ACTION OF WATER ON IRON. 295 



nor for a single day, which is the fact, then it would seem ab- 

 surd to expect that it will protect them for twenty-five j^ears ! 



" If I mistake not there is little difficulty in accounting for 

 the preservation of the iron under the circumstances noticed by 

 you, without having recourse to any fancied power of protection 

 in brass, which it really does not possess. 



" In Saunders' News-letter already referred to, which con- 

 tains the fullest report of your paper which I have seen, the 

 iron is stated to be ^an iron pin working in a brass socket, 

 which was again inclosed in an iron case ; all the iron in con- 

 nexion with the brass was in excellent preservation, whilst that 

 removed from it was corroded.' 



" Now it seems clear to me that the preservation of the ii'on, 

 under the circumstances here enumerated, was an effect due to 

 the mere condition in which the metal was placed, which was 

 such as precluded (almost entirely) the access of air, on which 

 its corrosion, both in salt and fresh water, depends. Under 

 similar conditions I entertain no doubt but that iron will pre- 

 serve iron, and brass, brass, and each of these metals the other 

 respectively; and glass, porcelain, &c., will equally preserve 

 both brass and iron from corrosion in salt and fresh water. 

 But the preservation of metals under such circumstances is not 

 protection in the sense in which it has been commonly under- 

 stood, since the first just views on the subject were advanced by 

 the late Sir Humphry Davy. 



" As the protection of cast and wrought iron in salt water by 

 brass is not only spoken of as a discovery, but has already been 

 acted upon as such in some of the great public works in Liver- 

 pool, and may soon be extended to other seaports, to our ship- 

 ping, and to innumerable cases where iron is exposed to salt 

 water, I lose no time in making you acquainted with my expe- 

 rience and views on the subject. 



" I beg, in conclusion, to remark, that my statements pro- 

 ceed on the ground that the brass spoken of, without any qua- 

 lification, is no other than the common brass of commerce. If 

 you haee used a different alloy containing more zinc or other 

 material, allow me to suggest to you the propriety of setting 

 the public right on such a matter, as well as your humble ser- 

 vant, 



" Edmund Davy." 



Professor Davy has since favoured me with the following ad- 

 ditional note containing the results of his more recent experi- 

 ments on the subject. He proceeds : — 



101. "As the protection of cast and wrought iron in salt 

 u 2 



