196 Oceanic and Littoral Manganese Nodules 



matter present, which shows that the shells were very old. 

 The insoluble residue was filtered, ignited, and weighed; it 

 weighed 0-0063 gramme = 0-4 per cent, insoluble residue. 

 To the filtrate from the insoluble residue added Fe 2 Q 6 and 

 precipitated all the P 2 O 5 with acetate of soda. In the filtrate 

 from this the manganese was precipitated with bromine. The 

 following results were obtained: 



Insoluble residue . . . . 0-40 per cent. 



P a O 5 0-09 



MnO i-oo 



Referring to Table II, page 180, it is apparent that, while 

 the percentage of insoluble residue in the oceanic and the littoral 

 nodules stands in the proportion 2:3, the percentage of silica in 

 these residues is almost identical. This is particularly remark- 

 able when it is borne in mind that the insoluble residue of the 

 Loch Fyne nodules consists principally of quartz sand, and 

 that in the nodules and muds of the great ocean the occurrence 

 of quartz is very exceptional, and then only in districts fre- 

 quented by icebergs. 



