184 On the Composition of Oceanic 



From these Tables it will be seen that nodules from all 

 localities have similar composition. The most important 

 difference between the littoral and the oceanic nodules is, that 

 in the former the manganese is less highly oxidised than in 

 the latter. In the oceanic nodules, when we consider the 

 manganese alone, the peroxide is very little short of MnO 2 ; 

 in the littoral ones it is very little over Mn 2 O 3 . In both oceanic 

 and littoral ones the manganese is more highly oxidised in the 

 kernels than in the rinds ; this difference is particularly marked 

 in the littoral ones. Nickel, cobalt, and copper are probably 

 present in all, but their relative proportions are different in 

 the littoral and in the oceanic nodules. Cobalt can be deter- 

 mined in both, and ranges from 0-02 per cent, in Loch Fyne 

 nodule M to 0-34 per cent, in oceanic nodule V. Nickel is 

 present in large though variable quantity in the oceanic nodules, 

 as much as 1-46 per cent, of oxide in II, falling to 0-47 per cent, 

 in V. In the Loch Fyne nodules the presence of nickel was 

 doubtful. Copper was present in both classes of nodule. In 

 the oceanic ones, however, the traces were not always very 

 distinct, whilst in the Loch Fyne ones they were very pro- 

 nounced. In testing for thallium, it was sufficient with oceanic 

 nodules to moisten a piece of the size of a bean with HC1 and 

 place it in a platinum triangle over a Bunsen burner to get a 

 strong thallium line in the spectroscope. Thallium could not 

 be detected in this way in the Loch Fyne nodules. 



The insoluble residues were always tested qualitatively, 

 and consisted, besides silica, of alumina and ferric oxide, with 

 smaller quantities of lime and magnesia. The silica, however, 

 of the Loch Fyne nodules was largely quartz, which was not 

 the case with the oceanic nodules. The percentage of insoluble 

 residue varies much in both sorts, but it is always greater in 

 the Loch Fyne ones than in the oceanic ones. The percentage 

 of silica in the Loch Fyne nodules varies very little from 25, 

 leaving from 2 to 6 per cent, of bases in the insoluble residue. 

 In the oceanic nodules, excepting IV, the silica varies between 

 14-68 and 17-46 per cent., leaving from 2 to 3 per cent, bases 

 in the residue. In IV the amount would be 4^. In the kernels 

 (K) the moisture driven off at 100, the carbonic acid, and the 



