28 University of California Publications in Zooloyij [Vol.15 



salinity {per mille) of sea-water is equal to the weight, in grants, of 

 all the salts dis.solved in one kilogram of water, when the carbonates 

 are converted into oxides, when the bromine and the iodine are re- 

 placed by chlorine, and the organic substances oxidated. ' ' 



While this method is used for obtaining the standard values of 

 salinit.y, it is not adapted to researches requiring a series of rapid 

 analyses and demanding a minimum of expense. To meet such require- 

 ments the methods used in practice are all indirect. 



(c) Methods of measurement in general use. — These methods de- 

 pend upon the definite relation of salinity to specific gravity, upon the 

 empirical assumption of a constant proportion of each salt to all the 

 others, or, very infrequently, upon the effect of the dissolved salts on 

 certain physical properties of water, such as its index of refraction 

 and electrical conductivity. For convenience, tables have been pre- 

 ' pared showing the magnitudes of physical and chemical properties 

 corresponding to salinities ranging from zero to the highest value 

 (about 40 V„o) required in oeeanographic investigations. It is cus- 

 tomary to measure either the specific gravity or the chlorine content 

 directly and obtain the correlative value (S Voo, -Sf > or CZ Voo) from 

 such reduction tables. The tables almost universally employed since 

 1901 were compiled by Knudsen (1901) and are based upon the values 

 of salinity obtained by the method of Knudsen and Sorensen as above 

 described. 



2. METHODS OF SALINITY DETERMINATION EMPLOYED BY THE 

 SCRIPPS INSTITUTION 



The determination of the salinities of all water samples so far col- 

 lected by the Scripps Institution are obtained from direct measure- 

 ments of the specific gravity or the chlorine content, and all reductions 

 are made by Knudsen 's (1901) tables. In measuring the specific 

 gravity, the pycnometer, hydrometer, and sinker are used, while the 

 chlorine content is measured by Mohr's titrimetric method. 



(a) The pycnometer method. — The pycnometer used is of the Gay- 

 Lussac pattern, provided with a ground-glass stopper having a fine 

 perforation through which an excess of water is forced when the bottle 

 is closed. Two sizes are used, one having a capacity of 50 c.c, and the 

 other of 100 c.c. Most of the determinations are made with the larger 



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