Fig. 86. Blow-off Valve.
The upper end of the pipe has a conically-ground seat, to receive a conical valve E, the stem of which is hinged, as at F, to the level. The weight may be adjusted to the pressure desired before blowing out and the only feature in this type of valve is the character of the valve seat,which is liable, through rust, and other causes, to leak.
Pop, or Safety Valve.—As it has been found more desirable and practical to use a form of valve which is not liable to deterioration, and also to so arrange it that it may be manually opened, theSafety Popvalve was devised.
Fig. 87. Safety Pop Valve.
This is shown inFig. 87, in which the valve seat base A, which is attached to the top of the boiler, has a cup-shaped outlet B, that is screwed to it, and this carries a lever C, by means of which the valve may be manually opened.
A vertical shell D is attached to the cup-shaped portion, and this has a removable cap E. The valve F is seated within a socket in the base, and has a disk head, to receive the lower end of a coiled spring G.
The spring is supported in position by a stem H which extends down from the head, and an adjusting nut I serves to regulate the pressure desired before the steam in the boiler can act.
CHAPTER XI
CAMS AND ECCENTRICS
More or less confusion arises from the termscamsandeccentrics. A cam is a wheel which may be either regular in shape, like aheart-wheel, or irregular, like awiper-wheel.
The object in all forms of cams is to change motion from a regular into an irregular, or reversely, and the motion may be accelerated or retarded at certain points, or inverted into an intermittent or reciprocating movement, dependent on the shape of the cam.
A cam may be in the shape of a slotted or grooved plate, like the needle bar of a sewing machine, where a crank pin works in the slot, and this transmits an irregular vertical movement to the needle.
A cam may have its edge provided with teeth, which engage with the teeth of the engaging wheel, and thus impart, not only an irregular motion but also a turning movement, such forms being largely used to give a quickly rising or falling motion.
What are calledwiper-wheelsare designed to give an abrupt motion and such types are used in trip hammers, and to operate stamp mills. In harvesters, printing presses, sewing machines, and mechanism of that type, the cam is used in a variety of forms, some of them very ingenious and complicated.
Fig. 88. Heart-shaped. Fig. 89. Elliptic. Fig. 90. Double Elliptic.
Cams are also used for cutting machines, or in tracing apparatus where it would be impossible to use ordinary mechanism. All such forms are special, requiring care and study to make their movements co-relate with the other parts of the mechanism that they are connected up with.
Simple Cams.—Fig. 88shows a form of the most simple character, used, with some modifications, to a larger extent than any other. It is called theheart-shapedcam, and is the regular type.
Fig. 89is an elliptical cam, which is also regular. What is meant byregularis a form that is the same in each half portion of its rotation.
Fig. 90is a double elliptic, which gives a regular movement double the number of times of that produced by the preceding figure, and the differences between the measurements across the major and minor axes may vary, relatively, to any extent.
Fig. 91. Single Wiper. Fig. 92. Double Wiper. Fig. 93. Tilting Cam.
Wiper Wheels.—Wiper wheels are cams which give a quick motion to mechanism, the most common form being the single wiper, as shown inFig. 91.
The double wiper cam,Fig. 92, has, in some mechanism, a pronounced difference between the lengths of the two fingers which form the wipers.
The form of cam shown inFig. 93is one much used in iron works for setting in motion the tilt hammer. Only three fingers are shown, and by enlarging the cam at least a dozen of these projecting points may be employed.
Cam Sectors.—Fig. 94shows a type of camwhich is designed for rock shafts. The object of this form of cam is to impart a gradually increasing motion to a shaft. Assuming that A is the driving shaft, and B the driven shaft, the cam C, with its short end D, in contact with the long end E of the sector F, causes the shaft B to travel at a more accelerated speed as the other edges G, H, approach each other.
Fig. 94. Cam Sector. Fig. 95. Grooved Cam. Fig. 96. Reciprocating Motion.
Cylinder Cam.—Fig. 95shows one form of cylinder A with a groove B in it, which servesas a means for moving a bar C back and forth. The bar has a projecting pin D, which travels in the groove.
This form of movement may be modified in many ways, as for instance inFig. 96, where the drum E has a sinuous groove F to reciprocate a bar G to and fro, the groove being either regular, so as to give a continuous back and forth movement of the bar; or adapted to give an irregular motion to the bar.
Fig. 97. Pivoted Follower for Cam.
Double Cam Motion.—Cams may also be so arranged that a single one will produce motions in different directions successively, as illustrated inFig. 97. The horizontal bar A, hinged at B to the upper end of a link C, has its free end resting on the cam D.
The arm A has also a right-angled arm E extending downwardly, and is kept in contact withthe cam by means of a spring F. Connecting rods G, H, may be hinged to the arm E and bar A, respectively, so as to give motion to them in opposite directions as the cam revolves.
Eccentrics.—An eccentric is one in which the cam or wheel itself is circular in form, but is mounted on a shaft out of its true center. An eccentric may be a cam, but a cam is not always eccentric in its shape. The term is one in direct contrast with the wordeccentric.
Fig. 98. Eccentric. Fig. 99. Eccentric Cam.
Fig. 98shows the wheel, or the cam, which is regular in outline, that is circular in form, but is mounted on the shaft out of its true center. In this case it is properly called an eccentric cam but in enginery parlance it is known as the eccentric, as represented inFig. 99.
Triangularly-Formed Eccentric.—Fig. 100illustrates a form of cam which has been used on engines. The yoke A being integral with the bar B, gives a reciprocating motion to the latter, andthe triangular form of the cam C, which is mounted on the shaft D, makes a stop motion at each half-revolution, then produces a quick motion, and a slight stop only, at the half turn, and the return is then as sudden as the motion in the other direction.
Fig. 100. Triangularly-formed Eccentric.
CHAPTER XII
GEARS AND GEARING
For the purpose of showing how motion may be converted from a straight line or from a circular movement into any other form or direction, and how such change may be varied in speed, or made regular or irregular, the following examples are given, which may be an aid in determining other mechanical devices which can be specially arranged to do particular work.
While cams and eccentrics may be relied on to a certain extent, there are numerous places where the motion must be made positive and continued. This can be done only by using gearing in some form, or such devices as require teeth to transmit the motion from one element to the other.
The following illustrations do not by any means show all the forms which have been constructed and used in different machines, but they have been selected as types merely, in order to give the suggestions for other forms.
Racks and Pinions.—The rack and pinion is the most universal piece of mechanism for changingmotion.Fig. 101illustrates it in its most simple form. When constructed in the manner shown in this figure it is necessary that the shaft which carries the pinion shall have a rocking motion, or the rack itself must reciprocate in order to impart a rocking motion to the shaft.
Fig. 101. Rack and Pinion. Fig. 102. Rack Motion.
This is the case also in the device shown in Fig. 102, where two rack bars are employed. A study of the cams and eccentrics will show that the transference of motion is limited, the distances being generally very small; so that the rack and pinions add considerably to the scope of the movement.
The Mangle Rack.—The device called themangle rackis resorted to where a back and forth, ora reciprocating movement is to be imparted to an element by a continuous rotary motion.
Fig. 103. Plain Mangle Rack. Fig. 104. Mangle Rack Motion. Fig. 105. Alternate Circular Motion.
The plain mangle racks are shown in Figs. 103 and 104, the former of which has teeth on the inside of the opposite parallel limbs, and the latter,Fig. 104, having teeth not only on the parallel sides, but also around the circular parts at the ends.
This form of rack may be modified so that an alternate circular motion will be produced duringthe movement of the rack in either direction.Fig. 105is such an instance. A pinion within such a rack will turn first in one direction, and then in the next in the other direction, and so on.
If the rack is drawn back and forth the motion imparted to the pinion will be such as to give a continuous rocking motion to the pinion.
Controlling the Pinion.—Many devices have been resorted to for the purpose of keeping the pinion in engagement with the teeth of the mangle rack. One such method is shown inFig. 106.
Fig. 106. Controlling Pinion for Mangle Rack.
The rack A has at one side a plate B, within which is a groove C, to receive the end of the shaft D, which carries the pinion E. As the mangle rack moves to such a position that it reaches the end of the teeth F on one limb, the groove C diverts the pinion over to the other set of teeth G.
All these mangle forms are substitutes for cranks, with the advantage that the mangle gives a uniform motion to a bar, whereas the to and fromotion of the crank is not the same at all points of its travel.
Examine the diagram,Fig. 107, and note the movement of the pin A which moves along the path B. The crank C in its turning movement around the circle D, moves the pin A into the different positions 1, 2, 3, etc., which correspond with the positions on the circle D.
Fig. 107. Illustrating Crank-pin Movement.
The Dead Centers.—There is also another advantage which the rack possesses. Where reciprocating motion is converted into circular motion, as in the case of the ordinary steam engine, there are two points in the travel of a crank where the thrust of the piston is not effective, and that is at what is called thedead centers.
In the diagram,Fig. 108, the ineffectiveness of the thrust is shown at those points.
Let A represent the piston pushing in the direction of the arrow B against the crank C. When in this position the thrust is the most effective, and through the arc running from D to E, andfrom H to G, the cylinder does fully four-fifths of the work of the engine.
Fig. 108. The Dead Center.
While the crank is turning from G to D, or from I to J, and from K to L, no work is done which is of any value as power.
If, therefore, a mangle bar should be used instead of the crank it would add greatly to the effectiveness of the steam used in the cylinder.
Fig. 109. Crank Motion Substitute.
Crank Motion Substitute.—InFig. 109the pinion A is mounted so that its shaft is in a verticalslot B in a frame C. The mangle rack D, in this case, has teeth on its outer edge, and is made in an elongated form. The pinion shaft moves up and down the slot and thus guides the pinion around the ends of the rack.
Fig. 110. Mangle Wheel.
Mangle Wheels.—The form which is the most universal in its application is what is called themangle wheel. InFig. 110is shown a type wherein the motion in both directions is uniform.
Mangle wheels take their names from the ironing machines calledmangles. In apparatus of this kind the movement back and forth is a slow one, and the particular form of wheels was made in order to facilitate the operation of such machines. In some mangles the work between the rollers is uniform back and forth. In others thework is done in one direction only, requiring a quick return.
In still other machines arrangements are made to provide for short strokes, and for different speeds in the opposite directions, under certain conditions, so that this requirement has called forth the production of many forms of wheels, some of them very ingenious.
Fig. 111. Quick Return Motion.
The figure referred to has a wheel A, on one side of which is a peculiarly-formed continuous slot B, somewhat heart-shaped in general outline, one portion of the slot being concentric with the shaft C.
Within the convolutions of the groove is a set of teeth D, concentric with the shaft C. The pinion E, which meshes with the teeth D, has the end of its shaft F resting in the groove B, and it is also guided within a vertical slotted bar G.
The pinion E, therefore, travels over the same teeth in both directions, and gives a regular to and fro motion.
Quick Return Motion.—In contradistinction to this is a wheel A,Fig. 111, which has a pair of curved parallel slots, with teeth surrounding the slots. When the wheel turns nearly the entire revolution, with the pinion in contact with the outer set of teeth, the movement transmitted to the mangle wheel is a slow one.
Fig. 112. Accelerated Circular Motion.
When the pinion arrives at the turn in the groove and is carried around so the inner teeth are in engagement with the pinion, a quick return is imparted to the wheel.
Accelerated Motion.—Aside from the rack and mangle type of movement, are those which arestrictly gears, one of them being a volute form, shown inFig. 112. This gear is a face plate A, which has teeth B on one face, which are spirally-formed around the plate. These mesh with a pinion C, carried on a horizontal shaft D. This shaft is feathered, as shown at E, so that it will carry the gear along from end to end.
Fig. 113. Quick Return Gearing.
The gear has cheek-pieces F to guide it along the track of teeth. As the teeth approach the center of the wheel A, the latter impart a motion to the gear which is more than twice the speed that it receives at the starting point, the speed being a gradually increasing one.
Quick Return Gearing.—Another much more simple type of gearing, which gives a slow forwardspeed and a quick return action, is illustrated inFig. 113. A is a gear with internal teeth through one half of its circumference, and its hub B has teeth on its half which is opposite the teeth of the rim.
A pinion C on a shaft D is so journaled that during one half of the rotation of the wheel A, it engages with the rim teeth, and during the other half with the hub teeth. As the hub B and gear C are the same diameter, one half turn of the pinion C will give a half turn to the wheel A.
Fig. 114. Scroll Gearing.
As the rim teeth of the wheel A are three times the diameter of the pinion C, the latter must turn once and a half around to make a half revolution of the wheel A.
Scroll Gearing.—This is a type of gearingwhereby at the close of each revolution the speed may be greater or less than at the beginning. It comprises two similarly-constructed gears A, B, each with its perimeter scroll-shaped, as shown.
The diagram shows their positions at the beginning of the rotation, the short radial limb of one gear being in line with the long limb of the other gear, hence, when the gears rotate, their speeds relative to each other change, being constantly accelerated in one or decreased in the other.
CHAPTER XIII
SPECIAL TYPES OF ENGINES
In describing various special types of motors, attention is first directed to that class which depend on the development of heat in various gases, and this also necessitates some explanation of ice-making machinery, and the principles underlying refrigeration.
It is not an anomaly to say that to make ice requires heat. Ice and boiling water represent merely the opposites of a certain scale in the condition of matter, just as we speak of light and darkness, up and down, and like expressions.
We are apt to think zero weather is very cold. Freezing weather is a temperature of 32 degrees. At the poles 70 degrees below have been recorded. In interstellar space,—that is, the region between the planets, it is assumed that the temperature is about 513 degrees Fahrenheit, below zero, called absolute zero.
The highest heat which we are able to produce artificially, is about 10,000 degrees by means of the electric arc. We thus have a range of over10,500 degrees of heat, but it is well known that heat extends over a much higher range.
Assuming, however, that the figures given represent the limit, it will be seen that the difference between ice and boiling water, namely, 180 degrees, is a very small range compared with the temperatures referred to.
In order to effect this change power is necessary, and power requires a motor of some kind. Hence it is, that to make a lower temperature, a higher degree of heat is necessary, and in the transit between a high and a low temperature, there is considerable loss in this respect, as in every other phase of power mechanism, as has been pointed out in a previous chapter.
In order that we may clearly understand the phenomena of heat and cold, let us take a receiver which holds a cubic foot of gas or liquid, and exhaust all the air from it so the vacuum will be equivalent to the atmospheric pressure, namely, 14.7 pounds per square inch.
Alongside is a small vessel containing one cubic inch of water, which is heated so that it is converted into steam, and is permitted to exhaust into the receiver. When all the water is converted into steam and fills the receiver we shall have the same pressure inside the receiver as on the outside.
It will be assumed, of course, that there has been no loss by condensation, and that the cubic inch of water has been expanded 1700 times by its conversion into steam.
In a short time the steam will condense into water, and we now have, again, a partial vacuum in the receiver, due, of course, to the change in bulk from steam to water. Each time the liquid is heated it produces a pressure, and the pressure indicates the presence of heat; and whenever it cools a loss of pressure is indicated, and that represents cold, or the opposite of heat.
Now, putting these two things together, we get the starting point necessary in the development of power. Let us carry the experiment a step further. Liquids are not compressible. Gases are. The first step then is to take a gas and compress it, which gives it an increase of heat temperature, dependent on the pressure.
If the same receiver is used, and say, two atmospheres are compressed within it, so that it has two temperatures, and the exterior air cools it down to the same temperature of the surrounding atmosphere, we are ready to use the air within to continue the experiment.
Let us convey this compressed gas through pipes, and thus permit it to expand; in doing so the area within the pipes, which is very muchgreater than that of the receiver, grows colder, due to the rarefied gases within. Now bearing in mind the previous statement, that loss of pressure indicates a lowering of temperature, we can see that first expanding the gas, or air, by heat, and then allowing it to cool, or to produce the heat by compressing it, and afterwards permitting it to exhaust into a space which rarefies it, will make a lower temperature.
It is this principle which is used in all refrigerating machines, whereby the cool pipes extract the heat from the surrounding atmosphere, or when making ice, from the water itself, and this temperature may be lowered to any extent desired, dependent on the degree of rarefaction produced.
Let us now see how this applies to the generation of power in which we are more particularly interested.
All liquids do not evaporate at the same temperature as water. Some require a great deal more than 212 degrees; others, like, for instance, dioxide-of-carbon, will evaporate at 110 degrees, or about one half the heat necessary to turn water into steam.
On the other hand, all gases act alike so far as their heat absorption is concerned, so that by using a material with a low evaporative unit, lessfuel will be required to get the same expansion, which means the same power.
To illustrate this, let us assume that we have equal quantities of water, and of dioxide-of-carbon, and that is to be converted into a gas. It will take just double the amount of fuel to convert the water into a gaseous state. As both are now in the same condition, the law of heat absorption is the same from this time on.
The dioxide-of-carbon engine is one, therefore, which uses the vapor of this material, which, after passing through the engine, is condensed and pumped back to the boiler to be used over and over.
In like manner, also, ether, which has a low point of vaporization, is used in some engines, the principle being the same as the foregoing type.
Rotary Engines.—Many attempts have been made to produce a rotary type of steam engine, and also to adapt it for use as an internal combustion motor.
The problem is a complicated one for the following reasons: First, it is difficult to provide for cut-off and expansion. A rotating type, to be efficient, must turn at a high rate of speed, and this makes the task a more trying one. Second, the apparent impossibility of properly packingthe pistons. The result is a waste of steam, or the gas used to furnish the power. Third, the difficulty in providing a suitable abutment so as to confine the steam or gas, and make it operative against the piston.
Fig. 115. Simple Rotary Engine.
InFig. 115is shown a type of rotary which is a fair sample of the characteristics of all motors of this form. It comprises an outer cylindrical shell, or casing, A, having a bore through the ends, which is above the true center of the shell, to receive a shaft B.
This shaft carries a revolving drum C of suchdimensions that it is in contact with the shell at its upper side only, as shown at D, leaving a channel E around the other portions of the drum.
The steam inlet is at F, which is one-eighth of the distance around the cylinder, and the exhaust is at G, the same distance from the point D, on the other side. The inlet and the outlet pipes are, therefore, at the contracted parts of the channel.
The drum has a pair of radially-movable blades H H´, which may move independently of each other, but usually they are connected together, thus dispensing with the use of any springs to keep their ends in contact with the shell.
When steam enters the inlet F the pressure against the blade H drives the drum to the right, and the drum and shell, by contacting at D, form an abutment. Each charge of steam drives the drum a little over a half revolution.
A great deal of ingenuity has been exercised to arrange this abutment so that the blades may pass and provide a steam space for a new supply of steam. In certain types a revolving abutment is formed, as shown, for instance, inFig. 116.
The shell A, in this case, has two oppositely-disposed inlet and outlet ports, B, C, respectively, and between each set of ports is a revolving gate, formed of four wings D, mounted on a shaft E,in a housing outside of the circular path F, between the drum G and shell A.
The drum G is mounted on a shaft H which is centrally within the shell, and it has two oppositely-projecting rigid blades I. When steam enters either of the supply ports B, the drum is rotated, and when the blades reach the revolving gates, the latter are turned by the blades, or, they may be actuated by mechanism connected up with the driving shaft.
Fig. 116. Double-feed Rotary Engine.
Caloric Engine.—This is an engine which is dependent on its action upon the elastic force ofair which is expanded by heat. The cylinder of such a motor has means for heating it, and thus expanding the air, and a compressor is usually employed which is operated by the engine itself, to force compressed air into the cylinder.
It is not an economical engine to work, but it is frequently used in mines, in which case the compressor is located at the surface, and the engine operated within the mine, thus serving a double purpose, that of supplying power, and also furnishing the interior with fresh air.
All engines of this character must run at a slow speed, for the reason that air does not absorb heat rapidly, and sufficient time must be given to heat up and expand the air, so as to make it effective.
Adhesion Engine.—A curious exhibition of the action of a gas against a solid, is shown in what is called anAdhesion Engine.Fig. 117shows its construction. A plurality of disks A are mounted on a shaft B, these disks being slightly separated from each other.
The steam discharge pipe C is flattened at its emission end, as shown at D, so the steam will contact with all the disks. The steam merely contacts with the sides of the disks, the movement of the steam being substantially on the plane of the disks themselves, and the action sets up a rapidrotation, and develops a wonderful amount of power.
Fig. 117. Adhesion Motor.
It will be understood that the disks are enclosed by a suitable casing, so that the steam is carried around and discharged at a point about three quarters of the distance in the circumference.
This motor is given to illustrate a phase of the subject in the application of a motor fluid, like steam, or heated gases, that shows great possibilities. It also points out a third direction in which an expansive fluid may be used.
Thus the two well-known methods, namely,pressure, andimpactforces, may be supplemented by the principle ofadhesion, in which the expansiveforce of a gas, passing alongside of and in contact with a plain surface, may drag along the surface in its train.
Such an exhibition of force has an analogy in nature by what is known as capillary attraction, which showsadhesion. For instance, sap flowing up the pores of trees, or water moving along the fibers of blotting paper, illustrates movement of liquids when brought into contact with solids.
CHAPTER XIV
ENGINERY IN THE DEVELOPMENT OF THE HUMAN RACE
The energy of a nation may be expressed by its horse power. It is not numbers, or intellect, or character, or beliefs that indicate the progress of a people in a material sense.
It is curious how closely related enginery is with the advancement of a people. Nothing can be more striking to illustrate this than railroads as a feature of development in any country.
Power in Transportation.—Without the construction and maintenance of mechanical power, railroads would be impossible. To be able to quickly and cheaply move from place to place, is the most important factor in human life. The ability of people to interchange commodities, and to associate with others who are not in their own intimate community, are the greatest civilizing agencies in the world.
Power vs. Education and the Arts.—Education, the cultivation of the fine arts, and the desire for luxuries, without the capacity for quickly interchanging commodities and to intermingle witheach other, are ineffectual to advance the interests of any nation, or to maintain its prosperity.
Lack of Power in the Ancient World.—The Greeks and the Romans had a civilization which is a wonder even to the people of our day. They had the arts and architecture which are now regarded as superb and incomparable. They had schools of philosophy and academies of learning; their sculpture excites the admiration of the world; and they laid the foundation theories of government from which we have obtained the basis of our laws.
The Early Days of the Republic.—When our forefathers established the Republic there were many misgivings as to the wisdom of including within its scope such a large area as the entire Atlantic seacoast. From Maine to Florida the distance is 1250 miles; and from New York to the Mississippi 900 miles, comprising an area of 1,200,000 square miles.
How could such an immense country ever hold itself together? It was an area nearly as large as that controlled by Rome when at the height of her power. If it was impossible for the force of Roman arms to hold such a region within its control, how much more difficult it would be for the Colonies to expect cohesion among their scattered peoples.
Lack of Cohesiveness in a Country Without Power.—Those arguments were based on the knowledge that every country in ancient times broke apart because there was no unity of interest established, and because the different parts of the same empire did not become acquainted or associated with each other.
The Railroad as a Factor in Civilization.—The introduction of railroads, by virtue of motive power, changed the whole philosophy of history in this respect. Even in our own country an example of the value of railroads was shown in the binding effect which they produced between the East and the West prior to the Civil War.
All railroads, before that period, ran east and west. Few extended north and south. It is popularly assumed that the antagonism between the North and the South grew out of the question of slavery. This is, no doubt, largely so, as an immediate cause, but it was the direct cause which prevented the building of railroads between the two sections.
It simply reënforces the argument that the motor, the great power of enginery, was not brought into play to unite people who were antagonistic, and who could not, due to imperfect communication, understand each other.
To-day the United States contains an areanearly as great as the whole of Europe, including Russia, with their twenty, or more, different governments. Here we have a united country, with similar laws, habits, customs and religions throughout. In many of those foreign countries the people of adjoining provinces are totally unlike in their characteristics.
It has been shown that wherever this is the case it is due to lack of quick and cheap intercommunication.
The Wonderful Effects of Power.—This remarkable similarity in the conditions of the people throughout the United States is due to the railroads, that great personification of power, notwithstanding the diverse customs and habits of the people which daily come to our shores and spread out over our vast country.
It has unified the people. It has made San Francisco nearer to New York than Berlin was to Paris in the time of Napoleon. The people in Maine and Texas are neighbors. The results have been so far reaching that it has given stability to the government greater than any other force.
But there is another lesson just as wonderful to contemplate. England has an area of only about 58,000 square miles, about the same size as either Florida, Illinois, or Wisconsin.
England as a User of Power.—The enginery within her borders is greater than the combined energy of all the people on the globe. Through the wonderful force thus set in motion by her remarkable industries she has become the great manufacturing empire of the world, and has called into existence a carrying fleet of vessels, also controlled by motors, so stupendous as to be beyond belief.
We may well contemplate the great changes which have been brought about by the fact that man has developed and is using power in every line of work which engages his activities.
The Automobile.—He does not, in progressive countries, depend on the muscle of the man, or on the sinews of animals. These are too weak and too slow for his needs. Look at the changes brought about by the automobile industry within the past ten years. What will the next century bring forth?
Artificial power, if we may so term it, is a late development. It is very young when compared with the history of man.
High Character of Motor Study.—The study of motors requires intellect of a high order. It is a theme which is not only interesting and attractive to the boy, but the mastery of the subjectin only one of its many details, opens up a field of profit and emoluments.
The Unlimited Field of Power.—It is a field which is ever broadening. The student need not fear that competition will be too great, or the opportunities too limited, and if these pages will succeed, in only a small measure, in teaching the fundamental ideas, we shall be repaid for the efforts in bringing together the facts presented.
CHAPTER XV
THE ENERGY OF THE SUN, AND HOW HEAT IS MEASURED
In the first chapter we tried to give a clear view of the prime factors necessary to develop motion. The boy must thoroughly understand the principles involved, before his mind can fully grasp the ideas essential in the undertaking.
While the steam engine has been the prime motor for moving machinery, it is far from being efficient, owing to the loss of two-thirds of the energy of the fuel in the various steps from the coal pile to the turning machinery.
First, the fuel is imperfectly consumed, the amount of air admitted to the burning mass being inadequate to produce perfect combustion.
Second, the mechanical device, known as the boiler, is not so constructed that the water is able to completely absorb the heat of the fuel.
Third, the engine is not able to continuously utilize the expansive force of the steam at every point in the revolution of the crankshaft.
Fourth, radiation, the dissipation of heat, and condensation, are always at work, and thus detract from the efficiency of the engine.
The gasoline motor, the next prime motor of importance, is still less efficient in point of fuel economy, since less than one-third of the fuel is actually represented in the mechanism which it turns.
The production of energy, in both cases, involves the construction of a multiplicity of devices and accessories, many of them difficult to make and hard to understand.
To produce power for commercial purposes, at least two things are absolutely essential. First, there must be uniformity in the character of the power produced; and, second, it must be available everywhere.
Water is the cheapest prime power, but its use is limited to streams or moving bodies of water. If derived from the air currents no dependence can be placed on the regularity of the energy.
Heat is the only universal power on the globe. The sun is the great source of energy. Each year it expends in heat a sufficient force to consume over sixty lumps of coal, each equal to the weight of the earth.
Of that vast amount the earth receives only a small part, but the portion which does come to it is equal to about one horse power acting continuously over every thirty square feet of the surface of our globe.
The great problem, in the minds of engineers, from the time the steam engine became a factor, was to find some means whereby that energy might be utilized, instead of getting it by way of burning a fuel.
One of the first methods proposed was to use a lens or a series of mirrors, by means of which the rays might be focused on some object, or materials, and thus produce the heat necessary for expansion, without the use of fuel.
Wonderful results have been produced by this method; but here, again, man meets with a great obstacle. The heat of the sun does not reach us uniformly in its intensity; clouds intervene and cut off the rays; the seasons modify the temperature; and the rotation of the globe constantly changes the direction of the beams which fall upon the lens.
The second method consists in using boxes covered with glass, the interior being blackened to absorb the heat, and by that means transmit the energy to water, or other substances adapted to produce the expansive force.
Devices of this character are so effective that temperatures much above the boiling point of water have been obtained. The system is, however, subject to the same drawbacks that are urged against the lens, namely, that the heat is irregular, and open to great variations.
These defects, in time, may be overcome, in conserving the force, by using storage batteries, but to do so means the change from one form of energy to another, and every change means loss in power.
The great problem of the day is this one of the conversion of heat into work. It is being done daily, but the boy should understand that thedirect conversionis what is required. For instance, to convert the energy, which is in coal, into the light of an electric lamp, requires at least five transformations in the form of power, which may be designated as follows:
1. The burning of the coal.
2. The conversion of the heat thus produced into steam.
3. The pressure of the steam into a continuous circular motion in the steam engine.
4. The circular motion of the steam engine into an electric current by means of a dynamo.
5. The change from the current form of energy to the production of an incandescent light in the lamp itself, by the resistance which the carbon film offers to the passage of the current. Should an inventor succeed in eliminating only one of the foregoing steps, he would be hailed as a genius, and millions would not be sufficient to compensate the fortunate one who should be ableto dispense with three of the steps set forth.
The Measurement of Heat.—To measure heat means something more than simply to take the temperature. As heat is work, or energy, there must be a means whereby that energy can be expressed.
It has been said that the basis of all true science consists in correct definitions. The terms used, therefore, must be uniform, and should be used to express certain definite things. When those are understood then it is an easy matter for the student to grope his way along, as he meets the different obstacles, for he will know how to recognize them.
Before specifically explaining the measurement it might be well to understand some of the terms used in connection with heat. The original theory of heat was, that it was composed of certain material, although that matter was supposed to be subtle, imponderable and pervading everything.
This imponderable substance was calledCaloric. It was supposed that these particles mutually attracted and repelled each other, and were also attracted and repelled by other bodies, so that they contracted and expanded.
The phenomenon of heat was thus accounted for by the explanation that the expansion andcontraction made the heat. This was known as theMaterial Theory of Heat.
But that phase of the explanation has now been abandoned, in favor of what is known as thedynamical, ormechanicaltheory, which is regarded merely as amodeofmotion, or a sort of vibration, wherein the particles move among each other, with greater or less rapidity or in some particular manner.
Thus, the movements of the atoms may be accelerated, or caused to act in a certain way, by friction, by percussion, by compression, or by combustion. Heat is the universal result of either of those physical movements.
Notwithstanding that the material theory of heat is now abandoned, scientists have retained, as the basis of all heat measurements, the name which was given to the imponderable substance, namely,Caloric.
It is generally writtenCalorie, in the text books. A calorie has reference to the quantity of heat which will raise the temperature of one kilogram of water, one degree Centigrade.
As one kilogram is equal to about two pounds, three and a quarter ounces, and one degree Centigrade is the same as one and two-thirds degrees Fahrenheit, it would be more clearly expressed by stating that a caloric is the quantity of heat requiredto raise the temperature of one and one-fifth pound of water one degree Fahrenheit.
This is known as the scientific unit of the thermal or heat value of a caloric. But the engineering unit is what is called the British Thermal Unit, and designated in all books as B. T. U.
This is calculated by the amount of heat which is necessary to raise a kilogram of water one degree Fahrenheit. According to Berthelot, the relative value of calorics and B. T. U. are as follows:
HEATS OF COMBUSTION
When it is understood that heat is transmitted in three different ways, the value of a measuring instrument, or a unit, will become apparent.
Thus, heat may be transmitted either byconduction,convection, orradiation.
Conductionis the method whereby heat is transmitted from one particle to another particle, or from one end of a rod, or other material to the other end. Some materials will conduct the heat much quicker than others, but if we have a standard, such as the calorie, then the amount of heat transmitted and also the amount lost on the way may be measured.
Convectionapplies to the transmission of heat through liquids and gases. If heat is applied to the top or surface of a liquid, the lower part will not be affected by it. If the heat is applied below, then a movement of the gas or liquid begins to take place, the heated part moving to the top, and the cooler portions going down and thus setting up what are calledconvection currents.
Radiationhas reference to the transference of heat from one body to another, either through a vacuum, the air, or even through a solid.
By means of the foregoing table, which gives the heats developed by the principal fuels, it is a comparatively easy matter to determine the calorific value of fuels, which is ascertained by making an analysis of the fuel.
The elements are then taken together, and the table used to calculate the value. Suppose, for instance, that the analysis shows that the fuel has seventy-five per cent. of carbon and twenty-fiveper cent. of hydrogen. It is obvious that if we take seventy-five per cent. of 8,137 (which is the index for carbon), and twenty-five per cent. of 43,500 (the index of hydrogen), and adding the two together, the result, 14,727, would represent the calorific value of the fuel.
GLOSSARY OF WORDSUSED IN TEXT OF THIS VOLUME