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