Decay of Gaspipes in certain Soils. 17 



me to present to your Society as a " laboratory note " what 

 would otherwise remain in its place among the daily memo- 

 randa of laboratory work. 



The facts of the case are the following : — Close to the site 

 of the Melbourne old Exhibition building it has been found 

 that the gas-mains are subject to an imusually rapid decay. 

 The ground in which this quick decay occurs is at a high 

 level (no less than one hundred feet above high-water mark 

 in Hobson's Bay). It is one of the highest points in the city ; 

 the position, in fact, affords an excellent panoramic view of 

 Melbourne. It would, therefore, appear to be favourably 

 situated for drainage by percolation through the porous soil. 

 The pipes, the subject of this note, are laid eighteen inches 

 below the surface, in a nearly white mottled clay, which to 

 mere inspection shows no external evidence suggestive of 

 any constituents favourable to a rapid destruction of the 

 pipes. 



The sample of decayed pipe as received by me presented 

 the following characters : — In some places it had entirely lost 

 its metallic properties; it had passed out of the metallic state, 

 but had retained its original form. In other places, an inner 

 shell of unconverted cast iron remained. In one of the 

 samples, which I submit, the converted portion is indicated by 

 the mark A , and the unchanged part by tlie mark B. Sample 

 is wholly converted. D shows that the wrought-iron plugs 

 are almost or quite exempt from the change. £1 is a sample 

 of the substance of the converted pipe reduced to powder in 

 a mortar ; an impalpable odorous brown powder. 



It may be here pointed out that the continuity of the 

 changed parts, the continuity of the unchanged metallic 

 portions, and the unchanged conditions of the wrought-iron 

 plugs, are facts suggestive of a gradual conversion of the cast 

 iron, progressive in space, and that the conversion proceeds 

 under a galvanic agency, in which the graphite of the cast 

 iron probably plays theg,part of the electro-negative element 

 in a simple circuit of two solids and one fluid. The decay 

 takes place from without inwardly. 



The specific gravities of the decayed and unaltered or 

 slightly altered portions of the pipe, are significant. 

 The specific gTavity of the sounder portions of the pipe 



was ascertained to be ... ... ••• 5 '99 



That of the decayed or converted portion ... ... 2 '57 



A sample with thin inner shell of metallic iron ... 2'88 



Gray cast iron (for comparison) being ... ... VI 



c 



