132 



G. H. PARKER. 



In the inactive condition, when coupled with Al, a general vigor- 

 ous growth of animals took place (Plate III.), and the same would 

 probably have occurred in the Zn couple had it not been for the 

 poisonous Zn ions or compounds liberated by the Zn half-plate. 

 When paired with Sn, Pb, and Cu, the growth was general, though 

 often not large in amount. The occasional small quantities were 

 probably due to the physical difficulty presented to the animals of 

 maintaining a foothold on a plate that was continually sloughing 

 its outer layer. 



The fourth and fifth metals are Sn and Pb. In the electromo- 

 tive series Sn stands below Al, Zn, and Fe and above Pb and Cu, 

 and Pb stands above only Cu. The corrosion of Sn and of Pb in 

 seawater follows expectancy in that Sn corrodes only when it is 

 combined with Pb and Cu, and Pb only when it is combined with 

 Cu (Tables V. and VI.). Since in all the combinations the Sn 

 and the Pb are either inactive or give rise to products almost in- 

 soluble and hence not ionic, it follows that a general growth of 

 animals is to be expected on Sn and Pb in all combinations, and 

 such appears to be the case (Tables V. and VI. and Plate IV.). 



TABLE V. 



COUPLES BETWEEN SN AND THE FlVE OTHER METALS, THREE OF WHICH, AL, 



ZN, AND FE, STAND ABOVE SN, AND Two OF WHICH, PB AND Cu, 

 STAND BELOW SN IN THE ELECTROMOTIVE SERIES. 



The animals are indicated as in Table I. 



TABLE VI. 



COUPLES BETWEEN PB AND THE FlVE OTHER METALS, FOUR OF WHICH, AL, 



ZN, FE, AND SN, STAND ABOVE PB, AND ONE OF WHICH, Cu, STANDS 



BELOW PB IN THE ELECTROMOTIVE SERIES. 



The animals are indicated as in Table I. 



