OLD COAL-PIT WATER UPON IKON. 



37 



of local actions on iron, and has added to their explanation the 

 facts he had previously discovered as to the effects of alkaline 

 and saline solutions in retarding or accelerating the corrosive 

 action of water on iron. Sir John Herschel, in a letter in 

 the Comptes Rendus for 1836, page 509, recommended an 

 engineer at the Cape of Good Hope to soak some iron pipes 

 with Roman cement, and it produced a good effect in pre- 

 venting their decomposition. 



Mr. Mallet f states that M. Payen's observations as to the 

 power of alkaline waters to protect iron from rust, though 

 seldom applicable, are worthy of further investigation, and 

 an attempt to preserve their rationale; and he then alludes 

 to the circumstance of workmen having been long aware of 

 the fact, and suggests that alkaline solutions might be of 

 considerable use in certain cases, but he makes no mention 

 of coatings of lime on the iron itself. 



I have thus given a brief description of the specimens of 

 altered iron, and, so far as I am able, of the circumstances 

 under which such alteration took place. The removal of 

 iron in acid solutions, where the softer portions are first 

 decomposed, is well known, and now generally attributed to 

 the want of homogeneity in its parts, which causes galvanic 

 currents. In waters of the Pendleton colliery, sulphuric, 

 hydro-chloric, and carbonic acids would all be present, and 

 produce their effects upon the iron ; but these would, doubt- 

 less, be much assisted and increased by the pressure of a 

 vertical column of 1,352 feet of water acting upon the air 

 and gases of the mine. This great pressure on the air and 

 gases (carbonic acid and light carburetted hydrogen) in the 

 mine, would cause the water to be charged with them in a 

 highly condensed state, and thus bring them into a condition 

 peculiarly appropriate for combination. 



The cast iron wheels lying in contact with coal, and im- 

 mersed in water containing acid solutions, would present 

 t 8th Report of the Brit. Ass., p. 305. 



