THE YOUNG SCIENTIST. 
41 
an electro-magnet; it will burn off very fine 
iron wire (wire not thicker than a human hair), 
and will deposit a coating of copper oa medals, 
etc. Two cells are comparatively stronger, 
and with half a dozen it is easy to send a cur- 
rent several hundred feet, and explode car- 
tridges or burn wires. Such a series will make 
powerful electro-magnets, and will heat to a 
white heat a considerable length of fine platina 
or iron wire. It will also give quite a bright 
spark between two pieces of hard carbon, such 
as that from gas retorts. Thus, at an expense 
not exceeding fifty cents any country teacher 
who has a class in philosophy can get up a 
battery that will enable him to illustrate most 
of the experiments described in the books. 
• 9 * 
A Shower of Fire. 
To those who see it for the first time, few 
experiments are more striking than the burn- 
ing of iron, Iron is generally regarded as an 
incombustible substance; we make our pokers 
out of iron and not out of wood, because the 
latter burns easily, while an iron poker resists 
a very hot fire. Our stoves, too, are made of 
iron lor the same reason, and when iron is seen 
burning fiercely it is a great surprise to most 
people. Dr. Priestly, the discoverer of oxygen, 
used to carry about with him a small flask of 
this gas for the purpose of amusing his friends 
by showing them the burning of a piece of 
iron, just as Wollaston, in after years, used to 
carry about a small battery made out of a lady's 
thimble, with which he was in the habit of ex- 
hibiting the ignition of a piece of very fine 
platinum wire. 
There are several ways by which the com- 
bustibility of iron may be shown. The most 
common method is to set fire to a piece of 
watch-spring in a jar of oxygen. Another is to 
throw a jet of oxygen on a piece of cast iron 
laid on ignited charcoal. The iron fuses and 
burns with wonderful brilliancy, throwing ofi" 
sparks until the effect is almost dazzling. We 
have fused as much as an ounce of metal at one 
time in this way. A third method is to drop 
iron filings into oxygen, passing them through 
a ring of flame, so that they became highly 
heated before they entered the pure gas. A 
fourth method is to support a mass of filings 
on the end of a magnet, and ignite them in a 
large jar of oxygen. The whole arrangement 
may be prepared in advance, and the filings 
may be ignited by passing a voltaic current 
through an iron wire which touches the filings. 
The combustion is exceedingly rapid and won- 
derfully brilliant. 
The simplest method of showing the com- 
bustion of iron consists in suspending iron 
filings from the poles of a magnet, and setting 
them on fire with a common spirit lamp. They 
burn slowly but brilliantly in the open air, and 
as they keep falling from the magnet they form 
a remarkably curious and brilliant shower of 
fire. If the magnet be slightly tapped, the 
shower is increased, and if it be swung through 
the air a shower of fire is projected in all direc- 
tions. Few experiments are more simple or 
more astonishingly brilliant than this. 
It is now nearly twenty years since this 
method of burning iron was described by Mag- 
nus, and yet even now it is not generally 
known. The reason for this is that although 
frequently described in books and papers, the 
points upon which success or failure turns has 
not been generally disclosed, and some of those 
who have understood it, have endeavored to 
keep it a secret. We have frequently exhibited 
the experiment in lectures, and sometimes, by 
means of electro-magnets, on a very large 
scale, and on every occasion it has produced a 
most profound impression. 
The secret of success lies in the use of very 
fine filings. Over and over again parties have 
written to us, '* We have tried your experiment 
with the iron filings, and have been unable to 
succeed." The fact was that they had gone to 
some blacksmith's shop, scraped up some of 
the iron filings from the bench, and used them. 
They might as well have used tenpenny nails. 
The filings must be of the finest kind, pro- 
duced by the finest files. Iron in large masses 
resists fire very well ; when in sufficiently fine 
powder it actually takes fire spontaneously, 
burning with great energy the moment it is 
brought into contact with the air. Fortunately, 
filings such as are necessary are an article of 
commerce, being manufactured extensively in 
Switzerland, and they may be procured from 
any large drug store. 
All that is necessary is to dip a magnet in 
the filings, and lift as much as it will carry. 
The flame of a spirit lamp is then passed over 
the filings once or twice, so as to ignite them 
over the whole surface, after which they will 
continue to burn, and if held high and shaken, 
they produce remarkably brilliant effects. 
