OF ARTS AND SCIENCES. 



29 



compounds of two metals, or one metal with a metalloid, united to form 

 a ductile body. 



" The chemical analysis, by the proximate way, of yellow-metal, has 

 shown that, when it is formed from pure copper and pure zinc, there 

 exist Uvo distinct alloys. One of these is the well-known alloy of two 

 equivalents of copper, united to one equivalent of zinc ; the other is 

 composed of one equivalent of each of these metals, in chemical union. 

 A mass of yellow-metal presents, therefore, a crystalline aggregate of 

 two alloys, in which the percentage proportion of copper is sixty, while 

 the zinc has the proportion of forty ; and analysis having in view the 

 percentage of these metals only, gives usually nearly these quantities. 



"As the relation of zinc to oxygen. dilFers remarkably from that of 

 copper, it might have been inferred that an alloy composed of one 

 equivalent of copper and one equivalent of zinc would also have a dif- 

 ferent relation to oxygen, when compared with one that contains two 

 equivalents of copper. Considering sea-water action simply as oxida- 

 tion, under the most favorable conditions for combination without the 

 application of artificial heat, the study of the corrosion of yellow-metal 

 under exposure offers a simple and unobjectionable course for obtaining 

 trustworthy facts. 



" It is well known that this yellow alloy, when carefully secured on 

 sailing-vessels, quickly exhibits marks of corrosive action when more 

 or less immersed in sea-water. The rapidity of this action diminishes 

 after the formation of a certain proportion of oxide, which, slightly 

 mixed with chlorides, serves as a protecting surface to the metal be- 

 low, by close adhesion. A serviceable duration of thirty-six to forty- 

 eight months is expected, in sheets of ordinary thickness. 



" The specimens which accompany this paper are parts of sheets 

 which have been exposed nearly forty-eight months. In the one which 

 represents the alloy in the condition it was in when it was placed on 

 the vessel, at one part, analysis shows a percentage composition — 

 neglecting traces of lead and other metals — of copper 60, zinc 40. 



" Another specimen, which has been corroded deeply, exhibits to the 

 naked eye a mechanical structure unlike that of the first jjiece : it re- 

 tains only part of its original ductility, and this unequally. Crystalline 

 particles are seen, and, even in the interior of the mass, oxygen has 

 penetrated, and combined with the metals. The composition of this 

 piece is, copper 63.6, zinc 33.9, oxygen 2.0, lead and other metals, 

 0.5 = 100. 



