The advantage of the bellows is that it can be easily transported and does the work perfectly, but it requires constant pumping, which soon tires the helper, and for that reason could not be used on jobs requiring more than four or five hours' labor.
The gasometer style of air holder is the easiest to use, if one does not employ a helper and has a large amount of work to do. The pressure can be regulated to suit the work by placing one or more weights upon it until the desired pressure is obtained. It does not require pumping up more than three or four times a day, which is its principal virtue. It is a perfect shop apparatus. Its disadvantage is that it requires a large quantity of water to fill it, which is not always available, and when full it is so heavy that it requires a truck to move it around.
By far the best air holder is the one shown as part of the apparatus in Fig. 9, and illustrated separately in Fig. 10. This only requires a few pails of water to fill it, and the exact pressure of the gas can be had by building it the same hight as the hydrogen gas generator. It does not require constant pumping, and I recommend this air holder for general use, as possessing more advantages, with less trouble, than any other air holder in use. However, all three will be described, and the beginner can make the one most suited to the material available.
Air Holder No. 1.
The beginner will notice in Fig. 10 that this air holder is so constructed that it gets its air pressure direct from the head of water, and also that this pressure can be varied by making the connecting piece of pipe longer or shorter, as may be desired. Of course, the pressure will vary slightly as the water descends into the air chamber, but not enough to make it objectionable, as it will be the helper's duty to watch the water line and renew pumping as often as the water falls below a certain point.
To make this holder, a tank, a, Fig. 10, 12 inches high and 18 inches in diameter, should be constructed of galvanized sheet iron. On this tank double seam a flat bottom. The top must be raised slightly, as shown, to give it strength. This can be done with the raising hammer, or it can be done by making the circle for the top ¾ inch larger than the bottom, then making a cut to the center. It can then be drawn together and riveted in any desired pitch. A hole must be punched in the center of this top large enough to receive a 1-inch galvanized pipe, b. Six inches apart and 2 inches from the edge punch two holes, c and d, large enough to receive pieces of ⅜-inch galvanized pipe. This top should then be fitted and placed on the body of the tank.
Fig. 10.—Air Holder No. 1.
Take a piece of 1-inch galvanized pipe, e, sufficiently long to touch the bottom and projecting 1 inch out of the top of the tank, cut a thread on the projecting end and drill the other end full of ¼-inch holes, f, to the hight of 1 inch, to allow the water to flow freely. This pipe rests on the bottom of the lower tank and carries the weight of the upper tank. Solder this pipe in place. Then take two ⅜-inch nipples, 1 inch long, and solder them into their places, and on these nipples screw two ⅜-inch hose end gas cocks, c and d. One of these cocks is for the purpose of connecting to the air pump, and the other to the mixing cock. As close as possible to the bottom of the tank solder in a ½-inch coupling, g. Into this coupling screw a plug. This is for the purpose of draining the tank when out of use.
Now make another tank, h, 19 inches in diameter and 11 inches deep, the top to be left open and wired with a heavy wire. Double seam a flat bottom on this tank. Directly in the center of this bottom punch a hole large enough to receive a 1-inch coupling. Then cut a 1-inch coupling in half and solder it into this hole, putting the thread side down and leaving it as near flush with the outside of the tank as possible, so that if it is desired to move the air holder to and from a job it can be taken apart and the lower tank nested in the upper tank, making a compact bundle and reducing the danger of damage by careless handling.