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adverbs and prepositions), which are combined with other words to vary or modify their signification. They are, also, often called Particles. The simple words with which they are united, are generally verbs; but often nouns and adjectives are, by prefixes, converted into verbs. Most of the prefixes are separable, that is, may stand apart from the radicals; some, however, are found to be inseparable; some are either separable | or inseparable, according to circumstances.

to which they lead are only more or less approximate in accor dance with the results of experiment.

There are several cases to be considered in the motion of liquids: viz., the efflux of a liquid-1st, from an orifice in the thin wall of a reservoir, the thickness of which is less than half the smallest dimension of the orifice; 2nd, from an orifice of the same kind furnished with an adjutage; 3rd, through tubes of large diameter; 4th, through capillary tubes; and (2) The prefixes are themselves, also, either simple or com- 5th, over a channel, as the beds of rivers. We shall particupound; as, herkommen, to come here or hither; herüberkommen, | larly consider four of these cases.

to come over here, or hither. In most instances, the prefixes 1. Efflux through orifices in a thin wall; and Liquid Vein.may be translated severally as above; but often they are found Let us first consider the flow of water from the orifice of a to be merely intensive or euphonic. This is likewise often vessel having thin walls or sides. If at any point in such a the case in English: thus, ex (which literally signifies wall we make a small opening, the liquid will issue from it out or out of,) has, in some words the signification very, ex-under the action of two forces: 1st, gravity, which acts upon ceedingly or the like; as, exasperate, to make very angry; so a, it in the vertical direction; and 2nd, the pressure of the liquid, in the word ameliorate is merely euphonic, the derivative form which acts perpendicularly to the wall, and proportionally, to (ameliorate) meaning nothing more than the simple one, the depth of the orifice. meliorate.

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down, downwards, under;

Absehen, to set or put down;
to depose.
Anfangen, to catch at, i.e. to
begin.

The jet of the liquid which thus issues from the reservoir is denominated the vein. If the orifice is made in the bottom of the reservoir, the action of gravity being in the same direction as the interior pressure of the liquid, these two forces are added together, and the vein is vertical and rectilinear. But if the orifice is made in a wall vertical or inclined, the two forces which act upon the liquid are such that the one is vertical, and the other horizontal or oblique in its direction. In this case, the liquid vein following the direction of the as-resultant, takes a curvilinear form, which, abstracting the resistance of the air, would be exactly that of the curve which projectiles describe in a vacuum, and known under the name of the parabola.

Aufgehen, to go up; to rise.
Ausnehmen, to take out; to
choose.

Beistehen, to stand by; to

sist.

Dableiben, to remain there, or
at, to stay; to persist.
Darreichen, to reach there, i.e.
to offer.

chase.

Structure of the Liquid Fein.-To the investigations of M. Savart we owe the following particulars relating to the nature Einkaufen, to buy in; to pur- of the liquid vein. It is composed of two distinct parts: the first, which is in contact with the orifice, is completely calm and transparent, and presents the appearance of the most limped crystal cylinder; the second, on the contrary, is troubled and agitated, and presents elongated swells, which are regularly arranged at intervals, as shown in fig. 41, and which may be termed protuberances.

Emporheben, to lift up.
Fortfahren, to drive or bear
on; to continue.
Gegenhalten, to hold against;
to resist; to compare.
Inwohnen, to dwell in.
Heimkehren, to turn home-
wards; to return.

Herbringen, to bring hither,
or along.

Hingehen, to go thither, or

away.

Mitnehmen, to take with, or
along.

Nachfolgen, to follow after; to
succeed.
Niederreißen, to pull down.

on, over, on account of; Obliegen, to lie cn, i.e. to ap-
ply one's self to; to be in-
cumbent on.

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for, before

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Vorgehen, to go before; to

surpass.

Wegbleiben, to stay away.
Zugeben, to give to; to grant.

ON PHYSICS OR NATURAL PHILOSOPHY.

No. XIII.

HYDRODYNAMICS.

Object of the Science.-It has been already stated that hydrodynamics is that part of Rational Mechanics which treats of the motion of liquids; and that the part of this science which particularly treats of the art of conducting and raising water, is called hydraulics; that is, hydraulics is the practical department of hydrodynamics.

Figs. 41, 42.

see

This second part of the vein is not continuous; for when an opaque liquid, such as mercury, is made to flow through the orifice, through the vein. Savart has observed that the protuberances are formed of discontinuous globules, elongated in a direction transverse to that of the vein; and that the contractions or nodes are formed, on the contrary, of globules elongated in the direction of the vein itself, as shown in fig. 42. He has also observed, by looking at the vein in a strong light, that the limped part is formed of annular swells which originate near the orifice, and are propagated at equal intervals until they reach the troubled part of the vein where they are separated. These swells proceed from periodic pulsations which take place near the orifice. Their number is in the direct ratio of the velocity of efflux, and in the inverse ratio of the diameter of the orifice.

The pulsations just mentioned may be so rapid as to give rise to a sound, which is increased by receiving the vein on any tightened membrane. By producing a sound in unison with that of the vein, by means of a musical instrument, Savart has modified the vein in such a manner, that the pro

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In hydrodynamics as well as in hydrostatics, liquids are considered to be incompressible, perfectly fluid, and conse-tuberances and nodes have taken a more regular form, and the quently free from all viscosity. But liquids possess these pro-transparent part of the vein has entirely disappeared. He has perties only imperfectly; hence the theoretical consequences also found that the resistance of the air has no effect on the

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form and dimensions of the vein, or on the number of pulsations. He has likewise observed that the structure of the horizontal or oblique veins does not essentially differ from that of veins which fall vertically.

Vena Contracta, or the Contraction of the Vein.-When efflux takes place through a circular orifice made in a thin wall or side of a vessel full of water, the liquid vein preserves the circular form in its transverse sections, but the diameter is variable. This diameter is at first equal to that of the orifice, it then rapidly diminishes, and at a distance from the orifice nearly equal to its diameter, the section of the vein is no more than of that of the orifice. If the direction of the vein is vertical as in fig. 41, the section decreases slowly till it reaches the troubled part. If the direction of the vein is horizontal, the section decreases insensibly. If the angle of inclination of the vein varies from 25° to 45o, the vein preserves nearly the same diameter; but if it exceeds 45°, the section increases from the part contracted to the part troubled. The part where the diameter of the section reaches its minimum, is called the contracted section.

The contraction of the vein originates in the converging directions which the liquid particles assume in the interior of the vessel, when they proceed towards the orifice. This phenomenon is rendered visible by putting the water in a transparent vessel, and mixing small light substances with it which are kept in suspension in it, the orifice being made in a thin wall or side of the vessel. If the orifice be half an inch in diameter, we see at twice or thrice that distance from it within the vessel, the substances suspended in the water drawn from all parts of the vessel towards the orifice, and describing curve lines, as if they were attracted towards a centre, as shown in fig. 43. The convergence of the particles which Fig. 43.

took place in the interior of the vessel is continued exteriorly, and the liquid vein is gradually contracted till it reaches the point where the particles, by the effect of their mutual action, take a parallel or diverging direction. The vein thus forms a species of truncated cone or frustrum, of which the greater base is the orifice, and the smaller base the contracted section. In the preceding remarks we have supposed that the orifice is of the circular form. If it be polygonal, or of any form different from that of a circle, the vein no longer preserves a section of the same form as the orifice. Its form changes as the vein recedes from the orifice, and continually gives rise to protuberances and nodes.

Theorem of Torricelli.-When a liquid issues from a reservoir by an orifice in a thin wall or plate, the velocity of the discharge is determined by the following theorem: The liquid particles as they issue from the orifice have the same velocity as if they fell freely in a vacuum, from a height equal to the vertical distance from the centre to the upper surface of the liquid in the re ervoir. This theorem was discovered by Torricelli in 1643, and was by him considered as a corollary to the laws of falling bodies established by his master, Galileo. This law can be experimentally proved to be a result of the principle demonstrated in mechanics, viz., that when a body is projected upwards with a given velocity, it will rise to the same height from which it would have fallen in order to acquire that velocity. Thus, when the discharge is made to take place vertically upwards, as represented in fig. 44, the liquid vein reaches very nearly the height of the level of the liquid in the vessel from which it is discharged, and the reason why it does not reach it entirely, is the resistance of the air, and the action of the liquid particles in falling, which oppose the ascent of the jet. Hence, at its issue from the orifice 2, the liquid spouts upwards with

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The following important corollaries are deduced from the Theorem of Torricelli: 1st. All bodies in a vacuum falling with equal velocity, it follows that the velocity of discharge is independent of the density of the liquid. For example, water and mercury issue with the same velocity, if the height of the level above the orifice be the same for both liquids. Experiment, indeed, proves that in the case of equal heights and orifices of the same diameter, equal volumes of these liquids are discharged in the same time. 2nd. The velocity of discharge at the issue of a liquid from the orifice, is proportional to the square root of the height of the level in the reservoir above the centre of the orifice. This is, in fact, a consequence of the laws of gravity, for we have seen, in a former lesson, that representing the velocity acquired by a moveable which falls in a vacuum by v, and the height of the fall by h, we have v=v2gh. The velocity calculated by this formula is called the theoretical velocity.

Theoretical and Effective Discharges. - The volume of a liquid which is actually discharged from an orifice in one second, is called its effective discharge; and the volume of a liquid equal to that of a cylinder or prism which has the orifice for its base, and the theoretical velocity above mentioned for its height, is called the theoretical discharge.

The effective discharge is always less than the theoretical discharge. The effective discharge is in reality the product of the contracted section of the vein, and the mean velocity of the liquid particles at the instant that they pass this section.

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area of the contracted section of the vein is considerably smaller than that of the orifice, as in discharges which issue from orifices in a thin wall; or, that the velocity at this section is less than the theoretical velocity, in consequence of the friction of the liquid particles issuing from orifices pierced in a thick wall. Thus, in either case, the effective discharge is less than the theoretical discharge; and in order to reduce the latter to the former, it is necessary to multiply it by a certain fraction which is called the co-efficient of correction. From numerous experiments, it has been found that the effective discharge is, in general and at a mean, only two-thirds of the theoretical discharge.

Constant Efflux.-In a great number of hydraulic experiments, it is necessary that the velocity of efflux should be constant, that is always the same, and this requires that the height of the liquid level above the orifice should be invariable. This result may be obtained in several ways. 1st, by means of a sluice, which is so regulated that it opens whenever the water in the reservoir tends to rise above the level, and permits it to run off by another channel; 2nd, by means of a siphon or Marriotte's bottle, instruments which will be described in the sequel; 3rd, by means of the float of M. de Prony. The latter apparatus, shown at fig. 45, is composed of a reservoir or vessel Pa full of water, in which are placed two floats FF, connected with each other by an iron rod, which stretches over the reservoir and is bent at both of its lower extremities in order to support a moveable reservoir B, placed under the former. A plate A, making part of the wall of the reservoir PQ, is pierced with orifices of different forms and sizes. A funnel placed under these orifices conveys the water which flows from them into the reservoir B. According to this arrangement, if one of the orifices of the plate be opened, and if three pounds of water be discharged from it, the weight of the floats is increased by three pounds; therefore, according to the conditions of equilibrium in floating bodies, laid down in a former lesson, these floats will sink and occupy the space of a quantity of water equal in volume to the water discharged, so that the level in the reservoir P Q remains constant, and therefore the velocity of efflux remains the same.

Efflux by Ajutages.-A short pipe or tube, see fig. 46, applied to or inserted in the orifice of a reservoir in order to increase the discharge is called an ajutage (French, from Lat. adjutare, to assist). The form of an ajutage is generally that of a hollow cylinder, or a truncated hollow cone.

Fig. 46.

When ajutages are applied to an orifice, results of two kinds present themselves; either the liquid vein passes through the ajutage without adhering to its sides, and the discharge remains the same as before; or the liquid vein adheres, in consequence of the molecular attraction existing between the sides of the tube and the particles of the liquid, and the contracted portion of the vein being increased by expansion, the discharge is likewise increased. The best form of a cylindrical ajutage for increasing the discharge, is that which has its length from two to three times its diameter, The liquid then issues with a full flow, and the discharge is increased by about one-third part.

Conical ajutages converging outwardly from the reservoir increase the discharge still more than the preceding. They produce very regular jets, and throw them to a greater distance or to a greater height than the cylindrical. Their effects, as to discharge and velocity of projection change with the angle of convergence, that is, with the angle formed by the production of two opposite sides of the truncated cone which forms the ajutage. Of all ajutages, those which give the greatest

discharge are those now described. Venturi concluded from his experiments that these ajutages gave an effective discharge 2-4 times greater than that delivered by an orifice in a thin wall having the same diameter as the smaller base, and 1·46 times greater than the theoretical discharge. The ancient Romans were acquainted with the value of these ajutages. The citizens of Rome, who enjoyed the privilege of drawing a certain quantity of water from the public reservoirs, found that by the use of these ajutages, the quantity permitted by their privilege might be greatly increased; and the fraud thus practised became so notorions, that a law was passed to prevent their use.

Efflux through Long and Wide Pipes-When a liquid flows through a pipe of great length, the efflux takes place either in consequence of the inclination of the pipe, as on an inclined plane, or in consequence of a pressure which acts on the liquid at the orifice of the pipe. In both these cases, the force being constant, the motion ought to be accelerated. Yet at a very short distance from the orifice, it is observed that the motion is uniform, which indicates the existence of a force tending to destroy or counteract the accelerated velocity which the liquid would naturally acquire by the force in question. This force is the resistance arising from the cohesion of the liquid particles to each other, and their adhesion to the sides of the pipe. Besides these resisting forces, there are others which arise from turns and contractions in the pipes thèmselves; but the former are always by far the most considerable. In consequence of these various resistances, the velocity of efflux, and therefore the discharge through pipes, becomes much less than the velocity and discharge through orifices in a thin wall.

Efflux through Capillary Tubes.-The efflux of liquids through tubes called capillary (from Lat. capillus, hair) because their bore or diameter is very small and fine, is of considerable importance in a physiological point of view. Dr. Poiseuille has made numerous experiments on this subject, varying the lengths of the tubes, their diameters or degrees of capillarity, and the pressures which produce the efflux of the liquids through them. In his experiments on capillary glass tubes, he discovered the three following laws: 1st, in the same tube, the discharge is proportional to the pressure; 2nd, in tubes of equal lengths and under equal pressures, the discharge is proportional to the fourth powers of their diameters; 3rd, in tubes of the same diameter and under the same pressure, the discharge is in the inverse ratio of the lengths.

Dr. Poiseuille has observed besides these laws that the velocity of efflux is modified by the nature of the liquid. The nitrate of potassa dissolved in water, causes a more rapid efflux of that liquid. Alcohol, on the contrary, has a retarding effect. The efflux of serum is only half as rapid as that of water; and when alcohol is added to serum, the velocity of efflux is diminished still more; but if to the mixture we add the nitrate of potassa, the serum resumes its original velocity. These different experiments were made with glass tubes; and it became important to know whether the results would be the same in the capillary vessels of organised bodies. Now, in experimenting on dead animals, which were cooled down to the temperature of the surrounding atmosphere, it was found by injecting serum into the principal artery of an organ, that the nitrate of potassa increased the efflux in the capillary organs of dead bodies, in the same manner as in glass tubes; and that alcohol, on the contrary, retarded it. These facts tend, therefore, to prove that the circulation of the blood in the arteries and the veins follows the same laws as the efflux of liquids in capillary tubes.

Jets d'Eau, or Spouts of Water.-Streams of water which spout up with force from an orifice in consequence of the pressure of a liquid column more or less elevated above that orifice, are called jets d'eau. If the orifice be made in the upper surface of a horizontal wall or tube below the level in the reservoir, the jet is vertical and upwards; if the wall or tube be inclined to the horizon the jet is inclined, and describes a curve, which, abstracting the resistance of the air, would be a parabola.

According to a principle formerly mentioned, a jet of water tends to rise to a height equal to that of the level of the water in the reservoir; but this is never exactly the case, as it meets

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with three resistances: 1st, the friction of the water in the tubes or pipes, which destroys a part of the velocity; 2nd, the resistance of the air; 3rd, the resistance which those liquid particles, falling from the highest part of the jet, present to those which are ascending.

of sulphuric acid. Now nine is the precise chemical equiva.
lent of water, and forty the precise chemical equivalent of sul-
phuric acid. A few remarks concerning equivalents have al-
ready been offered; I do not expect you, however, to under-
stand this rather abstruse subject perfectly just yet. I must,
nevertheless, have you to remember, even though you do not
understand it, the following fact: When I say that our strong-
est English oil of vitriol is a compound of one equivalent of
water and one of real sulphuric acid, I do not mean equal
forty and the other nine, as we have seen. The same remark
applies to all similar expressions. Well, then, in order to indi-
cate the kind of hydrate which oil of vitriol is, chemists term
it the protohydrate of sulphuric acid, or protohydrated sul-
phuric acid.
phuric acid. The Greek word prоs means first; that is to
say, this is the first in the ascending scale of many hydrates.

In order to obtain the maximum height of a jet, the diameters of the tubes must increase with their length; the tubes must be free from all inequalities and all sudden windings; and, the orifice of efflux must be made in a thin wall, and have a slight inclination in order to avoid the third resistance just men-weights, but equal equivalents; the equivalent of the one being tioned. Such orifices are those which raise the jet to the greatest height, and impart to it the greatest regularity and transpar ney. Conical ajutages also produce jets uniform and transparent, but the height is only about eight or nine-tenths of that produced by orifices in a thin wall. Lastly, cylindrical ajutages produce confused jets, of which the height is only about of that which is produced by orifices in a thin wall. In order that a jet may take the greatest range horizontally, it is found by analysis, that when the resistance of the air is abstracted from the calculation, the angle which it makes with the horizon must be 45°, or half a right angle; that is, mid-way between the horizontal and the vertical directions.

From this digression (a necessary one, however) let us now return to the materials in our flask-or rather let us investigate, by means of a diagram, the changes which have ensued.

The case stands thus :

Hydrochloric acid (Hydrogen
Chlorine
Sulphuret of Anti- ( Sulphur
Į Antimony.

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Hydrosulphuric acid

Chloride of antimony

mony If the resulting liquid be thrown into water, in certain proportions, which may be ascertained on trial, a powder (oxide of antimony) deposits. This powder is, however, readily dissolved by the addition of more hydrochloric, or a sufficient quantity of tartaric acid.

LESSONS IN CHEMISTRY.-No. XII. RESUMING the consideration of antimony, I now want the student to take a little of the orange or black sulphuret of the latter: powder it; and having thrown it into a Florence flask, pour upon it some hydrochloric or muriatic acid, known in commerce under the name of spirit of salt; applying now to the flask either the naked flame of a spirit-lamp, or, what is pre-water is the type of an important feature in the demeanour of ferable, the heat of a sand-bath, sulphuretted hydrogen gas

Fig. No. 1.

will be evolved, as you will readily discover by its disagreeable odour; and if a sufficient amount of hydrosulphuric acid have been added, the whole of the sulphuret will be dissolved. The result of this solution is termed the chloride of antimony, procurable in commerce under the name of butter of antimony. Let us see what decomposition must have ensued in order to furnish us with these results. Sulphuret of antimony is, as its name indicates, and as we demonstrated in our preceding lesson, a compound of sulphur and antimony.

The precipitate which occurs on throwing the chloride into antimony solutions, most of which are liable to become decomposed from the operation of very slight causes. Tartar emetic is not so prone to be unstable as the others are; it may be mixed with mere water, in any proportions, without throwing down a precipitate; but tea-infusion of galls, or indeed almost any vegetable or animal infusion, throws down, even with it, a copious precipitate. Try these experiments; the results will be found to have an important bearing upon circumstances to be mentioned hereafter. Assume, for example, that a person has taken an injurious dose of tartar emetic, and that the emetic action does not supervene; this is the case sometimes. What would you do? In the first place, propose to yourself the object you would desire to accomplish. There is a general rule to follow in all these cases-a rule which I have already into a solid. Give then-if tartar emetic be the poison under mentioned. It is this:-Convert the poisonous irritating fluid consideration-give copious draughts of tes; a fluid which, as we have seen, renders tartar emetic insoluble-more insolubie, at any rate, than it was originally.

Separation of Antimony from Zinc, Manganese, Cadmium, and Arsenic.-I trust that the student has sufficiently reflected upon the properties of these four metals to recognise an indication of a process by which this might be accomplished.

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We have not yet demonstrated the composition of hydroFirstly, It is evident that arsenic and antimony admit of chloric acid gas; but its name, if analyzed, evidently points to separation from the other metals by the operation of hydrogen, a compound of chlorine and hydrogen, just as the term hydro- which would remove them in the condition of arseniuretted sulphuric points to something which is a compound of sulphur and antimoniuretted hydrogen gases; and the latter, on comand hydrogen. Remember, therefore, the following general bustion, would deposit the two metals in a mixed crust. Fifact:-Whenever you see the syllabic prefix hydro (before anally, these metals would be separable from each other by the vowel hydr'), the prefix always means hydrogen-never water, prolonged action of boiling nitric acid, which, as we have seen, the presence of which is expressed, not by the syllabic prefix reduces the antimony to the condition of an insoluble white hydro or hydr', but by the full word, hydrated, or hydrate. powder, and changes the arsenic to soluble arsenic acid. The Thus, for instance, hydro-sulphuric acid is synonymous with latter proposition has not been demonstrated. Nitrate of potsulphuretted hydrogen, indicating the compound of sulphur ash produces this result, as I have explained (p. 42). Nitric and hydrogen; but hydrated sulphuric acid, or hydrate of sul-acid has the same effect; indeed, nitre acts by virtue of its conphuric acid, is a compound of sulphuric acid with water. tained nitric acid. Several other analytical processes suggest Practically we call oil of vitriol sulphuric acid; really it is hy- themselves from combinations of agencies already discussed; the drated sulphuric acid-or a compound of true sulphuric acid most evident process, however, is that which I have given; and (which is a solid) with water. But you will say-If I take oil my object not being to write a systematic course of analysis, I of vitriol and add more water to it, I get a liquid which is no need not detail the others. onger oil of vitriol, but it is still hydrated sulphuric acid. Truly-the remark is just; hence has arisen the necessity for certain precise terms. The strongest oil of vitriol which we in England obtain by our process of manufacture is composed of nine parts by weight of water united with forty parts by weight

Before concluding my remarks on this interesting metal, I will mention a curious fact. Two sulphurets of antimony have been spoken of: there exist others; one an orange-coloured sulphuret, generated artificially; the other a black substance, usually sold as antimony by druggists. Now, different thoug

the two are in general appearance, their chemical composition is precisely the same. Chemistry furnishes us with many similar examples, all of which are comprehended under the general term allotropism, from the two Greek words alλos, another, and тρɛw, I turn. Thus the diamond, coke, charcoal, трETW, and plumbago (the latterly commonly known as black-lead), have all a composition which is exactly similar. Chemists, indeed, have succeeded in changing the diamond to coke; but the other change, far more interesting than the last, remains to be accomplished. The substance phosphorus, again, the inflammable nature of which, in its ordinary state, is so remarkable, may be converted into a second state, in which it is no longer combustible, andi n which it is totally devoid of smell; nay, what is still more extraordinary, this allotropic phosphorus is totally devoid of all poisonous agency, although common phosphorus is a violent poison; its mere vapours rapidly destroying the jaw-bones of the workmen exposed to their influence, and causing a frightful death. Perhaps the question will occur to you of this sort-What can be the use of this allotropic phosphorus, a substance which, you tell us, is not inflammable? True, allotropic phosphorus is not inflammable; but, if heated beyond a certain temperature, this curious substance changes into the ordinary form. Now the mere friction of a phosphorus match is sufficient to generate this amount of heat; so, practically, allotropic phosphorus may be employed for the purpose of making matches. In England these matches of allotropic phosphorus have not as yet come much into use; but on the continent, especially in Prussia, they are common enough.

Whilst on the subject of allotropism, I will furnish you with another example as afforded by sulphur. Take some common sulphur (brimstone), put it into a Florence flask, and apply heat either by means of a spirit-lamp, or, what is preferable in this case, by a flowerpot charcoal furnace already described in a previous lesson, and here represented, No. 2. The sulphur fuses, giving rise to a limpid fluid, which retains this character

Fig. No. 2.

and hard, the new substance, allotropic sulphur, is black, ductile, soft; a substance capable of receiving the most exquisite impressions; indeed it is used in practice very advantageously for the purpose of copying the impressions of medals, coins, &c.

Judging from the appearance of this body, one might at first imagine it to be something else than sulphur; chemical analysis, however, proves them to be the same. In making the latter assertion, I am aware it must be taken with some qualifications. The truth is, the contemplation of allotropism leads us into the metaphysics of chemistry; the very term allotropism meaning another state is expressive of a change; a change in appearance you have had pointed out to you, but this is not all, there is a change of medical properties, a change as to solubility in certain fluids: yet when we come to combine this allotropic sulphur with other bodies, we obtain exactly the same results that we should have obtained with sulphur in the ordinary state.

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until every portion of the sulphur becomes melted. Keeping your eye on the flask, observe the period at which this perfect fusion of the sulphur takes place: being accomplished, remove the flask, and pour a little of the fused contents into water. The melted sulphur solidifies as a matter of course, and you get a result identical in every respect with the sulphur before it was fused; that is to say, the result is brittle-is yellow; physically and chemically similar in point of fact. Replace now the sulphur over the source of heat, and remark the changes which ensue. You will first observe a change of colour: the fluid becomes dark, almost black. You will next observe a change of aggregation, the material becomes thick, thicker still, and in a few instants a solid. By dexterous management it is possible to remove the flask whilst its contents are thus solid. Try to do so.

Replace the flask once more, and observe the result; the dark solid liquifies once more, and the liquid still remains black; pour some of this liquid into water, and a curious result will be obtained. Instead of ordinary sulphur, yellow, brittle,

The most elegant way of demonstrating the characteristics of allotropic sulphur, consists in pouring it in a small continuous stream into a basin of water, which contains a funnel, and around the latter in this way a thread of the substance may be obtained, in appearance very much .ike a. thread of india-rubber, No. 3.

The various phenomena of allotropism are directly at variance with the chemical doctrine long accepted, that identity of composition must necessarily accompany identity of chemical effects; and, curiously enough, these same phenomena are favourable to the idea of metallic transmutation, that longcherished hope of the alchemists.

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The use of this word very frequently coincides with the use of the case-sign, or preposition of, in English grammar:

I. When the questions of whom? of which? of what? whose? what kind or sort of? require the genitive also in English; e. g. L'a-mó-re del pá-dre, the love of the father; i paé-si del prín-ci-pe, the countries of the prince: la cle-mênza di Di-o, the clemency of God; la gran-déz-za dél-la città, the greatness of the town; il li-bro di Giá-co-mo, the book of James.

II. When geographical or other proper names indicating possession, domain, authorship, &c., or merely for the purpose of defining them, are joined to other nouns; e. g. la cit-tà di Ve-nê-zia, the city of Venice; il ré-gno di Spá-gna, the kingdom of Spain; il mé-se di Lu-glio, the month of July; il nó-me di Fran-cé-sco, the name of Francis; l'i-so la di Cor-fù, the

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