Killed acid or soldering fluid is usually applied with a small camel’s-hair brush set in a quill; sometimes a chicken feather is used for this purpose.
The flux, whether paste or acid, should be applied sparingly, but be sure that enough is applied to thoroughly cover the joint, as if it were painted on both sides of the metal where it joins.
See to it that the copper is well tinned and heated until it will melt and take up a good sized drop of solder at the point when held against a bar or strip of solder. Wire or strip solder is much easier for the beginner to handle than the heavier bar. It melts far more easily, as it is smaller.
If bar solder is used, place it on an anvil or stone and hammer one end out, until it is about ⅛ inch thick and much wider than the original bar. It will melt off much more quickly when thinned out.
Hold the semi-circular piece in position with the left hand and with the right bring the hot copper charged with molten solder at the tinned point and fit the point of the copper closely into the angle formed by the joint, moving the copper very slowly along the joint, starting at one side and finishing at the other.
When each side of the joint is thoroughly heated up to the melting point of the solder, some of the solder will leave the copper and flow into and over the joint; so that when starting to solder a joint the copper should be allowed to rest a moment where the soldering is to be started. The tin is then heated up and when the solder starts to flow into the joint, the copper is drawn slowly along, heating up the tin, and as it travels flowing the solder into the joint.
The following points should be well remembered when soldering:
That the tin, to be soldered, must be heated up to the melting point of the solder before the solder will leave the copper and adhere to the tin.
That the copper supplies the heat to the tin and that the tin will not be heated unless the copper is kept in contact with it long enough to heat it. Enough of the copper should be in contact with the tin to be soldered for the heat to flow quickly into the tin, see [Fig. 18]. Do not merely touch the point of the copper to the joint and expect it to heat that joint: it won’t. Two faces of the point of the copper should rest against the parts of the work to be soldered, thus transmitting heat to the pieces as shown in [Fig. 19]. If too much of the point is allowed to come in contact with the work, the solder will be smeared over the work in a broad unnecessary stream. This is the reason that the points of coppers are filed slightly rounding toward the point.