Geology Reference
In-Depth Information
the eyeball and affecting the retina'. One shudders to think of
the damage done to these poor individuals.
The third discovery concerned helium, the lighter-than-air-
gas we are all familiar with in party balloons which fly off into
the stratosphere when young children accidentally let them go.
Helium was not discovered until 1868, when it was first seen in
the sun during an eclipse, and it was not until 1895 that it was
identified here on Earth. But although helium is the second most
abundant element in the universe (after hydrogen), given its
chemical properties it is not surprising that it was discovered so
late - uranium for example was found in 1789. Once it was found
on this planet, however, it was soon noted that helium invari-
ably occurred in rocks that also contained radioactive elements
such as uranium and thorium. It was therefore not long before
Rutherford and Soddy suggested that the presence of helium in
rocks might be related to radioactive decay.
In 1903, Soddy left Rutherford's laboratory in Montreal to
work with Sir William Ramsay at University College in London,
so in order to avoid unnecessary duplication, Rutherford had out-
lined a scheme of future work for Soddy before he left and it was
agreed that Rutherford would examine whether helium was pro-
duced from radium. But Rutherford spent that summer in
England and heard that practically pure radium bromide was
being sold by the altruistic Professor Giesel at the very low price
of about one pound per milligram. Both Ramsay and he pur-
chased some of this material. Rutherford recalled what happened
next:
I remember well a visit I made to Soddy at University College on the
day when Ramsay and he were to collect the emanation [radon] from about
.20 milligrams of radium to test whether they could detect its spectrum.
Soddy told me he would take this opportunity of noting whether any heli-
um was released from the radium
.
Dissolving the precious radium bromide in water, the three of
them waited expectantly for a wild miracle. Sure enough, the
small bubble of gas that rose up through the water was found to
