USE OF RADIOACTIVE SUBSTANCES AS FERTILIZERS. 3 
PROPERTIES OF THE RADIO-ELEMENTS. 
The properties of the radio-elements have been investigated by 
many of the leading scientists of the present day and have conse- 
quently been determined with a degree of exactness and completeness 
which perhaps has never before been equaled in any other branch 
of science in the same length of time. 
The following points with regard to these properties may be 
enumerated as having bearing on the fertilizing value of radioactive 
material: 
1. An element is said to be radioactive when it has the property 
of disintegrating or changing into another element. This property 
of radioactivity as exhibited by radium, which is the best known 
popularly of the radio-elements, is one which is inherent in the atom. 
No substance can be radioactive which does not contain an element 
which would be radioactive if separated from the substance, and, 
conversely, if a substance contains such an element, it must be radio- 
active. Some of the radio-elements, like the ordinary elements, do not 
give off any rays; others give off one kind of rays only; while still 
others give off two different rays, each of which may differ from the 
single radiation, thus making altogether three different kinds of rays. 
No inactive substance can be made radioactive by exposure to any of 
_ these rays. The activity of a given quantity of a radioactive element, 
_ like uranium or radium, remains unchanged in whatever chemical or 
physical state it may exist, whether combined in a soluble or insolu- 
_ ble compound, and whether or noi it may be mixed with any sub- 
_ stance or substances whatsoever. It therefore follows that its activity 
- can not be intensified by mixing with barnyard manure, as is some- 
times claimed. 
2. Radium is a product of uranium and can not occur in nature in 
quantity exceeding the amount with which it is in equilibrium with 
uranium. For this reason the highest concentration of radium which 
can ever be found in any ore will amount to only one part of radium 
in 3,460,000 parts of ore. This quantity of radium is so small that 
if chemical tests alone had been applied neither radium nor any of 
its products could ever have been identified. There are physical 
_ tests, however, which are much more delicate than any chemical tests. 
_ Thus, when the spectroscopic test is applied to lithium, an element 
_ which according to chemical tests is of very limited distribution, it 
is found to be almost universal’y distributed, and in no spring water, 
| for example, dces the test fail to reveal its presence. The electro- 
a scopic test for radium is even much more delicate than the spectro- 
a scopic test just cited, and it thus happens that radium which occurs 
in soils, for eae in such minute quantities can nevertheless be 
identified in all soils. If the same delicate test could be applied to 
all the ordinary elements, it is universally admitted that they, too, 
