174 n th e Composition of Oceanic 



The analysis of these samples was undertaken at first only 

 to show the state of oxidation of the manganese. In the case 

 of the Loch Fyne nodules, it was carried further, with a view 

 of showing the nature of the other principal constituents. The 

 analyses under the letters X, Y, and Z constitute together a 

 complete analysis, though it was not at first intended to be 

 such, otherwise the whole of the requisite material would have 

 been prepared and extracted at once. These analyses were 

 made in 1879 by Dr George M'Gowan, F.R.S.E., now of 

 Bangor, and were carried out with the greatest care and 

 attention. 



ANALYTICAL METHOD FOLLOWED FOR THE DETERMINATION OF 

 THE STATE OF OXIDATION OF THE MANGANESE. 



The analysis of these nodules was conducted as follows 

 (any particular point relating to any one nodule will be given 

 in detail along with the analysis of that nodule) : 



A. The nodules were reduced to an impalpable powder in 

 an agate mortar, and were not dried previous to analysis. 



B. In two separate portions (of about 2 decigrams each) 

 the available oxygen was determined by Bunsen's iodometric 

 method. 



C. Two portions, of about 0-5 grams each, were dissolved 

 in about 5 c.c. of pure strong hydrochloric acid, in a small 

 covered beaker, heat being applied cautiously at first to prevent 

 loss by effervescence of chlorine. The mixture was then 

 evaporated to dryness over a water-bath, covered with a glass 

 shade ; the residue, when free from all excess of acid, moistened 

 with a few drops of strong hydrochloric acid, and the insoluble 

 residue filtered off, ignited, and weighed. 



(a) Insoluble Residue. This insoluble residue was kept in 

 a corked tube, and afterwards fused with (NaK)CO 3 (in the 

 proportion of about four parts of carbonate to one of residue) 

 for the estimation of silica. The filtrate from the silica was 

 examined qualitatively for the bases present. 



(b) The filtrate from the insoluble residue was treated with 

 a moderate excess of pure carbonate of baryta. In practice 



