A Note ofM. A, Van Seek. 4& 



was deprived as much as possible of air by means of the air- 

 pump, with steel wire immersed in it ; and, after the exhaustion, 

 the bottle was corked and inverted in water to prevent the re- 

 admission of air. The result now was different ; after twenty- 

 four hours only a stain just perceptible appeared at the end of 

 the wire, where in contact with the glass ; and no more appeared 

 after several days, the wire generally remaining bright : Whence 

 it appears to me, it may be inferred, that the oxidation of steel 

 in water, is analogous in theory to its oxidation in moist air, or 

 in heated air, or in acid -vapour, in all which circumstances the 

 contact of a more electrically positive metal, even of zinc, does 

 not defend it ; no more than iron, tin or zinc defend copper com- 

 pletely when similarly situated. 



The property of iron to rust in water and in moist air more 

 rapidly than tin, as is well known, and even than zinc, may per- 

 haps depend on the powerful affinity of the protoxide for oxy- 

 gen, to form the peroxide, — promoted by the predisposing affi- 

 nity of the latter to form a hydrate, a compound containing about 

 16 per cent., in two proportions of water, and in which the oxide 

 and water are united so firmly, that a temperature approaching to 

 a red heat is required to expel one proportion, and that of a red 

 heat to drive off the other. 



Relative to the statement with which M. Van Beek concludes 

 his note, that zinc should be used in every instance in which it 

 is desirable to afford protection to iron in the boilers of steam-en- 

 gines, it \B necessary to be cautious in giving an opinion. That 

 zinc is capable of defending iron in water, and even in salt water, 

 from rusting, I have satisfied myself by experiment. But as 

 gas is disengaged from the iron, whilst the zinc oxidates, it may 

 be a question whether danger may not arise from the inflam- 

 mable gas mixing with the steam, and more than counterbalan- 

 cing any little saving of the iron from rusting, owing to the ac- 

 tion of the air on the water previous to boiling. In regard to 

 theory, this instance of the protection of iron in water by zinc, 

 may be considered analogous to that of iron by tin in a weak 

 acid, such as the diluted muriatic which is capable of dissolving 

 the oxide of tin as it forms. 



After what has been brought forward, httle comment need be 

 made on M. Van Beek's assertion, that tin instead of preserving 



