70 A TEXTBOOK OF OCEANOGRAPHY 



similarity. . Practically the same ingrédients are présent, 

 bearing nearly the same proportion to each other. 



The salinity, or total weight in grams of dissolved sait in 

 1,000 grams of water, may be rapidly determined by titration 

 with silver nitrate solution. 



Another obvious method would be to evaporate off the 

 water and weigh the resulting salts. This is difficult in actual 

 practice, since in order to drive off ail the water the beat applied 

 drives off hydrochloric acid. The last portions of steam driven 

 ofï in evaporation bave also been found to contain appréciable 

 quantities of carbonic acid as well, and the loss of thèse two 

 substances reduces the total weight of the remainder, so that 

 the titration method is preferred. 



Since the ratio of the différent salts in sea-water is 

 practically constant, and since the halogens (chlorides and 

 bromides) can be rapidly determined by titration with silver 

 nitrate, it is possible to détermine easily the chief physical 

 characteristics of a given sample of sea-water. 



For instance, the spécifie gravity dépends on the salinity, 

 and can be determined if the latter is known. The spécifie 

 gravity of sea-water is its weight compared with an equal 

 volume of pure water at the same température. 



The density can also be determined from the same 



experiment. The density may be defined as the weight in 



grams of i ce. of sea-water at the température in situ, t°, 



compared with that of i ce. of pure water at 4° C. It is 



/° 

 generally expressed as S -5. 



Tables hâve been prepared by the Danish hydrographer, 

 Martin Knudsen, from which the ratios between salinity, 

 density, and the halogens as determined by titration can be 

 estimated. The salinity is determined with an accuracy of 

 005 per 1,000 parts, and the density up to 000004. According 

 to Knudsen, the formula for conversion is — 



Salinitv, S = 0030 + r 8050 Cl. 



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