44 Dr Dav3r's Observations cyti 



would protect iron, in contact with water, either cold or boiling, 

 or fresh or salt as my brother inferred it would, but which M. 

 Van Beek denies, maintaining, on the contrary, that the iron pro- 

 tects the tin, and the tin accelerates the corrosion of the iron. 

 To determine this experimentally, portions of steel wire, and of 

 tin unattached and attached, were kept in rain-water and sea- 

 Avater boiling for several hours. Neither the tin or steel had 

 lost ought ; the tin wire was not tarnished, and the steel very 

 slightly so; and, as well as I could judge, not more or less when 

 attached or unattached to the tin. This, then, was altogether 

 a negative result, seeming to shew, as I believe is true, that 

 neither tin nor iron has the power of decomposing water at its 

 boiling temperature ; and, therefore, that no protection is re- 

 quired for an iron boiler used for converting water into steam. 



Wires similar to the preceding were next put into fresh water 

 and sea-water and left exposed to the atmosphere, in a room of 

 about the temperature of 60° Fahrenheit. Examined after 

 twenty-four hours, the steel wire exhibited rust, and in about 

 the same degree, whether attached to the tin wire or not at- 

 tached, the tin wires both remaining bright. The experiment 

 being continued, the rusting of the steel proceeded, and in a 

 few days a deposit of yellow rust had taken place, which 

 augmented in quantity from day to day. But not so the tin 

 wires ; even after some days they continued pretty bright ; no 

 deposit of oxide was distinctly formed on them, excepting in the 

 instance of the solitary wire in salt-water, which in two or three 

 places was very partially incrusted with white matter most pro- 

 bably oxide of tin, its surface remaining bright. 



These results were different from what I expected : The 

 steel certainly was not protected by the tin. To what was this 

 peculiarity owing ? The rust on examination appeared to be 

 hydrated peroxide of iron. No disengagement of gas accom- 

 panied its formation. Reflecting on this, and the negative re- 

 sults in the experiments in which steel had been kept in boiling 

 sea-water, I was led to the conclusion that the oxide in ques- 

 tion was formed not by the decomposition of water, but by the 

 union of the iron with the oxygen of the air dissolved in the 

 water. 



To put this to the tcbt of experiment, a portion of sea-water 



