I've used a similar technique I learned in the oilfield.<p>To solder a splice - 1) strip both conductors to be soldered about 1/2" and form a loop on one. 2) Stick the second conductor through the loop formed in the first and bend a loop around to join the wires. 3) Cut or break about 1/2" of solder/flux and lay on something flat, clean, and hard - 2 out of 3 is good enough here. 4) Use a hammer, flat rock, end of pocketknife, etc to flatten the solder until it is about 1/8" wide and maybe twice as long. 5) Wrap the flattened solder around the loops so that the join is covered by solder. 6) Strike a match, use a lighter, a torch, etc to melt the solder and flux into the joint. 7) Cover with weather-tight electrical tape and go on about your business.<p>It never failed for me.
This is similar to solder seal wire connectors: <a href="https://www.youtube.com/watch?v=pGKsXSiFww4" rel="nofollow">https://www.youtube.com/watch?v=pGKsXSiFww4</a>
When I was at school I was in the combined cadet force, and being interested in electronics I gravitated to Signals as it was known.<p>On exercises it was our job to provide communications and quite often we would lay miles of copper wires in the woods for the field telephones and join the wires together with these devices.<p>The black powder is some kind of thermite I think - lighting it would melt the solder in the copper tube, you'd push the copper wires you'd pre stripped into it and you'd hold it long enough for it to solidify, which was sometimes long enough to burn your fingers!<p>In the UK in the 80s the CCF had lots of surplus WW2 equipment. Beautiful valve radios and classic 303 rifles!
Reminds me of rail road thermite welding:<p><a href="https://www.youtube.com/watch?v=5uxsFglz2ig" rel="nofollow">https://www.youtube.com/watch?v=5uxsFglz2ig</a>
What would actual use case for this look like? The post mentions communication, but the usefulness of laying communication lines behind enemy lines seems like it would be minimal. Lines would be easily discovered and would lead right back to the spy or scout. The other use could be for demolition which I could see, but if I were a saboteur I would just twist the lines together as it's very temporary and time is of the essence.
There's a similar technique used in plumbing when you need to solder together two pipes.<p>There's a pre-made fitting (H cross section) which has solder rings inside. You press the pipes in and heat it until the solder comes out on both ends.<p>The technique needs an external source of heat but that's not generally a problem in civilian plumbing.