This section is from the book "Spons' Mechanics' Own Book: A Manual For Handicraftsmen And Amateurs", by Edward Spon. Also available from Amazon: Spons' Mechanics' Own Book.
Various nostrums have been proposed from time to time which profess to be reliable methods of soldering without heat; but when tried, they have generally proved useless. The following recipe, which is due to Fletcher, of Warrington, will be found to be more trustworthy. It must be borne in mind that, though the first preparation is tedious, a large quantity of the materials can be made at once, and the actual soldering process is as simple and quick as it well can be.
Flux 1 part metallic sodium to 50 or GO of mercury. These combine on being well, shaken in a bottle. If this is too much trouble, the sodium amalgam can be bought, ready made, from any chemist or dealer in reagents. This sodium amalgam must be kept in a stoppered bottle closed from the air. It has the property of amalgamating (equivalent to tinning by heat) any metallic surface, cast iron included.
Solder Make a weak solution of copper sulphate, about 1 oz. to 1 qt. of water. Precipitate the copper by rods of zinc; wash the precipitate 2 or 3 times with hot water; drain the water off, and add, for every 3 oz. of precipitate, 6 oz. or 7 oz. mercury; add also a little sulphuric acid to assist the combination of the 2 metals. When combined, they form a paste which sets intensely hard in a few hours, and this paste should be made, whilst soft, into small pellets.
When wanted for use, heat one or more of the pellets until the mercury oozes out from the surface in small beads; shake or wipe them off, and rub the pellet into a soft paste with a small mortar and pestle, or by any other convenient means, until it is as smooth and soft as painters' white-lead. This, when put on a surface previously amalgamated by the sodium and mercury, adheres firmly, and sets perfectly hard in about 3 hours. The joint can be parted, if necessary, either by a hammer and cold chisel, or by a heat about sufficient to melt plumbers' solder.