Johnson's Soldering fluid contains no free acid. It is highly active when heated (becomes active at 150 ° F) yet it is nearly inactive when cold. Johnson's Soldering Fluid will do more soldering per pound than any other flux, liquid or powder. Johnson's Soldering Fluid may be diluted; mix with equal volume of water for radiator repair; use full strength for tough jobs. Reapply extra flux while work is hot if necessary for the most difficult jobs. Residues wash off with water.