ACTION OF WATER ON IRON. 299 



when wood, mica, paper, or another piece of the same iron took 

 its place. 



108. The larger was the proportion of the bi-ass present to 

 the quantity of iron exposed, the faster the latter corroded. 



109. When the brass was attached by solder to the iron, 

 whether cast or wrought, the action was the same, with in- 

 creased energy, provided the solder (composed of lead and tin) 

 was not immersed in the fluid. When it was, so the results 

 were anomalous, corrosion being retarded at first, and after- 

 wards accelerated, apparently from a change of electric relation 

 between the metals, as in Van Beek's experiments before 

 noticed. 



110. When a cylinder of brass, in composition the same as 

 Mr. Hartley's, was cast round a turned cylinder of wrought iron 

 at its fusing temperature, the iron on exposure to sea water was 

 rapidly acted upon, and carbonates of lime and magnesia were 

 deposited upon the brass, which remained bright. 



111. Corrosion in all cases commenced at the moment of 

 immersion, and continued without change for periods of nearly 

 two months. 



112. When cast or wrought iron was exposed to sea water or 

 fresh in the same vessel with a surface of this brass, but without 

 contact, but each communicating by a gold-soldered platina wire 

 outside the fluid, corrosion took place of the iron more rapidly 

 than when similar pieces were exposed without the presence of 

 the brass. 



113. No modification of alloy in the brass within the limits 

 of brass or gun metal seemed to produce any very remarkable 

 change in the increased rate of corrosion of iron by its presence, 

 nor did the results dififer materially whether brass proper, viz. 

 zinc and copper, were used, or Mr. Hartley's brass, which is, 

 in fact, impure gun metal, or copper and tin. 



114. As the proportion of zinc, however, in the brass in- 

 creased, a tendency to preservation should be manifested, and 

 conversely as the copper predominated, increased corrosion 

 would be expected. This view has suggested a very curious 

 branch of investigation now in progress, as to the changes of 

 electrical relations to a third metal of definite atomic alloys of 

 two other metals, whereof one is in a positive, and the other in 

 a negative electrical relation to the former. 



115. These results are sufficient to prove incontestably, that 

 brass or gun metal have no protective power over iron what- 

 ever, but, on the contrary, greatly promote its corrosion in sea 

 or fresh water, and, as we also found, in diluted acids. 



116. But as practical instances often come more home to the 



