EVERYDAY USES OF RADIUM
During the World War large quantities of radium were employed by the
Allies for night compasses, luminous dials on airplanes, gun-sights,
etc. In times of peace it is used on pendants for locating electric
lights and switches in the dark, key-holes, fire-extinguishers, poison
bottles, emergency call-bells, and in many other ways. For example,
some mining corporations use signs in their mines made luminous in the
dark by phosphorescent paint made from radioactive substances. These
luminous signs are not affected by atmospheric conditions.
Yet for all these uses, including “radium watches” and clocks, not more
than half an ounce of radium has been used since its discovery in 1898.
A few millionth parts of a gram of radium, in the form of radioactive
barium sulphate, a large portion of phosphorescent zinc sulphide
(crystallized zinc), mixed with varnish and some adhesive substance,
give enough material to illuminate 40 or 50 watches. One gram of
radium (= 16 grains) combined with 20,000 grams of secret process
phosphorescent zinc sulphide is sufficient to make 667,000 watches
luminous for many years. The factories of this country are now turning
out about four million radium watches annually.
Unless a special preparation--known only to the manufacturer--is
used, the luminosity of the material gradually disappears, owing to
the destruction of the zinc sulphide crystals by the powerful rays
constantly bombarding them, producing flashes at the rate of 200,000
a second. The radium itself does not glow, nor does it deteriorate in
power.
If we examine a luminous dial through a magnifying glass, after the
eyes have been in total darkness for a few minutes, tiny flashes of
light may be seen. These are caused by the explosion of hundreds of
millions of radium atoms. The more radium there is in the paint, the
greater the number of flashes per second, and the more durable the
luminosity. Since every flash means a blow upon a crystal of zinc
sulphide, the crystals gradually break under the strain. In this
process helium is released from the disintegrating radium atoms.
Mr. M. A. Henry (_Scientific American_, April 2, 1921) points out that
the problem of the chemist “is to produce a phophorescent substance
which will stand up longest under the terrific bombardment of the
radium rays and which, at the same time, will give off the most light.
Such progress is being made in this direction that today [1921] only
about one-twentieth the amount of radium used four years ago [1917] is
needed in the making of luminous material. And the chemist insists that
he has only scratched the surface of possibilities in this direction
and that even better results can be attained. At present the life of
the zinc crystals is from 15 to 20 years, although the radium lasts for
centuries.
“This life will be much longer if the instrument to which it is applied
is kept away from the light most of the time. The crystals, already
stressed by the radium rays, have an additional strain imposed by the
light and this hastens the process of disintegration. Strong sunlight,
especially at the seashore where the presence of much ozone in the air
intensifies the ultra-violet rays, has a very destructive effect on
luminous material. For this reason the manufacturers of this delicate
substance usually guarantee it for about half its normal life, or ten
years.”
A radium-lighted fish-bait is now on the market, and fishermen say that
this bait is very successful in attracting fish which haunt deep water.
RADIUM MAKES GEMS BLUSH
D. Berthelot, F. Bordes, C. Doelter, and others observed that the rays
from radium induced important changes in the colors of minerals.
Dr. T. Squance, of Sunderland, England, succeeded in transforming a
sapphire of faint pink hue into a gorgeous ruby color, and a faint
green sapphire into an oriental emerald hue. It was already known that
a diamond exposed to the rays of radium glows with a beautiful green
light.
In experiments carried out at the United States Bureau of Mines (1921),
in Reno, Nevada, a colorless Colorado topaz was tinted yellow by
exposure to penetrating radiation. If a method can be devised to make
the color permanent, the discovery will greatly increase the value of
the gem-stone material found in the west.
If we submit yellow phosphorous to the action of radioactive
substances, it becomes changed into the red “alotropic” variety.
Certain of the rays decompose ammonia, and water under their influence
is subjected to electrolysis, yielding oxygen and hydrogen.
A RADIUM CLOCK
A very interesting instrument was devised by Sir William Strutt (now
Lord Rayleigh) which has been called a “radium clock.” It consists of
a glass vessel containing a tube of radium salts in the center, from
which two gold leaves are hung. The inner surface of the containing
vessel is coated with tinfoil, and this foil is grounded. The radium
salts cause the leaves to become electrically charged. They then
diverge, and, coming in contact with the grounded tinfoil coating, they
are discharged, only to fall back again and repeat the process. This
clock will operate as long as the supply of radioactive material will
act, which in the case of pure radium would be nearly 2000 years.
G. Lentner has recently succeeded in utilizing atmospheric potential by
the aid of radioactive substances, which, in some way not yet clearly
understood, exert an influence upon the transformer. The method is
as follows: A post about 12 m. in height, forming a sort of antenna,
is erected; the post ends in a collector consisting of an aluminum
sphere provided with points covered with radioactive substances.
This collector communicates by a conducting wire with a special
transformer. Under these conditions the earth and atmospheric currents
attract each other through reciprocal induction.
Dr. S. A. Sochocky, the well known radium expert, has made radium
oil paints, and made paintings with them. “Pictures painted with
radium look like any other pictures in the daytime, but at night they
illuminate themselves and create an interesting and weirdly artistic
effect. This paint would be particularly adaptable for pictures of
moonlight or winter scenes, and I have no doubt that some day a fine
artist will make a name for himself and greatly interest us by painting
pictures which will be unique, and particularly beautiful at night in a
dark or semi-darkened room.”
Dr. Sochocky also predicts that “the time will doubtless come when
you will have in your own home (or someone you know will have) a room
lighted entirely by radium. It would be possible today to illuminate
a room, so that at night, without the aid of electricity or other
artificial illumination, you could read fine newspaper print without
difficulty. The light in such a room, thrown off by radium paint on
walls and ceiling, would in color and tone be like soft moonlight,
blue with a tint of yellow. Today, a room ten by nine feet could be
illuminated in this way at a cost of $400, and the illumination would
last ten years.
“However, such illumination will soon be much cheaper, because of new
discoveries as to the best materials to combine with radium to produce
light.”