ELECTROLYSIS OF GAS AND WATER MAINS. In the system of street railway traction in which an overhead trolley wire is employed, with direct current, in which the tracks are utilized as a return circuit for the current to the power-house, it has been found that damage has almost invariably ent sued to the gas and water mains adjacent to the tracks, from electrolysis. This is due pri marily to the electric current leaving the tracks and following the gas or water mains for some distance. At the points where the current leaves these pipes to return to the tracks or to the power-house, if the soil as damp and con tains soluble chlorides of magnesium, sodium or potassium, the current sets free acids or chlorine which attack the iron of the pipes; the rapidity and extent of the damage done thereby being dependent upon the strength of the current, the duration of its application and the constituents of the soil. The electrolytic
action results in c(pittine the pipes, and burst ing of water pipes and leakage of gas pipes is not uncommon from this cause. (See illustra tion). Experiments have shown that with as low a potential as 0.5 volt and a current of 0.03 ampere, noticeable electrolysis of an iron pipe has occurred in sand moistened with sea Pipes on which the difference of potential was found to be about six volts have burst in a few years. To prevent electrolysis due to this cause greater precautions are now taken, and with considerable success, to preserve the contil of the rails by bonding, welding them in situ bl electricity by providing separate metallic re turn circuits and by connecting the water am gas mains by means of heavy copper wire a places where the current would otherwise re turn to the tracks via the earth.