revailing conditions as to kilns were far from ideal.

The standard kilns then in use were about sixty feet in length, with an
internal diameter of about five feet. In all rotary kilns for burning
cement, the true clinkering operation takes place only within a limited
portion of their total length, where the heat is greatest; hence the
interior of the kiln may be considered as being divided longitudinally
into two parts or zones--namely, the combustion, or clinkering, zone,
and the zone of oncoming raw material. In the sixty-foot kiln the length
of the combustion zone was about ten feet, extending from a point six or
eight feet from the lower, or discharge, end to a point about eighteen
feet from that end. Consequently, beyond that point there was a zone of
only about forty feet, through which the heated gases passed and came
in contact with the oncoming material, which was in movement down toward
the clinkering zone. Since the bulk of oncoming material was small,
the gases were not called upon to part with much of their heat, and
therefore passed on up the stack at very high temperatures, ranging from
1500 degrees to 1800 degrees Fahr. Obviously, this heat was entirely
lost.

An additional loss of efficiency arose from the fact that the material
moved so rapidly toward the combustion zone that it had not given up
all its carbon dioxide on reaching there; and by the giving off of
large quantities of that gas within the combustion zone, perfect and
economical combustion of coal could not be effected.

The comparatively short length of the sixty-foot kiln not only limited
the amount of material that could be fed into it, but the limitation in
length of the combustion zone militated against a thorough clinkering of
the material, this operation being one in which the elements of time and
proper heat are prime considerations. Thus the quantity of good clinker
obtainable was unfavorably affected. By reason of these and other
limitations and losses, it had been possible, in practice, to obtain
only about two hundred and fifty barrels of clinker per day of
twenty-four hours; and that with an expenditure for coal proportionately
equal to about 29 to 33 per cent. of the quantity of clinker produced,
even assuming that all the clinker was of good quality.

Edison realized that the secret of greater commercial efficiency and
improvement of quality lay in the ability to handle larger quantities
of material within a given time, an