Fig. 5.—The Charging Screw.
The best, although a more expensive, charging screw is shown in Fig. 6. As will be seen from the cut, it consists of a base, k; cover, d; clamp, e, and screw, f. The base is simply a plain iron or brass ring, 4 inches in diameter, ⅛ inch thick and 1 inch high. The bottom is to be faced smooth, while the top is recessed 3-16 inch deep to receive the sheet lead and packing of putty, as at a. Two nubs, b and b, are cast on opposite sides, as shown, to act as grips for the clamp c. These nubs are ¾ inch long and project out from the body of the base ¼ inch, and are made sufficiently strong to stand the strain of the screw. The cover d is made of the same material as the base, the center being raised, as shown, to give it strength. Cast directly in the center and on the top is the nub e, ⅝ inch high and ⅝ inch in diameter. This is drilled to receive the ⅜-inch screw f. A groove 1-16 inch wide and 1-16 inch deep is cut all around the bottom of the screw, as shown at i. A hole is then drilled through the side of the nub e, and in line with the slot i. A pin can then be driven through the hole and will pass through the slot i, making a swivel joint that will connect the cover and screw together. The screw f is made of ⅜-inch round iron sufficiently long to give an action of about 1 inch. The top at n is filed square to receive a wheel such as is used on a common gate valve. A long thread should then be cut on this screw. The clamp c is made a half circle in shape, so as to clear the cover with ease. It should be ¾ inch wide, flat on the under side, while the top side should have a rib cast on it to prevent springing. The top at g should be reinforced with metal and made heavy enough to stand drilling and tapping to receive the screw f. A wood pattern can be made for these parts, and they can then be molded in any brass or iron foundry. In making the patterns they should be cut down as much as possible, so as to make the finished article as light as is consistent with the strength required. The same directions will answer for the cleaning screw. The hole to receive the sheet lead over the cleaning screw should not be over 1½ inches in diameter, and the rest of the screw should be made in proportion to this hole. The advantage of this screw over others is that it does not wrench the sheet lead in making it up, and, owing to its construction, it is always sure to make a tight joint without straining the generator.
Fig. 6.—The Best Charging Screw.
Building the Frame.
The frame can be made of galvanized iron, but wood is much superior, as it retains the heat generated in the gas chamber much better. To make the frame take the ⅞-inch board and cut off two pieces, 10 inches square, A and B in Fig. 8; 5 inches from one side and 2 inches from the back of one of these pieces bore a 1½-inch hole, C, and countersink it. This is for the acid supply pipe to pass through. These pieces are intended for shelves upon which to rest the acid and gas chambers. Cut the remaining board into two pieces 38 inches long. Lay these two boards together. Five inches from the side and 3 inches from the bottom bore a 1½-inch hole, d. Then saw out a V-shaped piece, Fig. 7. This will form the legs of the generator.
Fig. 7.—Making the Acid Chamber.
Take a square, and 12 inches from the top of these boards draw the lines e and e. Twenty-two inches below these lines draw the lines f and f. These lines represent the tops of the shelves. The shelves should be nailed or screwed into place. The shelf B should be placed on the top, keeping the hole C to the back. Take the ½-inch board and cut two pieces to measure 12 × 13 inches and two pieces 11 × 12 inches. These form the sides of the acid and gas chambers. The two 12 × 13 inch boards form the sides of the acid chamber and the 11 × 12 inch boards the sides of the gas chamber.