Part 38

One of the oldest and simplest forms of apparatus, for producing electric currents, is that which is known as the voltaic cell. This form of apparatus may very easily be constructed. Pour some water into a glass jar, and add a little sulphuric acid. Now place in the water a strip of clean zinc and one of clean copper. Do not let the strips of metal touch in the water, but connect them outside the water by means of a piece of wire. When this has been done, a current of electricity will be sent up along the wire and through the water between the two strips of zinc and copper. This current is said to flow along the wire from the copper, which is called the positive pole of the cell, to the zinc, which is called the negative pole. In the liquid in the cell (i.e., the jar), the current travels from the zinc to the copper, thus completing what is called the electric circuit. Whenever the circuit it broken, that is, whenever there is a gap made in the wire connecting the poles, or anything else is done to destroy the completeness of the path, along which the current travels, the current ceases; consequently, when it is desirable to stop the current, all that is necessary is to cut the wire connecting the two strips of copper and zinc.

The production of a current of electricity, by means of an apparatus of this sort, depends upon the chemical action of the acid in the water upon the strip of zinc. As long as the acid continues to act upon the zinc, the current is produced, and when the acid ceases to act upon the zinc, the current ceases to flow. If the zinc is clean, the chemical action of the acid ceases, whenever the circuit is broken, and consequently, when the cell is not being used to produce a current, the zinc is not destroyed by the acid. But if the zinc is not clean, small electric currents are set up, within the liquid, between the zinc and the impurities on its surface, and around the points where these impurities lie the acid acts upon the zinc and dissolves it. This

## action of the acid upon the zinc, when the circuit is broken, is known

as local action, and it is very desirable to prevent it, as far as possible. For this purpose the zinc is often rubbed with mercury, which soaks into the zinc and forms a film on its surface, upon which the impurities float. This treatment of the zinc is known as amalgamation, and it serves to prevent almost all the local action, due to impurities of the zinc.

Many other substances, besides zinc and copper, have been found capable of yielding an electric current, when placed in a suitable liquid, and many other fluids, besides water that contains a little sulphuric acid, have been employed to act upon the zinc and copper, or the substances used in their stead. Numerous cells of different kinds have, therefore, been devised, but, in all of them, the current is produced by chemical

## action. Most of them contain a liquid of some sort, which is called the

exciting fluid, and two solid substances, which are called the elements of the cell. One of these elements is always much more susceptible to the chemical action of the exciting fluid, than the other, and this one is known as the positive element. The other element, upon which the exciting fluid may have no action, is called the negative element. In cells in which the elements are zinc and copper, the zinc is always the positive element. This may seem strange to you, for you have already learned that the zinc is the negative pole of the cell, but, to avoid confusion, you must fix well in your mind the fact that the zinc is not the positive element of a voltaic cell, but its negative pole, and that the copper, which forms the negative element is the positive pole of the cell. The currents produced by the various forms of voltaic cells, vary considerably in strength, but none of them are very strong. In order to obtain a stronger current, a number of cells must be used together. Such a collection of cells forms a voltaic battery, and in some instances, as many as fifty thousand cells have been used in a single battery.

We have already learned in our study of water that it may be separated into its elementary gases by sending an electric current through it. The effect is a chemical one. Water, however, is not the only substance that is decomposed by electricity; almost all chemical compounds may be decomposed by the passage of a current through them, provided a current of sufficient strength is used.

Another effect of the current is its heating effect. It has been found that the passage of an electric current, through any body, is always productive of a certain amount of heat. The amount of heat produced depends upon the strength of the current of electricity, and the resistance to its passage that is offered by the body through which it travels. This amount is increased by increasing either the strength of the current or the resistance of the conductor along which it travels. We have already learned, that some substances allow electricity to pass over them very readily, and are therefore called conductors, while substances through which electricity does not flow readily are known as non-conductors. No substance is a perfect non-conductor, for electricity can be made to pass through any substance, if the current is sufficiently powerful. Neither is any substance a perfect conductor, for all substances offer some resistance to the passage of an electric current. Those substances that are ordinarily considered good conductors offer varying degrees of resistance to electric currents. For example, a copper wire offers less resistance than an iron wire of the same length and diameter.

The resistance of a body depends not only upon its material, but also upon its length and size. In conductors of the same material, the resistance is directly proportional to the length of the conductor, and inversely proportional to the square of its diameter. This is not surprising, for an electric current bears a strong resemblance to a current of water, in many of its properties, and you know that it is harder to force water through long, narrow pipes, than through short, wide ones.

From what has been stated about resistance, you may see, that a current will produce more heat, in passing through a long fine wire, than through a shorter and thicker one, and that, of two conductors of the same length and size, but of different material, one may be heated much more by a current than will another.

~HOW MAGNETS ARE MADE~

A third effect of the electric current, which has not previously been mentioned is its magnetizing effect. It is upon this, that some of the most important effects of electricity depend.

By coiling a wire around a bar of iron or steel, and then sending an electric current through it, the piece of iron, or steel, is made to show magnetic properties. By this is meant, as you doubtless know, that the iron will now attract other pieces of iron, or steel, to it. The strength of this attraction depends upon the strength of the current, and upon the number of turns of wire around the bar. By increasing either the strength of the current, or the number of turns in the coil of wire, around the bar of iron, the strength of its magnetic attraction is increased. When the current is stopped, the magnetic properties of the iron disappear almost completely. A magnet, that depends upon a current of electricity for its magnetic power, is called an electro-magnet.

Besides electro-magnets there are others, which are called permanent magnets. Electro-magnets are composed of soft iron, the softer the better, and, as soon as the current of electricity ceases to flow around them, their magnetic properties disappear. Permanent magnets, on the contrary, are made of steel, and their magnetism is independent of the action of a current of electricity. No coil of wire is wound around them, and no current is employed to maintain their magnetic properties. A piece of steel may be made to become a permanent magnet, by passing a current of electricity, for a considerable time, through a coil of wire wound around it, or by allowing a piece of steel to remain for some time in contact with a strong magnet. When a current of electricity passes through a coil of wire, wound around a bar of steel, it takes longer to magnetize the steel than it would to magnetize iron, but, when the current ceases, the magnetism does not all disappear from the steel. A portion of it remains, and the steel becomes permanently magnetic.

If a thin bar of steel is magnetized, and is then suspended by its middle, so that it can spring freely, it will be found that one end tends to point toward the north, and the other toward the south. Whenever the bar is swung out of this position, it swings back to it, and if the north end is turned entirely around to the south, it does not remain, but swings back to its former position. This shows that there is a difference in the magnetism at the two ends of the magnet. To indicate this difference, the north-seeking end of a magnet is called the positive pole of the magnet, and the south-seeking end is known as the negative pole.

By suspending two bar magnets, in the manner described, it can be shown that the positive and negative poles of the magnets act like positive and negative charges of electricity. Poles of the same kind repel, and poles of opposite kinds attract, each other.

Permanent magnets are usually made in two forms, either straight or horseshoe shaped. A compass needle, as has been shown, is an example of a straight magnet. The horseshoe variety, which has a little bar of iron, called the keeper, laid across the poles is a common toy. Electro-magnets are seldom seen, except in electrical instruments or machinery. The pictures shown on the following pages give us a bird’s-eye view of some of the wonders performed by these electro-magnets. Tons and tons of material are picked up and held securely by one of these magnets as easily as you can hold on to an apple.

Why Does a Bee Have a Sting?

The bee’s sting is given him as a weapon of defence. Primarily it is for the sole purpose of enabling him to help defend the hive from his enemies. Sometimes when he is attacked away from the hive he uses his sting to defend himself. When he does so, he injects a little quantity of poison through the sting and that is what causes the inflammation.

How Does a Honey Bee Live?

The bee lives in swarms of from 10,000 to 50,000 in one house. In the wild state the house or hive is located in a hollow tree generally. These swarms contain three classes of bees, the perfect females or queen bees, the males or drones, and the imperfectly developed females, or working bees. In each hive or swarm there is only one perfect female or queen whose sole mission is to propagate the species. The queen is much larger than the other bees. When she dies a young working bee three days old is selected as the new queen. Her cell is enlarged by breaking down the partitions, her food is changed to “royal jelly or paste” and she grows into a queen bee. The queen lays 2,000 eggs per day. The drones do not work and after performing their duty as males are killed by the working bees. The female bees do the work of gathering the honey. They collect the honey from the flowers, they build the wax cells, and feed the young bees. When a colony becomes overstocked, a new colony is sent out to establish a new hive under the direction of a queen bee.

THE BEGINNING OF A STEAMSHIP

[Illustration: Probably no form of construction is so interesting to everyone as the construction of a huge steamer, a wonderful “city” afloat, with its thousands of passengers, its thousand officers and crew, the tremendous stores of provisions and water, and the precision with which the great ship plows its way from one shore to the other.

This picture shows the first work in building a modern steamer, laying the keel and center plate, upon which the massive hull is constructed. The rivets are driven by hydraulic power, noiselessly but firmly. In the new “Britannic”--largest of all British steamers and the newest (1915) modern leviathan--over 270 tons of rivets--nearly three million in all--were required to give staunchness to the steel-plated hull. The cellular double bottom is constructed between the bottom and top of the center plate.]

[Illustration: A LONGER VIEW OF THE ABOVE OPERATION.]

[Illustration: THE CRADLE OF A STEAMSHIP CALLED A “GANTRY”

VIEW NEAR THE BOW.

The “ribs” of the “Britannic,” showing the deck divisions, in outline. The huge “gantry” or cradle of steel, in which “Britannic” was built, cost $1,000,000.]

[Illustration: THE DOUBLE BOTTOM OF MODERN STEAMSHIPS

THE “BRITANNIC” OF THE WHITE STAR LINE. VIEW OF THE DOUBLE BOTTOM PLATED.]

[Illustration: THE HUGE STEEL SKELETON OF THE “BRITANNIC” BEFORE THE PLATES WERE PLACED ON IT.

The plates are seen piled in the foreground. The largest of them are 36 feet long and weigh 4¹⁄₄ tons each.]

[Illustration: THE SHIP READY TO LAUNCH

NOT A “SKYSCRAPER,” BUT A FLOATING HOTEL IN PROCESS OF CONSTRUCTION.

THE HULL ITSELF IS 64′ 3″ DEEP, AND FROM THE KEEL TO THE TOP OF THE FUNNELS IS 175 FEET. THE NAVIGATING BRIDGE IS 104′ 6″ ABOVE THE KEEL.]

[Illustration:

WHITE STAR ROYAL MAIL STEAMER “BRITANNIC”

READY TO LAUNCH.

The “Britannic” on the ways at Belfast (Harland & Wolff’s). The largest gantries ever constructed to hold a ship.]

[Illustration: THE MACHINERY USED IN LAUNCHING A SHIP

FORWARD LAUNCHING GEAR (HYDRAULIC).

The ship went from the ways into the water in 62 seconds and was stopped in twice her own length.]

[Illustration: THE HUGE HULL LEFT THE WAYS EASILY AND CREATED ONLY A SMALL SPLASH.]

[Illustration: A CLOSE VIEW OF A SHIP’S RUDDER

“BRITANNIC” HELD UP JUST AFTER THE LAUNCH.]

[Illustration: “BRITANNIC.” THE 100-TON RUDDER. THE (CENTER) TURBINE PROPELLER SHAFT AND ONE OF THE “WING” PROPELLER SHAFTS.]

[Illustration: WHAT A SHIP’S PROPELLER LOOKS LIKE

THE COMPLETED SHIP

The center (the turbine) propeller, 16′ 6″ in diameter, cast of one solid piece of manganese bronze, 22 tons in weight. The “Britannic” like “Olympic,” is propelled by two sets of reciprocating engines, the exhaust steam from these being reused in the low-pressure turbine, effecting great economy in coal. The two “wing” propellers are 23′ 6″ in diameter and weigh 38 tons each.]

[Illustration: WHAT A SHIP’S TURBINE LOOKS LIKE

The turbine motor, 130 tons in weight (Parsons type). The steam plays upon the blades with such power that they develop 16,000 horse-power and revolve the propeller (turbine) 165 times a minute. The motor is 12 feet in diameter, 13′ 8″ long, the blades (numbering thousands) ranging from 18 to 25¹⁄₂ inches in length.]

[Illustration: THE IMMENSE TURBINE MOTOR FULLY ENCASED--WEIGHT 420 TONS.]

[Illustration: HOW A FUNNEL APPEARS BEFORE IT IS IN PLACE

One of the four immense funnels--without the outer casing. Each is 125 feet above the hull of the ship and measures 24′ 6″ by 19′ 0″.]

[Illustration: WHAT A GREAT STEAMSHIP WOULD LOOK LIKE IF SPLIT END TO END]

This view will give some idea of the interior arrangement of the huge White Star Line triple-screw steamer “Britannic.” Many features undreamed of a dozen years ago have been introduced in the passenger quarters of this ship. As many decks are necessary to provide the required space for state-rooms, public apartments, promenades, etc., several passenger elevators have been installed, which are a great convenience for those who find the use of stairs irksome. There is a fully equipped Gymnasium, a children’s Play Room for the younger passengers, a Squash Racquet Court, a Swimming Pool with sea-water, and the Turkish Bath establishment.

There are accommodations for over 2500 passengers as well as a crew of 950. The view shows how the ship is divided into numerous water-tight compartments, so that should several of these sections become flooded the rest of the ship would remain intact.

The lifeboats, of which there are sufficient to carry all on board, are handled by a new device, by means of which the boats can be launched, when filled, with greater ease and safety than hitherto. Each of the great davits can handle several boats and they are long enough to carry the boats clear of the side of the ship, should any accident cause her to list to one side.

The “Britannic” is nearly 900 feet in length, and with her gross tonnage of 50,000 is the largest British steamer in the world.

What Is Water Made Of?

Every kind of substance in the world is made up of tiny portions, each of which is distinctly just what the whole mass is, but which are so small you cannot see them. A pile of sand, or a cupful of sugar or salt consists of a great many small grains. A cup of water too is made up of what we would call small grains of water, or what we would call grains of water if we could think of them in the same way as we do sugar or salt or sand. These particles are so small that they could not be seen separately, even if the particles did not have the ability to stick so close together that we could not distinguish them even if they were large enough to be seen.

The word used in describing these tiny particles in any substance, water, sugar, sand, salt or anything else is molecule.

What Is a Molecule?

The word molecule means “smallest mass,” which indicates the very smallest division that can be made of any substance without destroying its identity. Every substance is made up of molecules, and in many cases the molecules of one substance will mix with those of another substance, while in other cases they will not. When you dissolve sugar in water or melt lead or change water into steam, the physical body of the substance is changed, but the molecules remain as they were. They are only changed in so far as their relations to each other and to those of another substance are concerned.

How Do We Know a Thing Is Solid, Liquid or Gas?

The relations of the molecules in any substance to each other is what determines whether a substance is a solid, a liquid or a gas. A gas is a substance in which the molecules are constantly moving rapidly about among each other, but always in straight lines. A liquid substance is one in which the molecules are also constantly moving about but which do not move in straight lines. Solids are substances in which the molecules stick together in one position by the power of cohesion which they have. Cohesion means the power of sticking together.

How Big Is a Molecule?

We do not as yet know all there is to be learned about molecules. We know through the wonders of chemistry that small as a molecule is, it is still made up of smaller particles called atoms. An atom is the smallest division of anything that can be imagined. We have found by chemistry that even a molecule is capable of being divided, i.e., it is made up of still smaller particles, but molecules are small enough. An eminent scientist, Sir William Thomson, has given us probably the nearest approach to a correct way of saying something of the size of a molecule. “If a drop of water were magnified to the size of the earth, the molecules would each occupy spaces greater than those filled by small shot and smaller than those occupied by cricket balls.”

To get at what water is made of we must separate it through chemistry into its parts or atoms. When we do this we find that a molecule of water is made of three atoms or parts. Two of these are exactly alike and consist of a gas called hydrogen, and the other part is another gas called oxygen, concerning which gases we have already learned much in the answers to other questions in this book. In other words, when we separate water, which is a liquid, into its parts, we change the relations of the molecules in the water which move in irregular lines, into parts which move in straight lines and, when the molecules of a substance, as we have already seen, move in straight lines, the substance becomes a gas. On the other hand, when you freeze water, it becomes a solid (ice), and in doing that you fix the molecules in the water so that they stick to each other.

Men thought for a long time that water was an element like oxygen and hydrogen, i. e., that its molecules could not be separated in its parts and was, therefore, considered one of the things which could not be divided up, but this was due to the fact that it requires a great amount of power to break up the molecules of water.

What Is an Element?

An element is any substance whose molecules cannot be broken up and made to form other substances. You can take one or more elements and make a compound, which is what water is. A compound is a substance in which the molecules are made up of at least two kinds of elements or elementary substances.

~THE DIFFERENCE BETWEEN ELEMENTS AND COMPOUNDS~

The things we find in the world are known as either compounds or elements. An element, as we have already learned, is something in which the molecules cannot be broken up. A compound is, therefore, a substance in which the molecules are made of molecules of one or more elements and is either gas, liquid or solid, according to the relations which these molecules have to each other. We have so far discovered less than eighty real elements in the world, although since we find a new one every little while, there are probably many more as yet undiscovered.

Not all elements are gases, of course. Solids like copper, gold, iron, lead and a number of others are elements. Among liquids we have mercury, and of the gases we find hydrogen, nitrogen and oxygen, which are the three wonderful gases about which we are about to learn something, and these three are also the world’s most important gases. Ammonia is an element, but, while we think of it as a liquid, the real ammonia is really a gas. Our household ammonia is really a compound of ammonia with something else.

What Is Hydrogen Gas?