390 British Association for the Advancement of Science. 



peared to be most considerable on the iron in the immediate vicinity 

 of the lead, where it was about one eighth of an inch deep, and the 

 metal was so much indented as to exhibit a coarse fibrous structure. 

 So rapidly had the iron-work corroded in about six months, that 

 had it continued at the same rate for two years the buoys (in the 

 opinion of competent judges) would have been quite unfit for the public 

 service. The copper and lead attached to the buoys were in a good 

 state of preservation. , 



The extraordinary corrosion of the iron- work appeared to be due 

 to an electrical action produced in sea water by the contact of the 

 iron with the lead joined to the copper, on the buoys; these metals 

 being preserved at the expense of the iron. The author submitted 

 his views on the subject to the Commissioners, and suggested the 

 propriety of removing a circle of about three or four inches of lead 

 from the iron-work at the bottom of each buoy, and of driving two 

 or three short large-headed iron nails through the remaining lead 

 into the wood, in order to protect both the lead and copper covering 

 of the buoys from corrosion. These suggestions being promptly car- 

 ried into effect, the author has during the last twelve months had 

 frequent opportunities of examining the state of the iron-work at- 

 tached to, and in the immediate vicinity of, the buoys, and he states 

 that the removal of the lead has put a stop to the very rapid corro- 

 sion of the iron-work. 



The action of sea-water on iron, under ordinary circumstances, 

 is, as is well known, by no means inconsiderable. The author 

 found that a piece of iron chain weighing 14 pounds 5 ounces, when 

 exposed for 24 hours in h\ quarts of sea-water, lost 70 grains, and 

 in a few days Upwards of a quarter of an ounce : these facts led him 

 to think it both desirable and practicable to coat the iron-work of 

 the buoys, &c. with a varnish or japan which should be impervious 

 to sea-water : and at the request of the Commissioners he made 

 many experiments, using different varnishes and japans ; but the 

 results obtained were for the most part of a negative kind, owing not 

 only to the action of sea-water on iron, but also to the constant fric- 

 tion to which the metal must be exposed, from the unceasing influ- 

 ences of tides, winds, and the strains from ships. He has hitherto 

 found no varnish or japan that he can recommend as a means of pre- 

 venting, for any length of time, the ordinary corrosion or oxidation 

 of iron in sea water. 



The author made a number of experiments with a view to apply 

 metallic protectors to the iron-work connected with the buoys, on 

 •the principle developed by the late Sir H. Davy. He found that 

 when small ingots of zinc were attached to pieces of chain cable in 

 sea-water, during several weeks, these lost no weight, and the cor- 

 rosion of the zinc was inconsiderable. Hence it seemed obvious, 

 that zinc will protect iron from corrosion in sea-water. These re- 

 sults were so satisfactory that the author recommended the expe- 

 riments to be tried on the buoys, and the Commissioners immedi- 

 ately requested him to carry the same into effect. He has had 

 under a course of trial for several months, in contact with the iron^ 



