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USE OF RADIOACTIVE SUBSTANCES AS FERTILIZERS. 13 
absence of uranium, or of such nonradioactive constituents as soluble 
salts and free acids. 
The subject of catalytic fertilizers is an interesting one, and worthy 
of careful investigation, but the manner in which they are able to 
influence so effectively the growth of plants is as yet but little under- 
stood. Until further knowledge is gained along this line, and par- 
ticularly until it is demonstrated that the application of such ma- 
terials to the soil will not lead to their accumulation with injurious 
results, the use of uranium, or of any of the other heavy metals, as a 
fertilizer in general farming is not to be recommended. 
SUMMARY. 
Attention is called to a new material which has recently been ex- 
ploited for use as a fertilizer, and which consists of the residual rock 
from which uranium has been removed, or of uranium-radium ores of 
too low grade to be used for the extraction of radium. This material, 
which is known as “radioactive manure,” is claimed by virtue of its 
activity to have a marked effect on stimulating the growth of plants 
when mixed with a relatively large amount of standard fertilizers 
and applied at the rate of 20 to 50 pounds per acre. 
When consideration, however, is taken of the facts: (1) That the 
ereatest quantity of radium which can exist in an ore amounts to 
only 0.00003 per cent; (2) that the intensity of the radium rays is 
limited by the quantity of radium present; (3) that all rays, like 
all chemical substances, must exceed in intensity or concentration, 
a certain limiting value to produce any noticeable results, or any 
results whatever; (4) that radium costs $120,000 a gram; and 
(5) that the activity of radium or any other radio-element can not 
be increased by any treatment whatsoever, but remains unchanged in 
whatever state of combination it may exist, it seems incredible that 
radium or any of its products can have any economical application 
as a fertilizer in general farming; and still less credible that the so- 
called radioactive manure has any value, as far as its radioactivity is 
concerned, since the radium already present, on an average, in an 
acre-foot of soil, is about 100 times greater than is contained in the 
quantity of radioactive manure commonly recommended for applica- 
tion to an acre. 
Many experiments have been made in studying the influence of the 
radio-elements, when freed from their ores, on the germination of 
seeds and the growth of plants, and from the results obtained it is to 
be expected that in botanical research, and possibly in greenhouse 
practice, where the results obtained may justify the expense involved, 
the radio-elements may prove of considerable value; but when con- 
sideration is taken of the scarcity of these elements it does not follow 
