The Project Gutenberg eBook ofFriction, Lubrication and the Lubricants in Horology

The Project Gutenberg eBook ofFriction, Lubrication and the Lubricants in HorologyThis ebook is for the use of anyone anywhere in the United States and most other parts of the world at no cost and with almost no restrictions whatsoever. You may copy it, give it away or re-use it under the terms of the Project Gutenberg License included with this ebook or online atwww.gutenberg.org. If you are not located in the United States, you will have to check the laws of the country where you are located before using this eBook.Title: Friction, Lubrication and the Lubricants in HorologyAuthor: W. T. LewisRelease date: January 19, 2011 [eBook #35001]Language: EnglishCredits: E-text prepared by the Online Distributed Proofreading Team (http://www.pgdp.net) from page images generously made available by Internet Archive/American Libraries (http://www.archive.org/details/americana)*** START OF THE PROJECT GUTENBERG EBOOK FRICTION, LUBRICATION AND THE LUBRICANTS IN HOROLOGY ***

This ebook is for the use of anyone anywhere in the United States and most other parts of the world at no cost and with almost no restrictions whatsoever. You may copy it, give it away or re-use it under the terms of the Project Gutenberg License included with this ebook or online atwww.gutenberg.org. If you are not located in the United States, you will have to check the laws of the country where you are located before using this eBook.

Title: Friction, Lubrication and the Lubricants in HorologyAuthor: W. T. LewisRelease date: January 19, 2011 [eBook #35001]Language: EnglishCredits: E-text prepared by the Online Distributed Proofreading Team (http://www.pgdp.net) from page images generously made available by Internet Archive/American Libraries (http://www.archive.org/details/americana)

Title: Friction, Lubrication and the Lubricants in Horology

Author: W. T. Lewis

Release date: January 19, 2011 [eBook #35001]

Language: English

Credits: E-text prepared by the Online Distributed Proofreading Team (http://www.pgdp.net) from page images generously made available by Internet Archive/American Libraries (http://www.archive.org/details/americana)

*** START OF THE PROJECT GUTENBERG EBOOK FRICTION, LUBRICATION AND THE LUBRICANTS IN HOROLOGY ***

ILLUSTRATED WITH HALF-TONES ANDDRAWINGS BY THE AUTHOR.CHICAGO:GEO. K. HAZLITT & CO.1896.Copyrighted 1896, by W. T. Lewis.Copyrighted 1896, by Geo. K. Hazlitt & Co.

Page.Introduction,7CHAPTER I.Lubricants in Horology—their Source and Methods of Refinement,9CHAPTER II.Elementary Physics Relating to Friction and Lubrication,21CHAPTER III.Friction—its Nature and Theory,29CHAPTER IV.Application of the Laws of Friction and Lubrication inHorology,43CHAPTER V.The Properties and Relative Values of Lubricants in Horology,61

Many books have been written on the various escapements, describing their action, construction and proportion, and the laws governing the same; learned writers have contributed much valuable information on adjusting; excellent attachments for the various lathes have been invented; and factories have expended fortunes to produce machinery of wonderful construction to finish all the parts of a watch in the most approved manner; but all this scientific research, all this painstaking effort, all this care and labor, are rendered abortive by the maker or repairer of a time piece if he does not thoroughly understand and apply the physical laws which govern the science of lubrication.

Many a watch, or chronometer, most excellent in all other respects, has come to an untimely end by an almost criminal neglect on the part of its maker to provide against wear in its various parts by such construction as would retain the oil at the places needed.

How often the repairer—clean he his work as well as he may—replace he the broken or worn part to put the time piece in as good condition as new—finds that its rate changes, that is loses time before long, and, at the end of one yearis badly out of repair, solely the result of lack of knowledge, or negligence, in properly lubricating, or on account of an oil having been used which was not suitable.

The object of this paper is to present in concise form the best of that which is furnished by the literature of the profession, together with that which has been written on friction and lubrication in general (so far as it may be applicable), by those not connected with this particular vocation; as well as the result of the practical experience of the manufacturers of time pieces in this country most of whom have furnished much useful data in answer to queries on the subject. The manufacturers of oils have also assisted by contributing valuable information.

The result of the author's experience, observation and experiments will also be incorporated; and he will be grateful to any who may read this work, who will call attention, through the trade papers, to any errors of omission or commission that they may find therein.

1. As but littleis to be found on the subject in the literature accessible to most of the craft, a few remarks concerning the source and general methods of refining the oils used in horology will, no doubt, be of interest.

A mechanic who would work intelligently should possess a thorough knowledge of the materials constantly used, and oil is used on every horological mechanism. In order that this paper may be of maximum benefit and interest, the author has spared no pains in procuring useful data.

2. Porpoise Jaw Oil and Black Fish Melon Oil(64) have become widely known and justly celebrated in all parts of the world, as they were found to be better adapted for the purpose of lubricating fine and delicate machinery than any substancepreviouslyused.

3. Blackfish-Melon Oil[1]"derives its name from the mass taken from the top of the head of the animal reaching from the spout hole to the end of the nose, and from the top of the head down to the upper jaw, from which it is extracted. When taken off in one piece this mass represents a half watermelon, weighing about twenty-five poundsordinarily. When the knife is put into the center of this melon the oil runs out more freely than the water does from a very nice watermelon. Porpoise jaw oil and blackfish melon oil are worth from $5 to $15 per gallon, according to supply. They are not only used in horology, but by manufacturers of fine firearms, philosophical apparatus, and in government lighthouses for the clocks of revolving lights."

4. The Blubber, or fat, taken from the jaw of the porpoise or the head of the blackfish was formerly rendered in iron pots over a fire, but the modern method of extracting the oil by steam is said to be much superior. The oil is washed with water by thorough agitation, after which it is allowed to stand for several days, when it is drawn off and the last traces of water removed by distillation. The oil is then subjected to a very cold temperature and pressed through flannel cloths, by which process the "oleine" is separated from the "stearine," the resulting oil being more or less limpid as the former or latter constituent predominates.

5. John Wing, of New Bedford, Mass., son-in-law of, and successor to, the late Ezra Kelley, states in answer to inquiries, that their supply of oil comes from the porpoise and blackfish taken during the summer months on the coast of Africa, above the equator; and that they find that this oil contains less glutinous matter than that obtained in and about the St. Lawrence river, which fact he attributes to the difference in the food of the fish, which in turn affects the oil.

6. D. C. Stull, of Provincetown, Mass., in answer to inquiries on the subject, has kindly furnished the following information and series of views:

Fig. 1.—Buying a Porpoise from a Fisherman.Fig. 1.—Buying a Porpoise from a Fisherman.

"The supply of porpoise-jaw oil and blackfish-melon oil comes mostly from Massachusetts Bay, the trap and gill net fishermen bringing them into Provincetown, sometimes alive, as shown at Fig. 1. The capture of fifteen hundred blackfish, Fig. 2, by the people of Provincetown, Truro and Wellsfleet, was one of the most exciting scenes in the annals of coast fishery. The fish were attracted to these shores by the large quantity of squid and herring, on which they feed. It is estimated that the catch was worth $25,000,some of the fish weighing two tons each. The relative size of a blackfish and a man is shown at Fig. 3. Seafaring men and whaling captains who catch the porpoise at sea, extract the oil from the head and jaw only, and bring it to the factories to be manufactured.

"Fig. 4 is a good view of a modern factory. The fat is cut from the head and jaw, (Fig. 5,) washed in fresh water and put into covered tin cans, then into iron retorts, (Fig. 6.) These retorts are then closed, screwed up tightly, and live steam turned on from the boiler. The fat is cooked by steam for five hours, with ten pounds pressure, at 230° F. By this means the crude oil is extracted from the fat."

7. Sperm Oilis the best known of all the lubricants and is, for general purposes, one of the most excellent.

The large cavity in the head of the sperm whale contains oil and solid fat, from which the former is separated, without heating, by pressure and crystalization. As it is not at present used to any great extent in horology, a more lengthy description of the method of refining will be omitted. (65.)

8. Bone Oilis made from the fat obtained by boiling the bones of animals. The finest quality is obtained from the leg bones of recently killed, healthy, young cattle, and the best method of treatment is given as follows[2]:

"Fill a bottle one third full of the oil to be purified. Then pour clarified benzine in small portions upon the oil, close the bottle and shake until the benzine has disappeared. By again adding benzine and shaking, a complete solution of the fat is finally effected. That this has actually taken place isrecognized by the contents of the bottle not separating after long standing. The bottle is then exposed to a low temperature for several hours, a solid fat deposits on the bottom, and the lower the temperature the greater is the deposit. Alongside the bottle containing the oil, place another bottle with a funnel, the lower end of which is closed by a cotton stopper; after thoroughly shaking the bottle with oil, pour the contents into the funnel; the fluid portion runs into the bottle, while the solid portion is retained in the funnel by the cotton stopper. The clear solution of bone oil in benzine collected in the bottle is then brought into a small retort which is connected with a thoroughly cooled receiver. Place the retort in a tin vessel filled with water and apply heat. The benzine readily distills off, leaving the purified bone oil in the retort." (66.)

9. Neat's-foot Oilis largely used in the arts, being one of the best of lubricants. The best oil, viz.: that used for clocks etc., is extracted by placing the thoroughly cleaned feet of cattle in a covered vessel near the fire or in the sun. The oil thus obtained is clarified by standing before bottling. (67.)

It was the practice of many olden time watchmakers to allow a large bottle of neat's-foot oil to stand in a position exposed to the direct rays of the sun in summer and to the extreme cold of the winter. Then after two or three years, on a very cold winter day, to pour off such oil as still remained fluid which was preserved for use.

10. Olive Oilhas been used as a lubricant since the early days of horology, the older writers giving manymethods of treating it. It is obtained from the fruit of theOlea Europea, one of the jasmines, which grows throughout Southern Europe and Northern Africa and other tropical countries.

Fig. 2.—A $25,000 Catch of Blackfish.Fig. 2.—A $25,000 Catch of Blackfish.

For the preparation of the finest oils, known as "Virgin oil," only the pulp of olives picked by hand is used. The pulp is packed in strong linen and the oil is expressed by twisting the linen together. The pulp sometimes contains as high as 70 per cent of oil.

Its last traces of adhering acid are removed by rigorous and repeated shaking with one hundredth part of their weightof caustic soda lye. After the mixture has stood for several days a large quantity of water is added and the oil floating on the top is poured off.

Though the oil is now free from acid, it still contains coloring matter and other substances which would prove injurious. It is then mixed with very strong alcohol, ten parts of the former to two of the latter, and thoroughly mixed by shaking. The bottle containing the mixture is then placed in the sun and the mixture shaken several times a day. In the course of two or three weeks the oil will have become white as water, when it is withdrawn from the alcohol, on the surface of which it floats. The purified oil is placed in small bottles, tightly corked, and kept in a dark, cool place. (68.)

Fig. 3.—Relative Size of a Blackfish and Man.Fig. 3.—Relative Size of a Blackfish and Man.

Fig. 4.—D. C. Stull's Watch Oil Factory, Provincetown, Mass.Fig. 4.—D. C. Stull's Watch Oil Factory, Provincetown, Mass.

11. Mineral Oilshave of late years taken immense strides in the popular and merited estimation of consumers, for general lubricating purposes. Their application in horology will be discussed in another part of this volume. They are obtained from the residuum of petroleum distillation, and vary so greatly in their properties that many of them are not applicable to delicate mechanism; but as the lighter varieties seem to fulfill all the necessary conditions, the writer will here consider their source and method of treatment.

12. Petroleumsare obtained from many different localities, being fluid, bituminous oils, all having the same general characteristics and origin. They are all hydrocarbons, and contain little or no oxygen. As their origin is thoroughly discussed in many works on that subject, and as there is such a diversity of opinion regarding it, the reader is referred to such works.[3]

13. Paraffine, both liquid and solid, is obtained by the distillation of crude petroleum by means of superheated steam. When the heavier hydrocarbons begin to come over the receiver is changed and the butyraceous distillate is filtered through a long column of well dried animal charcoal. The first portion of the percolate is colorless or nearly so.

The distillate is made water white by some refiners by an acid treatment, followed by a water-and-alkali washing. On exposing this mass to a low temperature it becomes thick, somewhat like "cosmoline" but white. (59.) It is then shoveled into cotton bags of very strong material and subjectedto powerful pressure by means of a hydraulic press. This operation divides the paraffine into two parts: the solid paraffine wax from which candles, etc., are made remaining in the bags, while that which is expressed is paraffine oil. If the operation is carefully performed the oil will be free from crystaline paraffine at a very low temperature.

Fig. 5.—Extracting Oil from the Head of a Porpoise.Fig. 5.—Extracting Oil from the Head of a Porpoise.

14. Neutral Oils[4]"are refined paraffine oils varying in specific gravity from 0.8641 to 0.8333. For the purposefor which these oils are employed it is especially necessary that they be thoroughly deodorized. They are largely used for the purpose of mixing with animal and vegetable oils. It is said that a mixture of 95 per cent of a good neutral oil of the right gravity, and 5 per cent of sperm oil, has been sold for pure sperm. Ordinary inspection as to the odor and general appearance would fail to detect the adulteration. Having been subjected to the usual process for the extraction of crystaline paraffine, they will stand a very low cold test, and having been passed through bone black cylinders, they are free from odor and have but little color. They are usually exposed for a few days in open shallow tanks for the purpose of removing the flurescence of petroleum oils. Unmixed with heavier oils they are too light in body(especially the lighter varieties) to be employed as spindle or machinery oils, but when mixed with such oils in the proper proportions they form admirable lubricating compounds for general lubricating purposes when very high speed is not required." (70-71.)

Fig. 6.—Rendering Room in D. C. Stull's Factory.Fig. 6.—Rendering Room in D. C. Stull's Factory.

FOOTNOTES:[1]Brannt. Animal and Vegetable Fats and Oils.[2]Brannt. Animal and Vegetable Fats and Oils.[3]Crew; Practical Treatise on Petroleum. Lesquereaux; Transactions American Philosophical Society. Winchell; Sketches of Creation. Henry; Early and Later History of Petroleum.[4]Crew. Practical Treatise on Petroleum.

[1]Brannt. Animal and Vegetable Fats and Oils.

[2]Brannt. Animal and Vegetable Fats and Oils.

[3]Crew; Practical Treatise on Petroleum. Lesquereaux; Transactions American Philosophical Society. Winchell; Sketches of Creation. Henry; Early and Later History of Petroleum.

[4]Crew. Practical Treatise on Petroleum.

15.Most of those who may read this work, are no doubt familiar with the laws of elementary physics; but asallmay not be, for a better understanding of that which follows, it may be well to treat briefly of some of the physical laws bearing on the subject.

16. The Molecule.[5]Every visible body of matter is composed of exceedingly small particles called molecules.This is the basis of the theory of the constitution of matter which physicists have usually adopted. It is estimated that if we should attempt to count the number of molecules in a pin's head, counting at the rate of 10,000,000 per second, we should require 250,000 years.

17. Porosity.The termporein physics is restricted to the invisible space that separates molecules. All matter is porous; thus dense gold will absorb (24) liquid mercury, much as chalk will water; but the cavities to be seen in a sponge are not pores.

18. Gravitation.That attraction which is exerted on all matter, at all distances, is called gravitation.Gravitation is universal, that is, every molecule of matter attractsevery other molecule of matter in the universe. The whole force with which two bodies attract one another is the sum of the attraction of their molecules, and depends upon the number of molecules the two bodies collectively contain, and the mass of each molecule. Hence, all bodies attract, and are attracted by, all other bodies.

In a ball suspended from the ceiling by a thread an attraction exists between the ball and the ceiling, but on account of a greater attraction existing between the ball and the earth, if we cut the thread the ball will move toward the earth, or in the direction of the greater attraction.

19. The Effect of Distance.Gravitation varies inversely with the distance by which two bodies are separated.

As the sun is many times greater than the earth, the attraction between the ball (18) and the sun would cause the ball to leave the earth and move toward the sun were it not for the fact that the ball is so muchnearerto the earth than to the sun.

20. Cohesion.The attraction which holds the molecules of the same substance together so as to form larger bodies is called cohesion.

It acts only at insensible distances and is strictly a molecular force. It is that force which prevents solid bodies from falling apart. Liquids like molasses and honey possess more cohesive force among the molecules of which they are composed than limpid liquids like water and alcohol. The former are said to be viscous, or to possessviscosity.

21. Adhesion.That force which causes unlike substances to cling together is called adhesion.It is that forcewhich keeps nails, driven into wood, in their places. You can climb a pole because of the adhesion between your hands and the pole. We could not pick anything up if it were not for adhesion. Glue, when dry, possesses both cohesion and adhesion to a great degree.

22. Capillarity.Examine the surface of water in a vessel. You find the surface level, except around the edge next the glass, as at A (Fig. 7.)

Fig. 7.Fig. 7.

Fig. 8.Fig. 8.

1. Thrust vertically into water three glass tubes, A, B and C (Fig. 8), open at both ends. You notice the water ascends in each to a different height, and thatthe ascension varies inversely as the diameter of the bore; i. e., the smaller the bore, the higher the water ascends.

2. Seal one of the tubes at its upper end. The water enters but little, as shown at D (Fig. 8), on account of the resistance of the air pressure within the tube.

3. Thrust vertically two plates of glass into water, and gradually bring the surfaces near to each other. Soon the water rises between the plates, and rises higher as the plates are brought nearer. If their surfaces be mutually parallel and vertical, the water rises to the same height at all points between the plates, as shown at A (Fig. 9.)

Fig. 9.Fig. 9.

4. If the plates be united by a hinge, and form an angle, the height to which the water ascends increases as thedistancebetween the plates decreases up to their line of junction, where it attains a maximum, as shown at B (Fig. 9.)

5. Decrease theanglebetween the plates, and the water ascends higher, as shown at C (Fig. 9.) Thus it is seen thatthe ascension varies inversely with the angle between the plates; i. e., the smaller the angle, the higher the water ascends.

6. When a drop of oil is placed between two glass plates arranged as shown at A (Fig. 10), if the surfaces are not too far distant, and if the oil touches both surfaces, it will be seen to work its way to the junction of the plates; showingthatoil between surfaces has a tendency to flow towards the apex of the angle.

Fig. 10.Fig. 10.

7. Place a drop of oil on a taper piece of metal, as shown at B (Fig. 10). The oil will gradually recede from the point to a place where there is more metal, showing thatoil on surfaces has a tendency to flow towards the largest part.

Fig. 11.Fig. 11.

8. When a drop of oil is placed between two watch glasses arranged with flat and convex sides adjacent, as at A (Fig. 11), or with convex sides adjacent, as at B (Fig. 11), if the glasses are rigidly fixed in their relative positions the drop of oil can be shaken from its location only with great difficulty; the oil at C holding its place with greater tenacity than the oil at D.

The foregoing phenomena are calledcapillary action, orcapillarity. Capillary action is due to the forces of cohesion (20), and to the forces of adhesion (21.)

23. Centrifugal Force.—The tendency of a body rotating round a point to escape from that point is called centrifugal force.

Place a small quantity of oil on the arm of a balance, near the arbor. Rotate the wheel rapidly. The oil is seen to flow towards the rim of the wheel.

24. Absorption of Gases by Liquidsdepends on molecular attraction and motion. Water at a temperature of 0° cen. (32° f.), is capable of condensing in itspores(17) six hundred times its own bulk of ammonia gas. The absorption of oxygen from the air causes some oils to become more viscous, to eventually become solid, without losing in weight, in fact sometimes gaining. Other oils dry up, orevaporate, leaving little or no residue.

25. Force.—Force is that which can produce, change or destroy motion.

We see a body move; we know there must be a cause; that cause we call force. We see a body in motion come to rest; this effect must have had a cause; that cause we attribute to force. The forces acting in machines are distinguished intodrivingandresistingforces. That component of the force which does the work is called the "effort."

26. Frictionis usually a resisting (29) force, tending to destroy motion; but it is sometimes the means of the transmission of motion.

27. Workis the result of force acting through space. When force produces motion, the result is work.Work is measured by the product of the resistance into the space through which it is overcome.

28. Energy, which is defined[6]as the capacity for doing work, is eitheractualorpotential.Actualorkinetic energyis the energy of an actually moving body, and is measured by the work which it is capable of performing while being brought to rest under the action of a retarding force.

Potential Energyis the capacity for doing work possessed by a body in virtue of its position, of its condition, or of its intrinsic properties. A bent bow or a coiled spring has potential energy, which becomes actual in the impulsion of the arrow or is expended in the work of the mechanism driven by the machine. A clock weight, condensed air and gunpowder are examples.

This form of energy appears in every moving part of every machine and its variations often seriously affect the working of machinery. (84.)

FOOTNOTES:[5]This and some of the definitions that follow are adapted from "Elements of Physics" by A. P. Gage.[6]Thurston. "Friction and Lost Work in Machinery," from which excellent work much of the next chapter is adapted.

[5]This and some of the definitions that follow are adapted from "Elements of Physics" by A. P. Gage.

[6]Thurston. "Friction and Lost Work in Machinery," from which excellent work much of the next chapter is adapted.

29. Friction.The relative motion of one particle or body in forced contact with another is always retarded, or prevented, by a resisting force called friction.

Friction manifests itself in three ways: Between solids it is calledslidingandrolling friction; between the particles of liquids, or of gasses, when they move in contact with each other, or with other bodies, it is calledfluid friction. Quite different laws govern these three kinds of friction, as they are quite different in character.

Friction can never of itself produce or accelerate motion, being always a resisting force, acting at the surfaces of contact of the two particles, or masses, between which it occurs, and in the direction of their common tangent, resisting relative motion in whichever direction it may be attempted to produce it. The greatest loss of energy in a timepiece in which all the parts are rigid enough to prevent permanent distortion, is that occurring through friction. Another source of loss of energy is the reduction in elasticity of springs caused by a rise of temperature.

30. The Cause of Sliding Frictionis the interlocking of the asperities of one surface with those of another; and only by the riding of one set over the other, or by a rubbing down or tearing off of projecting parts, can motion take place. It follows, then, that roughness is conducive tofriction; and that the smoother the surface the less the friction will be.

31. The Cause of Rolling Frictionis the irregularity and lack of symmetry of the surfaces between which it occurs. It acts as a resisting, or retarding, force when a smoothly curved surface rolls upon another surface, plane or curved.

Motion is prevented, or retarded, by the irregular variation of the distance between the center of gravity and the line of motion in the common tangent of the two bodies at the point of contact, caused by the irregularity of form, or of surface, in the one or the other body. Rolling friction is small where hard, smooth, symmetrical surfaces are in contact, and increases as the surfaces are soft, rough or irregular.

In a knife edge support, seen in some forms of pendulums, is exhibited a form of rolling friction.

32. Solid Friction, either sliding or rolling, could be overcome if it were possible to produceabsolutelysmooth surfaces. It is evident, then, that the character of the material, as well as the form of their surfaces, determines the amount of friction.

In all time-keeping mechanism both sliding and rolling friction manifest themselves; the former principally between the surfaces of pivots and bearings and in the escapements, the latter mainly between the surfaces of the teeth of wheels, and to some extent in some of the pivots, and sometimes in parts of escapements. It is not the intention of the author to treat of the proper shape of the teeth of wheels,leaves of pinions, or the proportions of the escapements, the nature and scope of this work not permitting of it; but he will confine his remarks principally to the parts that involve lubrication.

33. The Laws of Sliding Friction, as given by Thurston,[7]with solid, unlubricated surfaces, are, up to the point of abrasion, as follows:

1. The direction of frictional resisting forces is in the common tangent plane of the two surfaces, and directly opposed to their relative motion.

2. The point, or surface, of application of this resistance is the point, or the surface, on which contact occurs.

3. The greatest magnitude of this resisting force is dependent on the character of the surfaces, and is directly proportional to the force with which two surfaces are pressed together.

4. The maximum frictional resistance is independent of the area of contact, the velocity of rubbing, or any other conditions than intensity of pressure and condition of surfaces.

5. The friction of rest or quiescence, "statical friction," is greater than that of motion, or "kinetic friction."

He further states that these "laws" are not absolutely exact, as here stated, so far as they affect the magnitude of frictional resistance. It is found that some evidence exists indicating the continuous nature of the friction of rest and of motion.

When the pressure exceeds a certain amount, fixed for each pair of surfaces, abrasion of the softer surface or otherchange of form takes place, the resistance becomes greater and is no longer wholly frictional.

When the pressure falls below a certain other and lower limit the resistance may be principally due to adhesion, an entirely different force, which may enter into the total resistance at all pressures, but which does not always appreciably modify the law at high pressures.

This limitation is seldom observable with solid, unlubricated surfaces, but may often be observed with lubricated surfaces, the friction of which, as will presently be seen (41), follows different laws. The upper limit should never be approached in machinery.

The coefficient of friction is that quantity which, being multiplied by the total pressure acting normally to the surfaces in contact, will give the measure of the maximum frictional resistance to motion.

34. Sliding Friction is Proportional to Pressureaccording to the third law quoted above. This is easily demonstrated by ascertaining what force is necessary to produce, or continue, motion in a body lying on a plane surface; double the weight of the body and the force required to produce, or continue, motion, will have to be doubled. The converse is also true (36).

35. Sliding Friction is Independent of the Area Of Contact, the pressure remaining the same (law 4, 33).

This is accounted for by the fact that if, for example, the area of contact be doubled, though twice the number of asperities will present themselves, each individual retardingforce is only half of what it was previously, and the general effect is the same (36).

36. The Intensity of Sliding Friction is Independent of Velocity.(Law 4, 33.) This is explained by the fact that the interlocking of the asperities on each surface has a shorter time to take place in increased speed, and consequently cannot be so effective as with slow speed. But with high speed more asperities are presented than in low speed, so the effect is the same in both cases.

The above (33-36) are not exact, being the statement of experimental laws, and admit of considerable modification when applied in horological science, as will be shown (41-42.)

Fig. 12.Fig. 12.

37. The Effect of a Loose Bearingis an increase of friction, and consequently a loss of energy, resulting in the wear ofoneorbothsurfaces in contact, according to conditions. In Fig. 12, A is a loose bearing, B a journal at rest and C the point of contact. If the journal be now turned in the direction of the arrow by the motive force, it will have a tendency to roll over a short arc of the bearing to a newpoint of contact, as at D, when it begins to slide; so long as the coefficient of friction is unchanged it retains this position; but approaches or retreats from the point C, as the coefficient of friction diminishes or increases, continually finding new conditions of equilibrium. The arc of contact is thus too small to withstand the pressure without abrasion of one or both surfaces.

It will thus be seen that the journal, or pivot, should fit its bearing closely; but it should be borne in mind that no tendency to "bind" should be produced, the fitting being such that the wheel will turn readily with a minimum pressure.

The film of oil which must be interposed between the bearing surfaces of the journal, or pivot, and its bearing, will also occupysomespace; and this must be remembered, particularly in the case of pivots in the escapement.

38. The Laws of Rolling Frictionare not as yet definitely established, because of the uncertainty of the results of experiments, as to the amount of friction due to (1) roughness of surface, (2) irregularity of form, (3) distortion under pressure.

The first and second of these quantities vary inversely as the radius; and the third depends upon the character of the material composing the two surfaces in contact.

It follows, then, that in such minute mechanical contrivances as are used in horology, as the motive force is in some cases very light, the horologist should endeavor to produce, where rolling friction takes place, the maximum—smoothness of surface—regularity of form—adaptation of surfaces (31.)

There are many other points on which the writer would like to dwell, as engaging and disengaging friction, internal friction, etc., etc., but the scope of this paper will not permit.

39. The Friction Of Fluidsin horology is of grave importance. It is subject to quite different laws from those met with in the motion of solids in contact. When a fluid moves in contact with a solid the resistance to motion experienced is due to relative motion of layers of fluid moving in contact with each other. At surfaces of contact with a solid the fluid lies against the solid without appreciable relative motion; as the distance from the surface is increased by layer upon layer of the fluid, the relative velocity of the solid and the fluid becomes greater.Fluid friction is, therefore, the friction of adjacent bodies of fluid in relative motion.

While fluid friction acts as a retarding force in mechanism it converts the mechanical energy required to produce it into its heat equivalent, thus raising the temperature of the mass in a greater or lesser degree.

The resisting property which thus effects this conversion, and which is the cause of fluid friction, is calledviceosity.

It is thus apparent that avariation of the viceosityof the oil used on a watch would cause a variation of fluid friction and consequently a variation of the effort (11),and would seriously interfere with the rate of the watch. This will be discussed (84) more thoroughly in another paragraph.

40. The Laws of Fluid Frictionare:

1. Fluid friction is independent of the pressure between the masses in contact.

2. Fluid friction is directly proportional to the surfaces between which it occurs.

3. This resistance is proportional to the square of the relative velocity at moderate and high speeds, and to the velocity nearly at very low speeds.

4. It is independent of the nature of the surfaces of the solid against which the stream may flow, but it is dependent to some extent upon the degree of roughness of those surfaces.

5. It is proportional to the density of the fluid and is related in some way to its viscosity.

41. The Compound Friction of Lubricated Surfaces, as Thurston terms it, or friction due to the action of surfaces of solids partly separated by a fluid, is observed in all cases in which the rubbing surfaces are lubricated. The solids, in such instances, though partly supported by the layer of lubricant which is retained in place by adhesion (21) and cohesion (20), usually rub on each other more or less, as they are usually not completely separated by the liquid film interposed between them.

Wear is produced by the rubbing together of the two solids; and the rate at which the lubricant becomes discolored and charged with abraded metal indicates the amount of wear.

The journal and bearing are forced into close contact in the case of heavy pressures and slow speeds, as is shown by their worn condition; while the journal floats on the film of fluid which is continually interposed between it and the bearing, in the case of very light pressures, and high velocities; in the latter instancethe friction occurs between two fluid layers, one moving with each surface.

With heavy machinery, as the hardness and degree of polish of the surfaces cannot be increased in proportion to their weight, the solid friction is so great that while the interposition of a lubricant between the surfaces adds fluid friction, it also reduces the solid friction; and as the fluid friction is so insignificant as compared to the solid friction, the former is almost completely masked by the latter. In this case the laws of solid friction are more nearly applicable.

But in a delicate machine like a watch, especially in the escapement, where the power is so light, and where the rubbing surfaces are so hard, smooth and regular, the solid friction is so minute as compared to the fluid friction, that the former is relatively very slight, as compared with the latter. The laws of fluid friction are more nearly applicable in this instance.

There are thus, evidently, two limiting cases between which all examples of satisfactorily lubricated surfaces fall; the one limit is that of purely solid friction, which limit being passed, and sometimes before, abrasion ensues; the other limit is that at which the resistance is entirely due to the friction of the film of fluid which separates the surfaces of the solids completely.

42. The Laws of Friction of Lubricated Surfacesare evidently neither those of solid friction nor those of fluid friction, but will resemble more nearly the one or the other, as the limits described in the previous paragraph are approached. The value of the coefficient of friction varies with every change of velocity, of pressure, and of temperature, as well as with the change of character of the surfaces in contact.

Forperfectlylubricated surfaces, were such attainable, assuming it practicable with complete separation of the surfaces, the laws of friction, according to Thurston, would become:

1. The coefficient is inversely as the intensity of the pressure, and the resistance is independent of the pressure.

2. The friction coefficient varies as the square of the speed.

3. The friction varies directly as the area of the journal bearing.

4. The friction varies as the temperature rises, and as the viscosity of the lubricant is thus decreased (80).

43. The Methods of Reducing Waste of Energy Caused by Frictionin time keeping mechanisms are based upon a few simple principles. It is evident that to make the work and power so lost a minimum, it is necessary to adopt the following precautions:

1. Proper choice of materials for rubbing surfaces (29-32).

2. Smooth finish and symmetrical shape of surfaces in contact (29-32 and 38).

3. The use of a lubricant the viscosity of which is adapted to the pressure between the bearing surfaces (80).

4. The best methods for retaining the lubricant at the places required, and for providing for a continual supply of the lubricant.

5. The bearing surfaces of such proportions that the lubricant will not be expelled at normal pressure.

6. The reducing of the diameters of all journals, shoulders and pivots, to the smallest size compatible with the foregoingconditions, and with the stresses they are expected to sustain, thus reducing the space, through which the fluid friction acts, to a minimum (40); as well as reducing the distance from the axis of the arbor or pinion at which the friction, both solid and fluid, acts. The work done is independent of the length of the journal; except as it may modify pressure, and thus the coefficient of friction.

7. Proper fitting of bearing surfaces (37).

8. The reducing of the rubbing surfaces in escapements as much as the nature of the materials will allow without abrasion in the course of time (55).

44. Friction Between Surfaces Moving at Very Slow Speed, has been investigated by Fleming Jenkin and J. A. Ewing. A contrivance, which would be very excellent with some improvement, for the determination of the amount of friction under such conditions, is given in a paper[8]read before the Royal Society of London.

The arrangement employed by them was composed of a cast iron disk two feet in diameter and weighing 86 pounds. This disk, being turned true on its circumference, was supported by a spindle terminating in pivots 0.25 C. M. in diameter, the pivots resting in small rectangular bearings composed of the material the friction of which with steel is to be determined.

A tracing of ink was produced on a strip of paper which surrounded the disk, the ink being supplied by a pen actuated electrically by a pendulum, as in the syphon recorder.

As the traces thus left on the paper were produced without in any way interfering with the freedom of motion ofthe disk, they afforded a means of determining the velocity of rotation.

The relative velocities of the pivot to the bearing surfaces varied from .006 C. M. to 0.3 C. M. per second, being the velocities met with in the various parts of time keeping devices.

Experiments were made with the bearing surfaces successively in three different conditions: viz. 1, dry; 2, wet with water; and 3, wet with oil; and gave the following results:

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