Artificial Seaivater 29 



table 3. — {continued) 



Nitrate 0.014 Silver 0.0002 



Iron 0.0036 Nitrite 0.0001 



Manganese 0.003 ? Arsenic 0.00004 



Phosphorus 0.002 Zinc 0.00003 



Copper 0.002 Hydrogen Ion 0.00001 



Barium 0.0015 Gold 0.00000025 



Iodine 0.00035 



There are, however, a number of elements, such as cobalt, vanadium, 

 lead, nickel, tin, caesium, and rubidium, the presence of which has not 

 yet been detected in seawater but is postulated because they are found 

 in the tissues of marine animals and plants or in the salt deposits left by 

 the evaporation of large quantities of seawater.* 



On account of the exceeding complexity of seawater it was only after 

 a great deal of effort that biologists succeeded in elaborating a formula 

 for an artificial solution which possesses the same properties as the 

 ocean water. There exist at present several formulae for the preparation 

 of artificial seawater which may be used in experimentation with marine 

 animals. 



For embryological studies on echinoderms Herbst (1903-4) employed 

 the following solution: 



To this solution 1 cc. of 4.948% NaHC0 3 must be added. 



In Van't Hoff's formula the principal salts are given in the molecular 

 proportions in which they occur in the sea: namely, 100 NaCl; 7.8 

 MgCl 2 ; 2.2 KC1; 3.8 MgS0 4 ; and from 1.5 to 2.2 CaCl 2 . After the 

 M/i solutions of the salts have been mixed in the above mentioned pro- 

 portions the solution is diluted to the same concentration as that of the 

 seawater in which the animals normally lived. A trace of sodium 

 bicarbonate should be added to bring the pH to 8.0-8.2. Water re- 

 distilled from glass must be used. While such a solution would serve 

 for experimental purposes it is not suitable for maintaining the animals 

 over a long period of time. Lacking in phosphates and nitrates, it is 

 obviously unsuitable for the marine algae. A more complex solution 

 prepared according to McClendon's formula answers this purpose. 



*For further discussion regarding the composition of the seawater and its significance 

 to the life in the sea the reader is referred to the papers of Quinton (1912), Yernadsky 

 (1923), Thompson and Robinson (1932), and Galtsoff (1932, 1934)- 



