Fig. 3276.
In some practice the tubes are arranged as in [Fig. 3276], being wider pitched or spaced in the middle of the boiler to increase the circulation of the water in the boiler.
Fig. 3277.
Another arrangement is shown in [Fig. 3277], the tubes being staggered or arranged zigzag. This permits of the employment of a greater number of tubes, but does not afford such free circulation of the water.
Fig. 3278.