_Smoke Staining._—This method of coloring barrels is as follows: The barrels are washed with a little sulphuric acid, to cause the metal to receive the effects of the gas more readily; it is then washed off, and the barrels rubbed dry. A fire is built with coal possessing as much hydrogen gas and as little sulphur as possible. Burn the coals until they give a clear, white flame, with no black smoke. Pass the barrels through that flame, backward and forward, until the whole are covered with a black, sooty coating. Place them in a damp, cool cellar and let them stand about twenty-four hours, and if the place be sufficiently damp, the iron parts will be covered with a red rust, while the steel portions still retain the sooty coat. Scratch them off with a wire card and rub with a piece of cloth, and wash or polish with water, using on the cloth a little flour of emery. The steel will be found to be of the original bright color, while the iron will be a little darker. Rub dry, and pass the barrels through the flame again. Allow them to stand about twelve hours to rust, and then polish as before. With every smoking the colors will be a little darker. The darkest color to be obtained is a fine purple-black color on the iron; the steel inclining to a copper color. The principle of this stain is simply the hydrogen gas contained in the coal acting on the iron, iron being of a softer nature than the steel, which it does not affect, the flame also possessing a quantity of tar, it is imperceptibly embodied by the iron during the action of the oxide, and, when finished, by filling up the spaces created, it becomes decidedly more impervious to damp or wet than any other stain or browning which is composed entirely of oxide of iron. CHAPTER XXXI. RECIPES FOR BROWNING GUN BARRELS. _Solution for Browning Gun Barrels._—Make a solution by putting together in a glass vessel, spirits of nitre, three-quarter ounce; tincture of steel, three-quarter ounce; black brimstone, one-quarter ounce; blue vitriol, one-half ounce; corrosive sublimate, one-quarter ounce; nitric acid, one drachm, and copperas, one-quarter ounce. Mix with one and one-half pints of rain water, and bottle for use. Clean the barrel till entirely bright, rubbing it over with finest emery paper, then apply the solution with a clean white cloth. Set away for twenty-four hours. At the end of this time a rust will have formed over the barrel. Go over it with a steel scratch-brush, then rub off all the rust with a woolen cloth. If you find the brown not dark enough, cover again with the solution and set away twenty-four hours longer. Remove the rust exactly as in the first instance, then, the color suiting, wash off with a wet cloth, rub to thorough dryness, and finish by rubbing with linseed oil, to prevent further rusting. This application browns the barrel beautifully, and in case of twist leaves the markings prominently plain.