Chapter 5

This process of manufacture is almost identical in principle and in practice with that described and patented by Mr. Joseph Aspden in the year 1824; and though various methods have been patented for utilizing the waste heat of the kilns in drying the slurry previous to calcination, still the main feature of burning the material in mass in large and expensive kilns remained the same, and is continued in practice to the present day. The attention of the author was directed to this subject some time since in consequence of the failure of a structure in which Portland cement formed an essential element, and he had not proceeded far in his investigation of the cause of the failure when he was struck with what appeared to him to be the unscientific method adopted in its manufacture, and the uncertain results that must necessarily accrue therefrom. Admitting, in the first place, that the materials employed were considered the best and most economical for the purpose readily accessible, viz., chalk and an alluvial deposit found in abundance on the banks of the Thames and the Medway, and being intimately mixed together in suitable proportions, was it necessary, in order to effect the chemical combination of the ingredients at an intense heat, to employ such massive and expensive structures of masonry, occupying such an enormous space of valuable ground, with tall chimney stacks for the purpose of discharging the objectionable gases, etc., at such a height, in order to reduce the nuisance to the surrounding neighborhood? Again, was it possible to effect the perfect calcination of the interior of the lumps alluded to without bestowing upon the outer portions a greater heat than was necessary for the purpose, causing a wasteful expenditure of both time and fuel? And further, as cement is required to be used in the state of powder, could not the mixture of the raw materials be calcined in powder, thereby avoiding the production of such a hard clinker, which has afterward to be broken up and reduced to a fine powder by grinding in an ordinary mill?

The foregoing are some of the defects which the author applied himself to remove, and he now desires to draw attention to the way in which the object has been attained by the substitution of a revolving furnace for the massive cement kilns now in general use, and by the application of gaseous products to effect calcination, in the place of coke or other solid fuel. The revolving furnace consists of a cylindrical casing of steel or boiler plate supported upon steel rollers (and rotated by means of a worm and wheel, driven by a pulley upon the shaft carrying the worm), lined with good refractory fire brick, so arranged that certain courses are set so as to form three or more radial projecting fins or ledges. The cylindrical casing is provided with two circular rails or pathways, turned perfectly true, to revolve upon the steel rollers, mounted on suitable brickwork, with regenerative flues, by passing through which the gas and air severally become heated, before they meet in the combustion chamber, at the mouth of the revolving furnace. The gas may be supplied from slack coal or other hydrocarbon burnt in any suitable gas producer (such, for instance, as those for which patents have been obtained by Messrs. Brook & Wilson, of Middlesbrough, or by Mr. Thwaite, of Liverpool), which producer may be placed in any convenient situation.

The cement mixture or slurry, instead of being burnt in lumps, is passed between rollers or any suitable mill, when, it readily falls into coarse dry powder, which powder is thence conveyed by an elevator and fed into the revolving furnace by means of a hopper and pipe, which, being set at an angle with the horizon, as it turns gradually 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 Alumina and oxide of iron 10.56 Lime 61.48 Magnesia, water, and alkalies 2.02 ------ 100

Again, fineness of the particles results in their being speedily heated to a uniform temperature, so that they do not serve as nuclei for the condensation of the moisture existing in the furnace gas. The calcined material, on reaching the lower end of the furnace, is discharged on to the floor or on to a suitable "conveyer," and removed to a convenient locality for cooling and subsequent grinding or finishing. It, however, is not in the condition of hard, heavy clinkers, such as are produced in the ordinary cement kiln, which require special machinery for breaking up into smaller pieces before being admitted between the millstones for the final process of grinding; nor does it consist of an overburnt exterior and an underburnt core or center portion; but it issues from the cylindrical furnace in a condition resembling in appearance coarse gunpowder, with occasional agglutinations of small friable particles readily reduced to fine powder in an ordinary mill, requiring but small power to work, and producing but little wear and tear upon the millstones. The operation is continuous. The revolver or furnace, once started, works on night and day, receiving the adjusted quantity of powdered material at the upper or feed end, and delivering its equivalent in properly burnt cement at the opposite end, thus effecting a great saving of time, and preventing the enormous waste of heat and serious injury to the brickwork, etc., incidental to the cooling down, withdrawing the charge, and reloading the ordinary kiln.

Cement, when taken from the furnace, weighed 110 lb. per bushel. Cement, when ground, leaving 10 percent. on sieve with 2,500 holes to the inch, weighed 121 lb. per bushel, and when cold 118 lb. per bushel. When made into briquettes, the tensile breaking strain upon the square inch:

At 4 days was 410 lb. per square inch. At 6 days " 610 " " " " At 14 days " 810 " " " " At 49 days " 900 " " " " At 76 days " 1,040 " " " "

A cylindrical furnace, such as the author has described, is capable of turning out at least 20 tons of good cement per day of twenty-four hours, with a consumption of about 3 tons of slack coal. It will be readily understood that these furnaces can be worked more economically in pairs than singly, as they can be so arranged that one producer may furnish a sufficient quantity of gas for the supply of two cylinders, and the same labor will suffice; but in order to provide for possible contingencies the author advises that a spare gas producer and an extra furnace should be in readiness, so that by a simple arrangement of valves, etc., two cylinders may always be in operation, while from any cause one may be undergoing temporary repairs, and by this means any diminution in the output may be avoided.

The author considers it unnecessary here to discuss either the advantages or the economy of fuel effected by the employment of gas producers for such a purpose. These have been abundantly proved in steel and glass making industries, where a saving of from 50 to 70 per cent. of the fuel formerly employed has been made. Their cost is small, they occupy little room, they can be placed at any reasonable distance from the place where the gas is to be burnt; any laborer can shovel the slack into them, and they do not require constant skilled supervision. It is claimed by the author of this paper that the following are among the many advantages derivable from the adoption of this method of manufacturing Portland cement, as compared with the old system:

(1) Economy of space--the furnaces, with their appurtenances, requiring only about one-fourth the space of what would be occupied by the ordinary kilns for producing the same quantity of finished cement.

(2) Continuous working, and consequent economy of fuel lost by cooling and subsequent reheating of the kiln walls.

(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.

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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.

In microphones in which the sound plates are arranged vertically (as shown in Fig. 2), these disturbances assume such a character that there is no possibility of understanding the speaker, for in this case the horizontally directed oscillations of the sound plate, _m_, cause themselves a backward and forward motion on the part of the carbon rollers without increasing or decreasing at the same time the lying-on pressure of the roller journals, and by doing so bring the places of contact one on the other, and thus occasion a conducting resistance of greater or less force. This circumstance serves as an explanation of the reason why the sound plates in Ader's microphones are not arranged vertically, although this way of arranging them offers many advantages over a horizontal or slightly inclined arrangement of the sound plates. Speaking is more convenient in the vertical arrangement, and moreover the plates can be fitted on to instruments better in this way.

All the drawbacks just enumerated and found in Ader's microphones are avoided in the apparatus made by Messrs. Mix & Genest. A sort of braking contrivance operates on the carbon rollers in such a way as to prevent their journals from lying on the lower points in the flutings of the beams. Thus, for instance, if in a microphone with a horizontal sound plate, as illustrated in Fig. 3, the carbon rollers are pressed upward by outward force, it is evident that only a very trifling rolling and disturbing motion can occur, and only small pieces of carbon can be knocked off, which would act injuriously as a secondary contact. The same may be said of the journals of microphones with vertical sound plates, as represented in Fig. 2, when the carbon rollers are pressed in the direction of the arrow, _p_, that is to say, against the sound plate. In this case the journals, _a_, are fixed in the flutings of the beams, _b_, in a direction given them by the power and gravity operating on them, which is clearly represented in the accompanying design, Fig. 2.

In all such cases the regulating contrivance applied to brake the carbon rollers in their motion has the result that only the oscillations transmitted from the sound plate on to the contacts come in operation, whereas disturbing mechanical shocks resulting from any outward influences occasion very insignificant vibrations, which are not perceptible in the telephone. The separate contacts thus form a firm system with the sound plate, so that the former are influenced in their motions and effects solely and alone by the shocks and oscillations which operate direct on these sound plates. The roller motion of the carbon is thus removed, and the distinctness of the words spoken is greatly augmented.

The above Figs. 1 and 2 show the microphone in side view and in cross section.

A metal ring, R (see Fig. 1), is fastened by means of the four screws, _r_{1}_ _r_{2}_ _r_{3}_ _r_{4}_, on a wooden mouthpiece. In a recess of the above ring is the diaphragm, M, which is provided on its outer edge with an India rubber band and is held in position by the two clamps, _a_ and _a_{1}_. The diaphragm is cut out of finely fibered firwood and is well lacquered to preserve it against dampness. On it there are two carbon beams, _b_, and in the perforations of the latter are the journals of the carbon rollers, _k_. The alterations in contact take place in the touching points. The cross piece, _f_, that runs straight across the carbon rollers serves as a braking contrivance, which is regulated as may be necessary by the large projecting screws.

Fig. 3 shows the apparatus in cross section. T is the mouth piece, R the metal ring, M the diaphragm, _f_ the breaking cross piece. On the latter is a metal block fastened by means of two screws. On this metal block is a soft elastic strip (d) of felt or similar material. The letters _s_ and _s_ indicate the regulating screws for the braking contrivance.

The excellent qualities of other microphones, in particular their extreme sensibility for the very least impressions, are undeniable; but it is just this sensibility that is the cause of the complaints made by the public. In practical use this overgreat sensibility proves to be a fault.

In the apparatus constructed by Messrs. Mix and Genest the well-known deficiencies of other systems are avoided. The effect of the sound and the distinctness of the human voice are clearer and far more intelligible. One simple regulation of the microphone suffices for the installation, for there is no danger of its getting out of order. Owing to its peculiar construction, this new microphone is very firm and solid, and for this very reason offers another advantage, namely, the possibility of transmitting sound over very long distances. In the competitive trials instituted by order of the imperial postal department, apparatus of various systems and constructions were subjected to tests, and the apparatus we are speaking of showed the favorable results just mentioned. This microphone has overcome in particular the difficulties connected with the using of combined lines above and below ground, and with the aid of it the excellent telephonic communication is carried on in Berlin, in which city the telephone net is most extensive and complicated. At the same time this microphone transmits the sound over long distances (up to 200 kilom. even) in the most satisfactory manner. Another peculiar advantage of this construction is that it exercises a very small inductive effect on cables and free lines, and consequently the simultaneous speaking on parallel lines causes but little disturbance.

After repeated trials made by the German imperial postal department with the microphones constructed by Messrs. Mix and Genest, these apparatus have been introduced in the place of the telephones and Bell-Blake microphones hitherto used in the telephone service. At present we understand there are about 8,000 of these apparatus in use.

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ELECTROLYSIS AND REFINING OF SUGAR.

Mr. G. Fahrig, of Eccles, Lancashire, has invented a new process of refining sugar through electrolysis. The brown sugar is decolorized by means of ozone produced by electric currents of high tension from a dynamo. The electrodes consist of metal grills covered with platinum or some other inoxidizable metal, and are placed in a vat with the intervention of perforated earthenware plates. After being ground and dried in hot air, the crude sugar is placed between the plate and the grills, and the discharges passing between the electrodes produce ozone, which separates the sugar from the coloring matter. To purify the sugar still further, Mr. Fahrig dries it and places it in another vat, with carbon or platinum conducting plates separated by a porous partition. The sugar is placed on one side of this partition, and water circulates on the other side.

The current from a dynamo of feeble tension is sent through the vat between the plates. The water carries along the impurities separated by the current, and the sugar is further whitened and refined.

The accompanying figure shows a series of four vats arranged one above another, in order to permit the water to circulate. Here _i_ and _h_ represent the plates connected with the poles of the dynamo through the conductors, _f_ and _g_; _m_ represents the porous partition; L, the spaces filled with sugar; and _l_, the compartments in which the water circulates.--_La Lumiere Electrique._

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[THE ELECTRICIAN.]

A CURRENT METER.

We give a description of a meter we made in June, 1883. You will find a cross section of the meter and also a printed dial we had made at the time. We called it an ampere register, but no doubt we would give it a better name to-day. The meter consisted of a glass tube, _c_, both ends of which were fitted into two bent pieces of piping, D and F, as shown. Through these bent tubes, D and F, passed the wires, a and _b_, which were connected to the binding posts, A and B. The part of the wire where it passed into the tubes was well insulated. At the ends, _a'_ and _b'_, was connected the coil, R, which consisted simply of a few turns of copper wire whose diameter was less than the leading wires, _a_ and _b_. To the tube, D, was attached a square tube, E, which had a little opening at the top so as to permit a small undershot wheel, I, to revolve freely. This undershot wheel was well pivoted and constructed very light. To the axis of this wheel was connected another system of wheels with indicators, as shown, J. Now the tubes, E and F, were connected to a reservoir, G. This reservoir consisted of a square tank, in the inside of which were soldered in an alternating manner square sheets of copper as shown in the drawing, _g_ _g'_ _g''_ _g'''_ ... These sheets acted as diffusers. These plates or sheets presented a very large surface. On the outside of the tank, G, were also diffusers, _h_ _h'_ ... arranged all round and presenting an appearance as if two books were open so as to form a square with their covers, the leaves being the diffusers. The diffusers on the outside were at right angles to those inside.