a. Types of flux.
(1) General. There are two classes of flux: corrosive and noncorrosive. A
corrosive flux, such as borax, sal ammoniac, or zinc chloride, is used when
soldering galvanized iron, zinc, iron, and steel. A corrosive flux should seldom
be used on electrical work as it eats away the metal being soldered. When a
corrosive flux has been used, the joint must be thoroughly cleaned to remove any
trace of flux that may be left on it, thus preventing the flux from eating away any
of the material. Noncorrosive fluxes, such as stearine, rosin, and tallow, are
used when soldering tin, copper, lead, etc. The noncorrosive flux prevents the
forming of oxide and cleans the metal surfaces without eating away any of the
surface material. Rosin is the most common noncorrosive-type flux.