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forced concrete lies in the building of structures which are especially subject to the fumes arising from the stacks of locomotives. This applies not only to engine houses and coaling stations, but also to over-head highway bridges which cross railroads. The concentrated gases of combustion have a corrosive action on steel which wears it away in the course of a few years. No matter how much the steel may be protected by paint, even the paint will be worn off by the mechanical action of the fine cinders which are blown out by the exhaust and which act as a very effective form of sand blast. Probably most kinds of paints are chemically affected more or less but the combination of chemical action and mechanical wear will destroy any protective covering in a comparatively short time. Reinforced concrete is absolutely unaffected chemically while the mechanical sand-blast action of the exhaust is so utterly insignificant that it need not be considered. Although a wooden structure is not seriously affected by the exhaust, its lack of durability, its danger from destruction by fire and the recent very great increase in the price of lumber, have combined to render wood an unsatisfactory and uneconomical material for such structures.
The advantages of reinforced concrete in the construction of coaling stations also is now being recognized. A frame. work of structural steel, with steel plates for the floors and sides of the pockets, has been tried in order to obtain a noncombustible structure. But the sulphuric acid, always present in the coal, corrodes the steel very rapidly and the life of such a structure is short. If the steel is adequately protected against corrosion by concrete, the cost is considerably in excess of a steel structure, but far greater permanence is secured.
In its application to the construction of masonry dams, reinforced concrete has entered another field. A solid masonry dam is usually constructed on the gravity principle, which means practically that the volume of its masonry is so great and so heavy that it is supposed to be safe against over-turning, but the cost of such a construction is so great that the cross section of the dam is usually reduced to the lowest limit which is considered permissible. The upper face of such a dam
usually makes an usually makes an angle considerably. greater than 45° with the horizontal and, under such conditions, a flood over the dam will raise the line of pressure and decrease the factor of safety. The higher the flood, the greater the danger. Under such conditions, a weakening of the foundation or an unsuspected washing out of the sub-soil may cause a settlement and a shifting of the line of pressure until the factor of safety, which for the sake of "economy" has been made very low, is wiped out and the result is a disaster which perhaps spreads destruction through a valley.
Another type of dam is illustrated in an old fashioned timber dam which is always constructed with a comparatively flat up-stream face, the angle of the upper face with the horizontal being less than 45°. Even the line of the resulting water pressure lies inside the base of the dam. There is never any tendency to over-turn and a flood only increases the pressure of the dam on its foundation.. As long as such a dam is kept tight, so that there is no flow of water through the dam to disintegrate the foundation, the dam is usually safe, but, being constructed of timber which is usually alternately wet or dry, the life of such a dam is exceedingly limited, and, considering the present price of lumber, is not even economical.
A reinforced concrete hollow dam combines all of the safe principles and advantages of a timber dam with the indefinite durability of first class masonry construction. The up-stream face of a concrete dam is made with a comparatively flat slope, usually less than 45° with the horizontal. Hydraulic pressure being a perfectly definite quantity, it enables the engineer to design such a dam with a full knowledge of the stresses to which it will be subjected. These stresses are such that they may be easily provided for by the skeleton construction which is adopted for these dams. The dams consist essentially of an upstream "deck" whose chief duty is to withstand the direct and definite pressure of the water above it. This deck is supported at intervals by vertical walls which are parallel with the line of the stream and which transfer the pressure to the foundation of the dam. One great advantage in the method of construction is
rapidly and at such a reduction of cost below that of ordinary masonry dams that such designs have rendered practicable the utilization of water powers which would not financially justify the construction of an ordinary stone masonry dam. The construction of these hollow concrete dams has even permitted the utilization of the space within them for gates and even for the location of water wheels and dynamos, thus permit ting a very great reduction in the cost of the entire plant. Such a dam may even contain a passageway which will permit crossing the river in times of the highest floods, and thus save the construction of a bridge at that point. The
permits a reinforced concrete beam to be deflected for a very considerable percentage of its span without showing any cracks on the stretched side. It is wellknown that plain concrete cannot be stretched more than a very minute fraction of its length without cracking. A very long monolith of plain concrete will nearly always develop cracks which are caused by a concentration of the stretching at the weakest points in the concrete and since the proportional amount at which concrete may be stretched without rupture is very small, a concentration of the extension at one place will cause rupture at that point. If the metal is properly imbedded in the concrete, so that the concrete and the metal will stretch together, then the deformity of the concrete by stretching will be distributed uniformly throughout its length instead of being confined to a few points. Objection is sometimes made to the policy of not using expanded joints on the ground that there have been several instances of monolithic reinforced concrete structures in which temperature cracks have developed. In such cases it is easily demonstrable that the metal was not well distributed through the body of the concrete. The effectual prevention of cracks is only accomplished by such an intimate union of the concrete and the steel that they must act together under all circumstances and conditions of temperature. It is not an easy matter to compute theoretically just what proportion of metal will be neeeded to insure a wall against cracking. It is probably true that the metal which will ordinarily be needed for reinforcement will also be able to take care of such stresses and it is certainly true that the uniform distribution of the metal is of far greater importance than its amount. The Harvard stadium has a length of fourteen hundred feet and was constructed without expansion joints. It has already experienced three northern winters. No cracks have developed in this structure
except at a point where the straight portion joins the semi-circular end and even here the cause of the crack is not considered due to changes of temperature.
Reinforced concrete has even invaded the realm in which stone masonry has been considered from ancient times the best building material and is now strongly competing with it in the construction of arch bridges both because it is cheaper and also better. Stone arch bridges have been built for many hundreds of years. Some of them have been built by men who probably had no knowledge of the theoretical mechanical principles now used in designing such arches. And yet these men constructed arches of long span which had comparatively little rise. But since the stone arch depends purely on compressive stresses the design has very definite limitations. It is almost invariably found that the dead weight of a stone arch is several times the maximum live load which may be safely placed on it and that even a portion of this load, if placed near one end of the arch, may test it more severely than the full load uniformly distributed. The ability of a reinforced concrete arch to withstand transverse stresses furnishes a large element of safety which is wholly unobtainable with plain stone masonry and actually permits dimensions and proportions which would be unsafe in a stone arch.
Although a reinforced concrete arch is usually designed so that the "line of pressure" for full loading will pass nearly through the center of the arch, which means that every portion of the arch is under compression, yet the arch will not necessarily fail if, for an eccentric loading, the line of pressures should pass entirely outside of the arch ring. In such a case, its stability would depend on the transverse strength of the arch. section. A plain stone arch with the same dimensions and loaded in the same way would necessarily fail: Reinforced concrete is superior for such a purpose.
The trees were planted to protect the apiary from the hot rays of the summer sun.
"How doth the busy little bee
Since the foregoing lines were written. the only feature of bee-keeping that has remained unchanged is the bee's industry. Whereas only a few decades ago the bees used to store up their honey in rough boxes, hollow trees, or straw hives, necessitating their own destruction with brimstone fumes before the owner could obtain the sweets, now they make their homes in machine-prepared hives, store their honey in machine-made frames, build their combs on machine-made bases of wax, prepared to save them work, and, if they are kept for the production of "strained" honey, are robbed regularly of the combs, which are emptied of honey in an extractor, a metal invention of machinists of recent years. "Hand
made honey," according to the old standards, is a thing of the past.
Constant improvement in the management of bees is being made. Before the introduction of the movable comb honey was cut out in chunks, after being produced in an old box placed on top of the body of the hive. Practically all hives now are of the same general construction, the lower part being box-like, about twenty inches long, fifteen inches wide, and eleven inches high, with a movable bottom projecting as an alighting board for the bees. In this box are hung eight frames, on which the bees build their combs. A frame from one hive may be placed in any other.
The equipment for securing comb honey for sale consists of a box set on top of the body of the hive and containing twenty-four sections or frames four and one-fourth inches square, in which the combs are built. Each of these will con
tain a pound of honey. Rows of four each are set lengthwise of the hive, in racks, and to secure straight combs wooden partition boards--a recent invention-having holes as doorways for the bees, are put between each row.
The most important invention, which has increased the yield of first-class honey at least one-half, is "comb foundation," which now is used by almost every apiarist. This consists of thin sheets of wax run between steel die rollers, which stamp upon them the bases of the cells and make them of the same thickness, shape, etc., as the base of the comb built by the bees themselves. The labor expended by the bees in making a pound of wax for comb has been found to equal that which would be required in producing thirty pounds of honey, so the supplying of this foundation to the bees. saves them an immense amount of labor. Pieces of this prepared beeswax, which is so delicate that a pound contains fifteen square feet, are attached to the inside of the sections or boxes for comb honey, and are called "starters." bees extend the bases of the cells and the foundation insures straight combs.
In handling the bees their owner uses several other recent inventions, among them the "smoker." With a silk veil over his face and armed with the "smoker," the apiarist can overcome the most pugnacious colony of bees which ever has
HANDLING THE BEES.
READY FOR SWARM. Side of hive is removed, showing construction.
existed. The smoker consists of a tin firepot with a nozzle, attached to a bellows. The apparatus is about eighteen inches long and is arranged so that whenever the bellows is pressed a stream of smoke issues from the nozzle. Rags, corncobs, and the like are used for fuel, and when the smoke is blown into the entrance of the hive the bees immediately are terror-stricken and begin to gorge themselves with honey. Their idea, it is supposed, is that they will be driven out of their home and that they must provision themselves for their wanderings; at any rate, while they are eating they can
not sting, and, come what will, they will not stop eating.
Queens may be grown at will-through recent inventions and discoveries and thousands are sent by mail from apiaries to bee-keepers who wish to improve their stock, for there are thoroughbred bees as well as horses or cattle,. and a fine queen of the Italian variety, coming from a strain whose ancestors made 200 pounds of honey per hive per annum, was sold last summer for $100. Fortunes have been made in queen rearing.