OF VITAL PHENOMENA 185 



Artificial sea water may be made as follows, out of the purest 

 reagents especially free from Ba, As and heavy metals, dissolved 

 in water that has been redistilled with a silica condensing tube 

 and aerated several days with outside air. The numbers denote 

 cc of normal solutions (0.5 mol in case of bivalent salts) in a liter. 



After mixing, the solution is aerated with outside air several 

 hours in order to bring the alkalinity to PH=8. 1-8.2 which is 

 the PH of the surface of the ocean. This should show a faint 

 pink with phenolphthalein. The C0 2 tension of surface sea water 

 is about 0.04 per cent of an atmosphere, whereas outside air 

 averages 0.03 per cent C0 2 . It is therefore possible to make the 

 sea water slightly hyperalkaline by prolonged aeration with out- 

 side air, but the addition of animals or bacteria quickly brings it 

 back to normal and the problem is to aerate it sufficiently. The 

 curve of PH with varying C0 2 tension is similar to that of blood 

 (Fig. 18) or any other bicarbonate solution. 



The other constituents of sea water exist as traces. They may 

 be present as impurities in the salts used in making artificial sea 

 water even in excess of their concentration in natural sea water, 

 or they may get into the water from the air or by solution of the 

 glass vessels used to store it. 



In order to investigate the significance of the composition of 

 sea water on marine organisms the effect of changing its com- 

 position has often been studied. If the alkalinity is increased 

 to PH=9.oo there is finally a slight precipitate of lime (calcite) 

 and the alkalinity returns to normal, so that it is difficult to 

 increase the alkalinity and keep it so for many days. Herbst 

 (1898) and Loeb (1898 b) observed that an increase in the alka- 

 linity increased the rate of development of sea urchin eggs, and 

 O. Warburg (1810 a) found that this was accompanied by an 

 increase in respiration of the eggs. Herbst found that CI, Na, 

 K, Ca and OH ions are necessary for the development of these 

 eggs from the beginning, but S0 4 , C0 3 and Mg are necessary 

 only for later stages. Plants are less affected by changes in the 

 composition of the sea water, but Osterhout (1912 b) has found 

 plants that require Na. Diatoms grow better if 4 cc of n KNO a 



