and there results a compound differing in all respects from the acid or the marble. But if a piece of glass, quartz, gold, or silver, be thrown into the acid, no change is produced on either, because these particles have no affinity.

Sulphur and quicksilver, when heated together, will form a beautiful red compound, known under the name of vermilion, and which has none of the qualities of sulphur, or quicksilver.

Oil and water have no affinity for each other, but potash has an attraction for both, and therefore oil and water will unite, when potash is mixed with them. In this manner, the well known article called soap is formed. But the potash has a stronger attraction for an acid than it has for either the oil or the water; and therefore when soap is mixed with an acid, the potash leaves the oil, and unites with the acid, thus destroying the old compound, and at the same instant forming a new one. The same happens when soap is dissolved in any water containing an acid, as the water of the sea and of certain wells. The potash leaves the oil, and unites with the acid, thus leaving the oil to rise to the surface of the water. Such waters are called hard, and will not wash, because the acid renders the potash a neutral substance.

Magnetic Attraction. There is a certain ore of iron, a piece of which, being suspended by a thread, will always turn one of its sides to the north. This is called the loadstone, or natural Magnet, and when it is brought near a piece of iron, or steel, a mutual attraction takes place, and under certain circumstances, the two bodies will come together and adhere to each other. This is called Magnetic Attraction. When a piece of steel or iron is rubbed with a Magnet, the same virtue is communicated to the steel, and it will attract other pieces of steel, and if suspended by a string, one of its ends will constantly point towards the north, while the other of course, points towards the south. This is called an artificial Magnet. The magnetic needle is a piece of steel, first touched with the loadstone, and then suspended, so as to turn easily

What is the effect when glass and this acid are brought together? What is the reason of this difference? How may oil and water be made to unite? What is the composition thus formed called? How does an acid destroy this compound? What is the reason that hard water will not wash? What is a natural magnet? What is meant by magnetic attraction? What is an artificial magnet? What is a magnetic needle'

on a point. By means of this instrument, the mariner guides his ship through the pathless ocean. See Magnetism.

Electrical Attraction. When a piece of glass, or sealing wax is rubbed with the dry hand, or a piece of cloth, and then held towards any light substance, such as hair, or thread, the light body will be attracted by it, and will adhere for a moment to the glass or wax. The influence which thus moves the light body is called Electrical Attraction. When the light body has adhered to the surface of the glass for a moment, it is again thrown off, or repelled, and this is called Electrical Repulsion. See Electricity.

We have thus described and illustrated all the universal, or inherent properties of bodies, and have also noticed the several kinds of attraction which are peculiar, namely, Chemical, Magnetic, and Electrical. There are still several properties to be mentioned. Some of them belong to certain bodies in a peculiar degree, while other bodies possess them but slightly. Others belong exclusively to certain substances, and not at all to others. These properties are as follows.

Density. This property relates to the compactness of bodies, or the number of particles which a body contains within a given bulk. It is closeness of texture. Bodies which are most dense, are those which contain the least number of pores. Hence the density of the metals is much greater than the density of wood. Two bodies being of equal bulk, that which weighs most, is most dense. Some of the metals may have this quality increased by hammering, by which their pores are filled up and their particles are brought nearer to each other. The density of air is increased by forcing more into a close vessel than it naturally contained.

Rarity. This is the quality opposite to density, and means that the substance to which it is applied is porous, and light. Thus air, water, and ether, are rare substances, while gold, lead, and platina are dense bodies.

Hardness. This property is not in proportion, as might be expected, to the density of the substance, but to the force with which the particles of a body cohere, or keep their

What is its use? What is meant by electrical 'attraction? What is electrical repulsion? What is density? What bodies are most dense? How may this quality be increased in the metals? What is rarity? What are rare bodies? What are dense bodies? How does hardness differ from density?

places. Glass, for instance, will scratch gold or platina, though these metals are much more dense than glass. It is probable, therefore, that these metals contain the greatest number of particles, but that those of the glass are more firmly fixed in their places.

Some of the metals can be made hard or soft at pleasure. Thus steel when heated, and then suddenly cooled, becomes harder than glass, while if allowed to cool slowly, it is soft and flexible.

Elasticity is that property in bodies by which after being forcibly compressed or bent, they regain their original state when the force is removed.

Some substances are highly elastic, while others want this property entirely. The separation of two bodies after impact, or striking together, is a proof that one or both are elastic. In general, most hard and dense bodies, possess this quality in greater or less degree. Ivory, glass, marble, flint, and ice are elastic solids. An ivory ball, dropped upon a marble slab, will bound nearly to the height from which it fell, and no mark will be left on either. India rubber is exceedingly elastic, and on being thrown forcibly against a hard body, will bound to an amazing distance.

Putty, dough, and wet clay, are examples of the entire want of elasticity, and if either of these be thrown against an impediment, they will be flattened, stick to the place they touch, and never like elastic bodies, regain their former shapes.

Among fluids, water, oil, and in general all such substances as are denominated liquids, are nearly inelastic, while air and the gaseous fluids, are the most elastic of all bodies.

Brittleness is the property which renders substances easily broken, or separated into irregular fragments. This property belongs chiefly to hard bodies.

It does not appear that brittleness is entirely opposed to elasticity, since in many substances, both these properties are united. Glass is the standard, or type of brittleness, and yet

Why will glass scratch gold or platina? What metal can be made hard or soft at pleasure? What is meant by elasticity? How is it known that bodies possess this property? Mention several elastic solids. Give examples of inelastic solids. Do liquids possess this property? What are the most elastic of all substances? What is brittleness? Are brittleness and elasticity ever found in the same substance? Give examples.

a ball, or fine threads of this substance are highly elastic, as may be seen by the bounding of the one, and the springing of the other. Brittleness often results from the treatment to which substances are submitted. Iron, steel, brass, and copper, become brittle when heated and suddenly cooled, but if cooled slowly, they are not easily broken.

Malleability. Capability of being drawn under the hammer, or rolling press. This property belongs to some of the metals, but not to all, and is of vast importance to the arts and conveniences of life.

The Malleable metals are, gold, silver, iron, copper and some others. Antimony, bismuth, and cobalt are brittle metals. Brittleness is therefore the opposite of malleability.

be

Gold is the most malleable of all substances. It may drawn under the hammer so thin that light may be seen through it. Copper and silver are also exceedingly malleable.

Ductility, is that property in substances which renders them susceptible of being drawn into wire.

We should expect that the most malleable metals would also be the most ductile; but experiment proves that this is not the case. Thus tin and lead may be drawn into thin leaves, but cannot be drawn into small wire. Gold is the most malleable of all the metals, but platina is the most ductile. Dr. Wollaston drew platina into threads not much larger than a spider's web.

Tena

Tenacity, in common language called toughness, refers to the force of cohesion among the particles of bodies. cious bodies are not easily pulled apart. There is a remarkable difference in the tenacity of different substances. Some possess this property in a surprising degree, while others are torn asunder by the smallest force.

Among the malleable metals, iron and steel are the most tenacious, while lead is the least so. Steel is by far the most tenacious of all known substances. A wire of this metal no larger than the hundreth part of an inch in diameter sustained a weight of 134 pounds, while a wire of platina of

How are iron, steel and brass, made brittle? What does malleability mean? What metals are malleable, and what ones are brittle? Which is the most malleable metal? What is meant by ductility? Are the most malleable metals, the most ductile? What is meant by tenacity? From what does this property arise? What metals are most tena

cious?

the same size, would sustain a weight of only 16 pounds, and one of lead only 2 pounds. Steel wire will sustain 39,000 feet of its own length without breaking.

Recapitulation. The common, or essential properties of bodies are Impenetrability, Extension, Figure, Divisibility, Inertia, and Attraction. Attraction is of several kinds, namely, attraction of cohesion, attraction of gravitation, capillary attraction, chemical attraction, magnetic attraction, and electrical attraction.

The peculiar properties of bodies are density, rarity, hardness, elasticity, brittleness, malleability, ductlity and tena. city.

Force of Gravity.

The force by which bodies are drawn towards each other in the mass, and by which they descend towards the earth when let fall from a height, is called the force of gravity.

The attraction which the earth exerts on all bodies near its surface, is called terrestrial gravity, and the force with which any substance is drawn downwards, is called its weight.

All falling bodies tend towards the centre of the earth, in a straight line from the point where they are let fall. If then a body be let fall in any part of the world, the line of its direction will be perpendicular to the earth's surface. It follows, therefore, that two falling bodies, on opposite parts of the earth, mutually fall towards each other.

Suppose a cannon ball to be disengaged from a height opposite to us, on the other side of the earth, its motion in respect to us, would be upward, while the downward motion from where we stand, would be upward in respect to those who stand opposite to us, on the other side of the earth.

In like manner, if the falling body be a quarter, instead of half the distance round the earth from us, its line of direction would be directly across, or at right angles with the line already supposed.

What proportion does the tenacity of steel bear to that of platina and lead? What are the essential properties of bodies? How many kinds of attraction are there? What are the peculiar properties of bodies? What is gravity? What is terrestrial gravity? To what point in the earth do falling bodies tend? In what direction will two falling bodies from opposite parts of the earth tend, in respect to each other? In what direction will one from half way between them meet their line?