Q. We have a tank lined with copper and supplied with water from a well. There is some substance in the water that causes the solder to corrode. Can you inform us of anything with which we can cover the inside of the lining that will prevent the action on the solder?

A. We think that a coat of "black varnish," put on when the tank is perfectly dry, would prevent the water from coming in contact with the solder, and consequently prevent the corrosion.