[Hartley118]

Having learned my chemistry from obsolete textbooks originally owned by my grandfather, I recall that ‘spirits of salt’ is the old name for hydrochloric acid. ISTR it being the original flux used when I was taught soldering by my father with a big gas-ring-heated iron. Later, in my apprenticeship, it was used in sheet metal soldering. I’ve always found it very effective, but it does need washing off thoroughly!

I have seen bottles of descaling fluid labelled ‘spirits of salt’, but haven’t tried it as a flux.

Martin