Southern Branch of the University of California Los Angeles Form L-l This book is DUE on last date stamped below * 4 t9 1958 BOOKS BY MINNIE GOODNOW, R. N. First-Year Nursing 12mo of 351 pages, illustrated. Cloth, $1.75 net. Second Edition. Outlines of Nursing History 12mo of 370 pages, with 88 illus- trations. Cloth, $2.00 net. War Nursing 12mo of 172 pages, illustrated. Cloth, $1.50 net. Practical Physics for Nurses 12mo of 203 pages, with 100 illus- trations. Just Ready. PRACTICAL PHYSICS FOR NURSES By MINNIE GOODNOW, R. N. Author of " First-Year Nursing," " Outlines of Nursing History," " War Nursing," "Ten Lessons in Chemistry for Nurses," and "The Nursing of Children"; formerly Directress of Nurses, Milwaukee County Hospital; formerly Superintendent of the Woman's Hospital, Denver, and of the Bronsonl Hospital, Kalamazoo ; Specialist in Hospital Equipment WITH 100 ILLUSTRATIONS PHILADELPHIA AND LONDON W. B. SAUNDERS COMPANY 1919 Copyright, 1919, by W. B. Saunders Company PAINTED IN AMERICA PRESS OF W. B. SAUNDERS COMPANY PHILADELPHIA G FOREWORD THE criticism is often made that nurses are not intelligent about the handling of ordinary household . and hospital appliances, and that they make no attempt A 1 to understand the workings of plumbing, heating and ventilating apparatus, surgical instruments and appa- _, ratus, etc. The fault lies not so much in the nurse herself, nor in any lack of inclination to learn, as it does in the fact N that she has not been taught the laws which govern & some of the simplest activities of life. Very many ** nurses are not high-school graduates, and of those who are, not all have studied physics, nor know how to apply their knowledge to nursing. I Both Physics and Chemistry are of great impor- I tance to a nurse, because they are, at bottom, sciences of common life. The human anatomy is built in accord- ance with the laws of physics, and its movements are governed by them. It is necessary, therefore, if a nurse is to do intelligent work, that she should know some of the existing laws of physics, and how her patients, her hospital environment, and all her work are controlled by them. This subject has been a much-neglected one in hospital training-schools, chiefly because there was no text-book concerning it which was suited to nurses. 13 14 FOREWORD The following lessons have been prepared in the endeavor to give briefly some of the more important laws of physics, especially those which apply to daily life and to a nurse's work. No effort has been made to cover the whole subject, but only to select from it some of the principles which apply most obviously and directly to hospital life and to nursing. There are many laws of physics not even mentioned in the following pages. The apparatus and supplies for the illustrative ex- periments are of the simplest sort. Most hospitals will already have them in stock. The author wishes to acknowledge her indebtedness to Mr. William H. Smiley, educator, and to Dr. Horace Greeley Wetherill, surgeon, for careful and invaluable criticism of the manuscript, and to Miss Kinsey for cor- rection. MINNIE GOODNOW, R. N.. September, 1919. CONTENTS PAGE SUPPLIES 17 INTRODUCTION.. . CHAPTER I MATTER. ITS COMPOSITION. . . CHAPTER II MECHANICS 32 CHAPTER III MECHANICS (Continued) 41 CHAPTER IV HYDRAULICS 60 CHAPTER V PNEUMATICS 73 CHAPTER VI PNEUMATICS (Continued) 85 CHAPTER VII HEAT 98 CHAPTER VIII HEAT (Continued) 115 CHAPTER IX SOUND 130 CHAPTER X LIGHT. . . . 141 16 CONTENTS CHAPTER XI PAGE ELECTRICITY 163 CHAPTER XII THE X-RAY. RADIUM 180 CHAPTER XIII QUESTIONS FOR REVIEW OF PRINCIPLES AND ORIGINAL THINKING 190 INDEX . 197 PRACTICAL PHYSICS FOR iNURSES SUPPLIES THE following will be sufficient to enable one to make the experiments suggested in this book: Two quart flasks. Several large corks, one which shall fit flask, being perforated for two tubes. Glass tubing, pieces 6 to 18 inches long, two sizes; one piece bent into a U-shape. Rubber tubing, a few short pieces to fit glass tubing. One dozen test-tubes, with holder. A few microscope slides. Two bath thermometers, or other unmounted thermometers. One thermometer with scale to 250 F. A glass prism. A square bottle. Two lamp chimneys. Small quantities of sulphuric acid, copper sulphate, alum, sugar, touch-paper. APPARATUS If possible, bring into class or arrange to have class see the following: Axis-traction forceps. Bulb syringe. Electric cautery. Electric battery or cell, wet form. Electric toaster. Glass dressing syringe. Glass irrigator, with uterine point. 2 I 7 18 PRACTICAL PHYSICS FOR NURSES Head-mirror. Hypodermic syringe. Laryngoscope. Microscope. Obstetric chart, showing progress through pelvis. Rectal dilators. Reading glass. Stomach-tube. Sphygmomanometer. Urine centrifuge. Urinometer. Uterine dilator. x-Ray apparatus. INTRODUCTION Physics is the science of every-day life, and relates to most of our ordinary activities. The wind and weather, our houses and their contents, all work and play, all personal and commercial activities involve the laws of physics. We find ourselves annoyed or defeated because things "won't work" as we wish them to. Usually the reason is that we are attempting to make them act in opposi- tion to the laws of nature; we do this because we do not know what those laws are, nor to what extent they govern the world. A very elementary knowledge of these common laws will not only help us to do our daily tasks with greater ease, but will make them vastly more interesting and meaningful. A knowledge of physics is essential not only to the skilful use of hospital and nursing appliances and equip- ment, but to an understanding of the structure and func- tions of the human body. Dr. John C. Draper says: "There is not a tissue, organ, nor function of the body the proper comprehension of which does not involve a knowledge of the laws of physics. There is hardly a principle of physics which does not apply to the human body." The bony structure, the attachment of muscles, the 19 20 PRACTICAL PHYSICS FOR NURSES working of the heart, blood-vessels and respiratory organs, the acts of seeing and hearing, etc., all depend upon the laws of physics; while apparatus and ap- pliances for the treatment of disease can hardly be used intelligently or effectively without a comprehension of these same laws. Physics, in its logical limits, is an abstruse and diffi- cult subject. The fundamental principles are, however, extremely simple and can be understood even by un- trained minds. The mere committing to memory of some of its laws will serve to elucidate, throughout one's life, many appliances and occurrences. It is recommended that all the experiments given, however simple or familiar, be actually made in class, so that the full force of their meaning and application may come at the psychologic moment. CHAPTER I MATTER. ITS COMPOSITION MAN has always been eager to know of what things were made, and why inanimate objects act as they do. Physics and Chemistry are the two sciences which have been developed in this search for knoweldge. Chemistry is, in reality, a branch of Physics. Physics is the science of matter, its properties, changes, and motions. Matter is anything which we can see, feel, or handle; anything which occupies space. Simple and Complex Substances.- Some substances, or portions of matter, are simple; some are complex. Wood, for example, is a complex substance. If, in attempting to find out of what it is made, we divide it into minute pieces, we spoil or destroy it and cannot make it into wood again. If we heat it, we also de- stroy it. Iron, on the other hand, is a simple substance. If we divide it into ever so fine particles, we can still iden- tify it as iron; if we heat it ever so hot, as soon as it cools it is plainly iron ; we have not spoiled nor destroyed it by what we have done to it. The Ultimate Composition of Matter. With even the 22 PRACTICAL PHYSICS FOR NURSES simplest substance, after we have divided it into the smallest particles possible, we have not found out its real composition. We imagine that if we were able to divide it still further we might get at this knowledge. We find that scientists have been able, in what seem rather roundabout ways, but which are none the less exact, to accomplish this. Scientists have agreed that all matter is made up of tiny particles, called molecules, 1 which in a simple sub- stance like iron are all alike. It is agreed that molecules are composed of still smaller particles, called atoms, which may or may not be alike, but which together form a definite substance, either simple or complex. There may be few or many atoms in a molecule, the number varying from two to fifty or more. The assumption that matter is composed of mole- cules, which are themselves composed of atoms, is called the Atomic Theory, While merely a theory which it is not possible to prove, it so well accounts for every- thing which man has observed that it is generally ac- cepted as fact. A particle is the smallest subdivision of matter that can be obtained by mechanical means. A molecule is the smallest portion of matter which can exist alone. 1 It is estimated that there are 2,000,000,000,000,000,000,000,000 molecules in a drop. MATTER. ITS COMPOSITION 23 An atom is the smallest portion of matter which can exist in combination. Much modern research has been directed toward discovering the make-up of atoms; the electron theory has been formulated, and is by some scientists regarded as proved. This theory holds that each atom is com- posed of many infinitely small particles, which are called corpuscles. All of these corpuscles are electric- ally charged, part of them being positive and part negative; such being the case, they mutually attract one another and hold together to form the atom. Heat or other forces may loosen the attraction, so that some of the negatively electrified corpuscles may fall off, in which case they promptly attach themselves to some other atom. In certain substances which we call "radio-active" (See Chapter XII) corpuscles are more or less constantly and forcibly being expelled from the atom. Physics concerns itself with molecules. Chemistry concerns itself with atoms, and deals with the minute structures and. change of matter. Chemical and Physical Changes. If we heat water to the boiling-point, it changes into steam. If we sub- ject it to sufficient cold, it changes into ice. These are changes inform only. They are called physical changes. If we heat sugar, it melts, bubbles, boils, turns brown, gives off smoke, and finally becomes a charred, black mass, which is plainly no longer sugar. 24 PRACTICAL PHYSICS FOR NURSES Experiment. Take a small tin plate or dish, grasp it with for- ceps, place on it a small amount of white sugar, and hold it over a gas, alcohol, or other flame. Note the various changes which take place as the heating progresses, and the resulting black mass, which is almost pure carbon. This is a change in composition. It is called a chemical change. A physical change is a change in inform of a substance. A chemical change is a change in the composition of a substance. PROPERTIES OF MATTER The molecules of any substance, no matter how com- pact it seems to be, do not touch each other. In hard, firm substances they are close together; in soft or loose substances, further apart; but they are always slightly separated, the distance between being very little, yet enough to admit of motion. (See Heat.} The force which holds molecules in place or together is called cohesion. The force which holds atoms together is called chemical affinity. Cohesion holds molecules of the same sort together, as iron to iron. It is cohesion which makes an iron bar or a piece of wood firm and strong. Adhesion is the force which holds molecules of unlike substances together; for example, grease or dirt adheres to a utensil. Experiment. Press two plates of glass (microscope slides or window glass) together. You will find it somewhat difficult to separate them; it is most easily done by sliding, which separates them particle by particle. Wet the surface with water or oil and again press together; they will separate with still greater difficulty. The water or oil has greater adhesion than the glass. MATTER. ITS COMPOSITION 25 Reduce the force of cohesion and you increase the force of adhesion. Water or oil has less cohesion than glass i. e., is less firmly held together and therefore adheres more closely to the solid object. Grind rock salt to powder and it dissolves more readily; the cohesion in the large lump being broken up, adhesion between the salt and water, unlike substances, takes place more easily. Some of the properties, or inherent qualities, of matter are as follows: GENERAL PROPERTIES Extension is self-evident. Divisibility is also self- evident. Mobility. It is readily apparent that all substances are movable if sufficient force is applied. Impenetrability. One thing cannot occupy the same space as another at the same time. In instances where it seems to occur, as when a sponge is placed in water, it is merely that the molecules of one substance are between those of the other; the water, in this case, fits around the sponge, but is not occupying the same space. Experiment. Fit a funnel tightly into the mouth of a bottle, so that no air can pass around the stem of the funnel. Pour water into the funnel; only a little of it runs into the bottle, though the latter is apparently empty. Why? Because the bottle is already full of air. Loosen the funnel so that the air in the bottle can es- cape, and the water readily runs in. Difficulty in filling a hot- water bag arises when so large a stream of water is used that it blocks the exit of the air; a smaller stream overcomes the difficulty. 26 PRACTICAL PHYSICS FOR NURSES Inertia is a quality which all matter possesses to a marked degree. It is the property which makes matter, when let alone, continue to do what it is doing. If it is moving, it tends to keep on. If it is at rest, it tends to remain so. When we attempt to move an object, we feel the resistance of its inertia; when we attempt to stop a moving object, we also feel the resistance of in- ertia. A railroad train, for example, is difficult to either start or stop because of its inertia. A ball thrown from the hands stops only because of the pull of gravity and the resistance of the air; it tends to go on. Experiment. Place a card on the end of the finger, and a coin on the card. Strike the card lightly out of its place. The coin will remain, because of its inertia. Porosity. If we accept the molecular theory, all matter is porous. We usually apply the term, however, only to substances in which the quality is marked. Experiment. Take a quantity of loose absorbent cotton, and put it piece by piece into a small tumblerful of alcohol; nearly a quart can be put into the alcohol before the tumbler overflows. This is due to the porosity of both alcohol and cotton. Examine the stone filter from a water-sterilizing apparatus; one would say that it is not porous at all, yet water goes through it if under pres- sure. Porosity involves compressibility. All substances are compressible, but in varying degrees; it is merely a question of applying sufficient force to drive the mole- cules closer together. Air and all gases are readily compressible. Some solids are. Liquids are hardly compressible at all. MATTER. ITS COMPOSITION 27 Elasticity is a quality which substances possess in varying degrees. Some return to their original shape and size when compressed, some do to an extent, some not at all. Some substances are rapidly elastic, some slowly. SPECIFIC QUALITIES There are numerous special qualities, those possessed only by certain substances. Hardness occurs in varying degrees. Lead and wood seem hard, but may be easily cut. The diamond is the hardest known substance. Opacity, the quality which prevents light from passing through a substance, and transparency, the quality which permits its passage, are important qualities which vary greatly in different sorts of matter. Tenacity, that is, the ability to keep its particles to- gether, varies greatly in different substances. Its op- posite is brittleness. Important manifestations of te- nacity are: malleability, the quality which permits a sub- stance to be hammered into thin sheets, and ductility, the quality which permits it to be drawn out into fine threads. For example, gold may be beaten into sheets 4000000 inch in thickness, or so thin that 1 ounce will cover 100 square feet. Platinum is extremely ductile, but the finest thread we know is that of the spider's web; this is used in some scientific apparatus (the mi- croscope, surveying instruments) because no artificial thread is so fine. 28 PRACTICAL PHYSICS FOR NURSES Tendency to crystallize is a property of nearly all solid substances. Under favorable circumstances most substances tend to arrange themselves in the form of crystals. Experiment. Make a tumblerful of a saturated solution of alum, hot. Hang in it a circle of wire or stiff string and leave it overnight or longer; the circle will be covered with crystals. When water crystallizes, in freezing, the crystals require more room than the liquid and insist upon expanding; this is the reason that water-pipes burst when they freeze. FORMS OF MATTER Original Forms of Matter. Matter exists normally in three forms: solid, liquid, and gas. These forms are due to the weakness or strength of the force of cohesion between their molecules. Solids have their molecules close together and are held firmly; in liquids the molecules are farther apart and are held loosely; in gases they are still farther apart and tend to recede from each other. We think of these three forms as characteristic of certain substances themselves, whereas, in reality, they depend entirely upon temperature. Change of Form. Water is the best example of a substance which can be converted into the form of a solid, liquid, or gas. The same changes are possible in all substances, but with many the change is difficult to accomplish, and in some cases we have not yet learned how to do it without damage. For example, iron can be liquefied by applying a very high temperature; it may MATTER. ITS COMPOSITION 29 also be vaporized, but it takes an incredible degree of heat to accomplish it. Sugar is an example of a solid substance which, if carefully heated, may be changed to a liquid. Air, which we think of as a gas, can be made liquid by an extreme degree of cold; and it has even been changed into a solid mass by still greater cold. Diffusion. Solids may be diffused i. e., the molecules driven farther apart (1) by melting; (2) by solution; (3) by dialysis. Fig. I. Dialyzer (Bliss and Olive). In dialysis, the given mixture is placed in a small jar having a parchment paper bottom; this is set into a jar of pure water. Any crystalloid substance will soak out through the parchment into the water, where its presence may be discovered by chemical tests. This method is used for examining stomach contents in cases of suspected poisoning. It is not applicable to colloid substances. 30 PRACTICAL PHYSICS FOR NURSES BRANCHES OF PHYSICS Mechanics is the branch of physics which deals with solid bodies and the laws that govern them. Hydraulics is the branch which deals with liquids and the laws that govern them. Pneumatics is the branch which deals with gases and the laws that govern them. All three of these branches of science apply to daily life, to the human body, and to nursing. SUMMARY Physics is the science of every-day life. It treats of matter, its properties, changes, and motions. A knowl- edge of it is necessary in order to deal satisfactorily with household or hospital appliances, and for a correct understanding of the human body and its functions. Substances are simple or complex, i. e., composed of one or several elements. The Atomic Theory has been accepted because it accounts for all natural phenomena. It assumes that all matter is composed of molecules (the smallest por- tions of matter that can exist alone), which are them- selves composed of atoms (the smallest portions of mat- ter that can exist in combination). Physics concerns itself with molecules. Chemistry, a branch of physics, concerns itself with atoms. A physical change is the change in the form of a sub- stance. MATTER. ITS COMPOSITION 31 A chemical change is the change in the composition of a substance. Neither atoms nor molecules are in actual contact with each other. Atoms are held together by chemical affinity; molecules of the same sort by cohesion; mole- cules of different sorts by adhesion. The general properties or characteristics of matter are extension, divisibility, mobility, inertia, porosity, compressibility, etc. Some of the specific properties of matter are hardness, opacity, transparency, tenacity, brittleness, tendency to crystallize, etc. Matter exists in three forms solid, liquid, and gas. These forms are due to the strength or weakness of co- hesion between their molecules. This depends upon their temperature, which is a relative matter. As a rule, low temperatures cause matter to solidify, high temperatures cause it to liquefy, still higher cause it to become gaseous. Mechanics is the science of solids. Hydraulics is the science of liquids. Pneumatics, the science of gases. CHAPTER II MECHANICS LAWS RELATING TO SOLIDS Gravity is the force which the earth exerts on all sorts of matter. The earth pulls everything solids, liquids, or gases toward its center. This pull is exerted in a straight line, directly to the center of the earth. It is called the "line of direction." The exact direction of this pull is shown by the plumb line used by builders, artists, etc. A building which is "out of plumb" is likely to fall sooner or later, since the foundation may be unable to hold the top against the pull of the earth. It is this pull of the earth which causes objects to fall when not supported, makes the rain and snow de- scend, water to run down hill, etc. Weight. Another manifestation of the pull of the earth is what we call weight. Since the earth pulls equally on every molecule, it give us a convenient method of finding out the quantity of matter in a mass. Weight may be denned as the measure of the force of gravity upon an object. We must distinguish clearly between amount of matter, which refers to the number of molecules in it; and volume, which refers to the space it occupies. There is the same amount of matter in a pound of lead and a MECHANICS 33 pound of feathers, but there is a very great difference in the volume of the two. Weight indicates the amount of matter, but has no relation to volume. The specific gravity, or specific weight, of any sub- stance is its weight as compared with an equal volume of some substance taken as a standard. In the case of solids and liquids water is used as the standard (dis- tilled water at a temperature of 4 C.); with gases, hy- drogen gas at C. For- example, water is called 1.000. Gold is 19.5 (meaning that it is 19| times as heavy as an equal volume of water); copper is 8.788; coal, 1.270; urine, about 1.020; olive oil, .970; alcohol, .797; ether, .734; wood, .580; cork, .240, and so on. Fig. 2. Center of gravity. The Center of Gravity of an object is the point on which it will just balance itself, no matter in what position it is placed. It is, to state it differently, the weight center of the object. 34 PRACTICAL PHYSICS FOR NURSES Equilibrium is poise or balance between two or more forces. It causes a body to remain stable when there are forces tending to move it. The stability of an object depends upon the relation of its center of gravity to its base. A large base or a low-down center of gravity gives a greater stability. There are three sorts of equilibrium : (a) Stable when a body has a broad or heavy base and a low center of Fig. 3. Stable and unstable equilibrium. gravity. Examples, a cone or pyramid, a chair with four spreading legs, a quadruped. (6) Unstable, when a slight force will push an object over, that is, when its center of gravity is high up or falls toward one side of the base. Examples, a book standing on edge, a biped; extreme examples, a person standing on one leg, a tight-rope walker, (c) Neutral, when a slight force would not act upon it, nor change its center of gravity. Example, a three-legged stool, which stands well until a heavy weight is put upon one side of it, bringing the center of gravity outside of the base. Standing and Walking. Learning to stand or walk is MECHANICS 35 difficult because in the human body the center of gravity is high up from the ground (in the abdomen), and the base (the space enclosed by the feet) is small in pro- portion. Standing is the process of maintaining one- self in equilibrium on a small base. Walking is a proc- ess of alternately falling forward and saving oneself, the center of gravity being thrown first over one foot, then over the other. When one carries a load on his back he bends forward so as to have the center of gravity well inside his base; in carrying a weight in the hand he bends to one side for the same reason. Both standing and walking are accomplished by the combined action of many muscles, corresponding sets on each side pulling against each other to stiffen the framework and maintain it erect, while other muscles are moving a portion or the whole. The processes are exceedingly complex, and it is not surprising that it takes some months to acquire them. In using a cane or crutches one enlarges his base, thereby making his equilibrium more stable. ENERGY. WORK Whenever anything happens, or is done, there is some driving force behind it. This driving force is what we call energy. There are various sorts of energy, heat being the commonest; others are light energy, sound energy, muscular energy, electric energy, chemical energy, etc. All these bring about changes in matter. 36 PRACTICAL PHYSICS FOR NURSES One form of energy may be changed into another, as chemical action may produce heat, motion may produce heat, electricity may produce light, etc. All sorts of methods and appliances have been devised to ac- complish such changes. Energy is Indestructible. It may change from one form to another, but none of it is lost. When it dis- appears at one spot, it reappears at another. This is called the law of conservation of energy. Examples: coal (stored-up energy derived primarily from the sun) is burned, producing heat, which in its turn produces steam, which in its turn produces motion, which may be utilized in various ways; energy used in winding a clock reappears in the movements of the clock; electricity may be converted into sound by means of the mechanism of a bell. Many examples will occur to anyone. Work. Whenever any of the forms of energy mani- fest themselves, work is done. Whenever work is done, it means that an opposition of some sort, a resistance, is overcome, and some change in condition results. This change may be motion or any other form of action. WORK AND MOTION Whenever force produces motion, work is done. This amount of work is measured by the distance through which a body is moved multiplied by the force which moves it. MECHANICS 37 The fundamental laws of motion are those formulated by Sir Isaac Newton. They are as follows: 1. A moving body always follows a straight line, unless it is acted upon by another force which changes its direc- tion. A stone dropped from a height moves in a straight a b Fig. 4. a, Cream separator; b, detail of mechanism. line because it is acted upon by but one force, that of gravity. A ball thrown from the hand moves in a curve because it is being acted upon by two forces, the muscular energy which started it and the pull of the earth; the resultant of the two forces determines its path. 1 1 In neither case do we take into account the resistance of the air. 38 PRACTICAL PHYSICS FOR NURSES Centrifugal Force. Swing a weight around by a thread; one is conscious that it is trying to fly off in a straight line, but is held by the thread; therefore it moves in a circle; if the thread breaks, it flies in a straight line un- til pulled toward the earth by gravity. This tendency of a moving body to flee from a fixed center is called centrifugal force (from centrum, center, and fugere, to flee, Latin). The cream separator comes under this law. The milk is whirled rapidly and tends to fly into space, but is held back by the container. Cream and skimmed milk being of different densities, they separate in the whirling, the milk going to the outer part of the container, the cream remaining nearer the center. The urine centrifuge works upon the same principle, the lighter fluid being whirled to the outside, the heavier sediment remaining at the center. 2. Every change in motion is in proportion to the force or forces applied, and lakes places- in the straight line in which that force (or forces) act. 3. To every action there is always an equal and op- posite reaction. This principle of rebound is important and should be borne constantly in mind. Surprisingly enough, it has a counterpart in the realm of psychology; one notes how depression invariably follows excitement. MACHINES Machines are devices by which work may be done more conveniently or advantageously than without them. Man's hands are unsuited to many processes, so he calls MECHANICS 39 things, or combinations of things, to his aid. A pencil is a machine, strictly speaking, because it enables us to do easily what would otherwise be very troublesome. Machines convert a small force acting through a long distance into a great force acting through a small distance, or vice versa. In the first case we obtain greater power; in the second, we obtain greater exactness. Machines enable us to do things which without them would be too large for us, too rapid for us, or too exact for us, to accomplish. The body is sometimes referred to as "the human machine." This is in a sense correct, since many parts of it are constructed like other machines, and portions literally are machines. The Driving Force. A machine does not, by itself, literally do the work demanded of it. There must always be a driving force, and it is this which in reality does the work. The machine is that through which the driving force acts. Our most interesting and useful machines are those in which the power, or driving force, is some other than our own. Some machines are driven by horse power or the energy of other animals; some run by the forces of nature, as wind or water; steam engines use the energy stored up in coal; motor cars utilize that stored in gaso- line; electric appliances make use of the power obtained from electricity, which may in its turn be derived from some other source of energy. Types and Classes of Machines. Machines are of 40 PRACTICAL PHYSICS FOR NURSES two general types and are divided into six classes. The lever, the -wheel and axle, and the pulley are of one type; the inclined plane, the wedge, and the screw are of the other type. SUMMARY Gravity is the force by which the earth pulls everything toward its center. Its action produces weight, which enables us to know the amount of matter in any given mass or object. Specific gravity is the weight of any given substance compared with water as a standard. Equilibrium, the balance between two or more forces, may be stable, unstable, or neutral. Man, in walking upright, is in a state of unstable equilibrium, as his base is small and his center of gravity high up. The driving force behind any action is called energy. There are various forms of energy, light, heat, chemical, muscular, electric, etc. One form of energy may be changed into another, but none is ever lost or destroyed. Manifestations of energy are called work. This is an overcoming of resistance or some change in condition. Newton's three laws of motion cover the fundamentals. Machines are devices by means of which we may ac- complish things otherwise too large, too rapid, or too exact for us to do unaided. Behind the machine there must always be a driving force, such as that supplied by the strength of animals, by water-power, wind, electricity, gasoline, coal, etc. There are six classes of machines. CHAPTER III . MECHANICS (Continued) THE lever is the most common and most useful ma- chine; in fact, nearly all machines are, in a sense, va- rieties of lever or combinations of levers. A lever is a rigid bar, straight or curved, resting on a fixed point or edge, called the fulcrum. It is used to move weight or overcome resistance. The hand-spike is a common form of the simple lever. There are three things concerned in the action of a lever: 1. The weight to be lifted or moved. 2. The power which shall move it. 3. The fulcrum, or point upon which the movement is to take place. There are three classes of levers: In the first class the fulcrum is between the weight and the power. In the second class the weight is between the fulcrum and the power. In the third class the power is between the fulcrum and the weight. In all cases it is possible to calculate, by mathematical means, the exact power that will be required to move a given weight through a given distance. In levers of the first class, the fulcrum being between the power and the weight, the weight moves in an op- posite direction to that in which the power is applied. Com- 41 42 PRACTICAL PHYSICS FOR NURSES mon examples are the tack lifter, the can opener, the pump handle, the grocer's scales, etc. II III -A. Fig- 5- The three classes of lever. Scissors, pliers, artery clamps, etc., are double levers of the first class, the weight being between the blades, MECHANICS 43 the power the force applied by the hand, the fulcrum the joint. The bivalve speculum is a double lever, the weight being the walls of the cavity into which it is in- Fig. 6. Levers of the first class: A, Uterine dilator; B, can opener; C, claw hammer; D, chisel. (Butler, "Household Physics.") 44 PRACTICAL PHYSICS FOR NURSES serted. The long uterine dilator with two handles is also a double lever. (The small, graduated dilators are wedges, not levers.) If the power arm of the lever is long and the weight arm short, the work is more easily done than if the re- verse is the case; the distance an object can be moved in this case is lessened, but force and time are gained. Fig. 7. Levers of the first class, with long and short power arms: a, Paper-cutting shears; b, metal-cutting shears. (Butler, "Household Physics.") In the large uterine dilator great force is gained because of the excessive length of the handles. It is for this reason that metal-cutting shears have long handles, while scissors for cutting paper have very short handles; the first requires great power; the second, little power but a long sweep. In the human anatomy there are many portions which can be used as levers of the first class. In grasping an object with the hand, the object is the weight, the ringer joints are the fulcrum, the flexor muscles the power. In putting the head back the joint at the top of the spine is the fulcrum, the head is the weight, and the muscles at the back of the neck are the power MECHANICS 45 (see Fig. 11). In pushing an object with the foot, the object is the weight, the ankle- or knee-joint is the ful- crum, the leg muscles the power. AF Fig. 8. Levers of the second class: a, Nut-cracker; b, wheelbarrow. (Butler, "Household Physics.") In levers of the second class the weight being be- tween the power and the fulcrum, the weight moves in Fig- 9- Levers: a, Jaw of human being; b, foot when we rise on the toes. (Butler, "Household Physics.") the same direction as that in which the power is applied. The wheelbarrow is a common example. The nut 4 6 PRACTICAL PHYSICS FOR NURSES cracker and the lemon squeezer are double levers of the second class. Fig. 10. Levers of the third class: a, Sugar tongs; b, fork; c, forearm; d, spoon, knife, potato masher, pliers, wrench, and fire tongs. (Butler, "Household Physics.") MECHANICS 47 In lifting the weight of the body to the tip-toes, the toes form the fulcrum, the calf muscle the power. In this class of lever also, if the weight is near the ful- crum, and the power arm is long, the work is more easily accomplished. In levers of the third class the fulcrum is at one end, the weight at the other, the power between them. Com- mon examples are the fork and spoon, as used in eating. Sugar tongs and thumb forceps are double levers of the third class. It will readily be seen that this form of lever is not of advantage in lifting weights, since the power must always be greater than the weight to be lifted. It is used chiefly when we wish to produce a rapid motion through a considerable distance, or to facilitate small, exact movements. The flexing of the forearm constitutes a lever of the third class. The weight is the hand and anything it may contain, the fulcrum is the elbow-joint, the power is the biceps muscle, applied at its point of attachment below the elbow. It is clear that this is not designed for the lifting of great weights, but for quick, dextrous movements. The bending of the head forward is done by a leverage of the third class; the sternomastoid muscle is the power, the sternoclavicular attachment the fulcrum, the head the weight. Another example is the use of the lower jaw in masti- 4 8 PRACTICAL PHYSICS FOR NURSES cation. The weight or resistance is the food between the teeth, the fulcrum is the articulation near the ear, the power is the masseter muscle. Complicated Movements. Most of the movements of the body are complicated, two or more fulcrums and a number of muscles being brought into play. (This is also true of a great many machines.) We commonly Fie. ii. Muscles of neck as levers (Dorland's Dictionary). lift a heavy object by using the muscles of the shoulders and back, somewhat assisted by those of the arm, the elbow and shoulder-joints being the fulcrums, and the action being a combination of W e rs of the first and third classes. An example of a powerful double lever is observed when the body is raised from a squatting position. The knee-joints are the fulcrums, the power is the leg MECHANICS 49 muscles. In machinery such an arrangement is called the toggle-joint or Stanhope lever. OTHER MACHINES The crank-and-axle (or wheel-and-axle) is a variety of lever, a sort of continuous lever. Common examples are the coffee-mill, the clothes-wringer, the bread-mixer, Fig. 12. The crank and axle: a, Treadle of sewing machine; b, bread mixer. (Butler, "Household Physics.") the Dover .egg-beater, the ice-cream freezer, etc. The weight is the material to be acted upon or moved, the fulcrum the axle or bearing upon which the movement takes place, the power the muscle of the operator, acting through the wheel or crank. The driving mechanism of a sewing machine is a 5 PRACTICAL PHYSICS FOR NURSES combination of the wheel-and-axle and a lever (the treadle). The pulley consists of a grooved wheel called a sheave, set into a frame, the block; the weight to be lifted is at- tached to one end of a rope which runs over the sheave, a b Fig. 13. The pulley: a, Simple; b, compound. the power being applied at the other end of the rope. Adding more sheaves multiplies the power, so that very little force may be needed to move a considerable weight. The extension apparatus used in fractures of the thigh is a simple pulley, the weight being the body of the patient, the power being the weights attached at MECHANICS 51 the foot of the bed. The action is not movement, but merely pull. The superior oblique muscle of the eye is a pulley, also the omohyoid muscle. The inclined plane needs little explanation, it being obvious that a weight can be pushed or pulled up an incline with much less effort than it can be lifted verti- cally to the same height. P Fig. 14. The inclined plane. A series of rules have been formulated by which one may calculate the exact force necessary to move a given weight up an incline of a given angle. The screw is a curved inclined plane. It is com- monly used to increase the pressure of one object upon another, usually with the purpose of holding one or both in place. It is also used to produce a small, very exact adjustment. The adjusting mechanism of the micro- scope is an example of how a screw changes a long move- ment into a short, exact one. The screw-driver is a lever which assists the placing of the screw. In forms of screw like the letter press, the beef-juice press, the meat grinder, the bread slicer, 52 PRACTICAL PHYSICS FOR NURSES etc., the handle is a lever; in the two latter the handle is a modified lever, the crank and axle. The wedge is a double inclined plane which is forced in between two surfaces or portions of matter in order to separate them or in order to hold them against re- sistance. The power used is applied in the form of blows rather than as a continuous push. The wedge is a very powerful machine. Fig. 15. The wedge. Knives are wedges with delicate edges. Rectal di- lators and the small uterine dilators are round wedges. The mechanics of obstetrics is most interesting, though somewhat complicated. The child is the weight, and the tissues of the cervix, the vagina, and perineum the resistance to be overcome. The muscles of the ab- dominal wall and of the uterus are the power. If the MECHANICS 53 woman is on her feet, gravity assists the process. If she is in bed, additional force may be obtained by the pull of her arm and leg muscles against some firm objects. The child's head, in combination with the sac of amniotic fluid which acts as a cushion to prevent in- jury to the tissues, acts as a wedge to force the tis- Fig. 16. Child's head acting as wedge (DeLee). sues apart. Note how the power is applied inter- mittently during the pains. The great force employed is appreciated by anyone who has actually delivered a child. The birth canal is not straight, but much curved, being about one-third of a circle. It is, in effect, a series of inclined planes, which in succession change the direction of the child's progress. 54 JPRACTICAL PHYSICS FOR NURSES If the natural forces are not sufficient to produce the necessary progress, the obstetric forceps, a double lever Fig. 17. Diagram showing the advancement of the head through the pelvis (Leishman). Fig. 18. Forceps: a, Obstetric; b, axis-traction. of the first class, is used to assist the process. With them the obstetrician holds the progress that has been MECHANICS 55 made, or aids it by pulling in the direction that the other forces are pushing, and in which the child's head is moving. Since the passage is not straight, the for- ceps must be curved, and the pull must be made in the direction that the child's head is traveling. "Axis- traction" forceps enable the operator to get his pull in the proper direction while the head is still far up and the curve is very great. Watch the direction taken by the handles of the forceps during a delivery and note how great a curve they describe during the descent of the child. At first they point somewhat downward, and at the end of the delivery almost upward. FRICTION When the surface of one body is made to move over that of another, a resistance to the movement is felt. This resistance is friction. If perfectly smooth surfaces could be obtained, there would be little or no friction; but this is impossible. There is always more or less roughness, and therefore some resistance. Roughness increases friction, smoothness reduces it. Without the action of friction we should find it ex- ceedingly difficult to hold anything in place; everything would tend to slip from our hands or slide away at a touch. Without friction we should be unable to walk or drive, as we should constantly slip. It is an impor- tant factor in life. There are two sorts of friction, rolling and sliding. 56 PRACTICAL PHYSICS FOR NURSES The former gives the least resistance. In machines with which we wish to do work easily we make use of smooth, rolling surfaces, since they move with greater ease. Fig. 19. Friction. Sliding and rolling. The so-called ball-bearings, where there are a number of parts which roll over one another, produce a very easy-running joint. CoronoicL -Ulna* Fig. 20. Construction of joint (after Toldt). On the other hand, a brake set to a wheel changes rolling into sliding friction, and so checks the motion. Lubricants reduce friction; it is for this reason that we oil or grease machinery. MECHANICS 57 Great friction produces heat (see page 98) which may interfere markedly with the action of a machine. The human body presents very perfect examples of reduction of friction. The joints are nearly all rolling joints, rather than sliding, thus offering the least re- sistance to movement, and constitute a great economy of force or power. The cartilages that cover the working portions of the joints are practically perfect in their smoothness, and the synovial fluid is a fine and perfect lubricant, continually renewed. It is when joints are roughened or dried by disease that they work with difficulty. SUMMARY The lever is one of the most used of mechanical devices. There are three essentials to its -action the weight, the power, and the fulcrum or point on which the motion takes place. There are three classes of levers; they vary according to the relative positions of weight, power, and fulcrum. Examples of each sort, may be found among appliances in every-day use, and in muscular actions taking place in the human body. Many of the body movements are complicated, being produced by the combined action of many muscles, and involving two or more joints as fulcrums. The wheel-and-axle is a continuous lever. It is used in many domestic appliances. $8 PRACTICAL PHYSICS FOR NURSES The pulley consists of a sheave set into a block; over this runs a cord attached to both weight and power. A pulley with several sheaves facilitates the moving of a weight. The inclined plane is another machine which de- creases labor in the lifting of weights. The screw is a curved inclined plane with a rather complex mechanism. It has many applications in domestic and hospital life. A wedge is a double inclined plane driven by inter- mittent blows; it is used when great force is needed to separate or hold objects. Most of our so-called machines are complex combina- tions of two or more of the simple machines. An obstetric delivery is essentially a mechanical proc- ess. The child's head acts as a wedge to overcome the resistance of the cervical, vaginal, and perineal tissues. The force employed is that of the abdominal and uterine muscles; it may when necessary be aided by the pull of obstetric forceps. The birth canal being curved prac- tically a series of inclined planes the shape of the forceps and the direction of the pull must correspond with it. Friction is the resistance between two surfaces, one of which moves over the other. It is inevitable, since a perfectly smooth surface is impossible to obtain. It is of advantage in holding or placing objects, but is a disadvantage when we wish to move them. Sliding MECHANICS 59 friction may be changed to rolling friction, and therefore reduced, by the use of lubricants. The human body presents many excellent examples of the advantages of the reduction of friction. CHAPTER IV HYDRAULICS LAWS RELATING TO LIQUIDS Properties of Liquids. Liquids tend to keep their molecules together, but not strongly. The force of their cohesion is not enough to overcome the action of gravity; therefore they "run" to the earth unless pre- vented by other forces. Different liquids possess different degrees of cohesion. We note this in the varying size of drops of different liquids. Castor oil, for example, coheres rather strongly, and its drops are correspondingly large. Alcohol has less cohesive force, and its drops are smaller. Chloro- form drops are very small. (Sixty drops of water make a dram by measure. Carbolic acid takes 118 drops to make a dram; tincture of aconite, 150; ether, 180; chloroform, 240.) Liquids are very much less compressible than solids; in fact, most of them are not compressible to any appreciable extent. This is an important characteristic in their use in practical life. Water is the most common and the most important liquid. It is therefore used as a standard for measuring the qualities of other fluids. 1 1 Specific gravity, or the weight of a substance compared with the same amount of water, as before noted, refers to both liquids and solids. 60 HYDRAULICS 61 Liquids vary greatly in their weight. Note the dif- ference in weight of equal-sized bottles of oil and of sulphuric acid. A cubic foot of cold water weighs 62.42 pounds. In hot water the molecules are farther apart, therefore it requires a little more space and weighs a little less. Fig. 21. Water pressure on bottom of container. Pressure in Liquids. If 1 cubic foot of water is placed on top of another, the weight is 124.84 pounds; that is, the pressure upon the bottom of the container is that amount. So, if water is 5 feet deep, the bottom of the container must bear a weight of more than 300 pounds to the square foot. From this one can see that the 62 PRACTICAL PHYSICS FOR NURSES pressure in deep water is very great. It is for this reason the great pressure that sea divers cannot Fig. 22. Irrigator hung high. The whole column of water makes pressure (DeLee). go to any great depth; and they must always wear suits of material heavy enough and stiff enough to re- HYDRAULICS 63 sist the weight of the water and keep it from crushing them. The irrigators which we use in hospital work also illustrate the pressure of fluids. If an irrigator is hung high, there is more water in the tube, i. e., it is deeper, Fig. 23. Irrigator hung low. There is very little pressure, because the depth of water in irrigator and tube is not great (DeLee). and the pressure exerted upon its lower part, upon the small surface which is the caliber of the tube, is that of the whole column of water in both irrigator and tubing. If hung low, there is very little pressure, and the water when released finds its escape easily and gently. It 64 PRACTICAL PHYSICS FOR NURSES is, we observe, the depth and not the amount of water which regulates the pressure upon the bottom. Pascal's law formulates another important fact. The pressure in a liquid is tlie same in all directions.. Solids press only downward; liquids press sideways and upward as well. Experiments. (a) Fill a hot-water bag quite full of water, getting out all the air; lay on the hand; press the top or side of the bag and note that the resistance is as great in one place as in another. (b) Let water run from an irrigator to the tubing of which is at- tached a uterine tip, one having several holes; note that the water runs with equal force from all of the holes, not more forcibly from the bottom hole, as one would expect. The discomfort of a patient from a full bladder is due to this law, because the urine is pressing in all directions. A water-bed is useful because it makes pressure upon the surface of the patient's body equally in all places, Fig. 24. Water-bed. unlike the ordinary bed, which presses harder against the more prominent portions. It is this law which causes the force of the heart-beat to be distributed evenly throughout the body, so that blood-pressure is the same in all arteries, large or small, far away from or near to the heart. It is this law which makes the sac of amniotic fluid so HYDRAULICS 65 efficient yet so gentle a dilator in obstetric cases. It presses in every direction at once, yet without possi- bility of injury to the tissues. Water Seeks its Own Level. Because water presses in all directions it runs through any available openings, and stops only when there is a resistance ahead of it equal to the force or weight behind it. Our city water systems are based upon this law. The source of supply is a lake or river higher than the city, or, failing this, the water is pumped up to a reservoir Fig. 25. Diagram of artesian well. or standpipe situated upon high ground. (The supply in this case may be a low river, a spring, a well, etc.) All water which is permitted to flow from this reservoir or source of supply attempts to rise as high as its origin. The great height of the large body of water gives us the desired pressure. Water coming from a hose used to sprinkle a lawn would rise to the top of the water in the reservoir from which it flows if it were not for other 66 PRACTICAL PHYSICS FOR NURSES forces, the friction against the inside of the hose, the re- sistance of the air, and the action of gravity. Artesian wells are produced by water trying to find its level. The source of the water is in the hills that are above the well; the water, soaking through the earth and running along an impervious layer of rock or clay, finds an opening and pushes up through it, or, more correctly, is pushed up through it by the body of water behind it. In some cases artesian wells spout high above the ground. Buoyancy. Push a block of wood under water and release it; it rises to the surface and floats with its bulk almost out of the water. This is due to the buoyancy (not of the wood, but) of the water, i. e., its tendency to raise all bodies to its surface. This is due to the facts already discussed, that pressure increases with depth and that it acts in all directions. This results in the pressure upward on the bottom of a submerged object being greater than the pressure downward upon its top. If the additional weight of the body itself is not more than this difference of pressure against top and bottom, the object floats. Heavy substances, which displace less than their own weight of water, sink. Light substances, which dis- place more than their weight, float. The law of Archim- edes a floating body sinks until it displaces its own weight of liquid is a summary of the above facts and other similar ones. HYDRAULICS 67 Swimming. The human body, partly because of the air in its tissues and in the lungs, is but slightly heavier than water, so that it floats just below the sur- face. With slight effort a portion of the head mouth, nose, and eyes can be kept above the water, making it possible for a person to swim. The balance is so nearly equal that it takes only a small quantity of water getting into the lungs and replacing the air to cause one to sink, i. e., drown. 1 Experiment. A fine needle, especially if dipped in oil, can be made to float on water if it is laid gently and evenly upon the surface. Its weight is not sufficient to overcome the force of the cohesion of the molecules of water. Loss of Weight in Water. On account of this quality of buoyancy, all objects weigh less in water than they do in air. The water pushes up or sustains a con- siderable portion of their weight. Experiments are easily made which prove this. Hydrometers. The hydrometer is a device used for ascertaining the specific gravity of liquids. It is based upon the law of Archimedes. It consists of a tube weighted at one end with the requisite amount of mer- cury, and marked with a scale. The point marked is the point to which it sinks in water. Placed in a liquid 1 Bodies of drowned persons sometimes float after being in water a considerable length of time. This is because chemical changes have taken place, producing in the tissues gases that are lighter than water. 68 PRACTICAL PHYSICS FOR NURSES heavier than water, it tends to float; in a liquid lighter than water, it sinks deeply. The scale is arranged so that it designates the specific gravity. The urinometer and the cream tester are hydrometers. The urinometer is of impor- tance because: (1) If urine is of low specific gravity, i. e., nearly that of water, it indi- cates that not enough solid matter is being eliminated from the body. (2) If it is of high specific gravity, there is too much solid matter, i. e., not enough fluid is being taken, or some abnormal con- dition is causing the elimina- tion of materials that should remain in the body. The specific gravity of nor- mal milk is 1029. If the cream tester shows it lower than this, there is a suspicion that water may have been added. Excess of cream may change the test somewhat. Fig. 26. Hydrometers. HYDRAULICS 69 CAPILLARITY Capillarity, or capillary attraction, is the quality that causes liquids to adhere to solids in opposition to the force of gravity. Its action is most marked in fine tubes and in porous substances. Experiments. Hang a wick of gauze over the edge of a tumbler half full of water; water will soon be dripping from the outer end of the wick. Hang up a cloth so that its lower edge or corner dips into water; the whole cloth will gradually become wet. Dip the corner of a lump of sugar into coffee or cocoa; the whole lump very quickly becomes colored with the fluid. Place a white carna- tion or other white flower for a few hours in a bottle of red ink; the ink stains it, especially along the veins. It is capillarity which causes the sap to rise in plants, since they have no circulatory system. It is this force which helps the small blood-vessels of the intestines, the lacteals, and the lymphatics, to absorb liquid nourish- ment from the intestinal contents. It is this which makes possible the capillary circulation and the flow of blood in the very small veins; the force of the heart- beat pushes the blood only part way through the smallest vessels, but capillarity assists and continues the process, especially when it is necessary for the blood to ascend, in opposition to gravity. It is capillarity upon which we depend largely in our drainage of wounds. Gravity, of course, assists the process, but a gauze wick will drain even though the fluid to be removed must go upward. Drainage stops when the gauze becomes blocked with solid particles. 70 PRACTICAL PHYSICS FOR NURSES Waterproofed cloth is that which has been treated with something which prevents capillary action. DIFFUSION Diffusion is the force that makes fluids tend to mix when they are brought into contact. Experiments. Put some solution of blue vitriol in the bottom of a test-tube; tip the tube and with a medicine-dropper put carefully on top of it a layer of water; left undisturbed, they gradually mix, till the whole is blue. Put milk at the bottom of a test-tube and water on top; watch them mix. Osmosis. A similar process takes place through thin animal or vegetable membranes. It is called osmosis. It applies only to solutions of crystalline substances, however. Experiment. Procure a pig's bladder or other thin animal membrane; put some colored fluid into it a solution of potassium permanganate is good and hang it in or touching some water. The colored fluid will penetrate the membrane, and color the water, the latter exchanging places with it. It is the combination of this force with capillarity which makes possible the absorption of stomach and intestinal contents. Osmosis occurs rapidly through the stomach wall. Note that the drinking of hot water causes diuresis within fifteen or twenty minutes, long before the fluid could have reached the intestines; it is absorbed directly from the stomach. Medicines given in hot water are quickly absorbed and an effect produced in a short time. Osmosis effects this by carrying the medication through the stomach wall into the circulation. HYDRAULICS 71 When a saline cathartic is given, the saline matter absorbs much water from the tissues of the intestines, pulling it through the membrane of the intestinal wall; the excess of fluid so obtained produces a watery or very soft bowel movement. Edema. We find that osmosis takes place toward the more concentrated solution, and that saline substances increase it. When, therefore, in certain diseased con- ditions the kidneys fail to eliminate a sufficient quantity of saline material from the body and it accumulates in the tissues, it produces an osmosis of the body fluids and we have the condition which we call edema. SUMMARY Cohesion is not strong in liquids, therefore they are easily affected by gravity. Liquids are very slightly compressible. It is the depth of water rather than the amount pres- ent which determines the pressure upon the bottom of the container. This law is illustrated by the ordinary hospital irrigator. The pressure in a liquid is the same in all directions. This is illustrated by the fact that quality of pulse is the same in all parts of the body. Water seeks its own level. City water systems, artesian wells, irrigators, etc., illustrate this law. A floating body sinks until it displaces its own weight 72 . PRACTICAL PHYSICS FOR NURSES of the liquid. This law governs the use of the urinom- eter, etc., and explains ability to swim. Capillarity is the property that causes liquids to rise in small tubes and other restricted places in opposition to the action of gravity. It is this force which aids the capillary circulation, absorption from the alimentary canal, the drainage of wounds, etc. Waterproofing is the prevention of capillarity. Diffusion is the property which causes liquids to mix when they are brought into contact. When it takes place through a membrane it is termed "osmosis." Osmosis is especially active in saline solutions; it takes place toward the more concentrated solution. This explains the occurrence of edema when there is faulty elimination. CHAPTER V PNEUMATICS LAWS RELATING TO GASES Properties of Gases. In gases the molecules are con- siderably separated and have no cohesion; in fact, they are always trying to get farther apart and fail only be- cause outside forces prevent them. Experiment. Produce dense smoke by burning sugar or setting fire to "touch-paper" (unsized paper soaked in a strong solution of saltpeter and dried). The smoke quickly becomes diffused through the room, even though there are no apparent currents of air. The law of diffusion of gases corresponds to that of liquids. Gases which are in contact tend to mix. If it were not for this law we should, in a closed room, be- come quickly surrounded by a lake of impure air which we should be compelled to rebreathe.; this is prevented by the rapid diffusion of gases, and by the fact that air is so readily disturbed, so that the opening of a door or the moving of an object in the room keeps the air "stirred up." Elasticity of Gases. Gases, because of the tendency of their molecules to get away from each other, are very elastic. Note the great elasticity of the air confined in an air-cushion, an automobile or bicycle tire. Observe 7? 74 PRACTICAL PHYSICS FOR NURSES the rapidity and force with which it escapes when even" a small opening is made. Compressibility of Gases. All gases are compressible, most of them to a very marked degree. It is well known that a large quantity of oxygen, compressed air, carbon dioxid, etc., may be forced into a tank. Illuminating gas is collected in very large iron tanks, the weight of which is sufficient to hold it in place. The tank is set in a deep cistern of water, through which the gas passes with great difficulty, and the tank rises or falls in it according to the amount of gas it con- tains. Pipes are laid from this tank; the weight of the tank and the elasticity of the gas itself force it through the pipes in every direction and with an even pressure. Air is the Most Important Gas. It is composed of a mixture (not a combination) of two gases, nitrogen (four-fifths) and oxygen (one-fifth). 1 If it were not for the constant action of the law of diffusion of gases the air would be an irregular mixture, somewhat like marble cake, with spots and streaks of the two gases, causing endless inconvenience and danger. The air surrounds the earth, but is not very deep over its surface, about 50 miles. There is probably some air as far up as 200 miles, but at a distance of 7 or 8 miles above the surface it is very rare, i. e., its molecules 1 There is also a small amount of carbon dioxid, watery vapor, and of various impurities in minute quantities. PNEUMATICS 75 are far apart. Man has never been more than about 5 miles (25,000 feet) above sea-level. Air has Weight. Air is matter and all matter is at- tracted by the earth. In the case of air, the force with which the molecules try to get away from each other is slightly less than the attraction of gravity. The weight of air is 1.28 ounces per cubic foot. Some gases are lighter than air, some heavier. A balloon rises in the air because it is filled with some gas lighter than air, usually hydrogen. Air Pressure. Air is like water in that the pressure increases with its depth. It is denser at the bottom, i. e., near the earth's surface, or, rather, at sea-level. Fig. 27. Diagram illustrating increase of pressure with depth. Illustration. Place several pillows in a pile; note that the lower one is much flattened, each successive one less so. This illustrates how the weight of the upper air compresses the lower portions and drives the molecules closer together. The air pressure at any point equals the weight of the column of air which is above it, the height of this column being the distance that the atmosphere extends. 76 PRACTICAL PHYSICS FOR NURSES It can be readily seen that this pressure is greater at sea-level than at an altitude. Experiments. Tie a piece of thin rubber (the wrist of an old rubber glove is suitable) over the mouth of a small funnel. Connect the funnel with a piece of rubber tubing. With your mouth with- draw some of the air in the funnel and clamp the tube. The rub- ber stretched over the funnel will bulge inward because of the external air pressure. Remove the rubber, leave the tubing. Place the funnel against the cheek, if it is small enough to fit snugly; withdraw air by means of the tubing. The cheek will be pulled into the funnel, or, in reality, pushed in by the air in the tissues and the cavity of the mouth pressing outward. The blood in the small vessels is also forced in shown by the redness which appears because the blood-pressure from within remains the same while the air pressure from without is relieved. This is the principle of dry cupping, which is used to bring blood to the surface of a small area. The breast-pump works upon the same principle. Fig. 28. Breast-pump and cupping-glass. The air pressure at sea-level is 14.7 pounds to the square inch. Our bodies, therefore, are constantly sustaining a weight of about 15 tons of air. We do not feel it (1) because the solid portions of the body are very resist- ant, (2) because the body fluids are not compressible, PNEUMATICS 77 (3) but chiefly because the gases in the body are of the same density as the air and so equalize the pressure. The feeling of pressure experienced by those who climb high mountains is due to the fact that the air in their tissues does not escape nor become thin as rapidly as that outside. The ear drum has been known to burst at a high altitude on account of the difference in air pressure on its two sides, especially if the eustachian tube be partly blocked- Effects of Air Pressure. Scientists of the old times formulated a law, "Nature abhors a vacuum." Later scientists explained this law by the discovery of the laws of air pressure. A vacuum is the term used to describe an enclosed space where there is little or no air. A perfect vacuum has never been obtained. When we begin to expel the air from any space, more air tries to get in. If a possible opening is blocked by liquid or solid material, the external air will, if possible, push the liquid or solid in ahead of itself in its struggle to enter. In using a medicine-dropper we press the air out of the rubber bulb and dip the glass point into a liquid; since the air outside, pressing on all the liquid in the container, is kept away from the entrance to the tube by it, it forces the fluid into the tube. Experiments. Push an empty tumbler mouth downward into water. Note that the water rises only a very little way into the glass, being kept out by the air which is there. Note the shape of the surface of the water inside the glass. Push a large cork into the water and release it under the tumbler. What occurs, and why? 78 PRACTICAL PHYSICS FOR NURSES Fill a glass tube with water, close the upper end with the finger, and dip the lower end in water. The water remains in the tube because of the pressure of the air upon the surface of the water in Fig. 29. Tumbler inverted in water, showing how the air prevents the water from entering. (Note shape of water surface.) the vessel. When the finger is removed from the top of the tube, the air pressure comes directly upon the water in the tube and causes it to fall. Fig. 30. Upward pressure of the air (Butler, "Household Physics"). Fill a small tumbler brimful of water; press a smooth piece of paper on top; holding the paper tightly, turn the tumbler upside down; remove the hand which holds the paper in place. The paper PNEUMATICS 79 remains. The water also remains in the tumbler. Both are held in place by the air pressure from below upward, the glass prevent- ing the air pressure from above from acting upon the water. (Grav- ity is also partly overcome by the adhesion between the wet paper and the edge of the tumbler.) Vacuum Fountain (Fountain in Vacua). Have a quart flask fitted with a tight cork, through which is a Fig. 31. Fountain in vacua. small glass tube reaching halfway to the bottom. Ex- haust as much air as possible from the flask by suction upon the tube, put the ringer tightly over the end of the tube, dip the end in water, and release the finger. The 8o PRACTICAL PHYSICS FOR NURSES water will rush into the flask with force enough to pro- duce a fountain. Hero's Fountain. Put some water into the flask, well above the end of the tube. Blow through the tube until the air inside is compressed as much as possible. Fig. 32. Hero's fountain. Place the finger over the end of the tube to keep the com- pressed air from escaping. Release it suddenly, and the confined air will force water out through the tube like a fountain. Applications of the Laws of Air Pressure. Hypoder- mic or dressing syringes to work well must have pistons PNEUMATICS 8 1 that are air-tight. When the end of the syringe is dipped in fluid and the piston drawn back in an attempt to create a vacuum, the pressure of the outside air forces the fluid up into the syringe and so fills it. Any air remaining in the syringe will force the fluid out ahead of it, so long as the syringe is held with its needle pointing down. If we wish to get the air all out of the syringe, we must hold it with the needle pointing directly up, so that the lighter air may make its exit through the needle before the heavier fluid. (In injecting under the skin, we force the liquid, by means of the piston and our fingers, into the resisting tissues.) The atomizer is dependent upon the principles of air pressure. A stream of air from the bulb is forced over the top Fig> 33- Hypo- dermic syringe of the upright tube which dips into the (Morrow). reservoir of liquid; this reduces the ex- ternal air pressure upon the contents of this tube. The pressure upon the surface of the body of fluid in the reservoir pushes the fluid up this tube in consequence. The jet of air from the bulb at the same time blows the liquid away in the form of a fine spray. The siphon is a tube bent into a U shape, open at both ends, one arm being longer than the other. Fill the entire 2 PRACTICAL PHYSICS FOR NURSES tube with water, and holding a finger over the end to prevent its escape, dip the short arm into a container of water, dropping the longer arm outside. Release the Fig. 34. Diagram of atomizer. finger and the water will run out through the siphon so long as the short arm dips into the water in the container. The explanation is as follows: The pressure upon the fluid in either arm is the atmosphere minus the weight Fig- 35- The siphon. of the water in that arm. This makes the pressure greater in the short arm and less in the long arm; the fluid moves in the direction of least resistance. PNEUMATICS 83 The stomach-tube is a siphon. The short arm is in- side the stomach, the long arm outside. Water poured into the container (the stomach) will run out again when the long arm is lowered, providing the tube re- mains filled with water while the change in the position of the long arm is being made. If all the fluid in the tube is allowed to run into the stomach before reversing, there will be no siphon action. 1 The bulb which is placed on some of the stomach-tubes is a variety of pump (see Chapter VI) which can be used instead of the siphon. SUMMARY In gases the molecules have no cohesion, but tend to flee from each other. Gases are very elastic and very compressible. Whenever gases are brought into contact, they dif- fuse as liquids do, but more rapidly. Upon this fact depends our ability to ventilate rooms and buildings. Air is the most important gas. It is a mixture of four-fifths nitrogen, one-fifth oxygen, a little carbon dioxid, watery vapor, and other materials. It covers the earth's surface 7 or 8 miles deep, being more dense at sea-level because of the weight of the upper layers. Air pressure increases with depth. The air pressure at sea-level is 14.7 pounds to the square inch. We do not feel it because the solid por- 1 It is wise to have this actually illustrated in class, using a pitcher or other container in place of the stomach. 84 PRACTICAL PHYSICS FOR NURSES tions of our bodies are very resistant, because the body fluids are not compressible, and because the body con- tains considerable air and so equalizes the pressure outward and inward. The breast-pump, the hypodermic, the dressing syr- inge, cupping-glasses, the stomach-tube, etc., are based upon the laws of air pressure. Explain the working of each of them. CHAPTER VI PNEUMATICS (Continued) LAWS RELATING TO GASES Pumps are machines for lifting and transferring fluids from one place to another. Their action depends upon air pressure. They are of two sorts lifting and force- pumps. The lifting pump has a tube which dips into water or other fluid, at its lower end, where there is placed a valve that opens only inward. High above this, at- tached to the pump handle, there is a "sucker," a tight-fitting piston pierced by a valve that opens only upward. When the sucker is raised by means of the handle (a lever), air pressure is taken off the surface of the small body of water in the tube; the air pressure upon the surface of the water in the well forces it up the tube. (See Laws and Experiments in Chapter V.) When by the action of the pump handle the sucker is lowered, the weight of the water in the tube closes the valve at its lower end and prevents the contents from running back into the well. By repeating the process, more and more water accumulates in the tube until it is high enough to run out of the spout near the top. The force-pump has a one-way valve at the lower 85 86 PRACTICAL PHYSICS FOR NURSES end of the tube the same as in the lifting pump, but its piston is solid. The second valve is at the side of the tube, and opens only outward, emptying into a tube which forms the spout. When the piston is raised, the Fig. 36. Lifting pump (Butler, "Household Physics"). main tube partly fills with water, exactly as in the lift- ing pump; when it is lowered, the weight of the water closes the valve at the bottom. The movement being PNEUMATICS 87 repeated, continued pressure forces the side valve open and the water up the side tube and out at the spout. A Davidson (or bulb) syringe is a variety of force- pump, at least so far as the action of the valves is con- cerned. Pressing the bulb while the end of the tube dips into water tends to create a vacuum, and when the pressure is released, water runs up into the tube and Fig- 37- Force-pump (Butler, "Household Physics"). bulb. A second pressure forces the water in the tube against the valve at its lower end and closes it, at the same time pushing it against the outward-opening valve of the rectal or delivery tube and forcing the wa- ter out through it. The bulb of a stomach-tube works exactly as does that of a Davidson syringe. 88 PRACTICAL PHYSICS FOR NURSES The heart is a force-pump. The hollow organ re- sembles the bulb of a syringe, except that the force which contracts it is furnished by the heart muscle itself, situated in the wall. There is no piston, but the expansion and relaxation makes the cavity alternately larger and smaller. When the auricles contract, the one- way valves (the bicuspid and tricuspid) are forced open and the blood runs into the ventricles. When the Fig. 38. Dilation and contraction of ventricles of the heart. ventricles contract, these valves are forced shut by the weight of the blood against them, and the semilunar valves are pushed open; the blood is thus forced out into the vessels, from the right ventricle to the lungs for purification, and from the left ventricle into the aorta, and so through the body. The impulse of the heart- beat as it forces the blood out through the arteries is transmitted to the very ends of the vessels and starts the blood on its way through the capillaries. In the return venous circulation the flow is largely PNEUMATICS 8