MARINE ANIMALS ON SUBMERGED METALS. 



129 



considered by taking the single metals first. The conditions of 

 these metals and the kinds of growth that they harbored are indi- 

 cated in Table I. and on Plate I. All the metals were acted on by 

 the seawater; Al, Zn, Sn, and Pb were slightly corroded, Fe was 

 rusted, and Cu was coated green. A general growth of all five 

 animals to a maximum extent occurred on Al, Fe, and Pb, and a 

 similar growth though to less extent on Sn. Zn carried only a 

 very small amount of Bugula and Cu was without any growth at 

 all. In general the metals fall into two groups, Cu and Zn with 

 practically no animals upon them and the other four metals sup- 

 porting large growths of this kind. 



TABLE I. 



THE Six COMMON METALS USED ix THESE EXPERIMENTS ARRAXGED IN THE 

 ORDER OF THEIR SOLUTION PRESSURES (ELECTROMOTIVE FORCES). 



The effect of the seawater is indicated under the heading State of metal. 

 When all five animals are present the term general is used in the table ; when 

 fewer are present they are designated by their generic names. A rough esti- 

 mate of the amount of growth on the plates is indicated by numbers with 10 

 as the maximum. 



Professor A. B. Lamb, who has given me much help with the 

 chemical side of this problem, has pointed out to me that the marine 

 corrosion of the six metals tested is influenced by other factors 

 than simply their solution tendencies. Among these factors are 

 the solubilities of the hydroxides and basic carbonates of these 

 metals in seawater and the tenacity with which films of these sub- 

 stances cling to the metallic surfaces. Aluminum hydroxide is only 

 sparingly soluble in seawater and forms a firmly adherent coating. 

 Zinc hydroxide and basic zinc carbonate are more soluble and cling 

 less tenaciously. Hence Al will not corrode in seawater so quickly 

 as Zn does. For similar reasons Sn and Pb, though having higher 

 solution pressures than Cu, will actually be less corroded than Cu. 



