82 



HYDROGRAPHY. 



It may perhaps be considered as superfluous to indicate the %<, of chlorine, when the salinity 

 S in proportion to this appears in the tables. If for all that I have done so, it is only because I 

 consider it as a question of time, when another system than the present one will be adopted for the 

 indication of the salinity of sea-water. 



The determination of -5", the sum of the quantities of salts (expressed in grms) existing in 1 

 kilo, of sea-water, is a rather complicated matter requiring a great deal of analyses, which again may 

 lead to as many causes of error. Furthermore the direct determination of S by the drying of a 

 quantity of sea-water, the weight of which has been measured, and the heating and weighing of the 

 salts, does not always give results to be entirely relied upon, as transitions and decompositions are 

 taking place during the process of drying and heating, so that correction of determinations and cal- 

 culations has to be made, new causes of errors. 



Being attended with a great deal of trouble to make an analysis of this kind, it is generally 

 customary — instead of the aforesaid method — to determine the surplus of the specific gravity of 

 the sea-water above 1 or its amount of chlorine (grms per kilo of sea-water), and by means of this to 



