540 THE POPULAR SCIENCE MONTHLY. 



that remains liquid. Under the influence of variations of temperature, 

 all the chlorides in the block will gradually disappear : some go into 

 the sea and are dissolved ; while the rest appear on the surface and 

 form hydrated crystals, or a kind of " salt-snow." The sulphates thus 

 prevail exclusively in old ices, which, according to Mr. Petterssen, 

 constitute mixtures of solidified water and a peculiar chemical com- 

 pound, the criohydrate of sulphate of soda, a body which, containing 

 five parts of soda to ninety-five of water, is decomposed at a little be- 

 low the ordinary freezing-point. 



By these phenomena of selection, ice, under atmospheric vicissi- 

 tudes, approaches a limit when its composition Avould be fixed, without 

 reaching it in reality. Usually, the expulsion of chlorides is not com- 

 plete, and sudden changes of temperature may liquefy it at once. The 

 Swedish observer compares the ice of salt-water with a kind of granite, 

 each constituent of which should take its turn at decomposing under 

 special circumstances. The warm waters farthest from the pole would 

 bear only the stable constituents brought down by the Arctic current, 

 so that, to continue our comparison, the river, which has gradually 

 eaten away the granite block, finally transports the last remains of the 

 rock in the form of sands and clays, which are destined to accumulate 

 in the sedimentary deposits. 



Over and above the substances that exist in considerable propor- 

 tions, many rarer elements are found in the waters of the ocean ; min- 

 erals, gases, and organic remains, difficult perhaps to recognize, some- 

 times impossible to estimate, but which nevertheless play an important 

 part. The phenomena of accumulation which we have considered are 

 absolutely insignificant in comparison with the absorbing power of 

 some of the algte. In them Courtois discovered iodine in 1812, and 

 Malagutti, after laborious researches, detected copper, lead, silver, and 

 ii'on, metals which he afterward found in sea-water itself. The quan- 

 tity of iodine contained is so little appreciable that many doctors have 

 denied the therapeutic virtues which others have attributed to this 

 water. Nevertheless, absorbed and condensed by marine plants, it 

 becomes abvmdant enough to be extracted with profit. It likewise 

 accumulates in animal oi'ganisms ; and cod-liver oil owes its beneficent 

 properties to it. The silver was absurdly attributed by Proust to the 

 treasures of shipwrecked vessels. But the quantity, though infinitesi- 

 mal in a measured quantity of water, is in the aggregate immense. 

 Malagutti more rationally refers its origin to the solution of the lead- 

 ores, very abundant all over the globe, with which sulphurets of silver 

 and copper are combined. By the action of salt, the sulphurets are 

 converted into chlorides. As to iron, it would be strange if so uni- 

 versal a substance were not found in the sea ; and the same may be 

 said of phosphoric acid. 



The researches of M. Dieulefait into the presence of lithium in 

 sea-water have shown that the Dead Sea is an independent body of 



