4 BULLETIN 149, U. S. DEPARTMENT OF AGRICULTURE. 



would be found in all soils x and in much larger amounts than radium, 

 for the reason that they occur in nature in much larger quantities. 

 The ordinary elements could not have been discovered if this were 

 not the case. Most soils differ but little in their radium content, as 

 must follow from the fact that almost all rocks 2 which do not contain 

 uranium ores contain pretty much the same quantity of radium. 



On an average the radium present in an acre-foot of soil amounts 

 to about 3.6 milligrams- 3 The radium present in 1 ton of carnotite 

 ore containing 2 per cent of uranium oxide (U 3 O s ) amounts to 5 

 milligrams. To duplicate the amount of radium in an acre-foot of 

 soil would therefore require about three-fourths of a ton of 2 per 

 cent carnotite ore from which radium has not been extracted, and 

 which brings about $80 a ton wholesale. It is thus quite evident that 

 to increase the radium content of the soil to any great extent by the 

 use of carnotite or any other radium ore is out of the question as an 

 economic proposition. 



The chemical properties exhibited by an element in combination 

 depends on whether the element occurs in a soluble or insoluble form. 

 Thus, the addition of a comparatively small amount of a soluble 

 potash salt has a marked effect on the growth of plants, while the cor- 

 responding amount of an insoluble potash silicate would have little or 

 no effect so long as it remained insoluble. As already explained, the 

 property of radioactivity does not change in this way with the form 

 of combination and a given weight of radium in the soil has exactly 

 the same activity as the same weight of radium in any other form of 

 combination that can be added. The argument, therefore, can not 

 be advanced that the radium in radioactive manure is in a more active 

 form than that already present in the soil. 



3. When a preparation of radium which has been freed from its 

 products is allowed to stand for a time, the products are again formed 

 and finally reach a state of equilibrium with the radium. When this 

 is the case, the material has its greatest activity, and any prepara- 

 tion which is allowed to stand for a time always consists of a mixture 

 of radium and its products. The first of the products to be formed 

 from radium is a gas called radium emanation. Since radium itself 

 gives off rays, while radium emanation is a product of radium, the 

 activity of radium emanation in equilibrium with its products must 

 always be less than that of radium in equilibrium with its products. 

 It therefore follows that no preparation of radium emanation can be 

 obtained which is more active than the radium available. 



When the radium emanation is removed from a preparation of 

 radium, the total radiation evolved from the two sources remains the 



1 The presence of the rare earths and other rare elements in all soils examined has 

 been demonstrated by W. O. Robinson of the Bureau of Soils. Bui. 122, U. S. Dept. Agr. 

 2 Strutt, Proc. Roy. Soc. Lond., (A) 77, 472 (1906). 

 3 Moore, J. Ind. Eng. Chem., 6, 373 (1914).' 



