I'm afraid that this is a bit of a badly-curated wander, where I mostly just popped out to find out a little of the history of Underfall Yard and poke around the various open workshops, and, in hindsight, really didn't take pictures in any kind of coherent order. So there's a lot of pictures, but they don't really tell the story that, in hindsight, I seem to have been trying to tell, of the unusual electrical substation in Avon Crescent, the Bristol Electricity that predates the National Grid but is still in use, the history of the hydraulic power house... It's a bit of a mess.
But I suppose sometimes these wanders—always chronologically presented in the order I walked and took photos—simply will sometimes be a bit of a mess. Let's hope you still get something out of it, anyway...
Borax powder being used as flux here, helping to prevent oxidation of the metal surface during the joining of the ends of the link.
Random aside: borax was also used to prepare boracic acid, used in medical dressings, especially for the treatment of leg ulcers. The medical lint was soaked in boric acid and gycerine, and then left to dry, producing "boracic lint". The was then used in cockney rhyming slang to mean "skint".