The "battery" is a large kettle or boiler open at the top, having a fire beneath it, and eight planks ascending obliquely from the margin, so as to form a sort of octagonal work-bench, five or six feet in diameter, at which eight men may work; the planks are made of lead near the kettle, and of mahogany at the outer part, and at each plank a workman operates on a conical cap until the process of felting or "planking" is completed. The "battery" contains hot water slightly acidulated with sulphuric acid. The cap is dipped into the hot liquor, laid on one of the planks, and subjected to a long felting process; it is rolled and unrolled, twisted, pressed, and rubbed with a piece of leather or wood tied to the workman's hand, and rolled with a rolling-pin. From time to time the cap is examined, to ascertain whether the thickness is sufficient in every part, and if any defective places appear, they are wet with a brush dipped in the hot liquor, and a few additional fibers are worked in. Considerable skill is required in order to preserve such an additional thickness of material at one part as shall suffice for the brim of the hat. When this felting process has been continued about two hours, it is found that the heat, moisture, pressure and friction have reduced the cap to one-half its former dimensions, the thickness being increased in a proportionate degree, assuming a conical shape. The "cap" is then taken to the "water-proofing" or "stiffening" room, where the odor of gum, resins and spirits gives some intimation of the materials employed. Gum-lac, gum-sandrach, gum-mastic, resin, frankincense, copal, caoutchouc, spirits of wine and spirits of turpentine, are the ingredients (all of a very inflammable nature) of which the water-proofing is made. This is laid on the cap by means of a brush, and the workman exercises his skill in regulating the quantity at different parts, since the strength of the future brim and crown depends much on this process. After another heating in a hot room, called "stoving," by which the spirit is evaporated, the exterior of the cap is scoured with a weak alkali, to remove a portion of the gummy coating, and thereby enable the beaver fur with which it is to be "napped" or "coated," to adhere.