The cement mixture or slurry, instead of being burnt in lumps, is passed between rollers or any suitable mill, when, it readily falls into coarse dry powder, which powder is thence conveyed by an elevator and fed into the revolving furnace by means of a hopper and pipe, which, being set at an angle with the horizon, as it turns gradually conveys the cement material in a tortuous path toward the lower and hotter end, where it is discharged properly calcined.  The material having been fed into the upper end of the cylinder falls through the flame to the lower side of it; the cylinder being in motion lifts it on its advancing side, where it rests against one of its projecting fins or ledges until it has reached such an angle that it shoots off in a shower through the flame and falls once more on the lower side.  This again causes it to travel in a similar path, and every rotation of the cylinder produces a like effect, so that by the time it arrives at the lower and hotter end it has pursued a roughly helical path, during which it has been constantly lifted and shot through the flame, occupying about half an hour in its transit.

To some who have been accustomed to the more tedious process of kiln burning, the time thus occupied may appear insufficient to effect the combinations necessary to produce the required result; but it will be seen that the conditions here attained are, in fact, those best suited to carry out effectively the chemical changes necessary for the production of cement.  The raw material being in powder offers every facility for the speedy liberation of water and carbonic acid, the operation being greatly hastened by the velocity of the furnace gases through which the particles pass.  That such is practically the case is shown by the following analysis of cement so burnt in the revolving furnace or cylinder: 

Per cent. 
Carbonic acid, anhydrous 0.4
Sulphuric acid, anhydrous 0.26
Silica soluble 24.68
Silica insoluble 0.6
Alumina and oxide of iron 10.56
Lime 61.48
Magnesia, water, and alkalies 2.02
------
100

Again, fineness of the particles results in their being speedily heated to a uniform temperature, so that they do not serve as nuclei for the condensation of the moisture existing in the furnace gas.  The calcined material, on reaching the lower end of the furnace, is discharged on to the floor or on to a suitable “conveyer,” and removed to a convenient locality for cooling and subsequent grinding or finishing.  It, however, is not in the condition of hard, heavy clinkers, such as are produced in the ordinary cement kiln, which require special machinery for breaking up into smaller pieces before being admitted between the millstones for the final process of grinding; nor does it consist of an overburnt exterior and an underburnt core or center portion; but it issues from