—When the surface of metal to be soldered is badly corroded, and it is difficult to obtain a clean, bright surface preparatory to soldering, it should be treated to a liberal application of raw spirits of salts (hydrochloric acid), which will soon remove the cause of the trouble, but all traces of the acid should be washed away with clean water before attempting the soldering. It is also a good plan in these cases to tin the surface by repeatedly rubbing it with a hot bit and solder, together with plenty of killed spirits, before proceeding with the actual soldering process.
Soldering Small Work.
—When soldering two small awkward-shaped pieces together, they can be held in position by pressing slightly into a piece of damp clay. When the work has several soldered joints it can be buried in sand or covered with clay to confine the heat to the part being operated on.
Although care should be taken to limit the solder to the area of the joint, there are circumstances in many cases where it is difficult to prevent some of it from straying. To clean this off, resort may be had to the blowpipe, applying the blast and quickly wiping the surface while the solder is in a molten state. Or it may be filed off while cold and finished with a scraper or a knife and emery-cloth. Or if there is only a thin film the knife or emery-cloth alone will suffice.
Soldering Pipe Joints.
—Most joints in lead, tin and compo. pipe are now preferably made by means of a blowlamp, or with a mouth blowpipe, strip-solder being used. When making the joint, heat the pipe in the immediate vicinity, and, dipping the solder in the flux, stroke it around the pipe to form the joint.
In soldering block tin or compo. pipe with a bit, if this is too hot it will promptly melt the pipe. This is also liable to happen with very thin zinc. The only way to prevent this is to have the bit just hot enough to melt the solder, and not to let it rest any length of time on the soft metal.
Figs. 42 and 43.—Soldered Branch Joint on Tin or Compo. Pipe