Gun Barrels (To Brown). Take of nitric acid, half an ounce ; sweet spirit of nitre, half an ounce; blue vitriol, two ounces; tincture of steel, one ounce; mix all together in eight gills of water; apply this mixture with a sponge, then heat the barrel a little, and move the oxide with a hard brush. This operation may be repeated a third or fourth time, till you have the brown required; it is then to be carefully wiped and sponged with boiling water, in which there has been put a small quantity of potass. The barrel, being taken from the water, must be made perfectly dry, and then rubbed smooth with a burnisher of hard wood ; afterwards heated to the height of boiling water, and varnished with the following varnish : Varnish for Gun Barrels that havb Undergone the Process of Browning. Take of spirits of wine, two parts ; dragon's blood, powdered, three drachms; shellac, bruised, one ounce; dissolve all together. This varnish, being laid on the barrel, and become perfectly dry, must be rubbed with a burnisher to render it smooth and glossy.