Important: Safety Warning
This page describes trade processes that use dangerously toxic materials such as cyanide solutions, mercury amalgams, or strong acids. These processes require training, equipment, and precautions far beyond what the text describes.
This information has been left in for historical purposes but should not be acted upon.
Soldering Fluxes
For hard solder use borax rubbed to a paste with water on a slate. For soft soldering dissolve a small piece of zinc in pure hydrochloric acid until effervescence ceases. Take out the undissolved zinc after 24 hours, filter the solution, add 1/3 its volume of spirits of salammoniac and dilute with rain water. This fluid is non-corrosive.
Soft Solder for Smooth Surfaces. Where two smooth surfaces are to be soldered one upon the other, you may make an excellent job by moistening them with the fluid, and then, having placed a sheet of tin foil between them, hold them pressed firmly together over your lamp until the foil melts. If the surface is fitted nicely, a joint may be made in this way so close as to be almost imperceptible. The bright looking lead, which comes as a lining for tea boxes, is better than tin foil,