176 On the Composition of Oceanic 



a water-bath to get rid of all excess of hydrochloric acid ; the 

 residue taken up with water; the solution filtered again if 

 necessary ; and the manganese precipitated by pure carbonate 

 of soda solution, only a very slight excess being used. The 

 MnCO 3 was washed first by decantation, then dried, and ignited 

 to Mn 3 O 4 . 



The filtrate from the MnCO 3 was always kept over-night, 

 when sometimes a second minute precipitate came down. 

 The Mn 3 O 4 was kept, and the nickel and cobalt in it determined 

 afterwards. 



(b) The filtrate from the MnO 2 precipitate with bromine 

 was, in the case of the "Challenger" nodules, neutralised with 

 NH 4 OH, and then excess of NH 4 HS added, the flask filled 

 up and corked, and allowed to stand for one or more days. 

 Generally a minute black precipitate, accompanied by much 

 barium sulphate, came down. This was filtered off, ignited, 

 dissolved in HC1, the solution evaporated to dryness in a 

 small basin, the residue taken up with water, and preferably 

 a drop of H 2 SO 4 , and filtered. In the filtrate the nickel oxide 

 was precipitated by a drop or two of pure caustic potash. 

 After ignition this precipitate was always tested for purity. 

 It is better, however (and this was done in the case of the 

 Loch Fyne nodule), to neutralise the filtrate from the MnO 2 

 with NH 4 OH, add NH 4 HS, and then acetic acid in excess, and 

 pass H 2 S gas through the gently-warmed solution (as is done 

 in the separation of MnO from NiO and CoO). Thus, after 

 standing over-night, minute traces of nickel came down, which 

 remained dissolved in the NH 4 HS solution. 



E. The Mn 3 O 4 precipitates were dissolved in a few drops of 

 strong HC1 in a small basin, the solution evaporated to dryness 

 over the water-bath, taken up with water, and the solution 

 filtered. To the filtrate, after neutralising any trace of acid 

 present with NH 4 OH, sulphide of ammonium and acetic acid 

 were added, and sulphuretted hydrogen gas passed through the 

 gently-warmed solution to precipitate the nickel and cobalt 

 as sulphides. After standing over-night (the flask being full 

 and corked) this precipitate was filtered off, and the filtrate 

 treated in the same manner with ammonia, ammonium sulphide, 



