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Page 21
(3) Economy of repairs, which are of a simple and comparatively
inexpensive character, and of much less frequent occurrence, as
the continuous heat avoids the racking occasioned by the
alternate heating and cooling.
(4) Economy in first cost.
(5) Economy in grinding, a friable granular substance being
produced instead of a hard clinker, whereby crushers are quite
abolished, and the wear and tear of millstones greatly
reduced.
(6) Economy of labor, the conveyance to and removal from, the
revolving furnace being conducted automatically by mechanical
elevators and conveyers.
(7) Improved quality of the cement, from non-mixture with
fuel, ash, or other impurities, and no overburning or
underburning of the material.
(8) Thorough control, from the facility of increasing or
diminishing the flow of crushed slurry and of regulating the
heat in the furnace as desirable.
(9) Absence of smoke and deleterious gases.
It is well known that in some localities the materials from which
Portland cement is made are of such a powdery character that they have
to be combined or moulded into balls or bricks previous to calcination
in the ordinary way, thus entailing expense which would be entirely
obviated by the adoption of the patent revolving furnace, as has been
proved by the author in producing excellent cement with a mixture of
slag sand from the blast furnaces of the Cleveland iron district, with
a proper proportion of chalk or limestone, which, in consequence of
the friable nature of the compound, he was unable to burn in the
ordinary cement kiln, but which, when burnt in the revolving furnace,
gave the most satisfactory results. The cement so made possessed
extraordinary strength and hardness, and it has been a matter of
surprise that iron masters and others have not adopted such a means of
converting a waste material--which at the present time entails upon
its producers constant heavy outlay for its removal--into a
remunerative branch of industry by the expenditure of a comparatively
small amount of capital. The demand for Portland cement has increased
and is still increasing at a rapid ratio. It is being manufactured
upon a gigantic scale.
Great interests are involved; large sums of money are being expended
in the erection and maintenance of expensive plant for its production;
and the author submits that the development of any method which will
improve the quality and at the same time reduce the cost of
manufacture of this valuable material will tend to increase the
prosperity of one of our great national industries, and stimulate
commercial enterprise. Works are in progress for manufacturing cement
by this improved process, and the author trusts the time is not far
distant when the unsightly structures which now disfigure the banks of
some of our rivers will be abolished--the present cement kilns, like
the windmills once such a common feature of our country, being
regarded as curiosities of the past, and cement manufacturers cease to
be complained of as causing nuisances to their neighbors.
* * * * *
MIX AND GENEST'S MICROPHONE TELEPHONE.
We illustrate in the annexed engraving the microphone-telephone
constructed by Messrs. Mix & Genest, of Berlin, which, after extended
trials, has been adopted in preference to others by the imperial
postal department of Germany. There are now more than 5,000 of these
instruments in use, and we need scarcely mention that the invention
has been patented in many countries.
In some microphones a rattling noise is frequently occasioned, which
borne along with the sound of the human voice causes an audible
disturbance in the telephone. The chief cause of these disturbances
may be ascribed to the fact that the carbon rollers in their journals,
rest loose in the flutings of the beam, which is fastened to the sound
plate. Owing to the shocks given to the entire apparatus, and
independent of the oscillations of the sound plate, they are set in
motion and roll to and fro in their bearings.
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