[Illustration: Fig. 14.--Gas-stove for Heating Bits]
=Stoves for Heating Soldering Bits.=--Although a copper bit may be heated in any fire, it is better to avoid the dirt, smoke and tarry stickiness which are often present in a coal fire. In the absence of gas, a bright, clear coke fire or a charcoal fire should be used whenever available. Portable oil stoves of the wickless type can also be employed, but the ideal fuel is gas, which may be regulated at will to give a uniform temperature. Two gas-stoves specially constructed for copper bits are shown by Figs. 14 and 15.
[Illustration: Fig. 15.--Gas-stove for Heating Bits]
=Tinning a Bit.=--Before a bit can be used, it must be “tinned,” that is, coated with solder in a smooth complete covering, for which purpose--by one method, not the best, but the most general--the end is heated to a dull red, rubbed quickly with the file on the facets, dipped in killed spirit or “fluxite,” or rubbed against a piece of sal-ammoniac, and then applied to a stick or lump of solder, the facets being quickly wiped or rubbed on a piece of tinplate so as to spread the solder evenly. When properly done, the nose of the bit is coated with a smooth film of solder. This must always remain so, or the bit will not act, and when it is honeycombed, or the “tinning” is present in patches, it must be re-tinned. A bit must never be raised to a red heat sufficient to melt the tinning. The bit does not operate well at such a heat, because its contact makes solder too fluid and apt to run too quickly.
When dipping a hot bit, prepared for tinning, into killed spirit, a sharp pop, without smoke or spluttering, denotes the right temperature. If, on withdrawing the bit, it is damp and still unclean, it had not been heated sufficiently.
Another method of tinning may be mentioned. Into a small and clean tin box (a 2-oz. tobacco tin about 3/4 in. deep) put some scraps of solder and powdered resin. Heat the bit to a very dull red, quickly file up clean on one side of the point, and then plunge into the solder and resin and rub about; it will at once take on a coat of the alloy. A second side of the bit may be tinned by then repeating the operation, re-heating if necessary. The bottom of the box should be covered with solder, which adheres easily enough, with a film of resin on top. It is probably most convenient to tin the under side and the left-hand working face of the bit. “Tinol” could be used in this way without admixture with anything.