292 EIGHTH REPORT — 1838. 



publications of Sir H. Davy, Pepys, and Edmund Davy ; and still 

 more, how a French patent is to be maintained for a process 

 which, although its principle was doubtless then not under- 

 stood, was, with little variation, before patented on the 26th of 

 September, 1791, by Madame Leroi de Jaucourt, for preserving 

 metals from rust by covering with an alloy of zinc, bismuth, 

 and tin. I may add, that Professor Davy informs me he used 

 the method of zincking over the surface of iron as a preserver 

 so far back as 1834. 



95. M. Sorel's patent is described as capable of being ap- 

 plied in three ways, viz. 1st, by covering the surface with fluid 

 zinc ; 2nd, by the application of a paint made from zinc ; 3rd, 

 by covering with a powder made from zinc. Unless the second 

 mean a paint made from ground metallic zinc, it is similar to 

 Lapadius' varnish, before described ; and if the former, then it 

 does not differ from the third mode described, appai'ently. We 

 have, however, not been furnished with specimens of either of 

 these modes, which would seem beforehand not likely to answer 

 their intended purpose, from a want of that continuity of me- 

 tallic connexion which appears essential to preservation in this 

 way. 



96. Sir H. Davy erroneously supposed that tin also possessed 

 the property of preserving iron in sea water. -This opinitm has 

 been controverted by the experiments of M. Van Beck, of Utrecht, 

 and of M. Mulder, of Rotterdam, and more recently by Profes- 

 sor E. Davj'^, in a paper communicated to this Association, in 

 which he shows that iron, on the contrary, will preserve tin, but 

 that zinc will preserve both. 



Sir H. Davy, and his brother Dr. John Davy, who has 

 defended his opinion, appear both to have been led astray by 

 merely considering and experimenting upon the galvanometri- 

 cal relations of tin to iron when first ]ilaced in contact. But 

 Van Beek, in the paper alluded to [Edin. New Phil. Journal 

 for October 1837,) has cleared this up by the discovery of the 

 remarkable and anomalous fact, that although it is certain that 

 tin is to iron in a positive relation in atmospheric air, yet when 

 both are plunged into sea water, after a period, never greater 

 than half an hour, has elapsed, the astatic needles of the galva- 

 nometer, which had before indicated the above relation, gradu- 

 ally return to zero, and pass through it to the opposite side, 

 and indicate that the iron has become positive with respect to 

 the tin, thus showing the singular fact apparently, that metals 

 retain for a longer or shorter time the electrical condition they 

 have once acquired. 



97. By decisive and direct experiments also, M. Mulder, of 



