Sal Ammoniac is a small brick or block of ammonium chloride. They are also known as a tinning block. While working with solder and your soldering iron, you can swipe the tip of the soldering iron against the sal ammoniac block and heat of the soldering iron cause a reaction that clears away built up residue and cleans the tip. This allows for a smoother soldering surface.

Sal ammoniac blocks only take a moment to use and one block will last years and years. A very small investment to protect your soldering iron and produce better work. They run about $7 and weigh about half a pound.