Phosphoric acid (30g)

Excellent soldering of non-ferrous metals (copper, brass), stainless steel, chrome, nickel.
It is difficult to solder ferrous metals, but it perfectly cleans oxide compounds and rust before mounting electronic components.
For soldering ferrous metals, it is better to use soldering acid (hydrochloric acid etched with zinc).
After the soldering (or cleaning) process is completed, acid residues must be washed off with water.