22 Decay of Gaspipes in certain Soils. 



gas mains. This would make the life say 6Q years, or nearly 

 two-thirds of a century, according to which computation 

 renewal of the gas mains laid at the beginning of the present 

 century, when gas lighting was coming into general use, 

 would now be falling due. Recently, in Melbourne, for 

 business purposes — that is to say, as the basis of a 

 commercial transaction— a duration of 50 years was 

 arbitrarily assumed and accepted as the " life " of local gas 

 mains. Between the normal rate, if approximated in these 

 quotations, and that which may take place in a salt soil, the 

 difference is very great, and the subject is therefore one 

 deserving of a full investigation. In laying down a service 

 like that of the Yan Yean, we are, perhaps, too apt to regard 

 the work as of an absolutely permanent character. Several 

 years ago, the writer recommended, in reference to that 

 particular service, that sample portions of the pipes should 

 be set aside, properly labelled, so as to afford the means of 

 future comparisons. He would now suggest the possibility. 

 of decay of cast-iron buried in the soil taking place at an 

 accelerating, rather than an uniform rate— in a manner, for 

 example, comparable ^,0 what takes place in the decay of 

 timber. It might be well worth while to ascertain something 

 concerning the earliest stages of molecular and chemical 

 changes of cast-iron mains ; when their conductivity for 

 sound, for heat, and for electricity is first measurably affected ; 

 when the specific gravity is first sensibly altered ; when the 

 strength is first in any sensible degree impaired ; and when 

 the proportion of carbon, silicon, &c., to that of iron, is first 

 measurably altered? Notwithstanding the inquiries of 

 Hallet, under the auspices of the British Association, 

 concerning the oxidation of iron, and admitting the value of 

 the various researches by other workmen, if we are to judge 

 from what appears in the books on this important subject, 

 there is yet an ample field and much promise for those who 

 will devote their time to a further opening of the inquiry. 

 Anyone devoting effort to this particular subject of the decay 

 of gas and water mains would, it is believed, reap results of 

 great value a,nd interest. 



Apart from this larger work, there is a set of observations 

 of another class, easy of performance, and which would 

 always repay attention — that, namely, of ascertaining 

 the nature of ground opened for the reception of mains, 

 particularly as to saltness or freedom from salt. The writer 

 is inclined to the belief that salt soils are far more common 



