392 British Association for the Advancement of Science. 



will exhibit an incipient oxidation, which will gradually increase ; 

 the tin will be preserved at the expense of the iron, which will be 

 corroded. But if a small surface of zinc is attached to a piece of 

 tin plate and immersed in sea-water, both the tin and iron will be 

 preserved, whilst the zinc will be oxidated, on the principle first 

 made known by the late Sir H. Davy. 



The author has exposed for nearly eight months in sea-water a 

 surface of tin plate nailed to a piece of wood by means of tinned iron 

 tacks, inserting between the wood and the tin plate a small button 

 of zinc. Under these circumstances the tin plate has remained 

 clean and free from corrosion ; the zinc has of course been corroded. 

 In a comparative experiment, in which a similar piece of tin plate 

 was nailed to the same piece of wood, and exposed during the same 

 period to the same quantity of sea-water, without the zinc, the edges 

 on two sides of the tin plate were quite soft from the corrosion, 

 which had extended to about ith of an inch. These experiments 

 seem worthy of being repeated and extended. 



The present demand for tin plate is very great ; should these 

 statements be confirmed, a vast increase in its consumption might 

 be anticipated. The opinion may be entertained that it is practi- 

 cable to substitute double tin plate for sheet copper in covering 

 the bottoms of ships, &c, using zinc in small proportion as a pro- 

 tector. Such applications would probably occasion a saving of 

 nearly three fourths of the present expense of copper sheathing. 



It also seems deserving of inquiry whether tin plate vessels, pro- 

 tected by zinc, may not be advantageously substituted for copper 

 vessels in many of our arts and manufactures, and even in domestic 

 ceconomy. Although it might be presumed from Sir H. Davy's ex- 

 periments and observations* that zinc would protect tin plate from 

 corrosion in sea-water, the author is not aware that any direct ex- 

 periments on the subject have been published. Sir H. Davy briefly 

 refers to some obvious practical applications of his researches to the 

 preservation of finely divided astronomical instruments of steel by 

 iron or zinc ; and that Mr. Pepys had taken advantage of this last 

 circumstance in inclosing fine cutting-instruments in handles or 

 cases lined with zinc. The author has not heard whether such ap- 

 plications have succeeded, but he has made a number of experiments 

 with a view to protect brass, iron, copper, &c. from tarnish and 

 corrosion in the atmosphere by means of zinc ; the results obtained, 

 however, lead to the conclusion that contact with zinc will not protect 

 those metals in the atmosphere, the electricity thus produced, with- 

 out the intervention of a fluid, being apparently too feeble to coun- 

 teract the chemical action of air and moisture on the surfaces of these 

 metal*. f 



• Phil. Trans, vol. cxiv. for 1824 [or Phil. Mag., first series, vol. lxiv. 

 p. 30, 233 ; vol. lxv. 203.— Edit.] 



f [The negative results thus obtained by Mr. E. Davy, agree exactly with 

 those of some trials which 1 have witnessed for protecting steel by this 

 means.— E. W. B.] 



