IRON RUST. 309 



converted into ferric hydrate. (See Decay of Gas Pipes in 

 certain Soils. G. Foord. Transactions Royal Society of 

 Victoria, 1874). 



It was found that the gas pipes near the site of the Mel- 

 bourne Old Exhibition were subject to very rapid decay. 

 The site is one hundred feet above high water-mark of 

 Hobson's Bay. The porous soil of harsh nearly white 

 mottled permeable clay is also favourable to drainage by 

 percolation, and described as free from any constituent likely 

 to corrode the pipes unduly. 



He found the specific gravity to be — 



A. — Undecayed portions 5'99 



B. — Decayed portions 2-57 



C. — Portion with thin inner shell of metallic iron... 2-88 



D. — Grey cast iron, for comparison 7-10 



" The decayed portion had lost to some extent, but not 

 altogether, its magnetic properties. It is easily reduced to a 

 greenish brown powder, approaching the tint of raw umber. 

 On solution in hydrochloric acid it evolves no hydrogen, a 

 fact which shows that it contains no residue of iron in the 

 metallic state ; when thus dissolved it leaves a bulky residue 

 of graphite, with silicon, carbon, and sulphur compounds of 

 iron and manganese." 



" The converted portion when newly taken from the 

 ground is soft, but hardens on exposure." 



Further details are given, but the above are sufficient for 

 my present purpose, except that it may be stated that Mr. 

 Foord attributes the rapid oxidation and decay to the action 

 of soluble chlorides in the soil, as has been stated to be the 

 cause in other places. 



A piece of the decayed pipe was forwarded by Mr. Foord 

 in 1869 to the late Dr. Smith, Professor of Physics in the 

 Sydney University, who gave it to me some years ago when 

 I was examining some cast iron which had been acted upon 

 by sea water. (Journal Royal Society of New South Wales. 

 Vol. 14. 1880.) 



The fragment resembles a curved shell-like piece of 

 limonite. On crushing it yields an ochre-coloured powder, 

 which is in part attracted by the magnet, but free from par- 

 ticles of metallic iron. Another piece weighing 7*397 

 grammes yielded a little iron to iodine in potassium iodide, 

 but was still wholly magnetic after the removal of the 

 metallic iron. Other portions di(l not yield any iron to iodine 

 in potassium iodide. 



