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In the first of these the combustion is completed in the fire box directly in connection with the boiler or what is required to be heated. In the second the material is gasified only in the fire box or producer and conducted elsewhere for use either directly or through regenerators.

DIRECT FIRING.

STEP GRATES.

For all industrial purposes, and especially in making steam, the very best results in direct firing are secured from the brown coal by use of the step grate—the treppenrost—of the Germans. This differs from the flat grate in ordinary use at present in its greater angle of inclination and in the form and position of the grate bars themselves.

In the ordinary grate the bars stand on their edge, run lengthwise of the fire box, and the grate is horizontal or rarely slightly inclined. In the step or stair grate the bars lie on their sides, run across the fire box, and the grate is inclined at an angle of 29 to 40 degrees.

The inclination of the grate is varied according to the fuel to be burned, the rule being the finer the fuel the higher the angle of inclination; or conversely, the coarser the fuel the flatter the grate.

This grate is intended for use with all fuels which are in a more or less pulverulent condition—sawdust, spent tanbark, breeze or slack coal, etc.; but more especially for brown coal or lignite, and is used for all purposes, either in direct, half gas, or gas firing.

The grates from which the drawings here reproduced on Plates II and III were made are those in use at Donawitz and Zeltweg, in Styria, where I found them burning brown coal very closely resembling that which we have in Texas in character and in composition. The measurements which are given in the drawings are all millimeters, of which 25.4 are equal to one inch.

These are the simplest of the forms in use and represent two kinds of the step grate as applied to stationary boilers. The upper drawing of each plan gives the vertical section of the grate and boiler, while from the ground plan at the bottom it will be seen that the grate bars under each boiler are in three sections. The simpler form of the step grate is shown in Plate II. At the bottom of this grate a wrought iron support, four by six inches, extends across the furnace, and is built into the walls from three to five inches in order to make