EXPERIMENTS.

1. Make a strong solution of alum, or of sulphate of copper, or blue vitriol, and place in them rough and irregular pieces of clinker from stoves, or wire-baskets, and set them by in a cool place, where they will be free from dust, and in a few days crystals of the several salts will deposit themselves on the baskets, &c.; they should then be taken out of the solutions, and dried, when they form very pretty ornaments for a room.

2. Fill a Florence flask up to the neck with a strong solution of sulphate of soda, or Glauber's salt, boil it, and tie the mouth over with a piece of moistened bladder while boiling, and set it by in a place where it cannot be disturbed. After twenty-four hours it will probably still remain fluid. Pierce the bladder covering with a penknife, and the entrance of the air will cause the whole ma.s.s instantly to crystallize, and the flask will become quite warm from the latent caloric, of which we have spoken before, given out by the salt in pa.s.sing from the fluid to the solid state. It is better to prepare two or three flasks at the same time, to provide against accidents, for the least shake will often cause crystallization to take place before the proper time.

CHANGES OF COLOUR PRODUCED BY COLOURLESS LIQUIDS.

Make a strong infusion of the leaves of the red cabbage, which will be of a beautiful _blue_ colour; drop into it a few drops of dilute sulphuric acid, and the colour will change to a bright red; add some solution of carbonate of potash, or soda, and the red colour will gradually give way to the original blue; continue adding the alkaline solution, and the fluid will a.s.sume a bright _green_ colour. Now resume the acid, and as it is dropped in, the colour will again change from green to blue, and from blue to red. Now this simple experiment ill.u.s.trates three points: first, that acids change the colour of most vegetable blues and greens to red; second, that alkalies change most blues and reds to green; and third, that when the acid and alkali are united together, they both lose their property of changing colour, and become what is called a _neutral_ salt, _i. e._ a compound possessing the properties of _neither_ of its const.i.tuents.

[Ill.u.s.tration]

ELECTRICITY.

No branch of science is more capable of affording amus.e.m.e.nt, combined with instruction, than electricity, and there are few sciences in which the experiments are more easily performed. We would therefore especially recommend it to our young friends.

The term electricity is derived from the Greek word _electron_, signifying amber, because electrical attraction was first discovered from its being noticed that when amber was rubbed into a certain degree of warmth, it had the power of attracting small bodies to itself.

Electricity therefore primarily treats of the phenomena and effects produced by the friction or rubbing together of certain bodies called electrics. These consist of gla.s.s, amber, resinous matters, silks, hair, wool, feathers, various vegetable substances, and atmospheric air, and the electricity so obtained is usually called Frictional Electricity, to distinguish it from that produced by chemical action, and called Voltaic Electricity.

SIMPLE MEANS OF PRODUCING ELECTRICITY.

To show the nature of electrical action, rub a piece of sealing-wax or amber upon the coat-sleeve, and it will attract light bodies, such as straws or small pieces of paper. If a clean gla.s.s tube be rubbed several times through a silken or leather cloth, and presented to any small substances, it will immediately attract and then repel them; and if a poker suspended by a dry silk string be presented to its upper end, then the lower end of the poker will exhibit the same phenomena as the tube itself, which shows that the opposite electrical condition may be induced upon other bodies by the mere neighbourhood and approach of another electrified body, and the effect so produced is called induced electricity.

[Ill.u.s.tration]

When an electrified conductor is supported by non-conductors, so that the electric fluid cannot pa.s.s from the conductor to the earth, it is said to be insulated: thus the human body is a conductor of electricity--but if a person standing on a gla.s.s stool (as represented in the drawing) be charged with electricity, the electric fluid cannot pa.s.s from him to the earth, and he is said to be _insulated_; and if he be touched by another person standing on the ground, sparks will be exhibited at the point of contact, where also the person touching will feel a p.r.i.c.king sensation.

[Ill.u.s.tration]

ATTRACTION AND REPULSION EXHIBITED.

[Ill.u.s.tration]

In order to ill.u.s.trate certain remarkable facts in this science of an amusing character, attention must be directed to the figure A B, which is a metal stand; C is a small piece of cork or pith, which is suspended from the hook by a dry silken thread. Having rubbed an electric, as a dry rod of gla.s.s, and presented it to C, the ball will be instantaneously attracted to the gla.s.s and will adhere to it. After they remain in contact for a few seconds, if the gla.s.s be withdrawn without being touched by the fingers, and again presented to the ball, the latter will be _repelled_ instead of attracted, as in the first instance. By being touched with the finger, the ball can be deprived of its electricity, and if after this has been done we present a piece of sealing-wax in the place of the gla.s.s formerly employed, the very same phenomena will take place. On the first application the ball will be _attracted_, and on the second _repelled_.[8]

[8] For a more complete account of this interesting science we would refer the young reader to "The Boy's Playbook on Science," or, if more advanced, to "Noad's Manual of Electricity."

Before the young reader can perform any very important experiments with electricity, he must become possessed of an ELECTRICAL MACHINE, which is an instrument contrived for the purpose of rubbing together the surfaces of gla.s.s and leather. They generally consist of a cylinder, or plate of gla.s.s, and a piece of silk or leather for it to rub against, covered with an amalgam, the method of preparing which we shall hereafter describe.

HOW TO MAKE AN ELECTRICAL MACHINE.

[Ill.u.s.tration]

It is very easy to make a gla.s.s machine of the cylindrical form, if the maker cannot afford to buy one. First procure a common wine bottle of good dimensions, and thickish gla.s.s. Drill a hole through its bottom, with a file moistened with dilute sulphuric acid. A blacksmith, if supplied with the acid, would undertake to do this part of the work.

Through this hole and the mouth pa.s.s a spindle, as represented in the cut. The end of B should be squared to fix a handle on, and the spindle should be fixed firmly in the bottle. The bottle is then to be fixed in a frame in the following manner: the end of the spindle C pa.s.ses through a hole at B; and the other end at C has the handle for turning the machine.

[Ill.u.s.tration]

Next make a cushion of wash-leather stuffed with wool, and fastened to the top of a frame of the following figure. This frame is to be of such a height that the cushion shall press against the sides of the bottle, and a piece of black silk is sewn on to the top of the cushion, and hangs over the bottle D. The cushion should be smeared with an amalgam, formed by melting together in the bowl of a tobacco-pipe one part of tin with two of zinc; to which, while fluid, should be added six parts of mercury. These should be stirred about till quite cold, and then reduced to a fine powder in a mortar, and mixed with a sufficient quant.i.ty of lard to form a thickish paste. When all is done, the machine is complete.

[Ill.u.s.tration: CUSHION.]

THE CONDUCTOR.

The electricity being generated by the friction produced between the rubber and the bottle from the motion imparted by the handle, it is necessary to draw it off for use. This is performed by what is called a conductor. This is made by covering a cylinder of turned wood six inches long and two and a half inches in diameter, and nicely rounded at the ends, with tinfoil, which is then mounted on a stand on a gla.s.s rod.

When used, it is to be placed in the direction of the length. In it some pins are inserted, with the points outside, in a line even with, and about half an inch from, the bottle, and it should be of such a height as to come just below the silk ap.r.o.n. When it is wished to charge a Leyden jar, it is to be placed at the round end of the conductor. By these simple means a great variety of pleasing experiments may be performed; but to show the various phenomena connected with this interesting study, we shall now describe an electrical machine of the newest construction, and perform our experiments with it.

THE PLATE ELECTRICAL MACHINE.

[Ill.u.s.tration]

Formerly the electrical machine was made in the form of a cylinder, but now it consists of a plate A, as seen in the engraving. The plate is turned by the handle F through the rubber B B, which diffuses the excitement over the gla.s.s. The points or b.a.l.l.s at each side of the plate carry off a constant stream of positive electricity to the prime conductor C. Negative electricity is generated by insulating the conductor to which the cushion is attached, and continuing the prime conductor with the ground, so as to carry off the fluid collected from the plate.

HOW TO DRAW SPARKS FROM THE TIP OF THE NOSE.

If the person who works the machine be supported on a stool having gla.s.s legs, and connected with the conductor by means of a gla.s.s rod, the electricity will pa.s.s from the conductor to him, and as it cannot get away, owing to the gla.s.s on which he stands being a non-conductor, any person on touching him can draw the electricity from him, which will exhibit itself in small sparks as it pa.s.ses to the person who touches him. If touched on the nose, sparks of fire will issue from it.

HOW TO CHARGE A LEYDEN JAR.

[Ill.u.s.tration]

A most useful piece of electrical apparatus is called the Leyden jar, here represented. It is employed for the purpose of obtaining a quant.i.ty of electricity, which may be applied to any substance. It consists of a gla.s.s jar, coated both inside and without, four-fifths of the way up, with tinfoil. A k.n.o.b rises through a wooden top communicating with the inside of the jar. When it is wished to charge the jar, this k.n.o.b is applied to the prime conductor of the electrical machine when in action, and a quant.i.ty of electricity being given off, the jar will remain charged with it till a connexion is made, by some good conductor of electricity, between the k.n.o.b and the outside tinfoil. A piece of bra.s.s chain must hang from the stem that carries the k.n.o.b, and connect it with the interior of the jar.

THE ELECTRICAL BATTERY.

[Ill.u.s.tration]

If several of these jars be united, a large quant.i.ty of electricity can be collected; but, in arranging them, all the interior coatings must be made to communicate by metallic rods, and a similar union must be effected among the exterior coatings. When thus arranged, the whole series may be charged as if they formed but one jar.

[Ill.u.s.tration]

For the purpose of making a direct communication between the inner or outer coatings of a jar or battery, by which a discharge is effected, an instrument called a discharging rod is employed. It consists of two bent metallic rods, terminating at one end by bra.s.s b.a.l.l.s, and connected at another by a joint which is fixed to the end of a gla.s.s handle, and which, acting like a pair of compa.s.ses, allows of the b.a.l.l.s being separated at certain distances. When opened to the proper degree, one of the b.a.l.l.s is made to touch the exterior coating, and the other ball is then brought into contact with the k.n.o.b of the jar, when a discharge is effected; while the gla.s.s handle secures the person holding it from the effects of the shock.

DANCING b.a.l.l.s AND DOLLS.

[Ill.u.s.tration]