112 



equator, is 1027'77, and therefore a little exceeds that prevalent in 

 the Northern hemisphere, while it is decidedly less than that of the 

 Southern Ocean. There is no material difference between different 

 east and west longitudes at the equator, nor in the same hemisphere. 

 In general, the salt seems most abundant in the deepest water, and 

 in that furthest from land ; the vicinity of ice also diminishes the 

 saltness : if therefore this quality should increase in approaching the 

 pole, it may be considered as militating against the probability of the 

 ocean being extensively frozen in those regions. In general, small 

 inland seas, communicating with the ocean, are less salt than the 

 ocean itself. The waters of the Mediterranean, however, are more 

 saline, and in attempting to account for this circumstance, the au- 

 thor's attention is directed to the relative densities of water from dif- 

 ferent depths of the ocean ; and though in some cases it 'appeared 

 lightest at the surface, such a result was generally referable to the 

 vicinity of thawing ice, for, in ordinary circumstances, the density at 

 great. depths in no instance exceeded the mean density of the waters 

 of the ocean. In regard, however, to different seas or arms of the 

 ocean, the case is often different, in consequence of local circum- 

 stances. At the entrance of the Dardanelles, for instance, the dif- 

 ference between the upper and lower strata is as 1020 to 1028. 



Dr. Marcet next details some researches upon the congelation of 

 sea-water which takes place at 28, and when slowly effected, is 

 always attended by the total separation of the salt, which forms a 

 strong brine that is washed away by the neighbouring water. The 

 different specimens of water obtained from the ice in the late Northern 

 Expedition, varied very little in specific gravity ; the water was sweet, 

 and in many instances its specific gravity did not exceed that of dis- 

 tilled water. 



The second section of the author's paper relates to the saline con- 

 tents of different seas. In his experimental inquiries connected with 

 this subject, his objects were to ascertain the quantity of saline matter 

 in a known weight of the water, and to compare it with the specific 

 gravity : to precipitate the muriatic acid from a known weight of 

 the water by nitrate of silver ; the sulphuric acid by nitrate of ba- 

 rytes ; the lime by oxalate of ammonia ; and the magnesia, from the 

 clear liquor remaining after the separation of the lime, by phosphate 

 and carbonate of ammonia. The soda is inferred from calculation. 

 The details of these experiments are thrown into a tabular form ; 

 whence it appears that sea- water, however different in specific gra- 

 vity, contains the same ingredients all over the world, and that these 

 bear nearly the same proportions to each other ; the difference in 

 specific gravity is therefore dependent upon the whole quantity of 

 saline matter which they contain. The author concludes this com- 

 munication by announcing the discover)' of traces of potash in sea- 

 water by Dr. Wollaston. He detected it by the addition of muriate 

 of platina to the water, after evaporation to about one twentieth 

 part. 



