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XXIII. — On the Chemical Changes ivhich take place in the Composition of the Sea- 

 Water associated with Blue Muds on the Floor of the Ocean. By John Murray, 

 LL.D., Ph.D., and Kobert Irvine, F.C.S. 



(Read March 7, 1892 ; Revised June 1893.) 



The numerous analyses of sea- water by Forchhammer previous to 1865, and the later 

 analyses by Dittmar, from samples collected during the " Challenger" Expedition, show 

 that while the salinity — i.e., the amount of dissolved salts contained in 100 parts of sea- 

 water — varies greatly in different regions of the ocean, still the composition of these 

 dissolved salts — i.e., the ratio of the constituents of sea-salts — remains practically the 

 same in all the superficial waters of the ocean. Consequently, it is only necessary to 

 determine the chlorine in a definite weight of water to ascertain at once the respective 

 quantities of the other salts present in the sample. Dittmar's examination of the 

 " Challenger " waters has, however, shown that lime is slightly, although distinctly, more 

 abundant in samples of sea-water collected in greater depths than in those samples 

 collected nearer the surface of the ocean, and Dittmar's tables showing the difference 

 between the chlorine calculated from the specific gravity and the chlorine found by 

 analysis * point to differences in the composition of the sea-salts, but the observations 

 are relatively so few, these differences so slight, so mixed up with observational errors, 

 and so irregular in their geographical and bathymetrical distribution, that they cannot be 

 said to indicate any general law other than a greater quantity of lime in deep water. 



The variations in the composition of sea-water salts, here alluded to, cannot in any 

 appreciable degree be referred either to precipitation or to fresh water poured into the 

 ocean from the land by rivers, nor, except the case of the lime in the deep waters, can they 

 be regarded as constant, for just as in the air any chance deviations from the normal com- 

 position are soon rectified through aerial circulation, so in the ocean any deviation from 

 the normal composition of sea-salts is soon, though more slowly, set right by oceanic 

 circulation. It is, however, important to investigate the causes of these variations. 



There is abundant evidence that great changes in chemical composition take place in 

 the substances deposited on the floor of the ocean, and, with the view of throwing some 

 light on the manner in which these changes are brought about, it has occurred to us to 

 examine the composition of the sea-water associated or mixed up with marine deposits 

 on the floor of the ocean, and especially with that variety of marine deposits known as 

 Blue Mud. 



The marine deposits, which everywhere cover the floor of the ocean, are divided into 



* Dittmar, " Challenger Report on the Composition of Ocean Water," Phys. Cliem. Chall. Exp., pt. i. p. 43. 

 VOL. XXXVII. PART II. (NO. 23). 4 D 



