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"She made all nations drink of the wine."-(Rev. xiv. 8.) However, whether simple or compound, transitive verbs govern an object, that is, the action of the verb falls on a noun which is hence cailed the object of the verb. This is a case of dependence, the noun which is the object is dependent on the verb of which it is the object. The relation is one purely of thought, for the relation involves in the noun no change of form. With the personal pronoun there is a change of form, corresponding to the change of sense, so that the nominatives I, we, they, become as objects, or become in what is called the objective case, me, us, them. The verb drinks, may be resolved into these terms, is drinking, as

The sick man is drinking a beverage; whence we learn that present participles have the same government as the verbs to which they belong.

Intransitive verbs, though in general incapable of an object, may take an object in a noun of kindred meaning; e. g.,

"Let me die the death of the righteous."-(Numb, xxiii. 10.) "Let us run the race that is set before us."(Heb. xii. 1.) Intransitives have the force of transitives also in certain idiomatic phrases; e. g.,

"He laughed him to scorn."-(Matt. ix. 24.)

"We ought to look the subject fully in the face."—Channing.
"And talked the night away."-Goldsmith.

The Object.

the object) to the verb commands, and the subject to the infinitiv to remain; son, therefore, may be considered as the objective cas before the infinitive to remain.

The object, "his son to remain," may be enlarged, thus:-
The man commands his son and daughter to remain.
The man commands his only son to remain.

The man commands his son forthwith to go home and remain there, All these constructions, and others of a similar kind, hold to the verb the same relation that I have indicated, that is to say, they are severally the objects to the verb commands. These objects are compound, and being compound, they may be resolved into their component parts, and the relations set forth which those parts head, the verb commands. bear to each other, as well as that which they bear to their common

Instead of the second object, a noun might be given, as

The man teaches his son Greek.

Here the noun Greek (that is, the Greek language) holds to teaches the relation which to remain holds to commands. It is not every verb, however, which has after it two nouns as objects. But as in Latin, so in English, verbs which signify to learn and to teach may have dependent on them two separate objects.

In some instances where two objects appear after a verb, the construction is in reality elliptical; e. g.,

He gave his son a book;

that is, in full,

He gave a book to his son.

He bought his son a book;

the construction really is,

The object of a proposition may, as we have seen, appear in a variety of forms. The object also assumes several shapes. The So in the sentence, chief variations may be presented as follows:The object of a proposition may be either

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5. A proposition:

He teaches his son Latin.

The man declares he is ill,

He bought a book for his son.

You will now have the less difficulty in understanding how a sentence may be the object of a verb; as,

The man says (that) he is ill.

The words he is ill you will at once recognise as a sentence or If dependent on the verb, that is, if it receives the action of the statement, and a little reflection will show you that the sentence verb, the noun is the object of the verb; e. g.,

"Preventing fame, misfortune lends him wings, And Pompey's self his own sad story brings."

Rowe's Lucan.

Equally simple is the case of a pronoun viewed as the object of a verb; e. g.,

"Did I request thee, Maker, from my clay

To mould me man?"-Milton.

The construction of a noun and infinitive as the object of a verb may be slightly varied. For the noun, a pronoun may be substituted; as,

The man bids me remain.

Before most verbs thus related, the preposition to is placed; as, The man commands his son to remain.

In this construction the to may be considered as a connective. And here I may notice a vulgarism in the custom, among the uneducated, of prefixing for to the infinitive with to; as,

The landlord is coming for to receive his rent.

Like many vulgarisms now in use, this form of speech was once good English, as may be seen by its appearance in our English translation of the Sacred Scriptures; e. g.,

"They pressed upon him for to touch him."-(Mark iii. 10.) Yet we retain the for in such phrases as

For me to speak is of no avail;

bears to the verb says the relation of an object to its verb. The conjunction that is merely an explanatory word, or, indeed, an expletive.

A sentence as the object of the verb may also be enlarged :— The man says he is sick and likely to die,

The man says he is sick and has been given over by the faculty for a long time.

The compound object in our model sentence will now be readily understood, viz.,

The man drinks a beverage made of wine and water. In this compound object, which consists of the words in italics, analysis shows us a noun, beverage, depending on the verb drinks; a participle, made, agreeing with beverage, and therefore conjointly with beverage dependent on drinks; a preposition, of, connecting made with wine and water; a noun, water, dependent on the preposi tion of; a conjunction, and, connecting water with wine; and, finally, another noun, wine, connected with water and the preposition of, and consequently standing to the preposition of and to the sen tence generally in the relation held by the noun water.

I must subjoin a few words respecting the object. Observe, then, that wine and water do not hold to drinks exactly the same relation which the words "his son Greek" holds in the above example. If so, a verb might be said to have several

objects; e. g.,

The man bequeathed money, wine, books, and land. where the words "for me to speak" form the subject to the they are a compound object made by repetition; whereas in the It is true that the nouns form the object to the verb bequeathed, but proposition

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The position of the object is after the verb. And the observance | tween the directions, AP and Aa, of those forces; the reason of this law is in English so imperative that by disregarding it you of this is plain, namely, that the point cannot move in both create ambiguity, if you do not change the object into the subject and the subject into the object; e. g.,

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As an instance of ambiguity from the inversion of the object, take this instance :

"This power has praise that virtue scarce can warm,

Till fame supplies the universal charm."-Johnson. Which is the subject, and which the object? Do you mean that power has praise, or that praise has power?

When, however, the perspicuity of the sentence is not abated, the object may, for the sake of emphasis, be placed before the verb; e. g.,

"Silver and gold have I none."-(Acts iii. 6.) Especially with pronouns; e. g.,

"Me he restored to mine office and him he hanged."-(Gen. xli. 18.) You may find sentences in which one object stands before and another after the verb; e. g.,

"Ye have the poor always with you, but me ye have not always."(Matt. xxvi. 11.)

Intransitive verbs have no object. The untaught are apt to confound the transitive with intransitive verbs, using the one for the other. This error may be exemplified in the verbs

Transitive:
Intransitive:

Thus, they say,

lay lie

He laid a-bed all day.

The hen has lain an egg.

raise
rise

The price of butchers' meat has risen.
The lark rises itself in the sky.

The principal parts of the verbs are

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Fig. 4.

No. III.

Fig. 5.

directions at once; and as no rea son can be assigned why it should move in the one direction more than in the other, it must move in some intermediate direction, and this direction is exactly that of the resultant of the two forces P and Q.

All problems which relate to the composition and resolution of forces depend upon the following theorems, for the demonstration of which we must refer our mathematical students to the Elementary Treatises on Statics, which are to be found both in French and English. In particular, we would mention the elegant demonstrations of M. Poisson, in his Traité de Mécanique, imitations of which have been published in English Treatises on Mechanics, by Whewell, Pratt, Earnshaw, and many others.

Composition and Decomposition of Parallel Forces.-Theorem 1.When two parallel forces are applied at the same point, their resultant is equal to their sum, when they act in the same direction, and to their difference when they act in contrary directions, For example, if two men drag a load in parallel directions force, that is, their resultant, will be denoted by 35 if they drag with forces respectively denoted by 20 and 15, their combined in the same direction, and by 5 if they pull in opposite directions. In like manner, when a number of horses are attached to the same vehicle, and all pull in the same direction, it will be urged along the road as if it were drawn by a single force equal to the sum of all the forces of the different animals employed.

Theorem 2.-When two parallel forces, which act in the same direction, are applied at the extremities of a rigid straight line (a rod), their resultant is equal to their sum, acts in the same direction, and its point of application divides the straight line into two parts, which are inversely proportional to the numbers which express the intensity of the forces. Thus, in fig. 6, if

Fig. 6.

ON THE COMPOSITION AND RESOLUTION OF FORCES. AB denote the rigid straight line, A and B its extremities, p and Composants and Resultants.-When several forces, such as s, Q the parallel forces, AP and BQ their directions, and c the P, and Q, are applied to the same material point, a, fig. 4, and point of application of their resultant R; then CR, parallel to produce an equilibrium at that AP or BQ, will be its direction, and P:Q:: BC: CA, that is, if point, it is evident that the action the force P be two, three, &c., times the force a in magnitude, of any one of these forces, for then the part BC will be tuo, three, &c., times the part ac in example s, resists the combined magnitude. Whence it follows, that when the forces P and Q action of all the rest; for were the are equal, the point of, application of their resultant divides the force s to act in the direction AR, straight line AB into two equal parts. Conversely to this procontrary to its own direction, AS, position, any single force R applied at the point o in a given it would produce the same effect rigid straight line, A B, may be resolved into two parallel forces as the two forces P and Q, acting P and Q, whose sum is equal to R, if their points of application, in the directions AP and a Q. Every A and B, be in the same straight line with the point o, and if force which produces the same they be so divided, that they are to one another in the inverse effect as a combination of any ratio of their distances from c; that is, if BO: AC:: P: Q. number of forces is called the To find the resultant of any number of parallel forces actresultant of such forces, and these ing in the same direction, we have only to find by the precedconsidered in relation to their resulting theorem the resultant of two of these forces, then the ant, are called component forces, or resultant of this resultant force and another of the given forces, composants. and so on, until all the given forces have been compounded. The last resultant thus obtained will be a force equal to the sum of the given forces, and having the same direction; and its point of application will be determined.

R

When a body is put in motion by the action of several forces, it can be demonstrated that the motion always takes place in the direction of the resultant of all the forces. Thus, if a material point, as at a, fig. 5, be acted on by two forces, P Composition and Resolution of Forces acting on a Single Point→→ and a, it will move in some intermediate direction, RA, be- If two forces, as r and a, fig. 7, act on a single material point

6

at A, and AP and AQ be the directions of these forces, we can
determine their resultant by the following theorem. Before
we enunciate this theorem, let us take on the straight lines A P
and a Q, parts ▲ B and ac having to each other the same ratio
Fig. 7.
as the intensities of the forces;
let us then complete the paral-
lelogram A B DC, by drawing
BD parallel to A c, and CD
parallel to A B, and let us
draw the diagonal AD. This
figure is the parallelogram of

forces, and the theorem which
expresses the relation between

the composants P and Q and their resultant R, is called The Theorem of the Parallelogram of Forces; viz., if any two forces acting on a material point be represented in magnitude and direction by the two adjacent sides of a parallelogram, their resultant will be represented in magnitude and direction, by the diagonal of that parallelogram which is drawn from the point where these two sides meet. Thus, in the parallelogram A B C D, if A B and A c represent in magnitude and direction any two forces P and Q, acting on a material point at A, then will the diagonal A D, drawn from the point A, represent in magnitude and direction the resultant R of these two forces; in other words, the direction of the resultant R of the forces P and Q, will be the straight line AR, and the resultant R will contain the unit of force as many times as the diagonal AD contains the linear unit of measurement, which was applied to the determination of the lengths of AB and a c, in order to make them represent the forces P and Q. Conversely, a single force applied to a material point may be decomposed into two other forces applied to the same point, and having their directions in given straight lines, that is, straight lines which shall make given angles with the direction of the resultant and with each other. For if we construct on the given straight lines a parallelogram, whose diagonal represents in magnitude and direction the given force, then its sides will represent in magnitude and direction the required composants. The solution of problems relating to forces acting on a single point will be seen by the mathematical student to resolve itself into the application of trigonometry to the determination of the sides and angles of the parallelogram of forces. Thus, if P and a represent any two forces in numbers, and a denote the angle between their directions, then their resultant R will be represented in numbers by the following formula :

:-

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When a number of forces are applied to the same point in various directions, their resultant will be found by applying the preceding theorem first to two of these forces, and then to the resultant thus obtained and a third of these forces, and so on successively till the last force has been taken into the account. The last resultant thus obtained will be the result

ant of all the forces combined.

The effects of the composition and the resolution of forces are frequently presented to our notice. For example, when a boat rowed by oars crosses a river, it does not make way in the real direction in which the oars propel it; neither does it advance in the direction of the current; but it is urged along in the direction which exactly corresponds to the resultant of the two forces which act upon it, viz., the force which puts the oars in motion and the force of the current in the river. In like manner, when several men are employed to ring a great bell each by a short rope attached to the main rope, the resultant of their united forces acts along the main rope as the line of its direction, and their individual forces form the composants, their lines of direction being that of the short ropes at which the ringers pull, in order to produce the desired effect. When any number of forces are in equilibrium about a point, any one of them may be said to be the resultant of all the rest, but its direction, of course, is contrary to that of the balancing force; and the resultant of any number of forces in equilibrium, is nothing.

ON MOTION.

Different Kinds of Motion.-Motion is said to be rectilinear or
is a straight line or a curve; and either of these motions may be
curvilinear according as the path described by the moveable body
uniform or variable. Uniform motion is the most simple kind of
motion, and is that in which the moveable body describes
equal spaces in equal times. Every momentary force produces
a motion which is rectilinear and uniform, when the moveable
body is not subjected to the action of any other force, and
meets no resistance to its progress. Under the momentary
action of a force, the moveable, when left to itself, will continue
to preserve, in consequence of its inertia, the direction and the
velocity which were communicated to it by the momentary
action of the force. Under the continued action of forces, a
moveable may likewise be made to preserve uniform motion;
as in the case where the resistances opposed to the motion
continually destroy the increments of velocity which such
forces tend to communicate to the moveable. We see an
the motion is produced by the continued action of a certain
example of this in the motion of a train on a railway, where
force, but that motion is nevertheless still uniform; this result
arises from the loss of force due to the continued resistance of
the air, the friction of the rails, &c., a resistance which in-
creases as the velocity increases, and which soon establishes
such an equilibrium between the moving and resisting forces,
as produces the uniform motion required.

the space described in a unit of time is called relocity.
Velocity, and Law of Uniform Motion.--In uniform motion,

This unit, although entirely arbitrary, is generally a second of time. From the definition of uniform motion, it is plain that in this species of motion the velocity is constant, that is, always the same; as, for example, in two units of the time, the space described is double, in three units triple, in four units law is usually expressed by saying that in uniform motion the quadruple, &c., that of the space described in one unit. This spaces described are proportional to the times, or in other words, the spaces described increase with the times.

denote the velocity, t the time, and s the space described. This law may be represented by a very simple formula; let Now since e denotes the space described in a unit of time, the space described in 2, 3, 4, &c., units of time will be 2o, 3o, 46, &c.; and generally, in the time t, it will be te; hence, we have the formula ste. From this formula we have = hence we say, that in uniform motion, the velocity is the ratio of the space described to the time employed in describing it.

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Variable Motion is that in which a moveable body describes unequal spaces in equal times. This species of motion may be varied in an infinite number of ways, but we shall at present only consider that in which it uniformly varies.

described in equal times constantly increase or decrease by the Motion Uniformly Variable is that in which the spaces uniformly accelerated; such is the motion of a falling body. same quantity. In the first case, the motion is said to be when the resistance of the air is removed. In the second case the motion is said to be uniformly retarded; such is the motion of a stone thrown vertically upwards from the ground.

a force continually acting with the same intensity; and it is Motion uniformly varied arises from a constant force, that is, considered either as a power or a resistance, according as the motion is accelerated or retarded,

uniformly accelerated, the spaces described in equal times not Velocity, and Laws of Uniformly Accelerated Motion.-In motion being equal, the velocity is no longer the space described in a unit of the time, as it is in uniform motion. In the former species of motion, we understand by the velocity at a given instant, the space which, commencing from that instant, would be uniformly described by the moveable in every second, if the action of the accelerating force were instantly to cease, that is, if the motion were to become uniform. For example, if a moveable were to acquire a velocity of 60 yards per second, after the lapse of ten seconds, during which it had proceeded with uniformly accelerated motion, and if the uniformly accelerating force were suddenly to cease its action after these 10 seconds, the moveable would, in consequence of its inertia, continue its motion uniformly at the rate of 60 yards per second,

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On this principle, every uniformly accelerated motion, whatever may be its increments of velocity, is reduced to the two following laws :-

1st. The velocities increase proportionally to the times; that is, after a time, double, triple, quadruple, &c., any given time, the velocity acquired is double, triple, quadruple, &c., greater than that after the given time. The action of the continued force, indeed, which produces any accelerated motion, may be compared to a series of equal impulses which succeed one another at equal but infinitely small intervals of time. Now, as each of these impulses produces in each interval a constant velocity, which is continually added to that which the moveable already possessed in the preceding interval, it follows that the velocity goes on constantly increasing by equal quantities in equal times.

2nd. The spaces described are proportional to the squares of the times employed in describing them; that is, if we denote the space described in 1 second by 1, the spaces described in 2, 3, 4, 5, &c., seconds will be denoted by 4, 9, 16, 25, &c., which are the squares of the former.

These laws are mathematically demonstrated in the scientific treatises on Dynamics, or the laws of motion; when we come to treat of gravity, we shall exhibit their experimental demonstration.

Momentum, Measure of Force.-The momentum of a body is the product of the number expressing its mass by that expresing its velocity. Thus, if a body moves with a velocity of 10 feet per second, and its mass is represented by 20, then its momentum is said to be 200. When a force communicates a certain velocity to a given mass, the momentum can be taken as the measure of this force. Thus, if a body moves with a velocity of 20 feet per second, and its mass is represented by 10, then its momentum is, as before, said to be 200; whence, in this case, the moveable has the same force as in the preceding case. The momentum of a body is frequently called its quantity of motion.

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In mechanics, therefore, these principles are established,
that, in equal masses, the forces are proportional to the
velocities; and that, in equal velocities, the forces are pro-
portional to the masses; in other words, that a force double
another imparts to the same mass a double velocity; or, to
double the same mass, an equal velocity. Now, let there be
two forces F and ƒ acting upon the two masses M and m, and
communicating to them the velocities Vand v respectively. If
we suppose a third force P such that it communicates to the
mass M the velocity v, we shall then have, according to the
preceding principles, the following proportions:-
--

(1.) FP:: :v, and

(2.) Pƒ:: M:m: whence,
F Ꮴ
P

we have = and

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P

=噐:

M

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(3.) F: ƒ:: MV: my; that is, any two forces are to each other as
their momenta or the quantities of motion which they commu-
nicate to any two moveables. Thus we see that if we take for
the unit of force the momentum which the unit of velocity
would communicate to the unit of mass, forces may be
measured by their quantity of motion. This species of mea-
surement is equally applicable to instantaneous and to con-
tinued forces; but in the case of continued forces, we only
consider the velocity which the force communicates in a

second.

Forces being proportional to their momenta or quantities of motion, it follows that for the same force the product me is constant; that is, if the mass become twice, thrice, &c., greater, the velocity will become, twice, thrice, &c., smaller. This conclusion is drawn from proportion (3) above demonstrated; for by making rf, we have Mvmv; whence, it follows (Cassell's Arithmetic, p. 101) that M:m::v: V; that is, the velocities communicated by the same forces to two different masses, are to one another in the inverse ratio of

these masses,

LESSONS IN CHEMISTRY.-No. III. RESUMING the consideration of the metal zinc, the learner will remember that he has dissolved a portion of this metal in sulphuric acid and water; that he has evaporated this solution to dryness, and redissolved the dried mass. He will have now obtained a colourless solution of sulphate of zinc; that is to say, a solution of oxide of zinc in sulphuric acid. However, I only at the present time desire the learner to remember the single fact, that the zinc is by some means held in solution by the liquid employed, .e. sulphuric acid and water. The exact state of its combination we need not discuss just now, this point will come under discussion hereafter. The zinc is there, and we require to obtain it, or at least satisfactory evidence of its existence; that is our proposition. How is this to be accomplished? A person conversant with Chemistry would almost arrive at the conclusion that zinc was present by the peculiar taste of the liquid. And indeed the sense of taste is a very valuable test: a far more precise indication, however, is afforded by hydro-sulphuric acid, or its watery solution, as we shall see. into a test tube; that is to say, a little glass tube of the followIf the learner pour a little of the sulphate of zinc ing shape, or a wine glass, and add to this sulphate of zinc a portion of the hydro-sulphuric acid solution already procured, a white powder will fall, this white powder being a combination of sulphur and zinc, and therefore called sulphuret or sulphide of zinc.

Fig. 14.

Let the reader impress upon his memory the fact that sulphuret or sulphide of zinc is white, and that it is the only metal which yields a white compound with the same agent, applied in the same manner.

If a sufficient amount of hydro-sulphuric acid solution be poured into the sulphate of zinc, all the metal will be thrown down in this condition of sulphuret or sulphide, and accordingly this process is sometimes followed in the course of analysis. The student, however, will not fail to perceive that, supposing the solution of sulphate of zinc to be very strong, a very large portion of hydro-sulphuric acid solution must be added, a treatment which would, under many circumstances, produce an inconvenient bulk of liquid. This being the case, it follows that when hydro-sulphuric acid is merely used as a test or indicator, it is commonly employed in the state or aqueous solution; when, however, it is employed as a separator, then the more convenient plan is to cause it to permeate the metalliferous fluid as a gas; this remark brings me to the consideration of the mechanical arrangement necessary to the use of this gas.

Fig. 15.

B

If a mixture of oil of vitriol and water (about 1 to 6 by measure) be poured upon sulphuret of iron sulphuretted hydrogen, or sulphuric acid gas, will be liberated, as we have seen; but as thus liberated it usually carries before it little particles of liquid, i.e. sulphuric acid and water, consequently it is not well adapted to be employed as a delicate precipitating agent. To speak more precisely, the gas requires to be passed through water in smal. bubbles, or washed, by means of an apparatus similar to that represented in fig. 15; A and B are two wide-mouthed eight or ten-ounce bottles, to each of which is adapted a cork, and each of which corks is perforated with two holes, as represented. Previously to securely fixing the cork of the vessel A, some fragments of sulphuret of iron are thrown in; the bottle is then corked

water is now poured into the vessel B, and the latter is also corked. It will be evident now, from the merest consideration of the various parts of this apparatus, that if a mixture of sulphuric acid and water be poured into A, all the sulphuretted hydrogen liberated will be obliged to traverse the water B before it can finally escape; in other words, it will be washed. A portion of the gas is absorbed by the water, but this matters not; the maximum of absorption is soon arrived at, and the gas comes over uninterruptedly so long as it is developed. Only one matter remains to be spoken of in connexion with the apparatus just described, it relates to the portion marked r. This consists of a small tube of india-rubber vulcanized by preference, and which is interposed between the two glass tubes. By this arrangement not only does a flexible joint result, but the bent glass tube admits of being removed and another placed in its stead; for, as a general rule, the same tube should not be used for testing consecutively two fluids of different compositions. In most large towns, vulcanized rubber tubes of any length may be readily procured, and the operator, having become possessed of them, may cut them into lengths according to his necessities; but supposing them not procurable, the reader should be able to manufacture a substitute out of india-rubber sheet. The best material for this purpose is the rubber manufactured into sheets, but even the native bottle rubber will answer perfectly well.

Supposing the artificial sheet rubber to be procured, it may be formed into tubes simply by warming it before the fire, winding it round a glass rod or tube, pressing the sides closely together, and cutting them off by a sharp pair of scissors. Thus treated the two cut edges will adhere, and a tube will result. Fig. 16.

Fig. 16.

form of a circle. Then bending the disc on itself, form a sẽmicircle. Then binding the semi-circle on itself form a quadrant Lastly draw the quadrant into this form, fig. 17, and the filter is complete. Large filters require to be supported on funnels; small filters may and indeed are better used without funnels, they may be rested on the edge of the glass itself; but a far better method consists in using a filter support made of porce lain, and of the shape annexed. Fig. 18.

Fig. 18.

By means of this little apparatus a filter may be rested on the edge of its corresponding glass, or removed at pleasure, with the greatest facility. Whatever is the size of the filter employed, it should be wetted with distilled water before the liquid to be filtered is poured upon it. A special apparatus is employed for wetting filters and washing precipitates collected upon them. The apparatus is of the following kind.

A thin flask slightly flattened at its base, in such a manner that it can stand without support, is furnished with a perfo rated cork and two tubes, as represented in the diagram, a mere casual examination of which will suffice to show that, if air be blown in through the tube a, water will emerge in a jet from the tube B, fig. 19. This jet may be so nicely regulated, that even the most delicate filter paper can be wetted without any fear of rupture.

Fig. 19.

If, however, the artificial sheet rubber cannot be procured and the bottle rubber has to be substituted, the latter material requires to be boiled in water for a considerable time, in order that the necessary amount of adhesiveness may be imparted to it. Generally speaking, india-rubber tubes, thus manufactured, are strong enough for all uses to which they are applied; if additional strength be desired, it can be imparted by first constructing one tube, then overlaying it with another, the seam of which does not correspond with the first, but is on the opposite side of the tube.

The two bottles forming the compound apparatus just described, are usually attached for convenience to a slab of wood, as represented in fig. 15. The apparatus is procurable coinplete at the philosophical instrument shops, but I strongly recommend the young chemist to manufacture this and similar apparatus himself.

Return we now to the metal zine. By passing a stream of hydro-sulphuric acid through it sufficiently long, the whole of the zinc will be thrown down. The operator may know when this point has been arrived at, by filtering a little of the solution from time to time, and testing the filtrate or fluid which passes through the filter. This remark leads us to another digression-the operation of filtering, so necessary to the prosecution of chemical investigations. The usual material employed by chemists, as a filtering agent, is paper. Filtering paper is of various kinds. The coarser sort is made chiefly of wool, and is of a brown colour; the finer sort resembles in its general aspect white blotting paper, which indeed may be used

Fig. 17.

as filter paper, if the true material cannot be obtained. The way to make a filter is this: first cut out the paper into the

By means of a little filter, as just described, it may easily be determined when the point corresponding with the total preci pitation of zinc has been arrived at, and this operation may be considered as the type of thousands which constantly occur in the course of chemical analysis.

Here we may, with advantage, take leave of zinc for a time, and begin the consideration of another metal; not that we have nothing more to say concerning zinc, but that our future remarks will most profitably come before the reader by way of comparison. We will take up another metal, and that metal shall be manganese, a very abstruse metal in many respects. The abstruse points, however, connected with it I shall omit, merely directing the student's attention to two points-a means of obtaining it in solution, and a means of precipitating or throwing it down from this solution.

We succeeded in dissolving zinc by means of diluted sulphuric acid. We cannot readily dissolve manganese, or, more properly, commercial black oxide of manganese in this manner. Concentrated sulphuric acid, and oil of vitriol, dissolves a portion of it readily; but I shall have recourse to an indirect process of solution, as follows:-Rub together in a mortar two parts by weight of manganese, and one part by weight of sal ammonia. Put the mixture into a crucible of silver or platinum, if the reader possess one of these instruments; if not, into a white gallipot, and heat to dull redness over a powerful flame of gas or spirit, or a charcoal fire in preference; but a common fire will do: allow the mixture to cool, add distilled water, and filter. The filtered solution contains manganese held in soli tion by chlorine. How the chlorine got there, or why i

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