1843.] on the effects of Sea-water on Iron. 1069 



experiments conducted in this way, the corrosion was found to in- 

 crease, in an arithmetical proportion to the increase of the surface 

 exposed. These experiments were carried as far as the exposure of 

 100 superficial feet. 



6th. The influence of density was also studied, both on the waters 

 sent by the Marine Board, and artificial saline solutions. The general 

 result is, that so long as the temperature continues the same, no differ- 

 ence of corrosion occurs within the limits of the natural variations in 

 the density of the sea-water under edsperiment. 



The nature of the Corrosion. 

 7th. This is simple oxidation, the red oxide of iron being deposited 

 in loose flakes on the exposed surface. The presence of air in the 

 water accelerates the commencement of the action, but is not essential 

 to its continuance. I have found that corrosion will not occur in boil- 

 ed distilled water, hermetically sealed up. It takes place more slowly 

 in salt-water, previously boiled, and then hermetically sealed up ; and it 

 occurs in the ordinary manner in common salt-water, not boiled, but 

 secluded from access of air. 



Obviation of Corrosion. 



8th. The experiments made on this head may be classified as fol- 

 lows : — 



a. Protection by Galvanic action. 



b. Protection by Cements. 



c. Protection by Varnishes. 



9th. a. The experiments on this head were very numerous, and 

 may be thus described. 



Pieces or arrangements of sheet iron, ranging from eight superficial 

 inches to 100 superficial feet, were tried for equal periods with zinc 

 protectors, ranging from an equal size to one-hundreth the size of the 

 sheet iron. The results I obtained are as follow : — 



10th. For the protection of the iron the zinc must undergo corrosion, 

 and when this ceases from any cause, the iron is attacked as usual. The 

 corrosion or loss of 60 grains of zinc daily protects 100 superficial feet 

 of iron, less than this will not suffice. On the other hand, increasing 

 the surface of the zinc protectors increases the amount of corrosion of 



