Chapter XI: TECHNOLOGY--A New Monster Revolving Black Ash Furnace and the (2)

After the cocoons are brushed they are, in the ordinary process, cleaned by hand, which is another tedious and wasteful operation performed by the reeler, and concerning which we shall have more to say further on. Whatever may be the preparatory operations, they result in furnishing the reeler with a quantity of cocoons, each having its floss removed, and the end of the filament ready to be unwound. Each reeler is provided with a basin containing water, which may be heated either by a furnace or by steam, and a reel, upon which the silk is wound when put in motion by hand or by power. In civilized countries heating by steam and the use of motive power is nearly universal. The reeler is ordinarily seated before the reel and the basin. The reeler begins operations by assembling the cocoons in the basin, and attaching all the ends to a peg at its side. She then introduces the ends of the filaments from several cocoons into small dies of agate or porcelain, which are held over the basin by a support.

The ends so brought in contact stick together, owing to the adhesive substance they naturally contain, and form a thread. To wring out the water which is brought up with the ends, and further consolidate the thread, it is so arranged as to twist round either itself or another similar thread during its passage from the basin to the reel. This process is called "croisure," and is facilitated by guides or small pulleys. Having made the croisure, which consists of about two hundred turns, the operator attaches the end of a thread to the reel, previously passing it through a guide fixed in a bar, which moves backward and forward, so as to distribute the thread on the reel, forming a hank about three inches wide.

The reel is now put into movement, and winds the thread formed by the union of the filaments. It is at this moment that the real difficulties of the reeler begin. She has now to maintain the size and regularity of the thread as nearly as possible by adding new filaments at the proper moment. The operation of adding an end of a filament consists of throwing it in a peculiar manner on the other filaments already being reeled, so that it sticks to them, and is carried up with them. We may mention here that this process of silk reeling can be seen in operation at the Manchester exhibition.

It is only after a long apprenticeship that a reeler succeeds in throwing the end properly. The thread produced by the several filaments is itself so fine that its size cannot readily be judged by the eye, and the speed with which it is being wound renders this even more difficult. But, in order to have an idea of the size, the reeler watches the cocoons as they unwind, counts them, and, on the hypothesis that the filament of one cocoon is of the same diameter as that of another, gets an approximate idea of the size of the thread that she is reeling. But this hypothesis is not exact, and the filament being largest at the end which is first unwound, and tapering throughout its whole length, the result is that the reeler has not only to keep going a certain number of cocoons, but also to appreciate how much has been unwound from each.

If the cocoons are but slightly unwound, there must be fewer than if a certain quantity of silk has been unwound from them. Consequently their number must be constantly varying in accordance with their condition. These facts show that the difficulty of maintaining regularity in a thread is very great. Nevertheless, this regularity is one of the principal factors of the value of a thread of "grege," and this to such an extent that badly reeled silks are sold at from twenty to twenty-five francs a kilogramme less than those which are satisfactorily regular.

The difficulty of this hand labor can be still better understood if it be remembered that the reeler being obliged to watch at every moment the unwinding of each cocoon, in order to obtain one pound of well reeled silk, she must incessantly watch, and without a moment of distraction, the unwinding of about two thousand seven hundred miles of silk filaments. For nine pounds of silk, she reels a length of filament sufficient to girdle the earth. The manufacturer, therefore, cannot and must not depend only on the constant attention that each reeler should give to the work confided to her care. He is obliged to have overseers who constantly watch the reelers, so that the defects in the work of any single reeler, who otherwise might not give the attention required by her work, will not greatly diminish the value either of her own work or that of several other reelers whose silk is often combined to form a single lot. In addition to the ordinary hand labor, considerable expense is thus necessitated for the watching of the reelers.

Enough has now been said, we think, to give a good idea of silk reeling, as usually practiced, and to show how much it is behind other textile arts from a mechanical point of view. To any one at all familiar with industrial work, or possessing the least power of analysis or calculation, it is evident that a process carried on in so primitive a manner is entirely unsuitable for use in any country in which the conditions of labor are such as to demand its most advantageous employment. In the United States, for instance, or in England, silk reeling, as a great national industry, would be out of the question unless more mechanical means for doing it could be devised. The English climate is not suitable for the raising of cocoons, and in consequence the matter has not attracted very much attention in this country. But America is very differently situated. Previous to 1876 it had been abundantly demonstrated that cocoons could be raised to great advantage in many parts of that country. The only question was whether they could be reeled. In fact, it was stated at the time that the question of reeling silk presented a striking analogy to the question of cotton before the invention of the "gin." It will be remembered that cotton raising was several times tried in the United States, and abandoned because the fiber could not be profitably prepared for the market. The impossibility of competing with India and other cheap labor countries in this work became at least a fact fully demonstrated, and any hope that cotton would ever be produced in America was confined to the breasts of a few enthusiasts.

As soon, however, as it was shown that the machine invented by Eli Whitney would make it possible to do this work mechanically, the conditions were changed; cotton raising become not only possible, but the staple industry of a great part of the country; the population was rapidly increased, the value of real estate multiplied, and within a comparatively short time the United States became the leading cotton country of the world. For many years much more cotton has been grown in America than in all the other countries of the world combined; and it is interesting to note that both the immense agricultural wealth of America and the supply required for the cotton industry of England flow directly from the invention of the cotton gin.

Attention was turned in 1876 to silk raising, and it was found that all the conditions for producing cocoons of good quality and at low cost were most favorable. It was, however, useless to raise cocoons unless they could be utilized; in a word, it was seen that the country needed silk-reeling machinery in 1876, as it had needed cotton-ginning machinery in 1790. Under these conditions, Mr. Edward W. Serrell, Jr., an engineer of New York, undertook the study of the matter, and soon became convinced that the production of such machinery was feasible. He devoted his time to this work, and by 1880 had pushed his investigations as far as was possible in a country where silk reeling was not commercially carried on. He then went to France, where he has since been incessantly engaged in the heart of the silk-reeling district in perfecting, reducing to practice, and applying his improvements and inventions. The success obtained was such that Mr. Serrell has been enabled to interest many of the principal silk producers of the Continent in his work, and a revolution in silk reeling is being gradually brought about, for, strangely enough, he found that the work which he had undertaken solely for America was of equal importance for all silk-producing countries.

We have described the processes by which cocoons are ordinarily cooked and brushed, these being the first processes of the filature. Instead of first softening the gum of the cocoons and then attacking the floss with the points of a brush, Mr. Serrell places the cocoons in a receptacle full of boiling water, in which by various means violent reciprocating or vortex currents are produced. The result is that by the action of the water itself and the rubbing of the cocoons one against the other the floss is removed, carrying with it the end of the continuous filament without unduly softening the cocoon or exposing any of the more delicate filament to the rough action of the brush, as has hitherto been the case. The advantages of this process will be readily understood. In brushing after the ordinary manner, the point of the brush is almost sure to come into contact with and to break some of the filament forming the body of the cocoon. When this occurs, and the cocoon is sent to be reeled, it naturally becomes detached when the unwinding reaches the point at which the break exists. It then has to be sent back, and the end of the filament detached by brushing over again, when several layers of filament are inevitably caught by the brush and wasted, and very probably some other part of the filament is cut. This accounts for the enormous waste which occurs in silk reeling, and to which we have referred. Its importance will be appreciated when it is remembered that every pound of fiber thus dragged off by the brush represents a net loss of about 19s. at the present low prices.

The mechanical details by which Mr. Serrell carries out this process vary somewhat according to the nature of the different cocoons to be treated. In one type of machine the water is caused to surge in and out of a metal vessel with perforated sides; in another a vertical brush is rapidly raised and lowered, agitating the water in a basin, without, however, actually touching the cocoons. After a certain number of strokes the brush is automatically raised, when the ends of the filaments are found to adhere to it, having been swept against it by the scouring action of the water. The cleaning of the cocoons is performed by means of a mechanism also entirely new. In the brushing machinery the floss is loosened and partially detached from the cocoon. The object of the cleaning machine is to thoroughly complete the operation. To this end the cocoons are floated under a plate, and the floss passed up through a slot in the latter. A rapid to and fro horizontal movement is given to the plate, and those cocoons from which the floss has been entirely removed easily give off a few inches of their filament, and allow themselves to be pushed on one side, which is accomplished by the cocoons which still have some floss adhering to them; because these latter, not being free to pay off, are drawn up to the slot in the plate, and by its motion are rapidly washed backward and forward in the water. This washing soon causes all the cocoons to be freed from the last vestiges of floss without breaking the filament, and after about twenty seconds of movement they are all free and clean, ready for reeling.

We have now to explain the operation of the machine by which the thread is formed from the prepared cocoon. At the risk of some repetition, however, it seems necessary to call attention to the character of the work itself. In each prepared cocoon are about a thousand yards of filament ready to pay off, but this filament is nearly as fine as a cobweb and is tapering. The object is to form a thread by laying these filaments side by side in sufficient number to obtain the desired size. For the threads of raw silk used in commerce, the sizes vary, so that while some require but an average of three filaments, the coarsest sizes require twenty-five or thirty. It being necessary keep the thread at as near the same size as possible, the work required is, in effect, to add an additional cocoon filament to the thread which is being wound whenever this latter has tapered down to a given size, or whenever one of the filaments going to form it has become detached. Those familiar with cotton spinning will understand what is meant when it is said that the reeling is effectively a "doubling" operation, but performed with a variable number of ends, so as to compensate for the taper of the filaments. In reeling by hand, as has been said, the size of the silk is judged, as nearly as possible, by a complex mental operation, taking into account the number, size, and state of unwinding of the cocoons. It is impossible to do this mechanically, if for no other reason than this, that the cocoons must be left free to float and roll about in the water in order to give off their ends without breaking, and any mechanical device which touched them would defeat the object of the machine. The only way in which the thread can be mechanically regulated in silk reeling is by some kind of actual measurement performed after the thread has left the cocoons. The conditions are such that no direct measurement of size can be made, even with very delicate and expensive apparatus; but Mr. Serrell discovered that, owing to the great tenacity of the thread in proportion to its size, its almost absolute elastic uniformity, and from the fact that it could be stretched, two or three per cent. without injury, it was possible to measure its size indirectly, but as accurately as could be desired. As this fact is the starting point of an entirely new and important class of machinery, we may explain with considerable detail the method in which this measurement is performed. Bearing in mind that the thread is of uniform quality, it is evident that it will require more force to stretch a coarse thread by a given percentage of its length than it will to stretch one that is finer. Supposing the thread is uniform in quality but varying in size, the force required to stretch it varies directly with the size or sectional area of the thread itself. In the automatic reeling machine this stretch is obtained by causing the thread to take a turn round a pulley of a given winding speed, and then, after leaving this pulley, to take a turn around a second pulley having a somewhat greater winding speed.

By this means the thread which is passing from one pulley to the other is stretched by an amount equal to the difference of the winding speed of the two pulleys. In the diagram (Fig. 2) the thread passes, as shown by the arrows, over the pulley, P, and then over the pulley, P¹, the latter having a slightly greater winding speed. Between these pulleys it passes over the guide pulley, G. This latter is supported by a lever hinged at S, and movable between the stops, TT¹. W is an adjustable counterweight. When the thread is passed over the pulleys and guided in this manner, the stretch to which it is subjected tends to raise the guide and lever, so that the latter will be drawn up against the stop, T¹, when the thread is so coarse that the effort required to stretch it is sufficient to overcome the weight of the guide pulley and the adjustable counterweight. But as the thread becomes finer, which, in the case of reeling silk, happens either from the tapering of the filaments or the dropping off of a cocoon, a moment arrives when it is no longer strong enough to keep up the lever and counterweight. These then descend, and the lever touches the lower stop, T. It will be readily seen that the up and down movements of the lever can be made to take place when the thread has reached any desired maximum or minimum of size, the limits being fixed by suitably adjusting the counterweight.

In the automatic reeling machine this is the method employed for regulating the supply of cocoons. The counterweight being suitably adjusted, the lever falls when the thread has become fine enough to need another cocoon. The stop, T, and the lever serve as two parts of an electric contact, so that when they touch each other a circuit is completed, which trips a trigger and sets in motion the feed apparatus by which a new cocoon is added. In practice the two drums or pulleys are mounted on the same shaft, D (Fig. 1), difference of winding speed being obtained by making them of slightly different diameters.

The lever is mounted as a horizontal pendulum, and the less or greater stress required according to the size to be reeled is obtained by inclining its axis to a less or greater degree from the vertical. An arrangement is also adopted by which the strains existing in the thread when it arrives at the first drum are neutralized, so far as their effect upon the lever is concerned. This is accomplished by simply placing upon the lever an extra guide pulley, L¹, upon the side opposite to that which corresponds to the guide shown in the diagram, Fig. 2.

An electric contact is closed by a slight movement of the lever whenever the thread requires a new filament of cocoon, and broken again when the thread has been properly strengthened. It is evident that a delicate faller movement might be employed to set the feed mechanism in motion instead of the electric circuit, but, under the circumstances, as the motion is very slight and without force, being, in fact, comparable to the swinging of the beam of a balance through the space of about the sixteenth of an inch, it is simpler to use a contact.

The actual work of supplying the cocoons to the running thread is performed as follows: The cleaned cocoons are put into what is called the feeding basin, B1 (Fig. 1), a receptacle placed alongside of the ordinary reeling basin, B, of a filature. A circular elevator, E, into which the cocoons are charged by a slight current of water, lifts them over one corner of the reeling basin and drops them one by one through an aperture in a plate about six inches above the water of the reeling basin.

The end of the filament having been attached to a peg above the elevator, it happens that when a cocoon has been brought into the corner of the reeling basin, the filament is strung from it to the edge of the hole in the plate in such a position as to be readily seized by a mechanical finger, K (Fig. 3), attached to a truck arranged to run backward and forward along one side of the basin. This finger is mounted on an axis, and has a tang projecting at right angles to the side of the basin, so that the whole is in the form of a bell crank mounted on the truck.

There are usually four threads to each basin. When neither one of them needs an additional cocoon, the finger of the distributing apparatus remains, holding the filament of the cocoon at the corner of the basin where it has been dropped. When a circuit is closed by the weakening of any one of the threads, an electromagnetic catch is released, and the truck with its finger is drawn across the basin by a weight. At the same time the stop shown dotted in Fig. 3 is thrown out opposite to the thread that needs strengthening. This stop strikes the tang of the finger, and causes the latter to be thrown out near to the point at which the filaments going to make up the weakened thread are being drawn from the cocoons. Here the new filament is attached to the new running thread by a kind of revolving finger, J, called in France a "lance-bout." This contrivance takes the place of the agate of the ordinary filature, and is made up, essentially, of the following parts:

(1) A hollow axis, through the inside of which the thread passes instead of going through the hole of an agate. This hollow axis is furnished, near its lower end, with a ridge which serves to support a movable portion turning constantly round the axis. (2) A movable portion turning constantly round the axis. (3) A finger or hook fastened on the side of the movable portion and revolving with it. This hook, in revolving, catches the filament brought up by the finger and serves it on to the thread.

Such are the principal parts of the automatic reeling machine. Although the fact that this machine is entirely a new invention has necessitated a somewhat long explanation, its principal organs can nevertheless be summed up in a few words: (1) A controlling drum which serves to give the thread a constant elongation; (2) a pulley mounted on a pivot which closes an electric current every time that the thread becomes too fine, and attains, in consequence, its minimum strength, in other words, every time that a fresh cocoon is needed; (3) electromagnets with the necessary conducting wires; (4) the feeding basin; (5) distributing finger and stops; and (6) the lance-bout.

Our illustration, Fig. 1, shows diagrammatically a section through the cocoon frame and reel. The thread is composed of three, four, or more filaments, and after passing through the lance-bout, it travels as shown by the arrows. At first it is wound round itself about two hundred times, then passed over a fixed guide pulley, and over a second guide pulley lower down fixed to the frames which carry the lance-bouts, then up through the twist and over the smaller of the pulleys, D. Taking one complete turn, it is led round the guide pulley, L, from there round the larger of the pulleys, D, round the second guide pulley, L¹, then back to the large wheel, and over a fixed guide pulley across to the reeling frame. Power is supplied to the latter by means of a friction clutch, and to insure even winding the usual reciprocating motion of a guide is employed. The measuring apparatus is pivoted at F, and by raising or lowering the nuts at the end of the bar the required inclination is given.

We had recently an opportunity of examining the whole of this machinery in detail, and seeing the process of silk reeling in actual operation, Mr. Serrell having put up a complete set of his machines in Queen Victoria Street, London. Regarded simply as a piece of ingenious mechanism, the performance of these machines cannot fail to be of the highest interest to engineers, the reeling machine proper seeming almost endowed with human intelligence, so perfectly does it work. But, apart from the technical perfection, Mr. Serrell's improvements are of great importance as calculated to introduce the silk-reeling industry in this country on a large scale, while at the same time its effect upon India as a silk-growing country will be of equal importance.--_Industries._

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APPARATUS USED FOR MAKING ALCOHOL FOR HOSPITAL USE DURING THE CIVIL WAR BETWEEN THE STATES.[1]

[Footnote 1: Read at the Cincinnati meeting of the American
Pharmaceutical Association.]

By CHARLES K. GALLAGHER, Washington, N.C.

A is an ordinary farm boiler or kettle, with an iron lid securely bolted on; B, a steam pipe ending in a coil within a trough, D. C, D, two troughs made of gum logs, one inverted over the other, securely luted and fastened together by clamps and wedges. The "beer" to be distilled was introduced at E and the opening closed with a plug. The distillate--"low wine"--was collected at F, and redistilled from a set of similar troughs not shown in above figure, and heated by a continuation of the steam coil from D.

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CONFEDERATE APPARATUS FOR MANUFACTURING SALTPETER FOR AMMUNITION.

By CHARLES K. GALLAGHER, Washington, N.C.

Any convenient number of percolators, made of rough boards, arranged over a trough after the style of the old fashioned "lye stand," similar to the figure. Into these was placed the earth scraped from around old tobacco barns, from under kitchens and smokehouses. Then water or water and urine was poured upon it until the mass was thoroughly leached or exhausted. The percolate was collected in a receptacle and evaporated, the salt redissolved, filtered, again evaporated, and crystallized from the mother water.

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THE TELEMETER SYSTEM.

By F.R. UPTON.

In this paper, read before the British Association, the author explained that the "Telemeter System," invented by C.L. Clarke, of New York, is a method by which the slow movement of a revolving hand of any indicating instrument may be reproduced by the movement of a similar hand at a distant place, using electricity to convey the impulse. The primary hand moves until it makes electrical contact, thus sending an impulse. It is here that all previous methods have failed. This contact should be absolute and positive, for if it is not, the receiver will not work in unison. The contact could often be doubled by the jarring of the instrument, thus making the receiver jump twice. Clarke has overcome this defect by so arranging his mechanism that the faintest contact in the primary instrument closes two platinum points in multiple arc with it, thus making a firm and positive contact, which is not disturbed by any jar on the primary contact. This gives the instruments a positive start for the series of operations, instead of the faint contact which would be given, for example, by the light and slowly moving hand of a metallic thermometer. The other trouble with previous methods was that the contact points would corrode, and, in consequence of such corrosion, the instrument would fail to send impulses. Corrosion of the contacts is due to breaking the circuit slowly on a small surface. This is entirely remedied by breaking the circuit elsewhere than at the primary contact, using a quick motion, and also by giving this breaking contact large surface and making it firm. The instrument, as applied to a thermometer, is made as follows: From the free end of the light spiral of a metallic thermometer fixed at the other end, an arm, C, is attached, the end of which moves over an arc of a circle when the temperature varies. This end carries on either side of its extremity platinum contacts which, when the thermometer is at rest, lie between two other platinum points, A B, carried on radial arms. Any variation in temperature brings a point on the thermometer arm in contact with one of these points, and thus gives the initial start to the series of operations without opposing any friction to the free motion of the instrument. The first result is the closing of a short circuit round the initial point of contact, so that no current flows through it. Then the magnets which operate one set of pawls come into play. The two contact points are attached to a toothed wheel in which the pawls play, and these pawls are so arranged that they drive the wheel whenever moved by their magnets; thus the primary contact is broken.

In the receiver there is a similar toothed wheel carrying the hand of the indicating instrument, and actuated at the same moment as the transmitter. The primary contacts are so arranged that the contact is made for each degree of temperature to be indicated. This series of operations leaves the instruments closed and the pawls home in the toothed wheel. To break the circuit another wire and separate set of contacts are employed.

These are arranged on the arms carrying the pawls, and so adjusted that no contact is made until after the toothed wheel has moved a degree, when a circuit is closed and a magnet attracts an armature attached to a pendulum. This pendulum, after starting, breaks the circuit of the magnets which hold the pawls down, as well as of the short-circuiting device. As the pendulum takes an appreciable time to vibrate, this allows all the magnets to drop back, and breaks all circuits, leaving the primary contacts in the same relation as at first. The many details of the instruments are carefully worked out. All the contacts are of a rubbing nature, thus avoiding danger from dirt, and they are made with springs, so as not to be affected by jar.

The receiving instruments can be made recorders also by simple devices. Thus, having only a most delicate pressure in the primary instrument, a distinct ink record may be made in the receiver, even though the paper be rough and soft. The method is applicable to steam gauges, water indicators, clocks, barometers, etc., in fact, to any measuring instrument where a moving hand can be employed.

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A NEW MONSTER REVOLVING BLACK ASH FURNACE AND THE WORK DONE WITH IT.

By WATSON SMITH, Lecturer in Chemical Technology in the Victoria University, etc.

The Widnes Alkali Company, limited, to which I am indebted for permission to describe this latest addition to a family of revolving black ash furnaces, of late not only increasing in number, but also individual size, has kindly allowed my friend, Mr. H. Baker, to photograph the great revolver in question, and I have pleasure now in throwing on the screen a picture of it, and also one of a revolver of ordinary size, so as to render a comparison possible. The revolver of ordinary size measures at most 18½ ft. long, with a diameter of 12½ ft. The boiling down pans connected with such a furnace measure 60 ft. in length. Each charge contains four tons of salt cake, and some of these revolvers get through 18 tons of salt cake per day and consume 13 cwt. of coal per ton of cake decomposed.

With regard to the larger revolver, it may be just said that the Widnes Alkali Company has not at once sprung to the adoption of a furnace of the immense size to be presently given, but in 1884 it erected a revolver only about 3 ft. to 4 ft. short of the length of that one, and having two discharging holes. The giant revolving furnace to be described measures in length 30 ft. and has a diameter of 12 ft. 6 in. Inside length is 28 ft. 6 in., with a diameter of 11 ft. 4 in. It is lined with 16,000 fire bricks and 120 fire-clay blocks or breakers, weighing each 1¼ cwt. The bricks weigh per 1,000 about four tons. The weight of salt cake per charge (i.e., contained in each charge of salt cake, limestone, mud, and slack) is 8 tons 12 cwt. For 100 tons of salt cake charged, there are also charged about 110 tons of lime mud and limestone and 55 tons of mixing slack. In a week of seven days about 48 charges are worked through, weighing of raw materials about 25 _tons per charge_. The total amount of salt cake decomposed weekly is about 400 tons, and may be reckoned as yielding 240 tons of 60 per cent. caustic soda. As regards fuel used for firing, this may be put down as 200 tons per week, or about 10 cwt. per ton of salt cake decomposed. Also with regard to the concentration of liquor from 20° Tw. to 50° Tw., there is sufficient of such concentrated liquor evaporated down to keep three self-fired caustic pots working, which are boiled at a strength of 80° Tw. Were it not for this liquor, no less than seven self-fired pots would be required to do this work, showing a difference of 80 tons of fuel.

The question may be asked, "Why increase the size of these huge pieces of apparatus?" The answer, I apprehend, is that owing to competition and reduction of prices, greater efforts are necessary to reduce costs. With automatic apparatus like the black ash revolver, we may consider no very sensible addition of man power would be needed, in passing from the smallest sized to the largest sized revolver. Then, again, we may, reckoning a certain constant amount of heat lost per each revolver furnace of the small size, consider that if we doubled the size of such revolver, we should lose by no means double the amount of heat lost with the small apparatus; but only the same as that lost in the small furnace _plus_ a certain fraction of that quantity, which will be smaller the better and more efficient the arrangements are. Then, again, there is an economy in iron plate for such a large revolver; there is economy in expense on the engine power and on fuel consumed, as well as in wear and tear.

Just to mention fuel alone, we saw that with an ordinary large sized revolver, the coal consumption was 13 cwt. per ton of salt cake decomposed in the black ash process; but with the giant revolver we have been describing, that consumption is reduced to 10 cwt. per ton of cake decomposed.

The question will be probably asked, How is it possible to get a flame from one furnace to carry through such a long revolver and do its work in fusing the black ash mixture effectively from one end to the other? The furnace employed viewed in front looks very like an ordinary revolver fireplace, but at the side thereof, in line with the front of the revolver, at which the discharge of the "crude soda" takes place, there are observed to be three "charging holes," rather than doors, through which fuel is charged from a platform directly into the furnace through those holes.

The furnace is of course a larger one than furnaces adjusted to revolvers of the usual size. But the effect of one charging door in front and three at the side, which after charging are "banked" up with coal, with the exception of a small aperture above for admission of air, is very similar to that sometimes adopted in the laboratory for increasing heating effect by joining several Bunsen lamps together to produce one large, powerful flame. In this case, the four charging holes represent, as it were, the air apertures of the several Bunsen lamps. Of course the one firing door at front would be totally inadequate to supply and feed a fire capable of yielding a flame that would be adequate for the working of so huge a revolver. As an effort of chemical engineering, it is a very interesting example of what skill and enterprise in that direction alone will do in reducing costs, without in the least modifying the chemical reactions taking place.--_Journal Soc. Chem. Industry._

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IMPROVEMENTS IN THE MANUFACTURE OF PORTLAND CEMENT.[1]

[Footnote 1: A paper recently read before the British
Association.]

By FREDERICK RANSOMS, A.I.C.E.

So much has been said and written on and in relation to Portland cement that further communications upon the subject may appear to many of the present company to be superfluous. But is this really so? The author thinks not, and he hopes by the following communication, to place before this meeting and the community at large some facts which have up to the present time, or until within a very recent date, been practically disregarded or overlooked in the production of this very important and valuable material, so essential in carrying out the great and important works of the present day, whether of docks and harbors, our coast defenses, or our more numerous operations on land, including the construction of our railways, tunnels, and bridges, aqueducts, viaducts, foundations, etc. The author does not propose to occupy the time of this meeting by referring to the origin or the circumstances attendant upon the early history of this material, the manufacture of which has now assumed such gigantic proportions--these matters have already been fully dealt with by other more competent authorities; but rather to direct the attention of those interested therein to certain modifications, which he considers improvements, by means of which a large proportion of capital unnecessarily involved in its manufacture may be set free in the future, the method of manufacture simplified, the cost of manipulation reduced, and stronger and more uniformly reliable cement be placed within the reach of those upon whom devolves the duty and responsibility of constructing works of a substantial and permanent character; but in order to do this it will be necessary to allude to certain palpable errors and defects which, in the author's opinion, are perpetuated, and are in general practice at the present day.

Portland cement is, as is well known, composed of a mixture of chalk, or other carbonate of lime, and clay--such as is obtained on the banks of the Thames or the Medway--intimately mixed and then subjected to heat in a kiln, producing incipient fusion, and thereby forming a chemical combination of lime with silica and alumina, or practically of lime with dehydrated clay. In order to effect this, the usual method is to place the mechanically mixed chalk and clay (technically called slurry), in lumps varying in size, say, from 4 to 10 lb., in kilns with alternate layers of coke, and raise the mass to a glowing heat sufficient to effect the required combination, in the form of very hard clinker. These kilns differ in capacity, but perhaps a fair average size would be capable of producing about 30 tons of clinker, requiring for the operation, say, from 60 to 70 tons of dried slurry, with from 12 to 15 tons of coke or other fuel. The kiln, after being thus loaded, is lighted by means of wood and shavings at the base, and, as a matter of course, the lumps of slurry at the lower part of the kiln are burned first, but the moisture and sulphurous gases liberated by the heat are condensed by the cooler layers above, and remain until the heat from combustion, gradually ascending, raises the temperature to a sufficient degree to drive them further upward, until at length they escape at the top of the kiln. The time occupied in loading, burning, and drawing a kiln of 30 tons of clinker averages about seven days. It will be readily understood that the outside of the clinker so produced must have been subjected to a much greater amount of heat then was necessary, before the center of such clinker could have received sufficient to have produced the incipient fusion necessary to effect the chemical combination of its ingredients; and the result is not only a considerable waste of heat, but, as always occurs, the clinker is not uniformly burnt, a portion of the outer part has to be discarded as overburnt and useless, while the inner part is not sufficiently burnt, and has to be reburned afterward. Moreover, the clinker, which is of excessively hard character, has to be reduced by means of a crusher to particles sufficiently small to be admitted by the millstones, where it is ground into a fine powder, and becomes the Portland cement of commerce.

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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