The Wonder Book Of Knowledge Part 72

All magnets, whether natural, permanent or electric, possess the same magnetic properties. Every magnet has two poles commonly called a north pole and a south pole. It has also been found that when a magnet is broken in two each piece becomes a magnet in itself with its own north and south poles.

For practical purposes it has been found convenient to a.s.sume that magnetism consists of a series of "lines of force" running through the magnet from one end to the other and back again through the air. Each one of these lines is a.s.sumed to have a certain strength, and the power of any magnet is determined by the number of lines of force flowing through it. These lines are clearly shown in Fig. 1, which was made by sprinkling iron filings on a sheet of paper over a bar magnet, and tapping the paper slightly so that the filings could arrange themselves along the magnetic lines of force.

Since Oersted's first electric magnet in 1820, electric magnets have been made in a variety of forms and for many different purposes. The simplest form of electric magnet is shown in Fig. 2. It consists of an iron bar with an insulated electric wire wound around it carrying an electric current.

[Ill.u.s.tration: FIG. 2]

Another form of the electric magnet is shown in cross-section in Fig. 3.

This consists of a short steel cylinder with a groove in its face for the electric coil. The modern lifting magnet is a highly specialized form of this type of electric magnet.

Although the use of a magnet for lifting purposes seems to be a very simple idea and easily adopted, many difficulties had to be overcome and years of experimenting done before the lifting magnet was a commercial success. Nearly all electrical machinery may easily be protected from rough usage and moisture, but the lifting magnet must be so strongly designed that it will withstand the countless blows due to heavy pieces of iron flying against it, and the banging it must get against the sides of cars, ships, etc. All light parts must be placed inside of the magnet or in such a position that they can never be knocked off or broken. To moisture in some form or other nearly all lifting-magnet troubles can be traced. Hence the importance of an absolutely moisture-proof construction. The result of moisture in the interior of a magnet is to weaken the effectiveness of the installation, leading eventually to short circuits and burn-outs. It is necessary not only to guard against moisture in the form of rain, snow or dew, but precaution must also be taken against the entrance into the magnet of moisture-laden air, since moisture so introduced will presently be condensed in the form of drops of water.

[Ill.u.s.tration: FIG. 3]

[Ill.u.s.tration: A 43-INCH MAGNET HANDLING PIG IRON]

A very natural question is, how much such a magnet will lift. For a given size of magnet, the lifting capacity varies greatly with the nature of the load handled. With a magnet sixty-two inches in diameter, this may vary from in the neighborhood of 1,000 pounds for light sc.r.a.p, to from 4,000 to 5,000 pounds for pig iron, and as high as 60,000 pounds for a solid ma.s.s of steel or iron such as, for instance, a skull-cracker ball or a casting affording surface for good magnetic contact.

The lifting magnet has been adopted for the handling of materials in all branches of the steel and iron industry. It is used for handling pig iron, sc.r.a.p, castings, billets, tubes, rails, plates, for loading and unloading cars and vessels, and for handling skull-cracker b.a.l.l.s and miscellaneous magnetic material.

Probably one of the best ill.u.s.trations of the saving accomplished by means of a lifting magnet is its use in unloading pig iron from steamers. By the old hand method it required twenty-eight men, two days and two nights, to unload a cargo of 4,000,000 pounds. When the lifting magnet was introduced, the total time for unloading was reduced to eleven hours, and was done by two men whose labor consisted in manipulating the controllers in the cages of the cranes. Thus two men and two magnets did the work of twenty-eight men in less than one-fourth of the time. Furthermore, the vessels were enabled to double their number of productive trips.

[Ill.u.s.tration: 36-INCH LIFTING MAGNET PICKING UP 3,500-POUND WINDING DRUM]

In railroad work, lifting magnets are at the present time used princ.i.p.ally in sc.r.a.p yards and around store-room platforms, where it is necessary to handle iron and steel rapidly and economically. For this cla.s.s of work magnets are generally used in connection with a locomotive crane, making a self-contained, self-propelled unit which may be operated over the shop-yard tracks as required. The use of this combination has reduced very greatly the cost of handling both new and sc.r.a.p material, both by reducing the actual expense of handling and by enabling the material to be handled much more rapidly than was before possible.

Probably the best possible endors.e.m.e.nt of the waterproof construction of the modern lifting magnet is the fact that one of them was successfully operated seventy feet below the surface of the Mississippi River. At New Orleans a large load of kegged nails was raised from a depth of seventy feet. A load of steel cotton ties was raised near Natchez and a barge of iron wire near Pittsburgh. And these are only a few instances of such work.

The magnets used in this river work were three and one-half feet in diameter. They were dropped into the stream, the current turned on, and five or six kegs of nails or bundles of wire were raised each trip. The nails weighed 200 pounds to the keg, so there were lifted each time, from 1,000 to 1,200 pounds from the bed of the river.

The variety of uses to which these magnets may be put are shown by the accompanying ill.u.s.trations and there are many industries handling iron and steel where the introduction of the modern, high-duty lifting magnet will effect a great saving in time and labor.

[Ill.u.s.tration: 36-INCH MAGNET HANDLING HEAVY CASTINGS

Note that there is no hoisting tackle to be adjusted.]

An amusing incident occurred recently in a factory where a large lifting magnet is used in connection with a crane to carry pig iron through the shop. Just as the operator was bringing it across the shop unloaded, he saw two laborers ahead of him in altercation. One held a short pinch bar and the other a heavy shovel. As he approached, they both raised their tools like weapons. In a flash the operator switched on the current and the two men stood as if transfixed, hanging desperately to their weapons that were held aloft as by some giant's hand. The laughter of everyone who saw the tableau ended the quarrel.

Why is the Thistle the Emblem of Scotland?

According to tradition, the Danes were attempting to surprise an encampment of the Scotch one night, and had come very near to it without being observed, when a Dane stepped on a thistle and its sharp points made him cry out with pain. The Scotch were then awakened and succeeded in defeating their a.s.sailants. Ever since that time the thistle has been made the insignia of Scotland.

How are Animals Identified on Cattle Ranges?

The question of how to mark animals started with the first stock raisers. In those days the main object was to provide some way animals could be identified as to ownerships, and many crude and more or less cruel methods were used, such as notching or lopping off part of the ear or branding with a hot iron, burning a letter or figure often ten or twelve inches high on the side of an animal. Branding in this way was used mostly by cattle raisers when large herds were grazed on the western plains. The large brand made it possible for cowboys on horseback to separate the cattle of different owners, as the brand could be seen at some distance.

[Ill.u.s.tration: _Courtesy of Wilc.o.x & Harvey Mfg. Co._

BRANDS FOR IDENTIFICATION]

As the industry advanced the methods of marking improved. At the present time a mark in the ear made of metal is most commonly used. These are in many different styles such as narrow bands looped into the edge or in the form of a b.u.t.ton fastened through the ear.

Tags are lettered with owner's name and address and numbered, which serves not only as a mark for identification of ownership but as a means of keeping a record of each animal by number; also in making health tests before shipping from one point to another.

How is Glue Made?

The best quality of glue is obtained from fresh bones, freed from fat by previous boiling, the clippings and parings of ox hides, the older skins being preferred; but large quant.i.ties are also got from the skins of sheep, calves, cows, hares, dogs, cats, etc., from the refuse of tanneries and tanning works, from old gloves, from sinews, tendons and other offal of animal origin.

By a process of cleaning and boiling the alb.u.minoid elements of the animal matter are changed into gelatine. This, in a soft, jelly-like state, const.i.tutes "size;" dried into hard, brittle, gla.s.sy cakes, which, before use, must be melted in hot water, it forms the well-known glue of the joiner, etc.

When a solution is mixed with acetic or nitric acid it remains liquid, but still retains its power of cementing; in this state it is called liquid glue.

Marine glue is a cement made by dissolving India rubber in oil of turpentine or coal-naphtha, to which an equal quant.i.ty of sh.e.l.lac is added.

Why does a Hot Dish Crack if We Put Ice Cream in It?

If we take a hot dish and put ice cream in it, it cracks because the dish when hot has expanded. All the tiny particles that make up the dish have absorbed some heat and have expanded. When the ice cream is put in the particles composing the inside of the dish are cooled off and begin to contract, while the outside particles have not cooled and they pull away from each other, causing the dish to crack.

Footnotes

[1] Ill.u.s.trations by courtesy of the Lake Torpedo Boat Co., unless otherwise indicated.

[2] The following information and statistics by courtesy of The Panama Ca.n.a.l, Washington office.

[3] Ill.u.s.trations by courtesy of the Columbia Graphophone Co.

[4] Ill.u.s.trations by courtesy of the Hendee Manufacturing Co.

[5] Courtesy of the Waltham Watch Company, and "The American Boy."

[6] Ill.u.s.trations by courtesy of the Remington Arms-Union Metallic Cartridge Company, unless otherwise indicated.

[7] Ill.u.s.trations by courtesy of Plymouth Cordage Co.

[8] Ill.u.s.trations by courtesy of Colt's Patent Fire Arms Manufacturing Co.

[9] Ill.u.s.trations by courtesy of Consolidated Fireworks Company of America.

[10] Ill.u.s.trations by courtesy of Eastman Kodak Company.