18 Decay of Gaspipes in certain Soils. 



The decayed portion liad 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 of the pipe, when newly taken from 

 the ground, is soft, but hardens on exposure. During this 

 induration shrinkage takes place, the converted portion 

 separates from the unconverted, and cracks appear in the 

 mass. 



But another interesting manifestation takes place when 

 the pipe is exposed to the air ; after it has lost the greater 

 part of its free-moisture, droplets of a solution of protochloride 

 of iron are extruded from its pores. The drops of pale green 

 fluid soon become covered with a rust-red film of hydrated 

 sesquioxide of iron ; the little fluid drops soon disappear by 

 evaporation, leaving hollow sheUs of iron oxide, with possibly 

 some oxychloride. It is pretty clear that in the fluid forming 

 these drops the chlorine of the chloride of iron acts chemically 

 as a " carrier," and is conducive to the ultimate conversion 

 of the iron to the state of oxide ; it is also clear that the 

 chlorine, by combining with the iron and forming a soluble 

 salt with it, enables the water to remove the metal through 

 sensible distances of space. In pseudomprphic changes of 

 the kind considered, this purely mechanical transposition of 

 the materials is always an essential part of the process of the 

 rebuilding, in new chemical forms, of the old materials. 



The general composition of the altered portion of the pipe 

 is shown by the following figures : — The powdered material 

 gives ofl" over. 13 per cent, of moisture when heated, and it 

 leaves as undissolved residue 28 per cent, of its original 

 weight when digested in hydrochloric acid. The iron solu- 

 tion obtained by thus treating it contains protochloride of 

 iron equal to oxide and chloride of iron in the decayed pipe 

 to the extent of a little over half its weight. 



How far these contents of the altered pipe account for all 

 or only a portion of the original constituents of the metallic 

 cast iron, or what proportion of the metal is removed in 

 solution, I have not ascertained ; the low specific gravity of 

 the altered portion would imply either removal or expansion, 

 probably both have taken place. 



