392 



J. G. Sanderson — Radio-active Content of 



Macbe units the increase was 107 per cent. Some poppies 

 gained 117 per cent in the fruit and 32 per cent in the stems. 

 Various vegetables and grains were grown in ordinary soil, 

 but with the air surrounding them charged with radium 

 emanation ; these showed earlier maturity and increased yield 

 of from 30 to 90 per cent. In all cases they found that large 

 quantities of emanation, in either the soil or the air, injured 

 and retarded the plants. Dr. H. H. Rusby, of Columbia 

 University, has done some very interesting work along these 

 lines. Unfortunately only a popular account of it is at hand. 

 He used radium ore tailings, containing small residual quanti- 

 ties of radium, to enrich several acres of land. Great care was 



Fig. 1. 



fcto 



A 





A 



VOJ 



~~\o L_ecx4 



M 



taken to standardize the work, and all plots, enriched and con- 

 trol, were treated exactly alike. Only three of twenty-seven 

 kinds of vegetables failed to show a gain due to the radio-active 

 enrichment, and the average increase was fully thirty per cent. 

 Dr. Rusby also found that too much radio-active material had 

 a detrimental effect. 



In view of these results, it seemed desirable to determine the 

 radio-active content of several soils from different localities, to 

 see whether there is any apparent interdependence between 

 the radio-activity of a soil and its fertility. First it was neces- 

 sary to modify the radium method so that it became. applicable 

 to comparatively same samples of soils. 



Apparatus. 



The electroscope and ionization vessel were of the same type 

 as those described in the article cited above. The cylindrical 

 ionization vessel, 35 centimeters in height and 14 centimeters 

 in diameter, was provided with brass connecting tubes, one 

 near the top and one near the bottom. The central electrode, 



