10 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 56 



Erom the figures previously given, for the average composition of river 

 waters and the total chemical denudation of the globe, 175,040,000 metric 

 tons of sodium are annually discharged into the sea. The crude quotient, 



Na in ocean ^gQQQQ 

 Na in nvers 



the time in years needed to furnish the entire amount of marine sodium ; 

 assuming a sodium-free ocean at the start and a uniform rate of supply 

 throughout all geological time. Any probable change in either of these 

 assumptions will reduce the quotient, although other considerations may 

 tend to increase it. The first correction to be examined operates in the 

 latter direction. 



A part of the sodium found in the discharge of rivers is the so-called 

 " cyclic sodium " ; that is, sodium in the form of salt lifted from the sea 

 as spray and blown inland to return again to its source in the drainage 

 from the land. ISTear the sea coasst this cyclic salt is abundant; inland its 

 quantity is small. For example, by careful analyses of rainfall, con- 

 tinued over long periods of time, the following amounts of cyclic salt have 

 been determined. The figures represent pounds per acre per annum of 

 sodium chloride. 



Locality. NaCl in rain. 



Rothamsted, England 24. 



Cirencester, England 36.1 



Perugia, Italy 37.95 



Barbados 193. 



In central Massachusetts, according to Mrs. Ellen S. Richards,^ the 

 cyclic salt, at distances of 50 to 100 miles from the coast, amounts to 

 23.2 pounds per acre per annum. 



The Rothamsted figures are very suggestive. Rothamsted lies in the 

 Thames valley, and if its figure for sodium chloride in rain be taken as a 

 fair average for the entire drainage basin, 6100 square miles, the quantity 

 there brought down amounts to 41,732 British tons annually, or 16,445 

 tons reckoned as sodium alone. Analyses of the Thames give sodium as 

 3.26 per cent of the total inorganic matter in solution, or, in terms of the 

 discharge already cited, 17,872 tons. Here the cyclic sodium is nearly as 

 much as the total amount carried by the stream ; but of course one cannot 

 assume that all of the cyclic portion finds its way back to the ocean in any 

 brief or relatively brief time. It is enough to say that in the British 

 islands the correction for cyclic salt must be large; while for the great 

 continental rivers like the Mississippi, St. Lawrence, Amazon, Danube, 

 or Nile it is very much smaller. 



1 Private communication. For the other figures, see Data of Geochemistry, p. 47. 



