those intimately associated with or interested in the
art. Not the least of the mechanical questions was settled by Edison's
decision to make this tremendously long kiln in sections of cast-iron,
with flanges, bolted together, and supported on rollers rotated by
electric motors. Longitudinal expansion and thrust were also important
factors to be provided for, as well as special devices to prevent the
packing of the mass of material as it passed in and out of the kiln.
Special provision was also made for injecting streams of pulverized coal
in such manner as to create the largely extended zone of combustion. As
to the details of these and many other ingenious devices, we must refer
the curious reader to the patents, as it is merely intended in these
pages to indicate in a brief manner the main principles of Edison's
notable inventions. The principal United States patent on the long kiln
was issued October 24, 1905, No. 802,631.

That his reasonings and deductions were correct in this case have been
indubitably proven by some years of experience with the long kiln in its
ability to produce from eight hundred to one thousand barrels of
good clinker every twenty-four hours, with an expenditure for coal
proportionately equal to about only 20 per cent. of the quantity of
clinker produced.

To illustrate the long cement kiln by diagram would convey but little
to the lay mind, and we therefore present an illustration (Fig. 1) of
actual kilns in perspective, from which sense of their proportions may
be gathered.

XVIII. EDISON'S NEW STORAGE BATTERY

GENERICALLY considered, a "battery" is a device which generates electric
current. There are two distinct species of battery, one being known as
"primary," and the other as "storage," although the latter is sometimes
referred to as a "secondary battery" or "accumulator." Every type of
each of these two species is essentially alike in its general make-up;
that is to say, every cell of battery of any kind contains at least
two elements of different nature immersed in a more or less liquid
electrolyte of chemical character. On closing the circuit of a primary
battery an electric current is generated by reason of the chemical
action which is set up between the electrolyte and the elements.
This involves a gradual consumption of one of the elements and a
corresponding exhaustion of the active properties of the electrolyte. By
reason of this, both the element and the electrolyte t