DEEP-SEA RADIUM 121 



units of the twelfth decimal place, i. e. 50 X 10'^^ 

 gr Ra / gr sediment," would require a concentration 

 of uranium 3,000,000 times higher, or 150 X 10"'^ 

 gr U / gr sediment I Nevertheless it appeared desirable 

 to find out by dependable measurements how much 

 uranium is actually present in sediment cores, especially 

 in layers where there is a high concentration of radium. 



The fluorescence method worked out for measuring 

 uranium in sea water is excellent, but in sediment sam- 

 ples the presence of certain other chemical elements 

 like magnesium and manganese, difficult to separate 

 completely from the uranium, interferes with the 

 fluorescence in ultraviolet light of the latter element. 



In earlier attempts to apply the fluorescence method 

 to uranium determinations of deep-sea sediments these 

 difficulties were not completely overcome, and the 

 results were accordingly inaccurate. Thanks to helpful 

 cooperation from Hecht, who devoted two months in 

 Goteborg to collaboration with Kroll, the difficulties 

 were finally surmounted, so that accurate uranium 

 measurements could be carried out on a number of 

 sediment samples. Some of the results obtained by 

 Hecht and Kroll on samples from cores raised by the 

 "Albatross" are set out in the following table. The first 

 column gives the number of the core, the second the 

 depth below its upper end from which the samples 

 analyzed were taken, the third the uranium content in 

 millionths of the weight, the fourth the corresponding 



* Gram of radium per gram of sediment. 



