40 



The Sea-water and ifs Physical and Chemical Properties 



the elements that are present in somewhat greater concentration may be mentioned 

 iron, copper and gold. Iron is present in extremely small quantities and sea-water 

 is probably one of the naturally occurring materials poorest in iron. The importance 

 of copper can be seen from its occurrence in place of iron in the blood pigments of 

 many marine animals (hccmocyanin). The occurrence of gold in sea-water at one 

 time aroused particular interest since, according to older determinations, the isola- 

 tion of gold from sea-water was technically promising. These older determinations 

 have, however, been shown by the results of Haber (1928) and Jaenicke (1935) to 

 be incorrect, and the gold found came largely from the reagents used, from the air and 

 from the glass of the apparatus. The gold content of sea-water found by analysis of 

 the samples collected on the "Meteor" Expedition was only 4 x lO"'* g/kg of sea- 

 water, a concentration which would be of no technical use. 



Table J I. Concentrations of the trace elements present in sea- 

 water in milligrams per cubic metre 

 (According to Kalle, 1945) 



The radioactivity of sea-water has been accurately investigated in recent times, and 

 detailed examinations have been made principally by Pettersson (1937, 1938), and 

 Thompson and his collaborators (1932). According to these investigations the radium 

 content of sea-water with a salinity of 35%o varied between 0-04 and 0-2 x IQ-^^ o/^ 

 (or between 0-04 and 0-2 billionth parts of a gramme per litre); 0-07 x 10-^^ 0/^ 

 radium can be taken as mean value. Deep water has a uranium content of 1-5-2 x 

 10"'' %o; surface water has a somewhat lower value. The thorium content is less 

 than 0-5 x 10-« %«. 



Since the radium content of sea-water is 10-000 times less than that of rocks of the 

 Earth crust, it is extremely small and corresponds to only 10% of the amount that 

 would be in equilibrium with the uranium content. According to the view of Petters- 

 son, this remarkable deficiency of radium in the sea can be attributed to the very 

 rapid precipitation of the iron carried into the sea, almost entirely as ferric hydroxide. 

 In the precipitation the thorium and its isotope ionium that immediately precedes 

 radium in the disintegration series are co-precipitated. The ionium produced from the 

 uranium in solution in the sea is thus steadily removed by precipitation of the iron. 



