HAMILTON SCIENTIFIC ASSOCIATION 123 



to the experienced engineer the whole electric (if it may be so 

 termed) situation, and points ont the places where he may 

 expect electrolysis to be proceeding. Investigations are 

 made at the points so indicated and openings are made to the 

 pipes. It is surprising to find how truly the information 

 obtained from the plan or map is verified, as in almost all 

 cases where electrolysis is expected to be found, on digging 

 up the ground these predictions are found to be correct. 

 Having from these maps and from excavations obtained the 

 requisite knowledge of the places where electrolysis is 

 proceeding, the next thing is to suggest a remedy. 



There is, I believe, some difference of opinion as to this. 

 Some authorities holding that any system of electric propul- 

 sion necessitating a return of current through the rails is 

 unsafe, and insisting that the double trolley system or some 

 analagous system is the only way to entirely be rid of damage 

 to the water and gas mains. 



Others hold that by the proper bonding of the rails and 

 by metallic connections in the positive area near the power 

 house, or the places where the difference of potential is great- 

 est, the current flowing from the pipes to the rails will be 

 reduced to a negligable quantity. Again it has been said 

 that if the alternating current could be employed instead of 

 the direct current, as is usually done now in electric railways, 

 the evil complained of would be done away with. 



The ordinances for the prevention of electrolysis to 

 metallic structures, which have been introduced into cities, 

 have some of the following provisions inserted. These are 

 taken from Atlantic City ordanances : — 



" No bonding will be allowed to be made to the water or 

 gas mains in order to equalize the potential between the con- 

 ductors and rail, but means must be taken by furnishing an 

 insulating or complete metallic circuit to effectually prevent 

 current from the wires or rails of the railway. 



" The company or individual operating the street rail- 

 way may select the particular method of securing this 

 protection, and will be held responsible only for the result. 



