Now, in considering the question of the proper proportion of steam for the production of gas for power purposes we must bear in mind that as much heat as possible should be utilized in the producer itself. Some manufacturers of plant go so far as to state that as much as 1 lb. of steam per lb. of coal should be used, but we are safe in saying that 0.5 lb. to 0.7 lb. should be the figure for a power plant. The common practice is to use a blast saturation of 55% whenever the clinkering character of the coal renders it possible. This figure corresponds to about .57 of steam per lb. of coal gasified. It is of the utmost importance that the proportion of steam and air should be constant, and the best figure being determined, it should not be varied to any degree. It is equally important that the fuel depth should be left constant. By this I mean that not only should the coal in the producer be kept at a specific level, but the position of the fire on the ash bed should be kept as near as possible a fixed point. Ashes should be drawn at regular intervals, or, if desired, continuously by mechanical means. Further, the supply of air and steam should be regularly distributed, so that the velocity of the gases through the fuel shall be as nearly as possible regular across its whole area. In some cases the by-products of a producer, such as ammonia, tar, etc., have a commercial value, and if a large amount of gas is generated it will sometimes pay to select a fuel that is rich in these particular substances. (16) Coal. Coal which is the basis of producer gas, is composed generally speaking of the combustible matter, moisture, ash and sulphur. The combustible element may be subdivided into the =HYDROCARBONS, OR VOLATILES=, and the solid fixed carbon. The exact composition of coal is generally given by what is known as =PROXIMATE= analysis, which analysis divides the constituents of the coal into five groups, viz.: =MOISTURE=, =VOLATILES=, =FIXED CARBON=, =ASH=, and =SULPHUR=. Ultimate analysis resolves the coal into its ultimate chemical elements, such as hydrogen, carbon, nitrogen, sulphur, etc., and being a difficult and tedious process it is not much used. The proximate analysis gives all the necessary information and takes less time to perform. VALUES OF COAL