RADIUM
Experiments of Becquerel--Work of the Curies--Discovery of
Radium--Enormous Energy--Various Uses.
Early in 1896 just a few months after Roentgen had startled the
scientific world by the announcement of the discovery of the X-rays,
Professor Henri Becquerel of the Natural History Museum in Paris
announced another discovery which, if not as mysterious, was more
puzzling and still continues a puzzle to a great degree to the present
time. Studying the action of the salts of a rare and very heavy mineral
called uranium Becquerel observed that their substances give off an
invisible radiation which, like the Roentgen rays, traverse metals and
other bodies opaque to light, as well as glass and other transparent
substances. Like most of the great discoveries it was the result of
accident. Becquerel had no idea of such radiations, had never thought
of their possibility.
In the early days of the Roentgen rays there were many facts which
suggested that phosphorescence had something to do with the production
of these rays It then occurred to several French physicists that X-rays
might be produced if phosphorescent substances were exposed to sunlight.
Becquerel began to experiment with a view to testing this supposition.
He placed uranium on a photographic plate which had first been wrapped
in black paper in order to screen it from the light. After this plate
had remained in the bright sunlight for several hours it was removed
from the paper covering and developed. A slight trace of photographic
action was found at those parts of the plate directly beneath the
uranium just as Becquerel had expected. From this it appeared evident
that rays of some kind were being produced that were capable of passing
through black paper. Since the X-rays were then the only ones known
to possess the power to penetrate opaque substances it seemed as though
the problem of producing X-rays by sunlight was solved. Then came the
fortunate accident. After several plates had been prepared for exposure
to sunlight a severe storm arose and the experiments had to be abandoned
for the time being. At the end of several days work was again resumed,
but the plates had been lying so long in the darkroom that they were
deemed almost valueless and it was thought that there would not be
much use in trying to use them. Becquerel was about to throw them away,
but on second consideration thinking that some action might have
possibly taken place in the dark, he resolved to try them. He developed
them and the result was that he obtained better pictures than ever
before. The exposure to sunlight which had been regarded as essential
to the success of the former experiments had really nothing at all to
do with the matter, the essential thing was the presence of uranium
and the photographic effects were not due to X-rays but to the rays
or emanations which Becquerel had thus discovered and which bear his
name.
There were many tedious and difficult steps to take before even our
present knowledge, incomplete as it is, could be reached. However,
Becquerel's fortunate accident of the plate developing was the beginning
of the long series of experiments which led to the discovery of radium
which already has revolutionized some of the most fundamental
conceptions of physics and chemistry.
It is remarkable that we owe the discovery of this wonderful element
to a woman, Mme. Sklodowska Curie, the wife of a French professor and
physicist. Mme. Curie began her work in 1897 with a systematic study
of several minerals containing uranium and thorium and soon discovered
the remarkable fact that there was some agent present more strongly
radio-active than the metal uranium itself. She set herself the task
of finding out this agent and in conjunction with her husband, Professor
Pierre Curie, made many tests and experiments. Finally in the ore of
pitchblende they found not only one but three substances highly
radio-active. Pitchblende or uraninite is an intensely black mineral
of a specific gravity of 9.5 and is found in commercial quantities in
Bohemia, Cornwall in England and some other localities. It contains
lead sulphide, lime silica, and other bodies.
To the radio-active substance which accompanied the bismuth extracted
from pitchblende the Curies gave the name _Polonium_. To that which
accompanied barium taken from the same ore they called _Radium_ and to
the substance which was found among the rare earths of the pitchblende
Debierne gave the name _Actinium_.
None of these elements have been isolated, that is to say, separated
in a pure state from the accompanying ore. Therefore, _pure radium_
is a misnomer, though we often hear the term used. [Footnote: Since
the above was written Madame Curie has announced to the Paris Academy
of Sciences that she has succeeded in obtaining pure radium. In
conjunction with Professor Debierne she treated a decegramme of bromide
of radium by electrolytic process, getting an amalgam from which was
extracted the metallic radium by distillation.] All that has been
obtained is some one of its simpler salts or compounds and until
recently even these had not been prepared in pure form. The commonest
form of the element, which in itself is very far from common, is what
is known to chemistry as chloride of radium which is a combination of
chlorin and radium. This is a grayish white powder, somewhat like
ordinary coarse table salt. To get enough to weigh a single grain
requires the treatment of 1,200 pounds of pitchblende.
The second form of radium is as a bromide. In this form it costs $5,000
a grain and could a pound be obtained its value would be
three-and-a-half million dollars.
Radium, as we understand it in any of its compounds, can communicate
its property of radio-activity to other bodies. Any material when
placed near radium becomes radio-active and retains such activity for
a considerable time after being removed. Even the human body takes on
this excited activity and this sometimes leads to annoyances as in
delicate experiments the results may be nullified by the element acting
upon the experimenter's person.
Despite the enormous amount of energy given off by radium it seems not
to change in itself, there is no appreciable loss in weight nor
apparently any microscopic or chemical change in the original body.
Professor Becquerel has stated that if a square centimeter of surface
was covered by chemically pure radium it would lose but one thousandth
of a milligram in weight in a million years' time.
Radium is a body which gives out energy continuously and spontaneously.
This liberation of energy is manifested in the different effects of
its radiation and emanation, and especially in the development of heat.
Now, according to the most fundamental principles of modern science,
the universe contains a certain definite provision of energy which can
appear under various forms, but which cannot be increased. According
to Sir Oliver Lodge every cubic millimeter of ether contains as much
energy as would be developed by a million horse power station working
continuously far forty thousand years. This assertion is probably based
on the fact that every corpuscle in the ether vibrates with the speed
of light or about 186,000 miles a second.
It was formerly believed that the atom was the smallest sub-division
in nature. Scientists held to the atomic theory for a long time, but
at last it has been exploded, and instead of the atom being primary
and indivisible we find it a very complex affair, a kind of miniature
solar system, the centre of a varied attraction of molecules, corpuscles
and electrons. Had we held to the atomic theory and denied smaller
sub-divisions of matter there would be no accounting for the emissions
of radium, for as science now believes these emissions are merely the
expulsion of millions of electrons.
Radium gives off three distinct types of rays named after the first
three letters of the Greek alphabet--Alpha, Beta, Gamma--besides a
gas emanation as does thorium which is a powerfully radio-active
substance. The Alpha rays constitute ninety-nine per cent, of all the
rays and consist of positively electrified particles. Under the
influence of magnetism they can be deflected. They have little
penetrative power and are readily absorbed in passing through a sheet
of paper or through a few inches of air.
The Beta rays consist of negatively charged particles or corpuscles
approximately one thousandth the size of those constituting the Alpha
rays. They resemble cathode rays produced by an electrical discharge
inside of a highly exhausted vacuum tube but work at a much higher
velocity; they can be readily deflected by a magnet, they discharge
electrified bodies, affect photographic plates, stimulate strongly
phosphorescent bodies and are of high penetrative power.
The radiations are a million times more powerful than those of uranium.
They have many curious properties.
If a photographic plate is placed in the vicinity of radium it is
almost instantly affected if no screen intercepts the rays; with a
screen the action is slower, but it still takes place even through
thick folds, therefore, radiographs can be taken and in this way it
is being utilized by surgery to view the anatomy, the internal organs,
and locate bullets and other foreign substances in the system.
A glass vessel containing radium spontaneously charges itself with
electricity. If the glass has a weak spot, a scratch say, an electric
spark is produced at that point and the vessel crumbles, just like a
Leyden jar when overcharged.
Radium liberates heat spontaneously and continuously. A solid salt of
radium develops such an amount of heat that to every single gram there
is an emission of one hundred calories per hour, in other words, radium
can melt its weight in ice in the time of one hour.
As a result of its emission of heat radium has always a temperature
higher by several degrees than its surroundings.
When a solution of a radium salt is placed in a closed vessel the
radio-activity in part leaves the solution and distributes itself
through the vessel, the sides of which become radio-active and luminous.
Radium acts upon the chemical constituents of glass, porcelain and
paper, giving them a violet tinge, changes white phosphorous into
yellow, oxygen into ozone and produces many other curious chemical
changes.
We have said that it can serve the surgeon in physical examinations
of the body after the manner of X-rays. It has not, however, been much
employed in this direction owing to its scarcity and prohibitive price.
It has given excellent results in the treatment of certain skin
diseases, in cancer, etc. However it can have very baneful effects on
animal organisms. It has produced paralysis and death in dogs, cats,
rabbits, rats, guinea-pigs and other animals, and undoubtedly it might
affect human beings in a similar way. Professor Curie said that a
single gram of chemically pure radium would be sufficient to destroy
the life of every man, woman and child in Paris providing they were
separately and properly exposed to its influence.
Radium destroys the germinative power of seeds and retards the growth
of certain forms of life, such as larvae, so that they do not pass
into the chrysalis and insect stages of development, but remain in the
state of larvae.
At a certain distance it causes the hair of mice to fall out, but on
the contrary at the same distance it increases the hair or fur on
rabbits.
It often produces severe burns on the hands and other portions of the
body too long exposed to its activity.
It can penetrate through gases, liquids and all ordinary solids, even
through many inches of the hardest steel. On a comparatively short
exposure it has been known to partially paralyze an electric charged
bar.
Heat nor cold do not affect its radioactivity in the least. It gives
off but little light, its luminosity being largely due to the
stimulation of the impurities in the radium by the powerful but
invisible radium rays.
Radium stimulates powerfully various mineral and chemical substances
near which it is placed. It is an infallible test of the genuineness
of the diamond. The genuine diamond phosphoresces strongly when brought
into juxtaposition, but the paste or imitation one glows not at all.
It is seen that the study of the properties of radium is of great
interest. This is true also of the two other elements found in the
ores of uranium and thorium, viz., polonium and actinium. Polonium,
so-called, in honor of the native land of Mme. Curie, is just as active
as radium when first extracted from the pitchblende but its energy
soon lessens and finally it becomes inert, hence there has been little
experimenting or investigation. The same may be said of actinium.
The process of obtaining radium from pitchblende is most tedious and
laborious and requires much patience. The residue of the pitchblende
from which uranium has been extracted by fusion with sodium carbonate
and solution in dilute sulphuric acid, contains the radium along with
other metals, and is boiled with concentrated sodium carbonate solution,
and the solution of the residue in hydrochloric acid precipitated with
sulphuric acid. The insoluble barium and radium sulphates, after being
converted into chlorides or bromides, are separated by repeated
fractional crystallization.
One kilogram of impure radium bromide is obtained from a ton of
pitchblende residue after processes continued for about three months
during which time, five tons of chemicals and fifty tons of rinsing
water are used.
As has been said the element has never been isolated or separated in
its metallic or pure state and most of the compounds are impure. Radium
banks have been established in London, Paris and New York.
Whenever radium is employed in surgery for an operation about fifty
milligrams are required at least and the banks let out the amount for
about $200 a day. If purchased the price for this amount would be
$4,000.