DENSITY OF SEA WATER 



AT 



COAST AND GEODETIC SURVEY TIDE STATIONS 



ATLANTIC AND GULF COASTS 



EXPLANATION 



The monthly mean and the yearly mean and extreme densities 

 of sea water given on the following pages are based on hydrometer 

 readings made at tide stations maintained by the U. S. Coast and 

 Geodetic Survey along the Atlantic and Gulf coasts of the United 

 States. The readings are usually made once each day, except Sun- 

 days and holidays, from water samples which are drawn from near 

 the surface. Inferred values are given in parentheses. 



The UNIT OF DENSITY is the density of fresh water at a tem- 

 perature of 4° C. The actual density of the water at tide sta- 

 tions may vary from a little less than unity for fresh water at 

 a temperature other than 4° C. to approximately 1.031 for the 

 heaviest sea water. Since the density of sea water as observed 

 depends not only upon the amount of soluble matter contained in 

 a unit volume but also upon the temperature of the water at the 

 time the reading is made, it is necessary to reduce the observed 

 densities to some standard temperature in order that they may be 

 comparable and indicate the amount of matter held in solution. 

 IN THIS PUBLICATION THE OBSERVED DENSITIES HAVE BEEN REDUCED TO 

 A STANDARD TEMPERATURE OF 15° C The density of pure water at a 

 temperature of 15° C. is taken as 0.9991. 



The SALINITY of sea water is defined as the number of grams 

 of salts contained in 1,000 grams of sea water. While the total 

 amount of salts contained in a given volume of sea water varies 

 in different places, the relative portions of the different kinds 

 of salts are nearly constant in all parts of the ocean. The 

 salinity of sea water may be determined by several different 

 methods, one of the simplest being based upon the density of the 

 water as obtained from the use of the hydrometer. The table on 

 the last page gives the salinity corresponding to different den- 

 sities at the standard temperature of 15° C, to which the densities 

 in this publication are reduced. 



