The air so admitted does not necessarily require a whirling motion, but experiments show that where the air is brought into contact with the oil spray with the right "twist", better combustion is secured and lower air pressures and less refinement of adjustment of individual burners are required. Mechanical burners have a distinct advantage over those in which steam is used as the atomizing agent in that they lend themselves more readily to adjustment under wider variations of load. For a given horse power there will ordinarily be installed a much greater number of mechanical than steam atomizing burners. This in itself is a means to better regulation, for with the steam atomizing burner, if one of a number is shut off, there is a marked decrease in efficiency. This is due to the fact that with the air admitted under the burner, it is ordinarily passing through the checkerwork regardless of whether it is being utilized for combustion or not. With a mechanical burner, on the other hand, where individual burners are shut off, air that would be admitted for such burner, were it in operation, may also be shut off and there will be no undue loss from excess air. Further adjustment to meet load conditions is possible by a change in the oil pressure acting on all burners at once. A good burner will atomize moderately heavy oil with an oil pressure as low as 30 pounds per square inch and from that point up to 200 pounds or above. The heating of the oil also has an effect on the capacity of individual burners and in this way a third method of adjustment is given. Under working conditions, the oil pressure remaining constant, the capacity of each burner will decrease as the temperature of the oil is increased though at low temperatures the reverse is the case. Some experiments with a Texas crude oil having a flash point of 210 degrees showed that the capacity of a mechanical atomizing burner of the Peabody type increased from 80 degrees Fahrenheit to 110 degrees Fahrenheit, from which point it fell off rapidly to 140 degrees and then more slowly to the flash point. The above methods, together with the regulation possible through manipulation of the boiler dampers, indicate the wide range of load conditions that may be handled with an installation of this class of burners. As has already been stated, results with mechanical atomizing burners that may be considered very successful have been limited almost entirely to cases where forced blast of some description has been used, the high velocity of the air entering being of material assistance in securing the proper mixture of air with the oil spray. Much has been done and is being done in the way of experiment with this class of apparatus toward developing a successful mechanical atomizing burner for use with natural draft, and there appears to be no reason why such experiments should not eventually produce satisfactory results.