IRON RUST. 319 



It consisted of a brownish substance, in which were 

 embedded numerous shining black particles, and resembled 

 very much in appearance a piece of rusty grey pig iron. 

 Specific gravity, 263 only, and extremely friable. A full 

 analysis is given ; there was 42"33 per cent, of ferrous oxide 

 and 2*21 per cent, of ferric oxide present. 



He states also that a specimen of ordinary iron rust scraped 

 from some cast iron (which had rusted in moist air) gave 

 65*42 per cent, ferric and 7*42 per cent, of ferrous oxide. 



Dr. F. Muck {Stahl und Eisen, viii., p. 837-41, also 

 Journal Iron and Steel Institute, 1889, i., p. 385), states that 

 the rust in a boiler formed in pits near the feed pipe had a 

 fungoid form, and dried at 100'^ C. It had the following 

 composition : — 

 Fe^O^ FeO CaO MgO SiO, SO3 CO, C H,(J Organic 

 66-84 23*24 2-60 -.39 1-18 -28 2-32 -22 2-75 -18 



The organic matter was soluble in ether, and probably 

 derived from the lubricants used. " The rust therefore 

 mainly consists of magnetic oxide." 



Professor W. Spring (Bull. Sac. Chim., vol. 50, pp. 215- 

 18, and Journal Society Chemical Industry, Nov. 30, 1888), 

 says that the cause of iron rails rusting less rapidly when in 

 use than when not subjected to traffic is not due to the vibra- 

 tion of passing trains nor to currents of electricity, nor to a " 

 film of grease derived from the engine and carriages, but 

 rather to the formation of a layer of magnetic oxide on their 

 upper surface formed by the pressure of the wheels on the 

 moist ferric oxide with which they naturally become coated. 

 He mixed damp ferric hydrate with minute particles of 

 metallic iron, and subjected the mixture to a pressure of 1000 

 to 1200 atmospheres, and found that the two adhered, and 

 that the liydrate became black to the depth of "5 mm. 

 Analysis showed that magnetic oxide had been formed. 

 He also found that the rust taken from a rail contained some 

 magnetic oxide and a little free iron mixed with the ferric 

 oxide, and came to the conclusion that rails in use are pro- 

 tected by the magnetic oxide thus formed by the pressure, 

 just as in the case of iron artificially coated with magnetic 

 oxide. 



From the foregoing experiments, and those detailed in the 



