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62 RICHARDSON'S BLUEBOOK OF PROJECTION
he understand the process of soldering very thoroughly. A poorly soldered connection in a power line may be a fire hazard, or at the least the cause of serious trouble. In sound apparatus it may produce noisy sound, or temporary, "mysterious" stoppages of sound. Since there are hundreds of soldered connections in any sound equipment, and since almost all of them may and probably will cause trouble if improperly made, and since the exact source of such difficulties is not easy to find, it is necessary that every connection be a good one. As a matter of routine precaution all the soldered contacts in a sound system should be inspected once a year, and those that look doubtful in any way remade.
(13) Soldering is a special form of welding. If two copper conductors be brought together and extreme heat applied, the surfaces of the metals will melt into each other, and when the heat is removed the two metals will have become one. This is "welding." Welding is not used in the projection room because of the extreme heat required for it. Soldering is a modification of the process which works at a far lower temperature.
(14) If two lumps of sugar are brought together and a thin film of water is run between them (at temperatures below the freezing point) the water will melt into the surface of each lump and when it freezes it will freeze the sugars into one piece. This is essentially the process of soldering. Solder is an alloy of metals having a low melting point, and capable when molten of dissolving into the surfaces of other metals just as liquid water dissolves into a lump of sugar. When the source of heat is removed the solder freezes (solidifies) and holds the two metals together mechanically; moreover, because it has dissolved into the two surfaces, it provides a most intimate metal-to-metal contact of excellent conductivity. But this result will be obtained only if the soldering is properly done. There are a number of reasons why the process sometimes fails. It must be applied properly by projectionists, with certain precautions.
(15) Soldering involves three requirements: cleanli ness, the right "flux," and the right heat.