726 DR JOHN MURRAY AND MR ROBERT IRVINE ON THE 



mouths of the streams was evidently due to the oxidation of the carbonate and its conse- 

 quent deposition on the stones of the bed of the stream as dioxide. We have, on the other 

 hand, examined large quantities of carefully-filtered sea- water from various regions of 

 the open ocean, but have never been able to detect manganese in solution, although, 

 as above stated, we have found traces of manganese in the clayey matter in suspension 

 in many of the sea-waters we have examined. The soluble bicarbonate of manganese, 

 which, as we have seen above, exists in the water of fresh-water streams, is probably all 

 deposited as dioxide on meeting with the alkaline and oxygenated water of the ocean. 

 It is generally stated that all elementary substances can be detected in solution in ocean 

 water ; still, as a matter of fact, all the samples of normal sea-water which Ave have had 

 under examination have not yielded any traces of manganese in solution.* A large 

 number of deposits from the boilers of sea-going steamships were likewise examined for 

 manganese, but no traces were found. These investigations seem conclusively to show 

 that manganese is not present in solution in the normal sea-waters of the ocean, and 

 consequently the material for the formation of the manganese nodules, so abundant in 

 the abysmal regions of the deep sea, cannot be derived from solution in the waters of 

 the open ocean. 



Manganese in Mud- Waters.^ — It has been shown that the sea- water associated with 

 the deposits on the floor of the ocean has a very different composition from the normal 

 superincumbent sea-water. A further examination of these mud-waters, and of the 

 changes taking place in the muds, has furnished important indications as to the source and 



* To determine the limits of detection of manganese in sea-water, standardised solutions of pure chloride of 

 manganese (in sea-water) were prepared, and after boiling with excess of bromine for some time the precipitated MnO a 

 was estimated. With solutions containing from 1 part in 15,000 to 1 part in 100,000, the separation was rapid and 

 apparently complete, and the precipitated dioxide was collected on a filter and weighed, after ignition, as Mn 3 4 ; with 

 solutions containing 1 part in 1,000,000, Mn0 2 separated out after boiling with bromine for some time. On treating a 

 solution of 1 part MnCl 2 in 10,000,000 of sea-water, the precipitate of Mn0 2 , after prolonged boiling with bromine, 

 was quite distinct, but in this case appeared as a brown scum on the surface of the liquid, and formed a distinct brown 

 ring round the walls of the white porcelain basin above the evaporating surface of the liquid. 



Having established this point, we endeavoured to find manganese by this method in fresh, clear, filtered sea-water, 

 obtained from the German Ocean. Two gallons were evaporated until the contained sea-salts began to crystallise out. 

 The liquid was filtered clear of deposited sulphates and carbonates, and treated with bromine. There was not even the 

 faintest trace of coloration. The basin in which this sea- water was evaporated was washed with hot hydrochloric acid, so 

 aa to decompose carbonates thrown down during evaporation, and the filtered liquid so obtained exactly neutralised with 

 ammonia, and thereafter treated with bromine. In this case there was not the faintest trace even of coloration. We 

 therefore conclude that in the sea-water samples examined by us, manganese, if present, could not have been there to 



ater extent than 1 part in 10,000,000. 



To confirm the above by more delicate tests, the two portions from the sea-water — viz., the strong brine and the 

 residue of salts treated witli hydrochloric acid — were boiled down until most of the salts had crystallised out. The 

 1 were separated, washed with pure hydrochloric acid, and the washings added to the mother liquor, which was 

 vaporated to dryness, ami ignited to drive off ammoniacal salts. This residue— in which we assume any man- 

 ganese present in solution in the original sea-water would appear — was then fused with carbonates of potash and soda 

 and a little potassium nitrate. The fluxed mass when cold was absolutely milk-white. This result (when the 

 extreme delicacy of this method of detecting manganese- is taken into account) points to the conclusion that manganese 

 is not present in solution in ordinary sea-water, at least within the chemical limits of observation at our disposal, 

 an 1 therefore ordinary sea-water cannot provide the material lor the formation of manganese nodules. 



t Murray and Ihvine, " On I In- ( Ihemical Changes which take place in the Composition of the Sea- Water associated 

 with Blue Muds on the Floor of the Ocean," Tram. Roy. Sot: Edin., vol. xxxvii. p. 481, 1893. 



