MAGNET AND MAGNETISM 



3594 



MAGNET AND MAGNETISM 



when blown through an alcohol or gas flame 

 makes a brilliant white light. Mixed with po- 

 tassium chlorate, magnesium powder is often 

 used for a flash light in photography. The 

 pure metal is of but little value except for its 

 brilliant light, and probably not over twenty 

 tons of it are manufactured annually. A small 

 quantity is used in making alloys, of which 

 magnalium (ninety-eight per cent aluminum) is 

 the most useful. Among the important com- 

 pounds of magnesium are the oxide, magnesia, 

 or calcined magnesia (magnesia usta), a very 

 infusible, or "refractory," substance used in 

 lining electric furnaces; the carbonate, which 

 occurs naturally as magnesite; the basic car- 

 bonate, magnesia alba, used in tooth powders 

 and silver polishes and in medicine; and the 

 sulphate, Epsom salts (which see). The chlo- 

 ride is used for obtaining the pure metal, which 

 is separated from it by electricity.. 



Magnesium is widely distributed, occurring in 

 asbestos, carnallite, dolomite, hornblende, mag- 

 nesite, serpentine, soapstone, tourmaline, meer- 

 schaum and a few other minerals. J.F.S. 



MAGNET AND MAGNETISM. Magnetism 

 is the power possessed by a certain variety of 

 iron ore and by artificial magnets which en- 

 ables them to attract iron and steel. 



Magnets. Many boys have among their pos- 

 sessions small u-shaped magnets like the one 

 shown in Fig. 1, and with this magnet many 

 interesting experiments may be performed. If 

 the magnet is large it may lift a hammer, a 



FIG. 1 



wrench or other objects of equal weight. A 

 small magnet will lift nails, tacks and iron 

 filings. 



With a bar magnet, which is a straight piece 

 of magnetized steel, other interesting experi- 

 ments may be tried. Place a piece of glass or 

 paper over this magnet and sift iron filings on 

 it, then tap the glass or paper lightly. The 

 filings will arrange themselves in curves around 

 each end of the magnet (Fig. 2). This is one 

 way of showing that the magnetic force is 

 strongest at the ends of the magnet and that 

 it decreases towards the middle of the bar, 

 where it seems to disappear. This is also true 

 of the u-shaped magnet, which is a bar magnet 

 bent into the shape of a u, or horseshoe. 



The ends of a magnet are called the poles. 

 When a bar magnet is suspended in a horizon- 

 tal position so that it can move freely it comes 



to rest pointing nearly north and south, and the 

 same end always points north. The magnetic 

 needle is a small bar magnet so mounted that 

 it is free to move on a pivot, and it points 

 practically north and south. 



The end of the magnet which points north is 

 called the north pole, and is marked by N or 

 +. The end pointing south is called the south 

 pole, and is marked S or . If we bring the 

 north pole of a magnet near the north pole of a 

 magnetic needle, the north end of the needle 

 turns away from the magnet, but if we present 

 the south pole of the magnet, the north pole 

 of the needle turns towards it. From this and 

 a number of other experiments the law of the 

 poles was discovered. It is this: Like poles 

 repel, and unlike poles attract, each other. 



How to Make a Magnet. When a piece of 

 iron or steel is brought in contact with a mag- 

 net it becomes magnetized. Stick a nail end- 

 wise on your magnet. You can stick a smaller 

 nail to the other end of the first and a tack 

 to the further 

 end of the sec- 

 ond, and the tack 

 will pick up iron 

 filings. Take the 

 first nail from the 

 magnet and the 

 others drop from 

 it and from each 

 other. However, 



FIG. 2 



were a piece of hard steel used instead of the 

 nail it would have retained its magnetism for 

 some time after the magnet was removed. On 

 the other hand, it would have been magnetized 

 much more slowly than the nail. We have 

 learned by repeated experiments that hard 

 steel magnetizes slowly but retains its mag- 

 netism a long time, and that soft iron is mag- 

 netized quickly but loses its magnetism in- 

 stantly 'when contact with the magnet is broken. 

 Rub your knife blade over a magnet from the 

 middle towards the end, carrying it back 

 through the air, and in a short time it will 

 become magnetized. You may also magnetize 

 it by letting it lie on the magnet for several 

 hours. A knife thus treated will pick up 

 needles, tacks and sometimes small nails. Any 

 piece of steel can be magnetized in the same 

 way. One peculiarity of a magnet is that it 

 never loses any of its power through magnetiz- 

 ing other objects. A current of electricity pass- 

 ing through an insulated wire wound about a 

 piece of soft iron will magnetize the iron. See 

 ELECTROMAGNET. 



