_Soldering Fluid._—A soldering fluid for jewelers’ use is made by adding to alcohol all the chloride of zinc it will dissolve. _Brazing._—This consists in uniting iron and other hard-melting metals with a brass solder. Put the parts together as for soft soldering, lay the brass between the pieces or along the upper edge of the joint, if it can be held vertically, and add a goodly supply of pulverized borax to act as a flux. Heat over a charcoal fire till the brass melts and runs down into the joint, then take from the fire and cool. Before beginning the operation of brazing the parts to be put together must be made entirely clean, and then freshly filed to brightness. _To Braze Lugs on Gun Barrels._—When not practicable to fasten the lugs by means of pins or rivets, hold them in place with binding wire. Take a piece of iron, say ¼ inch thick and 2 inches or more in width, and make in it a slot some larger than the lug to be brazed. Lay the barrel on the iron sideways, and pack up the lug so as to lie level, if necessary, also taking care that it is on straight. Pure copper is excellent for all kinds of brazing, when the color of the copper is not objectionable. _Hard Soldering._—See “To Solder Brass,” in Chapter XII, which about covers the whole thing, varying only in the composition of the solder for different metals. The brass solder there described acts equally well for soldering copper, but for silver a solder is made composed of two parts silver and one part brass. _Hard Solders._—1. A hard solder that is yellow and easily fusible is made of copper, 4½ parts, and zinc, 5½ parts. 2. To hard solder iron use good tough brass or sheet copper, with borax as a flux. 3. Pure copper, cut in thin strips, with borax as a flux, is excellent for brazing iron or steel. _Alloy for Adhering to Iron or Steel._—Melt together, tin 3 parts, zinc 7½ parts, and copper 39½ parts. Clean the iron or steel, file to brightness and cast the alloy upon it. The iron or steel should be heated up to about the melting temperature of the alloy. This alloy will adhere firmly to the other metal, and as its rate of expansion is about the same as the iron or steel, under all circumstances, it will never come loose. It finishes up nicely and presents a very neat, light yellow appearance. Some gunsmiths use it for brazing purposes on account of its adhesive properties and its ease of fusion. It does not make so strong a joint as brass or copper, and therefore would not give so “honest” a job. _Gun Oil._—A good quality of sperm oil is undoubtedly the best oil to apply to gun work, especially the locks. Any fine animal oil may be used as a substitute. The oil from the fat of the woodchuck or ground-hog is admired by many. Fine quality of sewing-machine oil is very good. It must not be thinned or “cut” with kerosene or benzine, as this reduces its wearing quality. It must not thicken with exposure to the cold.