D

E

A is a glass rod, supporting a small stand of baked wood. B is a button of metal, let into the stand, and connected with the chain C. E is a glass rod, fitted in a cap, which is fixed to the foot D. G is a cap of metal, fitting on the top of the glass rod E. Screwed into the top of it is the bent wire F F, which is terminated by a little ball situated at about half an inch from B. H is the wetted thread, (a common piece of pack-thread, doubled, about three inches long, will do,) to the end of which is fastened the chain I.

Ex.-Place some dried gunpowder on the metal button B. Wet the thread, and connect one of the chains to the outside of a charged Leyden phial, and the other to the discharging rod-upon passing the shock the gunpowder will be fired.

Ex.-Take away the thread, and put a chain in its place-upon passing the shock the gunpowder will be scattered, but not inflamed.

With a dry thread, or one that is too long, the shock will not pass at all, but with a little previous arrangement the experiment will never fail. It may, also, be fired at any distance, with wires of appropriate length, and even under water, provided only that the connecting wires are covered with a tube of glass, or Indian rubber varnish.

REVIVAL OF THE INSCRIPTIONS ON COINS AND MEDALS.

It has been long known though we have not been able to ascertain to whom we owe the discovery that a coin from which the inscription and the figures have been entirely effaced, so as not to present the slightest trace of an impression, may have the inscription and figure partly or wholly restored by placing it upon a hot iron. In order to perform this experiment with the fullest effect, the coin employed should be one equally worn down, and in which very little of the metal has been worn off the hollow parts by which the letters are surrounded.

When a coin of this kind, or what is still better, a coin on which an illegible trace of the letter still remains, is placed upon a heated iron, it will be seen that an oxidation takes place over its whole surface, the film of oxide changing its tint with the

intensity or continuance of the heat. The parts, however, where the letters of the inscription had existed, oxidate at a different rate from the surrounding parts, so that these letters exhibit their shape, and become legible in consequence of the film of oxide which covers them having a different thickness, and therefore reflecting a different tint from that of the parts adjacent. The tints thus developed sometimes pass through many orders of brilliant colors, particularly pink and green, and settle in a bronze, and sometimes a black tint; resting upon the inscription alone. In some cases the tint left on the trace of the letters is so very faint that it can just be seen, and may be easily removed by a slight friction of the finger.

When the experiment is often repeated with the same coin, and the oxidation successively removed after each experiment, the film of oxide continues to diminish, and at last ceases to make its appearance. It recovers the property, however, in the course of time. When the coin is first placed upon the heated iron, and consequently when the oxidation is the greatest, a considerable smoke rises from the coin, and diminishes like the film of oxide by frequent repetition. A coin which has ceased to give out this smoke, smoked lightly after twelve hours exposure to the air, having been removed from the hot iron at the beginning of that interval, and replaced upon it at the end of it by a pair of pincers.

From a great number of experiments, it is found raised parts of the coin, and in modern coins, that the elevated ledge round the inscription oxidate first. This ledge, in an English shilling of 1816, began by exhibiting a brilliant yellow tint before it appeared on any other part of the coin.

In examining a number of old coins, a brilliant red globule, accompanied with a smell of sulphur, appeared on one or two points of the coin; and sometimes small globules, like those of quicksilver, exuded from the surface. Other coins exhaled a most intolerable smell; and an Indian pagoda became perfectly black when placed upon the heated iron.

Such being the general facts respecting the oxidation of coins, it becomes an interesting inquiry to determine its cause. If we take a homogeneous and uniform piece of silver, and place it upon a heated iron, its surface will oxidate equally, if all the parts of it are exposed to the same degree of heat. A coin, however, differs from a piece of silver of uniform texture, as it has been struck with great force during the act of coining. In this process the sunk parts have obviously been most compressed by the prominent parts of the die, and the elevated parts least compressed, the metal being left as it were in its natural condition. A coin, therefore, is a piece of metal in which the raised letters and figures have less density than the other parts, and consequently these parts oxidate sooner, or at a lower temperature. When the letters themselves are rubbed off by use, the parts immediately below them have also less density than the metal which surrounds them, and consequently, they receive from heat an oxidation and a color different from that of the surrounding surface. Hence, the reason is obvious, why the invisible letters are revived by oxidation.

A similar effect takes place in the beautiful oxidations which are produced on a surface of polished steel. When the steel has hard portions, called pins by the workmen, the uniform tint of the oxide stops near these points, which always display colors different from the rest of the mass.

The smoking of the coin, the diminution of its oxidating power, by a repetition of the experiment, and the recovery of that power by time, seem to indicate that the softer parts of the metal absorb something from the atmosphere which promotes oxidation. Whether this is oxygen or not, remains to be determined.

THE MECHANICAL POWERS. MECHANICAL Powers are simple arrangements by which we gain power at the expense of time; thus, if a certain weight can be raised to a certain height by unassisted strength, and the same thing is afterwards done with one-tenth part of the exertion, through the use of a mechanic power, it will be found to require ten times as much time.

In many cases, however, loss of time is not to be put in competition with the ability to do a thing; and since the advantages which the mechanical powers afford to man, by enabling him to perform feats which, without their assistance, would have been for ever beyond his reach, are incalculably great, the waste of time is overlooked, and is much more than balanced in the general result. It is true that if there are several small weights, manageable by human strength, to be raised to a certain height, it may be full as convenient to elevate them one by one, as to take the advantage of the mechanical powers in raising them all at once; because the same time will be necessary in both cases; but suppose we should have an enormous block of stone or a great tree to raise; bodies of this description cannot be separated into parts proportionable to the human strength, without immense labour nor perhaps without rendering them unfit for those purposes to which they are to be applied; hence then the great importance of the mechanical powers, by the use of which a man is able to manage with ease a weight many times greater than himself.

There are six mechanic powers, viz. the lever, wheel and axle; the inclined plane; the screw; the pulley; and the wedge; out of the whole or a part of which, it will be found that every mechanical engine or piece of machinery is constructed.

The Lever being the simplest of all the mechanic powers, is in general considered the first. It is an inflexible rod or bar of any kind, so disposed as to turn on a pivet or prop, which is always called its fulcrum. It has the weight or resistance to be overcome attached to some one part of its length, and the power which is to overcome that resistance applied to another; and, since the power, resistance, and fulcrum admit of various positions with regard to each other, so is the lever divided into three kinds or modifications, distinguished as the first, second, and third kinds of lever. That portion of it which is contained between the fulcrum and the power, is called the acting part or arm of the lever; and that part which is between the fulcrum and resistance, its resisting part or arm.

In the lever of the first kind, the fulcrum is placed between the power and the resistance. A poker, in the act of stirring the fire, well illustrates this subject; the bar is the fulcrum, the hand the power, and the coals the resistance to be overcome. Another common application of this kind of lever is the crow-bar, or hand-spike, used for raising a large stone or weight. In all these cases, power is gained in proportion as the distance from the fulcrum to the power, or part where the men apply their strength, is greater than the distance from the

fulcrum to that end under the stone or weight. A moment's reflection will show the rationale of this fact; for it is evident that if both the arms of the lever be equal, that is to say, if the fulcrum be midway between the power and weight, no advantage can be gained by it, because they pass over equal spaces in the same time; and, according to the fundamental principle already laid down, as advantage or power is gained, time must be lost; but, since no time is lost under such circumstances, there cannot be any power gained. If now, we suppose the fulcrum to be so removed towards the weight, as to make the acting arm of the lever three times the length of the resisting arm, we shall obtain a lever which gains power in the proportion of three to one, that is, a single pound-weight applied at the upper end will balance three pounds suspended at the other. A pair of scissors consist of two levers of this kind, united in one common fulcrum; thus the point at which the two levers are screwed together is the fulcrum; the handles to which the power of the fingers is applied, are the extremities of the acting part of the levers, and the cutting part of the scissors are the resisting parts of the levers; the longer, therefore, the handles, and the shorter the points of the scissors, the more easily you cut with them. Α person who has any hard substance to cut, without any knowledge of the theory, diminishes as much as possible the length of the resisting arms, or cutting part of the scissors, by making use of that part of the instrument nearest the screw or rivet. Snuffers are levers of a similar description; so are most kind of pincers, the power of which consists in the resisting arm being very short in comparison with the acting

one.

In the lever of the second kind, the resistance or weight is between the fulcrum and the power. Numberless instances of its application daily present themselves to our notice; amongst which may be enumerated the common cutting knife, used by last and pattern makers, one end of which is fixed to the work-bench by a swivel-hook. Two men carrying a load between them, by one or more poles, as a sedan chair, or as brewers carrying a cask of beer, in which case either the back or front man may be considered as the fulcrum, and the

other as the power. Every door which turns upon its hinges is a lever of this kind; the hinges may be considered as the fulcrum, or centre of motion, the whole door is the weight to be moved, and the power is applied to that side on which the handle is usually fixed. Nut-crackers, oars, rudders of ships, likewise fall under the same division. The boat is the weight to be moved, the water is the fulcrum, and the waterman at the oar is the power. The masts of ships are also levers of the second kind, for the bottom of the vessel is the fulcrum, the ship the weight, and the wind acting against the sail is the moving power. In this kind of lever the power or advantage is gained in proportion as the distance of the power is greater than the distance of the weight from the fulcrum; if, for instance, the weight hang at one inch from the fulcrum, and the power acts at five inches from it, the power gained is five to one; because in such a case, the power passes over five times as great a space as the weight. It is thus evident why there is considerable difficulty in pushing open a heavy door, if the hand is applied to the part next the hinges, although it may be opened with the greatest ease in the usual method. In the third kind of lever, the fulcrum is

again at one of the extremities, the weight or resistance at the other; and it is now the power which is applied between the fulcrum and resistance. As in this case the weight is farther from the centre of motion than the power, such a lever is never used, except in cases of absolute necessity, as in the case of lifting up a ladder perpendicularly, in order to place it against a wall. The man who raises it cannot place his hands on the upper part of the ladder; the power, therefore, is necessarily placed much nearer the fulcrum than the weight; for the hands are the power, the ground the fulcrum, and the upper part of the ladder the weight. The use of the common fire-tongs is another example, but the circumstance that principally gives this lever importance is, that the limbs of men and animals are actuated by it; for the bones are the levers while the joints are the fulcra, and the muscles which give motion to the limbs, or produce the power, are inserted and act close to the joints, while the action is produced at the extremities; the consequence of such an arrangement is, that although the muscles must necessarily exert an enormous contracticle force to produce great action at the extremities, yet a celerity of motion ensues which could not be equally well provided for in any other manner. We adduce one example in illustration of this fact. In lifting a weight with the hand, the lower part of the arm becomes a lever of the third kind; the elbow is the fulcrum; the muscles of the fleshy part of the arm the power; and as these are nearer to the elbow than the hand it is necessary that their power should exceed the weight to be raised. The disadvantage, however, with respect to power, is more than compensated by the convenience resulting from this structure of the arm; and it is no doubt that which is best adapted to enable it to perform its various functions. From these observations it must appear, that although this arrangement must be mentioned as a modification of the lever, it cannot, in strictness, be called a mechanical power; since its resisting arm is in all cases, except one, longer than the acting arm, and that one case is equal to it, on which account it never can gain power, but in most instances must lose it.

(Continued on page 155.)

COPPER IN AMMONIA.

BY J. MACCULLOCH, M.D.F.R.S.F.L.S.

Ir is an unaccountable omission of chemists, not to have observed that copper is soluble in ammonia; I mean, of course, in the metallic state. This solution takes place rapidly in the heat at which the water of ammonia boils. The water is decomposed during the process, for the purpose of oxidating the metal, and hydrogen is obtained.

This fact may be turned to use in the arts. Gold trinkets, such as chains, are often made of a very inferior alloy; and in this country, I believe, they are never better than eighteen carat gold. They of course require to be colored, to use the jeweller's term. This is done by dissolving the copper of the alloy to a certain depth on the surface; so that, after this operation, the metal is in fact gilded, nothing but pure gold being visible. The coat of pure gold is thus so slight, that it easily wears off in use; so that the operation, of cleaning, (as it is supposed to be by the owners), requires to be fre

quently performed, and this is done by a fresh process of solution, or coloring.

The method used by the artists is the application of a mixture of neutral salt, intended to disengage nitric acid, with the assistance of heat. In whatever manner, however, this is managed, there is much gold also dissolved in the operation; so much indeed, that where much work of this nature is performed, the quantity of metal rescued from the solutions amounts to a very considerable quantity annually. Artists are accused of doing this with fraudulent views; with what truth I shall not pretend to say. Whatever the fact may be as to this, a few repetitions of the coloring process are sufficient to destroy the finer kinds of workmanship, to the great regret of our ladies.

Boiling in ammonia is a safe substitute for this pernicious process, as it dissolves the copper from the alloy, and leaves in the same manner, a gilded or yellow surface. It has the advantage that it can be performed by any one, without the necessity of employing an artist.

MISCELLANIES.

A Correspondent informs us, that he has found that simple immersion in hot water will effectually fix photogenic drawings, the paper for which has been made by nitrate of silver only, and that this paper is very sensitive.

Different Species of Silkworms.-The silk imported from India is by no means the production of the larva of only one species of moth. MM. Helfer and Hugon have given the following list of the insects, the silk of which is known in commerce. 1. Bambyx mori. The common silkworm.

2. Bombyx religiosa, (Helf.) Assam. The cocoon of this phalana has a finer filament, more gloss, and is softer to the touch than that of the former. The larva lives on the banyan tree, (Ficus religiosa.)

3. Saturnina silhetica, (Helf.) is found in the mountains near Silhet and Dacca; the cocoons are very large.

4. Saturnia papia, (Linn.) The most common of the Indian silkworms. The silk most highly prized in Europe is its produce. In its wild state the larva feeds on the jujube plant. (Zizyphus jujuba,) and on the Terminalia alata, from which the inhabitants gather the cocoons. It has not been reared in Europe, but M. Helfer found that it could bear domestication well.

5. Saturnia assamensis, (Helf.) from Mooga in Assam. Its larva is found on the Laurus obtusifolia and the Teranthera macrophylla. This insect produces five generations in the year; the cocoons collected twice during the winter, are the finest and most abundant.

6. Phalana cynthia, (Drury,) a species commonly reared throughout Hindoostan for producing silk the larva feeds on the Ricinus, grows rapidly, and is very hardy; its silk is coarse, but strong, so that a dress made from it lasts for more than a person's life, and such dresses are transmitted from mother to daughter.

It is commonly considered that Indian is inferior to European silk, but this more from the slovenly way the worms are reared in the East than from any inferiority in the staple. Attention is now much attracted to the subject in India, and ere long this produce will most probably rival in quality that from Italy.

Action of Water on Melted Glass.-Mr. Parkes, in his Essays, has adverted to some appearances produced by water flung upon glass when in the furnace, which appear extremely strange, although they were related to him by the most undisputed authorities.

If a small quantity, even a pint of water, were to be thrown into a crucible of glass in a melted, or rather melting state, while the scum or sandiver is upon its surface, the water would be converted instantly into steam, so that an explosion would take place; and if the quantity of water were more considerable, the furnace would probably be blown down.

But when the sandiver has been scummed off, and the glass in quiet fusion, if water is thrown on it, the globules dance upon the surface of the melted glass for a considerable time, like so many globules of quicksilver upon a drum head, while the drummer is beating it.

There is, however, a similar appearance to this that takes place in iron; for water evaporates sooner from a plate of iron that is heated to redness only, than from a plate that has been brought to a welding heat, or very nearly to the heat necessary to melt it,

But in the manufacture of black bottles, it frequently happens, that while the workmen are employed in moulding and blowing the bottles, that the glass, or metal as it is called, becomes too cold to work, so that they find it necessary to desire the firemen to throw in cold and increase the heat.

This, however carefully it may be done, will sometimes produce so much dust that the surface of glass becomes covered with coal dust. When this accident occurs, it occasions such a motion within the melting pot, that the glass appears as if it were actually boiling; and if the metal was used in this state, every bottle would be speckled throughout and full of air bubbles.

Now, as it would be very inconvenient to wait for the whole of this coaly dust to be consumed by the fire, and, besides, it might occasion the glass to boil over the edges of the melting pot, the workmen have to endeavour to discover an easy and effectual remedy for this accident; and this remedy is no other than common water.

Whenever this circumstance taxes place, the workmen throw a little water into each of the melting pots. This water has the effect, not only of stilling the boiling of the glass immediately, but it also renders the metal as smooth and pure as before.

Mr. Parkes considers this curious and almost instantaneous effect, as probably owing to the water becoming decomposed, and affording its oxygen to the coal dust, and thus converting it into carbonic acid gas, which immediately escapes and is dissipated in the atmosphere.

Simple Remedy to Purify Water.-It is not so generally know as it ought to be, that pounded alum possesses the property of purifying water. A large table-spoonful of pulverized alum, sprinkled into a hogshead of water, (the water stirred round at the time,) will, after a lapse of a few hours, by precipitating to the bottom the impure particles, so purify it that it will be found to possess nearly all the freshness and clearness of the finest spring water. A pailful, containing four gallons, may be purified by a single tea-spoonful.

Carbonate of Potash from Green and Dry Plants. -M. Becquerel has made some experiments on the manufacture of potash. The comparative analysis of a great number of ashes have proved that those of green wood yield a much greater proportion of saline matter than dry wood. This difference is especially striking with the ashes of fern; the ley of the ashes contains a mixture of subcarbonate and sulphate of potash; the proportion of the former varies from 0:45 to 0.65; it is this variation which causes the great difference of quality and price in potash of commerce; it becomes, therefore, very important, in the manufacture of potash, to separate the sulphate with which the subcarbonate is mixed. M. Becquerel effected this by concentrating the solution to spec. grav. about 1.4, and allowing it to cool: the greater part of the sulphate of potash crystallizes on cooling, and the saline matter which remains in solution contains afterwards 0.90 of subcarbonate. M. Becquerel has also ascertained, by his numerous analysis of different kinds of ashes, that those of the limeburner contain very little sulphate of potash, which is undoubtedly due to the action of the lime upon the sulphate of potash, with the assistance of charcoal. This fact, M. Becquerel remarks, may lead to some advantage, by adding lime to the wood, the ashes of which are intended for the manufacture of potash.

Filtering Machine.-Take a large flower-pot, and put either a piece of sponge or some cleanly washed moss (Sphagnum is to be preferred) over the hole at the bottom. Fill the pot full with a mixture of equal parts of clean sharp sand and charcoal broken into pieces about the size of peas. On this lay a piece of linen or woollen cloth, large enough to hang over the sides of the pot. Pour the water to be filtered into the basin formed by the cloth, and it will come out pure through the sponge in the bottom. The cloth must be frequently taken out and washed, as must the sand and charcoal, and the piece of sponge or moss in the bottom. The larger the pot, the more complete will be the filtration. The charcoal is easily procured, by burning a few pieces of wood in a slow fire. This is the cheapest description of filter which we know of.-Gardener's Mag.

113-How are glass seals, bread seals, and gum seals made? Answered in page 184.

114-If you place a pail of water in a fresh-painted room a film of oil will come on the surface. What is the reason of it? Answered in page 207.

115-How are the colored flames of rocket stars, and other fire works, produced? Answered in pages 256 and 328.

116-When an effervescing draught is mixed in a tumbler, and stirred with a spoon or glass rod, this striking the edge of the glass emits a different sound as the effervescence proceeds. Why is this? Answered in page 207.

117-How are straw hats whitened? Answered in page

160.

DISTILLATION.

THE term distillation is understood to signify the process of purifying liquids by boiling, or first converting them into steam, and condensing that steam afterwards-by which means those impurities, which are not of a volatile nature, are retained in the still or vessel in which the boiling is carried on, while the steam itself contains the more ethereal particles of the original mass.

In its application to the purposes of life, distillation is of the utmost importance and extent, and would naturally be divided into various sections, according to the nature of the product required. Thus the distillation of ardent spirits-of acidsof essential oils-and of bituminous substances, as in the manufacture of tar, coal gas, &c., are processes, similar in principle, and in the apparatus employed, however much they may vary in detail and manipulation.

In considering this process it is first necessary to describe The Still, or, as it was once called, The Alembic.

A is the body of the still-it is shaped, set in brick-work, and furnished with a fire place, in the

SECOND EDITION.

same manner as a common brewing copper, except that it is contracted at the top into a narrow orifice, only sufficient for a man to creep in should such be requisite. B is the head, which fits closely over the upper part of A. The head is continued without an open joint till it arrives at C, which is the mouth of the worm, or condenser. The worm proceeds in a spiral form from the top to the bottom of the worm tub D-here it passes through the wood of the tub, ending in a short piece, called the nose. E is a can to receive the condensed steam, which F is a during the process passes from the worm. pipe connected with the cistern K, to keep the G is another worm tub supplied with cold water. pipe, fastened to the upper part of the tub, and carried through the floor to take off the warm or waste water. H is the fire place. I a trunk or shoot, to carry away the impure liquid remaining in the still after the spirit is extracted from it. J is the coal hole. K the water cistern, which may be at any convenient distance or situation.

The process is as follows:- The liquid, for example beer, is put into the vessel A, until about two-thirds full. The head B is put on so as to unite well with the body, and also with the mouth