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.
(6) For soldering without the use of an iron, the parts to be joined are made to lit accurately, either by filing or on a lathe. The surfaces are moistened with soldering fluid, a smooth piece of tinfoil is laid on, and the pieces are pressed together and tightly wired. The article is then heated over the fire by means of a lamp until the tinfoil melts. In this way 2 pieces of brass can be soldered together so nicely that the joint can scarcely be found.
(7) For soldering brass to platinum, put a piece of thick brass wire in a handle, and flatten and file the end like the point of a soldering bit; dip this end in soldering fluid, and, holding it in the flame of gas or lamp, run a little solder on it; now, having put some fluid on the platinum, which will require to be supported with a fine pair of tongs, place it near the flame, but not in it, at the same time heating the brass wire in the flame with the other hand, and as soon as the solder melts it will run on to the platinum; you must put very little on, and take care the solder does not run to the other side. Having applied soldering fluid or rosin to the brass, hold the two together in any convenient manner, and warm them in the flame till the solder runs. It is best to use rosin for electrical work, unless the work can be separated and thoroughly cleaned.
For making a chain, procure a piece of hard wood or metal, the cross section of which will be the same shape as the intended links. The wire must be wound on this - then, with a fine saw, cut through each link and form the chain (or a part thereof). Have a large piece of pumice or charcoal (preferably the latter), with a nice fiat surface, and arrange the chain on it ready for soldering, the points of each link being turned the same way; the solder must be hammered thin, and cut into very small pieces. Get a piece of borax, and grind it on a slate with water; now, with a small camel-hair pencil, touch each joint with the moist borax, and with the point of the pencil pick up a piece of solder and place it over the joint. When every link has been so treated, heat them with the blowpipe till the solder runs; do not attempt to heat them all at once, but direct the flame (and your attention) to one link after another, till all are soldered - then boil them in water, to which is added a little sulphuric acid. For this purpose you should use a copper or porcelain "pickle pan"; for solder, take a mixture of 1 part brass and 2 of silver, melted together and rolled or hammered very thin.
In order to make neat joints, the solder must be cut very small, and only put the borax just where you wish the solder to run. The charcoal or pumice-block you can grind flat on the hearthstone, or use an old file for the purpose; an ordinary blowpipe, which you can buy for id., will answer every purpose. You can also buy the silver solder ready for use. Spelter solder can be used for this purpose, but is not so convenient.