30 PROCEEDINGS OF THE AMERICAN ACADEMY 



" In the third piece, which is a part of the last, corrosion has pK)- 

 ceeded to the extent of destroying cohesion nearly : the particles re- 

 main attached only through an interlacing of contiguous parts, separat- 

 ing at once when the sheet is doubled, or beaten into crystalline grains, 

 coated by a tliin layer of oxide. By the chemical action the compo- 

 sition of this piece has undergone a great change, and analysis gives 

 the percentage of copper 74.5, zinc 22.8, oxygen 2.1, lead 0,6 = 100. 



" At several points deep cavities, and in many sheets holes, exist ; 

 these have been caused by the corrosion around grains of slag, which 

 had been rolled into the mass of the metal. In such cases the slag is a 

 negative body to the surrounding metal, after corrosion commeyices, and 

 an increased power of action is thus gained, locally. Carefully con- 

 ducted experiments prove the correctness of the theoretical deduction, 

 that the alloy represented by copper, two equivalents, and zinc, one 

 equivalent, has an inherent negatively electrical condition, when com- 

 pared with the alloy of one equivalent of copper and one equivalent of 

 zinc ; and this state has been found in the cleaned parts remaining of 

 sheets which have suffered the largest amount of corrosion. 



" But the chemical evidence which we thus obtain of the abstraction 

 of the most positive alloy by sea-water action, is not more interesting 

 than that of a physical character. Every piece which has been disin- 

 tegrated presents highly crystalline — almost regularly crystallized — 

 assemblages of the alloy of two equivalents of copper to one equiva- 

 lent of zinc, as its mass. 



" Now, in the ductile metal before exposure, we detect the facets of 

 these crystals of this alloy, which might be mistaken for those found in 

 many laminated pure metals, while the chemical action, being confined 

 to the most positive alloy, brings them more and more distinctly to view, 

 enabling us to prove that these large masses of metal, in corroding, 

 divide mechanically, as well as chemically, into two pre-existing alloys ; 

 one oxidizing and being washed away, while the other, nearly pure, 

 remains coherent to some extent. 



" It had been long known that the corroded metal, when about to be 

 re-manufactured, called for the addition of zinc, in order to form the 

 normal alloy ; the facts here stated prove that the abstraction of the 

 larger proportion of zinc arises from the removal of the most positive 

 of two alloys, which were united in the perfect metal as a homogeneous 

 mass. 



" As multiplied observations have shown that the merchant service 



