerous, and exist in nature, and by burning plants we can obtain potash (" pearlash "). Nitrate of potassium, or nitre (saltpetre), POTASSIUM. 129 (KNO3), is a very important salt. It is found in the East Indies. It is a constituent of gunpowder, which consists of seventy-five parts of nitre, fifteen of charcoal, and ten of sulphur. The hydrated oxide of potassium, or " caustic potash " (obtained from the carbonate), is much used in soap manufactories. It is called " caustic " from its pro- perty of cauterizing the tissues. Iodide, bromide, and cyanide of potassium, are used in medicine and photography. Soap is made by combining soda (for hard soap), or Preparation of potassium. potash (for soft soap), with oil or tallow. Yellow soap has turpentine, and occasionally palm oil, added. Oils and fats combine with metallic oxides, and oxide of lead with olive oil and resin forms the adhesive plaster with which we are all familiar vi'hen the mixture is spread upon linen. Fats boiled with potash or soda make soaps ; the glycerine is sometimes set free and purified as we have it. Some- times it is retained for glycerine soap. Fancy soap is only common soap coloured. White and brown Windsor are the same soap — in the latter case browned to imitate 130 CHEMISTRY. age ! Soap is quite soluble in spirits, but in ordinary water it is not so greatly soluble, and produces a lather, owing to the lime in the water being present in more or less quantity, to make the water more or less " hard." Sodium is not unlike potassium, not only in appear- ance, but in its attributes ; it can be obtained from the carbonate, as potassium is obtained from its carbonate. Soda is the oxide of sodium, but the most common and useful compound of sodium is the chloride, or common salt, which is found in mines in England, Poland, and elsewhere. Salt may also be obtained by the evaporation of sea water. Rock salt is got at Salz- burg, and the German salt mines and works produce a large quantity. The Carbonate of Soda is manufactured from the chloride of sodium, al- though it can be procured from the salsoda plants by burning. The chloride of sodium is converted into Machine for cutting soap in bars. sulphate, and then ignited with carbonate of lime and charcoal. The soluble carbonate is extracted in warm water, and sold in crystals as soda, or (anhydrous) "soda ash." The large quantity of hydrochloric acid produced in the iirst part of the process is used in the process of making chloride of lime. A few years back, soda was got from Hungary and various other countries where it exists as a natural efflorescence on the shores of some lakes, also by burning sea-weeds, especially the common bladder wrack {Fiicus vesiculosus), the ashes of which were melted into masses, and came to market in various states of purity. The bi-carbonate of soda is obtained by pass- LITHIUM. 131 ing carbonic acid gas over the carbonate crystals. Soda does not attract moisture from the air. It is used in wash- ing, in glass manufactories, in dyeing, soap-making, etc. Sulphate of Soda is "Glauber's Salt"; it is also employed in glass-making. Mixed with sulphuric acid and water, it forms a freezing mixture. Glass, as we have seen, is made with silicic acid (sand), soda, potassa, oxide of lead, and lime, and is an artificial silicate of soda. Lithium is the lightest of metals, and forms the link Soap-boiling house. between alkaline and the alkaline earth metals. The salts are found in many places in solution. The chloride when decomposed by electricity yields the metal. CESIUM and Rubidium require no detailed notice from us. They were first found in the solar spectrum, and resemble potassium. Ammonium is only a conjectural metal. Ammonia, of 132 CHEMISTRY. which we have already treated, is so like a metallic oxide that chemists have come to the conclusion that its com- pounds contain a metallic body, which they have named hypothetically AMMONIUM. It is usually classed amongst the alkaline metals. The salts of ammonia are important, and have already been men- tioned. Muriate (chloride) of ammonia, or sal-ammoniac, is analogous to chloride of sodium and chloride of potas- sium. It is decomposed by Mottled soap-frames. heating it with slakcd lime and then gaseous ammonia is given off. The Metals of the Alkaline Earths. Barium is the first of the four metals we have to notice in this group, and will not detain us long, for it is little known in a free condition. Its most im- portant compound is heavy spar {sulphate of baryta), which, when powdered, is employed as a white paint. The oxide of barium, BaO, is termed baryta. Nitrate of Baryta is used for " green fire," which is made as follows : — Sulphur, twenty parts ; chlorate of potassium, thirty-three parts ; and nitrate of baryta, eighty parts (by weight). Soda furnace. Calcium forms a considerable quantity of our earth's crust. It is the metal of lime, which is the oxide of CHALK. I 3 3 calcium. In a metallic state it possesses no great interest, but its combinations are very important to us. Lime is, of course, familiar to all. It is obtained by evolving the carbonic acid from carbonate of lime (CaO). The properties of this lime are its white appearance, and it develops a considerable amount of heat when mixed with water, combining to make hydrate of lime, or " slaked lime." This soon crumbles into powder, and as a mortar attracts the carbonic acid from the air, by which means it assumes the carbonate and very solid form, which renders it valuable for cement and mortar, which, when mixed with sand, hardens. Caustic lime is used in white- washing, etc. Carbonate of Lime (CaCOj) occurs in nature in various forms, as lime-stone, chalk, marble, etc. Calc-spar (arra- gonite) is colourless, and occurs as crystals. Marble is white (sometimes coloured by metallic oxides), hard, and granular. Chalk is soft and pulverizing. It occurs in mountainous masses, and in the tiniest shells, for carbonate of lime is the main component of the shells of the Crus- tacea, of corals, and of the shell of the egg ; it enters like- wise into the composition of bones, and hence we must regard it as one of the necessary constituents of the food of animals. It is an almost invariable constituent of the waters we meet with in Nature, containing, as they always do, a portion of carbonic acid, which has the power of dissolving carbonate of lime. But when gently warmed, the volatile gas is expelled, and the carbonate of lime is deposited in the form of white incrustations upon the bottom of the vessel, which are particularly observed on the bottoms of tea-kettles, and if the water contains a large quantity of calcareous matter, even our water-bottles and drinking-glasses become covered with a thin film ot car- bonate of lime. These depositions may readily be removed by pouring into the vessels a little dilute hydrochloric acid, 134 CHEMISTRY. or some strong vinegar, which in a short time dissolves the carbonate of lime. Sulphate of Lime (CaSO^ is found in considerable masses, and is commonly known under the name of Gypsum. It occurs either crystallized or granulated, and is of dazzling whiteness ; in the latter form it is termed Alabaster, which is so soft as to admit of being cut with a chisel, and is admirably adapted for various kinds of works of art. Gypsum contains water of crystallization, which is expelled at a gentle heat. But when ignited, ground, and mixed into a paste with water, it acquires the property of entering into chemical combination with it, and forming the original hydrate, which in a short time becomes perfectly solid. Thus it offers to the artist a highly valuable material for preparing the well-known plaster of Paris figures, and by its use the noblest statues of ancient and modern art have now been placed within the reach of all. Gypsum, moreover, has received a valu- able application as manure. In water it is slightly soluble, and imparts to it a disagreeable and somewhat bitterish, earthy taste. It is called " selenite " when transparent. Phosphate of Lime constitutes the principal mass of the bones of animals, and is extensively employed in the pre- paration of phosphorus ; in the form of ground bones it is likewise used as a manure. It appears to belong to those mineral constituents which are essential to the nutrition of animals. It is found in corn and cereals, and used in making bread ; so we derive the phosphorus which is so useful to our system. Chloride of Lime is a white powder smelling of chlorine, and is produced by passing the gas over the hydrate of lime spread on trays for the purpose. It is the well-known "bleaching powder." It is also used as a disinfectant. The Fluoride of Calcium is Derbyshire spar, or " Blue John.'' Fluor spar is generally of a purple hue. We MAGNESIUM. I 3 5 may add that hard water can be softened by adding a Httle powdered lime to it. Magnesium sometimes finds a place with the other metals, for it bears a resemblance to zinc. Magnesium may be prepared by heating its chloride with sodium. Salt is formed, and the metal is procured. It burns very brightly, and forms an oxide of magnesia (MgO). Magne- sium appears in the formation of mountains occasionally. It is ductile and malleable, and may be easily melted. Carbonate of Magnesia, combining with carbonate of lime, form the Dolomite Hills. When pure, the carbonate is a light powder, and when the carbonic acid is taken from it by burning it is called Calcined Magnesia. The Sulphate of Magnesia occurs in sea-water, and in saline springs such as Epsom. It is called " Epsom Salts." Magnesium wire burns brightly, and may be used as an illuminating agent for final scenes in private theatricals. Magnesite will be mentioned among Minerals. Strontium is a rare metal, and is particularly useful in the composition of " red fire." There are the carbonate and sulphate of strontium ; the latter is known as Celesiine, The red fire above referred to can be made as follows, in a dry mixture. Ten parts nitrate of strontia, \\ parts chlorate of potassium, 3 J parts of sulphur, i part sulphide of antimony, and \ part charcoal. Mix well without mois- ture, enclose in touch paper, and burn. A gorgeous crimson fire will result. Metals of the Earths. Aluminium (Aluminum) is like gold in appearance when in alloy with copper, and can be procured from its chloride by decomposition with electricity. It occurs largely in nature in composition with clays and slates. 10 1 36 CHEMISTRY. Its oxide, alumina (Al^Oj), composes a number of mine- rals, and accordingly forms a great mass of the earth. Alumina is present in various forms {see Minerals) in the earth, all of which will be mentioned under Crystallo- graphy and Mineralogy. The other nine metals in this class do not call for special notice. Heavy Metals. Iron, which is the most valuable of all our metals, may fitly head our list. So many useful articles are made of it, that without consideration any one can name twenty. The arts of peace and the glories of war are all produced with the assistance of iron, and its occurrence with coal has rendered us the greatest service, and placed us at the head of nations. It occurs native in meteoric stones. Iron is obtained from certain ores in England and Sweden, and these contain oxygen and iron {see Miner- alogy). We have thus to drive away the former to obtain the latter. This is done by putting the ores in small pieces into a blast furnace (page 137) mixed with lime- stone and coal. The process of severing the metal from its ores is termed smelting, the air supplied to the furnace being warmed, and termed the "hot blast." The "cold blast" is somefhnes used. The ores when dug from the mine are generally stamped into powder, then " roasted," - — that is, made hot, and kept so for some time to drive off water, sulphur, or arsenic, which would prevent the "fluxes" acting properly. The fluxes are substances which will mix with, melt, and separate the matters to be got rid of, the chief being charcoal, coke, and limestone. The ore is then mixed with the flux, and the whole raised to a great heat; as the metal is separated it melts, runs to the bottom of the " smelting furnace," and is drawn off into moulds made of sand ; it is thus cast into short thick bars called "pigs," so we hear of pig-iron, and pig-lead. Iron is HEAVY METALS. 137 smelted from " ironstone," which is mixed with coke and limestone. The heat required to smelt iron is so very great, that a steam-engine is now generally employed to blow the furnace. (Before the invention of the steam- engine, water-mills were used for the same purpose.) The Blast furnace. smelting is conducted in what is called a blast furnace. When the metal has all been " reduced," or melted, and run down to the bottom of the furnace, a hole is made, out of which it runs into the moulds ; this is called "tapping the furnace." 138 CHEMISTRY. Smelting is often confounded with melting, as the names are somewhat alike, but the processes are entirely- different ; in melting, the metal is simply liquefied, in smelting, the metal has to be produced from ores which often have no appearance of containing any, as in the case of iron-stone, which looks like brown clay. The cone of the furnace. A, is lined with fire-bricks, ii, which is encased by a lining, //; outside are more fire- bricks, and then masonry, fn-n ; C is the throat of the fur- General foundry, Woolwich Arsenal. nace ; D the chimney. The lower part, B, is called the boshes. As soon as the ore in the furnace has become ignited the carbon and oxygen unite and form carbonic acid, which escapes, and the metal fuses at last and runs away. The coal and ore are continually added year after year. The glassy scum called " slag " protects the molten iron from oxidation. The metal drawn from the blast furnace is "pig" iron or "cast" iron, and contains carbon. This kind of iron is WIRE DRAWING. 139 used for casting operations, and runs into sand-moulds It contracts very little when cooling. It is hard and brittle. Bar Iron is the almost pure metal. It is remarkably tena- cious, and may be drawn into very fine wire or rolled. But it is not hard enough for tools. It is difficult to fuse, and must be welded by hammering at a red heat. Wire-drawing is per- formed by taking the metal as a bar, and passing it between rollers, which flatten it, and then between a new set, which form cutting edges on the rolled plate, the projections of one set fit- ting into the hollows of the wire rollers. other closely as in the two illustrations on this page. The strips of metal come out at the aperture seen at A, in illustration on next page. These rods are drawn through a series of diminishing holes in a steel plate, occasionally being heated to keep it soft and ductile. When the wire has got to a certain fineness it is attached to a cylinder and drawn away, at the same time being wound round the cylinder over a small fire. Some metals can be drawn much finer than others. Gold wire can be obtained of a " thickness " (or thinness) of only the 5,000th part of an JiJ inch, 550 feet weighing one grain! But Cutting edges. platiuum has exceeded this marvellous thin- ness, and wire the 30,000th part of an inch has been produced. Ductility and malleability are not always fpund in the same metal in proportion. The sizes of" I40 CHEMISTRY. wires are gauged by the instrument shown in the margin. The farther the wire will go into the groove the smaller its " size." Steel contains a certain amount of carbon, generally about I to 2 per cent. Cast steel is prepared from cast iron. Steel from bar-iron has carbon added, and is termed bar-steel. The process is called " cementation," and is carried on by packing the bars of iron in brick- work boxes, with a mixture of salt and soot, or with char- .H^IH-H'-'HHH- - ' 1 1 1 1 1 1 1 1 Wire size. Rollers. Coarse wire-drawing. coal, which is termed " cement." Steel js really a carbide BESSEMER STEEL. 141 of iron, and Mr. Bessemer founded his process of making- steel by blowing out the excess of carbon from the iron, so that the proper amount — 1-$ per cent. — should remain. A brief summary of the Bessemer process may be interesting. If a bar of steel as soft as iron be made red- hot and plunged into cold water, it will become very hard. If it be then gently heated it will become less hard, and is then fitted for surgical instruments. The various shades of steel are carefully watched, — the change of colour being Fine wire-drawing. due to the varying thickness of the oxide ; for we know that when light falls upon very thin films of a substance, — soap-bubbles, for instance, — the light reflected from the under and upper surfaces interfere, and cause colour, which varies with the thickness of the film. These colours in steel correspond to different temperatures, and the " temper " of the steel depends upon the tempera- ture it has reached. The following table extracted from Haydn's " Dictionary of Science " gives the " temper,'' the colour, and the uses of the various kinds of steel. 142 CHEMISTRY. Cent. Fahr. Colour. Uses of Steel. 220° = 430" Faint yellow Lancets. 232° = 450° Pale straw . Best razors and surgical instruments. 243° = 470° Yellow Ordinary razors, pen-knives, etc. 2S4° = 490° Brown Small shears, scissors, cold chisels, etc. 265° = 510° Brown and purple spots "Vxes, pocket-knives, plane-irons, etc. 277° = 530° Purple Table-knives, etc. 288° = 550° Light blue . Swords, watch-springs, etc. 293' = 560° Full blue . Fine saws, daggers, etc. 316° = 600° Dark blue . ^and and pit saws. The Bessemer process transfers the metal into a vessel in which there are tubes, through which air is forced, which produces a much greater heat than a bellows does. Thus in the process the carbon of the iron acts as fuel to main- tain the fusion, and at the same time by the bubbling of the carbonic acid mixes the molten iron thoroughly. During the bubbling up of the whole mass of iron, and the extreme elevation of temperature caused by the union of the carbon of the impure iron with the oxygen of the air, the oxide of iron is formed, and as fast as it forms fuses into a sort of glass ; this unites with the earthy matters of the " impure" iron, and floats on the upper part as a flux, thus ridding the " cast iron" of all its impurities, with no other fuel than that contained in the metal itself, and in the air used. When the flame issuing from the " converter " contracts and changes its colour, then the time is known to have arrived when the iron is " de- carbonked." The amount of carbon necessary is arti- ficially added, ebullition takes place, a flame of carbonic oxide comes out, and the metal is then run into ingots. The compounds of iron which are soluble in water have a peculiar taste called chalybeate (like ink). Many mineral springs are so flavoured, and taste, as the immortal Samuel Weller put it, "like warm flat-irons." Iron is fre- quently used as a medicine to renew the blood globules. OXIDES OF IRON. 143 Protoxide of Iron is known only in combination. Sesqui-Oxide of Iron is "red ironstone." Powdered it is called English rouge, a pigment not altogether foreign to our use. In a pure state it is a remedy for arsenical poisoning, and is really the " rust " upon iron. Bisulphide of Iron is iron pyrites, and is crystalline. Bessemer's process. Chloride of Iron is dissolved from iron with hydro- chloric acid. It is used in medicine. Cyanide of Iron makes, with cyanide of potassium, the well-known prussiate of potash (ferro-cyanide of potas- sium), which, when heated, precipitates Prussian blue (cyanogen and iron). The Sulphate of the Protoxide is known as copperas, or green vitriol, and is applied to the preparation of Prussian blue. 144 CHEMISTRY. Manganese is found extensively, but not in any large quantities, in one place ; iron ore contains it. It is very hard to fuse, and is easily oxidised. The binoxide is used to obtain oxygen, and when treated with potassium and diluted, it becomes the permanganate of potassium, and is used as "Condy's fluid." It readily oxidizes organic matters, and is thus a disinfectant. It cry.stallizes in long, deep, red needles, which are dissolved in water. It is a standard laboratory test. There are other compounds, but in these pages we need not detail them. Cobalt and Nickel occur together. They are hard, brittle, and fusible. The salts of cobalt produce beautiful colours, and the chloride yields an "invisible" or sympa- thetic ink. The oxide of cobalt forms a blue pigment for staining glass which is called " smalt." Nickel is chiefly used in the preparation of German silver and electro- plating. The salts of nickel are green. Nickel is difficult to melt, and always is one of the constituents of meteoric iron, which falls from the sky in aerolites. It is magnetic like cobalt, and is extracted from the ore called kupfer- nickel. A small United-States coin is termed a " nickel." Copper is the next metal we have to notice. It has been known for centuries. It is encountered native in many places. The Cornish copper ore is the copper pyrites. The fumes of the smelting works are very injurious, containing, as they do, arsenic and sulphur. Tiie ground near the works is usually bare of vegetation in consequence of the " smoke." Sheet copper is worked into many domestic utensils, and the alloy with zinc, termed Brass, is both useful and ornamental. Red brass is beaten into thin leaves, and is by some supposed to be "gold leaf"; it is used in decorative work. Bronze is also an alloy of copper, as are gun-metal, bell-metal, etc. LEAD. 1 4 5 Next to silver, copper is the best conductor of electricity we have. It is very hard and tough yet elastic, and possesses malleability and ductility in a high degree. It forms two oxides, and there are several sulphides ; the principal of the latter are found native, and worked as ores. The sulphate of copper is termed blue vitriol, and is used in calico-printing, and from it all the (copper) pigments are derived. It is also used in solution by agriculturists to protect wheat from insects. When copper or its alloys are exposed to air and water, a carbonate of copper forms, which is termed verdigris. All copper salts Native copper. are poisonous; white of eggs is an excellent remedy in such cases of poisoning. Lead is obtained from galena, a sulphide of lead. It is a soft and easily-worked metal. When freshly cut it has quite a bright appearance, which is quickly tarnished. Silver is often present in lead ore, and is extracted by Pattison's process, which consists in the adaptation of the knowledge that lead containing silver becomes solid, after melting, at a lower temperature than lead does when pure. Pure lead therefore solidiiies sooner. One great use of lead is for our domestic water-pipes, 146 CHEMISTRY. which remind us in winter of their presence so disagreeably. Shot is made from lead, and bullets are cast from the same metal. Shot-making is very simple, and before the days of breech-loading guns and cartridges, no doubt many readers have cast bullets in the kitchen and run them into the mould over a basin of water or a box of sand. For sporting purposes lead is mixed with arsenic, and when it Shot tower. is melted it is poured through a sort of sieve (as in the cut) at the top of a high tower. (See pages 146 and 148). The latter illustration gives the section of the shot tower ; A IS the furnace, b is the tank for melting the lead, and the metal is permitted by the workman ate to run through the sieve in fine streams. As the lead falls it congeals into drops, which are received in water below to cool them, TIN. 147 They are, of course, not all round, and must be sorted. This operation is performed by placing them on a board tilted up, and under which are two boxes. The round shot rush over the first holes and drop into the second box, but the uneven ones are caught lagging, and drop into box No. i. They are accordingly sent to the furnace again. The next process is to sort the good shot for size. This is done by sieves — one having holes a little larger than the size of shot required. This sieve passes through it all of the right size and smaller, and keeps the bigger ones. Those that have passed this examination are then put into another sieve, which has holes in it a little smaller than the size of shot wanted. This sieve retains the right shot, and lets the smaller sizes pass, and so on. The shot are sized and numbered, ■ s,^^ glazed by rolling them 'in a ^^ — !-'~T"'^A JL. barrel with graphite, and =---:'JJW 1 then they are ready for use. Bullets are made by ma- .sieve for sizeing shot. chinery by the thousand, and made up into cartridges with great speed. The compounds of lead are also poisonous, and •pro- duce " colic," to which painters are subject. Red lead, or minium, is a compound of the protoxide and the binoxide, and may be found native. The former oxide is litharge ; white lead, or the carbonate of lead^ is a paint, and is easily obtained by passing a stream of carbonic acid into a solu- tion of acetate of lead. It is used as a basis of many paints. Tin is another well-known metal. It is mentioned by Moses. It possesses a silver-like lustre, and is not liable to be oxidised. The only really important ore is called Tinstone, from which the oxygen is separated, and the 148 CHEMISTRY. ^\^\-j— metal remains. Cornwall has extensive tin mines. Tin is malleable and ductile, and can be beaten into /oil or '• silver leaf," or drawn into wire. It prevents oxidation of iron if the latter be covered with it, and for tinning copper vessels for culinary pur- poses. The Romans found tin in Cornwall, and the term "Stanneries" was applied to the courts of justice among the tin miners in Edward the First's time. We have already mentioned the alloys of tin. The oxides of tin, " Stannous " and " Stannic," are useful to dyers. The latter is the tin-stone (SnO^). Sulphide of tin is called " Mosaic gold," and is much used for decorative purposes. Zinc is procured from calamine, or car- bonate of zinc, and blende, or sulphide of zinc. It has for some years been used for many purposes for which lead was once employed, as it is cheap and light. Zinc is a hard metal of a greyish colour, not easily bent, and rather brittle; but when made nearly red-hot, it can be rolled out into sheets or beaten into form by the hammer. Zinc is about six-and-three-quarter times heavier than water. Like many other metals, it is volatile (when heated to a certain extent it passes off into vapour), and the probable reason that it was not known or used of old is that it was lost in the attempt to smelt its ores. Zinc is now obtained by a sort of distillation ; the ores are mixed with the flux in a large earthen crucible or pot. We have already noticed the alloy of zinc with copper (brass), and the use of zinc to galvanize iron by covering !ll:l Secrion of shot tower. CHROMIUM. 149 the latter with a coating of zinc in a bath is somewhat analogous to electro-plating. The metal is largely used as the positive element in galvanic batteries, and for the production of hydrogen in the laboratory. Zinc forms one oxide (ZnO), used for zinc-white. The sulphate of zinc is white vitriol, and the chloride of zinc is an "antiseptic." Certain preparations of the metal are used in medicme, as "ointments" or "'washes," and are of use in inflammation of the eyelids. Preparing lead for bullets. Chromium. This "metallic element" is almost un- known in the metallic state. But although little known, the beautiful colours of its compounds make it a very interesting study. The very name leads one to expect something different to the other metals — chroma, colour. The metal is procured from what is known as chrome- ironstone, a combination of protoxide of iron and sesqui- oxide of chromium (FeOCr,03). By ignition with potas- sium we get chromic acid and chromate of potassium, a: ISO CHEMISTRY. yellow salt which is used to make the other compounds of chromium. The metal is by no means easy to fuse. Sesqui-Oxide of Chromium is a fine green powder em- ployed in painting porcelain. Chromate of Lead is termed " chrome yellow," and in its varieties is employed as a paint. Type-casting Chromate of Mercury is a beautiful vermilion. There are numerous other combinations which need not be men- tioned here. Antimony was discovered by Basil Valentine. The Latin term is Stibium, hence its symbol, Sb. It is very crystalline, and of a peculiar bluish-white tint. It will take fire at a certain high temperature, and can be used for the manufacture of "Bengal Lights," with nitre and ANTIMONY. I 5 I sulphur in the proportions of antimony " one," the others two and three respectively. The compounds of antimony are used in medicine, and are dangerous when taken without advice. They act as emetics if taken in large quantities. Our "tartar emetic" is well known. Antimony, in alloy with lead and a little tin, form the ype metal to which we are indebted for our printing. Type-casting is done by hand, and requires much dexterity. A ladle is dipped into the molten metal, and the mould jerked in to fill it properly, and then the type is removed and the mould shut ready for another type ; and a skilful workman can perform these operations five hundred times in an hour, — rather more than eight times a minute, — producing a type each time ; this has afterwards to be finished off by other hands. The metal of which type is made consists of lead and antimony ; the antimony hardens it and makes it take a sharper impression. The letters are first cut in steel, and from these "dies " the moulds are made in brass, by stamping, and in these the types are cast Stereotype consists of plates of metal taken, by casting, from a forme of type set up for the purpose : an impression was formerly carried on by plaster-of-Paris moulds, but lately what is termed the papier-macM process is adopted. The paper used is now made in England, and the pre- pared sheet is placed upon the type and beaten upon it. Paste is then filled in where there are blanks, and another and thicker sheet of the prepared paper is placed over all, dried, and pressed. When this is properly done the paper is hardened, and preserves an impression of the type set up. The paper mould is then put into an iron box, and molten metal run in. In a very short time a "stereotype" • plate is prepared from the paper, which can be used again if necessary. The metal plate is put on the machine. There are several compounds of antimony, which, I 5 2 CHEMISTRY. though valuable to chemists, would not be very interesting to the majority of readers. We will therefore at once pass to the Noble Metals. The Noble Metals. There are nine metals which rank under the above denomination : — Mercury, Silver, Gold, Platinum, Palla- dium, Rhodium, Ruthenium, Osmium, Iridium. We will confine ourselves chiefly to the first four on the list. Mercury, or Quicksilver, is the first of the metals which remain unaltered by exposure to atmospheric air, and thus are supposed to earn their title of nobility. Mercury is familiar to us in our barometers, etc., and is fluid in ordinary temperatures, though one of the heaviest metals we possess. It is principally obtained from native cinnabar, or sulphide of mercury (vermilion), and the pro- cess of extraction is very easy. Mercury was known to the ancients, and is sometimes found native. In the mines the evil effects of the contact with mercury are apparent This metal forms two oxides, — the black (mercurous) oxide, or sub-oxide (Hg^O), and the red (mercuric) oxide, or red precipitate. The chlorides are two, — the sub- chloride, or calomel, and the perchloride, or corrosive sublimate. The sulphides correspond with the oxides ; the mercuric sulphide has been mentioned. Its crimson colour is apparent in nature, but the Chinese prepare it in a particularly beautiful form. Many amalgams are made with mercury, which is useful in various ways that will at once occur to the reader. Silver is the whitest and most beautiful of metals, and its use for our plate and ornaments is general. It is malleable and ductile, and the best conductor of electricity SILVER. 153 and heat that we have. It is not unfrequently met with in its native state, but more generally it is found in com- bination with gold and mercury, or in lead, copper, and antimony ores. The mines of Peru and Mexico, with other Western States of America, are celebrated — Nevada, Colorado, and Utah in particular. The story of the silver mine would be as interesting as any narrative ever printed. The slavery and the death-roll would equal in horror and in its length the terrible records of war or pestilence. We have no opportunity here to follow it, or its kindred metals with which- it unites, on the sentimental side ; but were the story of silver production written in full, it would be most instructive. Silver is found with lead (galena), which is then smelted. The lead is volatilized, and the silver remains. It is also extracted by the following process, wherein the silver and golden ore is crushed and washed, and quicksilver, salt, and sulphate of copper added, while heat is applied to the mass. From tank to tank the slime flows, and deposits the metals, which are put' into retorts and heated. The mercury flies off ; the silver' and gold remain in bars. In some countries, as in Saxony and South America,- recourse is had to another process, that of amalgamation, which depends on the easy solubility of silver and other metals in mercury. The ore, after being reduced to a fine- powder, is mixed with common salt, and roasted at a low' red heat, whereby any sulphide of silver the ore may contain is converted into chloride. The mixture is then! Native silver. 154 CHEMISTRY. placed, with some water and iron filings, in a barrel which revolves round its axis, and the whole agitated for some time, during which process the chloride of silver becomes reduced to the metallic state. A portion of mercury is then introduced, and the agitation continued. The mer- cury combines with the silver, and the amalgam is then separated by washing. It is afterwards pressed in woollen bags to free it from the greater part of the mercury, and then heated, when the last trace of mercury volatilizes and leaves the silver behind. Nitrate of Silver is obtained when metallic silver is dis- solved in nitric acid. It is known popularly as lunar caustic, and forms the base of " marking inks." Chloride of silver is altered by light, but the iodide of silver is even more rapidly acted on, and is employed in photography. Fulminating silver is oxide of silver' digested in ammonia. It is very dangerous in inexperienced hands. It is also prepared by dissolving silver in nitric acid, and adding alcohol. It cools in crystals. Fulminating mercury is prepared in the same way. Gold is the most valuable of all metals, — the " king of metals," as it was termed by the ancients. It is always found "native," frequently with silver and copper. Quartz is the rock wherein it occurs. From the disintegration of these rocks the gold sands of rivers are formed, and separated from the sands by "washing." In Australia and California "nuggets" are picked up of considerable size. It is a rather soft metal, and, being likewise costly, is never used in an absolutely pure state. Coins and jewel- lery are all alloyed with copper and silver to give them the requisite hardness and durability. Gold is extremely ductile, and very malleable. One grain of gold may be drawn into a wire five hundred feet in length; and the GOLD. I 5 5 metal may be beaten into almost transparent leaves ^o(/ooo of an inch in thickness ! Aqua-regia, a mixture of hydro-chloric and nitric acids, is used to dissolve gold, though free chlorine, or selenic acid individually, will dissolve it. Faraday made many experiments as to the relation of gold to light. {See "Phil. Trans.," 1857, p. 145.) The various uses of gold are so well known that we need not occupy time and space in recording thenr . Gilding can be accomplished by immersing the article in a hot solution of chloride of gold and bicarbonate of potash mixed ; but the electro Native gold. process is that now in use, by which the gold precipitates on the article to be plated. We have already described the process of electro-plating in the case of silvered articles, and we need only mention that electro-gilding is performed very much in the same way. But gilding is also performed in other ways ; one of which, the so-called water gilding, is managed as follows. Gilding with the gold-leaf is merely a mechanical opera- tion, but water-gilding is effected by chemistry. Water-gilding is a process (in which, however, no water is used) for covering the surface of metal with a thin 156 CHEMISTRY. coating of gold ; the best metal for water-gilding is either brass, or a mixture of brass and copper. A mixture of gold and mercury, in the proportion of one part of gold to eight of mercury, is made hot over a fire till they have united ; it is then put into a bag of chamois-leather, and the superfluous mercury pressed out. What remains is called an " amalgam " ; it is soft, and of a greasy nature, so that it can be smeared over any surface with the fingers. The articles to be gilt are made perfectly clean on the surface, and a liquid, made by dissolving mercury in nitric acid (aqua-fortis), is passed over them with a brush made of fine brass wire, called a " scratch-brush." The mercury immediately adheres to the surface of the metal, making it look like silver ; when this is done, a little of the amalgam is rubbed on, and the article evenly covered with it. It is then heated in a charcoal fire till all the mercury evapo- rates, and the brass is left with a coating of gold, which is very dull, but may be burnished with a steel burnisher and made bright iif necessary. In former times articles were inlaid with thin plates of gold, which were placed in hollows made with a graver, and melted in, a little borax being applied between. When a solution of " chloride of gold " is mixed with ether, the ether takes the gold away from the solution, and may be poured off" the top charged with it. " This solution, if applied to polished steel by means of a camel-hair pencil, rapidly evaporates, leaving a film of gold adhering to the steel, which, when burnished with any hard substance, has a very elegant appearance. In this way any ornamental design in gold may be produced, but it is not very durable. The gilt ornaments, scrolls, and mottoes on sword-blades, are sometimes done in this way. Platinum is the heaviest of all metals, gold being next. Platinum is practically infusible, and quite indifferent to reagents. It is therefore very useful in certain manufac- PLATINUM. 157 tories, and in the laboratory. It can be dissolved by aqua-regia. The stills for sulphuric acid are made of platinum, and the metal is used for Russian coinage, but must be very difficult to wor'k on account of its infusible property. In the finely-divided state it forms a gray and very porous mass, which is known as spongy platinum, and pos- sesses the remarkable property of condensing gases within its pores. Hence, when a jet of hydrogen is directed upon a piece of spongy platinum, the heat caused by its con- densation suffices to inflame the gas. This singular power has been applied to the construction of a very beautiful apparatus, known as Dobereiner's lamp, which consists of a glass jar, a, covered by a brass lid, e, which is furnished with a suit- able stop-cock, c, and in connection with a small bell jar, /, in which is suspended, by means of a wire, a cylinder of metallic zinc, z. When required for use, the outer jar is two-thirds filled with a mixture of one part sulphuric acid and four parts water, and the stop-cock opened to allow the escape of atmospheric air, the spongy platinum con- tained in the small brass cylinder, d, being covered by a piece of paper. The stop-cock is then closed, and the bell jar, /, allowed to fill with hydrogen, and after it has been filled and emptied several times, the paper is removed from the platinum and the cock is again opened, when the gas, which escapes first, makes the metal red-hot and finally inflames. This property of platinum is also used in the " Davy " lamp. The remaining metals do not call for detailed notice. In conclusion, we may refer to the following statement, which in general terms gives the properties of the metal •, their oxides and sulphides for ordinary reader^, Dobereiner's lamp. 158 CHEMISTRY. General Classification of the Metals. The metals admit of being really distinguished by the following table, in which they are presented in several groups, according to their peculiar properties, and each distinguished by a particular name : — Metals. CA.) Light Metah. Specific gravity from o'8 to I ; never occur in the uncombined state. (a.) Alkaline Metals. 1. Potassium. 2. Sodium. (Ammonium.) (b.) Metals of the Alkaline Earths. 3. Calcium. 4. Barium. 5. Strontium, Properties of the Oxides. Powerful bases ; posses sing a strong affinity for water, and form with it hydrates. They yield their oxygen to carbon only at a white heat. Powerful bases, which oxidize in the air, and form sulphates ; when treated with acids evolve hydrosulphuric acid. Highly caustic ; powerful bases, separate all other oxides from their com- binations with acids ; are very soluble water, and do not lose their water of hydra- tion at the highest tem- peratures; attract car- bonic acid rapidly from the air. Caustic ; strong bases ; very soluble in water, and dissolve a large quantity of sulphur, wliich is separated on addition of an acid as a white powder, termed milk of sulphur ; they were formerly termed iiver of sulphur. Caustic ; strong bases ; slightly soluble in water ; lose their water of hydration at a mode- rate heat, and power- fully absorb carbonic acid. (c.) Metals of the Earths proper, (6.) Magnesium. (7.) Aluminium. (B.) Heavy Metals. Specific gravity from 5 to 21 ; are found chiefly in combination with oxy gen, and frequently with sulphur and ar- senic ; some are native. Feebly caustic. Not caustic. iWea k bases insolu- ble in water. Feebler bases than the foregoing, some are acids ; insoluble in water, and lose their water of hydration at a moderate heat. Sulphides. Caustic ; strong bases ; dissolve sulphur, and are partly soluble in water, and partly in- soluble. Insoluble in water. Neutral compounds ; in- soluble in water ; anti- mony and several of the rarer metals pro- duce compounds with sulphur, which deport themselves as acids. LIST OF METALS. IS9 Metals. Properties of the (a.) Common Metals. Become oxidized in the air. 8. Iron. 9. Manganese. 10. Cobalt. 11. Nickel. 12. Copper. 13. Bismuth. 14. Lead. 15. Tin. 16. Zinc. 17. Chromium. 18. Antimony. With few .exceptions, are soluble in acids, and, when ignited with car- bon at a red heat, yield their oxygen ; are, for the most part, fusible and non-volatile. (b.) Noble Metals. Unchangeable in the air. 19 Mercury. 20. Silver. 21. Gold. 22. Platinum. Oxides. Those occurring in nature aresomewhatbrass-like in appearance, and are termed pyrites and blendes. Those which are artificially prepared have peculiar colours ; by heat they are con- verted into sulphates. Have more the properties of acids than of bases are decomposed by ignition into oxygen and metal. Sulphides. With the exception of sulphide of mercury, they leave the pure metal when ignited. CHAPTER VII.— ORGANIC CHEMISTRY. RADICALS ACIDS BASES N EUTRALS. : N the introduction to these brief chapters upon Chemistry, we said that the science was divided into two sections, the first section consisting of the simple combinations, and the other o^ compound combinations. The latter being met with chiefly in animal and vegetable matter, as distinguished from dead or inert matter, was termed Organic. This distinction will be seen below. COMBINATIONS OF SIMPLE GROUPS. Inorganic. I. Elements and their Combinations, (i) Non-Metallic. (2) Metallic. II. Peculiar Decompositions of the above, (i) By Electricity. (2; By Light. COMBINATIONS OF COMPOUND GROUPS. Organic I. Compound Radicals and their Combinations. II. Peculiar Decompositions of the above, (i) Spontaneous. (2) Dry Distillation. .Ve have already placed before our readers the elements and their simple combinations, and have incidentally men- tioned the decomposition by electricity and by light. In marvels of Electricity the positive and negative poles RELATION OF ELEMENTS. i6i are explained. Oxygen appears always at the positive pole, potassium at the negative. The other simple bodies vary. Chlorine, in combination with oxygen, is evolved at the negative pole, but when with hydrogen at the posi- tive pole. In the series below each element behaves e\&ctro-negatively to those following it, and &\cztro-positivefy to those above it; and the farther they are apart the stronger their opposite affinities are. Electrical Relation of the Elements. Oxygen. Carbon. Copper. Aluminium. Sulphur. Chromium. Bismuth. Magnesium. Nitrogen. Boron. Lead. Calcium. Chlorine. Antimony. Cobalt. Strontium. Bromine. Silicium. Nickel. Barium. Iodine. Gold. Iron. Sodium. Fluorine. Platinum. Zinc. Potassium. Phosphorus. Mercury. Hydrogen. Arsenic. Silver. Manganese. The importance of these facts to science is unmistak- able, and, indeed, many attempts hafve been made to explain, from the electrical condition of the elements, the nature of chemical affinity, and of chemical phenomena in general. Electrotyping is another instance of decomposition by means of electricity, and respecting decomposition by light we know how powerful the action of the sun's rays is upon plants, and for the evolution of oxygen. The daguerreotype and photographic processes are also in- stances which we have commented upon. So we can pass directly to the consideration of the compound groups. In nearly every complex organic compound we have a relatively simple one of great stability, which is termed the radical, which forms, with other bodies, a compound radical.* In these complex groups we find certain *• Cyanogen, ethyl, and cacodyl, are compound radicals. 1 62 CHEMISTRY. elements generally, — viz., carbon, hydrogen, nitrogen, sul- phur, and phosphorus. Some compounds may consist of two of these, but the majority contain three (hydrogen, oxygen, and carbon). Many have four (carbon, oxygen, hydrogen, and nitrogen), and some more than four, in- cluding phosphorus and sulphur. Others, again, may con- tain chlorine and its relatives, arsenic, etc., in addition. Now we will all admit that in any case in which carbon is present in composition with other simple bodies forming an organic body, and if that body be ignited in the air, it burns and leaves (generally) a black mass. This is a sure test of the presence of carbon, and forms an organic com- pound. Similarly in decomposition nitrogen and sulphur in combination inform us they are present by the odour they give off. We need not go farther into this question of radicals and compound radicals than to state that a compound radical plays the part of an element in com- bination. We iind in alcohol and ether a certain combi- nation termed Ethyl. This "compound radical" occurs in same proportions in ether, chloride of ethyl, iodide of ethyl, etc., as C2H5 ; so it really acts as a simple- body or element, though it is a compound of carbon and hydrogen. A simple radical is easily understood ; it is an element, like potassium, for instance. We may now pass to the organic combinations classified into AciDS, BASES, and INDIF- FERENT, or Neutral, Bodies. I. Acids. There are several well-known organic acids, which we find in fruits and in plants. They are volatile and non- volatile ; acids are sometimes known as " Salts of Hydro- gen." We have a number of acids whose names are familiar to us, — viz., acetic, tartaric, citric, malic, oxalic, tannic, formic, lactic, etc. ACIDS. 163 Acetic acid (HCgH^O^) is a very important one, and is easily found when vegetable juices, which ferm ent, are exposed to the air, or when wood and othe r vegetable matter is subjected to the process of " dry distillation." Vinegar contains acetic acid, which is distilled from wood, as we shall see presently. Vinegar is made abroad by merely permitting wine to get sour ; hence the term Vin-aigre. In England vinegar is made from " wort," of malt which is fermented for a few days, and then put into casks, the bung-holes of which are left open for several vinegar ground. weeks, until the contents have become quite sour. The liquid is then cleared by isinglass. The vinegar of com- merce contains about 6 per cent, of pure acetic acid, and some spirit, some colouring matter, and, of course, water. Wood vinegar (pyroligneous acid) is used for pickles. The ordinary vinegar when distilled is called white vinegar, and it may also be obtained from fruits, such as goose- berries or raspberries. Acetic acid, or " wood vinegar/' is prepared as follows ; 1 64 CHEMISTRY. . There are some large iron cylinders set in brickwork over furnaces, and these cylinders have each a tube leading to a main pipe in which the liquid is received for conden- sation. The cylinders, which contain about seven or eight hundredweight, are filled with logs of wood, either oak, beech, birch, or ash, the door is closely fastened, and the joints smeared with clay ; the fires are now lighted and kept up all day, till the cylinders are red-hot ; at night they are allowed to cool. In the morning, the charcoal, into which the wood is now converted, is withdrawn, and a fresh charge supplied ; it is then found that Boiler or copper. about thirty or forty gallons of liquid has condensed in the main tube from each cylinder, the remainder being charcoal and gases which pass off; the liquid is acid, brown, and very offensive, and contains , acetic acid, tar, and several other ingredients, among which may be named creo- sote ; it is from this source all the creosote, for the cure of toothache, is ob- tained. To purify this liquid it is first distilled, and this separates much of the tar ; it is then mixed with lime, evaporated to vinegar-cooling process. dryness, and heated to expel the remaining tar and other impurities ; it is next mixed with sulphate of soda and water, and the whole stirred together ; the soda, now in CITRIC ACID. 165 union with the acetic acid, is washed out from the lime and strained quite clear ; it is afterwards evaporated till it crystallises, and vitriol (sulphuric acid) then added; finally the acetic acid is distilled over, and the sulphuric acid left in union with the soda, forming sulphate of soda, to be used in a similar process for the next batch of acid. The acetic acid is now quite colourless, transparent, and very sour, possessing a fragrant smell. This is not pure acetic acid, but contains a considerable quantity of water. The acetic acid of commerce, mixed with seven times its bulk of water, forms an acid of about the strength of malt vinegar, perfectly wholesome, and agreeable as a condiment. Pure acetic acid may be made by mixing dry acetate of potash with oil of vitriol in a retort, and distilling the acetic acid into a very cold receiver ; this, when flavoured with various volatile oils, forms the aromatic vinegar sold by druggists. It is a very strong acid, and if applied to the skin will quickly blister it. Acetate of lead, or sugar of lead, is obtained by dis- solving oxide of lead in vinegar. A solution of this salt makes the goulard water so familiar to all. Acetate of lead is highly poisonous. Acetate of copper is verdigris, and poisonous. Other acetates are used in medicine. We may pass quickly over some other acids. They, arc as follows: — Tartaric Acid (C^H^Og) is contained in grape juice, and crystallizes in tabular form. The purified powdered salt is creani of Tartar. Citric Acid (CsHgO^) is found native in citrons and lemons, as well as in currants and other fruits. It is an excellent anti-scorbutic. 1 66 CHEMISTRY. Malic Acid (C^HjOj) is found chiefly in apples, as its name denotes {malum, an apple). It is prepared from mountain-ash berries. Oxalic Acid (C^H.O^). If we heat sugar with nitric acid we shall procure this acid. It is found in sorrel plants. Tannic Acid (Q^N^.O^^). It is assumed that all Tan-yard and pits. vegetables with an astringent taste contain this acid. Tannin is known for its astringent qualities. The name given to this acid is derived from the fact that it possesses a property of forming an insoluble compound with water, known as leather. Tanning is the term employed. Tannin is found in many vegetable substances, but oak bark is usually employed, being the cheapest. The " pelts " hides or skins, have first to be freed from all fat or hair by TANNIC ACID. 167 scraping, and afterwards soaking them in lime and water. Then they are placed in the tan-pit between layers of the bark, water is pumped in, and the hides remain for weeks, occasionally being moved from pit to pit, or relaid, so as to give all an equal proportion of pressure, etc. The longer the leather is tanned — it may be a year — the better it wears. Skins for gloves and binding are tanned with " sumach," or alum and salt. Sometimes the leather is split by machinery for fine working. Parchment is prepared from the skins of asses, sheep, goats, and calves, which are cleaned, and rubbed smooth with pumice stone. Tannic acid, with oxide of iron, produces Ink, for the gall-nut con- tains a quantity of the acid. All the .black inks in use generally are composed of green vitriol (sulphate of iron) in union with some astrin- gent vegetable matter ; the best is the gall-nut, although, for cheap- ness, logwood and oak bark have each been used. An excellent black ink may be made by putting into a Unhairing .he hide. gallon stone bottle twelve ounces of bruised galls, six ounces of green vitriol, and six of common gum, and filling up the bottle with rain water ; this should be kept three or four weeks before using, shaking the bottle from time to time. Blue ink has lately been much used ; it is made by dissolving newly-formed Prussian blue in a solution of oxalic acid. To make it, dissolve some yellow prussiate of potash in water in one vessel, and some sulphate of iron in another, adding a few drops of nitric acid to the sulphate of iron ; now mix the two liquids, and a magnificent blue colour will appear, in the form of a light sediment ; this is 12 1 68 CHEMISTRY. to be put upon a paper filter, and well washed by pouring over it warm water, and allowing it to run through ; a warm solution of oxalic acid should now be mixed with it, and the Prussian blue will dissolve into a bright blue ink. Red ink is made by boiling chips or raspings of Brazil wood in vinegar, and adding a little alum and gum ; it keeps well, and is of a good colour. A red ink of more beautiful appearance, but not so durable, may be made by dissolving a few grains of carmine in two or three tea- spoonfuls of spirit of hartshorn. Drying rooms for hides. Marking ink is made by dissolving nitrate of silver in water, and then adding some solution of ammonia, a little gum water, and some Indian ink to colour it. Printers' ink is made by grinding drying oil with lamp-black. The powdered gall-nut is an excellent test for iron in water. It will turn violet if any iron be present. Formic Acid (C H,0 J is the caustic means of defence employed by ants, hence the term formic. It can be artificially prepared by distilling a mixture of sugar, binoxide of manganese, and sulphuric acid. On the skin it will raise blisters. BASES. 1 09 Lactic Acid (CgH^Oj) is present in vegetable and animal substances. Sour whey contains it, and the presence of the acid in the whey accounts for its power of removing stains from table-linen. When what is called " lactic fermentation " occurs, milk is said to be " turned." II. Bases. The definition of a base is not easy. We have de- scribed bases as substances which, combining with acids, form salts, but the definition of a base is as unsatisfactory as that of acid or salt. All vegetable bases contain nitro- gen, are usually very bitter, possess no smell or colour, and are insoluble in water. They are usually strong poisons, but very useful in medicine. The most important are the following bases : — Quinine is contained in the cinchona (yellow) bark. One hundred parts of the bark have been calculated to yield three of quinine. Morphine is the poisonous base of opium, which is the juice of the poppy, and is prepared chiefly in India and China. Nicotine is the active principle of tobacco, and varies in quantity in different tobaccos. Havannah tobacco possesses the least. It is a powerful poison, very oily, volatile, and inflammable. CONIA is prepared from the hemlock. It is fluid and volatile. It is also a deadly poison, and paralyses the spine directly. Strychnine is found in poisonous trees, particularly I70 CHEMISTRY. Hemlock. in the nux-vomica seeds of Coromandel. It produces lock- jaw and paralysis. There is no antidote for strychnine ; emetics are the only remedy. The above are chiefly remarkable for their uses in medicine, and in consequence of their highly poison- ous character are best left alone by unpractised hands. A German chemist, named Ser- turner, was the first to extract the active principle from Opium. The question of opium importation has lately been attracting much attention, and the opinions con- cerning its use are divided. Probably in moderation, and when used by ordinary people (not demoralized creatures), it does little harm. Opium is the juice of the "common" poppy, and de- rives its name from the Greek opos, juice. The plant is cultivated in India, Persia, and Turkey. After the poppy has flowered the natives go round, and with a sharp instrument wound, or puncture, every poppy head. This is done very early in the morning, and under the influence of the sun during the day the juice oozes out. Next morning the drops are scraped off The Poppy. STARCa. i;t The juice is then placed in pots, dried, and sent for export. The "construction" of opium is very complicated, for it contains a number of ingredients, the most important being morphia, narcotine, meconic acid, and codeia. It is to the first-named constituent that the somnolent effect of opium is due. III. Indifferent Substances. There are a great number of so-called "indifferent" sub- stances to which we cannot be indifferent. Such bodies as these have neither acid nor basic properties, and stand no comparison with salts. They are of great importance, forming, as they do, the principal nutriment of animals. Some contain nitrogen, some do not ; they may therefore be divided into nitrogenous and non-nitrogenous sub- stances ; the former for solid portions of the body, the latter for warmth. We will take the latter first, and speak of some of them — such as starch, gum, sugar, etc. Starch is found in the roots of grain, in the potato, dahlia, artichoke, etc., and by crushing the parts of the plant, and washing them, the starch can be collected as a sediment. In cold water and in spirits of wine starch is insoluble. The various kinds of starch usually take their names from the plants whence they come. Arrowroot is obtained from the West Indian plant Maranta Arundinacea. Cassava and tapioca are from the manioc ; sago, from the sago palm ; wheat starch, and potato starch are other examples. If starch be baked in an oven at a temperature of about 300° it becomes, to a great extent, soluble in cold water, forming what is called "British gum"; this is largely used I 7 2 CHEMISTRY. for calico printing and other purposes ; if boiled in water under great pressure, so that the temperature can be raised to the same degree, it is also changed into an adhesive sort of gum, " mucilage " ; this is the substance made use of by the government officials to spread over the backs of postage and receipt stamps to make them adhere. The starch of grain, during germination, or growth, contains Plantation of sugar-canes. diastase, which converts the starch into gum and sugar ; the same effect can be produced by heating starch with diluted sulphuric acid. Gum found in plants is chiefly procured from the Mimosa trees, from which it flows in drops, and is called Gum Arabic. There are other so-called " gums," but this is the one generally referred to. SUGAR. 173 Sugar exists in fruits, roots, and in the stalks of plants, in the juice of the cane, maple, and beet-root particularly. The canes are crushed, the juice is clarified with lime to prevent fermentation, and the liquid is evaporated. It is then granulated and cleared from the molasses. Sugar, when heated, becomes dark, and is called " caramel." It is used for colouring brandy, and gives much diiificulty to the sugar refiners. Sugar refining is conducted as follows. The raw (brown) li ^«_.. o N THE PRAXINOSCOPE. 83 substitution, not with the objects themselves, but with their virtual images. He then contrived the arrangement which we will now describe. A plane mirror, ab, is placed at a certam distance from an object, CD, and the virtual image M. Raynaud's Praxinoscope. will be seen at c'd'. If we then turn the plane mirror and object towards the point, o. letting BE and DF be their new positions, the image will be at c"d". Its axis, o, will not be displaced. In the positions, A B and c D, first occupied by the plane mirror and the object, we now place another mirror and object. Let us imagine the eye placed at M. 84 OPTICAL ILLUSIONS. Half of the first object will be seen at Od", and half of the second at o c'. If we continue the rotation of the instrument, we shall soon have mirror No. 2 at tt', and object No. 2 at SS'. At the same moment the image of object No. 2 will be seen entirely at C"'d"'. Mirror No. 2 and its object will soon after be at BE and DF. If we then imagine another mirror and its corresponding object at AB and CD, the same succession of phenomena will be reproduced. This experiment therefore shows that a series M Detail of the Pi ■axinoscope. of objects placed on the perimeter of a polygon will be seen successively at the centre, if the plane mirrors are placed on a concentric polygon, the '' apotheme " of which will be less by one-half, and which will be carried on by the same movement. In its practical form, M. Reynaud's apparatus consists of a polygonal or simply circular box (for the polygon may be replaced by a circle without the principle or result being changed), in the centre of which is placed a prism of exactly half a diameter less, the surface of which is covered with plane mirrors. A strip PRAXINOSCOPE THEATRE. 85 of cardboard bearing a number of designs ot the same object, portrayed in different phases of action, is placed in the interior of the circular rim of the box, so that each position corresponds to a plate of the glass prism. A moderate movement of rotation given to the apparatus, which is raised on a central pivot, suffices to produce the subtitution of the figures, and the animated object is reflected on the centre of the glass prism with remark- able brightness, clearness, and delicacy of movement. Constructed in this manner, the Praxinoscope forms an optical toy both interesting and amusing. In the evening, a lamp placed on a support ad hoc, in the centre of the apparatus, suffices to light it up very clearly, and a number of persons may conveniently assemble round it, and witness the effects produced. Besides the attractions offered by the animated scenes of the Praxinoscope, the apparatus may also be made the object of useful applications in the study of optics. It permits an object, a drawing, or a colour, to be substituted instantaneously in experiments on secondary or subjective images, etc., on the contrast of colours or the persistence of impressions, etc. We can also make what is called a synthesis of movevients by placing before the prism a series of diagrams of natural objects by means of photography, M. Reynaud has already arranged an apparatus which exhibits in the largest dimensions the animated reflection of the Praxinoscope, and which lends itself to the demonstra- tion of curious effects before a numerous auditory. The ingenious inventor has recently contrived also a very curious improvement in the original apparatus In the Praxinoscope Theatre he has succeeded in producing truly ornamental tableaux, as on a small Lilliputian stage, in the centre of which the principal object moves with startling effect. To obtain this result, M. Reynaud commences by cutting out in black paper the different figures, the whole of which 7 66 OPTICAL ILLUSIONS. M. reynaud's theatre. 87 will form an object animated by the rotation given to the Praxinoscope. To supply the decorations, he arranges on the black foundation the image of an appropriate coloured design by means of a piece of glass. It is well known that transparent glass possesses the property of giving a reflection of the objects on the nearest side as well as on the farthest. ^We may recall the applications of this optical effect in theatres, and also in courses of physics, under the title of impalpable spectres. It is also by reflection on thin, transparent glass, that M. Reynaud produces the image of the ornamentations in the Praxinoscope Theatre. The decorations are really placed in the lid, which is held by a hook in a vertical positon, thus forming the front side of the apparatus. In this side a rectangular opening is made, through which the spectator (using both eyes) perceives at the same time the animated reflection of the Praxinoscope, and the immovable image of the decorations reflected in the transparent glass. The position of the latter and its distance from the coloured decorations are arranged so that the reflection is thrown behind the moving figure, which consequently appears in strong relief against the back- ground, the effect produced being very striking. It is evident that to change the decorations it is only necessary to place in succession on a slide the different chromos representing landscapes, buildings, the interior of a circus, etc. It is easy to choose an arrangement suitable for each of the moving figures placed in the Praxinoscope. By this clever and entirely novel optical combination, the mechanism of the contrivance is entirely lost sight of, leaving only the effect produced by the animated figures, which fulfil their different movements on the little stage. The Praxinoscope Theatre can also be used as well in the evening as in the daytime. By daylight it is sufficient to place it before a window, and in the evening the same effects may be produced, perhaps in even a more striking 88 OPTICAL ILLUSIONS. manner, by simply placing a lamp on the stand, with a small plated reflector, and a lamp-shade. The illusion produced by this scentific plaything is very complete and curious, and M. Reynaud cannot be too much commended The Dazzling Top for so cleverly applying his knowledge of physics in the construction of an apparatus which is at the same time both an optical instrument and a charming source of amusement. Amongst the toys founded upon the persistency pf impressions upon the retina we may instance the " Dazzling TJte DAZZLING top. 89 Top." This remarkable invention is quite worthy of a place in every cabinet, and is an ingenious specimen of a perfected Helmholtz top. It is a metallic toy put in motion by means of a cord wound round a groove. The axis is hollow, admits a metallic stem, and fits into a handle which is held in the hand. The top is placed upon a little cup in an upright portion, and it is then set spinning in the usual way with the cord. The stem and handle are then withdrawn, and as the top will continue to spin for a long time, discs and various out- line shapes can be fixed upon it, and various objects "will be shadowed thereon. Cups, bowls, candlesticks, and jugs can be seen plainly revolving as the top carries the wire representation in outline rapidly past the eyes. Coloured cardboard can be worked into various patterns, and much amusement will be created amongst children and young people. CHAPTER VL— OPTICAL ILLUSIONS. (Continued.) EXPERIMENTS THE TALKING HEAD GHOST ILLUSIONS. f---^—^ HE enumeration of optical illusions is so con- siderable that we have no intention of describing them all, and we merely cite a few other examples. The following facts have been communicated to us by M. Nachet : — When examining alg^ under the microscope, we notice the spaces which separate the streaks ornamenting the silicious covering of these curious organisms, and it is explained that they are formed by hexagons visible only when we examine the object with a powerful microscope. " For a long time," says M. Nachet, " I occupied myself with the examination of the hexagonal appearance of the points constituting the streaks. Why should these hexagons show themselves, and how could they be other than the visible base of small pyramids piled very closely one on the other ; and if this were the case, why were not the points of the little pyramids visible .? Or, was the structure before me analogous to that of the eyes of insects 1 Then the carapace would be but a surface of perforated polygonal openings. This latter hypothesis was attractive enough, and would have explained many things ; but some careful observations with very powerful object-classes, quite free from blemishes, had shown me that these hexagons had round points, contrary to the MICROGRAPHS. 9 1 descriptions of micrographs. These observations, cor- roborated by the micrographic photographs of Lackerbauer, the much regretted designer, and by Colonels Woodward Hexagonal appearance formed by circles joined together. and Washington, left not the slightest doubt that it was necessary to discover why the eye persistently saw hexagons where there were circles. To elucidate this point, it was Another figure of the same kind. necessary to find some means of reproducing artificially what nature has accomplished with so much precision on the surfaces of algse. After many fruitless attempts, I decided on making a trial of a stereotype plate covered with dots arranged in quincunxes, very close together. 92 OPTICAL ILLUSIONS. The result was more successful than I had hoped ; the effect produced is exactly that of the arrangement of the so-called hexagons of the most beautiful of the alga:, the Pleiirosigma angulata. If these stereotypes are examined with one eye only, we shall be immediately convinced that we have to do with hexagonal polygons." It is useless to give any long exposition of a figure so clearly explanatory; it is simply an effect of the contrast and opposition of the black and white in the sensation of the retina. This effect is particularly striking with the figure below, a negative photograph heliographically engraved according to the Third figure. previous one. In this the white points seem to destroy the black spaces, and to approach each other tangentially, and the irradiation is so intense that the white circles appear much larger than the black of the former one, although of the same diameter. There are in these facts many points which may interest not only students of micrography, but also artists. As to the algae, the origin of this investiga- tion, it remains to be discovered if these circles which cover their silicious carapace arc the projection of small hemispheres, or the section of openings made in the thick covering. Certain experiments, however, seem to prove that they are hemispheres, and the theory is also con- MR. THOMPSON'S APPARATUS. 93 firmed by a microscopic photograph from Lackerbauer's collection, magnified 3,000 diameters, in which a black central point is seen in the centre of each circle, a certain reflection of the luminous source reproduced in the focus of each of the small demi-spheres which constitute the ornament of the algse. The microscope, which has pro- gressively shown first the streaks, then the hexagons, and then the round points, will surely clear up the point some day or other. Mr. Thompson's optical illusion. Give a circular movement to these figures, and the circleswill appear to turn round. Mr. Silvanus P. Thompson, Professor of Physics at University College, Bristol, has recently presented the French Society of Physical Science with a curious example of optical illusion, the true cause of which is not clearly known, but which we may compare with other facts made known some time ago, of which no precise explanation has been given. Let us first consider in what the effect discovered by Mr. S. P. Thompson consists, according to the description that has been given of it by M. C. M. Gariel ; the illustrations here given will also allow of our verifying the truth of the statements. 94 OPTICAL ILLUSIONS. The first illustration consists of a series of concentric circles of about the width of a millimetre, separated by white intervals of the same size. These dimensions are not absolute ; they vary with the distance, and may even be a few inches in width if it is desired to show the phenomenon to a rather numerous auditory. If we hold the design in the hand, and give it a twirl by a little Another figure of Mr. Thompson's. The different circles appear to turn round if we give the design a rotating movement. movement of the wrist, the circle appears to turn round its centre, and the rotation is in the same direction, and is equally swift ; that is to say, the circle appears to accomplish a complete turn, whilst the cardboard really accomplishes one in the same direction. For the second effect we draw a dark circle, in the interior of which are placed a number of indentations at regular intervals. Operating in the same manner as described above, this notched wheel appears to turn round its centre, but this RETINA IMPRESSIONS. 95 time in a different direction from the real movement. In this, however, as in the other design, the effect is more satisfactory if we do not look directly at it ; the movements also are particularly striking in combinations such as that represented on page 94, in which the multiplicity of circles does not allow us to fix one specially. We may add that the same effects may be obtained with eccentric wheels, or even with other curves than circles. By means of a photograph on glass, Mr. Thompson has been able to reflect these designs on a screen where they were obtained on a large scale ; a circular movement was communicated to the photographic plate, so that the design moved in a circular manner on the screen, and in this case also there existed the illusion that every circle seemed turning round its centre. And what is the explanation of these curious effects ? Mr. Thompson does not believe (and we share his opinion) that the faculty possessed by the retina of preserving images during a certain time {persistence of impressions on the retina) can entirely explain these phenomena. Without desiring to formulate a decided theory, Mr. Thompson is of opinion that we may class these facts with others which have been known for some time, and that perhaps it is necessary to attribute to the eye some new faculty which may explain the whole at once. Brewster and Adams have described phenomena which are equally curious, the principal of which we will de- scribe, adding also some analogous investigations due to Mr. Thompson. The result seems to be that there exists in the eye a badly-defined purpose of nature, which in a certain way compe7isates (Brewster) for the real pheno- menon, because it has a contrary effect, which will con- tinue for some time after the cessation of the phenomena, and which gives by itself a sensation contrary to that which the real movement would have produced. Thus, 96 OPTICAL ILI,USIONS. after having fixed our eyes for two or three minutes on a rushing waterfall, if we suddenly turn our glance on the adjacent rocks, the latter appear to move from top to bottom. It is not a question here of the effect of the relative movement to be observed on regarding simul- taneously the falling water and the rocks ; if one can succeed in abstracting oneself to such an extent that the water appears motionless, the rocks appear to take a contrary movement. In the phenomenon we describe Experiment on complementary colours. there is no simultaneous comparison , the eyes are turned successively first on the water, and then on the rocks. In a rapid river, such as the Rhine above the fall at Schaffhausen, the stream is not equally swift in every part, and the current is noticeably more rapid in the middle of the river than near the banks. If we look fixedly at the centre of the stream, and then suddenly turn our eyes towards the banks, it will appear as though the river were flowing back towards its source. This kind of compensation does not only produce an apparent THE "DARK SPOT." 97 displacement, but also changes in size. When travelling at great speed in a railway train, the objects of the surrounding country as one flies by them gradually appear smaller and smaller. If, when this occurs, we suddenly remove our eyes to the interior of the railway carriage, and fix them on immovable objects, such as the sides of the compartment, or the faces of our travelling com- panions, the images on the retina will really preserve the same size, and yet the objects will appear larger. Such are some of the interesting facts among those discovered by Mr. Thompson; and though we do not intend to push the inquiry further, we think it may not be without interest Design for experiment of the ptmchtin ctEciim. to describe here another illusion of that organ whose pro- perties are in every way so curious and remarkable. Another experiment to show the existence of impres- sions received by the retina can be made with the figure on page 96. If the gaze be fixed upon the dark spot in the centre of the white figure for about half a minute, and the eyes then directed to the ceiling, or a sheet of white paper, the white figure will be reproduced in black. This result is based upon the principle of complementary colours. A red design, for instance, will be reproduced in green. There is a dark spot in every human eye — ^that is, a spot which is insensible to light. The eye is generally regarded as a perfect instrument, but it is not yet so by any means. One of our great philosophers remarked that 98 OPTICAL ILLUSIONS. if an instrument were sent home to him so full of errors he would feel justified in returning it to the optician. But the eye has its dark place, the ptincUun cceciivi, and it can be discovered by covering the left eye with the hand, and holding the present page at arm's length with the other. An optical illusion. Then fix the gaze on the small cross in the picture, and bring the book close up. At a little distance the white ball will disappear from the page. The illustration shows us a very curious optical ilhision, and one very easy to practise. Roll up a sheet of paper, and look through it» as through a telescope, with the DIVIDED TELESCOPE. 99 right eye, keeping both eyes open. Then place the left hand open palm towards you against the roll of paper, you will then appear to be looking through a hole in your left hand-. Sometimes the effect is produced without holding up the other hand to the roll, as shown on page 98. Among optical illusions there are a great number that may be produced by means of mirrors. The divided telescope is an example. The apparatus, raised on a firm stand, allows of one apparently seeing an object through a stone or other opaque object, as shown in the cut above. lOO OPTICAL ILLUSIONS. The illustration shows the arrangement of the apparatus. The observer, looking through it, plainly perceives the object through the glass ; the image is reflected four times before reaching his eye, by means of small mirrors concealed in the instrument. Cylindrical Mirror and Anamorphosis. Convex or concave mirrors distort images in a singular manner, and produce very interesting effects. Anamorphoses constitute particular objects belonging specially to the class of experiments relating to cylindrical mirrors. They are images made according to determined rules, but so dis- ANAMORPHOUS DESIGNS. lOI torted that when regarding them fixedly we can only distinguish confused strokes. When they are seen reflected in the curved mirrors, they present, on the contrary, a perfectly regular appearance. The illustration exhibits an Anamorphosis made, by a cylindrical mirror. It will be seen that the confused image of the horizontal paper is reflected in the cylindrical mirror, producing the figure of a juggler. It is easy to contrive similar designs one's-self ; Anamorphous design for the ten of hearts. and conical mirrors may also be employed which produce particular effects of a no less interesting kind. The next illustration is of a set of figures which -in a cylindrical mirror look like the ten of hearts. One of the most remarkable applications of mirrors in amusing experiments is undoubtedly that of the severed and talking head. A few years back this trick obtained considerable success in Paris and a number of other towns. The spectators beheld a small space set apart, in which I02 OPTICAL ILLUSIONS. / THE TALKING HEAD. I03 was placed a table on three legs ; on this table was a human head, placed in cloth on a dish. The head moved ,its eyes and spoke ; it evidently belonged to a man whose body was completely hidden. The spectators thought they saw an empty space beneath the table, but the body of the individual who was really seated there was concealed by two glasses placed at an inclination of 45° to the walls on the right and left. The whole was arranged in such a manner that the reflection of the walls coincided with the visible part of the wall at the back of the room. The three walls were painted in one colour, and a' subdued light increased the illusion, the effect of which was remarkable. The spectres designed by Robin also attracted con- siderable public attention within recent times. They were Images formed by the medium of transparent glass. Glass panes often produce the phenomenon of spectres. In the evening, when it is dark out of doors, it is easy to prove that the reflection of objects in a lighted room can be reproduced behind the window panes by reason of the darkness outside.' If we approach the window pane, we see also the real objects outside, a balcony, tree, etc. These real objects mingle with the reflected image, and combine to produce very curious effects. In i this way Mr. Robin has contrived the effects of the theatre. He throws on the stage the reflection of a person dressed as a Zouave, and he himself, armed with a sabre, stabs the spectre through the body, A great number of other singular effects have been obtained in the same manner. Pepper's Ghost was managed in this way. Within recent times, images produced in a similar way have been utilized to facilitate the study of drawing. A piece of glass is fixed vertically on a black board. A model to copy from is placed on one side of the piece I04 OPTICAL ILLUSIONS. DRAWING BY REFLECTION. I05 of glass, and is arranged so fhnt- th^ ■ 1 obliquely through the glass and wVn ^.''""'/^y P^^^^^ r *.u J ■ s'ass, and we perceive the reflecfinn of the design very clearly on the other side. It is tLn very eas.ly reproduced with a pencil on a sheet o white paper by tracing the outlines. ^^ Drawing by reflection. CHAPTER VII.— OPTICAL APPARATUS. THE EYE THE STEREOSCOPE SPECTRUM ANALYSIS — THE SPECTROSCOPE — THE TELESCOPE AND MICRO- SCOPE PHOTOGRAPHY DISSOLVING VIEWS LUMINOUS PAINT. ;HE eye and vision are such important subjects to all of us that we may be excused for saying something more concerning phenomena con- nected with them, and the instruments we use for assisting 4:hem. We do not propose to write a treatise upon the physiology of vision, for we know the image in the eye is produced physically in the same manner as the image in a camera obscura. In the eye the sides of the box are represented by the sclerotic ; the dark inner surface has its parallel in the pigment of the choroid ; the opening in the box in the pupil of the eye ; the convex lens in the crystalline and the cornea ; and the retina receives the image. But why we see — beyond the fact that we do see — no one can explain. Science is dumb on the subject. Thought and consciousness elude our grasp ; and, as Professor Tyndall says on this subject, " we stand face to face with the incomprehensible." But there are many interesting facts connected with our vision which may be plainly described. Some people are obliged to carry an object (or a book) to within ten inches of the eye to see it distinctly; and a person who does not possess convergent power of the eye will have to move it THE RETINA OF THE EYE. I07 farther off, or use convex glasses ; while a " near-sighted " person, whose eyes are too quickly convergent, will use concave glasses to bring the object near to the eye. There is but one small place in the retina of the eye which admits of perfect vision. This, the most sensitive portion, is called the " yellow spot," and vision becomes more and more indistinct from this point towards the circumference. This can be proved by any one ; for in reading we are obliged to carry our eyes from word to word, and backwards and forwards along the lines of print. Another very important element in our vision is the contraction and enlargement of the iris around the pupil. In cases where strong light would only dazzle us the iris expands, and the pupil is contracted to a sufficient size to accommodate our vision. At night, or in a darkened room, the pupil is enlarged. This change will account for our not being immediately able to see objects when we have passed from darkness to great light, or vice versd The iris must have time to accommodate itself to the light. Now, outside the small space of perfect vision above mentioned, there is a circle of considerable extent, called the "field of vision." In man this field, when the eyes are fixed, subtends an angle of about 180°, because beyond that the rays cannot enter the pupil of the eye. But in the lower animals, the fish and birds, — notably the ostrich, — the field of vision is much more extensive, because the pupils are more prominent, or the eyes are set more towards the sides of the head. The ostrich can see behind him, and fish can see in any direction without ■ apparent limit. Man can only see indistinctly; and though he can move his eyes rapidly, he can see distinctly but a small portion of any object at a time, yet he sees with both eyes simultaneously a single object, because the two lines of vision unite at a single point, and as the two images cover each other we perceive only one image. Io8 OPTICAL APPARATUS. Beyond or within this point of meeting the vision is indistinct, but the angle of convergence is always varied according to the distance of the object. If we hold tip a penholder in front of us, and in a line with any other defined object, — say an ink-bottle, — we can see the pen- holder distinctly, and the ink-bottle indistinctly, as two images. If we then look at the ink-bottle we shall see it single, while the penholder will appear double, but with imperfect outlines. Again, if we look at a box both eyes will see it equally The Sterco-.cope. well, but the right eye will see a little more on its right side and the left eye on the left. It is on this principle that the Stereoscope is constructed. Sir Charles Wheat- stone was the inventor, and the instrument may be thus described : — Two pictures are taken by photography — one as the landscape is seen by the right eye, the other as it is viewed by the left ; the points of view thus differing slightly. When both eyes are simultaneously applied to the instrument the view is seen exactly as it would appear to the beholder at the actual place it repre- sents. The views are taken singly ; one side at one time, and another after, as in the camera. A is the first view; THE STEREOSCOPE. 109 B is kept dark ; c is the shutter for A. There are Reflect- ing and Refracting Stereoscopes. In the former a mirror reflects the image into each eye; in the latter the views are pasted on a card side by side, and looked at through prismatic lenses. The principles of Binocular Vision have been applied to the Microscope. In foregoing chapters we have given many examples v/ith diagrams of the temporary impressions made upon the retina of the eye. It is a fact that a wheel revolving at a great rate will appear to be standing still when suddenly illuminated by a flash of lightning, because the Mode of taking photograph for Stereoscope. eye has not time to take in the motion in the instant of time, for the spokes of the wheel are not moving fast enough to convey the impression of motion in that half second to the eye ; yet the perfect outline of the wheel is distinctly visible. Indeed, distinct vision can be exercised in a very small fraction of a second. It was calculated by Professor Rood, and proved by experiment, that forty billionths of a second is sufficient time for the eye to distinguish letters on a printed page. It this instance the illuminating power was an electric spark from a Leyden Jar. We have remarked upon the distinctness with which I lO OPTICAL APPARATUS. we can see an object when we direct our gaze upon it, and this appears a self-evident proposition ; but have any of our readers remarked the curious fact that when they want to see a faint and particular star in the sky it will at once disappear when they gaze at it ? The best way to see such very faint orbs as this is to look away from them, — a little to one side or the other, — and then the tiny point will become visible again to the eye. There is also a degree of phosphorescence in the eye, which any one who receives a blow upon that organ will readily admit. Even a simple pressure on the closed lid will show us a circle of light and " colours like a peacock's tail," as the great Newton expressed it. There are many occasions in which light is perceived in the eye — generally the result of muscular action ; and the Irish term to " knock fire out of my eye" is founded upon philosophical facts. We are many of us aware of " spots" on our eyes when our digestion is out of order, and the inability of the eye to see figures distinctly in a faint light — -within a proper seeing distance, too — has often given rise to the " ghost." These shadowy forms are nothing more than affections of the eye, and, as well remarked in Brewster's Letters on Natural Magic, "are always white because no other colour can be seen." The light is not sufficiently strong to enable the person to see distinctly; and as the eye passes from side to side, and strives to take in the figure, it naturally seems shadowy and indistinct, and appears to move as our eyes move. " When the eye dimly descries an inanimate object whose different parts reflect different degrees of light, its brighter parts may enable the spectator to keep up a continued view of it ; but the disappearance and reappearance of its fainter parts, and the change of shape which ensues, will neces- sarily give it the semblance of a living form ; and if it THE SOLAR SPECTRUM. I II occupies a position which is unapproachable, and where animate objects cannot find their way, the mind will soon transfer to it a supernatural existence. In like manner a human figure shadowed forth in a feeble twilight may undergo similar changes, and after being distinctly seen while it is in a situation favourable for receiving and reflecting light, it may suddenly disappear in a position before and within the reach of the observer's eye ; and if this evanescence takes place in a path or roadway where there is no sideway by which the figure could escape, it is not easy for an ordinary mind to efface the impression The Solar Spectrum, which it cannot fail to receive." This will account for many so-called " ghosts." Accidental colours, or ocular spectra, are, so to speak, illusions, and differently-coloured objects will, when our gaze is turned from them, give us different '■ spectra'' or images. For instance, a violet object will, when we turn to a sheet of white paper, give us a yellow " spectrum '' ; orange will be blue ; black and white will change respec- tively; red will become a blue-green-. From a very strong white light the accidental colours will vary. The Solar Spectrum is the name given to the coloured band formed by the decomposition of a beam of light into its elementary colours, of which there are seven. This is an easy experiment. A ray of light can be I I 2 OPTICAL APPARATUS. admitted into a darkened room through a. hole in the shutter, and thus admitted will produce a white spot on the screen opposite, as at £■ in the diagram. If we interpose a prism — a triangular piece of glass — the " drop " of a chandelier will do — we cause it to diverge from its direct line, and it will produce a longer streak of light lower down. This streak will exhibit the pris- matic colours, or the "colours of the rainbow"; viz., red (at the top), orange, yailow, green, blue, indigo (blue), and violet last. These are the colours of the Solar Spectrum. The white light is thus decomposed, and it is called mixed light, because of the seven rays of which it is composed. These rays can be again collected and re- turned to the white light by means of a convex lens. " White light," said Sir Isaac Newton, " is composed of rays differently refrangible," and as we can obtain the colours of the rainbow from white light, we can, by painting them on a circular plate and turning it rapidly round, make the plate appear white. Thus we can prove that the seven colours make "white" when intermingled But Newton (1675) did not arrive at the great importance of his experiment. He made a round hole in the shutter and found that the various colours overlapped each other. But, in 1802, Dr. WoUaston improved on this experiment, and by admitting the light through a tiny slit in the wood, procured an almost perfect spectrum of " simple " colours, each one perfectly distinct and divided by black lines. But twelve years later, Professor Fraunhofer made a chart of these lines, which are still known by his name. Only, instead of the 576 he discovered, there are now thousands known to us ! To Fraunhofer's telescope Mr Simms added a coUimating lens, and so the Spectroscope was begun ; and now we use a number of prisms and almost perfect instruments, dispersing the light through THE SPECTROSCOPE. I I 3 each. We have here an illustration of a simple Spectro- scope, which is much used for chemical analysis. In the spectrum we have long and short waves of light, as we have long and short (high and low) waves in music, called notes. The long or low notes are as the red rays, the high notes as the blue waves of light. (Here we have another instance of the similarity between light and sound.) But suppose we shut out the daylight and sub- 1 [ 1 1 T 1 1^^ J The Spectroscope. stitute an artificial light. If we use a lamp burning alcohol with salt (chloride of sodium), the spectrum will only consist of two yellow bands, all the other colours being absent. With lithium we obtain only two, one orange and one red. From this we deduce the fact that different substances when burning produce different spectra ; and although a solid may (and platinum will) give all seven colours in its spectrum, others, as we have seen, will only give us a few, the portion of the spectrum 114 OPTICAL APPARATUS. between the colours being black. Others are continuous, and transversed by " lines " or narrow spaces devoid of light ; such is the spectrum of the sun, and by careful and attentive calculation and observation we can get an approximate idea of the matter surrounding the heavenly bodies. We have said there are lines crossing the spectrum transversely ; these are called Fraunhofer's lines, after the philosopher who studied them ; they were, however, discovered by WoUaston. These lines are caused by light from the lower portion of the sun passing through the metallic vapours surrounding the orb in a state of incan- descence, such as sodium, iron, etc. One of Fraunhofer's lines, a black double line known as D in the yellow portion of the spectrum, was known to occupy the same place as a certain luminous line produced by sodium compounds in the flame of a spirit lamp. This gave rise to much consideration, and at length Kirchkoff proved that the sodium vapour which gives out the yellow light can also absorb that light ; and this fact, viz., that every substance, which at a certain tetnperature emits light of a certain refran^ibility, possesses at that temperature the power to absorb that same light. So the black lines are now considered the reversal of luminous lines due to the incandescent vapours by which the sun is surrounded. Thus the presence of an element can be found from black or luminous lines, so the existence of terrestrial elements in celestial bodies has been discovered by means of pre- paring charts of the lines of the terrestrial elements, and comparing them with the lines of stella. spectra. We have supposed the beam of light to enter through a slit in the shutter, and fall upon a screen or sheet. The solar spectrum shown by the passage of the beam through a prism is roughly as below, Fraunhofer substituted a telescope for the lens and the THE SPECTROSCOPE. 115 screen, and called his instrument a Spectroscope. He then observed the lines, which are always in the same position in the solar spectrum. The principal of them he designated as A, u, C, D, E, F, G, H. The o first three are in the red part of the spec- trum ; one in the yellow, then one in the green ; F comes between green and blue, G in the indigo-blue, and H in the violet. But these by no means exhaust the lines now visible. Year by year the study of Spectrum Analysis has been perfected more and more, and now we are aware of more than three thousand " lines " existing in the solar spectrum. The spectra of the moon and planets contain similar dark lines as are seen in the solar spectrum, but the fixed stars show different lines. By spectrum analysis we know the various constituents of the sun's atmosphere, and we can fix the result of our observations made by means of the Spectroscope in the photographic camera. By the more recent discoveries great advances have been made in " solar chemistry." What can we do with the Spectroscope, or rather. What can we not do t By Spec- troscopy we can find out, and have already far advanced upon our path of discovery, " the measure of the sun's rotation, the speed and direction of the fierce tornados which sweep over its surface, and give rise to the ' maelstroms ' we term • sunspots,' and the mighty alps of glowing gas that shoot far beyond the visible orb, ever changing their form and size ; even the temperature and pressure of the several layers and their fluctuations "2 Il6 OPTICAL APPARATUS. are in process of being defined and determined." This is what science is doing for us, and when we have actually succeeded in ascertaining the weather at various depths in the atmosphere of the sun, we shall be able to predict our own, which depends so much upon the sun. Recently (1880) Professor Adams, in his address to the British Association, showed that magnetic disturbances, identical in kind, took place at places widely apart simultaneously. He argues that the cause of these identical disturbances must be far removed from the earth. " If," he says, " we imagine the masses of iron, nickel, and magnesium in the sun to retain even in a slight degree their magnetic power in a gaseous state, we have a sufficient cause for all our magnetic changes. We know that masses of metal are ever boiling up from the lower and hotter levels of the sun's atmosphere to the cooler upper regions, where they must again form clouds to throw out their light and heat, and to absorb the light and heat coming from the hotter lower regions ; then they become condensed, and are drawn back again' towards the body of the sun, so forming those remarkable dark spaces or sunspots by their down rush to their former levels. In these vast changes we have abundant cause for those magnetic changes which we observe at the same instant at distant points on the surface of the earth." So we are indebted to the Spectroscope for many wonderful results — the constitution of the stars, whether they are solid or gaseous, and many other wonders. The manner in which we have arrived at these startling conclusions is not difficult to be understood, but some little explanation will be necessary. The existence of dark lines in the solar spectrum proves that certain rays of solar light are absent, or that there is less light. When we look through the prism we perceive the spaces or lines, and we can produce these ourselves SPECTRUM ANALYSIS. 117 by interposing some substance between the slit in the shutter before mentioned and the prism. The vapour of sodium will answer our purpose, and we shall find a dark line in the spectrum, the bright lines being absorbed by the vapour. We can subject a substance to any tempera- ture we please, and into any condition — solid, liquid, or gaseous ; we can also send the light the substance may give out through certain media, and we can photograph the spectrum given out under all conditions. The distance rj the source cf the light makes no difference. So whether it be the sun, or a far-distant star, we can tell by the light sent to us what the physical condition of the star may be. It was discovered in 1864 that the same metallic body may give different spectra; for instance, the spec- trum might be a band of light,— like the rainbow, — or a few isolated colours ; or again, certain detached lines in groups. The brightness of the spectrum lines will change with the depth of the light-giving source, or matter which produces it. We have become aware by means of the Spectroscope that numerous metals known to us on earth are in com- bustion in the sun, and ne,w ones have thus been discovered. In the immense ocean of gas surrounding the sun there are twenty-two elements as given by Mr. Lockyer, including iron, sodium, nickel, barium, zinc, lead, calcium, cobalt, hydrogen, potassium, cadmium, uranium, strontium, etc. Not only is the visible spectrum capable of minute examina- tion, but, as in the case of the heat spectruin already men- tioned when speaking of Calorescence, the light spectrum has been traced and photographed far beyond the dark space after the blue and violet rays, seven times longer than the visible solar spectrum-^a spectrum of light invisible to our finite vision. Although a telescope has been invented for the examination of these "ultra violet" rays, no human eye can see them. But — and here science I 1 8 OPTICAL APPARATUS. comes in — when a photographic plate is put in place of the eye, the tiniest star can be seen and defined. Even the Spectroscope at length fails, because light at such limits has been held to be " too coarse-grained for our purposes " ! " Light," says a writer on this subject, " we can then no longer regard as made of smooth rays ; we have to take into account — and to our annoyance — the fact that its ' long levelled rules ' are rippled, and its texture, as it were, loose woven " ! Twenty years ago Professors Kirchkoff and Bunsen ap- plied Fraunhofer's method to the examination of coloured flames of various substances, and since then we have been continually investigating the subject ; yet much remains to be learnt of Spectrum Analysis, and Spectroscopy has still much to reveal. From Newton's time to the present our scientists have been slowly but surely examining with the Spectroscope the composition of spectra, and the Spec- troscope is now the greatest assistant we possess. " Spectrum Analysis, then, teaches us the great fact that solids and liquids give out continuous spectra, and vapours and gases give out discontinuous spectra instead of an unbroken light" (Lockyer). We have found out that the sunlight and moonlight are identical, that the moon gives a. spectrum like a reflection of the former, but has no atmosphere, and that comets are but gases or vapours. The most minute particles of a grain of any substance can be detected to the millionth fraction. The Twiy of a grain of blood can be very readily distinguished in a stain after years have passed. The very year of a certain vintage of wine has been told by means of "absorption," or the action of different bodies on light in the spectrum. It is now easy, " by means of the absorption of different vapours and different substances held in solution, to determine not only what the absorbers really are, but also to detect a minute quantity." The SPECTRUM ANALYSIS. I 19 application of this theory is due to Dr. Gladstone, who used hollow prisms filled with certain substances, and so thickened the "absorption lines." By these lines, or bands, with the aid of the Spectrum Microscope, most wonderful discoveries have been made, and will continue to be made. We will close this portion of the subject with a brief description of the Spectroscope in principle. The instrument consists of two telescopes arranged with two object-glasses on a stand. A narrow slit is put in place of the eye-piece of one, the arrangement admitting of the slit being made smaller or larger by means of screws. The glass to which the slit is attached is called the collimating lens. The light, at the end of the slit seen from the other telescope, being separated by the prisms Ibetween the. two telescopes, will produce the spectrum. The Spectroscope is enclosed, so that no exterior light ■shall interfere with the spectra the student wishes to ■observe. This merely indicates the principle, not the details, of the Spectroscope, which vary in different instruments. We tnay now pass from the Spectroscope to the Telescope and the Microscope, instruments to which we are most largely indebted for our knowledge of our •surroundings in earth, air, and water. The word Telescope is derived from the Greek tele, ■far, and skopein, to see ; and the instrument is based upon the property possessed by a convex lens or concave mirror, ■of converging to a focus the rays of light falling on it •from any object, and at that point or focus forming an image of the object. The following diagram will illustrate this. Let vw be a lens, and AB an object between the glass, and F the focus. The ray, he, is so refracted as to appear to come from a. The ray from b likewise appears in a similar way, and a magnified image, ab, is the result. I20 OPTICAL APPARATUS. The ordinary Telescope consists of an object-glass and an eye-lens, with two intermediates to bring the object into an erect position. A lens brings it near to us, and a magnifier enlarges it for inspection. We will now give a short history of the Telescope and its, improved con- struction. Roger Bacon was supposed to have had some knowledge of the Telescope, for in 1 5 5 i it was written : " Great talke there is of a glass he made at Oxford, in which men see things that were don." But a little later, Baptista Converging rays to a focus. Porta found out the power of the convex lens to bring objects " nearer." It was, however, according to the old tale, quite by an accident that the Telescope was discovered about the year 1608. In Middleburg, in Holland, lived a spectacle-maker named Zachary Jansen, and his sons, when playing with the lenses in the shop, happened to fix two of them at the proper distance, and then to look through both. To the astonishment of the boys, they perceived an inverted image of the church weathercock much nearer and much larger than usual. They at once told their father what they had seen. He fixed the glasses in a tube, and THE TELESCOPE. 121 having satisfied himself that his sons were correct, thought httle more about the matter. This is the story as told, but there is little doubt that for the first Telescope the world was indebted either to Hans Lippersheim or Joseph Adriansz, the former a spectacle-maker of Middleburg ; and in October 1608, Lippersheim presented to the Government three instruments, with which he "could see things at a distance." Jansen came after this. The The Microscope. report of the invention soon spread, and Galileo, - who was then in Venice, eagerly seized upon the idea, and returning to Padua with some lenses, he managed to construct a telescope, and began to study the. heavens. This was in i6og. Galileo's Tube became celebrated, and all the first telescopes were made with the concave eye-lens. Rheita, a monk, made a binocular telescope, as now used in our opera and field-glasses approximately. But the prismatic colours which showed themselves in the early telescopes were not got rid of, nor was it till 122 OPTICAL APPARATUS. 1729 that Hall, by studying the mechanism of the eye, managed a combination of lenses free from colour. Ten years before (in 171 8) Hadley had established the Reflector Telescope ; Herschel made his celebrated forty-foot " re- flector" in 1789. However, to resume. In 1747, Euler declared that it was quite possible to construct an arrangement of lenses so as to obtain a colourless image, but he was at first chal- lenged by John Dollond. The latter, however, was afterwards induced to make experiments with prisms of crown and flint glass. He then tried lenses, and with a concave lens Image on the Retina, of iflint, and a convex lens of crown, he corrected the colours. The question of proper curvature was finally settled, and the "Achromatic" Telescope became an accomplished fact There are two classes of Telescopes — the reflecting and refracting. Lord Rosse's is an instance of the former. Mr. Grubb's immense instrument is a refractor. The Microscope has been also attributed to Zacharias Jansen, and Drebbel, in 16 19, possessed, the instrument in London, but it was of little or no use. The lens invented by Hall, as already mentioned, gave an impetus to the Microscope. In the simple Microscope the objects are seen directly through the lens or lenses acting as one. The compound instrument is composed of two lenses (or THE MICROSCOPE. 123 a number formed to do duty as two), an eye-lens, and an object-lens. Between these is a " stop" to restrain all light, except what is necessary to view the object distinctly. The large glass near the object bends the rays on to the eyeglass, and a perfect magnified image is perceived. We annex diagrams, from which, the construction will be readily understood. We have in the previous chapter mentioned the effect of light upon the eye and its direction, and when an object is placed very near the eye we know it cannot be distinctly seen ; a magnified image is thrown upon the The Microscope lenses. Concave lens. retina, and the divergency of the rays prevents a clear image being perceived. But if a small lens of a short " focal length " be placed in front of the eye, having PQ for its focus, the rays of light will be parallel, or very nearly so, and will as such produce " distinct vision," and the image will be magnified at pq. In the Compound Refract- ing Microscope, BAB is the convex lens, near which an object, PQ, is placed a little beyond its focal length. An inverted image, pq, will then be formed. This image is produced in the convex lens, bab', and when the rays are 124 OPTICAL APPARATUS. reflected out they are parallel, and are distinctly seen. So the eye of the observer at the point E will see a magnified image of the object at PQ brought up to pq. I. Focus of parallel rays. 2. Focus of divergent rays. 3. Focus of divergent rays brought forward by more convex lens. Sir Isaac Newton suggested the Reflecting Microscope, and Dr. WoUaston and Sir David Brewster improved the instrument called the " Periacopic Microscope," in which two hemispherical lenses were cemented together by the plane surfaces, and having a "stop" between them to limit Diverging rays. the aperture. Then the " Achromatic " instrument came into use, and since then the Microscope has gradually attained perfection. We have so frequently mentioned lenses that it may be as well to say something about them. Lenses may be spherical, double-convex, plane-convex, plane-concave, LENSES. I 2 5 double-concave, and concave- convex. Convex lenses bring the parallel lines which strike them to a focus, as we see in the "burning-glass." The concave or hollow lens appears as in first cut, page 123. The rays that follow it parallel to its axis are refracted, and as if they came from a point Hypermetropia (long sight). F in the diagram. But converging rays falling on it emerge in a parallel direction as on page 123, or diverge as in the second illustration on page 124. The use of spectacles to long or short-sighted people is a necessity, and the lenses used vary. The eye has Myopia (short sight). usually the capacity of suiting itself to viewing objects — its accommodation, as it is termed — near or far. But when the forepart of the eye is curved, and cannot adapt itself to distant objects, the person is said to be short- sighted. In long sight the axis of the eyeball is too short, and the focus falls beyond the retina ; in short sight it is too long. In the diagrams herewith (see above) 126 OPTICAL APPARATUS, the first shows by the dotted lines the position of the retina in long sight, and in the second in short sight, the clear lines showing in each case the perfectly-formed eye. For long sight and old sight the double-convex glass is used, for short sight the double-concave. We know the burning-glass gives us a small image of Concave and convex lenses. the sun as it converges the rays to. its focus. But lenses will do more than this, and in the Photographic Camera we find great interest and amusement. Photography (or writing by light) depends upon the property which certain preparations possess of being blackened by exposure to light while in contact with TxTises :or Jong and short sight. matter. By an achromatic arrangement of lenses the camera gives us a representation of the desired object The cut on page 127 shows the image on the plate, and the lower illustration gives the arrangement of lenses. To Porta, the Neapolitan physician, whose name we have already mentioned more than once, is due the first idea of the Photographic Camera He found that if light was admitted through a small aperture, objects from which THE CAMERA. 127 rays reached the hole would be reflected on the wall like a picture. To this fact, we are indebted for the Camera Obscura, which receives the picture upon a plane surface by an arrangement of lenses. In fact, Porta nearly arrived =□=_>. The Camera. at the Daguerreotype process. He thought he could teach people to draw by following the focussed picture with a crayon, but he could not conquer the aerial perspective. So the camera languished till 1820, when Wedgwood and Sir Humphrey Davy attempted to obtain some views Arrangement of lenses. with nitrate of silver, but they became obliterated when exposed to the daylJght. As early as 18 14, however, M. Niepce had made a series of experiments in photography, and subsequently having heard that M. Daguerre was turning hi,s attention to the same subject, he commuincated with him. In 128 OPTICAL APPARATUS. 1827 a paper was read before the Royal Society, and in 1829 a partnership deed was drawn up between Daguerre and Niepce for " copying engravings by photo- graphy." Daguerre worked hard, and at length succeeded in obtaining a picture by a long process, to which, perhaps, some of our readers are indebted for their likenesses forty years ago. By means of iodine evaporated on a metal plate covered with " gold-yellow," and exposing the plate then in a second box to mercurial vapour, he marked the image in the camera, and then he immersed the plate in hyposulphate of soda, and was able to expose the image obtained to daylight. But the mode now in use is the " collodion " process. We have all seen the photographer pouring the iodized collodion on the plate, and letting the superfluous liquid drain from a corner of the glass. When it is dry the glass-plate is dipped into a solution of nitrate of silver, and then in a few minutes the glass is ready. The focus is then arranged, and the prepared plate conveyed in a special slide — to keep it from the light — to the camera. When the " patient " is ready, the covering of the lens is removed, and the light works the image into the sensitive plate. The impression is then " brought up," and when developed is washed in water, and after by a solution which dissolves all the silver from the parts not darkened by the light. Thus the negative is obtained and printed from in the usual manner. Instantaneous photography is now practised with great success. An express train, or the movements of a horse at full speed, can thus be taken in a second or less. These results are obtained by using prepared plates, and the "emulsion process," as it is called, succeeds admirably. The mode of preparation is given in a late work upon the subject, and the photographic plates may also be obtained ready for use. Gelatine and water, mixed with PHOTOGRAPHY. 1 29 bromide of ammonium, nitrate of silver, and carbonate of ammonium, mixed with certain proportions of water, form the "emulsion." We need not go into all the details here. Information can easily be obtained from published works, and as the plates can be purchased by amateurs, they will find that the best way. Aside from the art interest in the new plates there is another, that springs from the fact that it is now possible to take pictures of men, animals, and machinery in rapid motion, thus enabling us to view them in a way that would be impossible with the unaided eye. The first experiments in this direction were applied to the move- ments of a horse moving at full speed. The pictures, taken in series, showed that he performed muscular actions that were not before comprehended or even imagined. These pictures at the time attracted great attention, and instantaneous pictures have been since taken of dancers in a ball-room, of vessels and steam-boats in rapid move- ment, of all kinds of animals in motion, and of machinery in operation. As the pictures represent the movements at one instant of time, they give, as it were, a fixed view of a motion, precisely as if it were suddenly alrrested in full action. In the case of animals, the motions of the nostrils are represented in the most singular manner, and the spokes of a steam -boat's paddle-wheel are shown apparently perfectly still while the spray and waves appear in active motion, or, rather, as they would look if they could be instantly frozen. It is clear the new process and pictures will open a wide and instructive field in art and in the study of mechanical action. While on the subject of Photography we may mention a very ingenious little apparatus called a SCENOGRAPH, the invention of Dr. Candize. It is really a pocket-camera, and is so easily manipulated that it will be found a most pleasant and useful holiday companion. Any one may 130 CHEMlSTRV. age ! Soap is quite soluble in spirits, but in ordinary water it is not so greatly soluble, and produces a lather, owing to the lime in the water being present in more or less quantity, to make the water more or less " hard." Sodium is not unlike potassium, not only in appear- ance, but in its attributes ; it can be obtained from the carbonate, as potassium is obtained from its carbonate. Soda is the oxide of sodium, but the most common and useful compound of sodium is the chloride, or common salt, which is found in mines in England, Poland, and elsewhere. Salt may also be obtained by the evaporation of sea water. Rock salt is got at Salz- burg, and the German salt mines and works produce a large quantity. The Carbonate of Soda is manufactured from the chloride of sodium, al- though it can be procured from the salsoda plants by burning. The chloride of Machine for cutting soap in bars. sodium is Converted into sulphate, and then ignited with carbonate of lime and charcoal. The soluble carbonate is extracted in warm water, and sold in crystals as soda, or (anhydrous) " soda ash." The large quantity of hydrochloric acid produced in the first part of the process is used in the process of making chloride of lime. A few years back, soda was got from Hungary and various other countries where it exists as a natural efflorescence on the shores of some lakes, also by burning sea-weeds, especially the common bladder wrack {Fucus vesiculosus), the ashes of which were melted into masses, and came to market in various states of purity. The bi-carbonate of soda is obtained by pass- LITIilUM. 131 ing carbonic acid gas over the carbonate crystals. Soda does not attract moisture from the air. It is used in wash- ingi Jn glass manufactories, in dyeing, soap-making, etc. Sulphate of Soda is "Glauber's Salt"; it is also employed in glass-making. Mixed with sulphuric acid and water, it forms a freezing mixture. Glass, as we have seen, is made with silicic acid (sand), soda, potassa, oxide of lead, and lime, and is an artificial silicate of soda. Lithium is the lightest of metals, and forms the link Soap-boiling house. between alkaline and the alkaline earth metals. The salts are found in many places in solution. The chloride when decomposed by electricity yields the metal. CESIUM and Rubidium require no detailed notice from us. They were first found in the solar spectrum, and resemble potassium. Ammonium is only a conjectural metal. Ammonia, of 132 OPTICAL APPARATUS. The illustration shows a small apparatus by which on thin plates small photographs can be taken and fixed till it is found desirable to enlarge them. The Photophone, one of the most recent contributions to science, is an instrument which, in combination v/ith the telephone principle, makes it possible to convey sounds by means of a ray of light, and by means of a " quivering beam " to produce articulate speech at a dis- tance. The success of the Photophone depends upon a rare element, selenium, which has its "electrical resistance" affected by light. Professor Adams demonstrated that the resistance of selenium was reduced just in proportion as the intensity of the light which was acting upon it. Here was the key to the Photophone as thought out by Professor Belli He fancied that he might by means of his telephone produce sound if he could vary the intensity of the beam of light upon the selenium, which he con- nected with his telephone and battery. The Photophone consists of a transmitter for receiving the voice and conveying it along the beam of light, and a receiver for taking the light and converting it into sound — the receiver being the telephone. There is a small mirror (silvered mica has been used) suspended freely for vibration. A lens is used to transmit to this the beam of light, and this beam is again reflected by another lens to the receiver, which consists of a reflector which has a cell of selenium in its focus, connected, as already stated, with the telephone and battery. The speaker stands behind the mirror, and the sound of his voice against the reverse side makes it vibrate in unison with the sounds uttered. The movements cause a quivering in the reflected beam, and this in its changing intensity acts on the sele- nium, which changes its resistance accordingly, and through the telephone gives forth a sound ! This is the apparently complicated but really simple. POLARIZATION. I 3 3 and at the same time wonderful, invention of Professor Bell. By the Photophone not only sounds but movements can be converted into sound ; even the burning of a candle can be heard! The Photophone is still capable of im- provement, and has not as yet arrived at its full develop- ment, for it is stated it can be made quite independent of a battery or telephone. There are many phenomena connected with the Polari- zation of Light. This requires some notice at our hands. We know that a ray of ordinary light is supposed to be caused by vibrations of the highly attenuated medium, aether. These vibrations occur across the direction of the ray; but when they occur only in one plane the light is said to be " polarized." Polarization means possessing poles (like a magnet) ; the polarized rays have " sides," as Newton said, or, as explained by Dr. Whewell, " opposite properties in opposite directions, so exactly equal as to be capable of accurately neutralizing each other." There are some crystals which possess the property of " double refraction," and thus a ray of common light passing through such a crystal is divided into two polarized rays, taking different directions. One is refracted according to the usual laws of refraction ; the other is not, and the planes of polarization are at right angles. It is difficult within the limits of this chapter to explain the whole theory of Polarization. In order to account for certain phenomena in optics, philosophers have assumed that rays possess polarity ; and polarized h'ght is light which has had the property of Polarization conferred upon it by reflection,' refraction, or absorption. Common light has been com- pared to a round ruler, and polarized light to a fiat ribbon. Huygens found out, when engaged upon the investigation of double refraction, that the rays of light, divided by passing through a crystal (a rhomb) of Iceland spar, possessed certain qualities. When he passed them through 10 134 OPTICAL APPARATUS. a second rhomb, he found that the brightness, relatively, of the rays depended upon the position of the second prism, and in some positions one ray disappeared entirely. The light had been reduced to vibrations in one plane. In I 808, Malus, happening to direct a double refracting prism to the windows then reflecting the sunset, found that as he turned the prism round, the ordinary image of the window nearly disappeared in two opposite positions ; and in tv'-i other positions, at right angles, the " extra- ordinary '■ image nearly vanished. So he found that polarization was produced by reilection as well as by transmission. The differences between common and polarized light have been summed up by Mr. Goddard as follows : — Common Light Polarized Light " Is capable of reflection at ob- " Is capable of reflection at ob- lique angles of incidence in lique angles only in certain every position of the reflector. positions of the reflector. " Will pass through a bundle of " Will only pass through such plates of glass in any position glasses when they are in cer- vix which they may be placed. tain positions. "Will pass through a plate of "Will only pass in certain posi- tourmaline, cut parallel to the tions, and in others will not axis of the crystal, in every pass at all." position of the plate." The bundle of glass plates or the tourmaline plate is thus the test for polarized light, and is termed an analyzer. The arrangement called a " Nichol's prism," made by cutting a prism of Iceland spar and uniting the halves with a cement, so that only one polarized ray can pass through it, is termed a Polarizer. It only permits one of the two rays produced by " double refraction " to pass, and the ray (as said above) will contain none but transverse vibrations. Polarized light will produce beautiful colours. The whole subject is very interesting to the scientist, but rather a difficult one for the general reader to understand. LACTOSCOPE. 135 Amongst the uses to which light has been put is that of a milk-tester. The LACTOSCOPE will show the quantity of butter contained in a certain quantity of milk, by diluting it till it displays a certain degree of transparency. There is another method, by the transmission of light. The first test is obtained by means of a glass tube about nine inches long, closed at one end, and containing a small porcelain rod marked with black lines. A small quantity of milk is measured and placed in the tube. The black lines cannot at first be seen through the tube, but by adding water the milk is rendered transparent, and the black lines become visible. The surface of milk in the tube, by a graduated scale upon it, shows the percentage of butter. The second method is not so simple. A short tube of tin, blackened on the inside, and supported upright, has an opening on one side, and opposite this, inside the tube, is a mirror placed at an angle of 45°. "By placing a lighted candle at a known distance opposite the opening, its light is reflected in the mirror and thrown upward through the tube. On top of the tube is placed a round vessel of glass or metal, closed at the bottom by a sheet of clear glass. The vessel is closed at the top by a cover having an opening in the centre, in which slides up and down a small tube closed at the bottom with glass, and having an eye-piece at the top. The milk to be tested is placed in this vessel on the top of the tin tube, so that the light of the candle reflected from the mirror passes upward through the milk. Then, by looking through the sliding tube and moving it up and down, a point may be found where the image of the candle in the mirror can be seen through the milk. This device depends, as will be seen, on observing the light transmitted through a film of milk, and the thickness of- the film is the measure of the value of the milk. The movable tube contains a graduated 136 OPTICAL APPARATUS. scale, and by comparison of this with a printed table, the percentage of butter in the milk may be ascertained." In concluding this chapter we give a few hints for some pleasant relaxation for young people, which has many a time created amusement. The experiment consists in cutting out in paper or cardboard certain por- tions of a face or figure, as per the illustration herewith No. I gives the card as cut with the scissors, and the two subsequent faces are the result of the same held at a less or greater I distance from a screen I The illustrations shown S herewith will assist those 3 who wish to amuse chil- dren by making rabbits, etc., on the wall, The shadows will be seen perfectly thrown if the hands be carefully fixed near a good light. We are all so familiar with the " Magic Lan- tern," and the apparatus for dissolving views by an arrangement of lenses and manipulation of slides, that we need do no more than refer to them. The various ghost illusions, etc., produced by indirect mirrors, have already been referred to, the ghost being merely the reflection of an individual seen through a sheet HAND SHADOWS. 137 138 OPTICAL APPARATUS. of glass between the spectators and the stage. The strong light throws a reflection from a parallel mirror lower down, and this reflected image can he made to appear amongst the real actors who are behind the plate-glass in full view of the audience, who are, however, ignorant of the existence of the glass screen. For the winter evenings one may easily procure an apparatus for dissolving views by the oxy-hydrogen light. One, as shown in the illustration herewith (see opposite page), will answer every purpose, and by this double arrange- ment phantasmagoria may be produced, or a fairy tale may be illustrated. The effect of gradually-approaching night may be given to the picture by means of a special glass in the lower lanthorn. The apparatus is exhibited by means of a Drummond light, and is very simple, although a certain supply of gas is necessary for the performance. But this can be easily procured by an indiarubber tube, or in a bag supplied for the purpose. Almost any objects can be used, photographs, etc., etc., and many very comical arrangements can be made. We have -lately ^een reading a curious method of ■obtaining light from oyster-shells in a Trans-Atlantic magazine. We give an extract wherewith to close this chapter. The compound is " luminous paint." " It has been known that certain compounds of lime and sulphur had the property of absorbing light, and giving it out again when placed in the dark. A simple way to do this is to expose clean oyster-shells to a red heat for half an hour. When cold, the best pieces are picked out and packed with alernate layers of sulphur in a crucible, and exposed to a red heat for an hour. When cold, the mass is broken up, and the whitest pieces are placed in a clean glass bottle. On exposing the bottle to bright sunshine during the day, it is found that at night its contents will give out a pale light in the dark. Such a GHOST ILLUSION. 139 140 OPTICAL APPARATUS. bottle filled more than a hundred years ago still gives out light when exposed to the sun, proving the persistency of the property of reproducing light. Very many experi- ments have been more recently made in this direction, and the light-giving property greatly enhanced. The chemicals, ground to a flour, may now be mixed with oils or water for paints, may be powdered on hot glass, and glass covered with a film of clear glass, or mixed with celluloid, papier-mache, or other plastic materials. As a paint, it may be applied to a diver's dress, to cards, clock dials, signboards, and other surfaces exposed to sunlight during the day ; the paint gives out a pale violet light at night sufficient to enable the objects to be readily seen in the dark. If the object covered with the prepared paint is not exposed to the sun, or if the light fades in the dark, a short piece of magnesium wire burned before it serves to restore the light-giving property." CHAPTER VIII.— SPECTRAL ILLUSIONS. A SPECTRE VISIBLE CURIOUS ILLUSIONS GHOSTS. E have already given numerous examples of the effects produced by impressions on the retina by mechanical appliances. We can now in a short chapter speak of the cause of many spectral illusions, commonly supposed to be " ghosts " or " spirits." That there are many " well-authenticated ' ghost stories ' " no one can doubt who has read the literature of the day ; and we ourselves do not in any way desire to throw any doubt upon the existence of certain so-called " ghosts." That appearances of some kind or another are seen by people we know. We our- selves hava seen such, but we cannot say we believe in the popular ghost. In ancient times mirrors were much employed by the so-called magicians, and in our day many wonderful ghost effects have been shown at the (late) Polytechnic Institu- tion. Some people are believers in table-turning and spiritualism, and mesmerists still attract large audiences, and appear to possess extraordinary power over some individuals. But apparitions have been seen by people eminently worthy of credit. The experience of the learned Doctor, which appeared some time ago in the Athencemn, is a case in point. This narrative is concise and clear. The spectre was there. How did it get there .? Was 142 SPECTRAL ILLUSIONS. the " appearance " objective or subjective ? Let us give an extract from the Reverend Doctor's narrative, and comment upon it afterwards. We may premise that Dr Jessopp had gone over to Lord Orford's (Mannington Hall), and at eleven o'clock was busy writing in the library, and was " the only person downstairs." We will give this ghost story in the Doctor's own words. After taking up a certain volume — time about i a.m. : — " I had been engaged on it about half an hour, and was beginning to think my work was drawing to a close, when, as I was actually writing, I saw a large white hand within a foot of my elbow. Turning my head, there sat a figure of a somewhat large man with his back to the fire, bending slightly over the table, and apparently examining the pile of books that I had been at work upon." . . . After describing the appearance of the noc- turnal visitor. Dr. Jessopp proceeds : — • " There he sat, and I was fascinated ; afraid not of his staying, but lest he should go. Stopping in my writing I lifted my left hand from the paper, stretched it out to the pile of books, an-d moved the top one — my arm passed in front of the figure, and it vanished." ^ . . Shortly after the figure appeared again, and " I was penning a sentence to address to him, when I discovered I did not dare to speak. I was afraid of the sound of my own voice ! There he sat, and there sat I. I turned my head and finished writing. Having finished my task, I shut the book, and threw it on the table; it made a slight noise as it fell ; — the figure vanished." Now here we have a perfectly plain narrative, cleai" and full, A ghost appeared ; he is described distinctly. How can we account for the apparition ? In the first place, someone might have played a trick, but that idea was put aside by Dr. Wilks, who attempted to explain the appearances. He went fully into the question, and as it GHOSTS. 143 bears upon our explanation of the reality of Spectral Illusions, we may condense his evidence. It will of course be conceded that all the usual objects seen by people are material, and the image of what we look at is formed upon the retina in the manner already explained. But a// images upon the retina are not immediately observed; the impression may, to a certain extent, remain. Words are often impressed upon the brain, — words which we in our sober senses would never think of repeating, — and yet when we are delirious we give vent to these expres- sions, of whose very nature and meaning we are perfectly unconscious. It is, according to our reference (Dr. Wilks), "quite possible for the perceptive part of the brain to be thrown into an active condition quite independent of the normal stimulus conducted to it from the retina." If, under these circumstances, an object be viewed indepen- dently, and, as it were, unconsciously, it is merely, we believe, a parallel to the impression of words before noted. Sound and light are governed by the same laws. In fevers we fancy we see all kinds of things which have no existence. In dreams we hear noises ; and many a time people dreaming have been awakened by the report of a gun, or the ringing of a bell which had no material origin, — the nerves were excited, the "per- ceptive centre" of the brain was moved. But if sight and hearing thus have their origin from the brain and not from without, there must have been some predisposing cause, some excitement to induce such a condition of things. "The impressions become abnormal and subjective, — the normal condition being objective, — the impression is received from without, and impressed upon the eye. Now, let us consider the " ghost " ! Lately there have been many instances brought forward of "spiritual" appear- ances, but we" think nobody has ever seen a "material" 144 SPECTRAL ILLUSIONS. ghost ; yet on the other hand none of us have any know- ledge of anything in the likeness of a ghost, or that has not a material basis which can bring forward an image on the retina ! Therefore we are brought to the conclusion that apparitions are spectres emanating from within the brain, not from any outward manifestation, because it is within the experience of everybody that in bad health, or disordered digestive functions, images are produced in the brain and nerves of the eye. These remarks have perhaps been made before in one form or other, but as much popular interest is always awakened by the supernatural, or what is supposed to be supernatural, we may go a little farther, and inquire how it was that the ghost seen by Dr. Jessopp disappeared when he raised his arm. Would any ghost be afraid of the Doctor extending his hand .' The fact no doubt occurred as related. The explanation is that the narrator had been much impressed by a certain picture, which a correspondent soon identified as a portrait of " Parsons, the Jesuit Father." The description given is that of the priest who was described by the Doctor in one of his books. The association of ideas in the library of a Norfolk house connected with the Walpoles, with whom Parsons had been a leader, gave rise, during a period of " forty winks " at midnight, to the spectre. In the interesting letters written upon "Natural Magic" by Sir David Brewster, the subject of Spectral Illusions is treated at some length, and with undoubted authority. Sir David thought the subject worth discussing with reference to the illusions or spectres mentioned by Dr. Hibbert. Sir David Brewster gives his own experiences which occurred while he was staying at the house of a lady in the country. The illusions appear to have affected her ear as well as the eye. We shall see in the next chapter how intimately GHOSTS. 145 sound and light are connected, and how the eyes and ears are equally impressed, though in a different way, by the vibration of particles. The lady referred to was about to go upstairs to dress for dinner one afternoon, when she heard her husband's voice calling to her by name. She opened the door, and nobody was outside ; and when she returned for a moment to the fire she heard the voice again calling, "Come to me; come, come away," in a somewhat impatient tone. She immediately went in search of her husband, but he did not come in till half an hour afterwards, and of course said he had not called, and told her where he had been at the time — some distance away. This happened on the 26th December, 1830, but a more alarming occurrence took place four days after. About the same time in the afternoon of the 30th December, the lady came into the drawing-room, and to her great astonishment she perceived her husband standing with his back to the fireplace. She had seen him go out walking a short time previously, and was naturally sur- prised to find he had returned so soon. He looked at her very thoughtfully, and made no answer. She sat down close beside him at the fire, and as he still gazed upon her she said, " Why don't you say something ! " The figure immediately moved away towards the window at the farther end of the room, still gazing at her, " and it passed so close that she was struck by the circumstance of hearing no step nor sound, nor feeling her dress brushed against, nor even any agitation of the air." Although convinced this was not her husband, the lady never fancied there was anything supernatural in the appearance of the figure. Subsequently she was convinced that it was a spectral illusion, although she could not see through the figure which appeared as substantial as the reality. Were it advisable, we could multiply instances. In the Edinburgh Journal of Science these, and many more in- 146 SPECTRAL ILLUSIONS. stances of spectral illusions were narrated by the husband of the lady. She frequently beheld deceased relatives or absent friends, and described their dress and general appearance very minutely. On one occasion she perceived a coach full of skeletons drive up to the door, and noticed spectral dogs and cats (her own pets' likenesses) in the room, There can be no doubt upon these points ; the appearances were manifest and distinct. They were seen in the presence of other people, in solitude, and in the society of her husband. The lady was in delicate health, and very sensitive. The spectres appeared in daylight as well as in the dark, or by candle-light. Let us now, guided by what we have already written, and by Sir David Brewster's experience, endeavour to give a rational explanation of these illusions. "The mind's eye is really the body's eye, and the retina is the common tablet upon which both classes of impressions are painted, and by means of which they receive their visual existence according to the same optical laws." " In the healthy state of mind and body the relative intensity of the two classes of impressions on the retina are nicely adjusted — the bodily and mental are balanced. The latter are feeble and transient, and in ordinary temperaments are never capable of disturbing or effacing the direct images of visible objects. . . . The mind cannot perform two different functions at the same instant, and the direction of its attention to one of the two classes of impressions necessarily produces the extinction of the other; but so rapid is the exercise of mental power, that the alternate appearance and disappearance of the two contending impressions is no more recognized than the successive observations of external objects during the twinkling of the eyelids." We have before illustrated, by means of the pen and the ink-bottle, how one object is lost sight of when the SPECTRES. 147 other is attentively regarded, and a material picture or scene may be equally lost sight of, and a mental picture take its place in the eye, when we recall places or people we have seen or remembered. We have all heard numerous anecdotes of what is termed "absent-mindedness." Some people are quite absorbed in study, and can see or hear no one in the room when deeply occupied. We may be satisfied then that "pictures of the mind and spectral illusions are equally impressions upon the retina, and only differ in the degree of vividness with which they are teen." If we press our eyes the phosphorescence becomes apparent, and we can make a picture of the sun or a lamp visible for a long time to our closed eyes if we stare at either object for a few seconds, and shut our lids. So by in- creasing the sensibility of the retina we can obtain the image, and alter its colour by pressure on the eye. It is well known that poisons will affect sight, and belladonna applied to the eyes will so affect them as to render the sight nil, by enlargement of the "pupil." If one is out of health there is practically a poisoning of the system, and when we have a " bilious headache " we see colours and stars because there is a pressure upon the blood-vessels of the eye. The effects of a disordered stomach, induced by drinking too much, are well known ; objects are seen double, and most ghosts may be traced to a disordered state of health of mind or body, brought on by excitement or fatigue. We could relate a series of ghost stories, — some in our own experience, for we have seen a ghost equally with our neighbours, — but this is not the place for them. Although many apparently incontrovertible assertions are made, and many spectres have been produced to adorn a tale, we must put on record our own opinion, that every one could be traced to mental impression or bodily affection had we only 148 SPECTRAL ILLUSIONS. the key to the life and circumstances of the ghost-seer. Many celebrated conjurers will convince us almost against our reason that our pocket-handkerchief is in the orange just cut up. They will bring live rabbits from our coat- pockets or vests, and pigeons from our opera-hats. These are equally illusions. We know what ean be done with mirrors. We have seen ghosts at the Polytechnic, but we must put down all apparitions as the result of mental or bodily, even unconscious impressions upon the retina of the eye. There are numerous illusions, such as the Fata Morgana, the Spectre of the Brocken, etc., which are due to a peculiar state of the atmosphere, and to the unequal reflection and refraction of light. Those, and many other optical phenomena, will, with phenomena of heat and sound, be treated under METEOROLOGY, when we will consider the rainbow and the aurora, with many other atmospheric effects. CHAPTER IX.— ACOUSTICS. THE EAR, AND HEARING PHYSIOLOGY OF HEARING AND SOUND SOUND AS COMPARED WITH LIGHT WHAT IS SOUND ? — VELOCITY OF SOUND — CONDUCTIVITY — THE HARMONOGRAPH. ^EFORE entering upon the science of ACOUSTICS, a short description of the ear, and the mode in which sound is conveyed to our brain, will be no doubt acceptable to our readers. The study of the organs of hearing is not an easy one; although we can see the. exterior portion, the interior and delicate membranes are hidden from us in the very hardest bone of the body — the petrous bone, the temporal and rock-like bone of the head. The ear (external) is composed of the auricle, the visible ear, the auditory canal, and the drum-head, or membrana tympani. The tympanum, or " drum," is situated between the external and the internal portions of the ear. This part is the " middle ear," and is an air cavity, and through it pass two nerves, one to the face and the other to the tongue. The internal ear is called the " labyrinth," from its intricate structure. We give an illustration of the auditory apparatus of man. The auricle, or exterior ear, is also represented, but we need not go into any minute description of the parts. We will just name them. Sound is the motion imparted to tV..* auditory nerve, I50 SOUND. and we shall see in a moment how sound is produced. The undulations enter the auditory canal, having been taken up by the auricle ; the waves or vibrations move at the rate of i,ioo feet a second, and reach the drum-head, which has motion imparted to it. This motion or oscilla- tion is imparted to other portions, and through the liquid I . Temple bone. 2. Outer surface of temple. 3. Upper wall of bony part of hearing canal. 4. Ligature holding " hammer" bone to roof of drum cavity. 5. Roof to drum cavity. 6. Semi-circular canals. 7. Anvil bone. 8. Hammer bone. 9. Stirrup bone. 10. Cochlea. 11. Drum- head cut across. 12. Isthmus of Eustachian tube. 13. Mouth of tube in the throat. 14. Auditor^' canal. 15. Lower wall of canal. 16. Lower wall of cartilaginous part of canal. 17. Wax glands. 18. Lobule. 19. Upper wall of cartilaginous portion of canal. 20. Mouth of auditory canal. 21. Anti-tragus. in the labyrinth. The impressions of the sound wave are conveyed to the nerve, and this perception of the move- ment in the water of the labyrinth by the nerve threads and the brain causes what we term "hearing." Let us now endeavour to explain what sound is, and how it arises. There are some curious parallels between sound and light. When speaking of light we mentioned MUSIC AND NOISE. 15 I some of the analogies between sound and light, and as we proceed to consider sound, we will not lose sight o( the light we have just passed by. Sound is the influence of air in motion upon the hearing or auditory nerves. Light, as we have seen, is the ether in motion, the vibrations striking the nerves of the eye. There are musical and unmusical sounds. The former are audible when the vibrations of the air reach our nerves at regular intervals. Unmusical sounds, or irregular L. Pit of anti-helix, a, 6, lo. Curved edge of the auricle, 3. Mouth of auditory canal. 4. Tragus. 5. Lobe. 7. Anti-helix. 8. Concha. 9. Anti-tragus. vibrations, create noise. Now, musical tones bear the same relation to the ear as colours do to the eye. We must have a certain number of vibrations of ether to give us a certain colour (vide page 47). " About four hundred and fifty billion impulses in a second " give red light. The violet rays require nearly double. So we obtain colours by the different rate of the impingement of impulses on the retina. The eyes, as we have already learned, cannot receive any more rapidly-recurring impressions than those producing violet, although as proved, the spectrum is by I $2 SOUND. no means exhausted, even if they are invisible. In the consideration of Calorescence we pointed this out. These invisible rays work great chemical changes when they get beyond violet, and are shown to be heat. So the rays which do not reach the velocity of red rays are also heat, which is the effect of motion. Thus we have HEAT, Light, and Sound, all the ascertained results of vibratory motions. The stillness of the ether around us is known as " Darkness " ; the stillness of the air is " Silence " ; the comparative absence of heat, or molecular motion of bodies is " Cold"! In the first part we showed how coins impart motion to each other. When an impulse was given the motion was carried from coin to coin, and at length the last one in the row flew out. This is the case with sound. The air molecules strike one upon another, and the wave of " sound" reaches the tympanum, and thus the impression is conveyed to the brain. We say we hear — but why we hear, in what manner the movement of certain particles effects our consciousness, we cannot determine. That the air is absolutely necessary to enable us to hear can readily be proved. The experiment has frequently been made ; place a bell under the receiver of an air- pump, and we can hear it ring. But if we exhaust the air the sound will get fainter and fainter. Similarly, as many of us have experienced upon high mountains, sounds are less marked. Sound diminishes in its intensity, just as heat and light do. Sound is reflected and refracted, as are light and radiant heat. We have already shown the effect of reflectors upon heat. Sound is caught and reflected in the same way as light from mirrors, or as the heat waves in the reflectors. We have what we term " sounding boards " in pulpits, and speaking tubes will carry sound for us without loss of power. Echoes are merely reflected sounds. Velocity o¥ sound. ts3 The velocity of sound is accepted as 1,100 feet in a second, which is far inferior to the velocity of light. Fogs will retard sound, while water will carry it. Those who have ever rowed upon a lake will remember how easily the sound of their voices reached from boat to boat, and Dr. Hutton says that at Chelsea, on the Thames, he heard a person reading from a distance of a hundred and forty feet. Some extraordinary instances could be deduced of the enormous distances sound is said to have travelled. Guns have been heard at eighty miles distant, and the noise of a battle between the English and Dutch, in 1672, was heard even in Wales, a distance of two hundred miles from the scene of action. Sound always travels with uniform velocity in the air in the same temperature. But sound ! What is the cause of it .' How does it arise ? These questions can now be fully answered with reference to the foregoing observations. Phenomena of vibration render themselves visible by light, heat, and sound, and to arrive at some definite ideas of sound vibrations we may compare them to waves, such as may be produced by throwing a stone into a pond. There are, so to speak, " standing " waves and " pro- gressive" waves. The former can be produced (for instance) by thrumming a fiddle-string, and when the equilibrium of the cord is disturbed, the position of the equilibrium is passed simultaneously by the string-waves. In water the waves or vibrating points pass the position of equilibrium in succession. Waves consist of elevations and depressions alternately, and when we obtain two " systems " of waves by throwing two stones into water, we can observe some curious effects. It can be seen how one series of depressions will come in contact with the other series of depressions, and the elevations will likewise unite with the result of longer depressions and elevations resnprf-i^oi" • or it may very 154 SOUND. well be that elevation will meet depression, and then the so-called " interference " of waves will produce points of repose. These points are termed nodes. The waves of the string proceed in the plane of its axis ; water waves extend in circles which increase in circumference. The progression or propagation of sound may be said to begin when some tiny globule of matter expands in the air. The air particles strike one against the other, and so the motion is communicated to the air waves, which in time reach the ear. But the velocity of the sound is not equal in all substances. Air will convey it around our earth at the rate of 765 miles an hour, or 1,090 feet in a second. That is, we may accept such rate as correct at a temperature of 32° Fahr., and at a pressure of thirty inches, and the velocity increases almost exactly one foot per second for each degree of tempera- ture above 32°. Therefore on an average, and speaking in "round numbers," the estimate of 1,100 feet in a second may be accepted as correct. In hydrogen gas the rate is much higher. Through water again it is different, and still faster through iron, glass, and wood, as will be seen in the following table : — TAKING AIR AS I Whalebone .... 6f Tin 7i Silver 9 Walnut lof Brass lof Oak lof Earthen pipes ....11 Copper 12 I'ear-wood \2\ Ebony \^\ Cherry 15 Willow 16 Glass i6| Iron or Steel .... i6f Deal 18 So there is a considerable difference in the velocities of sound through the solid substances quoted, but these figures cannot be taken as exact, as different samples may give different results. In wires and bells the bodies themselves VIBRATION, 155 produce the sounds we hear. In wind instruments and the voice the air is the cause of the sound. The very deepest notes are produced by the fewest vibrations. Fourteen or fifteen vibrations will give us a very low note, if not the very lowest. The pipe of sixteen feet, closed at its upper end, will produce sound waves of thirty-two feet. High notes can be formed from vibrations up to 48,000 in a second. Beyond these limits the ear cannot accept a musical sound. We will explain the phenomenon of the vibration of strings by means of the illustration. In the cut we find a string or wire, which can be lengthened or shortened The vibration. at pleasure by a movable bridge, and stretched by weights attached to the end. We can now easily perceive that the shorter and thinner the string is, and the tighter it is the number of vibrations will be greater and greater. The density of it is also to be considered, and when these conditions are in the smallest proportion then the tone will be highest. The depth will naturally increase with the thickness, density, and length, and with a decreasing tension. But we have strings of same thickness stretched to different degrees of tension, and thus producing different notes. Some strings are covered with wire to iricrease their gravity, and thus to produce low notes. When a number of separate sound?; succeed each other 156 SOUND. in very rapid course they produce a sound, but to appear as one sound to the ear they must amount to fifteen or sixteen vibrations every second. The particles of matter in the air form a connected system, and till they are disturbed they remain in equilibrium; but the moment they are in any way thown out of this state they vibrate as the pendulum vibrates. The particles thus strike each other, and impart a motion to the elastic medium ether, so a sound comes to us. The intensity of sounds gets less the farther it goes from us, or the loudness of sound is less the greater its distance. The law is, that in an unvarying medium the loudness varies inversely as the square of the distance. But Poisson has shown that when air-strata, differing in density, are existing between the ear and the source of the sound, the intensity or loudness with which it is heard depends only on the density of the air at the place the sound originated. This fact has been substantiated by balloonists who heard a railway whistle quite distinctly when they were nearly 20,000 feet above the ground. It therefore follows that sound can be heard in a balloon equally well as on the earth at certain given distances. But as the density of the air diminishes the sound becomes fainter, as has been proved by the bell rung in the receiver of an air-pump. The velocity of sound, to a certain extent, depends upon its intensity, as Earnshaw sought to prove ; for he instanced a fact that in the Arctic regions, where sound can be heard for an immense distance, in consequence of the still and homogeneous air, the report of a cannon two miles and a half away was heard before the loud command to " fire," which must have preceded the discharge. Another instance showing the difference in hearing through mixed and homogeneous media may be referred to. In the war with America, when the English and their foes were on opposite sides of a stream, an ECHOES. 157 American was seen to beat his drum, but no sound came across. " A coating of soft snow and a thick atmosphere absorbed the noise." Glazed, or hard snow, would have a contrary effect. Reynault also experimentally verified his theory, that sound when passing through a space of nearly 8,ooo feet lost velocity as its intensity diminished, and in that distance between its arrival at 4,000 feet and at 7,5oo"feet, the sound velocity diminished by 2'2 feet per second. He also tried to demonstrate that sound velocity depended upon its pitch, and that lower notes travelled with the greater speed. The reflection and refraction of sound follows the same fundamental laws as the reflection and refraction of light. The reflection of sound is termed an Echo, which is familiar to all tourists in Switzerland and Ireland particularly. There are several very remarkable echoes in the world : at Woodstock, and at the Sicilian cathedral of Gergenti, where the confessions poured forth near the door to priestly ears were heard by a man concealed behind the high altar at the opposite end. It is curious that such a spot should have been accidentally chosen for the Con- fessional. The whispering gallery in St. Paul's is another instance of the echo. Echoes are produced by the reflection of sound waves from a plane or even surface. A wall, or even a cloud, will produce echoes. Thunder is echoed from the clouds. (The celebrated echo of " Paddy Blake," at Killarney, which, when you say "How do you do," is reported to reply, "Very well, thank you," can scarcely be quoted as a scientific illustration.) And the hills of Killarney con- tain an echo, and the bugle sounds are beautifully repeated. In the cases of ordinary echo, when the speaker waits for the answer, he must place himself opposite the rock. If he stand at the side the echo will reply to another person in a corresponding place on the farther side, for the voice 158 SOUND. then strikes the rock at an angle, and the angle of reflec- tion is the same, as in the case of light. But if it should happen that there are a number of reflecting surfaces the echo will be repeated over and over again, as at the Lakes of KiUarney. The Woodstock Echo, already referred to, and mentioned by several writers, repeats seventeen syllables by day, and twenty by night. In Shipley there is even a greater repetition. Of course the echo is fainter, because the waves are weaker if the reflecting surface be flat. But, as in the case of the mirrors reflecting light, a circular or concave surface will increase the intensity. A watch placed in one mirror will be heard ticking in the other focus. Whispering galleries carry sound by means of the curved surface. Sir John Herschel mentions an echo in the Menai Suspension Bridge. The blow of a hammer on one of the main piers will produce the sound from each of the crossbeams supporting the roadway, and from the opposite pier 576 feet distant, as well as many other repetitions. Refraction of sound is caused by a wave of sound meeting another medium of different density, just as a beam of light is refracted from water. One sound wave imparts its motion to the new medium, and the new wave travels in a different direction. This change is refraction. The sound waves are refracted in different directions, according to the velocity they can acquire in the medium. If a sound pass from water into air it will be bent towards the perpendicular, because sound can travel faster in water than in air. If it pass from air into water its force will cause it to assume a less perpendicular •direction, there being greater velocity in water. The velocity in air is only 1,100 feet in a second in our atmosphere. In water sound travels 4,700 feet in the sane time. When the wave of sound falls upon a VIBRATORY CURVES. 159 medium parallel to the refracting surface there is, however, no refraction — only a change of velocity, not direction. When sound waves are prevented from dispersing the voice can be carried a great distance. Speaking tubes and trumpets, as well as ear trumpets, are examples of this principle, and of the reflection of sound. There are many very interesting experiments in con- nection with Acoustics, some of which we will now impart to our readers. We shall then find many ingenious inven- tions to examine, — the Audiphone, Telephone, Megaphone, and Phonograph, which will occupy a separate chapter. We now resume. Amongst the experiments usually included in the course of professors arid lecturers, who have a complete apparatus at their command, and which at first appear very compli- cated and difficult, there are some which can be performed with every-day articles at hand. There is no experiment in acoustics more interesting than that of M. Lissajons, which consists, as is well known to our scientists, of projecting upon a table or other surface, with the aid of oxy-hydrogen light, the vibratory curves traced by one of the prongs of a tuning-fork. We can perform without difficulty a very similar experiment with the humble assistance of the common knitting-needle. Fix the flexible steel needle firmly in a cork, which will give it sufficient support ; fasten then at the upper extremity a small ball of sealing wax, or a piece of paper about the size of a large pea. - If the cork in which the needle is fixed be held firmly in one hand, and you cause the needle to vibrate by striking it, and then letting it sway of itself, or with a pretty strong blow with a piece of wood, you will perceive the little pellet of wax or paper describe an ellipse more or less elongated, or even a circle will be described if the vibrations be frequent. The effect is much enhanced if the experiment be performed beneath i6o SOUND. a lamp, so that plenty of light may fall upon the vibrating needle. In this case, the persistence of impressions upon the retina admits of one seeing the vibrating circle in successive positions, and we may almost fancy when the needle is struck with sufficient force, that an elongated Experiment showing vibration of sound waves. conical glass, like the old form of champagne glass, is rising from the cork, as shown in the illustration annexed. Acoustics may be studied in the same way as other branches of physical science. We will describe an in- teresting experiment, which gives a very good idea of the transmission of sounds through solid bodies. A silver CONDUCTION. i6i spoon is fastened to a thread, the ends of which are thrust into both ears, as shown in the illustration ; we then slightly swing the spoon until we make it touch the edge of the table ; the transmission of sound is in consequence so intense that we are ready to believe we Conduction of sound by solid bodies. are listening to the double diapason of an organ. This experiment explains perfectly the transmission of spoken words by means of the string of a telephone, another feontrivance which any one may make for himself without any trouble whatever. Two round pieces of cardboard are fitted to two cylinders of tin-plate, as large round as a 1 62 SOUND. lamp-glass, and four-and-a-half inches in length. If the two rounds of cardboard are connected by a long string of sixteen to eighteen yards, we can transmit sounds from one end to the other of this long cord ; the speaker pronouncing the words into the first cylinder, and the listener placing his ear against the other. It is easy to demonstrate that sound takes a certain time to pass from one point to another. When one sees in tne distance a carpenter driving in a stake, we find that the sound pro- HARMONOGRAPH. 163 duced by the blow of the hammer against the wood only reaches the ear a few seconds af^er the contact of the two objects. We see the flash at the firing of a gun, before hearing the sound of the report — of course on the condition that we are at a fairly considerable distance, as already remarked upon. We can show the production of the Gamut by cutting little pieces of wood of different sizes, which one throws on to a table; the sounds produced vary according to the size of the different pieces. The same effect may be obtained much better by means of goblets more or less filled with water ; they are struck with a short rod, and emit a sound which can be modified by pouring in a greater or less quantity of water ; if the performer is gifted with a musical ear, he can obtain, by a little arrangement, a perfect Gamut by means of seven glasses which each give a note. {See illustration.) A piece of music may be fairly rendered in this manner, for the musical glasses frequently produce a very pure silvery sound. We will complete the elementary principles of acoustics by describing a very curious apparatus invented by M. Tisley, the HARMONOGRAPH. This instrument, which we can easily describe, is a most interesting object of study. The Harmonograph belongs to mechanics in principle, and to the science of acoustics in application. We will first examine the apparatus itself. It is composed of two pendulums, A and B {see page 164), fixed to suspensions. Pendulum B supports a circular plate, P, on which we may place a small sheet of paper, as shown in the illustration. This paper is fixed by means of small brass clips. Pendulum A supports a horizontal bar, at the extremity of which is a glass tube, T, terminating at its lower extremity with a capillary opening ; this tube is filled with aniline ink, and just rests on the sheet of paper; the support and the tube are balanced by a 164 SOUND. counterpoise on the right. The two pendulums, A and B, are weighted with round pieces of lead, which can be moved at pleasure, so that various oscillations may be obtained. The ratio between the oscillations of the two pendulums may be exactly regulated by means of pen- M. Tiblcy s Harmonograpli. dulum A carrying a small additional weight, the height small wmdiass. If we give to pendulum A a slight move- iTne on ^r" "°"' *' P°'"^ '"' ^"t.^ ^ traces a straight B the n P^" P''-^^^ '■" ^ ■' ^"t ^f -- -°ve pendulum B, the paper also is displaced, and the point of tube T w^ trace curves, the shape of which varies with the nature of CURVES. t6s the movement of pendulum B, the relation between the oscillations of the two pendulums, etc. If the pendulums oscillate without any friction the curve will be clear, and the point will pass indefinitely over the same track, but when the oscillations diminish, the curve also diminishes in size, still preserving its form, and tending to a point corresponding with the position of repose of the two pendulums. The result is therefore that the curves traced Ratio 1 : 2. Ratio 2 ; 3. by the apparatus, of which we produce three specimens ■(see cuts above, and page i66), are traced in a continuous ^stroke, commencing with the part of the greatest amplitude. ' By changing the relation and phases of the oscillations we obtain curves of infinitely varied aspect. M. Tisley -has a collection of more than three thousand curves, which we have had occasion to glance over, in which we failed • to meet with two corresponding figures. The ratio between these curves corresponds with some special class, of which the analyst may define the general characters, but which 12 1 66 SOUND. is outside our present subject. By giving the plate P a rotatory movement, we obtain spiral curves of a very curious effect, but the apparatus is more complicated. Considered from this point of view it constitutes an in- Ratio 1 : 2 and a fraction. teresting mechanical apparatus, showing the combination of oscillations, and resolving certain questions of pure mechanics. From the point of view of acoustics it consti- tutes a less curious object of study. The experiments of j: if ^ 1 =J 1 „,. •.■ M «M .-. Hi, Construction of the Harmonograph. M. Lissajons have proved that the vibrations of diapasons are oscillations similar to, though much more rapid than those of the pendulum. We can therefore with this apparatus reproduce all the experiments of M. Lissajons, with this difference, that the movements being slower are easier to study. When the ratio between the number bf THE HARMONOGRAPH. 1^7 vibrations — we purposely use the term vibration instead of the term oscillation — is a whole number, we obtain ratios 1:2, and 2:3 {see page 165). If the ratio is not exact, we obtain figures on page 166, which is rather irregular in appearance, corresponding to the distortions noticeable in M. Lissajon's experiments. The first illus- tration has been traced in . the exact ratio 1:2; the second cut in the ratio 2:3; and the third corresponds to the ratio 1:2 and a small fraction, which causes the irregularity of the figure. ^ n ^TL Method of constructing an Harmonograph. In considering the harmony of the two first figures, — the first of which corresponds to the octave, the second to the fifth, whilst the third figure corresponds to the disagreeable interval of the ninth, — one is almost tempted to put a certain faith in the fundamental law of simple ratios as the basis of harmony. At first sight this appea-rs beyond doubt, but perhaps musicians would be hardly content with the explanation. M. Tisley's Harmonograph, - it will be seen, is a rather complicated apparatus ; and I will now explain how it may be constructed by means of a ie:'W pieces of wood. I endeavoured to construct as simple an apparatus as possible, and with the commonest 1 68 SOUND. materials, feeling that it is the best means of showing how it is possible for everybody to reproduce these charming curves of musical intervals. Also I completely excluded the employment of metals, and I constructed my apparatus entirely with pieces of wooden rulers, and old cigar boxes. I set to work in the following manner : on the two con- secutive sides of a drawing board I fixed four small pieces of wood {see cut, page 167), side by side in twos, having at the end a small piece of tin-plate forming a groove The apparatus completed. as in the cut above. In these grooves nails- are placod which support the pendulums. The piece of wood is placed on the corner of the table, so that the pendulums which oscillate in two planes at right angles, are in two planes that are sensibly parallel to the sides of the table. The pendulums are made of a thin lath, with two small pieces of wood fixed to them containing some very pointed nails, on which the pendulum oscillates. Page 167 gives us an illustration. The pendulums havea pin fixed in vertically, which passes through a piece of wood, and by means of a hinge connects the upper ends of the DETAILS OF HARMONOGRAPH. 169 two pendulums. This contrivance of the pin is very useful, and if care is taken to make the hole through the hinge in the form of a double cone, as shown in illustration on page 167, at c, it makes a perfect joint, which allows the piece of wood to be freely moved. To complete the apparatus, the heads of the two Details of mechanism. pendulums are united by the hinge, at the bend of which a slender glass tube is fixed, which traces the curves. The hinge is given in the illustration above, and to its two extremities are adjusted the two pins of the pen- dulum as in cut, page 168. The pendulums are encircled with round pieces of lead, which can be fixed at any height by means of a screw. CHAPTER X.— ACOUSTICS. (Continued!) THE TOPOPHONE THE MEGAPHONE THE AUTOPHONE THE AUDIPHONE — THE TELEPHONE THE PHO- NOTrRAPH THE MICROPHONE. E propose in this chapter to give as shortly as possible a description of the various instruments lately come into use, by means of which, and electricity, sounds can be carried from place to place, and their locality identified. It is only within the last few years that these wonderful inventions have come into use, and in a measure superseded the at one time invincible electric telegraph. The Telephone is now in daily use in London and other places, and its novelty, if not all its capability, has been discounted. The Phono- graph has also been frequently seen. So we will on this occasion commence with the ToPOPHONE, a rather novel instrument. As the name indicates, the ToPOPHONE is an apparatus for discovering the position of a sound, from the Greek words signifying a " place '' and " sound." The sources of sound can be found by it, and indeed this is its actual and practical use. It is claimed for this new apparatus that it stands in the same relation to the sailor as his old and trusty friends, the compass and sextant. These in navigation inform the steersman as to his course, and tells him his position by observation. The Topophone will tell him whence a sound arises, its origin wherever it THE TOPOPHONE. I71 may be ; and this in a fog is no mean advantage. Suppose a ship to be approaching a dangerous coast in a fog. Wc are all aware how deceptive sounds are when heard through such a medium. We cannot tell from what precise direc- tion the horn, whistle, or bell is sounding. The Topophone will give us the exact spot, and we can then, from our general knowledge of the locality, work our vessel up the river, or into the harbour, in safety. The Topophone was invented in 1880, by Professor Alfred Mayer, an American, and is based upon the well- known theory of sound waves. These, as we have already explained, exist in the air; and if the theory of sound waves has perfected the Topophone, we can fairly say that it has confirmed the supposed form of the sound waves. " Sound," says the inventor of the apparatus, "is supposed to be a particle continually expanding in the air, composed of a wave produced by compression, and followed by rarefaction. A continuous sound is a series of these particles or globules spreading and expanding as the water-rings in a pond." This much will be at once perceived. Now, suppose a person up to his shoulders in a pond of water; and someone throws a stone into it. If that person extend his arms and hands at right angles facing the sound, each hand would touch the edge of a ripple as it came towards him across the pond. He would then be facing the source of the ripples or waves, and look along a radius of the circle formed by the waves. But if he please, he can move his body so that both hands shall touch the same wave at the same time, or he might turn away from the source, and only one hand would touch the wave. But when both hands are actually washed by the same circular ripple he must be facing the source of it. Any position in which his fingers did not touch the ripple almost at the same instant, would not be 172 SOUND. facing the source of the wave ripples. So by turning and extending his hands, he could with his eyes shut find out whether he was or was not facing the original source of the waves. This applied to sound waves in the air is the whole theory of the Topophone, which, however, depends for its usefulness upon the same note being sounded by all horns and whistles. One note must be better than all the others, and that note, probably C (treble), caused by about two hundred and sixty vibrations per second, has been found most applicable. If all whistles and horns can by law be compelled to adjust themselves to this note, then the Topophone will be a real and lasting benefit. Let us now look at the apparatus itself. It being conceded that the resonators are in the same key as the Foghorn, — and this is necessary, — they are placed upon the deck of the vessel. An ear-tube of indiarubber is carried from each of these " resonators " into the cabin. These tubes unite and again separate, ending in small pieces ready to be fitted to the ears. The apparatus is fixed on deck, and the arrangement which supports it passes into the cabin, and can be turned about in any direction. Of course in this case a dial point is necessary to indicate the direction in which the instrument is turned. If the machine be worn on the shoulders of the officer of the watch he can move as he pleases, and wants no indicator. The Topophone when used is so constructed, that when a horn is heard, and when the listener is facing the sound, he can liear nothing ! When not facing the origin of the sound he can hear the horn very well, but the moment the resonators receive the sound together as they face the source, a very low murmur is heard, or perhaps no sound at all— Why .? "PITCH." 173 A certain pitch of tone is composed of vibrations or waves of equal length. In all waves there is a hollow and a crest. One neutralizes the other. The hollow of a sound, wave meeting the crest-of another wave "interferes" to produce silence, stillness, a dead level. So in " light " ; two rays will produce darkness. We will endeavour to explain this. If we have two equal strings, each performing an equal number of vibrations in a second, they will produce equal sound waves, and the sound produced by both together will be uninterrupted, and twice as loud as one of them. But if one string vibrate, say one hundred times, and the other one _hundred and one times in a second, they will not be in unison, and one will gain upon the other string, till after it has got to fifty vibrations it will be half a vibration ahead. At that moment they will neutralize each other, and silence will ensue for an appreciable time. In the case of light suppose a red ray strikes the eye, and another red ray to come upon it from somewhere else. If the difference between its distance and the other point from the spot in the retina on which the first ray fell, is the -j^o^q^o P^'^^ °f ^"^ inch, or exactly twice, thrice, four times as much, etc., that distance, the light will be seen twice as strong. Butif the difference in the distances between the points whence the light comes be only one- half the 1^0%^ P'^'''^ ^f ^^ ^'^'^^' °'' "i' 2^' si. or 4j times that distance, one light will extinguish the other, and dar'kness will be the result. Now this is precisely what happens in the case of the Topophone. To return to our simile of water waves. If two stones be cast into a pond, and two equal and similar waves produced, and if they reach at certain place at the same moment, they will make one large wave. But if one followed the other a little, so that the hollow of one coincided with the crest of the other, and vice versa, the waves would obliterate 174 SOUND. each other, and a dead level would result. One tube of the Topophone is half a wave length longer than the other, and when the resonators are in a line and receive the wave at the same time, one ear hears the elevation of the sound wave, and the other the depression,— the sound is neutralized, and comparative, if not actual, silence results. The sailor knows in what direction the land lies, and can calculate his distance, or anchor if he please. If amongst our readers there be any who wish to make for themselves an acoustic signalling apparatus there is physically nothing to prevent them from constructing such an instrument as that shown in the annexed woodcut. It is founded upon the speaking-trumpet principle, which is supposed to have been originated hy Samuel Markland, in 1670. Kircher, in his "Ars magna et umbra" and in his "Pkonurgia,'' mentions a kind of speaking-trumpet, or parte voix, of gigantic dimensions, and called the " Horn of Alexander." According to Kircher, the instrument was used by Alexander the Great to summon his soldiers from a distance of ten miles. The diameter of the circum- ference was about eight feet, and Kircher conjectured that the instrument was mounted upon three supports. During the last century, a German professor, named Huth, made a model of the horn, and found it answered every purpose of a speaking-trumpet with most powerful results, but we beg leave to doubt whether the instrument really carried the voice to any very great distance. The Acoustic Cornet, which is the counterpart of the speaking-trumpet, has been made in many different forms during the last two centuries, but none of them to the present time consist of anything more intricate than a simple tube with a mouthpiece and bell-shaped orifice. Professor Edison, however, in his researches regarding the conveyance of sounds, has made numerous and interest- THE MEGAPHONE. ^75 ing experiments. On one occasion, with his Megaphone he carried on a conversation at a distance of nearly two miles, without any other assistance from instruments except a few little cornets of cardboard. These constitute The Megaphone. the Megaphone, which may be regarded as a curiosity, considering the effects produced by such simple means. The illustration represents the instrument which is (or was lately) fixed upon the balcony of Mr. Edison's house. At a mile-and-a-half distant from the house, at a spot 176 SOUND. indicated by the two birds in the picture, another instru- ment was fixed, and conversation was carried on with ease. Perhaps the present opportunity will be the most con- venient to speak of the AUTOPHONE, although it is more a musical than an acoustic instrument. Until lately Barbary organs and piano organs have been the only means by which poor people have been able to hear any The Autophone. music, and that not of a very elevated class. ' Besides, there is a good deal of expense connected with the possession of an organ. But the Americans, with a view to popularize music, have invented the AuTOPHONE, which is simply a mechanical accordeon, manufactured by the Autophone Company, of Ithaca, New York. The principle of the instrument is represented in the illustration, and is extremely simple. An upright THE AUTOPHONE. 177 frame carries within it on one side a bellows, and on the other a flexible air chamber, which serves as a reservoir. The upper portion contains a set of stops like an accordeon, but the escape of the air throiagh the small vibrating plates can only take place by the upper surface of the frame work, upon which slides a thin plate of Bristol board pierced with holes at convenient distances, and set in motion by the mechanism shown in the annexed diagram. The figure represents an axle furnished with a series Detail of the Autophone. of " washers," which, acting upon the plate, cause it lo move round. It is the bellows movement that turns the axle by the aid of two '" catches," B and C, which work upon a toothed wheel fixed upon it. The " catch " B moves the paper on which the tune is " perforated," when the bellows is empty, the other catch when it is distended; but a counter catch, D, represented by the dotted lines in the illustration, is so arranged that the paper cannot pass on except the tooth of the catch D is opposite a hole pierced upon the plate above. In the contrary case there is no movement of the paper 178 SOUND. during the dilatation of the bellows. The effect of this very ingenious arrangement is to give to the "musical" band of "board" -an irregular movement, but it economises it in the case of sustained notes. The whole action of the instrument depends upon the correct working of the bellows. The effect, from an artistic point of view, certainly leaves something to be desired, but the instrument is cheap, and not cumbersome, and the slips of paper upon which the music is " cut out " can be made by machinery, and consequently are not dear. So far, the Autophone is fitted for popular favour and use, and may supersede the barrel organ. The AUDIPHONE is an instrument to conduct sound to the ear, to supplement it when temporary or partial deafness has occurred. Very likely many of our readers have observed ladies carrying large black fans on occasions, — at church, or lecture, or theatre, — and wondered why, perhaps. Those " fans " are Audiphones. The instrument is made of vulcanized rubber, and consists of a long flexible disc supported by a handle. To the upper edge of the " fan " are attached cords, which pass through a clip on the handle. If the person who wishes to hear by means of the Audiphone will hold the fan against the upper teeth, — the convex side of the fan outward, — he or she will hear distinctly, for the vibrations of sound are collected and strike upon the teeth and bones and act upon the auditory nerves from within, precisely as the vibrations act from without through the auricle. We need hardly add that if the ear be injured the Audiphone will be of no use. A writer says: "From personal observation with the Audiphone it appears to convey, the sonorous vibrations to the ear through the teeth, just as a long wooden rod held in the teeth will convey the vibrations of the sounding- board of a piano, though the piano is in another room THE AUDIPHONE. 179 and out of hearing by the ear. In using the Audiphone during conversation there is no movement or vibration felt by the teeth ; in Hstening to a piano there is a very faint sensation as if the Audiphone vibrated slightly, while with the handle of the Audiphone resting on the sounding-board of the piano the vibrations are so violent as to be painful to the teeth. By closing the ears a person with even acute hearing can observe the admirable manner in which the instrument conveys spoken words to the ear. The Audi- phone will prove to be of great value to deaf mutes, as it The Telephone, enables them to hear their own voices, and thus to train them to express words, while, before, they could only make inarticulate sounds." We have a variation of this instrument which has been introduced employing a diaphragm held in a telephone mouthpiece, and free to vibrate under the influence of sounds. This is connected by a string to a bit of wood that may be held in the teeth. . In use the hearer places the wood between his teeth, the string is drawn tight, and the speaker speaks through the telephone mouthpiece, the vibrations of the diaphragm being then conveyed to the teeth through the stretched string. This apparatus works l8o SOUND, very successfully, and ladies use it, but it is not so con- venient for general use as the Audiphone. The Telephone is now in daily use in London, and is by no means strange to the majority of our countrymen,, still some description of it will probably be acceptable, and a glance at its history may prove interesting. In speaking of the Telephone, we must not lose sight of the facts before mentioned, as regards our sense of hearing, and the manner in which the ear acts by the series of bones termed the hammer, the anvil, and stirrup. In the process of reproduction of tone in the magnetic instruments, the mechanism of the human ear was, to a The " receiving " apparatus. certain extent, imitated, and a diaphragm, by vibration«, generates and controls an electric current. Professor Wheatstone was the first person to employ the electric wire for the transmission of sounds, but Professor Ph.hp Reiss, of Friedrichsdorf, was the first to make the experiment of producing musical sounds at a distance. His first instrument was of a most primitive nature : subsequently he produced an instrument of which the first cut is the Telephone, the illustration above the receiver. ' In the first cut, it will be seen that there is an aper-^ ture on the top and one at the side; the latter is the mouthpiece. The top aperture is covered with a mem- THE TELEPHONE. l8l brane which is stretcked very tightly. When a person speaks or sings into the mouthpiece his voice is at once concentrated upon the tight membrane, which it causes tc vibrate in a manner corresponding with the vibrations of the voice. There are two binding screws, one at each side. To the centre of the tight membrane a piece of platinum is fixed, and this is connected with the binding screw on one side, in which a wire from the battery is fixed. On the membrane is a tripod, the feet of which (two) rest in metal cups, one of them being in a mercury cup connected with the binding screw at the opposite side to that already mentioned. The third " foot " — a platinum point — is on the platinum in the centre of the membrane or top, and moves with it. Every time the membrane is stretched by a vibration the platinum point is touched, and the closed circuit is broken by the return of each vibration. The receiving instrument {see page 1 80) consists of a coil enclosing an iron rod, and fixed upon a hollow sounding box. It is founded upon a fact discovered by Professor Henry, that iron bars when magnetized by an electric current become a little longer, and at the interrup- tion of the current resume their former length. Thus in the receiver - the iron will become alternately longer and shorter in accordance with the vibrations of the membrane in the box far away, and so the longitudinal vibrations of the bar of iron will be communicated to the sounding box, and become perfectly audible. This instrument, however, could only produce the "pitch" of sound, "not different degrees of intensity, or other qualities of tones." It merely sang with its own little trumpet whatever was sung into it; for all the waves were produced by an electric current of a certain and uniform strength, and therefore the sound waves were of the same size. But in 1874, Mr. Elisha Gray, of Chicago, improved 13 l83 SOUND. Reiss' instrument, and discovered a method by which the intensity or loudness of tones, as well as their " pitch," were transmitted and reproduced. In this method he S2 V O ^ s T3 . S *' bo 1 g o a n 2 M E a o employed electrical vibrations ot varying strength and rapidity, and so was enabled to reproduce a tune. Sub- sequently he conceived the notion of controlling the vibrations by means of a diaphragm, which responded to PROFESSOR -BELL. 183 every 'known sound, and by this he managed to transmit speech in an articulate manner. In 1876, Professor Graham Bell sent a Telephone to the Centennial' Exhibition at Philadelphia. Mr. Eell, according to the report, managed to produce a variation of strength of current in exact proportion to the particle of air moved by the sound. A piece of iron attached to a membrane, and moved to and fro in proximity to an electro magnet, proved successful. The battery and wire Bell's Telephone (Receiver). of the electro magnet are in circuit with the telegraph wire, and the wire of another electro magnet at the receiving station. This second magnet has a solid bar of iron for core, which is connected at one end, by a thick disc of iron, to an iron tube surrounding the coil and bar. The free circular end of the tube constitutes one pole of the electro magnet, and the adjacent free end of the bar core the other. A thin circular iron disc held (pressed against the end of the tube by the electro- magnetic attraction, and free to vibrate through a very r84 SOUND. small space without touching the central pole, constitutes the sounder by which the electric effect is reconverted External appearance of Bell Telephone. a Bobbin ofcoil wire round magnet, i. Dia- phragm, c. Mouthpiece, d. Permanent ™gn«'. f. Wires to binding screws. f. Both wires as one for convenience, .r- Adjusting screw-holding magnet. into sound. The accompanying illustrations {see page 1 82) show Mr. Bell's Telephone as described. The Telephone, subsequently simplified by Professor Bell, is shown in the two following illustrations. The MR. EDTSON. 1 85 voice strikes against the diaphragm, and it begins to vibrate. The sound is not conveyed by the wire; the motion is communicated, and the vibrations becoine sound waves again. The Telephone consists of a cyhndrical magnet encircled at one end by a bobbin, on which is wound a quantity of fine insulated copper wire. The magnet and coil are contained in a wooden case, the ends of the coil being soldered to thick copper wire, which traverse the " wooden envelope," and terminate in Mode of using the Telephone. the binding screws. In front of the magnet is a thin circular iron plate, in which is the mouthpiece. The drawings will explain the instrument. Mr. Edison also invented a Telephone like Gray's, and made the discovery, that when properly prepared, carbon ■would change its resistance with pressure, and that the ratio of these changes corresponded with the pressure. This solved the problem of the production of speech. The carbon is placed between two plates of platinum connected in the circuit and near the diaphragm, and 1 86 SOUND. the carbon receives the pressure from it by means of the mouthpiece. Q Wheii we come to MAGNETISM and Electricity we may have something more to say respecting the mysteries of the Teliiphone and its later developments. At present THE PHONOGRAPH. 187 we are only concerned with it as a sound conveyer, and it answers its purpose admirably, although somewhat liable to attract other sounds or vibrations from neighbouring wires. The Phonograph, a mechanical invention of Mr. Edison, does not make use of electricity, although the vibratory motion of the diaphragm is utilized. It, in a simple form, consists of a diaphragm so arranged as to operate upon a small stylus placed just opposite and below the centre, and a brass cylinder, six or eight inches long, by three or four in diameter, mounted upon a horizontal axis, extending each way beyond its ends for a distance about its own length. "A spiral groove is cut in the circumference of the cylinder, from one end to the other, each spiral of the groove being separated from its neighbour by about one- tenth of an inch. The shaft or axis is also cut by a screw thread corresponding to the spiral groove of the cylinder, and works in screw bearings ; consequently when the cylinder is caused to revolve, by means of a crank that is fitted to the axis for this purpose, it receives a forward or backward movement of about one-tenth of an inch for every turn of the same, the direction, of course, depending upon the way the crank is turned. The diaphragm is firmly supported by an upright casting capable of adjustment, and so arranged that it may be removed altogether when necessary. When in use, how- ever, it is clamped in a fixed position above or in front of the cylinder, thus bringing the stylus always opposite the groove as the cylinder is turned. A small, flat spring attached to the casting extends underneath the diaphragm as far as its centre and carries the stylus, and between the diaphragm and spring a small piece of indiarubber is placed to modify the action, it having been found that better results are obtained by this means than when the stylus is rigidly attached to the diaphragm itself. l88 SOUND. "The action of the apparatus will now be readily understood from what follows. The cylinder is first very smoothly covered with tin-foil, and the diaphragm securely fastened in place by clamping its support to the base of the instrument. When this has been properly done, the stylus should lightly press against that part of the foil over the groove. The crank is now turned, while, at the same time, someone speaks into the mouthpiece of the instrument, which will cause the diaphragm to vibrate, and as the vibrations of the latter correspond with the movements of the air producing them, the soft and yielding foil will become marked along the line of the groove by a series of indentations of different depths, varying with the amplitude of the vibrations of the diaphragm ; or in other words, with the inflections or modulations of the speaker's voice. These inflections may therefore be looked upon as a sort of visible speech, which, in fact, they really are. If now the diaphragm is removed, by loosening the clamp, and the cylinder then turned back to the starting point, we have only to replace the diaphragm and turn in the same direction as at first, to hear repeated all that has been spoken into the mouthpiece of the apparatus ; the stylus, by this means, being caused to traverse its former path, and consequently, rising and falling with the depressions in the foil, its motion is communicated to the diaphragm, and thence through the intervening air to the ear, where the sensation of sound is produced. "As the faithful reproduction of a sound is in reality nothing ii»ore than a reproduction of similar acoustic vibrations in a given time, it at once becomes evident that the cylinder should be made to revolve with absolute uniformity at all times, otherwise a difference more or less marked between the original sound and the reproduction will become manifest. To secure this uniformity of motion, and produce a practically working machine for automatically THE PHONOGRAPH. I 89 recording speeches, vocal and instrumental music, and perfectly reproducing the same, the inventor devised an apparatus in which a plate replaces the cylinder. This plate, which is ten inches in diameter, has a volute spiral groove cut in its surface on both sides from its centre to within one inch of its outer edge ; an arm guided by the spiral upon the under side of the plate carries a diaphragm and mouthpiece at its extreme end. If the arm be placed near the centre of the plate and the latter rotated, the motion will cause the arm to follow the spiral outward to the edge. A spring and train of wheel-work regulated by a friction governor serves to give uniform motion to the plate. The sheet upon which the record is made is of tin-foil. This is fastened to a paper frame, made by cutting a nine-inch disc from a square piece of paper of the same dimensions as the plate. Four pins upon the plate pass through corresponding eyelet-holes punched in the four corners of the paper, when the latter is laid upon it, and thus secure accurate registration, while a clamping- frame hinged to the plate fastens the foil and its paper frame securely to the latter. The mechanism is so arranged that the plate may be started and stopped instantly, or its motion reversed at will, thus giving the greatest con- venience to both speaker and copyist. " The articulation and quality of the Phonograph, although not yet perfect, is full as good as the Telephone was. The instrument, when perfected and moved by clock-work, will undoubtedly reproduce every condition of the human voice, including the whole world of expres- sion in speech and song, and will be used universally. "The sheet of tin-foil or other plastic material receiving the impressions of sound, will be stereotyped or electro- typed so as to be multiplied and made durable ; or the cylinder will be made of a material plastic when used, and hardening afterward. Thin sheets of papier mache. rgo SOUND. or of various substances which soften by heat, would be of this character. Having provided thus for the durability of the Phonograph plate, it will be very easy to make it separable from the cylinder producing it, and attachable to a corresponding cylinder anywhere and at any time. There -will doubtless be a standard of diameter and pitch of screw for Phonograph cylinders. Friends at a distance will then send to each other Phonograph letters, which will talk at any time in the friend's voice when put upon the instrument."* The Microphone (an outcome of the Telephone) was discovered by Professor Hughes, of London. It is an instrument which in its main features consists of a carbon " pencil," so suspended that one end rests upon a carbon " die." The instrument being connected with a Telephone by the circuit wires, will reproduce faint sounds very distinctly. Once a Microphone was put into a preacher's pulpit, and joined to a private telegraph wire which led to a gentleman's house. The owner was thus enabled to hear the sermon. So long as it is thus connected every minute sound, even h fly's footstep, will be faithfully reproduced. * Scribner's Magazine, CHAPTER XI.— ACOUSTICS, {Continued^ THE TUNING-FORK THE SYREN — SOUND FIGURES — SINGING FLAMES ■ E cannot close the subject of Sound without some mention of -the -Musical Pitch, and various in- struments and experiments which have from time to time been made to discov:er the pitch, sound', and vibrations, and even to see Sound. To under- stand' the vibrations or " pitch "of a musical note we may study the illustration, which shows us a tuning-fork ite vibration. You will perceive that each prong of the tuning-fork beats the air in an opposite direction at the sam« time, say from- « to ^ ^ee next page). The prong strikes the air, and the wave thus created strikes again outward, and the condensation thus created travels along the back beat, rarefying the air, and both these, the rarefaction and the condensation, move with the same rapidity one behind the other. The tuning-fork of course vibrates a very great many times in a second, every vibration generating a wave. " Pitch," in a general sense, is the number of vibrations per second which constitute a note. For instance, the note A, the standard pitch consists of four hundred and thirty-five complete vibrations per second. Concert pitch is slightly higher, for there are a few more vibrations in the second. The lowest sound pitch is forty vibrations. 193 SOUND. the highest forty thousand. "Pitch" may be determined by an instrument termed the "Syren," or by a tooth-wheeled apparatus. The Syren was invented by Cagniard de Latour. It consists of a metal cylinder, a tube passes through the bottom, and through the tube air is blown into the cylinder. On the top a number of holes are drilled, while just over the cylinder top, almost in contact with it, is a metallic disc, which rotates upon a vertical axis. The disc is Vibrations of tuning fork. perforated with holes equal in number to those in the cylinder top, but the holes are not perpendicular, they slope in opposite directions. So when the air is forced through the holes in the top of the cylinder it impinges upon one side of the holes in the rotating disc, and blows it round. The disc in one revolution will therefore open and shut as many holes as there are in the disc and cylinder, and the air blown in will escape in so many puffs — the number of puffs in a given time depending upon the rapidity of rotation. There is an arrangement to show the number SOUND FIGURES. 193 of turns. By these rotations a sound is produced which rises in pitch as the revolutions are increased in number. To determine the pitch of a certain sound we must find the number of times the plate revolves in that time, then we- shall have the number of vibrations per second required to produce the note we desire. The arrangement working in a notched wheel tells us the number of rotations of the disc. Successive, and rapidly-successive puffs or beats are lieard as the rotation increases, and at length the two sounds will disappear, and merge into one, which is perhaps that of the tuning-fgrk, whose note you require Sound Figures. to find the "pitch" of By maintaining this rate for a minute or less, and setting the gear to tell the revolutions, the number will be found marked on the dial of the apparatus. So by multiplying the number of revolutions of the disc by the number of the holes, and dividing the product by the number of seconds during which the disc was in connection with the recording gear, we shall have the number of vibrations per second necessary to produce the pitch corresponding to the given sound. The above is the description of one form of Syren ; there are others, which, however, we need not detail. We have seen that there are certain nodal points, or 194 SOUND. res'^ing-places, in vibrations, and this can easily be shown upon a fiddle-string-, from which paper discs will fall off except on the nodal point, showing that there is no vibration there. The same experiment may be made by means of plates, which will give us what are termed Chladni's figures. Suppose we strew a glass-plate with fine sand, and stroke the edge with a fiddle-bow. The vibrations of the plates will make certain patterns, and cast the sand upon those points of repose to form nodal lines in various directions. The plates must, of course, be held or fastened, and a variety of souitd figures may be produced. {See page 193). The relation between the number of segments on the plate and the pitch of the note, can be ascertained .by using a circular plate clamped in the centre. " if -tht finger on the plate and the fiddle-bow are one-eighth of the circumference apart, the fundamental note will "be produced. If one-sixteenth apart, the higher octave will be heard." Sensitive flames will detect air vibrations, and flames can also be made to sing. Sensitive flames were discovered by Mr. Barrett, who noticed the effect a shrill note had upon a gas flame from a tapering jet. The flame was a very long one (fourteen inches), and when the sound was produced it shortened at once, while the upper part expanded like a fan ; the same effects, in a less marked degree, were observable when the shrill sound was prolonged from a distance of forty feet. Professor Tyndall was immediately interested in this discovery, and in January 1867 he lectured upon it at the Royal Institution. If any one wish to try the experiment, a piece of glass tubing should be obtained, and let the mouth be tapered down to a small orifice one-sixteenth of an inch in diameter. Then when the highest pressure is on for SINGING FLAMES. I95 the evening, light the gas and sound a shrill whistle. The flame will sink down and spread out. The illuminating power may thus be increased, and many experiments may be made. For instance, if a person be in the room and try to read, he will probably not be able to do so at a little distance; but if his friend whistle to the gas it will so expand itself as to enable him to read, so long as the whistle lasts. A very ingenious burglar-detector was made upon the principle of the sensitive flame, which expands at a noise and heats a welded plate of gold, silver, and platinum. The plate swerves aside, the metals being unequally affected by heat, and as it is connected with a battery, rings a bell by electricity. A small high flame has been made sensitive to the chinking of coin, or even to the ticking of a watch. We will now give some explanation, derived partly from Professor Tyndall, of the cause of sensitive flames. A sensitive flame is one just on the point of " roaring," and about to change its aspect. "It stands," says Tyndall, " on the edge of a precipice. The proper sound pushes it over . . . We bring it to the verge of falling, and the sonorous pulses precipitate what was already imminent." The flame is in a state of vibration, so sounds being vibrations, practically increase the pressure; and the flame acknowledges the pressure thus invisibly applied by air waves. Singing Flames are produced by burning hydrogen in a tube ; a musical note is , thus produced in the same way as the air calises a note in an organ pipe. Faraday attributed the sound to rapid vibration caused by successive explosions of the burning gas. The Gas Harmonicon has been made on this principle. The air, being heated in the glass tube, ascends, and the flame is thus permitted fo come up more forcibly in the tube; so violent agitation 196 SOUND. results when the air tries to get into the opening above. The size of the flame and its position in the tube will give a certain note which will be the same note as the air would emit if in a pipe, for the vibrations give the sound. Sir Charles Wheatstone has shown by experiment how sound can be transmitted by placing a rod on a musical- box, and carrying the rod through the ceiling. When a guitar or violin was placed upon the rod, the sounds of the musical-box were distinctly heard in the upper room. A Phantom Band can be made by connecting certain instruments with others being played on under the stage. Every one will then appear to play by itself. MARVELS OF EARTH, AIR, AND WATER. INTRODUCTION. :HERE are some people who go through life practically blind. Indeed, for many purposes they might just as well be blind. Of them it might with truth be said, that " seeing, they see not.'' To their eyes and perceptions the sun is just a hot, bright body, that warms us too much sometimes ; sunset is simply the signal for lighting candles or gas, or for sitting idly, or groping awkwardly under the pretence of " blind man's holiday ; " a thunderstorm is a terrible nuisance, especially if, dressed for a visit, they happen to be caught in one; the star-spangled heavens afford a very pretty excuse for a walk, during which they never so much as lift their eyes to the splendid vision ; and life's pageant is but a round of duties or parties, which certainly do not lift their thoughts heavenward. How extraordinary and forceful is the contrast between this state of mind and that person's who possesses the seeing eye, the hearing ear. To such, among whom we venture to claim a place, the sun is a glorious orb of fire, emitting light and heat which are essential to the life of a world ; sometimes dazzling us with its full radiance, often warming us and cheering our hearts after a winter's cold, ripening the harvest and embrowning the complexion ; the leader, for us, of that continuous pro- cession of brightness across our sky ; now bold and ruddy at the beginning and close of his daily round, now pure VI 1NTRODUCTIO.N. and white as he is seen higher in the sky ; and anon showing, in the glories of sunset, the extraordinary effects which may be produced by simple light and cloud, with the varying distribution of vapour in the air. How can people be insensible to the charms of twilight, whether long drawn out or suddenly precipitated, the stillness of the air as the sun glides down, or the shrill whistle of the wind as the night storm rises, the graceful oscillation of the branches of trees, too often and too early shedding their leaves as they move ? Even the dull leaden sky, the gentle, steady downpour of rain, have their own points of interest, which the lover of nature is not slow to find out; while the consequences of rain in the general refreshment of plants, the cleansing of the air and of the ground, the washing of houses, the filling of streams and rivers, are among the most delightful of natural phenomena. Only at one atmospheric effect, in produc- ing which, however, man is a participator, do we not rejoice — namely, at the various kinds of fogs, laden with sooty particles from manufactories and locomotives, and all kinds of effluvia and germs of disease ; and we look upon it as a pretty sharp lesson, with its attendant colds and rheumatisms and accidents, to sluggish mankind to mend his ways and consume his own smoke, — a lesson which will probably become more severe each year till we learn it. But the thunderstorm, — how grand an event, how striking a study ! The lightning flash in all its varieties, sheet and forked, near and far, blinding or merely glow- ing in the distance ; the thunderclap, now sudden and sharp as a hammer blow, now slow and soft in sound, and gradually waxing to a climax of rattling peals, and dying away in the distance, and again seeming to shake houses to their foundations, and even to affect the solid earth with its violence ; and the rain, so often INTRODUCTION. Vll following with desperate energy, and keeping on with wonderful persistence, as if it would exhaust the foun- tains of heaven by its copious discharges ; and finally the stillness, freshness, and cleanliness succeeding the storm, — all these are rich treasures of delight to the instructed mind, which sees in these wonders but a faint expression of the surpassing glories and powers which belong to the supreme Worker of all. True it is that " the heavens declare the glory of God, and the firmament showeth His handiwork." The con- tinual procession of spots of beauty, each differing in magnitude and brightness, is a constant reminder to us to look to things above. The thought that each of these bright stars is a sun, essentially similar to our own sun, and supplying light to a number of non-luminous planets circling round it, is overwhelming when we consider the vast multiplicity of suns and planets that must exist in the universe. And the stately moon moves with soft grace through the sky, fulfilling its appointed task with as much regularity as the enormously greater and brighter sun. Can the dull soul of man, woman, or child remain blind to these glories after once having the attention vividly awakened, or forget them in a base surrender to evil jealousies and struggles ? How attrac- tive to the thoughtful mind it should be to penetrate, if but a little way, into the mystery of the forces which thus surround us and influence our being 1 But some will say, " Oh, but we can appreciate the beauties of nature without studying them in a book. It is so dry, what is said in books, compared to enjoying things." We are prepared to assert that what is found in books about nature need not be dry, and very often is not, and that some of the most entertaining of these accounts may be found in the following pages. Even should there be a little close attention demanded, in order vili INTRODUCTION. to understand some explanations, yet we maintain that this will be amply compensated by the great gain to our appreciation of nature which follows a closer acquaint- ance with the details. Does not a knowledge of the solar system, and the mode in which the planets revolve round the sun, — of the fact of the stars being so many suns at very great distances, — of the changes of day and night being produced by the revolution of the earth upon its axis, and the other wonders of astronomy, greatly enlarge the pleasure to be derived from their contempla- tion ? Does not the reference of everything to its course, and the realisation of the orderliness of the complex arrangements of the universe, both increase our enjoy- ment of the results and raise our minds to the wonderful powers of the great First Cause of all ? The basis of a satisfactory examination of the powers of nature must be the understanding of the simple pro- perties of the matter or substance of which they are composed. There arc certain properties which are found to be common to all matter, of whatever composition ; and when they are clearly grasped, we shall be equipped for a consideration of the differences between the properties of different kinds of matter. The familiar questions and answers, ''What is matter? Never mind. What is mind > Never matter," contain a great deal of truth, although some people have asserted that mind is a pro- duct of matter, a sort of fruit produced by its workings. But they have made this rather as an assertion than as a subject of proof. Because our thinking is done in connection with the brain, they have suggested that no thinking can be done anywhere without a brain. It is really idle to waste time on such conjectures, when there is so much to be done in studying what wc can understand. Others have suggested that matter is a delusion of the INTRODUCTION. ix senses, and that we only imagine we see or feel different objects. They say that matter has no real existence, and that the only real thing is our brain receiving certain impressions. But they will never persuade the mass of humanity to regard the world as anything but a very real thing. Try to make a man who has just hit his head against a wall, or fallen downstairs, believe that he has not really been struck, and that it is only a delusion of his senses, and he will either feel inclined to strike the persuasive person who makes the remark or to reply that it is quite as real to him whichever way it is ; and he knows, too, that the doctor's charge will really affect his pocket in the way of making his purse lighter. So the reality of matter is firmly fixed in the mind of mankind; and not even a surgical operation can make him believe that it is all a joke or a sport of nature. Having implanted in our minds the chief properties of matter, we shall then proceed to exemplify the various studies of nature that can be satisfactorily pursued in the open air without expensive apparatus. The variety of charming creatures that can be found on our field excursions is much greater than is ordinarily realised. Stones, mud, slime, pond water, insects, nests, flowers, leaves, fungi, seaweeds, all furnish subjects for many a day's examination. Air and water in their different conditions afford material for profoundly interesting observations which any one may make. Gradually we acquire a perception of different forces of nature which may be separately understood and followed out through a variety of purposes. Attraction and cohesion will lead us through very interesting phenomena. We shall gradually acquire a notion of what is meant by a centre of gravity, and how from this follows the prin- ciple of the balance, — a principle which in all its variations is well worth studying ; for the balance is used in an X Introduction. infinite number of operations in life, and many are the occasions on whicii it would be extremely useful to us to be able to say positively whether a balance is correct or not. The question of equilibrium, too, is of a most practical nature; for we continually have to arrange our own loads so as to balance, or to place things on tables or shelves so that they shall not fall down. The know- ledge of how to tell the relative weight of liquids is of great importance to us in estimating the purity of milk, oils, etc. The pressure of the air is of interest to every one, though it is so equally adjusted that we never feel it except when strong winds attack us ; but it produces many of the variations of the weather, and none of us can be really indifferent to it. The barometer, the air- pump, the diving-bell, the pendulum, ballooning, the syphon, the Bramah press, capillarity, and buoyancy, — these are a few of the many subjects upon which wc shall touch, each of which is calculated to reward the patient student, to enlarge the capacity of his mind, to give him new powers of appreciation of nature, and to make him in manifold ways a wiser and more capable being. CONTENTS. CHAPTER I.— THE STUDY OF NATURE. THE BOOK OF NATURE — THE SENSES NATURAL HISTORY NATURAL PHILOSOPHY — MATTER OBJECTS — -PROPERTIES OF MATTER I CHAPTER n.— SCIENCE IN THE OPEN AIR. APHIDES — EVAPORATION BY LEAVES — AN AQUARIUM — THE CATA- LEPTIC FOWL — NEEDLE POINTS AND THORNS — MICROSCOPIC AQUARIUM — CAPE GRISNEZ — CRYSTALS — ICE ON THE GAS LAMPS 8 CHAPTER III.— SIMPLE PHYSICS. THE MEANING OF PHYSICS — FORCES OF NATURE— GRAVITY CO- HESION — CHEMICAL ATTRACTION — CENTRE OF GRAVITY EXPERIMENTS — AUTOMATON TUMBLERS 3! CHAPTER IV.— SOLID BODIES. SOME PROPERTIES OF SOLID BODIES — INERTIA — MOTION — FRICTION — THE PENDULUM — EQUILIBRIUM 50 CHAPTER v.— GASES AND LIQUIDS. PRESSURE OF THE AIR — EXPERIMENTS — THE MADGEBURG HEMI- SPHERES—AIR-PUMPS — THE BAROMETER — THE PUMP . . 63 Xll CONTENTS. CHAPTER VI.— AERONAUTICS. PAGE PRESSURE OF AIR IN BODIES — EARLY ATTEMPTS TO FLY IN THE AIR -^DISCOVERY OF HYDROGEN THE MONTGOLFIER BAL- LOONS — FIRST EXPERIMENTS IN PARIS — NOTED ASCENTS . 86 CHAPTER VII.— WATER. ABOUT WATER — HYDROSTATICS AND HYDRAULICS LAW OF ARCHIMEDES — THE BRAMAH PRESS — THE SYPHON — SPECIFIC GRAVITY. ilO CHAPTER I.— THE STUDY OF NATURE. THE BOOK OF NATURE THE SENSES NATURAL HIS- TORY — NATURAL PHILOSOPHY MATTER — OBJECTS PROPERTIES OF MATTER. ERNARD PALISSY used to say that he wished " no other book than the earth and the sky," and that " it was given to all to read this wonderful book." It is indeed by the study of the material world that discoveries are accomplished. Let an attentive observer watch a ray of light passing from the air into water, and he will see it deviate from the straight line by refraction ; let him seek the origin of a sound, and he will discover that it results from a shock or a vibration. This is physical science in its infancy. It is said that Newton was led to discover the laws of universal gravitation by beholding an apple fall to the ground, and that Mont- golfier first dreamt of air-balloons while watching fogs floating in the atmosphere. The idea of the inner chamber of the eye may, in like manner, be developed in the mind of any observer, who, seated beneath the shade of a tree, looks fixedly at the round form of the sun through the openings in the leaves. THE STUDY OF NATURE. ''ii''' \ '^ '■ I Aquarium foi-med by ineanB of a melon-glass. glass bell was placed. I next scattered seme large pebbles and shells at the bottom of the vase to form a stony bed, poured in some water, placed a few reeds and water plants among the pebbles, and then threw a handful of water THE insects' palace, I 3 lentils on the surface ; thus a comfortable home was con- trived for all the captured animals* The aquarium, when placed under the shade of a fine tree in a rustic spot abounding with field flowers, became a favourite rendez- vous, and we often took pleasure in watching the antics of the little inmates. Sometimes we beheld very san- guinary scenes ; the voracious hydrophilus would seize a poor defenceless tadpole, and rend him in pieces for a meal without any compunction. The more robust tritons defended themselves better, but sometimes they also suc- cumbed in the struggle. The success of the aquarium was so complete that one of us resolved to continue this museum in miniature, and one day provided himself with an insects' palace, which nearly made us forget the tadpoles and tritons. It was a charming little cage, having the form of a house, covered with a roof; wires placed at equal distances forming the sides. In it was a large cricket beside a leaf of lettuce, which served as his food. The little creature moved up and down his prison, which was suspended from the branch of a tree, and when one approached him very closely gave vent to his lively chirps. The menagerie was soon further augmented by a hitherto unthought-of object ; namely, a frogs' ladder. It was made with much skill. A large bottle served for the base of the structure. The ladder which was fixed in it was composed of the twigs of very small branches, recently cut from a tree, and undivested of their bark, which gave to the little edifice a more picturesque and rustic appearance. The pieces of wood, cleverly fixed into two posts, conducted the green frogs (tree-frogs) on to a platform, whence they ascended the steps of a * It frequently happens that in a small aquarium, constructed after this fashion, the animals escape. This is avoided by covering the vase with a net. 14 OPEN-AIR SCIENCE. genuine ladder. There they could disport themselves at pleasure, or climb up further to a branch of birch-tree placed upright in the centre of the bottle. A net with Cage for j fine meshes prevented the little animals from escaping. We gave the tree-frogs flies for their food, and sometimes they caught them with remarkable dexterity. I have often seen a frog when at liberty watching a fly, on which AN AQUARIUM. IS It pounces as a cat does on a bird. The observations that we made on the animals of our menagerie led us to undertake others of a very different nature ; I recollect Small aqnnrinm, with frogs' ladder. particularly a case of catalepsy produced in a code. I will describe this remarkable experiment, certainly one of the most curious we ever performed. We place a cock on a table of dark colour, rest its i6 OPEN-AIR SCIENCE. beak on the surface, where it is firmly held, and with a piece of chalk slowly draw a white line in continuation from the beak, as shown in our engraving. If the crest is thick, it is necessary to draw it back, so that the animal Frog lying in wait for a fly. may follow with his eyes the tracing of the line. When the line has reached a length of two feet the cock has become cataleptic. He is absolutely motionless, his eyes are fixed, and he will remain from thirty to sixty seconds in the same posture in which he had at first only been head remains resting on the table in held by force. His THE CATALEPTIC COCIC U iS OPEN-AIR SCIENCE. the position shown. This experiment, which we have successfully performed on different animals, can also be accomplished by drawing a straight line with a piece of chalk on a slate. M. Azam declares that the same result is also produced by drawing a black line on a table of white wood. According to M. Balbiani, German students had formerly a great predilection for this experiment, which they always performed with marked success. Hens do not, when operated on, fall into a cataleptic condition so easily as cocks ; but they may often be rendered motionless by holding their heads fixed in the same position for several minutes. The facts" we have just cited come properly under the little studied phenomena, designated by M. Braid in 1843 by the title of Hypnotism. MM. Littri^ and Ch. Robin have given a description of the hypnotic condition in their Dictionnaire de MMecine. If any shining object, such as a lancet, or a disc of silver-paper gummed to a plate, is placed at about the distance of a foot from the eyes of a person, slightly above the head, and the patient regards this object fixedly, and without interruption for twenty or thirty minutes, he will become gradually motionless, and in a great number of cases will fall into a condition of torpor and genuine sleep. Dr. Braid affirms that under such circumstances he has been able to perfcrm surgical operations without the patient having any consciousness of pain. Later also, M. Azam has proved the complete insensibility to pricking on the part of individuals whom he has rendered cataleptic by the fixing of a brilliant object. The experiment of the cataleptic cock was first described under the name of Experimentum Mirahile, by P. Kircher, in his Ars Magna, published at Rome in 1646. It evidently belongs to the class of experiments which were performed at the Sal- pdtriere asylum at Paris, by M. Charcot, on patients suffering from special disorders. It must now be evident THORNS AND STINGS. 19 to our readers that our scientific occupations were suffi- ciently varied, and that we easily found around us many objects of study. When the weather was wet and cloudy we remained indoors, and devoted ourselves to micro- scopical examinations. Everything that came under our hands, insects, vegetables, etc., were worthy of observation. One day, while engaged over a microscopical preparation. Ordinary pin and needle, teen through a microscope (magnified 500 dianielers). I was making use of one of those steel points generally employed in such purposes, when Jiappening to pass it accidentally beneath the microscope, I was astonished to see how rough and uneven it appeared when highly magnified. The idea then occurred to me to have recourse to some- thing still more pointed, and I was thus led to make comparisons between the different objects represented. It will here be seen how very coarse is the product of our industry when compared with the product of Nature. 20 OPEN-AIR SCIENCE. No. I represents the point of a pin that has already been used, magnified 500 diameters. The point is evidently slightly blunted and flattened. The malleable metal has yielded a little under the pressure necessary to make it pass through a material. No. 2 is a little more pointed ; it is a needle. This, too, will be seen to be defective when regarded by the aid of the microscope. On the Thorn of a ros", and wasp's sting through a microscope ^magnified 500 diameters). other hand, what fineness and delicacy do the rose thorn and wasp's sting present when examined under the same magnifier ! See the two points in illustration. An examination of this exact drawing has led me to make a calculation which leads to rather curious results : at a half millimetre from the point, the diameters of the four objects represented are in thousandths of a milli- metre respectively, 3*4 ; 2'2 ; i"i ; 0'38. The corre- sponding sections in millionths of a square millimetre are : INFUSORIA. 2 1 907'92 ; 380-13; 95'03 ; ii'34; or, in round numbers, 908 ; 380 ; 95 ; II. If one bears in min"d, which is much below the truth, that the pressure exercised on the point must be propor- tional to the section, and admitting that a pressure of 1 1 centigrams suffices to thrust in the sting of a wasp half a millimetre, it will require more than 9 grams of pressure to thrust in a needle to the same extent. In fact, this latter figure is much too small, for we have not taken into acco.unt the advantage resulting from the elongated shape of the rose thorn, which renders it more favourable for penetration than a needle through a drop of tallow. It would be easy to extend observations of this kind to a number of other objects, and the remarks I have just made on natural and artificial points will apply incon- testably to textures for example. There is no doubt that the thread of a spider's web would far surpass the thread of the finest lace, and that art will always find itself completely distanced by nature. We amused ourselves frequently by examining the infusoria which are so easily procured by taking from some stagnant water the mucilage adhering to the vegetation on the banks, or attached to the lower part of water lentils. In this way we easily captured infusoria, which, when placed under a strong magnifier, presented the most remarkable spectacle that one can imagine. They are animalcules, having the form of transparent tulips attached to a long stem. They form bunches which expand and lengthen ; then, suddenly, they are seen to contract with such considerable rapidity that the eye can scarcely follow the movement, and all the stems and flower-bells are folded up into the form of a ball. Then, in another moment, the stems lengthen, and the tulip-bells open once more. One can easily encourage 22 OPEN-AIR SCIENCE. the production of infusoria by constructing a small micro- scopic aquarium, in which one arranges the centre in a manner favourable to the development of the lowest Arrangeinent of a m;croscop:c aqunnum for examining infusoria. organisms. It suffices to put a few leaves (a piece of parsley answers the purpose perfectly)* in a small vase The infusion of parsley has the advantage of not sensibl) obscuring the water. BUTTERFLIES. 2 3 containing water, over which a glass cover is placed, and it is then exposed to the rays of the sun. In two or three days' time, a drop of this water seen under the microscope will exhibit infitsoria. After a certain time, too, the different species will begin to show themselves. Microscopical observations can be made on a number of different objects. Expose to the air some flour moistened by water, and before long a mouldiness will form on it ; it is the penicillium glancum, and when examined under a magnifier of 200 to 300 diameters, cells are distinguish- able, branching out from an organism remarkable for its simplicity. We often amused ourselves by examining, almost at hazard, everything that came within our reach, and sometimes we were led to make very instructive investigations. When the sky was clear, and the weather favourable to walking, we encouraged our young people to run about in the fields and chase butterflies. The capture of butterflies is accomplished, as every one knows, by means of a gauze net, with which we provided the children, and the operation of chasing afforded them some very salutary exercise. It sometimes happens that butter- flies abound in such numbers that it is comparatively easy to capture them. During the month of June 1879, a large part of Western Europe was thronged with swarms of Vanessa algina butterflies, in such numbers that their appearance was regarded' as an important event, and attracted the lively attention of all entomologists. This passage of butterflies provided the occasion for many interesting studies on the part of naturalists. We cannot point out too strongly to our readers that the essential condition for the student of natural science, is the possession of that sacred fire which imparts the energy and perseverance necessary for acquiring and enlarging collections. It is also necessary that the investigator should furnish himself with certain indispensable tools. OPEN-AIR SCIENCE. STUDY OF STRATA. 25 For collecting plants the botanist should be armed with a good hoe set in a thoroughly strong handle, a trowel, of which there is a variety of shapes, and a knife with a sharp blade. A botanical case must also be included, for carrying the plants. The geologist, or mineralogist, needs no more elaborate instruments ; a hammer, a chisel, and a pickaxe with a sharp point for breaking the rocks, and a bag for carrying the specimens, will complete his outfit. We amused ourselves by having these instruments made by the blacksmith, sometimes even by manufacturing them ourselves ; they were simple, but solid, and ad- mirably adapted to the requirements of research. Often we directed our walks to the seashore, where we liked to collect shells on the sandy beach, or fossils among^ the cliffs and rocks. I recollect, in a walk I had taken some years previously along the foot of the cliffs of Cape Blanc-Nez, near Calais, having found an impression of an ammonite of remarkable size, which has often excited the admiration of amateurs ; this ammonite measured no less than twelve inches in diameter. The rocks of Cape Grisnez, not far from Boulogne, also afford the geologian the opportunity of a number of curious investigations. In the Ardennes and the Alps I have frequently procured some fine mineral specimens ; in the first locality-crystal- lized pyrites, in the-second fine fragments of rock crystal. I did not fail to recount these successful expeditions to the young people who accompanied me, and their ardour was thereby inflamed by the hope that they also should find something valuable. It often happened when the sun was powerful, and the air extremely calm, that my young companions and I remarked some very beautiful effects of mirage on the beach, due to the heating of the lower strata of the atmosphere. The trees and houses appeared to be raised above a sheet of silver, in which their reflectiong wer? visible as in a sheet of tranquil 26 OPEN-AIR SCIENCE. water. It can hardly be believed how frequently the atmosphere affords interesting spectacles which pass un- perceived before the eyes of those who know not how to observe. I recollect having once beheld at Jersey a magnificent phenomenon of this nature, on the 24th June, 1877, at eight o'clock in the evening : it was a column Gioup uf ruck crjsial. of light which rose above the sinking sun like a sheaf of fire. I was walking on the St. Helier pier, where there were also many promenaders, but there were not more than two or three who regarded with me this mighty spectacle. Columns and crosses of light are much more frequent than is commonly supposed, but they often pass unperceived before indifferent spectators. We will A SdUN cross. 27 describe an example of this phenomenon observed at Havre on the 7th May, 1877. The sun formed the centre of the cross, which was of a yellow golden colour. This cross had four branches. The upper branch was much mere brilliant than the others ; its height was about 15°. The lower branch was smaller, as seen in the sketch on page 2, taken from nature by Monsieur Albert Tissandier. The two horizontal branches were at times scarcely visible, and merged in a streak of reddish-yellow colour, which covered a large part of the horizon. A mass of cloud, which the setting sun tinged with a deep violet colour, formed the foreground of the picture. The atmosphere over the sea was very foggy. The pheno- menon did not last more than a quarter of an hour, but the conclusion of the spectacle was signalized by an interesting circumstance. The two horizontal branches, and the lower branch of the luminous cross, completely disappeared, whilst the upper branch remained alone for some minutes longer. It had now the appearance of a vertical column rising from the sun, like that which Cassini studied on the 21st May, 1672, and that which M. Renon* and M. A. Guillemin observed on the 12th July, i876.t Vertical columns, which, it is well known, are extremely rare phenomena, may therefore indicate the existence of a luminous cross, which certain atmospheric conditions have rendered but partially visible. How often one sees along the road, little whirlwinds of dust raised by the wind accomplishing a rotatory movement, thus producing the imitation of a waterspout ! How often halos encompass with a circle of fire the sun or * Detailed accounts \n Vol. Ixxxiii , pp. 243 and 292 of "La Nature." + .See "La Nature," 4th year, 1876, 2nd half-year, p. 167. M. A. Guillemin mentions, in connection with the phenomenon of July 12th, 1876, the presence of light masses of cloud of a greyish-blue colour, similar to those perceived in the phenomena just described. 2 8 OPEN-AIR SCIENCE. the stars ! How often we see the rainbow develop its iridescent beauties in the midst of a body of air traversed by bright raindrops ! And there is not one of these great natural manifestations which may not give rise to instructive observations, and become the object of study and research. Thus, in walks and travels alike, the study of Science may always be exercised ; and this method of study and instruction in the open air con- tributes both to health of body and of mind. As we consider the spectacles which Nature spreads before us, — from the insect crawling on the blade of grass, to the celestial bodies moving in the dome of the heavens, — we feel a vivifying and salutary influence awaken in the mind. The habit of observation, too, may be everywhere exercised — even in towns, where Nature still asserts her- self ; as, for example, in displays of meteorological pheno- mena. We will give an example of such. The extraordinary abundance of snow which fell in Paris for more than ten consecutive hours, commencing on the afternoon of Wednesday, January 22nd, 1880, will always be looked upon as memorable among the meteorological events of the city of Paris. It was stated that in the centre of Paris, the thickness of the snow that had fallen at different times exceeded fourteen inches. The snow had been preceded by a fall of small transparent icicles, of rather more than a millimetre in diameter, some having crystalline facets. They formed on the surface of the ground a very slippery glazed frost. On the evening of the 22nd January, flakes of snow began to hover in the atmosphere like voluminous masses of wool. The greater part of the gas-lamps were ornamented by frozen stalac- tites, which continually attracted the attention of passers- by. The formation of these stalactites, of which we give a specimen, is easy of explanation. The snow falling on the glass of the lamp became heated by the flame of gas, ICICLES ON THE LAMP. 29 melted, and trickled down, freezing anew into the shape of a stalactite below the lamp, at a temperature of 0° centigrade. Not only can meteorology be studied in towns, but certain other branches of natural science — entomology, for example. We will quote what a young Icicles on gas lamp. student in science, M. A. Dubois, says on this very subject : " Coleoptera," he declares, " are to be met with everywhere, and I think it may be useful to notice this fact, supporting it by examples. I desire to prove that there are in the midst of our large towns spots that remain unexplored, where some fine captures are to be 30 OPEN-AIR SCIENCE. made. Let us visit, at certain times, the approaches to the quays, even at low tide, and we shall be surprised to find there species which we have searched for far and near." This opinion is confirmed by the enumeration of several interesting captures. Was not the great Bacon right when he said, " For the keen observer, nothing in Nature is mute " ? The clifts of Cape Grisnex. CHAPTER III.— SIMPLE PHYSICS. THE MEANING OF n-IYSICS FORCES OF NATURE — GRAVITY COHESION CHEMICAL ATTRACTION — CENTRE OF GRAVITY EXPERIMENTS AUTOMATON TUMBLERS. [AVING now introduced our readers to Science ^ which they can find for themselves in the open ^ air, and the pursuit of which will both instruct and amuse, we will proceed to investigate the Branch of Science called PHYSICS. Physics may be briefly described as the Branch of Natural Science which treats of such phenomena as are unaccompanied by any important changes in the objects wherein such phenomena are observed. For instance, the sounding of a bell or the falling of a stone are physical phenomena, for the objects which cause the sound, or the fall, undergo no change. Heat is set free when coal burns. This disengagement of heat is a physical phenomenon ; but the change during combustion which coal undergoes is a chemical phenomenon. So the objects may be the same, but the circumstances in which they are placed, and the forces which act upon them, may change their appearance or position. This brings us at once to the Forces of Nature, which are three in number ; viz.. Gravity, Cohesion, and Affinity, or Chemical Attraction. The phenomena connected with the last-named forms the Science of Chemistry. We give these three Forces these names. But first we must see 32 SIMPLE PHYSICS. what is Force, for this is very important. Force is a CAUSE — the cause of Motion or of Rest. This may appear paradoxical, but a Httle reflection will prove it. It requires force to set any object in motion, and this body would never stop unless some other force or forces prevented its movement beyond a certain point. Force is therefore the cause of a change of " state " in matter. We have said there are three forces in nature. The first is Gravity, or the attraction of particles at a distance from each other. We may say that Gravity, or Gravita- tion, is the mutual attraction between different portions of matter acting at all distances, — the force of attraction being, of course, in proportion to the mass of the bodies respectively. The greatest body is the Earth, so far as our purposes are concerned. So the attraction of the Earth is Gravity, or what we call Weight. We can easily prove this. We know if we jump from a chair we shall come to the floor ; and if there were nothing between us and the actual ground sufficient to sustain the force of the attracting power of the earth, we should fall to the earth's surface. In a teacup the spoon will attract air bubbles, and large air bubbles will attract small ones, till we find a small mass of bubbles formed in the centre of the cup of tea. Divide this bubble, and the component parts will rush to the sides of the cup. This form of attraction is illustrated by the accompanying diagrams. Suppose two balls of equal magnitude, A and B. These being of equal magnitude, attract each other with equal force, and will meet, if not opposed, at a point (m) half- way between the two. Jkit they do not meet, because the attraction of the earth is greater than the attraction they relatively and collectively exercise towards each other. But if the size of the balls be different, the attrac- tion of the greater will be morq evident, as shown opposite GRAVITY. 33 where the points of meeting are indicated respectively. These experiments will illustrate the phenomena of falling bodies. Gravity is the cause of this, because every object on the surface of the earth is very much smaller than the earth itself, and therefore all bodies fall towards the centre of the earth. A certain time is -1 Attraction of gravitation (i\ thus occupied, and we can find the velocity or rapidity of a falling body very easily. On the earth a body, if let fall, will pass through a space sixteen feet in the first second ; and as the attraction of the earth still continues and is exercised upon a body already in rapid motion, this rate of progress must be proportionately increased. Just as when steam is kept up in an engine running down Attraction of gravitation (2), hill, the velocity of the train will rapidly increase as it descends the gradient. A body falling, then, descends sixteen feet in the first second, and for every succeeding second it assumes a greater velocity. The distance the body travels has been calculated, and the space it passes through has been found to increase in proportion to the square of the time it takes to fall. For instance, suppose you drop a stone from the top of a cliff to the beach, and it occupies two seconds in 34 SIMPLE PHYSICS. falling, if you multiply 2X2, and the result by sixteen, you will find how high the cliff is : in this (supposed) case it is (omitting decimals) sixty-four feet high. The depth of a well can also be ascertained in the same way, leaving out the effect of air resistance. But if we go up into the air, the force of gravity will be diminished. The attraction will be less, because we are more distant from the centre of the earth. This decrease is scarcely, if at all, perceptible, even on very high mountains, because their size is not great in com- parison with the mass of the earth's surface. The rule for this is that gravity decreases in proportion to the square of the distance. So that if at a certain distance from the earth's surface the force of attraction be i, if the distance be doubled the attraction will be only o?ie quarter as much as before — not one-half. Gravity has exactly the same influence upon all bodies, and the force of the attraction is in proportion to the mass. All bodies of equal mass will fall in the same time in a given distance. Two coins (or a coin and a feather in vacuo) will fall together. But in the air the feather will remain far behind the coin, because nearly all the atoms of the former are resisted by the air, while in the coin only some particles are exposed to the resistance, the density of the latter preventing the air from reaching more than a few atoms, comparatively speaking. The theory of weight and gravitation, and experiments relating to the falling of bodies, may be easily demonstrated with ordinary objects that we have at hand. I take a halfpenny and a piece of paper, which I cut in the shape of the coin, and holding them side by side, I drop them simultaneously ; the halfpenny reaches the ground some time before the p^per, a result quite in accordance with the laws of gravitation, as one must bear in mind the presence of air, and the different resistance it offers to two bodies differing COHESION. 3S in density. I next place the paper disc on the upper surface of the piece of money, and then drop them simul- taneously. The two objects now reach the ground at the same time, the paper, in contact with the halfpenny, being preserved from the action of the air. This experiment is so well known that we need not further discuss it ; but it must be plainly evident that it is capable of development in experiments on phenomena relating to falling bodies.* When a body influenced by the action of a force acts, in its turn, upon another, the latter reacts in an opposite manner upon the first, and with the same intensity. TJie attraction of Cohesion is the attraction of particles of bodies to each other at very small distances apart. Cohesion has received various names in order to expresu its various degrees. For instance, we say a body is tough or brittle, or soft or hard, according" to the degrees of co- hesion the particles exercise. We know if we break a glass we destroy the cohesion ; the particles cannot be reunited. Most liquid particles can be united, but not all. Oil will not mix with water. * M. A. G. has written us an interesting letter on the subject of similar experiments, which we here transcribe : — "When a siphon of seltzer water has been opened some little time, and the equihbrium of tension is nearly established between the escaped gas and the dissolved gas, a vertical stream of bubbles is seen to rise from the bottom of the apparatus, which present a very clear example of the law of ascension of bubbles ; that is to say (putting out of the question the expansion of the bubbles in their passage upwards), it is an inverse representation of the law of gravity affecting falling bodies. The bubbles, in fact, detach themselves from their starting point with perfect regularity; and as the interval varies in one file from another, we have before us a multiplied representation of that terrible law which Attwood's machine made such a bugbear to the commercial worid. I believe it is possible, by counting the number of bubbles that detach themselves in a second, in each file, and the number which the whole stream contains at a given instant, to carry the verification further ; but I must confess that I have not done so myself." 36 SIMPLE PHYSICS. The force of cohesion depends upon heat. Heat expands everything, and the cohesion diminishes as temperature increases. There are some objects or substances upon the earth the particles of which adhere much more closely than others, and can only, with very great difficulty, be separated. These are termed Solids. There are other substances whose particles can easily be divided, or their position altered. These are called Fluids. A third class seem to have little or no cohesion at all. These are termed Gases. Adhesion is also a form of attraction, and is cohesion existing on the surfaces of two bodies. When a fluid adheres to a solid we say the solid is wet. We turn this natural adhesion to our own purposes in many ways, — we whitewash our walls, and paint our houses ; we paste our papers together, etc. On the other hand, many fluids will not adhere. Oil and water have already been instanced. Mercury will not stick to a glass tube, nor will the oiled glass tube retain any water. We can show the attraction and repulsion in the following manner : — Let one glass tube be dipped into water and another into mercury, you will see that the water will ascend slightly at the side, owing to the attrac- tion of the glass, while the mercury will be higher in the centre, for .it possesses no attraction for the glass. If small, or what are termed capillary (or hair) tubes, be used, the water will rise up in the one tube, while in the other the mercury will remain lower than the mercury outside the tube. (See Capillarity}) Chemical attraction is the force by which two different bodies unite to form a new and different body from either. It is needless for us to dwell upon the uses of these Forces of Nature. Gravity and Cohesion being left out of our world, we can imagine the result. The earth and sun CENTRE OF GRAVITY. 37 and planets would wander aimlessly about ; we should float away into space, and everything would fall to pieces, while our bodies would dissolve into their component parts. The Balance and Centre of Gravity. — We have spoken at some length about Gravity, and now we must say some- thing respecting tliat point called the Centre of Gravity, and the Balance, and upon the latter we have a few remarks to make first, for a well-adjusted balance is a most useful thing, and we will show you how to make one, and then proceed to our illustrations of the Centre of Gravity, and explain it. All those who cultivate experimental science are aware Capillarity, that it is useful to unite with theoretical ideas that manual dexterity which is acquired by the student accustoming himself to practical operations. One cannot too strongly urge both chemist and physicist to exercise themselves in the construction of the appliances they require, and also to modify those already existing, which may be adapted to their wants. In a large number of cases it is possible to manufacture, at small expense, delicate instruments, capable of rendering the same service as the most elaborate apparatus. Important scientific labours have often been undertaken by men whose laboratories were most simple, who, by means of skill and perseverance, knew how to do great things with small resources. A delicate balance, for instance, indispensable alike to chemist and physicist, can be manufactured at little cost in different ways. A thin platinum wire and a piSce df Wood is all thit ia 4 38 SIMPLE PHYSICS. needed to make a balance capable of weighing a milligram; and to make a very sensitive hydrostatic balance, little is required besides a glass balloon. The cut represents a small torsion balance of extreme simplicity. A thin platinum wire is stretched horizontally through two staples, from the wooden supports, AB, which are fixed in a deal board. A very thin, delicate lever, CD, cut in wood, or made with a wisp of straw, is fixed in the centre of the platinum wire by means of a small clip, which secures it firmly. This lever is placed in such a manner that it is raised perceptibly out of the horizontal line. At D is fixed Torsion balance, which can ea<;ily be constructed, capable of weighing a milligram one-tenth of full size a paper scale, on which is put the weight of a centigram. The lever is lowered to a certain point, slightly twisting the platinum wire. Near the end of the lever a piece of wood, F, is fixed, on which is marked the extreme point of its movements. Ten equi-distant divisions are marked between these two points, which represent the distance traversed by the lever under the weight of the milligram. If a smaller weight than a centigram is placed on the paper scale the lever falls, and balances itself after a few oscillations. If it falls four divisions, it is evident that the substance weighs four milligrams. Taking a rather thicker platinum wire, to which a shorter lever must be adapted, THE BALANCE. 39 one can weigh the decigram, and so on. It would be an ^asy matter, also, to make, on the same model, balances 3r weighing considerable weights. The platinum wire iihould be replaced by iron wires of larger diameter, firmly tretched, and the lever should be made of a piece of very ■sistmg wood. One can also, by adaptation, find the exact alue of the most trifling eights. By lengthening very fine platinum wire svcral yards, and adapt- ing a long, slender lever, it will not be impossible to ascertain the tenth of a milligram. In this latter case the balance can be set when it is wanted. The next cut represents Nicholson's Areometer, which any one may con- struct for himself, and which, as it is here represented, constitutes another kind of balance. A glass balloon, filled with air, is hermetically closed with a cork, through which is passed a cylinder of wood, surmounted by a wooden disc, D. The apparatus is terminated at its lower end by a small tray, C, on which one can put pieces of lead in variable quantities. It is then plunged into a 3-lass filled with water. The pieces of lead on the tray, c, ire added by degrees, until the stem of the areometer rises ilmost entirely above the level of the water ; it is next passed th.rpugb a ring, which keeps it in position, and Nicholson's Areometer, contrived to serve as a balance. 40 SIMPLE PHYSICS. which is fastened to the upper part of the glass by means of four iron wires in the shape of a cross. The stem is divided in such a way that the space comprised in each division represents the volume of a cubic centimetre. Thus arranged, the apparatus constitutes a balance. The object to be weighed is placed on the disc, D, and the areometer sinks in the water, oscillates, and then remains in equilibrium. If the stem sinks five divisions, it is evident that the weight of the object corresponds to that of five cubic centimetres of displaced water, or five grams. It is obvious, therefore, from the preceding examples, that it is not impossible to construct a weighing apparatus with ordmary and very inexpensive objects. We can, in the same way, show that it is possible to perform instruc- tive experiments with no appliances at all, or, at any rate, with common things, such as eveiyone has at hand. The lamented Balard, whose loss science has had recently to deplore, excelled in chemical experiments without a labora- tory; fragments of broken glass or earthenware were used by him for improvising retorts, bottles and vases for form- ing precipitates, and carrying on many important opera- tions. Scheele also operated in like manner ; he knew how to make great discoveries with the humblest appliances and most slender resources. One cannot too earnestly endeavour to imitate such leaders, both in teaching others and instructing oneself The laws relating to the weight of bodies, the centre of gravity, and stable or unstable equilibrium, may be easily taught and demonstrated by means of a number of very familiar objects. By putting into the hands of a child a box of soldiers cut in elder-wood, the end of each fixed into half a bullet, we provide him with the means of making some easy experiments on the centre of gravity; According to some authorities on equilibrium, it is Hot EQUILIBRIUM. 41 impossible, with a little patience and delicacy of manipu- lation, to keep an egg balanced on one of its ends. This experiment should be performed on a perfectly horizontal surface, a marble chimney-piece, for example. If one can succeed in keeping the egg up, it is, according to the most elementary principles of physics, because the vertical line of the centre of gravity passes through the point of Experiment on '* centre of gravity." contact between the end of the egg and the surface on which it rests. Here is a curious experiment in equilibrium, which is performed with great facility. Two forks are stuck into a cork, and the cork is placed on the brim of the neck of a bottle. The forks and the cork form a whole, of which the centre of gravity is fixed over the point of support. We can bend the bottle, empty it even, if it contains fluid, with- out the little construction over its mouth being in the least 42 SIMPLE PHYSICS. disturbed from its balance. The vertical line of the centre of gravity passes through the point of support, and the forks oscillate with the cork, which serves as their support, thus forming a movable structure, but much more stable than one is inclined to suppose. This curious experiment Another experiment on the same sulject. is often perfoimed by conjurors, who inform their audience that they will undertake to empty the bottle without disturbing the cork. If a woodcock has been served for dinner, or any other bird with a long beak, take off the head at the extreme end of the neck ; then split a cork so that you can insert into it the neck of the bird, which must be tightly clipped to keep it in place ; two forks are AUlUMAiA. 43 then fixed into the cork, exactly as in the preceding example, and into the bottom of the cork a pin is inserted. This little contrivance is next placed on a piece of money, which has been put on the opening of the neck of the bottle, and when it is fr.irly balanced, we give it a rotatory Automatic puppets, movement, by pushing one of the forks as rapidly as we please, but as much as possible without any jerk. We then see the two forks, and the cork surmounted by the woodcock's head, turning on the slender pivot of a pin. Nothing can be more comical than to witness the long beak of the bird turning round and round, successively facing all the company assembled round the -table, some- 44 SIMPLE PHYSICS. times with a little oscillation, which gives it an almost life- like appearance. This rotatory movement will last some time, and wagers are often laid as to which of the company the beak will point at when it stops. In laboratories, wooden cylinders are often to be seen which will ascend an inclined plane without any impulsion. This appears very surprising at first, but astonishment ceases when we perceive that the centre of gravity is close to the end of the cylinder, because of a piece of lead, which has been fixed' in it. First posilion of the puppets. Above is a very exact representation oF a plaything which was sold extensively on the Boulevards at Paris. This little contrivance, which has been known for some time, is one of the most charming applications of the prin- ciples relating to the centre of gravity. With a little skill, any one may construct it for himself. It consists of two little puppets, which turn round axles adapted to two parallel tubes containing mercury. When we place the little toy in the position as above, the mercury being at a, the two dolls remain motionless, but if we lower the doll s, so that it stands on the second step (No. 2) of the flight, as indicated in the second cut, the mercury descends to b at the THE PUPPETS. 45 Other end of the tube ; the centre of gravity is suddenly displaced ; the doll R then accomplishes a rotatory move- ment, as shown by the arrow in the third cut, and finally ahghts on step No. 3. The same movement is also effected by the doll S, and so on, as many times as there are steps. The dolls may be replaced by a hollow cylinder of cartridge paper closed at both ends, and con- taming a marble ; the cylinder, when placed vertically on an mclined plane, descends in the same way as the puppets. The laws of equilibrium and displacement of Second positiun of the puppets. the centre of gravity, are rigorously observed by jugglers, who achieve many wonderful feats, generally facilitated by the rotatory motion given to the bodies on which they operate, which brings into play the centrifugal force. The juggler who balances on his forehead a slender rod, on the end of which a plate turns round, would never succeed in the experiment if the plate did not turn on its axis with great rapidity. But by quick rotation the centre of gravity is kept near the point of support. We need hardly remark, too, that it is the motion of a top that tends to keep it in a vertical position. Many experiments in mechanical physics may occur 46 SIMPLE PHYSICS. to one's mind. To conclude the enumeration of those we have collected on the subject, I will describe the method of lifting a glass bottle full of water by means of a simple wisp of straw. The straw is bent before being passed into the bottle of water, so that, when it is lifted, the Lifting a bottle witll a singie straw. centre of gravity is displaced, and brought directly under tlic point of suspension. It is \\ell to lia\e at hand several pieces of straw perfectly intact, and free from cracks, in case the experiment does not succeed with the first attempt. Having now seen how this point we call the centre of gravity acts, we may briefly explain it. CENTRE OF GRAVITY. 47 The centre of gravity of a body is that point in which the sum of the forces of gravity, acting upon all the particles, may be said to be united. We know the attraction of the earth causes bodies to have a property we call Weight This property of weight presses upon ■■liliiiiiii«iaiiiBii<...ii.m I .— Ti-^- iifM- f , , Balancing a v.^.^..! .^.i » uail and key. every particle of the body, and acts upon them as parallel forces. For if a stone be broken all the portions will equal the weight of the stone ; and if some of them be suspended, it will be seen that they hang parallel to each other, so we may call these weights parallel forces united in the whole stone, and equal to a single resultant. Now to find the centre of gravity, we must suspend the body, 48 SIMPLE PHYSICS. and it will hang in a certain direction. Draw a line from the point of suspension, and suspend the body again : a line drawn from that point of suspension will pass through the same place as the former line did, and so on. That point is the centre of gravity of that suspended body. If the form of it be regular, like a ball or cylinder, the centre of gravity is the same as the mathe- matically central point. In such forms as pyramids it will be found near the largest mass ; viz., at the bases, about one-fourth of the distance between the apex and the centre of gravity of the base. When the centre of gravity of any body is supported, that body cannot fall. So the well-known leaning towers Anotlier experiment. are perfectly safe, because their lines of direction fall within the bases. The centre of gravity is in the rentre of the leaning figure. The line of direction drawn vertically from that point falls within the base ; but if the tower were built up higher, so that the centre of gravity were higher, then the structure would fall, because the line of direction would fall without the base. We see that animals (and men) are continually altering the position of the centre of gravity; for if a man bears a load he will lean forward, and if he takes up a can of water in one hand he will extend the other to preserve his balance or equilibrium. The experiment shown in the foregoing illustration is apparently very difficult, but it will be found easy THE KEY BALANCED. 49 enough in practice if the hand be steady. Take a key, and by means of a crooked nail or " holdfast,'' attach it to a bar of wood by a string tied tightly round the bar, as in the picture. To the other extremity of the bar attach a weight, and then drive a large-headed nail into the table. It will be found that the key will balance, and even move upon the head of the nail, without falling. The weight, is under the table, and the centre of gravity is exactly beneath the point of suspension. Another simple experiment may prove amusing. Into a piece of wood insert the points of two knives, and at the centre of the end of the bar insert a needle between the knife handles. The wood . and the knives may then be balanced on another needle fixed in a cork at A. We may conclude this chapter by summing up in a few words what the Centre of Gravity is. We can define it as " that point in a body upon which the body, acted on solely by the force of gravity, will balance itself in all positions." Such a point exists in every body, and equally in a number of bodies fastened tightly together. The Centre of Gravity has by some writers been denomi- nated the Centre of Parallel Forces, or the Centre of Mag- nitude, but the Centre of Gravity is the most usual and best understood term. CHAPTER IV.— SOLID BODIES. SOME PROPERTIES OF SOLID BODIES INERTIA MOTION FRICTION— THE PENDULUM EQUILIBRIUM. HOSE who have followed us through the pre- ceding pages have now, we hope, some ideas upon Gravity and the Forces of Nature. In speaking of Forces we said "Force was a cause of Motion." Let us now consider Inertia, and Motion with its accompanying opponent, Friction. Inertia is the passiveness of Matter. This perfect indifference to either rest or m,otion makes the great distinction between living and lifeless matter. Inertia, or Vis Inertia, is this passiveness. Now, to overcome this indifference we must use force, and when we have applied force to matter we set it in motion ; that is, we move it. When we move it we find a certain resistance wtiich is always proportionate to the force applied. In mechanics this is termed Action, and Reaction, which are always equal forces acting in opposite directions. This is Newton's law, and may be explained by a "weight" on a table, which presses against the table with the same force with which the table presses against the "weight"; or v/hen j'ou strike a ball, it strikes the hand with the same force. We can communicate motion by elasticity. For in- stance, if we place a number of coins upon a table touching each other and in a straight line, . and strike the last coin of the line by pushing another sharply against it. the piece PROPERTIES OF BODIES. 5 I at the opposite extremity will slip out of its place from the effect of the shock transmitted by the coin at the other end. When two forces act upon a body at the same time it takes a direction intermediate. This is known as the re.sultant. The enormous forces.exercised by the heavenly bodies will be treated of later. We will first consider Inertia. Shoclc communicated by elasticity. There are several experiments relating to the subject of Inertia which may be performed. I once witnessed one quite accidentally when taking a walk. I was one day passing the Observatory at Paris, when I noticed a number of people collected round a professor, who after executing several juggling tricks, proceeded to perform the curious experiment I am about to describe. He took a broomstick and placed it horizontally, passing the ends through two paper rings. He then asked two 52 SOLID BODIES. A SIMPLE EXPERIMENT. 53 children to hold the paper rings by nieans of two razors, so that the rings rested on the blade. This done, the operator took a stout stick, and, with all his strength, struck the broomstick in the centre; it was broken into shivers, but the paper rings were not torn in the least, or Another experiment on the same subject. even cut by the razors ! One of my friends, M. M , a painter, showed me how to perform this experiment as represented in the illustration. A needle is fixed at each end of the broomstick, and these needles are made to rest on two glasses, placed on chairs ; the needles alone must be in contact with the glasses. If the broomstick is then struck violently with another stout stick, the former will be 54 SOLID BODIES. broken, but the glasses will remain intact. The experi- ment answers all the better the more energetic the action. It is explained by the resistance of inertia in the broom- stick. The shock suddenly given, the impulse has not time to pass on from the particles directly affected to the adjacent particles ; the former separate before the move- ment can, be transmitted to the glasses serving as supports.* The experiment next represented is of the same nature. A wooden ball is suspended from the ceiling by a rather slender thread, and a similar thread is attached to the lower end of the ball. If the lower thread is pulled forcibly it will break, as shown in the illustration; the movement communicated to it has not time to pass into the ball ; if, on the contrary, it is pulled very gradually and without any shock, the upper thread instead will break, because jn this case it supports the weight of the ball. Motion is not imparted simultaneously to all parts of a body, but only to the particles first exposed to a blow, for instance. One might multiply examples of this. If a * The experiment we have just described is a very old one. M. V. Sircoulon has told us that it was described at length in the works of Rabelais. The following remarks are in " Pantagruel," book II., chap. xvii. " Panuras then took two glasses of the same size, filled them with water, and put one on one stool, and the other on another, about five feel apart, and placed the staff of a javelin about five-and-a-half feet long across, so that the ends of the staff just touched the brim of the glasses. That done, he took a stout piece of wood, and said to the others : ' Gentlemen, this is how we shall conquer our enemies ; for in the same way that I shall break this staff between these two glasses, without the glasses being broken or injured, or spilling a single drop of water, so shall we break the head of our Dipsodes, without any injury to ourselves, and without getting wounded. But that you may not think there is magic in it, you, Eusthenes, strike with this stick as hard as yoa can in the centre.' This Eusthenes did, and the staff broke in two pieces, without a drop of water being spilt." INERTIA. 55 bullet be shot from a gun, it will make a round hole in a piece of wood or glass, whilst if thrown by the hand, — that is to say, with much less force, — it will shiver the wood or the pane of glass to pieces. When the celerity of the motive force is very great, the particles directly affected are disturbed so quickly that they separate from the adjacent particles before there is time for the move- ment to be communicated to the latter. Extracting a *' man " from a pile of draughts without overturning the pile. It is possible, for the same reason, to extract from a pile of money a piece placed in the middle of the pile without overturning the others. It suffices to move them forcibly and quickly with a flat wooden ruler. The experiment succeeds very well also if performed with draughtsmen piled up on the draught-board. Another experiment which belongs to the laws of resisting force is herewith shown. A sixpence is placed = 6 SOLID BODIES. on a table covered with a cloth or napkin. It is covered with a glass, turned over so that its brim rests on two penny pieces. The problem to be solved is how to extract the sixpence from underneath the glass without touching it, or slipping anything beneath it To do this Call ng out a sixpence from the glass. it is necessary to scratch the cloth with the nail of the forefinger ; the elasticity of the material communicates the movement to the sixpence, which slowly moves in the direction of the finger, until it finally comes out completely from beneath the glass. Wc may give another experiment concerning Inertia. Take a strip of paper, and upon it place a coin, on a EXPERIMENT OF ELASTICITY. 57 marble chimney-piece, as in the illustration. If, holding the paper in the left hand, you strike it rapidly and forcibly, you will be enabled to draw away the paper without causing the coin (say a five-shilling-piece) to fall down. Drawing a slip of paper from beneath a coin. It is not impossible to draw away a napkin laid as a tablecloth for one person's dinner, without disturbing the various articles laid upon it. A quick motion is all that is necessary, keeping the napkin tightly extended by the hands at the same time. This latter experiment, however, is not recommended to boys home for the holidays, as they -8 SOLID BODIES. may unwillingly practise a feat analogous to that executed by Humpty-Dumpty, and find equal difficulty to match the pieces. We will now examine the term Motion. A body is said to be in motion when it changes its position in relation to surrounding objects. To perceive motion the surrounding objects must be relatively at rest, for if they all hurried along at the same rate no motion would be perceptible. This is evident, for when we stand still trees and houses appear stationary, as do we ourselves, but we know we all are rushing round with the earth, though our relative positions are unchanged. Hence there is no absolute rest. What are the causes of motion i" — Gravity is one. The influence of heat, which is itself caused by the motion of atoms, the eflects of electricity, etc., and finally, the power of force in men or animals — any of these causes will pro- duce motion. But a body at rest cannot put itself in motion, nor can a body in motion stop itself, or change its condition of motion. But you may say a body will stop itself. Your ball on the ground, or even upon ice, will eventually come to a stop. Wc fire a bullet, and it will stop in time. We reply it docs not stop of itself. The resistance of the Air and Friction tend to bring the body in motion to a state of rest. In the case of a bullet gravity brings it down. There is no need .to insist upon the resistance offered by the air even when it is not rushing violently past to fill up a vacuum beyond us, and called a breeze, or high v/ind. But we may say something of Friction. Friction is derived from the Latin frico, to rub, and expresses th.e resistance to motion which arises from uneven surfaces. It is a passive resistance, and depends upon the force which keeps the bodies together. Thus a train running upon a smooth iron rail would never be able FRICTION. 59 to proceed but for friction, which gives the necessary purchase or grip to the wheel and rail in contact. No surface is perfectly smooth, for we must push a body upon the smoothest surface we possess. Friction tends to resist motion always, and is the cause of a great loss of power in mechanics, though it is employed to stop motion by certain appliances, such as " breaks " and " drags," for sliding friction is greater than rolling friction. But without friction most structures would fall to pieces, and all forward motion would cease. So though it is an in- convenient force to overcome, we could not do without it. If a body is set in motion, we see that the tendency of it is to go on for ever. Such, indeed, is the case with the stars ; but so long as we are within the influence of the earth's attraction, we cannot expect such a result. We know now what motion is ; we must also, to understand it perfectly, consider its direction and its velocity. The line which indicates the way from the starting point to the end is the direction of the object in motion, and the rate it rrttves at its velocity. The latter is calcu- lated at so many miles an hour, as a train ; or so many feet in a second if the object be a shot, or other very rapidly- moving body. In equal velocity the same distance is traversed in the same time ; and so if a train run a mile in a minute, we know it will travel sixty miles in an hour, and is therefore during that minute going at the rate of sixty miles an hour. We have already spoken of the velocity of a stone, falling from a cliff as sixteen feet in a second, and a stone thrown into the air to rise sixteen feet will be a second in going up, and a second in descend- ing. But the velocity will be accelerated in the descent after the first second of time, and retarded in the upward cast by gravity. So we have two terms — accelerated and retarded velocity — used to express an increased or de- creased force of attraction. / 6o SOLID BODIES. Perpetual motion has often been sought, but never discovered, nor will it ever be till the elixir of life has been found. It is quite impossible to construct any machine that will work without friction ; if any work be done energy will be expended and transformed into other energy, so the total must be diminished by so much as was employed to transform the remainder. No body can give unlimited work, therefore the perpetual motion theory is untenable and impossible. The pendulum is considered the nearest approach to perpetual motion. This is so well known that no descrip- .f.?v_ tion is needed, but we may / I \ say a few words concerning it. / i \ By the diagram, we see that \ if we lift the ball to b, and I '\ let it fall, it will descend to /, / j \ and pass it to a opposite, nearly as far from / as i^ is from it. So the oscillations will continue, each beat being _„ less and less, till rest is reached The pendulum. by the action of gravity. Were it not for friction and the pressure of the air, the oscilla- tions would continue for ever ; as it is, it declines by shorter swings till it remains in equilibrium. The seconds' pendulum oscillates sixty times an hour, and must be of a certain length in certain places. In London it is 39"I393 inches, and furnishes a certain standard of length, and by an Act of Parliament the yard is divided into 36 parts, and 39" 1393 such parts make the seconds' pendulum in the latitude of London (in vacuo) in a temperature of 62°. But the same pendulum will not perform the same number of oscillations in one minute in all parts of the globe. At the equator they will be less, and at the pole CENTRIFUGAL FORCE. 6l more. Thus it was discovered that, as the movements of the pendulum are dependent upon the force of gravity, and as this force decreases the farther we get from the centre of the earth, the equator must be farther from the earth's centre than the poles, and therefore the poles must Centrifugal force. be depressed. The decline of the pendulum at the equator is also, in a measure, due to Centrifugal Force. Centrifugal Force, which means " flying from the centre," is the force which causes an object to describe a circle with uniform velocity, and fly away from the centre ; the force that counteracts it is called the centripetal force. A very simple experiment will illustrate it. 62 SOLID BODIES. To represent its action we shall have recourse to an ordinary glass tumbler placed on a round piece of cardboard, held firmly in place by cords. Some water is poured in the glass, and we then show that it can be swung to Another Hlustrfition of centrifugal force. and fro and round without the water being spilt, even when the glass is upside down. Another experiment on the same subject is as shown in the above illustration, by which a napkin ring can be kept in revolution around the forefinger, and by a con- tinued force the ring may be even held suspended at the tip of the finger, apparently in the air, without support. CHAPTER v.— GASES AND LIQUIDS. PRESSURE OF THE AIR EXPERIMENTS THE MAGDE- BURG HEMISPHERES AIR-PUMPS THE BAROMETER — THE PUMP. I E have more than once referred to the pressure of the air which exerts a great influence upon bodies in motion, but a few experiments will make this more obvious, and clearly demon- strate the fact. We have also told you some of the properties of Solids, such as Weight, Inertia, Friction, and Resistance, or Strength. Solids also, as we have seen, occupy space, and cannot be readily compressed, nor bent to other shapes. Now the subject of the Pressure of the Air leads us to the other forms of Matter ; namely. Gases and Liquids, which it will be found very interesting to study. The force of air can very soon be shown as acting with considerable pressure upon an egg in a glass. By blowing in a claret glass containing a hard-boiled egg, it is possible to cause the egg to jump out of the glass ; and with practice and strength of lungs it is not impossible to make it pass from one glass to ancther, as per illustration. The force of heated air ascending can also be ascer- tained by cutting up a card into a spiral, and holding it above the flame of a lamp. The spiral, if lightly poised, will turn round rapidly. Now let us turn to a few experiments with the air, which is composed in two gases. Oxygen and Nitrogen, Qf which we shall bear more when we learn Chemistry, 64 GASES AND LIQUIDS. It is not intended here to prosecute researches, but rather to sketch a programme for instruction, based on amusing experiments in Physics, performed without apparatus. The greater part of these experiments are probably well known, and we desire to say that we Blowing an egg iVom one glass to another, merely claim to have collected and arranged them for our descriptions. We must also add that we have performed and verified these experiments ; the reader, therefore, can attempt them with every certainty of success. We will suppose that we are addressing a young auditory, and continue our course of Physics AIR PRESSURE. 65 with some facts relating to the pressure of air. A wine- glass, a plate, and water, will serve for our first experi- ments. Pour some water on the plate, light a piece of paper resting on a cork, and cover the flame with the glass which I turn upside down. What follows ? — ^r\ ^ cc Movement of heated air The water rises in the glass. Why .'— Because the burn- ing of the paper having absorbed a part of the oxygen, and the volume of confined gas being diminished, the pressure of the outer air has driven back the fluid. I next fill a goblet with water up to the brim, and cover it with a sheet of paper which touches both the edge of the glass and the surface of the water. I turn the glass 66 GASES AND LIQUIDS. upside down, and the sheet of paper prevents the water running out, because it is held in place by atmospheric pressure. It sometimes happens that this experiment does not succeed till after a few attempts on the part of the operator ; thus it is prudent to turn the glass over a Pressure of the air. basin, so that, in case of failure, the water is not spilt. Having obtained a vase and a bottle, both quite full of water, take the bottle, holding it round the neck so that the thumb can be used as a stopper, then turn it upside down, and pass the neck into the water in the vase. Remove your thumb, or stopper, keeping the bottle in AN EXPERIMENT. 67 a vertical position, and you will see that the water it contains does not escape, but remains in suspension. It is atmospheric pressure which produces this phenomenon. If, instead of water, we put milk in the bottle, or some other fluid denser than water, we shall see that the milk - .essure of the air. also remains suspended in the bottle, only there is a movement of the fluid in the neck of the bottle, and on careful examination we perceive very plainly that the milk descends to the bottom of the vase, and the water rises into the bottle. Here, again, it is atmospheric pressure which maintains the fluid in the bottle, but the 68 GASES AND LIQUIDS. milk descends, because fluids are superposed according to their order of density, and the densest Hquid falls to the bottom. This can be verified by means of the phial of ttie fotcf elements, which is a plain, long, and narrow bottle, contain- w'o adhering by pressure of air. ing equal volumes of metallic mercury, salt water, alcohol, and oil. These four liquids will lie one on the top of the other without ever mixing, even if shaken. Another experiment as to the pressure of the air may be made. Take a penny and press it against some oaken bookcase or press, rub the coin against the wood for a few seconds, then press it, and withdraw the fingers. The THE EGG EXPERIMENT. 69 coin will continue to adhere to the wood. The reason of this is, because by the rubbing and the pressure you have dispersed the film of air which was between the penny and the wood, and under those conditions the pressure of the atmospheric air was sufficient to keep the penny in its place. Hard-boiled egg. divested of its sliell, pnssing through the tiecTc ofa glass bottle, under the influence of atmospheric pressure. Or, again, let us now add a water-bottle and a hard- boiled Qgg to our appliances ; we will make use of the air- pump, and easily perform another experiment. I light a piece of paper, and let it burn, plunging it into a water- bottle full of air. When the paper has been burning a few seconds I close the opening of the water-bottle by 6 •JO GASES AND LIQUIDS. means of a hard-boiled egg, which I have previously divested of its shell, so that it forms a hermetic stopper The burning of the paper has now caused a vacuum of air in the bottle, and the egg is gradually thrust in by the atmospheric pressure outside. We see it slowly lengthening and stretching out as it passes through the aperture ; then it is suddenly thrust completely into the bottle with a little explosive sound, like that produced by striking a paper bag expanded with air. This is atmospheric pressure demonstrated in the clearest manner, and at little cost. If it is desired to pursue a little further the experi- ments relating to atmospheric pressure, it will be easy enough to add to the before-mentioned appliances a closed glass-tube and some mercury, and one will then have the necessary elements for performing Torricelli's and Pascal's experiments, and explaining the theory of the barometer. An amusing toy, well-known to schoolboys, called the "sucker," may also be made the object' of many disserta- tions on the vacuum and the pressure of air. It is com- posed of a round piece of soft leather, to the centre of which is attached a small cord. This leather is placed on the ground and pressed under foot, and when the cord is pulled it forms a cupping-glass, and is only separated with difficulty from the pavement. Atmospheric air, in common with other gases, has a tendency to fill any space into which it may enter. The mutual attraction of particles of air is nil : on the contrary, they appear to have a tendency to fly away from each other ; this property is called " repulsion." Air also possesses an expansive property — a tendency to. press against all the sides of any vessel in which it may be enclosed. Of course the larger the vessel containing a given quantity of air, the less actual pressure it will exert un the sides of the vessel, The felasticity of air therefore WEIGHT OF AIR. 7 1 decreases with increasing expansion, but it gains in elasticity or force when compressed. There is a law in Physics which expresses the relation between expansion and elasticity of gases, which may be said to be as follows : — The elasticity (of a gas) is in inverse ratio to the space it occupies, and therefore by compressing air into a small space we can obtain a great force, as in the air-gun and the pop-gun of our youthful days. In the cut below we can illustrate the principle of the pop-gun. The chamber full of air is closed by a cork and by an air-tight piston (s) at / and p. When the piston is pushed into the chamber the air is compressed between it and the stopper, which at length flies out forcibly with a loud report. The principle of the pop-gun. We have said that the tendency of air particles is to fly away from each other, and were it not for the earth's attraction the air might be dispersed. The height of the atmosphere has been variousl}' estimated from a height of 45 miles to 212 miles in an attenuated form ; but perhaps 100 miles high would be a fair estimate of the height to which our atmosphere extends. The pressure of such an enormous body of gas is very great. It has been estimated that this pressure on the average human body amounts to fourteen tons, but being balanced by elastic fluids in the body, the inconvenience is not felt. The Weight of Air can easily be ascertained, though till the middle of the seventeenth century the air was believed to be without weight. The following ex» periment will ptovie the weight of air. Takfe an GH-dittary 72 GASES AND LIQUIDS. balance, and suspend to one side a glass globe fitted with a stop-cock. From this globe extract the air by means of the air-pump, and weigh it. When the exact weight is Weighing the air. ascertained turn the stop-cock, the air will rush in, and the globe will then pull down the balance, thus proving that air possesses weight. The experiments of Torricelli and Otto Von Guerike, however, demonstrated that the air has weight THE AIR-PUMP. 73 Magdeburg Hemispheres. and great pressure. Torricelli practically invented the barometer, but Otto Von Guerike, by the cups known as Magdeburg Hemispheres, proved 'the pressure of the outward air. This apparatus is well known, and consists of two hollow copper hemispheres which fit very closely. By means of the air-pump which he invented in 1 6 5 o, Otto Von Guerike exhausted the air from the closed hemispheres. So long as air remained in them, there was no great difficulty in separating them ; but when it had been iinally exhausted, the pressure of the surrounding atmosphere was so great that the hollow spheres could not be dragged asunder even by horses harnessed to rings which had been inserted in the globes. The Air-Ptimp is a very useful machine, and we will now briefly explain its action. The inventor was, as remarked above, Otto von Guerike, of Magdeburg. The pump consists of a cylinder and piston and rod, with two valves opening upwards — one valve being in the bottom of the cylinder, the other in the piston. This pump is attached by a tube to a plate with a hole in it, one ex- tremity of the tube being fixed in the centre of the plate, and the other at the valve at the bottom of the cylinder. A glass shade, called the receiver, is placed on the top of the plate, and of course this shade will be full of air. When the receiver is in position we begin to work the pump. We have said there are two valves. So when the piston is drawn up, the cylinder would be quite empty did not the valve at the bottom, opening upwards, admit some air from the glass shade through the tube to enter the 74 GASES AND LIQUIDS. '^ 9 ] The air-pump. cylinder. Now the lower part of the cylinder is full of air drawn from the glass shade. When we press the piston down again, we press against the air in it, which, being „ compressed, tries to escape. It cannot go back, because the valve at the bottom of the cylinder won't open, so it escapes by the valve in the piston, and goes away. Thus a certain amount of air is got rid of at each stroke of the piston. Two cylinders and pistons can be used, and so by means of cog-wheels, etc., the air may be rapidly exhausted from the receiver. Many experiments are made with the assistance of the air-pump and receiver, though the air is never entirely exhausted from the glass. The " Sprengel " air-pump is used to create an almost perfect vacuum, by putting a vessel to be exhausted in connection with the vacuum at the top of a tube of mercury thirty inches high. Some air will bubble out, and the mercury will fall. By filling up again and repeat- ing the process, the air vessel will in time be completely exhausted. This is done by Mr. Sprengel'.s pump, and a practically perfect vacuum is obtained, like the Torricellian vacuum. The " Torricellian vacuum" is the empty space above the column of mercury in the i^° \^ barometer which we will proceed to describe. Air has a certain weight or pressure which is suf- ficient to raise a column of mercury thirty inches. We will prove this by illustration. Take a bent tube and fill it with mercury ; the liquid Air pressure. ^^.j^ ^^^^^ equally high in both arms, in consequence of the ratio of equilibrium in THE BAROMETER, 75 fluids, of which we shall read more when we come to consider Water. So the two columns of mercury are in equilibrium. (See A.) Now stop the arm a with a cork, and take out half the mercury. It will remain in one arm only. Remove the cork, and the fluid will fall in both TKe Barometer. arms, and remain in equilibrium. If a long bent glass tube be used, the arms being thirty-six inches high, the mercury will fall to a point, c, which measures 29-9 inches from the bottom. If the tube be a square inch in bore, we have 29-9 cubic inches of mercury, weighing I4|lbs., balancing a column of air one square inch thick and as high as the atmosphere. So the mercury and the column of air must 76 gaSes and liquids. weigh the same. Thus every square inch on the earth supports a weight of (nearly) i 5 lbs. The barometer invented by Pascal, working on the investigations of Torricelli, is a very simple and useful instrument. Fill a tube with mercury from which all moisture has been expelled, and turn it over in a dish of mercury : the mercury will rise to a certain height (30 inches), and no higher in vacuo. When the pressure of the air increases the mercury rises a little, and falls when the pressure is removed. Air charged with aqueous vapour is lighter than dry air, so a fall in the mercury indicates a certain amount of water-vapour in the air, which may. condense and become rain. The action of mercury is^ therefore used as a weather-glass, by which an index-point shows the movements of the fluid, by means of a wheel over which a thread passes, sustaining a float and a counterpoise. When the mercury rises the float goes up, and the weight falls, and turns the wheel by means of the thread. The wheel having a pointer on the dial tells us how the mercury moves. This weather-glass is the usual syphon barometer with the float on the surface and a weight. The Syphon Barometer is a bent tube like the one already shown, with one limb much shorter than the other. The Aneroid Barometer, so called because it is "without moisture," is now in common use. In these instruments the atmospheric pressure is held in equilibrium by an elastic metal spring or tube. A metal box, or tube, is freed from air, and then hermetically sealed. This box has a flexible side, the elasticity of which, and the pressure of the air on it, keep each other in equilibrium. Upon this elastic side the short arm of a lever is pressed, while the longer arm works an index- byphon baromeler. WATER BAROMETER. 77 When pressure point, as in the circular barometer, increases the elastic box " gives " ; when pressure diminishes it reti;rns to its former place, and the index moves in the opposite direction. It is neces- sary to compare and " set" the aneroid with the mercurial barome- ter to ensure correct- ness. A curved tube is sometimes used, which coils and un- coils like a spring, according to the pres- sure on it. There are other barometers, such as the Water Barometer, which can be fixed against the side of a house, and if the water be coloured, it will prove a useful indi- cator. As the name indicates, water is used instead of mercury, but as the latter is thirteen- and-a-half times heavier than water, a much longer tube is neces- sary ; viz., one about thirty-five feet in length. The con- struction is easy enough. A leaden pipe can be fixed The Water Barometer. 78 Gases and liquids. against the house ; on the top is a funnel furnished with a stop cock, and placed in a vase of water. The lower part of the tube is bent, and a glass cylinder attached, with another stop-cock — the glass being about three feet long, and graduated. Fill the tube with water, shut the upper stop-cock, and open the lower one. The vacuum will be formed in the top of the tube, and the barometer will act on a larger scale than the mercury. The Glycerine Barometer, invented by Mr. Jordan, and in use at the Times oiifice, registers as more than one inch movements which on the mercurial thermometer are only one-tenth of an inch, and so are very distinctly visible. The specific gravity of pure glycerine is less than one-tenth that of mercury, so the mean height of the glycerine column is twenty-seven feet at sea level. The glycerine has, however, a tendency to absorb moisture from the air, but Mr. Jordan, by putting some petroleum oil upon the glycerine, neutralized that tendency, and the atmospheric pressure remains the same. A full description of this instrument was given in the Times of 25th October, 1880. The uses of the barometer are various. It is employed to calculate the heights of mountains ; for if a barometer at sea level stand at 30° it will be lower on a mountain top, because the amount of air at an elevation of ten thousand feet is less than at the level of the sea, and consequently exercises less pressure, and the mercury descends. [The pressure is on the bulb of mercury at the bottom, not on the top, remember.] The pressure of the air at the tops of mountains some- times decreases very much, and it is not sufficiently dense for perfect respiration, as many people find. Some climbers suffer from bleeding at the nose, etc., at great altitudes. This is occasioned by the action of the heart, which pumps with great force, and the outward pressure DIVING-BELL. 79 upon the little veins being so much less than usual, they give way. Many important instruments depend upon atmospheric pressure. The most important of these is the pump, which will carry us to the consideration of water and The principle of the diving-bell. Fluids generally. The fire-engine is another example, but we will now proceed to explain the diving-bell already referred to. The experiment of the diving-bell, which is so simple, is explained farther on. It belongs to the same category of experiments as those relating to the pressure of air and 8o GASES AND LIQUIDS, compression of gas. Two or three flies have been intro- duced into the glass, and they prove by their buzzing Diver under water. about that they are quite at their ease in the rather confined space. The Diving-Bell in a crude form appears to have THE PUMP. 8 1 been used as early as 1538. It was used by two Greeks in the presence of the Emperor Charles V., and numerous spectators. In the year 1720 Doctor Halley improved the diving-bell, which was a wooden box or chamber open at the bottom. Air casks were used to keep the inmate supplied with air. The modern diving-bell was used by Smeaton in 1788, and was made of cast iron. It sinks by its own weight. The pressure of the air inside is sufficient to keep the water out. Air being easily com- pressed, it is always pumped in to keep the hollow iron " bell " full, and to supply the workmen. There are inventions now in use by which the diver carries a supply of air with him on his back, and by turning a tap can supply himself for a long time at a distance from the place of descent, and thus is able to dispense with the air-tube from the boat at the surface. This apparatus was exhibited at the Crystal Palace some years ago. The Pump. We have seen in the case of the Water Barometer that the pressure of the air will sustain a column of water about thirty feet high. So the distance between the lower valve and the reservoir or cistern must not be more than thirty-two feet, practically the distance is about twenty-five feet in pumps. We can see by the illustration that the working is much the same as in the air-pump. The suction pipe, B, is closed by the valve, C, the cylinder, D, and spout, E, are above, the piston rod, F, lifts the air-tight piston in which is a valve, H. When the piston is raised the valve, c, opens and admits the water into the cylinder. When the piston is depressed the valve, C, is closed, the water already in forces H open, and passing through the piston, reaches the cylinder and the spout. 82 GASES AND LIQUIDS. The hand fire-engine depends upon the action of com- pressed air, which is so compressed by pumping water into the air chamber, a. The tube is closed at g, and the pumps, e e, drive water into the air chamber. At length the tap is opened, and the air drives the water out as it is continually supplied. Compressed air was also used for driving the boring machines in the Mount Cenis tunnel. In this case also The Hand Fire-Engine the air was compressed by water, and then let loose, like steam, to drive a machine furnished with boring instru- ments. A pretty little toy may be made, and at the same time exemplify an interesting fact in Physics. It is called the ludion, and it " lies in a nut shell " in every sense. When the kernel has been extracted from the shell, fasten the portions together with sealing wax, so that no water can enter. At one endj Oj as in the illustration) leave a small PROPERTIES OF AIR. 83 hole about as large as a pin's head ; fasten two threads to the sealing wax, and to the threads a wooden doll. Let a weight be attached to his waist. When the figure is in equilibrium, and will float, put it into a jar of water, and tie a piece of bladder over the top. If this covering be pressed with the finger, the doll will descend and remount when the finger is removed. By quick successive pressure, the figure may be made to execute a pas seiil. The reason of the movement is because the ^ight cushion of air in the upper part of the vase is com- pressed, and the little water thus caused to enter the nut shell makes it heavier, and it descends with the figure. We have now seen that air is a gas, that it exercises pressure, that it possesses weight. We know it can be applied to many useful purposes, and that the air machines and inventions — such as the air-pump and the "Pneu- matic Despatch " — are in daily use Ivt - our laboratories, our steam engines, our condensed milk manufactories, and in many other industries, and for our social benefit. Compressed air is a powerful motor for boring machinery in tunnels where steam cannot be used, even if water could be supplied, for smoke or fire would suffocate the workers. To air we owe our life and our happiness on earth. Pneumatics, then, deals with the mechanical properties of elastic fluids represented by air. A gas is an elastic fluid, and diflfers very considerably from water ; for a gas win fill d lat-ge dr Small space with equal ieonveniencej like The Pump, 84 GASES AND LIQUIDS. the genii which came out of the bottle and obligingly retired into it again to please the fisherman. We have seen that the pressure of the air is 14* lbs. per square inch at a temperature of 3 2°. It is not so easy to determine The Lud.on. the pressure of air at various times as that of water. We can always tell the pressure of a column of water when we find the height of the column, as it is the weight of so many cubic inches of the liquid. But the pressure of the atmosphere per square inch at any point is equal to the weight of a vertical column of air one inch square, reach- ing from that point to the limit of the atmosphere above it. Still the density is not the same at all points, so we DENSITY OF AIR. 8S have to calculate. The average pressure at sea level is 147 per square inch, and sustains a column of mercury I square inch in thickness, 29-92, or say 30 inches high. These are the data upon which the barometer is based. Diving-bell. CHAPTER VI.— AERONAUTICS. PRESSURE OF AIR IN BODIES EARLY ATTEMPTS TO FLY IN THE AIR DISCOVERY OF HYDROGEN THE MONTGOLFIER BALLOONS FIRST EXPERIMENTS IN PARIS NOTED ASCENTS. E have now examined into the circumstances of air pressure ; and in " Marvels of the Elements " we shall be told about the atmosphere and its constituents. We know that the air around us is composed principally of two gases, oxygen and nitrogen, with aqueous vapour and some carbonic acid. An enormous quantity of carbonic acid is produced every day, and were it not for the action of vegetation the amount produced would speedily set all animal life at rest. But our friends, the plants, decompose the carbonic acid by assimilating the carbon and setting free the oxygen which animals consume. Thus our atmosphere keeps its balance, so to speak. Nothing is lost in nature. We have illustrated the pressure of the atmosphere by the Magdeburg hemispheres, and we know that the higher we ascend the pressure is lessened. The weight of the atmosphere is 15 lbs. to the square inch at sea level. This we have seen in the barometer. Now pressure is equal. Any body immersed in a liquid suffers pressure, and we remember Archimedes and the crown. It displaced a certain amount of water when EARLY ATTEMPTS TO FLY. 87 immersed. A body in air displaces it just the same. Therefore when any body is heavier than the air, it will fall just as a stone will fall in water. If it be of equal weight, it will remain balanced in the air, if lighter it will rise, till it attains a height where the weight of the atmosphere and its own are equal ; there it will remain till the conditions are altered. Now we will readily understand why balloons float in the air, and why clouds ascend and descend in the atmosphere. In this chapter we propose to consider the question of ballooning, and later the possibility of flying. We all have been anxious concerning the unfortunate balloonist who was lost in the Channel some years ago, so some details concerning the science generally, with the experiences of skilled aeronauts, will guide us in our selection of material. We will first give a history of the efforts made by the ancients to fly, and this ambition to soar above the earth has not yet died out. From a very early period man appears to have been desirous to study the art of flying. The old myths of Daedalus and Icarus show us this, and it is not to be wondered at. When the graceful flight of birds is noticed, we feel envious almost that we cannot rise from the earth and sail away at our pleasure over land and sea. Any one who has watched the flight of the storks around and above Strasburg will feel desirous to emulate that long, swift-sailing flight without apparent motion of wing, and envy the accuracy with which the bird hits the point aimed at on the chimney, however small. It is Httle wonder that some heathens of old time looked upon birds as deities. The earliest flying machine that we can trace is that invented by Archytas, of Tarentum, B.C. 400. The historian of the " Brazen Age " tells us how the geo- metrician, Archytas, made a wooden pigeon which was 88 AERONAUTICS. able to sustain itself in the air for a few minutes, but it came down to the ground after a short time, notwith- standing the mysterious " aura spirit " with which it was supposed to be endowed. The capability of flying has for centuries been regarded as supernatural. Putting angels aside, demons are depicted with wings like bats' wings, while witches, etc., possessed the faculty of flying up chimneys upon broomsticks. We even read in childish lore of an old woman who " went up in a basket " (perhaps a balloon-car), and attained a most astonishing altitude — an elevation no less than " seventy times as high as the moon ! " But to descend to history. It is undoubtedly true that in the time of Nero Simon Magus attempted to fly from one house to another by means of some mechanical con- trivance, and failing, killed himself. Roger Bacon, the " admirable doctor," to whom the invention of gunpowder is generally attributed, had distinct notions of flying by means of machines, and "hollow globes," and "liquid fire." But he did not succeed, nor did many successive attempts succeed any better in subsequent years. Bishop Wilkins treated of the art of flying, but most, if not all who dis- cussed the subject appear to have been indebted to Roger Bacon for the idea. When the nature and pressure of the atmosphere by Torricelli's experiments became better known, Father Lana, a Jesuit priest, constructed a flying machine or balloon of curious shape. He proposed to fix four copper globes, very thin, and about twenty feet in diameter, and to these he fastened a boat or car, looking very much like a basin. His idea was to empty his great copper globes, and that their buoyancy would then bear the weight of the traveller. But he overlooked or was ignorant of the effect of the atmospheric pressure, which would have speedily crushed the thin copper globes when , empty. MONTGOLFIER. 8g Lana's suggestion was made in 1670, the ba-rometer had been discovered in 1643. There were some fairly successful experiments made in flying in 1678 and in 1709. The former attempt was made by Besmir, a locksmith of Sable, who raised himself by mean3 of wings up to the top of a house by leaps, and then succeeded in passing from one house to another lower down by supporting himself in the air for a time. He started from an elevated position, and came down by degrees. Dante, a mathematician, also tried to fly, but without great success. He broke his thigh on one occasion. Laurence de Gusman claimed an invention for flying in 1709, and petitioned for a "patent," which was granted by the king's letter. The machine appears to have borne some resemblance to a bird. It was not till 1782, however, that the true art of aerial navigation was discovered. The knowledge of hydrogen gas possessed by Cavendish in 1766 no doubt led up to it, and in the year following its discovery Professor Black, lecturing in Edinburgh, stated that it was much lighter than the atmosphere, and that any vessel filled with the gas would rise in the air. We now come to the invention of the Balloon (so called from its shape being similar to a vessel used in the laboratory) by the Brothers Montgolfier. Stephen and James Montgolfier were paper-makers, and carried on their business at Annonay, near Lyons, but it was partly by accident that the great discovery was made. They had no knowledge of the buoyancy of hydrogen gas. They took their idea of the balloon (inflated) from noticing an ascending column of smoke. It occurred to Stephen that if a paper bag were filled with smoke it would ascend into the air. A large bag was made and some paper burnt beneath it in a room.. When the smoke had filled the bag it was released, and immediately 90 AERONAUTICS. ascended to the ceiling. Here was the germ of the Montgolfier or heated air balloon. The experiment was repeated in the open air with even greater success, and a trial upon a larger scale was immediately determined upon. A story is related of Montgolfier when prosecuting I *%* r ^ ^ (1 n H p Montgolfier balloon. his researches, that a widow whose husband had belonged to the printing firm with whom Montgolfier was then connected in business, saw the smoke issuing from the room in which the little balloon was being filled. She entered, and was astonished to see the difficulty ex- perienced by the experimenter in filling the balloon. It swerved aside, and increased the trouble he had to keep THE FIRST BALLOON. 91 it above the chafing dish. Montgolfier was greatly troubled, and seeing his disappointment, the widow said, " Why don't you fasten the balloon to the chafing dish.''" This had not occurred to the experimenter, and the idea was a valuable one. That was the secret of success. The Montgolfier Brothers determined to exhibit their successful experiment, and accordingly on the 5th of June, 1783, a great concourse assembled to see the wonderful sight. A large canvas or linen balloon was made and suspended over a fire of chopped straw. The heated air quickly filled the balloon, which rose high in the air, and descended more than a mile away. This balloon con- tained 22,000 cubic feet of heated air, which is lighter than cold air, and of course rising carried the globe with it. As soon as the air began to cool the balloon ceased to rise, and as it got colder descended. Here was the actual discovery of the science of Aero- statics. The intelligence of the success achieved soon spread from France to other countries. Paris, however, was in advance, and the Brothers Robert applied, hydrogen gas to a balloon which was sent up from the Champ de Mars in August 1783. There was some trouble ex- perienced in filling it, but when the balloon was at length released it realized all expectations by remaining in the air nearly an hour. When at length it fell it met with a worse fate than it deserved, for the ignorant and superstitious peasantry at once destroyed it. After this Montgolfier exhibited his experiment this time at Versailles in the presence of the Court. The first aerial travellers appeared on this occasion — viz., a sheep, a cock, and a duck, which were secured in the car. They all descended in safety, and this success encouraged M. Pilatre de Rozier to make an attempt in a " fire balloon." He went up first in a captive balloon, and at length he and a friend, the Marquis d'Arlandes, ascended from the Bois de 92 AERONAUTICS. Boulogne. The trip was a decided success, and the possibility of navigating the air was fully demonstrated. Soon after this, — viz., in December 1783, — an Italian Count, named Zambeccari, made an ascent in London, and came down safely at Pet worth. MM. Charles and Robert ascended from Paris in December, and in February MM. Charles' and Roberts' balloon. a balloon crossed the English Channel. We must pass over some time and come to the ascents of Lunardi, which caused great excitement in London. His balloon was a very large one, and was inflated, or rather partially so, at the Artillery ground. Some delay occun-cd, and fearing a riot, M. Lunardi proposed to go up alone with the partially-filled balloon. A Mr. Biggin who had in- LUNARDI S ASCENT. 93 tended to ascend was left behind, The Prince of Wales was present, and thousands of spectators. Lunardi cast off and ascended rapidly, causing great admiration from the whole metropolis. Judge and jury, sovereign and ministers, all turned out to gaze at the balloon ; a guilty prisoner was acquitted hurriedly, so that no time was lost Blanchard's balloon. in discussion, and one lady died of excitement. Lunardi was regarded as a hero, and made many other ascents. He died in 1806. In those earlier days one or two fatal accidents happened. Count Zambeccari and a companion were in a balloon which caught fire, and both occupants of the car leaped from it as they were descending. The Count was killed 94 AERONAUTICS. on the spot, and his companion was much injured. Pilatre de Rozier made an attempt to cross the channel to England in 1785 ; he had reached three thousand feet when the balloon caught fire, and the unfortunate traveller ♦5* • - w 4 .».' The Nassau balloon. was precipitated to the ground. His associate only sur- vived him a few minutes. It is to the celebrated English aeronaut, Mr. Green, that the substitution of carburetted hydrogen or street gas for hydrogen is due, and since his ascent in 1821 no other means of inflation have been used. A great many quite successful and a few un- MR. GREEN. 95 successful ascents have been made for pleasure or profit. Mr. Green, in the Nassau balloon, passed over to Nassau, a distance of five hundred miles, in eighteen hours. This exploit was the cause of the name being bestowed upon The " Giant" balloon of M. Nadar- the balloon. The Giant of M. Nadar was exhibited in England, and it was an enormoUs one, being an hundred feet high, and nearly as wide in the widest part. But even this machine was outdone by the Godard " Montgolfier '' balloon, which was one hundred and seventeen feet high, gb AERONAUTICS. and carried a stove. We give illustrations of these celebrated balloons, and will now pass on to the more scientific portion of the subject and the ascents of Mr. Glaisher and other aeronauts for the purpose of making meteorological observations, and the use of balloons for purposes of observation in war. It appears that the first ascent for scientific investiga- tion was made in the year 1803. The aeronauts were Messrs. Robertson and Lhoest. They ascended from Hamburg and came down at Hanover, and made mean- time several experiments with reference to the electrical condition of the atmosphere, its influence upon a magnetic needle, and some experiments with regard to acoustics and heat. The report was presented to the St. Petersburg Academy, and contains the result of their interesting obser- vations.^ The travellers ascertained that at the elevation to which they attained,- — viz., 25,500 feet, — the tempera- ture was on that July day fifty degrees colder, falling to I9'6°, while on the earth the thermometer had shown 68^. They ascertained that glass and wax did not become electric when rubbed, that the Voltaic battery lost much of its power, that the oscillation of a "dipping needle" increased as they mounted into the air, while sound was certainly less easily transmitted at that elevation, and struck them as less powerful in tone. The heat experi- ment was not a success, owing to the breaking of the thermometer. They wished to find the temperature of boiling water at that elevation, but when the experiment was about to be made Robertson accidentally plunged the instrument into the fire instead of into the water. So the question was not settled. The effect upon the aeronauts was a sensation of sleepiness, and two birds died. The muscular powers of the voyagers also appear to have been much affected, and similar sensations may be experienced by travellers GAY-LUSSAC. 97 On high mountains who find their breath very short and a disinclination to exertion oppress them. MM. Biot and Gay-Lussac made a very interesting ascent in 1804. We will detail their experiences at some length, for the coolness displayed and the value of the observations made are remarkable in the history of scientific ballooning. They started at 10 o'clock a.m. on the 23rd of August, and when the balloon had carried them up to an altitude of 8,600 feet they commenced their experiments. They had some animals in the car with them, a bee amongst the number, and the insect was let go first. It flew away swiftly, not at all in- convenienced apparently. The sun was very hot at 56° Fahr. Their pulses were beating very fast, but no inconvenience was felt. When 1 1,000 feet had been reached a linnet was permitted to go at large, but after a little time the bird returned to the balloon. It remained perched for a few minutes, and then dashed downwards at a tremendous pace. A pigeon was then liberated. It also appeared very uncertain, and wheeled around in circles for a time. At last it gained confidence and descended, and dis- appeared in the clouds beneath. They made ether experiments, but descended without having obtained as accurate results as had been anticipated. On the next occasion, however, every care was taken, and on the 15th of September the important ascent was made by Gay-Lussac alone. He fixed hanging ropes to the balloon with the view to check the rotating move- ments, and having provided himself with all necessary apparatus and two vacuum flasks to bring down some of the upper air, the young man started. The barometer marked 30"66°, the thermometer 82° (Fahr.). At an elevation of 12,680 feet Lussac perceived that the varia- tion of the compass was the same as on land. Two 98 AERONAUTICS. hundred feet higher up he ascertained that a key held in the magnetic direction repelled with the lower, and attracted with its upper extremity the north pole of a needle. This experiment was repeated with the same result at an elevation of 20,000 feet, which shows how the earth exercises its magnetic influence. The tempera- ture of the air was found to decrease in proportion as the ascent up to 12,000 feet, where the reading was 47'3°. It then increased up to 14,000 feet by 6°, and then regularly diminished again as the balloon rose, till at the greatest elevation reached, 23,000 feet, there was a difterence of 6"]° in the temperature on the earth, for at the maximum height attained the thermometer stood at I4'9°. But the most important fact ascertained, and one which set many theories at rest, was the composition of the atmosphere in those high altitudes. We mentioned that Gay-Lussac took up two empty flasks from which the air had been taken. The vacuum was almost perfect. When the aeronaut had reached 21,460 feet he opened one flask, and it was quickly filled ; he secured it carefully ; and when at his highest point, — four miles and a half above the sea-level, — he opened the other flask. The barometer stood at 1 2 '9 5 inches, and the cold was very great. The voyager felt benumbed, and experienced difficulty of breathing; his throat was parched and dry. So Lussac determined to return, he could go no higher. He dropped gently near Rouen, and soon reached Paris. As soon as possible the air in the flasks was submitted to very delicate tests, and to the satisfaction of the scientists engaged it was found to be in exactly the same proportions as that collected near the earth — two hundred and fifteen parts of oxygen to every thousand of atmospheric air. Messrs. Banal and Bixio, in 1850, also made some observations, and found the temperature very variable. M, FLAMMARION. 99 At 23,000 teet they found the thermometer at minus 38'2° Fahr., which was much below the cold experienced by Gay-Lussac. We may still conclude that the various currents of the atmosphere cause considerable variation, and that it is impossible to lay down any law respecting the degrees of heat and cold hkely to be found at certain elevations. We quote Arago's observations upon this ascent : — " This discovery " (the ice particles found in the air) " explains how these minute crystals may become the nucleus of large hailstones, for they may condense round them the aqueous vapour contained in the portion of the atmosphere where they exist. They go far to prove the truth of Mariotte's theory, according to which these crystals of ice suspended in the air are the cause of parahelia — or mock-suns and mock-moons. Moreover, the great extent of so cold a cloud explains very satisfactorily the sudden changes of temperature which occur in our climates." M. Flammarion gives in his " Voyages " some very interesting and amusing particulars, as well as many valuable scientific observations. During one ascent he remarked that the shadow of the balloon was white, '^u^ at another time dark. When white the surface upon which it fell looked more luminous than any other part of the country ! The phenomenon was an anthelion. The absolute silence impressed the voyager very much. He adds, "The silence was so oppressive that we cannot help asking ourselves are we still alive ! We appear to apper- tain no longer to the world below." M. Flammarion's observations on the colour of what we term the sky are worth quoting — not because they are novel, but because they put so very clearly before us the appearance we call the " blue vault." He says,- — speaking of the non-existence of the " celestial vault," — " The air reflects the blue rays of the solar spectrum from every side. The white light of 100 AERONAUTICS. the sun contains every colour, and the air allows all tints to pass through it except the blue. This causes us to suppose the atmosphere is blue. But the air has no such colour, and the tint in question is merely owing to the reflection of light. Planetary space is absolutely black ; The " Eagle'' of M. Godard. the higher we rise the thinner the layer of atmosphere that separates us from it, and the darker the sky appears." Some beautiful effects may be witnessed at night from a balloon, and considering the few accidents there have been in proportion to the number of ascents, we do not wonder at balloon voyages being undertaken for mere pleasure. When science has to be advanced there can be SOUND IN UPPER AIR. !01 no objection flnade, for then experience goes hand-in-nand with caution. It is only tlie ignorant who are rasli ; the student of Nature learns to respect her, and to attend to her admonitions and warnings in time. The details of the ascents of famous aeronauts give us a great deal of pleasant and profitable reading. The phenomena of the sky and clouds, and of the heavens, are all studied with great advantage from a balloon, or " aerostat," as it is the fashion to call it. The grand phenomena of " Ulloa's circles," or anthelia, which represent the balloon in air, and surrounded by a kind of glory, or aureola, like those represented behind saintly heads, appear, as the name denotes, opposite to the sun. The various experiments made to ascertain the intensity of sounds have resulted in the conclusion that they can be heard at great distances. For instance, the steam whistle is distinctly audible 10,000 feet up in the air, and human voices are heard at an altitude of 5,000 feet. A man's voice alone will penetrate more than 3,000 feet into the air ; and at that elevation the croak- ing of frogs is quite distinguishable. This shows that sound ascends with ease, but it meets with great resist- ance in its downward course, for the aeronaut cannot make himself audible to a listener on the earth at a greater distance than 300 or 400 feet, though the latter can be distinctly heard at an elevation of 1,600 feet. The diminution of temperature noted by M. Flammarion is stated to be 1° Fahr. for "every 345 feet on a fine day. On a cloudy day the mean decrease was 1° for every 354 feet of altitude. The temperature of clouds is higher than the air surrounding them, and the decrease is more rapid near the surface, less rapid as the balloon ascends. We may add that at high elevations the cork from a "water-bottle will pop out as if from a champagne flask. We have hitherto referred more to M. Flammarion and 8 102 AERONAUTICS. Other French aeronauts, but we must not be considered in Any way oblivious of our countrymen, iVIessrs. Glaisher, Green, and Coxwell, nor of the American, — one of the most experienced of aerial voyagers, — Mr. Wise. The scientific observations made by the French voyagers con- firmed generally Mr. Glaisher's experiments. This noted air-traveller made twenty-eight ascents in the cause of science, and his experiences related in " Travels in the Air," and in the "Reports" of the British Association, are both useful and entertaining. For " Sensational ballooti- ing" one wishes to go no farther than his account df his experience with Mr. Coxwell, when (on the 5 th of September, 1862J he attained the greatest elevation ever reached — viz., seven miles, or thirty-seven thousand feet. We condense this exciting narrative for the benefit of those who have not seen it already. The ascent was made from Wolverhampton. At 1.39 p.m., the balloon was four miles high, the temperature was 8°, and by the time the fifth mile had been reached the mercury was below zero, and up to this time obser- vations had been made without discomfort, though Mr. Coxwell, having exerted himself as aeronaut, found SQme difficulty in breathing. About 2 o'clock, the balloon still ascending, Mr. Glaisher could not see the mercury in the thermometer, and Mr. Coxwell had just then ascended into the ring above the car to release the valve line which had become twisted. Mr. Glaisher was able to note the barometer, however, and found it marked 10 inches, and was rapidly decreasing. It fell to pf inches, and this indicated an elevation of 29,000 feet! But the idea was to ascend as high as possible, so the upward direction was maintainisd. " Shortly afterwards," writes Mr. Glaisher, " I laid my arm upon the table possessed of its full vigour, and on being desirous of using it I found it powerless, — it must have lost power momentarily. A SENSATIONAL ASCENT. 103 I tried to move the other arm, and found it powerless also. I then tried to shake myself, and succeeded in shaking my body. I seemed to have no limbs. I then A descending balloon. looked at the barometer, and whilst doing so my head fell on my left shoulder." Mr. Glaisher subsequently quite lost consciousness, and " black darkness " came. While powerless he heard Mr. Coxwell speaking, and then the words, " Do try, now I04 AERONAUTICS. do." Then sight slowly returned, and rousing himself, Mr. Glaisher said, " I have been insensible." Mr. Coxwell replied, " You have, and I, too, very nearly." Mr. Cox- well's hands were black, and his companion had to pour brandy upon them. Mr. Coxwell's situation was a perilous one. He had lost the use of his hands, which were frozen, and had to hang by his arms to the ring and drop into the car. He then perceived his friend was insensible, and found insensibility coming on himself. There was only one course to pursue — to pull the valve line and let the gas escape, so as to descend. But his hands were powerless 1 As a last resource he gripped the line with his teeth, and bending down his head, after many attempts succeeded in opening the valve and letting the gas escape, The descent was easily made, and accomplished in safety. Some pigeons were taken up on this occasion, and were set free at different altitudes. The first, at three miles, " dropped as a piece of paper " ; the second, at four miles, " flew vigorously round and round, apparently taking a dip each time"; a third, a little later, " fell like a stone." On descending a fourth was thrown out at four miles, and after flying in a circle, " alighted on the top of the balloon." Of the remaining pair one was dead when the ground was gained, and the other recovered. The observations noted are too numerous to be included here. Some, we have seen, were confirmed by subsequent aeronauts, and as we have mentioned them in former pages we need not repeat them. The results differed very much under different conditions, and it is almost impossible to decide upon any law. The direction of the wind in the higher and lower regions sometimes differed, sometimes was the same, and so on. The " Reports " of the British Association (i 862-1 866) will furnish full particulars of all Mr. Glaisher's experiments. We have scarcely space left to mention the parachutes PARACHUTES. 105 or umbrella-like balloons which have occasionally been used. Its invention is traced to very early times ; but Gamerin was the first who descended in a parachute, in 1 797i '^nd continued to do so in safety on many subsequent occasions. The parachute was suspended to a balloon, and at a certain elevation the voyager let go and came down in safety. He ascended once from London, and let go when 8,000 feet up. The parachute did not expand as usual, and fell at a tremendous rate. At length it opened out, and the occupier of the car came down forcibly, it is true, but safely. The form of the parachute is not unlike an umbrella opened, with cords attaching the car to the extremities of the " ribs," the top of the basket car being fastened to the " stick " of the umbrella. Mr. Robert Cocking invented a novel kind of parachute, but when he attempted to descend by it from Mr. Green's balloon it collapsed, and the unfortunate voyager was dashed to pieces. His remains were found near Lee, in Kent. Mr. Hampton did better on Garneron's principle, and made several descents in safety and without injury. The problem of flying in the air has attracted the notice of the Aeronautical Society, established in 1873, but so far without leading to practical results, though many daring and ingenious suggestions have been put forth in the " Reports." It is not within our province to do more than refer to the uses of the balloon for scientific purposes, but we may mention the services it was employed upon during the French war, 1870-71. The investment of Paris by the German army necessitated aerial communication, for no other means were available. Balloon manufactories were established, and a great number were made, and carried millions of letters to the provinces. Carrier pigeons were used to carry the return messages to the city, and photography was applied to bring the correspondence into io6 AERONAUTICS. the smallest legible compass. The many adventures of the aeronauts are within the recollection of all. A few of the balloons never reappeared ; some were carried into Norway, and beyond the French frontier in other directions. Filling a balloon. The average capacity of these balloons was 70,006 cubic feet. Of course it will be understood how balloons are enabled to navigate the air. The envelope being partly filled with coal-gas-heated air and hydrogen is much lighter than the BALLOONING. I07 surrounding atmosphere, and rises to a height according as the density of the air strata diminishes. The density- is less as we ascend, and the buoyant force also is lessened in proportion. So when the weight of the balloon and its occupants is the same as the power of buoyancy, it will come to a stand, and go no higher. It can also be understood that as the pressure of the outside becomes less, the expansive force of the gas within becomes greater. We know that gas is very compressible, and yet a little gas will fill a large space. Therefore, as the balloon rises, it retains its rounded form, and appears full even at great altitudes ; but if the upper part were quite filled before it left the ground, the balloon would inevitably burst at a certain elevation when the external pressure of the air would be removed, unless an escape were provided. This escape is arranged for by a valve at the top of the balloon, and the lower part above the car is also left open very often, so that the gas can escape of itself When a rapid descent is necessary, the top valve is opened by means of a rope, and the balloon sinks by its own weight. Mr. Glaisher advises for great ascensions a balloon of a capacity of 90,000 cubic feet, and only filled one-third of that capacity with gas. Six hundred pounds of ballast should be taken. A very small quantity of ballast thrown away will make a great difference ; a handful will raise the balloon many feet, and a chicken bone cast out occasions a rise of thirty yards. The ballast is carried in small bags, and consists of dry sand, which speedily dissipates in the air as it falls. By throwing out ballast the aeronaut can ascend to a great height — in fact, as high as he can go, the limit apparently for human existence being about seven miles, when cold and rarefied air will speedily put an end to human life. It is a curious fact, that however rapidly the balloon I08 AERONAUTICS. may he travelling through the air, the occupants are not sensible of the motion. This, in part, arises from the impossibility of comparing it with other objects. We pass nothing stationary which would indicate the pace at which we travel. But the absence of oscillation is also remarkable ; even a glass of water may be filled brim-full, and to such a level that the water is above the rim of the glass, and yet not a drop will fall. This experiment was made by M. Flammarion. When the aeronaut has ascended some distance the earth loses its flat appearance, and appears as concave as the firmament above. Guide ropes are usually attached to balloons, and as they rest upon the ground they relieve the balloon of the amount of weight the length trailing would cause. They thus act as a kind of substitute for ballast as the balloon is descending. Most of the danger of aerial travelling lies in the descent ; and though in fine weather the aeronaut can calculate to a nicety where he will .descend on a windy day, he must cast a grapnel, which' catches with an ugly jerk, and the balloon bounds and strains at her moorings. Although many attempts have been made to guide balloons through the air, no successful apparatus has ever been completed for use. Paddles, sails, fans, and screws have all been tried, but have failed to achieve the desired end. Whether man will ever be able to fly we cannot of course say. In the present advancing state of science it may not be impossible ere long to supply human beings with an apparatus worked by electricity, perhaps, which will enable them to mount into the air and sustain them- selves. But even the bird cannot always fly without previous ^momentum. A rook will run before it rises, and many other birds have to " get up steam," as it were, before they can soar in the atmosphere. Eagles and such heavy birds find it very difficult to rise from the FLYING IN THE AIR. log ground. We know that vultures when gorged cannot move at all, or certainly cannot fly away ; and eagles take up their positions on high rocks, so that they may launch down on their prey, and avoid the difficulty of rising from the ground. They swoop down with tremen- dous rhomentum and carry off their booty, but often lose their lives from the initial difficulty of soaring immediately. We fear man's weight will militate against his ever becoming a flying animal. When we obtain a knowledge of the atmospheric currents we shall no doubt be able to navigate our balloons ; but until then — and the informa- tion is as yet very limited, and the currents themselves very variable — we must be content to rise and fall in the air, and travel at the will of tlic wind in the upper regions of the atmosphere. We shall have more to say upon this subject in a subsequent book about some novel modes of locomo- tion in water and air. We will now glance at water and its uses. I'he Resistance of the Aii CHAPTER VII.— WATER. ABOUT WATER — HYDROSTATICS AND HYDRAULICS — LAW OF ARCHIMEDES THE BRAMAH PRESS^THE SYniON SPECIFIC GRAVITY. T present we will pass from Air to Water, from Pneumatics to Hydrostatics and Hydraulics. We must remember that Hydrostatics and Hy- draulics are very different. The former treats of the weight and pressure of liquids when they are at rest, the latter treats of them in motion. We will now speak of the properties of Liquids, of which Water may be taken as the most familiar example. We have already seen that Matter exists in the form of Solids, Liquids, and Gases, and of course Water is one form of Matter. It occupies a certain space, is slightly compressible ; it possesses weight, and exercises force when in motion. It is a fluid, but also a liquid. There are fluids not liquid, such as air or steam, to take equally familiar examples. These are elastic fluids and compres- sible, while water is inelastic, and termed incompressible. We may state that water is composed of oxygen and hydrogen, and proportions of eight of the former to one of the latter by weight ; in volume the hydrogen is as two to one. From these facts, as regards water, we learn that volume and weight are very different things, — that equal volumes of various things may have different weights, and VOLUME AND WEIGHT. Ill that volume (or bulk) by no means indicates weight. Equal volumes of feathers and sand will weigh very differently. [The old " catch " question of the " difference in weight between a pound of lead and a pound of feathers " here comes to the mind. The answer generally given is that "feathers make the heavier 'pound,' because they are weighed by avoirdupois, and lead by troy weight." This is an error. They are both weighed in the same way, and pound for pound, are the same weight, though different in volume. Fluids in equilibrium have all their particles at the same distance from the centre of the earth, and although within small distances liquids appear perfectly level (in a direct line), they must, as the sea does, conform to the shape of the earth, though in small levels the space is too limited to admit of any deviation from the plane at right angle to the direction of gravity. Liquids always fall to a perfectly level surface, and water will seek to find its original level, whether it be in one side of a bent tube, in a watering pot and its spout, or as a fountain. The surface of the water will be on the same level in the arms of a bent tube, and the fountain will rise to a height corresponding with the elevation of the parent spring whence it issues. The waterworks com- panies first pump the water to a high reservoir, and then it rises equally high in our high-level cisterns. As an example of the force of water, a pretty little experiment may be easily tried, and, as many of our readers have seen in a shop in the Strand in London, it always is attractive. A good-sized glass shade should be procured and placed over a water tap and basin, as per the illustration over-leaf. Within the glass put a number of balls of cork or other light material. Let a stop-cock, with a small aperture, be fixed upon the tube leading into the glass. Another tube to carry away the water should, of course, be provided, but it may be used over again. 1 12 WATER. When the tap is properly fixed, if the pressure of the water be sufficient, it will rush out with some force, and catching the balls as they fall to the bottom of the glass shade bear them up as a juggler would throw oranges from hand to hand. If coloured balls be used the effect b and balls. may be enhanced, and much variety imparted to the experiment, which is very easy to make. Water exercises an enormous pressure, but the pressure does not depend upon the amount of v/ater in the vessel. It depends upon the vessel's height, and the dimensions of the base. This has been proved by filling vessels PRESSURE OF WATER. 113 whose bases and heights are equal, but whose shapes are different, each holding a different quantity of water. The pressure at the bottom of each vessel is the same, and de- pends upon the depth of the water. If we subject a portion of the liquid surface to certain force, this pressure will be dispersed equally in all directions, and from an acquaint- Pressure of water. ?J ance with this fact the Hydraulic Press was brought into notice. If a vessel with a horizontal bottom be filled with water to a depth of one foot, every square foot will sustain a pressure of 62-37 ^hs., and each square inch of 0^43 3 lbs. We will now explain the principle of this Water Press. In the small diagram, the letters AB represent the bottom of a cylinder which has a piston fitted in it (p). Into the op- posite side a pipe is let in, which leads from a force-pump, D, which is fitted with a valve, E, opening upwards. When the piston in D is pulled up water enters through the valve; " ^^^^^^^^^^ when the piston is forced down the valve shuts, and the water rushes into the chamber, AB. The pressure pushes up the large piston with a force multiplied as many times as the area of the small piston is contained in the large one. So if the large one be ten times as great as the small one, and the latter be forced down with a 10 lb. pressure, the pressure on the large one will be 100 lbs., and so on. 14 WATER. The accompanying illustration shows the form of the rlydraulic or Bramah Press. A B C D is a strong frame, !■ the force-pump worked by means of a lever fixed at G, ind H is the. counterpoise. E is the stop-cock to admit he water. The principles of hydrostatics will be easily explained. Eramah Press. fhe Lectures of M. Aim6 Schuster, Professor and -librarian at Metz, have taught us in a very simple nanner the principle of Archimedes, in which it is laid lown that " a body immersed in a liquid loses a portion )f its weight equal to the weight of the liquid displaced )y it." We take a body of as irregular form as we jlease ; a stone, for example. A thread is attached to he stone, and it is then placed in a glass of water full up UPWARD PRESSURE OF LIQUIDS. I I 5 to the briin. The water overflows ; a volume of the liquid equal to that of the stone runs over. The glass thus partially emptied is then dried, and placed on the scale of a balance, beneath which we suspend the stone ; equilibrium is established by placing some pieces of lead in the other scale. We then take a vase full of water, into which we plunge the stone suspended from the scale, supporting the vase by means of bricks. The equilibrium is now broken ; to re-establish it, it is necessary to fill up with water the glass placed on the scale ; that is to say, we put back in the glass the weight of a volume of water precisely equal to that of the stone. If it is desired to investigate the principles relating to connected vessels, springs of water, artesian wells, etc., two funnels, connected by means of an india-rubber tube of certain length, will serve for the demonstration ; and by placing the first funnel at a higher level, and pouring in water abundantly, we shall see that it overflows from the second. A disc of cardboard and a lamp-glass will be all that is required to show the upward pressure of liquids. I apply to the opening of the lamp-glass a round piece of cardboard, which I hold in place by means of a string ; the tube thus closed I plunge into a vessel filled with water. The piece of cardboard is held by the pressure of the water upwards. To separate it from the opening it suffices to pour some water into the tube up to the level of the water outside. The outer pressure exercised on the disc, as well as the pressure beneath, is now equal to the weight of a body of water having for its base the surface of the opening of the tube, its depth being the distance from the cardboard to the level of the water. Syringes, pumps, etc., are the effects of atmospheric pressure. Balloons rise in the air by means of the pressure of gas ; a balloon being a body plunged in gas, is con- Ii6 WATER. sequently submitted to the same laws as a body pluflged in water. Boats float because of the pressure of liquid, and water spurts from a fountain for the same reason, I recollect Demonstration of the upward pressure of liquids. having read a very useful application of the principles of fluid pressure. A horse was laden with two tubs for carrying a supply of water, and in the bottom of the tubs a valve was fixed.. When the horse entered the stream the tubs were partly immersed ; the water then exercised its upward pressure,, the valve opened, and the tubs slowly filled. When they WATER LEVEL. 117 were nearly full the horse turned round and came out of the water ; the pressure had ceased. Thus the action of the water first opened the valve, and then closed it. The particular phenomena observable in the water level Experiment on the convexity of a meniscus, in narrow spaces, as of a fine glass tube, or the level of two adjoining waves, capillary phenomena, etc., do not need any special appHance for demonstration, and it is the same with the convexity or concavity of meniscuses.* *> The curved surface of a column of liquid is termed a " meniscus," from the Greek word meniskos, meaning " a little' lens.'' y ii8 WATER. The foregoing cut represents a pretty experiment in con ■ nection with these phenomena. 1 take a glass, which I fill up to the brim, taking care that the meniscus be concave, and near it I place a pile of pennies. I then ask my young friends how many pennies can be thrown into the glass without the water overflowing. Everyone who is not familiar with the experiment will answer that it will only be possible to put in one or two, whereas it is possi- ble to put in a considerable number, even ten or twelve. As the pennies are carefully and slowly dropped in, the surface of the liquid will be seen to become more and more convex, and one is surprised to what an extent this convexity increases before the water overflows. The common syphon may be mentioned here. It consists of a bent tube with limbs of unequal length. We give an illustration of the syphon. The shorter leg being put into the mixture, the air is exhausted from the tube at o, the aperture at g being closed with the finger. When the finger is removed the liquid will run out. If the water were equally high in both legs the pressure of the atmo- sphere would hold the fluid in equilibrium, but one leg being longer, the column of water in it preponderates, and as it falls, the pressure on the water in the vessel keeps up the supply. Apropos of the syphon, we may mention a very simple application of the principle. Cut off a strip of cloth, and arrange it so that one end shall remain in a glass of water while the other hangs down, as in the illustration. In a short time the water from the upper glass will have passed through the cloth-fibres to the lower one. The Syphon CAPILLAKITY. 119 This attribute of porous substances is called capillarity, and shows itself by capillary attraction in very fine pores or tubes. The same phenomenon is exhibited in blotting paper, sugar, wood, sand, and lamp-wicks, all of which give familiar instances of capillarity. The cook makes use of An Improvised syphon. this property by using thin paper to absorb grease from the surface of soups. Capillarity (already referred to) is the term used to define capillary force, and is derived from the word capillits, a hair ; and so very small bore tubes are called capillary tubes. We know that when we plunge a glass tube into I20 WATER. water the liquid will rise up in it, and the narrower the tube the higher the water will go ; moreover, the water inside will be higher than at the outside. This is in accordance with a well-known law of adhesion, which induces concave or convex surfaces in the liquids in the tubes, according Molecular attraction. as the tube is wetted with the liquid or not. For instance, water, as we have said, will be higher in the tube and concave in form ; but mercury will be depressed below the outside level, and convex, because mercury will not adhere to glass. When the force of cohesion to the sides of the tube is more than twice as great as the adhesion of the Molecular attraction. 121 particles of the liquid, it will rise up the sides, and if the forces be reversed, the rounded appearance will follow. This accounts for the convex appearance, or " meniscus," in the column of mercury in a barometer. Amongst the complicated experiments to demonstrate 4 Vase of Tantalus. molecular attraction, the following is very simple and very pretty : — Take two small balls of cork, and having placed them in a basin half-filled with water, let them come close to each other. When they have approached within a certain distance they will rush together. If you fix one of them on the blade of your pen-knife, it will attract the other as a magnet, so that you can lead it round the basin. But 122 WATER. if the balls of cork are covered with grease they will repel each other, which fact is accounted for by the form of the menisques, which are convex or concave, according as they iJecepiiou jugs of old pattern. are moistened, op preserved from action of the water by the grease. This attribute is of great use in the animal and vegetable kingdoms. The rising of the sap is one instance of the latter. VASE OF TANTALUS. 123 Experience in hydrostatics can be easily applied to amusing little experiments. For instance, as regards the syphon, we may make an image of Tantalics as per illus- tration. A wooden figure may be cut in a stooping posture, and placed in the centre of a wide vase, as if about to drink. If water be poured slowly into the vase it will never rise to the mouth of the figure, and the unhappy Tantalus will remain in expectancy. This result is ob- tained by the aid of a syphon hidden in the figure, the shorter limb of which is in the chest. The longer limb descends through a hole in the table, and carries off the water. These vases are called vases of Tantalus. The principle of the syphon may also be adapted to our domestic filters. Charcoal, as we know, makes an excellent filter, and if we have a block of charcoal in one of those filters, — now so common, — we can fix a tube into it, and ^.^ar any water we may require. It sometimes (in the country) happens that drinking-water may be- come turgid, and in such a case the syphon filter will be found useful. The old " deception " jugs have often puzzled people. We, give an illus- tration of one, and also a sketch of the "deceptive" portion. This deception is very well managed, and will create much amuse- ment if a jug can be pro- cured ; they were fashionable in the eighteenth century and previously. A cursory inspection of these curious utensils will lead one to vote them utterly useless. They Section of jug. 124 WATER. are, however, very quaint, and if not exactly useful are ornamental. They are so constructed, that if an in- experienced person wish to pour out the wine or water contained in them, the liquid will run out through the holes cut in the jug. To use them with safety it is necessary to put the spout, A, in one's mouth, and close the opening, B, with the finger, and then by drawing in the breath, cause the water to mount to the lips by the tube which runs around the jug. The specimens herein delineated have been copied from some now existent in the museum of the Sevres china manufactory. The Buoyancy of Water is a very interesting subject, and a great deal may be written respecting it. The swimmer will tell us that it is easier to float in salt water than in fresh. He knows by experience how difficult it is to sink in the sea ; and yet hundreds of people are drowned in the water, which, if they permitted it to exercise its power of buoyancy, would help to save life. The sea-water holds a considerable quantity of salt in solution, and this adds to its resistance, or floating power. It is heavier than fresh water, and the Dead Sea is so salt that a man cannot possibly sink in it. This means that the man's body, bulk for bulk, is much lighter than the water of the Dead Sea. A man will sink in fresh, or ordinary salt water if the air in his lungs be exhausted, because without the air he is much heavier than water, bulk for bulk. So if anything is weighed in water, it apparently loses in weight exactly equal to its oWn bulk of water. Water is the means by which Specific Gravity of liquids or solids is found, and by it we can determine the relative densities of matter in proportion. Air is the standard for gases and vapours. Let us examine this, and see what is meant by SPECIFIC Gravity. We have already mentioned the difference existing SPECIFIC GRAVITY. between two equal volumes of different substances, and their weight, which proves that they may contain a different number of atoms in the same space. We also know, from the principle of Archimedes, that if a body be immersed in a fluid, a portion of its weight will be sustained by the fluid equal to the weight of the fluid displaced. [This theorem is easily proved by filling a bucket with water, and moving it about in water, when it will be easy to lift ; and likewise the hum.an body may be easily sustained in water by a finger under the chin.j Vveij^lung metal in water. The manner in which Archimedes discovered the dis- placement of liquids is well known, but is always interesting. King Hiero, of Syracuse, ordered a crown of gold to be made, and when it had been completed and delivered to His Majesty, he had his doubts about the honesty of the gold- smith, and called to Archimedes to tell him whether or not the crown was of gold, pure and simple. Archimedes was puzzled, and went home deep in thought. Still considering the problem he went to the bath, and ... his abstraction filled it to the brim. Stepping in he spilt a considerable quantity of water, and at once the idea struck him that any body put into water would displace its own bulk of the liquid. He did not wait to dress, but ran half-naked to the palace, crying out, "Eureka, Eureka ! I 126 WATER. have found it, I have found it ! " What had he found ? — He had solved the problem. Fie got a lump of gold the same weight as the crown, and immersed it in water. He found it weighed nineteen times as much as its own bulk of water. But when he immersed the king's crown he found it displaced more water than the pure gold had done, and consequently it had been adulterated by a lighter metal. He assumed that the alloy was silver, and by immersing lumps of silver and gold of equal weight with the crown, and weighing the water that overflowed from each dip, he was able to tell the king how far he had been cheated by the goldsmith. It is by this method now that we can ascertain the specific gravity of bodies. One cubic inch of water weighs about half an ounce (or to be exact, 252^ grains). Take a piece of lead and weigh it in air ; it weighs, say, eleven ounces. Then weigh it in a vase of water, and it will be only ten ounces in weight. So lead is eleven times heavier than water, or eleven ounces of lead occupy the same space as one ounce of water. [The heavier a fluid is, or the greater its density, the greater will be the weight it will support. Therefore we can ascertain the purity or otherwise of certain liquids by using hy- drometers, etc., which will float higher or lower in different liquids, and being gauged at the standard of purity, we can ascertain (for instance) how much water is in the milk when supplied from the dairy.] Hydrometer. g^^ ^q rctum tO SPECIFIC GRAVITY, wllich means the "Comparative density of any substance relatively to water," or as Professor Huxley says, " The weight of a SPECIFIC GRAVITY. 127 volume of any liquid or solid in proportion to the weight of the same volume of water, at a known temperature and pressure." Water, therefore, is taken as the unit ; so anything whose equal volume under the same circumstances is twice as heavy as the water, is declared to have its specific gravity 2; if three-and-a-half times it, is 3*5, and so on. We append a few examples ; so we see that things which possess a higher specific gravity than water sink, which comes to the same thing as saying they are heavier than water, and vice versd. To find the specific gravity of any solid body proceed as above, in the experiment of the lead. By weighing the substance in and out of water we find the weight of the water displaced ; that is, the first weight less the second. Divide the weight in air by the remainder, and we shall find the specific gravity of the substance. The following is a table of specific gravities of some very different substances, taking water as the unit. Substance. Specific Gravity. 1 Substance. Speciric Gravity. Substance. Specific . Gravity.. Platinum . 21-5 Iron . 779 Water I'OOO Gold . 19-5 Tin . 7-29 Sea Water . 1-026 Mercury i3'59 j Granite 2-62 Rain Water I -00 1 Ltad . 11-45 1 Oak Wood. 077 Ice . •916 Silver.. io'5o ; Cork . 0-24 Ether . 0-723 Copper 8-96 Milk . I 032 Alcohol 0-793 But we have by no means exhausted the uses of water. Hydrodynamics, which is the alternative term for hydraulics, includes the consideration of many forms of water-wheels, most of which, as mill-wheels, are under-shot, or over-shot accordingly as the water passes horizontally over the floats, or acts beneath them. These wheels are used in relation to the fall of water. If there is plenty of water and a slight fall, the under-shot wheel is used. If there is a good 128 WATER. fall less water will suffice, as the weight and momentum of the falling liquid upon the paddles will turn the wheel. Here is the Persian water-wheel, used for irrigation. The Archimedian Screw, called after its inventor, was one of the earliest modes of raising water. It consists of a cylinder somewhat inclined, and a tube bent like a screw within it. WATER-MIT,!,. 129 By turning the handle of the screw the water is drawn up and flows out from the top. The Water Ram is a machine used for raising water to a great height by means of the momentum of falling water. ^^f?Sis#i' Over-shot wheel of mill. The Hydraulic Lift is familiar to us all, as it acts in our hotels, and we need only mention these appliances here ; full descriptions will be found in Cyclopaedias.