Soldering
The act of joining two metallic surfaces by means of a more fusible metal, or metallic cement. Solders are commonly divided into two groups, known as hard solders and soft solders; the former fuse only at a red heat, while the latter fuse at low degrees of heat. In hard soldering, it is frequently necessary to bind the parts to be soldered together with what is known as binding wire, which is made of soft iron, or the repair clamps shown in Fig. 238, or soldering forceps shown in Fig. 257. The blow pipe is used most extensively for soldering, although small soldering irons are used on the larger kinds of work. It is of the utmost importance that the meeting edges of all articles to be soldered be scraped, or chemically cleaned. While soldering, articles are usually placed upon a piece of charcoal, though asbestos, or pumice stone is better for the purpose. Charcoal emits gases from the coal while under the blowpipe, which enter into the alloy of gold or silver and render it brittle. To prove this, reduce a small piece of 1ok gold to a liquid form on a piece of charcoal, and treat a piece similarly on a piece of asbestos or pumice stone, and after allowing each to cool, subject both to a heavy pressure, and note the difference in their malleability and ductility.