ACTION OF WATER ON IRON. 293 



Rotterdam, determines the corrosion of iron in presence of tin, 

 and its amount : — 1st. A plate of iron weighing 32-907 grains 

 was placed in a glass vessel containing one litre (= 61 -028 cub. 

 in.) of sea water, during 20 days, at the temperature of the 

 month of November 1836 (at Rotterdam namely). After the 

 experiment the weight of the iron was found to be = 32-72G 

 grains, loss by oxidation = 0*1 81 grain. 



2nd. A similar plate of iron, exactly of the same weight of 

 32-907 grains, but on whose surface was fixed a small piece of 

 tin weighing 8-140 grains, was in the same manner exposed for 

 20 days in one litre of sea water : the weight of the iron, after 

 the experiment, was found to be = 32'674, that of the tin 

 8-139 grains J hence loss by oxidation of the iron = 0-233 

 grain, and loss by oxidation of the tin = 0-001 grain. These 

 results show that the iron, when exposed to sea water as above, 

 alone lost by oxidation 0-052 grain less than when in contact 

 with the tin. 



Van Beek, in recording these experiments, observes, that the 

 action on the tin must have taken place at the first moment of 

 immersion of the metals, and before it had become negative 

 with respect to the iron. — {Netv Edin. Phil. Journ., Oci. 1837.) 



98. De la Rive has observed an analogous change of electri- 

 cal state in these metals in a different research, and the fact is 

 a very important one as regards our subject : it may possibly be 

 hereafter found that the diminished preservative power of zinc 

 to iron, after a length of time, has an analogous cause, as may 

 the following like phenomenon. It sometimes happens that 

 when one of Schoenbein's inactive wires, and another rendered 

 inactive by it, have remained together in a tube of nitric acid 

 for a very considei-able time perfectly passive, they at length 

 suddenly, and without any assignable cause, both become active, 

 and the reaction on the iron is so miusually violent, that most of 

 the acid is instantly driven out of the tube with a sort of ex- 

 plosion. 



99. We have now to consider the subject of a communication 

 made at the last meeting of this Association, at Liverpool, by 

 Mr. John B. Hartley of that town, upon the power of brass to 

 preserve cast and wrought iron in sea water. Mr. Hartley is 

 reported to have stated in the Chemical Section, that certain 

 iron sluices having brass in connexion with some of their parts, 

 had on examination been found perfectly sound and uncorroded 

 in the neighbourhood of the brass, after an exposure of twenty- 

 five years, but were corroded elsewhere; and that in conse- 

 quence of this discovery, all the iron work below the tidal level 

 employed in the Liverpool Docks had been placed in connexion 



VOL. VII. 1838. U 



