1080 Experiments and Papers, [No. 144. 



corrosion upon iron or copper when protected by contact with zinc ; 

 but here also I must be permitted to remark, that our best Chemists 

 are altogether in the dark as regards a knowledge of the nature of 

 these two powerful agents in the economy of the universe; we perceive 

 their effects, and theorise upon their probable mode of acting, but 

 nothing satisfactory or conclusive has yet been proved, except that we 

 see the exercise of their opposite actions in the result of the protected 

 metals before-mentioned, and are convinced, that analogy alone must 

 direct us at present, in any attempts to extend our knowledge of the 

 application of the anti-corrosive property of electro-galvanism, to use- 

 ful and beneficial purposes. 



But will the application of this principle or property of electro- 

 galvanism be useful in the construction of iron ships ; that is to say, 

 will the protection from oxydization thus afforded to the hulls, be 

 equivalent as a benefit obtained, to an evil which will certainly be 

 consequent upon non-oxydization, namely, the accumulation of marine 

 animals and their testaceous habitations upon the bottom of the 

 vessel, and the same question may be also asked in cases where the 

 iron is mechanically protected by thick layers of carbonaceous matter ? I 

 certainly think not; for independent of the retardation on the speed 

 occasioned by the extensive surface, and sinuous character of the 

 foreign bodies adhering, the necessity of every three or four months 

 placing the vessel upon shore for the purpose of removing them from 

 her bottom, must materially injure and strain her hull, besides the 

 chances on such occasions in unknown parts, of her bed being of a 

 rocky character, which would hazard at once her total loss, by the ex- 

 tensive injury she must sustain with her whole weight supported only 

 upon points of rocks. 



Let us, on the contrary, suppose, that an iron vessel starts for sea 

 completely unprotected, the naked metallic surface of the iron fully ex- 

 posed to the action of the water, we could anticipate no other conse- 

 quence would result after a voyage of a few months, than perhaps a 

 slight oxydization along the line of immersion, (owing to the combined 

 action in that situation of air and water,) whilst the remainder of her 

 bottom would be found to be clean, neither acted upon chemically by 

 oxydization, nor affording the least harbour for those masses of barna- 

 cles, pedunculate or sessile, which, in the other case, experience has 



