(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.