100

in length, containing on the surfaces semi-oval cavities, connected together by small channels, which allow the escape of air and excess of material; each cavity or recess communicates by four of these channels with the surrounding ones. These cavities extend in close proximity to each other, in regular rows, over the whole length of the rollers, the recesses of every other row being intermediately between those of the adjoining row, in the nature of the cells of a honey-comb, so that small metallic contact surfaces are formed, and the entire surfaec of the rollers is utilized for compressing the composition into lumps of an egg-shaped form. The shafts of the rollers are cast solid with the rollers, and they are ten and one-half inches in diameter. Each roller weighs over a ton. On top of these is a hopper thirty-six inches long and thirty inches wide, in which the materials to be compressed are discharged from the mixer. In this hopper a series of knives, screwed to a small horizontal shaft, revolve rapidly, and keep the material in a granulated state."

This description, taken from his paper in the Transactions American Institute of Mining Engineers, Vol. VI, 1877-78, p. 216, is the only one to which I have had access, although several machines made on this pattern are now in use in the United States for briquetting coal slack.

Presses with Endless Forms, or Stamping Presses.

The general principle of this character of presses is a rotating table, pierced with moulds of the size and shape desired in the briquette, the pressure being given by means of a plunger, operated by steam or water power. The pressure may be applied either by direct action of the power from the piston rod, or, as is most usual, indirectly by means of levers, etc.

STEAM PRESSES.

The principal press, which was formerly operated under the first of these methods—steam applied directly—is the Mazeline, the general operation of which will be given fully in its improved form under Hydraulic Presses.

Of the steam presses in which the power is applied indirectly, we have first the English press of Middleton, afterwards improved by Détombay, of which a great number have come into use in different parts of Europe.

The Watin press, and also that of Biétrix (model of 1878), are of the same general type as the Middleton-Détombay, but differ from it in