1915] Michael, et al. : Hydroyvaphic Records of Scripps Institution 27 



Grams per 1000 per cent of 



Salt of sea water the total 



NaCl 27.213 77.758 



MgCL 3.807 10.875 



MgSO, 1.658 4.737 



CaSO^ 1.260 3.600 



K,SO, 0.863 2.465 



CaCOj 0.123 0.345 



MgBr, 0.076 0.217 



Totol 35.000 99.997 



Many elements in addition to tliose included in this list are dis- 

 solved in one form or another. For instance, one gram of silver has 

 been estimated to be present in 100,000,000 grams of sea-water, while 

 about five times as much gold occurs. In fact, traces of almost all the 

 rare metals have been detected. But the total quantity of all dissolved 

 solids, except those listed above, is so small that it cannot be detected • 

 by any of the practical methods used in the measurement of salinity. 



(b) Direct measurement of salinity. — The most natural method of 

 determining the salinity of a given sample of water would seem to 

 be that of evaporating a definite quantity of the water and weighing 

 the residue. This method, however, has proved to be too inaccurate for 

 oceanographie purposes. In order to expel the last trace of water 

 vapor the residue must be heated to redness and, in doing this, hydro- 

 chloric acid and carbon dioxide escape in amounts which cannot, as 

 was formerly believed, be accuratelj^ determined. 



To overcome this difficultj^ a method was devised by Kuudseu and 

 Sorenson for obtaining a residue which could be accurately mea.sured. 

 Helland-Hansen (1911-12, p. 33) describes this method as follows: 



To a weighed quantity of sea-water was added hydrochloric acid and 

 cblorine-water; the whole was then vaporized, and the salts were dried and 

 weighed; the salt residue had first to be heated for some time at 480° C. to 

 render the weight invariable; by a special examination a correction was found 

 for the difference between the amount of chlorine in the vaporized salt and 

 that of the original water-sample. 



While this method gives exceedingly accurate results it does not, 

 strictly speaking, give the salinitj' as heretofore defined. However, it 

 differs but slightly, being only 0.10 to 0.15 "/„„ less, and their ratios 

 are so nearly constant that, for all practical oceanograjjliic purposes, 

 the value obtained by this method may be used instead of the salinity 

 proper. This is now done and the term salinity has taken on the fol- 

 lowing technical meaning (see Helland-Hansen, 1911-12, p. 33) : "The 



