Manganese nodules and oceanic radium 



337 



As in earlier experiments, thin layers were removed from the surface and from 

 layers immediately below it. Weighed quantities from these samples were dissolved 

 in hot hydrochloric acid, leaving a small undissolved residue, which was practically 

 free from radium. In some of the samples the content of manganese and of iron were 

 measured by colorimetric methods. The first column in Table 1 gives the average 

 " depth " of the sample below the surface of the nodule, the second column gives the 

 content of radium in the usual units of the 12th decimal place in gram per gram of the 

 sample. The maximum values obtained from the lower surface of the nodule are 

 seen to be 102 and 189 units of Ra, respectively, whereas from the upper surface the 

 values come out much lower, i.e. 38 and 61 units respectively. The fall-olf in radium 

 inwards is quite steep, to one half of the surface value or less for an increase in depth 



Table II 

 Station Albatross 173. Lat. S 8= 55'. Long. W 146 32'. Depth 4462 m 



of 1 mm. Attempts to calculate the rate of radial growth from the rate of this fall-off 

 gave values ranging from 0-6 mm to 1-4 mm in 1,000 years. The percentage of iron 

 is fairly high, between 13% and 18%, whereas the content of manganese is of the same 

 order varying between 18% and 29% of MnOj. 



Station 173. Lat. 18 55' S, long. 146 32' W, depth 2,440 fathoms. The description of the 

 nodules from this station given by Murray and Lf.f (1909, p. 146) runs as follows: 



" These nodules . . . constitute one of the most remarkable hauls of the cruise, .^t this station, 

 where the deposit is Red Clay, immense numbers were dredged, varying in size from that of a small 

 hazel-nut to potato-shaped nodules, three or four inches in diameter, and slabs over si.x inches in 

 length. . . . Although the shape varies, the surface characters are absolutely constant, and belong 

 to a type which was met with only at this particular spot. The surface of all the nodules, large and 

 small, is even, that is to say, not covered with protuberances, but it is not smooth, being covered with 

 numberless, closely set mammillae, giving it the appearance of shaga-en or coarse leather. On 

 account of the presence of these mammillae— I mm in diameter, as a rule— the surface is dull, not 

 shining. The colour is brown, never black. The external layer, from 1 to 2 mm in thickness, peels 

 off easily. In some cases the layer coming next to it shows shagreen structure; in other cases it docs 

 not, being smooth. This external layer is generally the only one that can be removed ; the rest of the 

 nodule is very compact, and so hard as to be scratched with a knife only with dilliculty. W hen whole 

 and with no fracture previously existing, the nodules cannot be broken in the hand, even when great 

 strength is exerted; the specific gravity is very high. 



