CHEMICAL CHANGES IN THE COMPOSITION OF SEA-WATER. 499 



Our attention has been recently drawn to a most interesting paper, read before 

 the British Association, Edinburgh (1892) Meeting, by N. Andrtjssow, on the Russian 

 Exploration of the Black Sea.* 



The condition of the water in the Black Sea below the 100-fathom line, in which 

 hydrosulphuric acid and sulphides exist in great abundance, is due to the same action as 

 that now being carried on so widely in the formation of the Blue Muds on the ocean 

 floor, viz., the deoxidation of the sulphates in the water by organic matter, and not, 

 as stated in Andrussow's paper, as simply the decomposition-products after death of a 

 great number of organisms. But a compound or double reaction appears in this instance 

 to be taking place, viz. — 



Firstly, on those portions of the bottom within a moderate distance from the shore 

 ordinary Blue Mud containing sulphide of iron (in large amount) is being deposited. 



Secondly, in the deep water, especially far from the shore, below 100 fathoms where 

 the oxygen has been used up, the hydrosulphuric acid, not having enough iron in the 

 form of floating mud to combine with, or to fix it as sulphide of iron (FeS) is found in 

 the free condition. At the same time there must be a large quantity of free or loosely- 

 combined carbonic acid in the water, the result of the deoxidation of the sulphates by 

 organic matter, which naturally would decompose the sulphides at their inception (or as 

 these are formed). That this is probably the case appears from the fact that in the 

 greater depths of the Black Sea, far from land, there exists a large deposit of mud con- 

 sisting principally of carbonate of lime, precipitated from its waters, which hold in solu- 

 tion lime and other salts as well as hydrosulphuric and carbonic acids. In the laboratory 

 experiments noted above we have the rationale of these conditions. 



Dr Andrussow has been so good as to send us samples of the Black Sea muds for 

 examination, but it would be of great interest could we have a complete analysis of the 

 light-coloured mud as it is in situ or before exposure to the air, for we are led to suspect 

 that it contains free sulphur, one of the products of the oxidation of hydrosulphuric acid. 

 Of course, this oxidation can only occur above the 100-fathom line, where the free oxygen 

 in the water has not all disappeared. 



We would recall attention to the somewhat curious reaction, referred to at page 497, 

 in which carbonic and hydrosulphuric acids displace one another from their combinations 

 whenever one or other is in excess, so that actually the condition of the deep water in 

 the Black Sea may be thus in a state of continual change, the alkalinity in this case 

 being due either to sulphides or carbonates in so far as carbonic acid or hydrosulphuric 

 acid predominates, and not wholly to carbonic acid as in the open ocean, where sulphides 

 cannot remain permanent owing to the constant excess of oxygen present ; but it is evident 

 that, since the light grey mud consists principally of carbonate of lime, the carbonic acid 



* " On Deep-Sea Research in the Black Sea," giving the results of an expedition (under the superintendence of Colonel 

 J. B. Spindler) sent out by the Russian Government in 1890 and 1891. These results have already been partly pub- 

 lished in the preliminary transactions of the Russian Geographical Society (in Russian), the physical results in German 

 by Prof. Woicjkoff in Petermann's Mitteilungen. An abstract of Andrussow's paper has been published in the 

 Royal Geographical Society's Journal, January 1893, giving a very fair epitome of the various points dealt with. 



