A flux is used to clean the surfaces of joints and seams to be soldered, also to keep them from oxidizing and to help the metals to fuse.

The following list gives the names of various fluxes in common use, how they are applied, and on what material they are most commonly used:

FluxHow appliedUsed on
RosinSprinkled onLead, tin, and brass
TallowMeltedLead and brass
Muriatic acid (reduced)With swabCopper, galvanized iron
and brass
Muriatic acid (raw)With swabDirty galvanized iron


Rosin is purchased by the pound and comes in chunks. It is very brittle and powders easily. Plumbers generally take a piece of 11⁄4 N. P. brass tubing, solder a trap screw in one end and a cone-shaped piece of copper on the other. The point of the cone is left open. Rosin is put into this tube and is easily sprinkled on work when needed.


A plumber's tallow candle answers the purpose for tallow flux. Some plumbers carry a can for the tallow, making it cleaner to handle.

Muriatic Acid

Muriatic acid or hydrochloric acid is used both raw and reduced. Raw acid is not diluted or reduced. Reduced acid is made as follows: Put some zinc chips in a lead receptacle and then pour in the muriatic acid. The acid will at once act on the zinc. The fumes should be allowed to escape into the outer air. When chemical action ceases, the liquid remaining is called reduced acid.