188 



MARINE BOTTOM SAMPLES OF LAST CRUISE OF CARNEGIE 



centration of 6 x 10" grams per cc, we find that the 

 uranium is not greatly different from other well-known 

 metallic constituents such as: 



Si02 1 ^ 10"^ g per cc 



Silver 1 x 10"'' g per cc 



Gold 6 X 10-10 g per cc 



There are probably several factors aiding in its separa- 

 tion and concentration in those places where it is found 

 to be most abundant. Skeletal remains may take down 

 some, also dust particles of volcanic or other origin ad- 

 sorb some and sweep it to the bottom, but probably the 

 greater proportion comes out as the result of oxidation. 

 Water which is near enough to continents or shallow 

 enough to have sufficient organic material at the bottom 

 to maintain a slightly reducing environment tends to 

 keep its uranium in solution, whereas the very deep bot- 

 tom waters far from land do not contain organic material 

 either washed from the land or as undestroyed organ- 

 isms, consequently they afford an oxidizing environment. 

 That these waters are oxidizing is borne out by the di- 

 rect measurements of the oxygen content with depth made 

 by the Carnegie, a typical graph of which findings is 

 shown in figure 2. This shows that the environment at 

 the bottom of the ocean is of an oxidizing rather than 

 reducing nature. In the deeper parts of the ocean where 

 there is little movement, the water at the bottom must 

 be at saturation with respect to the oxides of uranium. 



There is, therefore, a tendency for them to separate out 

 just as the iron and manganese do. Volcanic dust, de- 

 trital material, and skeletons of organisms modify the 

 possible concentration by diluting it. 



Summary 



The radium content of twenty-eight (twenty-seven 

 from the Pacific) samples of ocean-bottom sediments 

 was determined, and similar determinations reported by 

 Joly and Pettersson are included for comparison. These 

 comprise practically all such determinations that have 

 been made, and the paucity of these data in comparison 

 with the extent, importance, and high radium content of 

 the material is emphasized. Those bottoms composed 

 mostly or entirely of red clay generally contain more 

 radium. A mechanism for explaining the high radium 

 content of deep-sea sediments is suggested which does 

 not coincide with the opinions of either Joly or Petter- 

 sson. 



Acknowledgment 



Thanks are hereby extended to Dr. H. E. Merwinfor 

 his helpful cooperation in discussion, advice, and micro- 

 scopical examinations. 



LITERATURE CITED 



Fletcher, A. L. 1912. Phil. Mag., vol. 23, p. 279. 

 Joly, J. 1908. Phil. Mag., vol. 15, p. 385. 



1908. ibid ., vol. 16, p. 190. 



1912. ibid-, vol. 24, p. 702. 



Pettersson, Hans. 1930. Teneur en radium des depots 



merprofonde. R^sultats des campagnes scientif iques 

 accomplies sur son yacht par Albert icr. Prince 

 Souverain de Monaco, no. 81, pp. 50. 

 Strutt, R. J. 1907. Proc. R. Soc. London, vol. 78A, 

 p. 150. 



