52 Van Beek on the Supposed Property of Tin 



pears, that metals retain, for a longer or shorter time, the elec- 

 trical state once acquired. I discovered this interesting fact, by 

 making experiments on the preservation of copper by iron in 

 sea-water, and it forms the contents of my memoir containing 

 the note under discussion.* 



Very soon, however, the needles of the galvanometer, after 

 having returned to zero, shew an opposite deviation, and thus 

 prove evidently, that the electrical relation of the two metals is 

 wholly changed. The iron being more strongly oxidated than 

 tin in sea-water, becomes positive in respect to this metal ; and 

 this positive electrical relation of the iron remains and increases 

 by the increasing oxidation of this metal in sea-water. 



The time, during which tin preserves its positive electrical re- 

 lation to iron acquired in common air after the immersion in 

 sea- water, depends on the quality of the iron, and, perhaps, still 

 more on the condition of its surface, and the temperature of the 

 sea-water. In general, the brightest surface of iron retains the 

 longest its primitive electrical state, resisting powerfully the 

 stronger oxidation which it must soon undergo in sea-water. 



Generally, this phenomenon lasts only for a few minutes. I 

 have seen it once continue during about half an hour, when 

 making the experiment with bright polished steel, by a mean 

 temperature. 



The chemical purity of tin seems not to have any influence 

 on these experiments. 



It appears evident, that Dr John Davy, by his galvanome- 

 trical experiments, attended, as I did myself at first, only 

 to the direction of the needles soon afier the immersion of the 

 metals in sea-water, neglecting to extend the experiment during 

 a certain time, otherwise he would doubtless have remarked the 

 o])posite deviation of the needles. 



As to me, I am now perfectly convinced of the fact, that tin 

 cannot be made use of with success, to protect iron from corro- 

 sion in sea-water ; tin, on the contrary, being in that case pro- 

 tected by iron ; ind I invite all philosophers to repeat my ex- 

 periments, and so convince themselves of what I have advanced. 



It was very agreeable to me that an eminent philosopher of 

 the same name. Professor Edmund Davy of Dublin, was, on this 



• Professor A. de la Rive has discovered a similar property of the metals 

 bv a different process. 



