ACTION OF WATER ON IRON. .307 



These two electricities, notwithstanding their reciprocal attrac- 

 tion, remain in equilibrium at the surface of contact, which they 

 are not able to break, and they only recombine when we esta- 

 blish the communication between the iron and the solution by 

 means of a wire of gold or platina. Hence it results that the 

 iron rendered constantly negative is found in the least favoura- 

 ble state for combining with the oxygen of the air present in 

 the solution. 



It is unnecessary here to pursue the extract into the rationale 

 and objections thereto discussed by the authors, as I merely wish 

 to indicate the class of experiments which are the most valua- 

 ble as regards our subject. Others very analogous, in which 

 anthracite, plumbago, and sesquioxide of manganese are the 

 agents, are to be found in Becquerel's fifth volume of his Traits 

 de I' Elechncit^. 



138. The subject, of which I have thus given I fear a very 

 imperfect sketch, is a wide and important one, and many care- 

 ful experiments are wanting to complete our knowledge of it. 

 The following especially are desiderata immediately applicable 

 to the engineer and also to the chemist. 



1st. A series of experiments to determine the rate of pro- 

 gression of corrosion in sea water and fresh, at increasing 

 depths, from to say 10 fathoms. 



2nd. A comparative series for this reaction at the various 

 temperatures of the sea and of rivers, &c. known to be found 

 within the the range of our inhabited climates. 



3rd. A determination of the nature and amount of air con- 

 tained in sea Avater at various depths, as recommended by M. 

 Biot to the officers of the "Bonite." 



4th. A set of comparative experiments on the action of sea 

 water, diluted with various known proportions of fresh, as at 

 the mouths of tidal rivers. 



5th, Experiments are wanting as to the effects of the pre- 

 sence of animal matters in a state of putrid fermentation in sea 

 and river water, in modifying their action on iron, as in rivers, 

 &c. receiving the sewerage of cities. 



6th. Determinations of the amount and nature of the plum- 

 bago produced from various makes of iron, its precise compo- 

 sition, and the conditions of its heating or not spontaneously, 

 with the results of this action. 



A careful repetition of many of the experiments on the action 

 of pure water, and of air and water on iron, is also needed, the 

 results of former experiments being neither satisfactory nor 

 uniform. 



A paper of some novelty on this subject has just appeared in 



