i8o PRINCIPLES OF STRATIGRAPHY 



calculated from the following formula devised by Martin Knudsen 

 (Kriimmel— 20, 2jy), where S represents the salinity in permille. 



o-Q = — 0.093 + 0.8149 S — 0.000482 S^ + 0.0000068 S^ 

 According to this formula the density of the waters of the Kara- 

 bugas Gulf, which has a salinity of 285 permille, should be 1.353329 

 at 0° C. or (To = 353-329, though since the salts are not those of 

 normal sea water this figure is not wholly correct. While the 

 maximum density of distilled water (i) is at + 4° C. (+ 3.947° C.), 

 i. e., a density when ""^ = 0.00, that of sea water of different con- 

 centration varies greatly. 



The temperature at which any given water is at its greatest 

 density may be designated 0°. Substituting this in the general 



formula we have ^e = 1000 ('-4- ). When the salinity is 35 



\ S 40 / 



permille, 6° equals — 3.524° C., and '^e = 28.22 as compared with 



(To = 28.12. 



Variation in Osmotic Pressure in Sea Water. 



By osmotic pressure is meant that pressure which causes diffusion 

 between the solution of a substance and its solute, or between solu- 

 tions differing in concentration. It varies directly with the concen- 

 tration of the solution, and increases with the temperature. Thus 

 for Baltic water with a salinity of 7.5 "/oo, at a temperature of 

 18° C. the osmotic pressure is 4.9 atmospheres; in water of the Red 

 Sea, with 40 "/oo salinity and a temperature of 30° C., it is 26.7 

 atmospheres. Normal sea water with a salinity of 35 Voo has an 

 osmotic pressure of 23.12 atmospheres at 0° C. For water of i Voo 

 salinity at 0° C. the osmotic pressure is 0.66 atmosphere (Kriimmel= 

 20, table, p. 241). In general for each increase of one permille of 

 salinity there is an increase of 2/3 atmosphere in osmotic pressure, 

 equivalent to the pressure of a mercury column 500 mm. long. 



Osmosis may be considered either as Exosmosis, or that tendency 

 of the fluid within a submerged body to pass into the surrounding 

 fluid, and Endosmosis, the tendency for the outer fluid to pass into 

 the space occupied b}^ the inner; or that action of the fluid which 

 passes with greater rapidity into the other. The effect on organisms 

 of the different osmotic pressures is very marked. Thus a frog 

 placed into sea water loses, by exosmosis, which commences at once, 

 a considerable quantity of water, and in a short time its weight is 

 diminished by one-fifth. On the other hand, a salt-water fish" placed 

 suddenly into fresh water suffers through rapid increase by endos- 

 mosis of the water in its body, which results in swelling and death. 



