8 BULLETIN 149, U. S. DEPARTMENT OE AGRICULTURE. 



but not too great a concentration, is used stimulating effects are to be 

 expected in some cases at least. In fact it is to be expected, although 

 not yet clearly demonstrated, that in greenhouse practice and in 

 botanical research, where the results obtained might justify the ex- 

 pense involved, the radio-elements may prove of very great value, as 

 they have done in other branches of science. When consideration, 

 however, is taken of the scarcity of these elements, it does not follow 

 from any experiment so far described that such elements can have 

 any practical application as a fertilizer in general farming. To 

 increase the activit}^ of the atmosphere above the soil with radium 

 emanation would not be feasible in field practice, neither would it 

 be practical to add such a quantity of radioactive material to the soil 

 that the emanation in the underground air would be increased to 

 even the very low concentration used in Stoklasa's experiments, and 

 the same may be said with regard to making irrigating water radio- 

 active. 



COMPOSITION OF RADIOACTIVE MANURE. 



The source of the so-called radioactive manures consists of the 

 residual rock from which carnotite or other uranium ores have been 

 extracted; or of uranium ores which contain too low a percentage 

 of uranium to make it profitable to extract the radium. Since an ore 

 containing as low as 2 per cent of uranium oxide can be profitably 

 used in the manufacture of radium, it is not to be expected that this 

 percentage of uranium, or its equivalent of radium, will be found in 

 any radioactive manure. 



In the following table is given the composition of samples of radio- 

 active materials which have been applied as a manure. 



Analyses of samples of radioactive manure. 



Constituent. 



Silica (SiOs) 



Oxide of iron and alumina 



(Fe,0 3 +Al 2 3 ) 



Lime(CaO) 



Magnesia (MgO) 



Soda(Na-O) 



Potash (K 2 0) 



Sulphide (S) 



"Sulphuric acid " 



5.40 



85.90 



8.65 

 .91 

 .95 

 .50 



1.04 

 .16 



Constituent. 



Phosphoric anhydride (P0O5). 



" Soluble phosphoric acid " 



" Water, volatile organic mat- 

 ter'' 



"Soluble salts, soluble free 

 acids " 



Uranium (IT) 



Activity. 



1.37 

 10.54 



3.32 



Trace. 



Trace. 



0.93 



Too" 



.03 U 



.037U 



A. Radioactive manure. Analysis according to Foulkes. Bui. Bureau Agricultural 

 Intelligence and of Plant Diseases, 3, 1112. This apparently represents ore from which 

 the uranium has been extracted. The acidity of the material was equivalent to 65 grams 

 of sulphuric acid per kilogram. 



B. Radioactive manure. Analysis by author. This material represented the original 

 ore and therefore did not contain any free acid. 



FIELD TESTS WITH RADIOACTIVE MANURE. 



Field tests with radioactive manure (A in table) hate been made 

 by Foulkes 1 in England. The material used contained only a trace 

 of uranium, but had an activity equal to 0.03 time's that of uranium. 



1 Bui. Bureau of Agricultural Intelligence and of Plant Diseases, 3, 1111 (1912). 



