USE OF EADIO ACTIVE 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 

 greatest 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 



