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XXXII. — On the Manganese Oxides and Manganese Nodules in Marine Deposits* 

 By John Murray, LL.D., Ph.D., of the "Challenger" Expedition, and Robert 

 Irvine, F.C.S. 



(Read 21st May, 1894.) 



During the " Challenger " Deep-Sea Exploring Expedition a great many peculiar- 

 looking manganese nodules or concretions were dredged from the floor of the ocean at 

 great depths, chiefly in the Red Clay areas of the Pacific, but also in less abundance in 

 the Red Clays of the Atlantic. In the other varieties of Deep-Sea deposits these nodules 

 were much less abundant than in the Red Cla}^s. 



In still more recent soundings, both American and British ships have discovered in 

 many regions of the Pacific and Indian Oceans a dark-brown coloured deposit containing 

 a large amount of manganese dioxide, similar in character to the Red Clays from which 

 the " Challenger " procured the largest hauls of manganese nodules. There is then 

 every reason for supposing that manganese deposits and nodules are very widely dis- 

 tributed over the ocean's bed, especially in deep water at great distances from land. It 

 was only occasionally that manganese nodules were present in any abundance in a 

 Globigerina Ooze, and in these exceptional instances there was always much volcanic 

 debris associated with the deposit. In the Blue Muds surrounding continental shores 

 manganese nodules were rarely observed ; still, on some rocks and boulders dredged from 

 terrigenous deposits, a coating of manganese dioxide was observed on that portion of the 

 stone which had projected above the surface of the mud. 



The interest in these peculiar manganese deposits is much enhanced by the extra- 

 ordinary organic and mineral associates of the manganese nodules in the centre of the South 

 Pacific. In this region hundreds of sharks' teeth, many of them of gigantic size and 



* Manganese, symbol, Mn ; atomic weight, 55 (oxygen = 16), is a metal closely resembling iron, with which it is 

 most frequently associated. It is slightly magnetic. It has never been found native except in minute traces in 

 meteorites. When eliminated from its ores it is of a greyish- white colour, resembling cast-iron ; it has a specific gravity 

 of about 7 , 2-8 - (Mendeleeff). The metal was first isolated in 1774 by Salier. For a long time there was confusion 

 as to its name, and not till after the beginning of the present century was the name manganese generally adopted. The 

 Latin (manganesium) is arbitrarily altered from magnesium, and is rarely used in technical works. Magnesia was 

 the original name of the black oxide of manganese, which was used by the ancients for removing colouring matter from 

 glass, and was generally confounded with the lodestone (Magnes and Magnesius lapis). 



Its principal use is in the manufacture of ferro-manganese, which absorbs nine-tenths of the whole production. 

 The dioxide of manganese, in connection with hydrochloric acid, is the means at present adopted to produce chlorine 

 for bleaching purposes, but the decomposition of magnesium chloride, or the electrolysis of water with the production 

 of peroxide of hydrogen, may altogether revolutionise this process of bleaching. Small quantities of manganese are irj 

 demand to clear glass coloured by iron ; for certain alloys ; for the manufacture of pottery, electric piles, and colours. 

 Speaking generally, iron and manganese are the great pigments of nature. The annual production of manganese in 

 1891 was 316,000 tons, of which more than one-half was produced by Russia, principally from the Caucasus, where the 

 mineral is very rich, containing 90 per cent, of dioxide ; Germany, the United States, and Chili produce each between 

 25,000 and 40,000 tons annually ; Cuba, France, and Belgium each between 15,000 and 20,000 tons ; Great Britain 

 Sweden, and Austria each between 5000 and 10,000 tons. 



VOL. XXXVII. PART IV. (NO. 32). 5 R 



