248 GLOSSARY 



natural waters. The salinity of sea-water is expressed 

 in parts per thousand (as 35 per thousand) ; but it is 

 a conventional quantity obtained by appljring 

 factors to the chlorine-content or specific gravity, 

 since the direct determination of total dissolved 

 solids cannot be effected with accuracy. See also 

 Density. 



Salt. — Any compound of an inorganic base with an 

 inorganic acid, such as calcium carbonate, sodium 

 sulphate, magnesium chloride, etc., produced by the 

 replacement of the hydrogen of the acid by the metal 

 of the base. (Common salt = sodium chloride, but 

 the generic term " salt " connotes many other com- 

 pounds in addition.) 



Specific Gravity. — See Density. 



Symbiosis. — Literally " living together " : an intimate 

 association between two organisms, such as an alga 

 and a radiolarian, advantageous to both. 



Tbktosphere. — One of the geospheres; the shell of 

 materials in a state bordering on fusion which sur- 

 rounds the centrosphere, and upon which rests the 

 lithosphere. 



Viscosity. — The viscosity of liquids is the internal friction : 

 the resistance to the motion of the molecules of the fluid 

 body among themselves. It arises from the mutual 

 attraction of the molecules, and diminishes as the 

 temperature is raised and the molecules move farther 

 apart. 



