FIG. 131.—Carrying water home from the spring.FIG. 131.—Carrying water home from the spring.
182. The Air as Man's Servant.Long before man harnessed water for turbines, or steam for engines, he made the air serve his purpose, and by means of it raised water from hidden underground depths to the surface of the earth; likewise, by means of it, he raised to his dwelling on the hillside water from the stream in the valley below. Those wholive in cities where running water is always present in the home cannot realize the hardship of the days when this "ready-made" supply did not exist, but when man laboriously carried to his dwelling, from distant spring and stream, the water necessary for the daily need.
What are the characteristics of the air which have enabled man to accomplish these feats? They are well known to us and may be briefly stated as follows:—
(1) Air has weight, and 1 cubic foot of air, at atmospheric pressure, weighs 1-1/4 ounces.
(2) The air around us presses with a force of about 15 pounds upon every square inch of surface that it touches.
FIG. 132.—The atmosphere pressing downward on a pushes water after the rising piston b.FIG. 132.—The atmosphere pressing downward on a pushes water after the rising piston b.
(3) Air is elastic; it can be compressed, as in the balloon or bicycle tire, but it expands immediately when pressure is reduced. As it expands and occupies more space, its pressure falls and it exerts less force against the matter with which it comes in contact. If, for example, 1 cubic foot of air is allowed to expand and occupy 2 cubic feet of space, the pressure which it exerts is reduced one half. When air is compressed, its pressure increases, and it exerts a greater force against the matter with which it comes in contact. If 2 cubic feet of air are compressed to 1 cubic foot, the pressure of the compressed air is doubled. (See Section 89.)
183. The Common Pump or Lifting Pump.Place a tube containing a close-fitting piston in a vessel of water, as shown in Figure 132. Then raise the piston with the hand and notice that the water rises in the piston tube. The rise of water in the piston tube is similar to the raising of lemonadethrough a straw (Section 77). The atmosphere presses with a force of 15 pounds upon every square inch of water in the large vessel, and forces some of it into the space left vacant by the retreating piston. The common pump works in a similar manner. It consists of a piston or plunger which moves back and forth in an air-tight cylinder, and contains an outward opening valve through which water and air can pass. From the bottom of the cylinder a tube runs down into the well or reservoir, and water from the well has access to the cylinder through another outward-moving valve. In practice the tube is known as the suction pipe, and its valve as the suction valve.
In order to understand the action of a pump, we will suppose that no water is in the pump, and we will pump until a stream issues from the spout. The various stages are represented diagrammatically by Figure 133. In (1) the entire pump is empty of water but full of air at atmospheric pressure, and both valves are closed. In (2) the plunger is being raised and is lifting the column of air that rests on it. The air and water in the inlet pipe, being thus partially relieved of downward pressure, are pushed up by the atmospheric pressure on the surface of the water in the well. When the piston moves downward as in (3), the valve in the pipe closes by its own weight, and the air in the cylinder escapes through the valve in the plunger. In (4) the piston is again rising, repeating the process of (2). In (5) the process of (3) is being repeated, but water instead of air is escaping through the valve in the plunger. In (6) the process of (2) is being repeated, but the water has reached the spout and is flowing out.
FIG. 133. Diagram of the process of pumping.FIG. 133. Diagram of the process of pumping.
After the pump is in condition (6), motion of the plunger is followed by a more or less regular discharge of water through the spout, and the quantity of water which gushesforth depends upon the speed with which the piston is moved. A strong man giving quick strokes can produce a large flow; a child, on the other hand, is able to produce only a thin stream. Whoever pumps must exert sufficient force to lift the water from the surface of the well to the spout exit. For this reason the pump has received the name oflifting pump.
FIG. 134.—Force pump.FIG. 134.—Force pump.
184. The Force Pump.In the common pump, water cannot not be raised higher than the spout. In many cases it is desirable to force water considerably above the pump itself, as, for instance, in the fire hose; under such circumstances a type of pump is employed which has received the name offorce pump. This differs but little from the ordinary lift pump, as a reference to Figure 134 will show. Here both valves are placed in the cylinder, and the piston is solid, but the principle is the same as in the lifting pump.
An upward motion of the plunger allows water to enter the cylinder, and the downward motion of the plunger drives water throughE. (Is this true for the lift pump as well?) Since only the downward motion of the plunger forces water throughE, the discharge is intermittent and is therefore not practical for commercial purposes. In order to convert this intermittent discharge into a steady stream, an air chamber is installed near the discharge tube, as in Figure 135. The water forced into the air chamber by the downward-moving piston compresses the air and increases its pressure. The pressure of the confined air reacts against the water and tends to drive it out of the chamber. Hence, even when the plunger is moving upward, water is forced through the pipebecause of the pressure of the compressed air. In this way a continuous flow is secured.
FIG. 135.—The air chamber A insures a continuous flow of water.FIG. 135.—The air chamber A insures a continuous flow of water.
The height to which the water can be forced in the pipe depends upon the size and construction of the pump and upon the force with which the plunger can be moved. The larger the stream desired and the greater the height to be reached, the stronger the force needed and the more powerful the construction necessary.
The force pump gets its name from the fact that the moving piston drives or forces the water through the discharge tube.
185. Irrigation and Drainage.History shows that the lifting pump has been used by man since the fourth century before Christ; for many present-day enterprises this ancient form of pump is inconvenient and impracticable, and hence it has been replaced in many cases by more modern types, such as rotary and centrifugal pumps (Fig. 136). In these forms, rapidly rotating wheels lift the water and drive it onward into a discharge pipe, from which it issues with great force. There is neither piston nor valve in these pumps, and the quantity of water raised and the force with which it is driven through the pipes depends solely upon the size of the wheels and the speed with which they rotate.
FIG. 136.—Centrifugal pump with part of the casing cut away to show the wheel.FIG. 136.—Centrifugal pump with part of the casing cut away to show the wheel.
Irrigation, or the artificial watering of land, is of the greatest importance in those parts of the world where the land is naturally too dry for farming. In the United States, approximately two fifths of the land area is so dry as to be worthlessfor agricultural purposes unless artificially watered. In the West, several large irrigating systems have been built by the federal government, and at present about ten million acres of land have been converted from worthless farms into fields rich in crops. Many irrigating systems use centrifugal pumps to force water over long distances and to supply it in quantities sufficient for vast agricultural needs. In many regions, the success of a farm or ranch depends upon the irrigation furnished in dry seasons, or upon man's ability to drive water from a region of abundance to a remote region of scarcity.
FIG. 137.—Agriculture made possible by irrigation.FIG. 137.—Agriculture made possible by irrigation.
The draining of land is also a matter of considerable importance; swamps and marshes which were at one time considered useless have been drained and then reclaimed and converted into good farming land. The surplus water is bestremoved by centrifugal pumps, since sand and sticks which would clog the valves of an ordinary pump are passed along without difficulty by the rotating wheel.
FIG. 138.—Rice for its growth needs periodical flooding, and irrigation often supplies the necessary water.FIG. 138.—Rice for its growth needs periodical flooding, and irrigation often supplies the necessary water.
186. Camping.—Its Pleasures and its Dangers.The allurement of a vacation camp in the heart of the woods is so great as to make many campers ignore the vital importance of securing a safe water supply. A river bank may be beautiful and teeming with diversions, but if the river is used as a source of drinking water, the results will almost always be fatal to some. The water can be boiled, it is true, but few campers are willing to forage for the additional wood needed for this apparently unnecessary requirement; then, too, boiled water does not cool readily in summer, and hence is disagreeable for drinking purposes.
The only safe course is to abandon the river as a source of drinking water, and if a spring cannot be found, to drive a well. In many regions, especially in the neighborhood ofstreams, water can be found ten or fifteen feet below the surface. Water taken from such a depth has filtered through a bed of soil, and is fairly safe for any purpose. Of course the deeper the well, the safer will be the water. With the use of such a pump as will be described, campers can, without grave danger, throw dish water, etc., on the ground somewhat remote from the camp; this may not injure their drinking water because the liquids will slowly seep through the ground, and as they filter downward will lose their dangerous matter. All the water which reaches the well pipes will have filtered through the soil bed and therefore will probably be safe.
But while the careless disposal of wastes may not spoil the drinking water (in the well to be described), other laws of health demand a thoughtful disposal of wastes. The malarial mosquito and the typhoid fly flourish in unhygienic quarters, and the only way to guard against their dangers is to allow them neither food nor breeding place.
FIG. 139—A driven well.FIG. 139—A driven well.
The burning of garbage, the discharge of waters into cesspools, or, in temporary camps, the discharge of wastes to distant points through the agency of a cheap sewage pipe will insure safety to campers, will lessen the trials of flies and mosquitoes, and will add but little to the expense.
187. A Cheap Well for Campers.A two-inch galvanized iron pipe with a strong, pointed end containing small perforations is driven into the ground with a sledge hammer. After it has penetrated for a few feet, another length is added and the whole is driven down, and this is repeated until water is reached. A cheap pump is then attached to the upper end of the drill pipe and serves to raise the water. During the drilling, some soil particles get into the pipe through the perforations, and these cloud the water at first; but after the pipe has once been cleaned by the upward-moving water, the supply remains clear. The flow from such a well is naturallysmall; first, because water is not abundant near the surface of the earth, and second, because cheap pumps are poorly constructed and cannot raise a large amount. But the supply will usually be sufficient for the needs of simple camp life, and many a small farm uses this form of well, not only for household purposes, but for watering the cattle in winter.
If the cheapness of such pumps were known, their use would be more general for temporary purposes. The cost of material need not exceed $5 for a 10-foot well, and the driving of the pipe could be made as much a part of the camping as the pitching of the tent itself. If the camping site is abandoned at the close of the vacation, the pump can be removed and kept over winter for use the following summer in another place. In this way the actual cost of the water supply can be reduced to scarcely more than $3, the removable pump being a permanent possession. In rocky or mountain regions the driven well is not practicable, because the driving point is blunted and broken by the rock and cannot pierce the rocky beds of land.
FIG. 140.—Diagram showing how supplying a city with good water lessens sickness and death. The lines b show the relative number of people who died of typhoid fever before the water was filtered; the lines a show the numbers who died after the water was filtered. The figures are the number of typhoid deaths occurring yearly out of 100,000 inhabitants.FIG. 140.—Diagram showing how supplying a city with good water lessens sickness and death. The lines b show the relative number of people who died of typhoid fever before the water was filtered; the lines a show the numbers who died after the water was filtered. The figures are the number of typhoid deaths occurring yearly out of 100,000 inhabitants.
FIG. 141.—A deep well with the piston in the water.FIG. 141.—A deep well with the piston in the water.
188. Our Summer Vacation.It has been asserted by some city health officials that many cases of typhoid fever in cities can be traced to the unsanitary conditions existing in summer resorts. The drinking water of most cities is now understrict supervision, while that of isolated farms, of small seaside resorts, and of scattered mountain hotels is left to the care of individual proprietors, and in only too many instances receives no attention whatever. The sewage disposal is often inadequate and badly planned, and the water becomes dangerously contaminated. A strong, healthy person, with plenty of outdoor exercise and with hygienic habits, may be able to resist the disease germs present in the poor water supply; more often the summer guests carry back with them to their winter homes the germs of disease, and these gain the upper hand under the altered conditions of city and business life. It is not too much to say that every man andwoman should know the source of his summer table water and the method of sewage disposal. If the conditions are unsanitary, they cannot be remedied at once, but another resort can be found and personal danger can be avoided. Public sentiment and the loss of trade will go far in furthering an effort toward better sanitation.
In the driven well, water cannot reach the spout unless it has first filtered through the soil to the depth of the driven pipe; after such a journey it is fairly safe, unless very large quantities of sewage are present; generally speaking, such a depth of soil is able to filter satisfactorily the drainage of the limited number of people which a driven well suffices to supply.
Abundant water is rarely reached at less than 75 feet, and it would usually be impossible to drive a pipe to such a depth. When a large quantity of water is desired, strong machines drill into the ground and excavate an opening into which a wide pipe can be lowered. I recently spent a summer in the Pocono Mountains and saw such a well completed. The machine drilled to a depth of 250 feet before much water was reached andto over 300 feet before a flow was obtained sufficient to satisfy the owner. The water thus obtained was to be the sole water supply of a hotel accommodating 150 persons; the proprietor calculated that the requirements of his guests, for bath, toilet, laundry, kitchen, etc., and the domestics employed to serve them, together with the livery at their disposal, demanded a flow of 10 gallons per minute. The ground was full of rock and difficult to penetrate, and it required 6 weeks of constant work for two skilled men to drill the opening, lower the suction pipe, and install the pump, the cost being approximately $700.
FIG. 142.—Showing how drinking water can be contaminated from cesspool (c) and wash water (w).FIG. 142.—Showing how drinking water can be contaminated from cesspool (c) and wash water (w).
The water from such a well is safe and pure except under the conditions represented in Figure 142. If sewage or slops be poured upon the ground in the neighborhood of the well, the liquid will seep through the ground and some may make its way into the pump before it has been purified by the earth. The impure liquid will thus contaminate the otherwise pure water and will render it decidedly harmful. For absolute safety the sewage discharge shouldbe at least 75 feet from the well, and in large hotels, where there is necessarily a large quantity of sewage, the distance should be much greater. As the sewage seeps through the ground it loses its impurities, but the quantity of earth required to purify it depends upon its abundance; a small depth of soil cannot take care of an indefinite amount of sewage. Hence, the greater the number of people in a hotel, or the more abundant the sewage, the greater should be the distance between well and sewer.
By far the best way to avoid contamination is to see to it that the sewage discharges into the groundbelowthe well; that is, to dig the well in such a location that the sewage drainage will be away from the well.
In cities and towns and large summer communities, the sewage of individual buildings drains into common tanks erected at public expense; the contents of these are discharged in turn into harbors and streams, or are otherwise disposed of at great expense, although they contain valuable substances. It has been estimated that the drainage or sewage of England alone would be worth $ 80,000,000 a year if used as fertilizer.
A few cities, such as Columbus and Cleveland, Ohio, realize the need of utilizing this source of wealth, and by chemical means deodorize their sewage and change it into substances useful for agricultural and industrial purposes. There is still a great deal to be learned on this subject, and it is possible that chemically treated sewage may be made a source of income to a community rather than an expense.
189. Pumps which Compress Air.The pumps considered in the preceding Sections have their widest application in agricultural districts, where by means of them water is raised to the surface of the earth or is pumped into elevated tanks. From a commercial and industrial standpoint a mostimportant class of pump is that known as the compression type; in these, air or any other gas is compressed rather than rarefied.
Air brakes and self-opening and self-closing doors on cars are operated by means of compression pumps. The laying of bridge and pier foundations, in fact all work which must be done under water, is possible only through the agency of compression pumps. Those who have visited mines, and have gone into the heart of the underground labyrinth, know how difficult it is for fresh air to make its way to the miners. Compression pumps have eliminated this difficulty, and to-day fresh air is constantly pumped into the mines to supply the laborers there. Agricultural methods also have been modified by the compression pump. The spraying of trees (Fig. 143), formerly done slowly and laboriously, is now a relatively simple matter.
FIG. 143.—Spraying trees by means of a compression pump.FIG. 143.—Spraying trees by means of a compression pump.
190. The Bicycle Pump.The bicycle pump is the best known of all compression pumps. Here, as in other pumps of its type, the valves open inward rather than outward. When the piston is lowered, compressed air is driven through the rubber tubing, pushes open an inward-opening valve in the tire, and thus enters the tire. When the piston israised, the lower valve closes, the upper valve is opened by atmospheric pressure, and air from outside enters the cylinder; the next stroke of the piston drives a fresh supply of air into the tire, which thus in time becomes inflated. In most cheap bicycle pumps, the piston valve is replaced by a soft piece of leather so attached to the piston that it allows air to slip around it and into the cylinder, but prevents its escape from the cylinder (Fig. 144).
FIG. 144.—The bicycle foot pump.FIG. 144.—The bicycle foot pump.
191. How a Man works under Water.Place one end of a piece of glass tube in a vessel of water and notice that the water rises in the tube (Fig. 145). Blow into the tube and see whether you can force the water wholly or partially down the tube. If the tube is connected to a small compression pump, sufficient air can be sent into the tube to cause the water to sink and to keep the tube permanently clear of water. This is, in brief, the principle employed for work under water. A compression pump forces air through a tube into the chamber in which men are to work (Fig. 146). The air thus furnished from above supplies the workmen with oxygen, and by its pressure prevents water from entering the chamber. When the task has been completed, the chamber is raised and later lowered to a new position.
FIG. 145.—Water does not enter the tube as long as we blow into it.FIG. 145.—Water does not enter the tube as long as we blow into it.
Figure 147 shows men at work on a bridge foundation. Workmen, tools, and supplies are lowered in baskets through a central tubeBCprovided with an air chamberL, having air-tight gates atAandA'. The gateAis opened and workmen enter the air chamber. The gateAis then closed and the gateA'is opened slowly to give the men time to get accustomed to the high pressure inB, and then the men are lowered to the bottom. Excavated earth is removed in a similar manner. Air is supplied through a tubeDD. Such an arrangement for work under water is called a caisson. It is held in position by a mass of concreteEE.
FIG. 146—The principle of work under water.FIG. 146—The principle of work under water.
FIG. 147—Showing how men can work under water.FIG. 147—Showing how men can work under water.
In many cases men work in diving suits rather than in caissons; these suits are made of rubber except for the head piece, which is of metal provided with transparent eyepieces. Air is supplied through a flexible tube by a compression pump. The diver sometimescarries on his back a tank of compressed air, from which the air escapes through a tube to the space between the body and the suit. When the air has become foul, the diver opens a valve in his suit and allows it to pass into the water, at the same time admitting a fresh supply from the tank. The valve opens outward from the body, and hence will allow of the exit of air but not of the entrance of water. When the diver ceases work and desires to rise to the surface, he signals and is drawn up by a rope attached to the suit.
192. Combination of Pumps.In many cases the combined use of both exhaust and compression pumps is necessary to secure the desired result; as, for example, in pneumatic dispatch tubes. These are employed in the transportation of letters and small packages from building to building or between parts of the same building. A pump removes air from the part of the tube ahead of the package, and thus reduces the resistance, while a compression pump forces air into the tube behind the package and thus drives it forward with great speed.
193.It is by no means unusual for the residents of a large city or town to receive through the newspapers a notification that the city water supply is running low and that economy should be exercised in its use. The problem of supplying a large city with an abundance of pure water is among the most difficult tasks which city officials have to perform, and is one little understood and appreciated by the average citizen.
Intense interest in personal and domestic affairs is natural, but every citizen, rich or poor, should have an interest in civic affairs as well, and there is no better or more important place to begin than with the water supply. One of the most stirring questions in New York to-day has to do with the construction of huge aqueducts designed to convey to the residents of the city, water from the distant Catskill Mountains. The growth of the population has been so phenomenally rapid that the combined output of all available near-by sources does not suffice to meet the increasing consumption.
Where does your city obtain its water? Does it bring it to its reservoirs in the most economic way possible, and is there any legitimate excuse for the scarcity of water which many communities face in dry seasons?
194. Two Possibilities.Sometimes a city is fortunate enough to be situated near hills and mountains through which streams flow, and in that case the water problem is simple. In such a case all that is necessary is to run pipes, usually underground, from the elevated lakes or streams to theindividual houses, or to common reservoirs from which it is distributed to the various buildings.
FIG. 148.—The elevated mountain lake serves as a source of water.FIG. 148.—The elevated mountain lake serves as a source of water.
Figure 148 illustrates in a simple way the manner in which a mountain lake may serve to supply the inhabitants of a valley. The city of Denver, for example, is surrounded by mountains abounding in streams of pure, clear water; pipes convey the water from these heights to the city, and thus a cheap and adequate flow is obtained. Such a system is known as the gravity system. The nearer and steeper the elevation, the greater the force with which the water flows through the valley pipes, and hence the stronger the discharge from the faucets.
Relatively few cities and towns are so favorably situated as regards water; more often the mountains are too distant, or the elevation is too slight, to be of practical value. Cities situated in plains and remote from mountains are obliged to utilize the water of such streams as flow through the land, forcing it to the necessary height by means of pumps. Streams which flow through populated regions are apt to be contaminated, and hence water from them requires publicfiltration. Cities using such a water supply thus have the double expense of pumping and filtration.
195. The Pressure of Water.No practical business man would erect a turbine or paddle wheel without calculating in advance the value of his water power. The paddle wheel might be so heavy that the stream could not turn it, or so frail in comparison with the water force that the stream would destroy it. In just as careful a manner, the size and the strength of municipal reservoirs and pumps must be calculated. The greater the quantity of water to be held in the reservoir, the heavier are the walls required; the greater the elevation of the houses, the stronger must be the pumps and the engines which run them.
In order to understand how these calculations are made, we must study the physical characteristics of water just as we studied the physical characteristics of air.
When we measure water, we find that 1 cubic foot of it weighs about 62.5 pounds; this is equivalent to saying that water 1 foot deep presses on the bottom of the containing vessel with a force of 62.5 pounds to the square foot. If the water is 2 feet deep, the load supported by the vessel is doubled, and the pressure on each square foot of the bottom of the vessel will be 125 pounds, and if the water is 10 feet deep, the load borne by each square foot will be 625 pounds. The deeper the water, the greater will be the weight sustained by the confining vessel and the greater the pressure exerted by the water.
FIG. 149.—Water 1 foot deep exerts a pressure of 62.5 pounds a square foot. [209FIG. 149.—Water 1 foot deep exerts a pressure of 62.5 pounds a square foot. [209
Since the pressure borne by 1 square foot of surface is 62.5 pounds, the pressure supported by 1 square inch of surface is 1/144 of 62.5 pounds, or .43 pound, nearly 1/2 pound. Suppose a vessel held water to the depth of 10 feet, then upon every square inch of the bottom of that vessel there would be a pressure of 4.34 pounds. If a one-inch tap were inserted in the bottom of the vessel so that the water flowed out, it would gush forth with a force of 4.34 pounds. If the water were 20 feet deep, the force of the outflowing water would be twice as strong, because the pressure would be doubled. But the flow would not remain constant, because as the water leaves the outlet, less and less of it remains in the vessel, and hence the pressure gradually sinks and the flow drops correspondingly.
FIG. 150.—The pressure at an outlet decreases as the level of the water supply sinks.FIG. 150.—The pressure at an outlet decreases as the level of the water supply sinks.
In seasons of prolonged drought, the streams which feed a city reservoir are apt to contain less than the usual amount of water, hence the level of the water supply sinks, the pressure at the outlet falls, and the force of the outflowing water is lessened (Fig. 150).
196. Why the Water Supply is not uniform in All Parts of the City.In the preceding Section, we saw that the flowfrom a faucet depends upon the height of the reserve water above the tap. Houses on a level with the main supply pipes (Figs. 148 and 151) have a strong flow because the water is under the pressure of a columnA; houses situated on elevationBhave less flow, because the water is under the pressure of a shorter columnB; and houses at a considerable elevationChave a less rapid flow corresponding to the diminished depth(C).
Not only does the flow vary with the elevation of the house, but it varies with the location of the faucet within the house. Unless the reservoir is very high, or the pumps very powerful, the flow on the upper floors is noticeably less than that in the cellar, and in the upper stories of some high building the flow is scarcely more than a feeble trickle.
FIG. 151.—Water pressure varies in different parts of a water system.FIG. 151.—Water pressure varies in different parts of a water system.
When the respective flows atA,B, andC(Fig. 151) are measured, they are found to be far lower than the pressures which columns of water of the heightsA,B, andChave been shown by actual demonstration to exert. This is because water, in flowing from place to place, expends force in overcoming the friction of the pipes and the resistance of the air. The greater the distance traversed by the water in its journey from reservoir to faucet, the greater the waste force and the less the final flow.
In practice, large mains lead from the reservoir to the city, smaller mains convey the water to the various sections of the city, and service pipes lead to the individual house taps.During this long journey, considerable force is expended against friction, and hence the flow at a distance from the reservoir falls to but a fraction of its original strength. For this reason, buildings situated near the main supply have a much stronger flow (Fig. 152) than those on the same level but remote from the supply. Artificial reservoirs are usually constructed on the near outskirts of a town in order that the frictional force lost in transmission may be reduced to a minimum.
FIG. 152.—The more distant the fountain, the weaker the flow.FIG. 152.—The more distant the fountain, the weaker the flow.
In the case of a natural reservoir, such as an elevated lake or stream, the distance cannot be planned or controlled. New York, for example, will secure an abundance of pure water from the Catskill Mountains, but it will lose force in transmission. Los Angeles is undertaking one of the greatest municipal projects of the day. Huge aqueducts are being built which will convey pure mountain water a distance of 250 miles, and in quantities sufficient to supply two million people. According to calculations, the force of the water will be so great that pumps will not be needed.
FIG. 153.—A standpipe.FIG. 153.—A standpipe.
197. Why Water does not always flow from a Faucet.Most of us have at times been annoyed by the inability to secure water on an upper story, because of the drawing offof a supply on a lower floor. During the working hours of the day, immense quantities of water are drawn off from innumerable faucets, and hence the quantity in the pipes decreases considerably unless the supply station is able to drive water through the vast network of pipes as fast as it is drawn off. Buildings at a distance from the reservoir suffer under such circumstances, because while the diminished pressure is ordinarily powerful enough to supply the lower floors, it is frequently too weak to force a continuous stream to high levels. At night, however, and out of working hours, few faucets are open, less water is drawn off at any one time, and the intricate pipes are constantly full of water under high pressure. At such times, a good flow is obtainable even on the uppermost floors.
In order to overcome the disadvantage of a decrease in flow during the day, standpipes (Fig. 153) are sometimes placed in various sections. These are practically small steel reservoirs full of water and connecting with the city pipes. During "rush" hours, water passes from these into the communicating pipes and increases the available supply, while during the night, when the faucets are turned off, water accumulates in the standpipe against the next emergency (Figs. 151 and 154). The service rendered by the standpipe is similar to that of the air cushion discussed in Section 184.
198. The Cost of Water.In the gravity system, where an elevated lake or stream serves as a natural reservoir, the cost of the city's waterworks is practically limited to the laying of pipes. But when thesource of the supply is more or less on a level with the surrounding land, the cost is great, because the supply for the entire city must either be pumped into an artificial reservoir, from which it can be distributed, or else must be driven directly through the mains (Fig. 154).
FIG. 154.—Water must be got to the houses by means of pumps.FIG. 154.—Water must be got to the houses by means of pumps.
A gallon of water weighs approximately 8.3 pounds, and hence the work done by a pump in raising a gallon of water to the top of an average house, an elevation of 50 feet, is 8.3 × 50, or 415 foot pounds. A small manufacturing town uses at least 1,000,000 gallons daily, and the work done by a pump in raising that amount to an elevation of 50 feet would be 8.3 × 1,000,000 × 50, or 415,000,000 foot pounds.
The total work done during the day by the pump, or the engine driving the pump, is 415,000,000 foot pounds, and hence the work done during one hour would be 1/24 of 415,000,000, or 17,291,666 foot pounds; the work done in one minute would be 1/60 of 17,291,666, or 288,194 foot pounds, and the work done each second would be 1/60 of 288,194, or 4803 foot pounds.
A 1-H.P. engine does 550 foot pounds of work each second, and therefore if the pump is to be operated by an engine, the strength of the latter would have to be 8.7 H.P. An 8.7-H.P. pumping engine working at full speed every second of the day and night would be able to supplythe town with the necessary amount of water. When, however, we consider the actual height to which the water is raised above the pumping station, and the extra pumping which must be done in order to balance the frictional loss, it is easy to understand that in actual practice a much more powerful engine would be needed. The larger the piston and the faster it works, the greater is the quantity of water raised at each stroke, and the stronger must be the engine which operates the pump.
In many large cities there is no one single pumping station from which supplies run to all parts of the city, but several pumping stations are scattered throughout the city, and each of them supplies a restricted territory.
199. The Bursting of Dams and Reservoirs.The construction of a safe reservoir is one of the most important problems of engineers. In October, 1911, a town in Pennsylvania was virtually wiped out of existence because of the bursting of a dam whose structure was of insufficient strength to resist the strain of the vast quantity of water held by it. A similar breakage was the cause of the fatal Johnstown flood in 1889, which destroyed no less than seven towns, and in which approximately 2000 persons are said to have lost their lives.
Water presses not only on the bottom of a vessel, but upon the sides as well; a bucket leaks whether the hole is in its side or its bottom, showing that water presses not only downward but outward. Usually a leak in a dam or reservoir occurs near the bottom. Weak spots at the top are rare and easily repaired, but a leak near the bottom is usually fatal, and in the case of a large reservoir the outflowing water carries death and destruction to everything in its path.
If the leak is near the surface, as ata(Fig. 155), the water issues as a feeble stream, because the pressure against the sides at that level is due solely to the relatively small heightof water abovea(Section 195). If the leak is lower, as atb, the issuing stream is stronger and swifter, because at that level the outward pressure is much greater than ata, the increase being due to the fact that the height of the water abovebis greater than that abovea. If the leak is quite low, as atc, the issuing stream has a still greater speed and strength, and gushes forth with a force determined by the height of the water abovec.
FIG. 155.—The flow from an opening depends upon the height of water above the opening.FIG. 155.—The flow from an opening depends upon the height of water above the opening.
The dam at Johnstown was nearly 1/2 mile wide, and 40 feet high, and so great was the force and speed of the escaping stream that within an hour after the break had occurred, the water had traveled a distance of 18 miles, and had destroyed property to the value of millions of dollars.
If a reservoir has a depth of 100 feet, the pressure exerted upon each square foot of its floor is 62.5 × 100, or 6250 pounds; the weight therefore to be sustained by every square foot of the reservoir floor is somewhat more than 3 tons, and hence strong foundations are essential. The outward lateral pressure at a depth of 25 feet would be only one fourth as great as that on the bottom—hence the strain on the sides at that depth would be relatively slight, and a less powerful construction would suffice. But at a depth of 50 feet the pressure on the sides would be one half that of the floor pressure, or 1-1/2 tons. At a depth of 75 feet, the pressure on the sides would be three quarters that on the bottom, or 2-1/4 tons. As the bottom of the reservoir is approached, the pressure against the sides increases, andmore powerful construction becomes necessary.
Small elevated tanks, like those of the windmill, frequently have heavy iron bands around their lower portion as a protection against the extra strain.
Before erecting a dam or reservoir, the maximum pressure to be exerted upon every square inch of surface should be accurately calculated, and the structure should then be built in such a way that the varying pressure of the water can be sustained. It is not sufficient that the bottom be strong; the sides likewise must support their strain, and hence must be increased in strength with depth. This strengthening of the walls is seen clearly in the reservoir shown in Figure 152. The bursting of dams and reservoirs has occasioned the loss of so many lives, and the destruction of so much property, that some states are considering the advisability of federal inspection of all such structures.
FIG. 156.—The lock gates must be strong in order to withstand the great pressure of the water against them.FIG. 156.—The lock gates must be strong in order to withstand the great pressure of the water against them.
200. The Relation of Forests to the Water Supply.When heavy rains fall on a bare slope, or when snow melts on a barren hillside, a small amount of the water sinks into the ground, but by far the greater part of it runs off quickly and swells brooks and streams, thus causing floods and freshets.
When, however, rain falls on a wooded slope, the action is reversed; a small portion runs off, while the greater portion sinks into the soft earth. This is due partly to the fact that the roots of trees by their constant growth keep the soil loose and open, and form channels, as it were, along which the water can easily run. It is due also to the presence on the ground of decaying leaves and twigs, or humus. The decayingvegetable matter which covers the forest floor acts more or less as a sponge, and quickly absorbs falling rain and melting snow. The water which thus passes into the humus and the soil beneath does not remain there, but slowly seeps downward, and finally after weeks and months emerges at a lower level as a stream. Brooks and springs formed in this way are constant feeders of rivers and lakes.
In regions where the land has been deforested, the rivers run low in season of prolonged drought, because the water which should have slowly seeped through the soil, and then supplied the rivers for weeks and months, ran off from the barren slopes in a few days.
Forests not only lessen the danger of floods, but they conserve our waterways, preventing a dangerous high-water mark in the season of heavy rains and melting snows, and then preventing a shrinkage in dry seasons when the only feeders of the rivers are the underground sources. In the summer of 1911, prolonged drought in North Carolina lowered the rivers to such an extent that towns dependent upon them suffered greatly. The city of Charlotte was reduced for a time to a practically empty reservoir; washing and bathing were eliminated, machinery dependent upon water-power and steam stood idle, and every glass of water drunk was carefully reckoned. Thousands of gallons of water were brought in tanks from neighboring cities, and were emptied into the empty reservoir from whence it trickled slowly through the city mains. The lack of water caused not only personal inconvenience and business paralysis, but it occasioned real danger of disease through unflushed sewers and insufficiently drained pipes.
The conservation of the forest means the conservation of our waterways, whether these be used for transportation or as sources of drinking water.
201. Chemistry.Man's mechanical inventions have been equaled by his chemical researches and discoveries, and by the application he has made of his new knowledge.
The plain cotton frock of our grandmothers had its death knell sounded a few years ago, when John Mercer showed that cotton fabrics soaked in caustic soda assumed under certain conditions a silky sheen, and when dyed took on beautiful and varied hues. The demonstration of this simple fact laid the foundation for the manufacture of a vast variety of attractive dress materials known as mercerized cotton.
Possibly no industry has been more affected by chemical discovery than that of dyeing. Those of us who have seen the old masterpieces in painting, or reproductions of them, know the softness, the mellowness, the richness of tints employed by the old masters. But if we look for the brilliancy and variety of color seen in our own day, the search will be fruitless, because these were unknown until a half century ago. Up to that time, dyes were few in number and were extracted solely from plants, principally from the indigo and madder plants. But about the year 1856 it was discovered that dyes in much greater variety and in purer form could be obtained from coal tar. This chemical production of dyes has now largely supplanted the original method, and the industry has grown so rapidly that a single firm produced inone year from coal tar a quantity of indigo dye which under the natural process of plant extraction would have required a quarter million acres of indigo plant.
The abundance and cheapness of newspapers, coarse wrapping papers, etc., is due to the fact that man has learned to substitute wood for rags in the manufacture of paper. Investigation brought out the fact that wood contained the substance which made rags valuable for paper making. Since the supply of rags was far less than the demand, the problem of the extraction from wood of the paper-forming substance was a vital one. From repeated trials, it was found that caustic soda when heated with wood chips destroyed everything in the wood except the desired substance, cellulose; this could be removed, bleached, dried, and pressed into paper. The substitution of wood for rags has made possible the daily issue of newspapers, for the making of which sufficient material would not otherwise have been available. When we reflect that a daily paper of wide circulation consumes ten acres of wood lot per day, we see that all the rags in the world would be inadequate to meet this demand alone, to say nothing of periodicals, books, tissue paper, etc.
Chemistry plays a part in every phase of life; in the arts, the industries, the household, and in the body itself, where digestion, excretion, etc., result from the action of the bodily fluids upon food. The chemical substances of most interest to us are those which affect us personally rather than industrially; for example, soap, which cleanses our bodies, our clothing, our household possessions; washing soda, which lightens laundry work; lye, which clears out the drain pipe clogged with grease; benzine, which removes stains from clothing; turpentine, which rids us of paint spots left by carelessworkmen; and hydrogen peroxide, which disinfects wounds and sores.
In order to understand the action of several of these substances we must study the properties of two groups of chemicals—known respectively as acids and bases; the first of these may be represented by vinegar, sulphuric acid, and oxalic acid; and the second, by ammonia, lye, and limewater.
202. Acids.All of us know that vinegar and lemon juice have a sour taste, and it is easy to show that most acids are characterized by a sour taste. If a clean glass rod is dipped into very dilute acid, such as acetic, sulphuric, or nitric acid, and then lightly touched to the tongue, it will taste sour. But the best test of an acid is by sight rather than by taste, because it has been found that an acid is able to discolor a plant substance called litmus. If paper is soaked in a litmus solution until it acquires the characteristic blue hue of the plant substance, and is then dried thoroughly, it can be used to detect acids, because if it comes in contact with even the minutest trace of acid, it loses its blue color and assumes a red tint. Hence, in order to detect the presence of acid in a substance, one has merely to put some of the substance on blue litmus paper, and note whether or not the latter changes color. This test shows that many of our common foods contain some acid; for example, fruit, buttermilk, sour bread, and vinegar.
The damage which can be done by strong acids is well known; if a jar of sulphuric acid is overturned, and some of it falls on the skin, it eats its way into the flesh and leaves an ugly sore; if it falls on carpet or coat, it eats its way into the material and leaves an unsightly hole. The evil results of an accident with acid can be lessened if we know just what to do and do it quickly, but for this we must have a knowledge of bases, the second group of chemicals.
203. Bases.Substances belonging to this group usually have a bitter taste and a slimy, soapy feeling. For our presentpurposes, the most important characteristic of a base is that it will neutralize an acid and in some measure hinder the damage effected by the former. If, as soon as an acid has been spilled on cloth, a base, such as ammonia, is applied to the affected region, but little harm will be done. In your laboratory experiments you may be unfortunate enough to spill acid on your body or clothing; if so, quickly apply ammonia. If you delay, the acid does its work, and there is no remedy. If soda (a base) touches black material, it discolors it and leaves an ugly brown spot; but the application of a little acid, such as vinegar or lemon juice, will often restore the original color and counteract the bad effects of the base. Limewater prescribed by physicians in cases of illness is a well-known base. This liquid neutralizes the too abundant acids present in a weak system and so quiets and tones the stomach.
The interaction of acids and bases may be observed in another way. If blue litmus paper is put into an acid solution, its color changes to red; if now the red litmus paper is dipped into a base solution, caustic soda, for example, its original color is partially restored. What the acid does, the base undoes, either wholly or in part. Bases always turn red litmus paper blue.
Bases, like acids, are good or bad according to their use; if they come in contact with cloth, they eat or discolor it, unless neutralized by an acid. But this property of bases, harmful in one way, is put to advantage in the home, where grease is removed from drainpipe and sink by the application of lye, a strong base. If the lye is too concentrated, it will not only eat the grease, but will corrode the metal piping; it is easy, however, to dilute base solutions to such a degree that they will not affect piping, but will remove grease. Dilute ammonia is used in almost every home and is an indispensabledomestic servant; diluted sufficiently, it is invaluable in the washing of delicate fabrics and in the removing of stains, and in a more concentrated form it is helpful as a smelling salt in cases of fainting.
Some concentrated bases are so powerful in their action on grease, cloth, and metal that they have received the designationcaustic, and are ordinarily known as caustic soda, caustic potash (lye), and caustic lime. These more active bases are generally called alkalies in distinction from the less active ones.
204. Neutral Substances.To any acid solution add gradually a small quantity of a base, and test the mixture from time to time with blue litmus paper; at first the paper will turn red quickly, but as more and more of the base is added to the solution, it has less and less effect on the blue litmus paper, and finally a point is reached when a fresh strip of blue paper will not be affected. Such a result indicates infallibly the absence of any acid qualities in the solution. If now red litmus paper is tested in the same solution, its color also will remain unchanged; such a result indicates infallibly the absence of any basic quality. The solution has the characteristic property of neither acid nor base and is said to be neutral.
If to the neutral solution an extra portion of base is added, so that there is an excess of base over acid, the neutralization is overbalanced and the red paper turns blue. If to the neutral solution an extra portion of acid is added, so that there is an excess of acid over base, the neutralization is overbalanced in the opposite direction, and the solution acquires acid characteristics.
Most acids and bases will eat and corrode and discolor, while neutral substances will not; it is for this reason that soap, a slightly alkaline substance, is the safest cleansing agent for laundry, bath, and general work. Good soaps, being carefully made, are so nearly neutral that they will not fade thecolor out of clothing; the cheap soaps are less carefully prepared and are apt to have a strong excess of the base ingredient; such soaps are not safe for delicate work.
205. Soap.If we gather together scrapings of lard, butter, bits of tallow from burned-out candles, scraps of waste fat, or any other sort of grease, and pour a strong solution of lye over the mass, a soft soapy substance is formed. In colonial times, every family made its own supply of soap, utilizing, for that purpose, household scraps often regarded by the housekeeper of to-day as worthless. Grease and fat were boiled with water and hardwood ashes, which are rich in lye, and from the mixture came the soft soap used by our ancestors. In practice, the wood ashes were boiled in water, which was then strained off, and the resulting filtrate, or lye, was mixed with the fats for soap making.
Most fats contain a substance of an acid nature, and are decomposed by the action of bases such as caustic soda and caustic potash. The acid component of the grease partially neutralizes the base, and a new substance is formed, namely, soap.
With the advance of civilization the labor of soap making passed from the home to the factory, very much as bread making has done in our own day. Different varieties of soaps appeared, of which the hard soap was the most popular, owing to the ease with which it could be transported. Within the last few years liquid soaps have come into favor, especially in schools, railroad stations, and other public places, where a cake of soap would be handled by many persons. By means of asimple device (Fig. 157), the soap escapes from a receptacle when needed. The mass of the soap does not come in contact with the skin, and hence the spread of contagious skin diseases is lessened.