16 CLARKE— STATISTICAL METHOD [April 18 



given by Dittmar in the Report of the Challenger Expedition.^ 

 The maximum salinity observed by him amounted to 37.37 grammes 

 of salts in a kilogramme of water, and by taking this figure instead 

 of a lower average value, we can allow for saline masses enclosed 

 within the solid crust of the earth, and which would not otherwise 

 appear in our final estimates. Combining this datum with Dittmar's 

 figures for the average composition of the oceanic salts, we get the 

 second of the subjoined columns. Other elements, contained in 

 sea water, but only in minute traces, need not be considered here. 

 No one of them could reach o.ooi of i per cent. 



Composition of Salts. Composition of Ocean. 



NaCl 77.76 O 85.79 



MgClo 10.88 H 10.67" 



MgSO, 4-74 CI 2.07 



CaSO^ 3-6o Na 1.14 



K2SO4 2.46 Mg 14 



MgBr. 22 Ca 05 



CaCOa .34 K 04 



100.00 S °9 



Br 008- 



C .002 



100.00 



It is worth while at this point to consider how large a mass of 

 matter these oceanic salts represent. The average salinity of the 

 ocean is not far from 3.5 per cent.; its mean density is 1.027, and 

 its volume is 302,00x3,000 cubic miles. The specific gravity of the 

 salts, as nearly as can be computed, is 2.25. From these data it can 

 be shown that the volume of the saline matter in the ocean is a little 

 over 4,800,000 cubic miles, or enough to cover the entire surface of 

 the United States, excluding Alaska, 1.6 miles deep. In face of 

 these figures, the beds of rock salt at Stassfurt and elsewhere, which 

 seem so enormous at close range, become absolutely trivial. The 

 allowance made for them by using the maximum salinity of the 

 ocean instead of the average, is more than sujfficient ; for it gives 

 them a total volume of 325,000 cubic miles. That is, the data used 

 for computing the average composition of the ocean, and its average 



Hn Volume i, "Physics and Chemistry." 



