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From Fij^uro 4 tli(^ ]on«^tli of A is seen to ha tlnvo tinios that of li with a j)art of A roniainin^x; fi'xl ^>y compariii'^ tluj lines how many times thcj length of li contains that of the remaining part of A. ^ A B Firt. i. How many times then is the length of A that of IJ 'i Experiment 6. Find how many times the length of your desk contains that of your lead pencil. 1. Quantity- That which can be expresse«l as so many times, or such a fraction of, another of the same kind is a quantity. For example, the len<^th of each line in the above ii (( 2. What is the measure <>f uach of i\w alutve t net tciiiptiraturu / 2. Why do UHtioiiM in-osorvo curofully oopios of thoir staiMlttnls of moasurements ? 6. Metric System of Measurements. Hy general agreement, what is tenned the ]\Ietric System of Mejisurements has been adopted in most countries for scientific use. It has also been a .•{•2808i«»l> 3 1)3708 •.•i28081M) •3JKi71 •032S()» •O.SU37 (;();{L>8()!> I.N VaKKS. 1 •01>3<;;?31 •()l(M>3(i3 1 inrli 1 foot 1 yard - I 2 ■53{M)54 centimetres, .'i '0470449 decimetreH. •014;W.'i48 metres. PHYSICAL SCIENCE. 11. Approximate Values: Metre — 39*37 inches ; a ynrd mu\ oue-teiitli. Centimetre = g of an incli. Inch =25*4 millimetres. * Kilometre == § of a mile. 12- Denominations Most Commonly Used. The m., "85 cm., 93 Km. ? SIEASUHEMKNTS. 7 8. The iiieasme of a curtain length is .'io when the metre is tlie unit <»f length, what wuuhl he its nieasnre if the centi- metre were tlie unit { 13. Scale. The method employed in tlie experi- meiita, pages 1 and 2, of measuring by constantly repeating tlie standard, would be found to be too slow and too inaccu- rate for general use. For more rapid and accurate measurements a scale or rule is used. This consists of a bar, generally wood or steel, on which is laid off the unit, its subdivisions and nml- tiples. The length of the scale and the number of subdivisons of the unit will depend on the purposes for which it is to be used. Metric rules are generally graduated to millimetres. Fig. 5 shows a metric scale one decimetre in length. 14. Method of Using a Scale. The accuracy, of the result in measur- ing with a scale will depend upon the care with which the length to be mea- sured is compared with the scale. r^-i — b 1 CO — -TT - m ;^_ E^ - _z: u> - — m OJ — - 't- ;_- - - «»> ^ — - - — (M . X — ■ o z ef -v» [- or i.|U| 1- Ok) =^ UJ -z — ~i ^.L.^ Fig. 5. Since the observer has to depend on his eyesight, lie nmst be careful so to conduct liis observations that the coincidence of the marks shall be real anHg('. Express the result in centimetres. 2. Measure the length of a frM)t rule in centimetres. From your measurement calculate the ecjuivalent of an inch in centi- metres. 3. Measure tlu; distance hetw on the points A and 13 (Fig. 9). AX Fi«. 9. XB Estimatf^ to the tenth of a millimctn', 4. Make a drawing of the top of your lal)oratory table on a scale of one-twentieth. What arc the dimensions of the chawing in centimetres ? Fio. 10. 5. Draw a horizontal line A B 27 cm. long, and from l> a vertical line B C, 36 cm. long. ^Measure the distance A C. C. Estimate with 3'^our eye the length of your pencil in centi- metres. Verify the result by the use of a scale. 10 PHYSICAL SCIENCK. Do the same with the lengths of several other objects which you V)elieve to be not more than 15 cm. hni\tu\\\\\\\\\\\ \v\\\\\\\\\u\^ ^i^i2^ Fio. 12. Find the ratio of the circumference to the diameter of a circle b} comparing the reault obtained in this experiment with the mean of those obtained in Experiments 10 and 11. If the correct result is, the circumference is 3*1410 times the diameter, what is your percentage of error ? 1 3. Measure the diameter of any small sphere — a wooden ball or a large marble — with the blocks .used in Experiment 12. rims : i >^///f?/f/ >}!!ll)n/l "// / / / /y i I 1 1 I I I I H \ \\T yUV \ \VV ^ '. ■^\^^V\V,V\\ \\\V\n^>T Flu. la Take the mean of the measurements of seveial tliameters. 12 PHYSICAL SCIENCE. 14. MeaHure by means of a strip of pa{>er tlie circuinf<^renco of the snme spliere. Ohttiin the diamettn' by dividing the circumference by 3"1416, and compare this result with that o])tained in Experi- ment 13. r Q E 1 ::^ :^ FlO. 14. FlQ. 15. FlO. 16. For practical purposes mechanics use instruments called calipers or guages for measuring tlie diameters of spheres, cylinders, etc. Figures 14, 15 and 16 show some common foi*ms of these instruments. ni.— Metric Measurement of Surface. 16- Fnndamental and Derived Units. We have seen that in the measurement of length the unit employed is selected arbitrarily. Physical quanti- ties are so related to one another that by choosing certain MRASURRMENTS. 13 1 SQUARE eleinentaiy units all the othei*8 may be derived from the«e ill virtue of those relations. The former are called fundamental, the latter derived, units. 17. Unit of Surface. From the relation between length and surface, if a unit of length is assumed, a unit of surface may be derived from it. The most convenient unit of surface is a s(|uare, a side of which is the unit of length. For example, when the centimetre is taken as the unit of length the scjuare centi- metre (sq. cm.) is the unit of surface. 18- Measure of Surface. The measure of any surface is, of course, the iiumlxir of times the unit surface must be repeated to coNer it. QUESTIONS. 1. If a side of a square is one decimetre, how many surface units will be recjuired to cover it, the unit surface being the H(£uare centimetre ? Observe Fig. 18. Fio 18-Sqcarb Drcijiktrb( \ Size). Hi h 14 PHYSICAL PfiKNCK. 2. (/Jill llu! unit of smfate lir in any otliLT foriiiH iluiii tluit of a l\. Draw (»n tlio blackboard a H<|uare, a side of which is one metre. By drawing lines as in Fig. 18, divide it. into square decimetres. How many are there of them ' 4. Draw on ]»aper a s<|uare centimetre. l?y dividing it ny lines show hf)W many H(|uare millimetres it contains. 5. From the answers to 3, 4 and 5, fill up the l>lankH in the fol- lowing tables : — I square metre = sq. dm. = — sq. cm. = — sq. mm. 1 square millimetre = . • sq. cm. =" — sq. dm. == ... sq. mm. C. The surface of a book measures 35*.5 s) the iiuiiihur of culiiu iiiilliinetruH in h ciihic ctMitiiiiutre. r>. From tliuHiiHwerM to 4 and 5 till in the hlanks in the fttllowing tuhle: — 1 cubic ij:«*tre = c.dm.= — c.cm. - ...cmm. 1 cubic miiUmetre = . c.cm. = — c.dm cm. niit ? tiiat of a 7. How many cuhic centimetres in .531 5r> cm., 2.'ii')'78 c.nnn. i 8. If the measure of a volume is 6.324*56 when the cuhic centi- metre is the unit of v«>Iume, what would be its measure if the cubic metre were the unit ? 9. How many cubic millimetres in 50*23 c.cm., .32*75 c. m. ? 10. A litre is a cubic decimetre. How many (a) cubic centi- metres, (/>) cubic metres does it contain / 11. What is the measure of a litre when 5 cm. is the unit of length ? Observe 21. Experiments in the Measurement of Volume. The following relations l^etween the measures of solids and the measures of their lineal dimensions are assumed : A cube, the edge of which has a units of length, contains a^ units of volume. A rectangular bar, of which the edges are respectively a^ b and c units of length, contains abc units of volume. A cylinder, the height and radius of which have h and r units of length respectively, contains Tzr^h units of volume. 2 I ' J tft I'llYRK'AIi SCIKNCK. A sphere, the, radius of wliirh has r units of length, ((iii- taiius 1 77/3 units of volume. 1. Make of wood a cuIm', an (m1«,'«! of wlufli is 1 nii. 2. Make of wcmkI a litre }»lo<-k, that is, a cuImi tlio <*dg€? of which is one decimetre. IIow many cubic centiiniitrcs does if coiitHin i 3. Find the internal volume of a crayon hox. 4. Determine, by moasurin«^ its depth and its diameter, the capacity of any cylindrical vessel. Clive the result in cubic centimetres. 5. Find the volume of any spherical ball. G. Make a rectan«j;ular prism of hard wood, 1 s<|. cm. in sec- tion and 15 cm. long. (Iraduate one of the longest sides in centimetres. (Fig. 20). y y / y / / / / / J / / / / / 5 Fig. 20. What is the volume of the bar between any two consecutive division ujarks? li!''^ MKA81TRKMENTS. 19 nisecutive 1. What, is the volume of thu w.itor dis- pliiced by one division of the bar < 2. What is the internal volmno of the tube between any two consecutive division marks 'i 9. After it has been graduated, fill the tube A (Fig. 21) with water, and under it place a small test-tube B. Regulating the flow by the clamp, let the water pass slowly from A to 13, stopping the flow whenever one division of A has been emptied, and marking the j)osition of the surface of the water in B. Continue until the tube B is graduate purposes for which they are to be used. In using a burette be careful to see, (1) That the buretie is held in a vertical position. (2) That the reading is taken from the position of the centre of the curved sur- face as seen when the eye is level with it (Fig. 24). Fia. 22. # Fio. 23. .INCO?«??CT.. CORRCCr Fig. 24. 10. With a standard burette or graduate measure the volume of water ])ptween any two graduation marks on the tubes A and B (Fig. 21). MEASUREMENTS, 21 11. Run 10-5 c.cin. of water from ;i biirette into a •xraduate. Does the graduate indicate the same volume i 12. Measure the internal volume of a small bottle by filling it with water and measuring the volume of the water (a^ with a burette, (6) with a graduate. Compare the results. 13. Measure with a burette 100 c.cm. of water, and pour it into a small Florence flask that will just contain it. Mark on the neck of the flask the position of the surface of the water. 14. Use the flask prepared in Experiment 13 to make (a) a 500 c.cm. flask, (6) a litre flask. Fio. 25. 15. Determine the volume of water required to raise by one centimetre the levels of water contained in a beaker and in a test-tube. (Fig. 25). 1. What is the ratio of the area of the surface of the water iii the beaker to the area of the surface of the water in the tube 'if I •I' I' l:' 22 PHYSICAL SCIENCE. 2. Wh;it w(»ul(l he the area of the surface of the water in a tube, if one centimetre in length on a tul>e indicated 1 c.cni. of volume ? 3. With which can the volume of a liquid be measured with the greater accuracy, a narrow graduated vessel like A (Fig. 25), or a wide one like B ? Why ? 16. Obtain the volume of an irregular solid, for example a pebble, by placing it in a narrow graduated tube containing water, and noting the volume of water it displaces. How could you obtain by a similar method the volume of a solid lighter than v/nfcer ? -V: as ' iifijiiuiaH«u> (HxVlTKH IT. MATPEll. I. Matter and Energy. Ou'- knowledge of the pheiionien.'i of tlie external world is derived throu<;i;h the medium of our senses. An extended study of these phenomena leads to the belief that tlie sensible univ«>rse is made up of but two things, or entities, matter and energy. It is difficult to give precise definitions of these terms. Energy will be treated of in another chapter. In a gen- eral way, matter may be defined as that which occupies space. From this description we recognize at once wood, iron, Walter and other solid and liquid bodies as matter. 1. Is a Gas, Like Air, Matter? Experiment. >- To answer this question, take a clear glass timiltU'r filled with air, and, holding it in a v(M-tieal position with l)<>ttoiii upwards, push it down into water. (Fig 26). 1. Does the water till tli'- tumbler ? *2. Does the uir occupy spuce ? 15. Is it matter i [ -•3 1 F..1. 20. 24 PHYSICAL SCIENCK. .^ i 2. Substance, Body, Mass. Our most superficial observations show us that matter differs in kind and varies in quantity. Water differs from stone, sugar from salt, and air from ammonia. A definite kind of matter is called a substance, and a definite portion of matter, a body. The quantity of matter in a body is called its mass. II.— States of Matter. Experiment 1. Take any solid body, such as a piece of wood or iron, lift it and place it on the table. 1. Does the whole move when a part moves ? 2. Is its shape chan(;ed ? 3. What is necessary to change its shape ? 3. Solid. A solid is a body that possesses rigidity, that is the power to resist change of shape. Experiment 2- Put your fingers into a vessel containing water and try to lift the water ou^ With a si)0()n dip the water out of one vessel and place it in another of a different shape. Pour water on a horizontal surface. Try to grasp a handful of air. 1. Is tlie whole of the water lifted out when a part is raised ? 2. Has it a definite shape of its own ? 3. What shape does it take ? 4. Can you lift a piece of air and carry it from one point to another ? Has any portion of air a shape of its own i MATTKH. 25 Water and air belong to the class of bodies known as Fluids. 4. Fluid. A fluid is a body which possesses no rigidity what^ ever, but which is deformed by the action of any force, however small. Experiment 3. Take a glass tube (Fig. 27) closed at one end, till it nearly full of water or any other lic^uid, insert a piston and push in on it. Is there any change in the volume of the liquid 1 Fio. 27. Fio. 28. Experiment 4. Repeat Experiment 3, liavingthe tul)e filled witli air instead of w ater. 1. What change takes place in the volume of the u'r i 2. What causes the change ? r ' I III > 26 PHYSICAL SCIENCK. Experiment 5. Place an elsistic I'uhbcr ])allo(m paitiully filled witli air under the receiver of an air pumj) (Fig. 2S). Exhaust the air from the receiver. 1. What change in tlie vohune of the air in the balloon takes place ? 2. How did removing the air frcun the receiver affect the pressure to which the balloon is subjected / 3. What caused the change in the volume of the air in the balhxm ? 5. Liquid— Gas. On the basis of compressibility and expansibility fluids are divided into two classes, liquids and gases. A liquid is a highly incompressible fluid, that is, it is a body which possesses a definite volume but no definite shape, moulding itself into the shape of the containing vessel. A gas is a compressible and expansible fluid, that is, it is a body which possesses neither deflnite shape nor definite volume, taking not only the shape but also the volume of the containing vessel. 6. How Does a Powder like Flour or Sand Differ from a Liquid? Experiment 6. To answer this / the same substance are alike, but those of differ- ent substatices are different. Jf, Molec\dcs are not in permanent contact tiHth one another, but are separated bij inter molecular spaces which are often large as com- pared irith the molecules thetnselres. 5. The molecules hare a rapid to-and-fro motion and are constantly strikinif their neighbours and rebounding from them, thus keeping open the spaces beta'ee}i them. 28 PHYSICAL SCIRNCE. .'I 1/ '> 1^ 8. Molecular Oonditions of the States of Matter. Ill each of the states the molecules nva in Hctive vibratory, or to-and-fro, motion. In solids the molecules are not supposed to move from I)lace to place throuj^h the body, but each has, relatively to the othei*s, a definite position in which it moves. In fluids the molecules are free to move from any one part of the mass to any other, and in consequence licjuids and gases take easily the shapes of the vessels in which they are placed. In liquids the molecules are not so free to move as in gases. They simply glide around among one another, encountering and jostling those near them ; while in gases, since the intermolecular spaces are larger, they have periods of free motion and appear to be in a continual state of repulsion. Hence gases are com- pressible and expansible, while liquids are practically incompressible. (^KAITEH Iir. MOTION. 1- Position- J. Describe the position of tlie town of Barrie. 2. Can you describe its pi^sition without reference to some other jioint ? .3. Can you do so without making use of dist^mce and e accurately and in several ways the position »>f the point A on this page. xA From considerations such as the foregoing it becomes evident that we cannot even think of the absolute posi- tion of a body (i.e., of its position without reference to any other body). Hence we say that position is only relative. We also see that position involves the simple notions of distance and direction. Thus the position of A with respect to B may be made clear by stating the distance of A from B, and the direction of A ft'om B. 2. Motion. 1. What do you mean by say'ng that a railway train is in motion i 2. What would you mean by saying that one passenger in that train is moving alwut while another passenger is at rest ? 3. Are the seats in the railway coach moving ? With respect to what are the seats moving ? 4. With respect to what are they at rest ? Is the earth at rest ? [29] 30 PHYSICAL SriENCK. Il Ml •m m Fi'oin tlic }iiis\v«'i'H t() tlic abovo (jiic.stioiis it appears til at motion, like position, is relative. Wv nay that A is moving relatively to B when the position of A with respect to B is changing continuously. We often speak of tlie motion of one body without irientioiiing another Ixxly. In sucli a case the body not mentioned is easily understood, (iive examples of this. 3. Velocity. Often we have occasion to consider not only the total change of position wliich a body undergoes, but also the length of time during wliicli this change of position takes place. A train moves from Montreal to Toronto, ',ilV.i mile.s, in i> hours. 1. What is its averjvge speed or velocity I 2. When you »iy that the velocity of tliis train is 37 miles per hour, what velocity are you using as a unit in terms of winch to express tlio velocity of the train i 3. What unit are you using when you say that this sauie vch>city is .*i,2.5(i feet per minute ? 4. Ts your unit velocity a fundamental miit or a derived unit? 5. If the latter, from what is it derived ? 6. How many rods does the above train move in one minuted How many yards in one second '^ 7. Describe the train's speod in terms of the unit derived frf)m (a) the rod and the minute, (/>) the yard and the second, (c) the foot and the second. A i)5*rticle moves a distance of 16'42m. in 4 seconds. Describe its average speed in terms of each of the following units : — (a) ( )ne metre per second ; (/>) one centimetre per second ; (c) one centi- metre per minute ; (rf) one centimetre per second. MOTIOK. M it appoars ^ Hay that ition of A y without ; body not e.s of this. 'the total t also tho tioii takes II t> liours. miles per f wliicli to no velocity I unit? ■i mi mite i ived from [1, (o) the Describe a) ( )ne lie ceuti- The velocity of a particle is the time-rate at which it is moving, and the measure of the average velocity during a given interval is obtained by dividing the measihre of the distance traversed during that interval by the measure of the interval. If you divide the measure of the dic^tance in feet by the meuHure of the interval in hccoiuIs the quotient is the ineivsuro of the speed in terms of what unit i Experiment 1- Suspend a weij^ht liy means of a wire or a strong cord (Fig. 29). Make the distance from the point of suspension to the centre of the weight 993 mm. This will serve as a pendulum, and will swing in a period of one second approximately. Prei)are a straight, stiff plank about three metres long. On one side fasten lengthwise two narrow strips (as in Fig. 30). Place the plank on a table with tliis side upward and with one end enough liigher than the other to cause a mai'ble to roll down the channel between tlie two strips readily but not too rapidly. Set the pendulum swinging, and while A is counting the swings ^'^" ^" aloud, let B hold a marble at a marked point near the higher end of the teoard. When A says one, B should set tln^ marble FiQ. 30. free, but follow it with his hand, in which he should hold a I I 32 PIIYSK'AI. SriKNCK. /■^ 'T.' pirro of clijilk. Am A says two, lliifMi, four, etc., 1» should mako a mark on tlio Iwiard at tlio point at which tho nuirhle is at that instant. With a graduated ruler or tape determine the di.stanee tra- vers«»d ])y the niarhle dunnodies moving at clianging speed. 4. Velocity of a Particle at a Oiven Instant. If the motion of a body is not changing, it m obxious that its average velocity during any interval is its actual velocity at any instant of that interval. 1. If the motion of a body is changing, how would you approxi- mately determine its velocity at a given instant ? For example, how would you ascertain the speed of a railway train at the moment it passes a given point on the track ? 2. With the apparatus described above, find approximately the speed of the marble (a) at the middle of the 1st second, (h) at the middle of the 2nd second, (c) at the middle of the 3rd second. If a body is moving with a var3ring speed its actual speed at a given instant may be defined as the average speed during an infinitely short interval containing that instant. MOTION. 33 5. Acceleration. It' tlio inution of a pMrticlo is cliJiii;;in«;, the particle is said to 1)0 accc'lonitod poHitively or nrj^ativoly, acconlinj^ as its velocity i.s increasing or diniinishinj^. 1. At ono instant the volocity of a railway train is 40 iniloa per hour, 80 niinutus lator its velocity is IM) inilos pur hour. How much has its velocity changed during the whole interval / 2. How nmch, on the average, during eacli minute V 3. How much during one hour ? 4. Describe fully the change per niiinite in the velocity of this train. 5. Describe the change in the velocity of the marble as it rolls down the plank in the experiment above. ^ Rate of change of velocity is called acceleration. 1. In answering question 4 above, what unit of acceleration did you use ? 2. Answer the same question, using another unit. 3. Is your unit fund ament'il or derived? 4. If the latter, from what is it derived ! 6. Uniform Acceleration. If the velocity of a body is increasing or decreasing by e(iual amounts in all ecpial intervals of time, its acceleration is said to be uniform. When the acceleration is uniform the average velo- city during any interval is the actual velocity at the middle instant of that interval, and hence is equal to half the sum of the initial and the final velocities. 3 [ .'9 \, 34 Ifr PHYSICAL SCIENCK. QUESTIONS. 1. A particle moving with uniform acceleration has a velocity of 10 cm. j)er second, and 10 seconds afterwards has a velocity of 20 cm. per second. What is the acceleration in cm. per second per second ? 2. A particle moving wi(!h unifonn acceleration has a velocity of 10 feet per second at the beginning of a minute, and a velocity of 30 feet per second at the end of the minute. What is its average velocity during the minute ? How far does it move during the minute ? What is the acceleration ? 3. A particle starting from rest is accelerated 2 feet per second per second. What i ^ its velocity at the end of 5 seconds ? How far does it move during the 6 seconds ? 4. A particle which is uniformly accelerated has at iha beginning of a minute a velocity of 10 feet per minute, and at the end a velocity of 10 feet per sectmd. What is its accelersttion ? Whit is its average velocity ? How far does it go during the minute ? 5. A body starting with a velocity of 10 cm. per second is accelerated 5 cm. i)er second per second. How far does it go during one minute ? What is its final velocity ? CHAPTER IV. ENERGY AND WORK. Tlie terms energy and work are used in pliysics in niucli tlie same sense as in every-day speech. 1. Energy. 1. What is meant by the statement that a man possesses much energy ? 2. Can anything except man possess energy ? 3. Can inanimate objects possess energy ? 4. What would you accept as evidence that a body possesses energy ^ 5. Mention examples of bodies possessing energy. Energy is capacity for doing work. 2. Work. Let us consider the nature of work. If yon tln'ow a cricket ball you do work on the ball. 1. During what time are you doing this work ? 2. What is being done to the ball during this time ? A careful study of the subject leads to the belief that whenever a portion of matter does work it accelerates the motion of other portion of matter. Often this acceleration is not so obvious as in the example g^iven above. For example, if a lump of lead is laid on an anvil and is struck with a hannner the motion of the lead as a whole is not accelerated, but we have reasons [35 J I! 36 IMIYSICAL ftCEKKrR. m I (to be spokiju oF heroafter) for thiiikin<^ that tlie uiolo- cule.s of the lead liave tlieir motions accelerated. Again, if a body, say a pound weight, is lifted at a uniform speed vertically, work is certainly done, yet there is no acceleration of the body as a whole, nor have we reason to suppose that its particles are made to vibrate any more rapidly. Here it is supposed that the work done on the pound weight is not stored up in the pound weight itself, but is passed on to whatever that energy may be Virhich causes gravitation. The pound weight, however, is now ready to receive this energy at any time, and hence is said to possess potential energy. Experiment 1- Take the plank used in Experiment 1, page 31, and two glass spheres an incl; or more in diameter (large marbles will answer). Elevate one end of the plank so that if one of the spheres is very gently started to roll down the plank it will not stop, but do not elevate it enough to cause it to start from rest. Call the spheres A and B. Start A down the plank and send B after it au a greater velocity. Observe what takes place when B overtakes A. 1. How is B's velocity changed ? 2. How is A's velocity changed ? 3. Wliich sphere has work done upon it ? 4. What body does the work ? 5. What cliange which you can observe iakes place in the body doing tlie work ? ENK|{(;V AND WORK. 37 6. Can B do work on A (i()ngs so as just to touch the surface of some water (Fig. 31). 1. What evidence have you that the fork possesses energy ? 2. Is there i ly visihlu motion of tlie fork in this case ? 3. What is the nature of this motion ? 4. Mention other examples of similar motion '? 5. When the tuning fork is struck, what sensation is experienced by all within a moderate distance from the fork ? 6. Upon what part of the body is work done to produce this sensation ? 7. As the fork is not in contact with your ear, how can it do work on your ear ? 8. What is there between the fork and the drum of your ear? d. If this medium receives encriry from the fork and transfers it to your ear, what is the condition of this medium while it possesses the energy ? Experiment 4. Place a radiometer near a hot Innly such as the flame of a gas burner or a red-hot metal ball (Fig. 32). 1. What evidence have you that work is being done on the radiometer ? 2. What is the result when the radi- ometer is exposed to the sun light ? 3. Is the sun in a position to do work directly on the radiometer ? 4. What must therefore possess the energy after it leaves the sun and before j«,Q 82. i^ J"* received ])y the radiometer ? 1,(1. 40 PHYSICAL SCIENCE. ^1 'U We are thus led to see that tliere are various forms of energy, all doubtless possessed by matter of some kind having some mode of motion. 1. Energy of bodily onward motion. 2. Energy of bodily vibration. 3. Energy of molecular vibration, or heat. 4. Radiant energy, or the energy possessed by the intangible medium called luminiferous ether, which we suppose fo fill all space. 5 T r. vgterious forms of energy which produce gravltwki/jiju chemical affinity, magnetic attraction, magnctJCr repnlsion, etc., and which may be forms of radiant eno/ ^rv. 6. The energy of the electric current, which is well exhibited in the electric motor. This also is probably a form of radiakt energy. 4. Potential Energy— Kinetic Energy. When a body is in a position to be accelerated by energy of the form No. 5 above, as, for example, when a mass is raised above tlie surface of the eartli, it is customary to say that this body possesses potential energy. Other examples of this kind are a piece of iron separated from a magnet ; two substances such as coal and oxygen which have a tendency to chemically unite ; the spring of a watch wlien wound up, etc. The raised weight, bent spring, etc., do not, strictly speaking, possess actual energy, but only the possibility of acquiring it whenever left free to move. I p:\er(jy and work. 41 Since, however, tlie source wlience tliey receive it is not apparent, it is customary to speak of tlieni as if already possessing tlie energy whicli they have the power of acquiring. Actual energy, tliat is the energy possessed by a boiiy in virtue of its mass and its velocity, is often called kinetic energy. 5. Transmutation of Energy. When energy is changed, as it may be, from one form to another, we say that energy has been transfoi'med or transmuted. I 6. Conservation of Energy. Careful experiments, which are quite beyond the limits of an elementary w^ork, have led to the following general conclusion, which is now universally accepted. In all transformations and transferences of energy no energy is created or destroyed. In short the total of the energy of the universe is a constant quantity. This general conclusion is known as the law of conser- vation of energy. 7. Law of Nature. When, as in the case above, from many observe kii(>w that a Ixwly is s\i)»ji!ct, to a force, and that body is not apparently accclurated, what infurencc niust yon draw i 3. CSounterbalancing Forces. Experiment 3. Hold any object in your liand a few feet above; tl»e tablo and h't «ifo your hold. 1. What ovideneo have yon that this olgt'ct is subject to a force ? 2. Did this force exist before you let go your hohl ? 3. What evidence of its existence had you ? 4. If while you were holding the body this force had instantly ceased to exist, what would have happened ? The tenn a piece of silk or on your coat sleeve, ami having moved B and C away, touch A with it, allowing the ball to roll over the rubbed surface so that all parts of its surface may come in cont^ict with it. Now move B toward A, not allowing them to touch. What do you observe ? Do yoa find one or both balls subject to a force ? 3. Move B and C toward each other. Have you evidence of any unusual force ? 4. Move C toward A, and what is the result? 5. Roll A in the fingers for a moment and again bring it near B and C. . What is the result ? In the above experiment A lias been electrified l)y bringing it in contact with the rubbed vulcanite. We expended muscular energy in electritiying thii vulcanite, and hence some other form of energy must have resulted. The precise nature of this energy is not known, but we see that it can produce force. Experiment 5. Electrify loth A and B and bring tboni near each other. 1 . What is the result in this case ? 2. Bring each separately near C, and what is the result ? 3. How many bodies are concerned in any force of whose exist- ence you have evidence ( 4. Can ycni electrify C from A or B ? Try. 6. What is the result when an electrified ball is rolled in the fingers ? )\ 50 PHYSICAL SCIENCE. 7. Magnetic Attraction and Repulsion. Experiment 6. Fig. 34. Magnetize three sewing needles by rubbing them in one direction with a strong magnet (Fig. 34). Suspend two of them by silk fibres, as shown in Fig. 35. 1. What position does each a.ssunie when left to itself at a con- siderahle distance from the other ? What is the result if it is disturhed ? 2. What evidence have you that the needle is subject to one or more forces ? A magnetized needle suspended so that it is horizontal and is free to rotate about its point of support in a liori- zontal plane is called a compass needle. The end having a tendency to point toward the north is called the north pole, and the other end is called the south pole. ! FOROK, 51 Experiment 7- Take the remaining niagneti/ed needle in your hand and hold, first one end and then the other, near the north pole of one of the suspended needles. 1. What results do you observe ? 2. Of what forces have you evidence '( Repeat the experiment with the south pole of the sus- pended needle. Experiment 8- Place the two suspended ne(Hlles so that the north pole of one shall be near the s«)uth pole of the other. 1. Do you find one or both needles subject to force ? 2. What attractions or repulsions are observed when («) like poles are })rought near each ^>ther, (/>) unlike polos ^ Experiment 9- Stretch, in a direction north and south, a wire through which an electric current is flowing, first above and then below a compass needle (Fig. 36). Fi(». .'{0, An electric current may be obtained by placing a coj)pfM' and a zinc plate in a vessel containing dilute sulphuric acid in I \ III 1^^ 52 PHYSICAL SCIENCK. the projM)rti' I ¥ 64 PHYSICAL SCIENCE. i contact (Experiment 1, page 44). This pressure is sup- posed to be due to tlie innumerable impacts of the mole- cules of the gas against the surface. If no work is done on the surface it is found that the gas loses no energy ; but if work is done on the surface, for example, if the surface is heated (molecules accelerated), or accelerated bodily, it is found that the gas is cooled, that is, that it loses energy. 10. Modern View of Force. The modem view that force is always produced by energy, rests on the foUowuig basis : — 1. This view is in strict accordance with the law of conservsytion of energy. 2. It is not inconsistent with any known fact, and many facts are more satisfactorily explained by this hypothesis than by any other. It is, perhaps, in the case of the manifestation of force in connection with gravitation that it is most difficult to even imagine the nature of the energy which produces the force ; but to imagine " action at a distance " is still more difficult, and, to some minds at least, is quite im- possible. 11. Action of a Force. Although we hold the foregoing view regarding force, we shall, as a matter of convenience and because the practice is almost univei'sal, use the phrase action of a force ill speaking of acceleration or other effects, such £us compression, bending, stretch, etc., which are, strictly speaking, due to the action of energy. CHAPTER VI. MEASUREMENT OF MASS. I. — Determination of Equal Masses. 1. Equal Masses. We may define e) above (a), of (r) above (/>), of (d) above (c) ? 6. What is the acceleration observed I . . 7. Does the force producing this acceleration change i 8. Does the mass which is accelerated change ? From the above experiment, if carefully performed, we leaiTi that a constant force (in our experiment the weight of the body in the scale pan) acting on a con- stant mass produces a uniform acceleration. Experiment 2- Remove the lump of lead from the cart and replace it with a quantity of shot or sand, leaving exactly the same body in the scale pan. Repeat the experiment, and if you find the cart moves a greater distance in the first second than when the lump of lead was used, add some shot or sand to the cart, if a less distance, take some out. Keep trjang until you have such a quantity of shot or sand in the cart that it moves over MKASUHEMENT OF MASS. 67 tli(< NjuiH! (listjuico in the same time as it did wiu'ii you used the lump of lead. 1. What is the force produciiii; the acceleration in this case ? 2. What is the whole nuiss accelerated ? 3. According to our detinition of e(iual masses, what masses must bo e(iual ? 4. Since the cart, sc.de pan, and the body in tlie scale ]»an are exactly the same in both cases, what luxly must liave the same mass as the lump of lead jdaced in the cart in the first experiment ? Ezperime&t 3- Carefully remove the shot or sand from the cart and place it in one pan of an equal-arm balance, placing the lump of lead in the other pan. What is the result ? Experiment 4. Hang them successi^ely from the end of a strong rubber band and note the extent to which it is stretched in each case. What is the result ? Also place them successively in a scale-pan attached to a coil-spring, supported as shown in Fig. 38. A small pointer is fastened to the lower end of the spring, and the elongation of the spring is measured by means of a graduated scale. The position of the pointer on the scale may be determined with accuracy by so placing the eye that the pointer and its image in a mirror placed alongside the scale shall be in line. What is the result ? V, 08 IMIYSFCAIi SCIKNrK. i i* Tlio apparatus sliovvn in Jolly's balance. Fi^.. .S8 is UHualh' called These experimentH prove that equal masses counterpoise each other at the ends of an equal-arm balance, and that equal masses stretch the same elastic body to the same extent, and hence we liave two other and more simple methods of finding e(j[ual masses. Thus if we find that two masses counterpoise each other at the ends of an equal-arm balance, we may infer that these masses are equal. Also, if we find that two masses stretch to the same extent, the same rubber band or the same coil spring, we may infer that these masses are equal. We may also divide a given mass into two equal parts by so dividing it that tile two parts counterpoise each other at the ends of an equal-arm balance, etc. Fig. 38. 11. —Description of the Balance. The balance consists of a metal beam A B (Fig. 39), supported at the centre on the knife edge C, usually a three-cornered steel bar passing horizontally through the beam at right angles to it. The sharp lower edge of C rests on a smooth horizontal plate of steel or agate fixed on a pillar, P. Scale pans are hung by means of steel or agate plates on knife edges placed at E and F near the ends of the beam and at equal distances from its centre. MEASUMKMKNT OF MASS. 59 A pointer, p, which moves over a av«»inluiM»is pound. 2*2040213 jivoirdui)ois pound. •061798950 .^lams. 1 ouncd avoirdupois 1 pound " 28-349541 grams. '45359265 kilograms. 5. Approximate Values- if 1 gram = 15-4 grains. I kilograui ::^ pounds. 1 milligram = •01-54 grain. 1 grain = 64-8 milligrams. 1 ounce r= 28 jL. gi-ams. 1 pound ^= 451 grams. 1. How many milligrjuus in 20*34 gni., 30 42 cgm. , •.'i25 Kgm.? 2. How many kilograms in 856^3 mgm., 345' 8 cgm., 0[J4"2 gm. i 3. How mauy centigrams in 329 Kgm., 92'3 gm., 83^12 mgm.? 4. If 324 is the measure of a mass wlion the unit of mass is the gram, wiiat will bo its measure when the unit is {<() the kilogram, (/>) the milligram ? 5. Is the unit of mass a fundamental or a derived uii { 6. Weights- For convenience and accuracy in estimating i lass, sets of " weights " are used. These are pieces of metal ad- justed to contain multiples and fractions of the quantity of matter contained in the selected unit. MRASir .i-:ment op mass. r»i Metric wt'i<;lits ai'c iisiiully jirrjin;^'alaneo, a ruhhor band, or a spring balfince, prepare vseveral small equal masses. Arrange the cart as in Experiment 1, page 55. Place any convenient and fairl}^ large mass in the cart, and i)!aco one of the e(jual masses in the scale pan. Carefully determine the distance the cart moves from rest in 1, 2, or 3 seconds, llephice tlie mass in the scale pan with another of the ecpial masses and 6 [65] CG PHYSICAL SCIKNOE. il repent tlic (•xpcriinont, Jiiakini^ (Ik; s;uiic (tl)S('i\;it ions as l)off)rf\ 1. TIow do you find tlie dishinoes traversal I l>y the cart in uqual tinius to compare i 2. Compare the mass moved in one case with tliat moved in the otlier case. .*J. What is the total mass movtMl in lirst case / 4. What ill second case ? 5. From our detiniti(m of c^qnal forces, whar forces must he eJivt'ight of mass in pan. Now the pan is the same in both cases, therefore its weight must evidently be the same in both cases. Therefort! the weight of mass in 2)an in 1st case must etpial the weight of mass in pan in 2nd case. But these masses are e pial masses. There foi' equal masses have equal weights. This conclusion is confirmed by experiments MEAwUKKMKNT OP FOIK.'ES. G7 it e s iiiucli moi'c (lolicato th()n«^li not so simple as th(> oiu^ above. Since we know tliat in tlie same place e((ual masses liave equal weij^^lits, we can measure forces by balancing them against the weights of known masses. 3. Mass— Acceleration. Experiment 2. Arrange once more tlie curt, scale pan, etc., as in the pre- vious experiments. Load the cart ^ith shot or sand and place a small quantity of the same in the scaler |)an. Carefully ascertain the acceleration resulting. Transfer fiom the scale pan to the cart, until the mass supported l)y the sti'ing as ascertained by the use of a balance is reduced one half, and again carefully ascertain the acceleration resulting. 1. How does the whole nitiss acceler;itof B ? 3. How does the mass of A compare with that of B ? 4. How does the force acting on A during its fall compare with that acting on B ? 5. How does the i)roduct of the measure of the mass of A into the measure of its acceleration compare with the product of the measure of the mass of B into the measure of its acceleration ? From the foregoing experimentH we see that if two different forces act on two masses the product of the measure of the first mass into the measure of its accel- eration is to the product of the measure of the second mass into the measure of its acceleration as the force acting on the first mass is to the force acting on the second mass. 4. Second Law of Motion. Newton expressed this conclusion as follows : — " Change of motion is proportional to the impressed force, and takes place in the direction of the straight line in which the force acts." In this statement, " cliange of motion " means a quan- tity which is measured Ly the product of the measure of t^le mass accelerated iiivO the measure of the acceleration. It follows as a particular case of the foregoing hiw that no change whatever takes place in the motion of a body MKASUUEMENT OF FORCES. 69 which is siihj«'ct to no external force. This I'act may bo stated by itself as follows : — 5. First Law of Motion. " Every body continues in its state of rest or of uni- form motion in a straight line, except in so far as it may be compelled by force to change that state." This is generally known as Newton's First Law of Motion. 6. Unit of Force. The second law furnishes the most natural and scien- tific method of estimating the magnitude of a force, viz., by observing the "change of motion" it produces. However, for ordinary purposes it has been found con- venient to estimate a force by observing the mass it will support against gravity at the surface of the earth. In this case we take as jur unit force the force that will support the unit mass, e. QUESTIONS. 1. Is !i kilogram weight i\.isting on a tahlu a force 'i 2. Explain clearly what \h meant by a force of are the acceleration with that produced by the sanio force acting on (a) 20 grams mass, (/>) 5 grams mass. 4. A force acts on a mass of 10 grams and produces an accelera- tion of 10 cm. j»er sec. per sec. Anotlier force acts «»n a mass of 5 grams and produces the same acceleration. Compare the forces. 6. A force is cap.able of jaoducing in a certain mass an accelera- tion of 10 cm. per sec. j)er sec, and in anotlier mass an accelerati«jn of 20 cm. per sec. per sec. C< mi pare the masses. 6. AVhy is a rider fretpiently unhorsed when the liorse suddenly turns in a new direction i 7. Why is the outside bank worn away when a river takes a sharp turn ? 8. Why does a player in catching a cricket l)all allow his hand, the instant the ball touches it, to be carried backward in the direction in which the ball is moving ? 9. A ship in firing a broadside inclines to the opposite side. Why? 10. What eflect would tiring (a) the bow guns, (/*) the stern guns have on the speed of a vessel ? Explain the reason. 11. Why does a sky-rocket ascend ? 12. Exjdain the following facts derived from experience : (o) It is an advantage to run before a leap. (^) It is safest to skate quickly over thin ice. 13. If a mass of 10 grams were raised 50 cm. above the surface of the earth, what would happen if exactly at that instant gravity ;if m « 71 PIIVSK^VL H(IEN( K. COHH0.1 to act ^ What would happc. if j^ravity coa.se.l fo act aft.r tlio body liav does the weight of any mass at the Hnrfa.eof the earth compare with the weight of tho sauie mass at the surface of the moon / earil T''''^ '' ^'''' ''''*'''*' °^ '' ^""""^ '""'' "^ ^'"' "^"^'"^ "^ ^''" 1<5. At what distance from tho earth's surface is the wei-dit of any mass one fourth of its weight at the surface T If .-, pfli i\ (IIAITKR Vm. .>rEASlUKMK\T OK KN'KHCJV AND WOKK. 1. Energy— Mass. W(3 liuvo ii\\vai]y seen (pa^re HH) that a hoi]y po.sseases enL'rn. , Ciiises. l.il' III 86 PHYSICAL SC'IRNCK. The proccjHH of inakinj; a lianl and brittle metal Hot'ter and more tlexi))le i.s called annealing. How in iron Hiinoalud ? How in coppor ? 2. Hardness and Density- 1. Which is tho denser metHl, iron or gold? Which Ih the hiirder ? C. Which is the deiiHer metal, lead or platinum '( Which is the hardor '{ 3. Is there any relation between hardness and density ? II. Ductility. The property of being extended in length by being drawn out into wires or threads. Experiment 1. Take a piece of glass tubing or a glass rod, heat it in the Hame of a Bunsen burner or spirit lamp until it becomes quite soft, then draw it out (Fig. 47). FiQ. 47. Experiment 2. Compare tlie ductility of a piece of sealing wax at the ordi- nary temperature with that of a piece which has been heated for a short time in boiling water. PROPEKTIKS AND I.VWS OF SOLIDS. 87 Many metals are (piite ductile even when cold. The following is a list of the more common ones : — Gold, silver, platinum, iron, copper, aluminium, rinc, tin, lead. Is there any relation hotwoon {a) density Jind ductility, {!>) Imrd- nes8 and ductility i Wires are made by drawing the metal through holes in hard metal plates. III.— Malleability. The property of being extended in surface when hammered or rolled. Gold is the most malleable of metals. It can be beaten out into sheets so thin as to be quite transparent, having a thickness of not more than laTnTinr cm. 1. How are the relative positions of the molecules of a body affected by its being extended in (a) surface, (6) length ? 2. Why 13 it that most ductile metals are malleable ? I IV. —Plasticity. The property of changing shape under the action of a continuous force without exhibiting a tendency to regain the original form. IMAGE EVALUATION TEST TARGET (MT-3) 1.0 I.I ,50 ^^ t Its, u 1^ 1^ iy& 1.25 IIIJ^ 1.6 VQ yl /: 7 /A Hiotographic Sciences Corporation 33 WST MAIN STRiET WEBSTER, N.Y. US80 (716) a73-4503 \ k m 88 PHYSICAL SCiKNCE. Experiment 1 Support one end of a stick of sealing wax (Fig. 48) and hang a weight of about 50 grams from the other end. Allow it to stand for two or tlu'ee days. 1. What chaugu hti8 taken place in the shape of the sealing wax i Keinove the wei^lit. 2. Does the wax recover its original sliape ( 3. Name some plastic bodies. 4. Is ice plastic { Is glass ? H v.— Tenacity. The resistance which a body offers to the separa- tion of its parts. Experiment 1. Determine the strength of different wires by fastening one end of each to a peg and the other to a spring balance, and grad- 111: PROPERTIBS AND LAWS OF SOLIDS. 89 ually pulling on the balance until the wire breaks (Fig. 4''). Fio. 49. 1. What other i)roj)ertie8 of bodies are dependent upon tenacity ? 2. Wire ropes are usually stronger than bars of the sjinie metal of equal mass and length. How does drawing a metal into a wire affect its tenacity ? VI.— Elasticity. Experiment 1. Try to stretch a piece of i-ubber band or tubing. Press a ruV)ber eraser against a hard substance. Try to Inrnd it. Stjueeze in the hand a hollow rubber ball containing air. 1. W^hat clianges take place in the volume or the shape of the band, of the eraser, and of the ball, when force is a})plied t(» each '( 2. What happens when the force is reduced or ceases to act ? 3. Elasticity. The property of a body in virtue of which, after its size or shape has been altered by the action of force, it reacts against the force and returns to its original size or shape, more or less completely, on the removal of the force, is called elasticity. That is, the elasticity is the internal stress which is called out in a body when it is subject to a strain. 90 PHYSICAL SCIENCE. i 1 When the strain is one of change of volume (compres- sion or dilatation) tlie stress produced is called elasticity of volume; when the strain is one of change of shape ( LAWS <»F SOLIDS. 91 i Experiment 3. Fasten tme oiul of u picro of copptu* wiro A in u t-lanip or vise, as shown in Fig. 51. Place a point<,»r Ji ojipusite the other end. J Fio. r>i. Bend the wire a little by pulling the free end asient is called flexibility. 1. How does elasticity differ from flexibility? Give illustrations. 2. What change takes place in the arrangement <»f the molecules on (a) the convex, (6) the concave side of a body, when it is bent ? Experiment 4- Fasten one end of a copper wire, about No. 10 and 50 cm. long, to a support, and to the other end attjich a heavy weight to which is fastened a pointer (Fig. 52). Note the position of the pointer on a circular scale drawn on paper. Twist the weight around a little way. 92 PHYSICAL SCIKNCK. Does it return, after it ceiwes vibrating, to its original position ? R«*poat the ex|jonment, turning the weight more each time. Is there a hmit l)ey(»nil which, if the weight is turned, the pointer does not return to its original position. A body is siiid to be perfectly elastic when it recovens completely its volume or slia[)e after strain. Many solids are perfectly ehistic if not strained be- yond a certain limit called the limit of elasticity. When strained beyond this they do not completely recover their orijjinal volume or shape, but take a permanent *' set." 1. If a heavy load strains a bridge beyond its limit of elasticity, what effect is produced oa the shape of the bridge ? What effect would the same load pro- duce if it passed over again ? 2. Why do the springs of csirriiiges often become " sagged '" / 3. Name some bodies («) in which the limit of elasticity is soon reache«l, (/*) in which the limit of elasticity is near the l»reaking point, (c) which have a high limit of elasticity ( 4. Are there any Ixnlies belonging to (a) and (/*) { to (a) and (c) ? to (b) and (<) / If so, give examples. Fio. 52. 5. Has the length of time during which a force acts any effect on the limit of elasticity of a body ? Experiment 5- To answer this question, Uike a w«>oden bar A, support !\ I PROPERTIES AND LAWS OP SOLIDS. 93 it as sliiiwn in Fig. r).*l, and plaeo on it a \voi«,'ht wliin Fio. 53. 1. Ts tho bar permanently bent ? 2. Why do archers keep their hows r.nbent >\htn not in use? 3. Have gases a limit of elasticity ? have liquids ? 6. Measure of Elasticity. The elasticity of a IxKiy is measured, not by the ainount of change in sL;ij3e or in volnme wliicb it will undergo and still regain its original s]ia2)e or volume, but hy the force witb wbicb the displaced particles will tend to revert to their original j)ositions. This is the force necessary to produce tbe cliange in shape or volume. For example, liquids are more elastic tlian gases, because greater force is necessary to produce a specific change in the volume of a liquid than in tbe volume of a gas, since the particles of the liquid tend with greater force to return to their original positions. Generally, the elasticity of solids is greater than tliat of liquids. 1. To which must the greater force he applied to change its length by one millimetre, a ijar of rubber or one of steel of tho saaie size and length / H PHYSICAL SfrENCR. 2. Which Ih ihu iiiuru ulaatio / 3. Which Ih the iiK^re extensible ? 4. Which ia the more compresHible / 5. Why does a ball rebound when it strikes a hard surfaco ? To answer this question, cover the surface with ink or paint. Touch lightly the ball to the surface and note the size of the spots made on the ball and on the surface. Now let the ball drop from a height on the surface and again observe the size of the spots. 1. How do the spots made in the two cases compare ? 2. What change must have taken place in the ball when it came in contact with the surface ? 3. What would this cause ? VII.— StructicTe— Crystalline and Amorphous. Experiment 1 . Dissolve 100 grams of alum in 500 cubic centimetres of water. Hang several strings in the solution and set aside for a few hours. 1. Are the pieces of alum which have separated fruia the solution alike in shape ? 2. Study their forms and make drawings of some of them. Experiment 2- Kepeat Experiment 1, using ('/) a solution of copper sul- phate, (/>) a mixture of the solution of alum and the solution of copper sulphate. PIIOPEKTIKS AND LAWS OF SOLIDS. 95 Experiment 3. Clean a strip of glass, slightly warm it, aiul pour u|m>ii it a few di*()ps of a hot solution of aninioiiiuin fhlori> above are crystal- line and which amorphous % 2. Is ice crystalline? Observe it when it begins to form. Place a thin sheet of it before the condenser of a porto liuiiiere or pritjec- tion lantern and focus on the screen. 3. Is snow crystalline? Place a few flakes on a dark clotli and observe them through a magnifying glass. The variety of forms in which the particles of different substances arrange themselves is almost endless. Tliis is the case probably because the attraction of cohesion is not the same all round the molecule, but like the atti-ac- tion of a magnet, is concentrated at certain points or poles. When the molecules are free to move, these points, on account of their mutual attractions or rejjul- sions, take set positions, and the structure of the body thus becomes regular in form. This tendency to arrange themselves in regular order is perhaps possessed by the molecules of most botlies; and even when, on account of the lack of freedom of the molecules, it does not render itself aj)pareat, it is no doubt often still present. For example, wrought iron is amor- phous, but by constant jarring it becomes crystalline. Here the molecules receive a certain amount of freedom at each jar, and in course of time the constant tendency to regularity of structure becomes apparent. PK0PKKTIR8 AND LAWS OF 80UD8. QUESTIONS. dr Give the propertioM of the folK.wing 8»»1u1h which iimke them • UHefiil for the pur|)OHo8 iiulicuted : 1. Leml for (a) water pipes, (,'>) bullets. 2. Ruhl)er for fa) bicycle tires, (b) oversh.KJS. 3. Iron for (a) Iwiler plates, (b) chains. 4. Steel f.)r (a) pens, (/,) watch springs, (r) swords. 5. Silk for (a) clothes, (b) thread. 6. Hair for (a) inattrasHes, (/>) mixing in mortiir. 7. Cork for (a) bottle stoppers, (b) soles f,.r shoes. 8. Leather for (a) harness, (b) shoes. CHAPTER XL : PROPKIITIKS AND LAWS OF LlgiTFDS. I. Fluidity— Viscosity. Experiment 1. Pour several litiuids such as alcoliol, water, oil, syriip, honey, tar. 1. Do they all flow with equal free wir» 1)ont in the form hIiowh in Fig. 51. K«'<'|) trying until you whhhmkI in letiving the needle flatting on the HUi'foce of the water. What is the fuim of tho water Hiirfaro around the needle ? Break the surface of the water near the needle by thruHting a hnger into the water. What takeH place ? Experiment 3. Magneti/e a sewing needle by ruhhini,' it with a j)ennHnent magnet (Experinient G, page 50), and place it on the* surtiice (►f water as in the last experiment. Im vvhat direction does the needle set itsulf ? Place another magnetized needle on the surface of a soap solution. What position does this needle take on the surface ? Suijpend hy a ti]>ro tho magnetized needle heneath tlie surface (tf tite soap solution. What position does the needle now assume ? The superficial film of a liquid is more viscous tliau the interior. This film therefore is hard to break, and bodies whicb would naturally sink if placed in the interior of the liquid are borne up by it. II.— Cohesion— Adhesion. Experiment 1. Place a piece of wood in water, tiike it out and observe its surface. 1. What do you find on the surface of the wood ? 2. What force holds it together ? 3. What force holds it to the wood ? I Itk' ill • 100 Experiment 2. PHYSICAL ROlRNOfi. Repeat ExporiiiuMit 1, usiuj; iiM^rcury instead of water. How do you account for tlio diffcronco in tho result l Experiment 3. Fasten to the centre of a glass disc with sealing wax a wire staple of the form shown in Fig. 55, and tie to this a thin rubl)er band, and gently lower the disc until its surface touches tho sur- face of the watei*. Lift up on the rubber. Examine the lower surface of the disc when it has separated from the water. 1. What evitlence had you that you had to exert force to separate the disc from the water ? 2. In separating the disc from tho water, what force was over- come, the cohesion auiong the F'»- S-'i- articles of the disc, the adhesion between the disc and the water, or tho cohesion among the particles of the water ? Give your reasons. Experiment 4- Repeat ExperinuMit 3 after having greased the lower surface of the disc. Was force necessary to separate the disc from the water ? If so, what force had to bo overcome to cause the separation ? Experiment 5. Repeat Experiment 3, using mercury instead of water. 1. Is there any adhesion between the disc and the mercury ? 1-».^1 -^ ;r^==^-=?'^^=r==^=] -----^ : --.i;: 4^s^A^=i£i:^--:^ 1 PROPKRTFKS AND LAWS OF LIQUFDS, 101 2. Is thero uny coliesion among tho particles of the mercury ? '^. In pouring licpiids from vessels a glass rod is often placed as shown in Fig. 66. Why does this prevent the liquid from running Fio. 56. down the side of the vessel ? Would it be of any use in pouring mercury from a glass vessel ? Give reasons f..- y„ur answers. III. —Capillarity. Experiment 1. Dip a clean glass plate (a) in water ; (h) in mercury. 1. Make drawings of vertiwil sections of the surfaces of tlie water and the mercury around the plate. 2. Does the water wet the plate ? Does the mercury ? 3. The adhesion between the water and the glass is greater than the cohesion in the ^ -ter, and the cohesion in mercury is greater « M! ;i 102 PHYSICAL SCIENCE. than the adhesion })etween the mercury and the glass. How does this explain the diflference in tlie position of the liquid surfaces around the plate ? Experiment 2. Hold two glass plates with the edges together at one sitle, bat kept a little apart at the other (Fig. 57). Place the plates verti- cally in (a) water, (6) mercury. Make drawings showing the position of the surfaces of the water and of the mercury on the outside of the plates Fio. 57. and between them. Experiment 3- Dip vertically into (a) water, (A) mercury, a glass tube the bore of which is about one millimetre in diameter 1. Does the water or the mercury rise in the tube '( Is either depressed ? 2. Wliat is the form of the surface of (a) the water, (h) the mer- cury in the tube ? Repeat the experiment, using tubes of smaller bore. In which is there the greatest difference in level between the surface of the liquid in the vessel and its surface in the tube ? Experiment 4. Take two capillary tubes of the same bore, place one in alcohol and the other in water. Does the water rise to the same height in the one tube as the alcohol does in the other V Experiment 5. Take two capillary tubes of the same bore, dip one into any licjuid and the other into the same liquid at a higher tem- perature. PROPERTIES AND LAWS OF LIQUIDS. 103 In wliich is the difference of level between the liquid within the tube and that without, the greater ? Phenomena of the kind illustrated in the foregoing experiments are known as capillary phenomena, because they take place in tubes with capillary or hair-like open- ings. 3. Laws of Capillarity. 1. Liquids rise in tubes when they wet them, and are depressed when they do not. 2. The ascension or depression is inversely as the diameter of the bore of the tube for the same liquid, but differs with different liquids. 3. The ascension and depression increases when the temperature of the liquid decreases. Experiment 6- Take tuljes of the form shown in Figure 58 ; pour water into one and mercury into the other. Fio. 58. I ! 104 PHYSICAL SCIENCE. Account for the forms of the surfjices and the differences in level observed. Experiment 7. Place (a) one corner of a lump of sugar in water ; (b) the comer of a sheet of blotting paper in ink ; (c) the end of a piece of loosely-woven cloth, such as a lamp wick, in water. What takes place in each ease ? Porous bodies, such as blotting paper, wood, cloth, etc., absorb liquids by capillary action, the liquid rising in the irregular spaces within the bodies. 4. Will a liquid overflow a tube by capillary action ? Experiment 8. To answer this question, take a tul)e of very fine bore, place one end of it in water and hold it in a vertical position until the water rises to a considerable height in it, then depress it until the upper end comes near the surface of the water. What change takes place in the height of the liquid within the tube as it is depressed ? IV. — Surface Tension. Experiment 1. Let water fall in drops from the end of a glass rod. Let some of the drops rest on a greased surface. Place a few dix>ps of mercury on a table. 1. What is the shape of the drops of water when falling through the air ? What when on the greased surface ? 2. Wliat is the shape of the drops of mercury ? 3. How is small shot made 1 PROPKUTIKS AND LAWS OF Llt^UIDS. 105 a Experiment 2. Soften the end of a stick of sealing wax or of a glass ro(l by heating it. What shape does it take ? Experiment 3- Make a mixture of alcohol and water of the same density as olive oil. This is most quickly done by the use of a hydrometer. With a pipette introduce some of the oil into the centre of the mixture (Fig. 59). What shape does it Jissuine 1 Fio. 5fl. Fig. 60. Experiment 4. Make a soap solution, and with a thistle-tube blow a bubble. When the bubble has become fairly large, remove the end of the tube from the mouth and place it near the flame of a lighted candle (Fig. 60). What takes place ? Experiment 5. Dip the mouth of a glass funnel into the soap solution, and, keeping a finger over the narrow end, lift the funnel out of the solution and observe the film on the mouth of the funnel. Remove the finger from the narrow end. What change takes place in the film ? A liquid surface always tends to assume a inininium area, and therefore acts like an elastic inenibrane 106 PHYSICAL SCIKNPK. I i 1 ■ i e(inally Htretched in every direction by a constant ten- Hion. This phenomenon is known as the surface tension of the liquid. V. -Transmission of Pressure by Fluids. Experiment 1. Have made by a tinsmith a vessel of the form sliown in Fig. 61. Tlie short tubes inserted in the sides should he ahout one inch long, and from two to three inches in diameter. Ti«', or fasten by h(K)ps, pie or by using a bicycle pump. How do the resulting phen<»niena compare with thoso ohscrved when water was used ? 5. Law of Transmission of Pressure— Pascal's Principle- Pressure exerted anywhere upon a mass of fluid is transmitted undiminished in all directions, and acts with equal intensity upon all equal surfaces, and in directions at right angles to these surfaces. This is generally known as Pascal's principle. Experiment 3. Pour a small quantity of mer- cury into a tube of the form shown in Fig. 62. Now pour some water into the larger branch. 1. What changes take place in the levels of the mercury in the two branches? Why? 2. How much water do you suppose must be put into the smaller branch to bring the mercury to the same level in each branch ? Give reasons for your answer. Verify by pouring water into the smaller branch. 3. How does the weight of the water in the larger bmnch compare with that in the smaller one when the l'''"- 62. mercury is restored to the same level in each tube ? 108 PHYSICAL SCIKNCE. If 1 ' \ Fio. 63. VI.— Pressure due to Weight. Experiment 1. Cut the funnel shaped end from a thistle-tube, leaving about an inch of the stem connected with it. Over this slip a [)iece of rubber tubing about 30 or 40 cm. long, and tie a piece of thin sheet rubber (»ver the mouth of the funnel. Make a U shaped tube by bending a piece of glass tubing into the form shown in Fig. 63. Place this in a vertical position in a holder, partially fill it with water and connect it with the free end of the rubber tubing. Press the rubber membrane with a finger. 1. What change takes place in the position of the water in the tube? Why? 2. How is (a) an increase, (h) a decrease in tlie pressure on the membrane indicU od by the water in the tube ? Fill a large jar with water which is at the temperature of the air in the room- Place the thistle-tube in the water and gnid- ually lower it (Fig. 64). 1. What change takes place in the water in the U shaped tube ? 2. What change in pressure does this indicate ? When the membrane has reach- ed the bottom of the jar, gradually FiQ. 04. lift it up. 1. What change in pressure takes place as the funnel is raised in the water ? How do you know ? 2. What was in contact with the membrane ? t»KOPERTlRS AND LAWS OF LIQUmS. 109 'A. \Vli;it then uumt Imvo causod the juvssuro ? 4. Huw ) I'^pon which surface then will Fio. 68. the pressure of the water be the greater ? The resultant pressure exerted by a fluid on a body immersed in it is known as the buoyancy of the fluid. 7. What is the amount of the buoyant force which a liquid exerts on an immersed body. Experiment 2- To answer this question, take a brass C3'^linder A, which fits exactly into a hollow socket B. Hook the cylinder to the bottom of the socket and counterpoise them on a balance. Surround the cylinder with water (Fig. 69). What change takes place in the equilibrium of the balance ? f'l I V ' ■ . 112 I'llVHIOAL ftCIKKOK. Now jKiur water into tlio Kookot until tlu< ('<|uilittriuin ih restored. 1. When dooH tluH take place ? 2. How does the volume of the water in tlio gocket compare with the volume of the cylinder ? Fio. 69. 3. By the weight of what V(jlume of water then was the cylinder buoyed up ? 4. Is the mutual attraction between the earth and A lessened by surrounding it with water ? 8. Law of Buoyancy— Principle of Archimedes. The buoyant force exerted by a fluid upon a body immersed in it is equal to the weight of the fluid equal in volume to the body. PUOPEIiTIES AND I.AW8 OF LIQUIDS. 113 Or. A body when weighed in a fluid Ices in apparent weight an amount equal to the weight of the fluid which it displaces. FhiH is known as the principle of Archimedes. 9. Flotation. Experiment 3. Partially till a gmduated tube with water aiul pb.ce on tho surface of the water ill the tuhe a i.iece of w.hkI which has been weighed. 1. What is tho volume (.f tlio \vater diaplacecl by the muA ? 2. Wlmt then ia the weight ,»f the water displaced by the wood ? 3. How does tho weight «>f the w.umI conii.are with weight ,.f the water displaced by it ? 4. To what is the buoyaut force of water on tho wood cipjal ? 5. When will a body sink ? when ti..at ? Experiment 4- Try to float an egg on (.,,) fmsh water, (h) a saturated solu- tion of common salt. 1. What difference do you observt^ in the position of tlie e-.r ? 2. How does increase in the density of a li.piid affect its b ancy ? Why i uoy- 3. Will a body whose density is one gram per cubic centimetre smk or float in water ? Why ? 8 I I? < 114 PHYSICAL SriENCK. QUESTIONS. 1. Why will ail iron ship float on water while a piece of H(»li(J if on sinks ? 2. Why do birds float high on water ? 3. Why does (ul float on water while mercury sinks .' 4. Will air float on water ? 6. Pour into the same test-tulje (. What is the relation between the volume and the pres- sure of a gas ? Experiment 1. Take a tube about 25 cm. long and at least 4 mm. in diameter, one end of which is closed by a stopcock. A thistle- tube supplied with a stopcock answers well. Connect this by means of a heavy ru})ber tube not less than 50 cm. long with a glass tube, also about 50 cm. long. The joints should be wrapped with fine wire or string. Place the tube in a support as shown in Fig. 80, open the stopcock and pour mercury into the connected tubes until it reaches the same level at or near the centre of each glass tube. Close the stopcock. Take the reading of the barometer. Height of barometer (H)= I The pressure to which the encdosed air is subjected is measured by (1) The barometric reading (H) when the mercury surfaces are at the sanu^ level. ^^ hy ? (2) The barometric reading (H)±: the difference between the levels of the mercury surfaces when these surfaces are not at the same level. Why I If 9! I ( VV: in ■ 1:1 124 PHYSICAL SCIENCK. The plus sign is to l)e taken when the mercury in the open ^m -\u Fio. 80. I7t 1:19 M :IIO =50 S=W Fio. 81. -MO lOQ -in :70 teo tso £40 -20 Elt Fio. 82. tube is higher, and the minus sign when it is lower than in the closed tube. Why ? PROPERTIES AND LAWS OP OASRS. 125 HMl ban Place the open tu))e in several poHitions with the surfact? of the mercury in it either alxjve (Fig. HI) or Ix'low (Fig. 82) the surface of the mercury in the closed tul)e ; and measure (1) The lengths of the air column in the closed tul)e. (2) The vertical distances between the mercury levels in the two tul)es. Supposing that V represents the original volume of the en- close ®tc., represent the volumes of this air at successive observations ; and that Up H.„ H.j, H^ represent the differ- ences in mercury levels for these observations, fill up the following table : VOLIMKB. Prkshi-rrh. FRODltTS. \ = I' =H V X I' =. y^- l\=H ± Hj = \\ xP,= v.= P, = H ± H.,- Vo X P,= v« = P3 = H±H,= y, X p,.. v.== \\ = U ± 11,--= V, X P,= Etc. Etc. Etc. If the experiment is carefully performed, the products V X P, Vj X Pj, etc., will be found to be equal. This being the case, it is evident that the volume of the air is decreased at exactly the same rate as the pressure is increased, or is increased at the same rate as the pressure is decreased. That is, the volume of a given portion of air varies inversely as the pressure to which it is subjected. The extended researches of careful experimentei*s have shown that all gases, within certain limitations, conform to this law. 12C I'ltYSlCAL SriKNC !int, the reduction in volume is greater than that which the law would indicate. ■ 3 '5' B QUESTIONS. 1. If the volume of the air shut up in the tube, Experiment 1, page 12.'}, is 10 c.cui. when the mercury is at the same level in each tu})e and the barometer stands at 70 cm., what will be the ditfer- ence in level between tlie surfaces of the mercury in the tubes when the volume of this air occupies («) 5 c.cm., (h) 20 c.cm.^ 2. The differences in levels, Experiment 1, page 123, at four difterent observations are 10 cm., 90 cm., 170 cm., 250 cm., and the volume of the enclosed air at the first observation was 12 c.cm., what was the volume of the air at each of the other observations if the barometer stands at 70 cm.? 3. What effect would (a) raising, (6) lowering, the open tube, Ex- periment 1, page 123, have ui)on (I) the mass, (2) the density, (3) the expansive force of the enclosed air ? 4. The pressure of a gas is 10 grams per sq. cm. when its volume is 100 c.cm., what is the pressure when the volume is 150 c.cm.? I'ROI'KIJTIKS AND LAWS OF (iASK.^i. '-'< 6. The volunio of g;i.s slmt up in ft ruhlna' Imij^ in 2«H) c.rm. ulnii the bftroiiietor stiunls jit, 70 cm., wliiit will ho tlus volunu! <»f tho j,'ii« when the hftromutor hUiikIs at HO nn. ;• fi. If a gfts occupies a volmiu! of 25 c.cm. when tho buroinotor stftiuls ut 7(> cm., wliiit mu.st ho tho roading of tho barometer when the gas ineasuroH 30 c.cm.< 7. A gas holder c(mt)iins 224 litres of a gas mea-siirod when the banunetor stands at 72 cm., what will l>e tho volume of tho gas when the barometer stands at 7<> cm. ? 8. A rubber bag contains 100 c.cm. of air at the atmosplierie pressure, what will the volume of tho air become if tho bag is sunk to a depth of .'iO feet in water? What would bo tho ))u<»yant fono of tho water upon it i The water l>arometer stands at .'W feet. m \(: CHAPTER XIII. I I J ,,. Fia. 83. SOLUTION, DIFFUSION, 0(7CI.US10N. I.— Solution. 1- Solids in Liquids. Experiment 1. Place 15 grams of powdered potassic chlorate in a beaker containing 50 c.cni. of water at the temperature of the class room. Stir the mixture for a few minutes. Has the salt disappeared ? If not, fold and cut a filter paper ar» shown in Fig. 83, place it in a fun- nel, pour the mixture into it, and col- lect the liquid passing through the filter paper (the filtrate) in another be\ater i (See page 27.) U28] :^^^^ SOLUTION. 129 the Is Ill- Experiment 2. Repeat Experiment 1, placing the sarae quantity of the potassic chlorate in the same quantity of )>oiling water. How does increase in temperature affect the solution of this sjilt in water ? Experiment 3. Place 15 grams of common salt in 50 c.cm. of water at the temperature of the class room. Stir the mixture. Which is the more solulue in cold water, pot). What is tlie cause of the diflferonces in urusHuro indicated by the guage ? The above experiments prove tliat the rapidity of diftusion of a gas depends on its density. Tlie greater tlie density of a gas tlie less is its rate of diffusion. Exact experiments conducted by Loschmidt, who has investigated tlie phenomena of free diffusion, and by Graham, who has investi- gated the phenomena of diffusion through porous septa, have established the follow- ing law. 9- Law of Diffusion of Gases. The relative rates of diffusion of gases are in- versely proportional to the square roots of their densities. For example, the densities of oxygen and hydrogen are in the ratio, IG : 1, and their rates of diffusion are in the ratio, 1 : 4, that is, yl '. yl6. The diffusion of gases is of great importance in the economy of nature. If gases would float on one another, as oil on water, or water on mercury, the present forms of life could not exist. Tlie requisite proportion of nitrogen to ogyxen in the air would not be main- tained, and the noxious gases exiialed by animals and generated by the decomposition of organic matter would collect in dangerous proportions at the earth's surface. OCCLITSION. 139 III. Occlusion. Experiment 1- Heat a piece of charcoal to redness in a flame, allow it to cool, and iiiticMiuce it into a tube, filleil with ammonia i^'as as in Experiment 9, page 131. Place the tube in a vertical position with its open end in mercury (Fig. 96). What change takes jjIhco in I ho volunio of the gas in the tube ? For various reasons it is believed that the gas absorbed by the charcoal is condensed on its surface. All solids appear to possess to a greater or less extent this power of condensing gases on their surfaces. Fio. 96. The amount of the condensed gases is dependent on 1. The area of the surface of the solid. A small piece of charcoal, on account of its porous con- dition, presents a very large surface to a gas in which it is placed. 2. The nature of the solid and of the gas. Charcoal condenses about twice as much anunonia as it does carbon dioxide on the same surface. Certain metals, especially platinum and i>alhidium, possess this power in a high degree. f f Hi'' 140 PHYSICAL SCIENCE. 8. The Temperature- The absorption of a ^as by a metal litis received the name of occlusion. The efficiency of charcoal as a deodorant and disinfect- ant is probably duo to the action of the oxygen con- densed in its pores upon the noxious gasea cirArrKH xiv. SPECIFK; liKAVITV. I— Relation between Specific Gravity and Density. Tlie specific <(ravity of a Ixxly is the ratio of its wei^'Iit to the weight of an e(|ual volume of water at 4' C. Or .specific i^ravity of a Ixxly its weiglit weight of an equal volume of water We have seen that the density of a body is the mass of a unit volume of it. In the C. G. S. system of units, since the cubic centimeter is the unit of volume and the gram the unit of mass, and one cul)ic centimeter of water has a mass of one gram, the number expressing the den- sity of a body will also indicate its specific gravity. For example, the specific gravity of gold is 19.86 ; that is, a piece of gold weighs 19.36 times as much as the same volume of water ; but the density of water is one gram per cubic centimeter, therefore the density of gold is 19.36 grams per cubic centimeter. While the numbers are the same it should be remem- bered carefully that the measure of the density is the number of units of mass (grams) in a unit of volume (cubic centimeter), and the specific gravity of a body is the number of times the weight of any volume of the body contains the weight of the same volume of water. [141] I ' 141! PHYSICAL SCIENCE. II.— To Find the Specific Gravity of a Solid. 1. To Find the Specific Gravity of a Solid Heavier than Water. Method I. Experiment 1. Weigh a piece of lead. Weight (W) = gm. ? Tie a thread to it and sink it in a ffradu- ated tube partially filled with water (Fig. 97). Observe the volume of the water dis- placed by it. Volume (V) = c.cm. ? But 1 c.cm. of water weighs 1 gram. Therefore V gm. = weight of water equal in volume to the wood. Fio. 97. Specific gravity of lead = its weight weight of equal volume of water. w not If the solid is soluble in water another liquid in which it is used in the graduated tube. ay Method 2. Experiment 2. Weigh an iron nail in .air. '< Weight (W)= Tie a thread to it, suspend it from the scale pan of a balance and weigh it when surrounded with water (Fig. 98). Weight (Wj) = \ lliil SPECIFIC GRAVITY. 143 Therefore W - Wj = the loss in weight in water. = the buoyancy of the water = the weight of water equal in volume to the nail (page 112). But the specific gravity of a body its weight weight of an equal volume of water. Therefore the specific gravity of the nail its weight loss of weight in water, W W-Wj = ? i / / I. 1 \ B. HIP g, ■' -v mA^-: g^fe^^y • ^ — '-"Wl m iiiiE Experiment 3. Find in the same way the specific gravities of pieces of glass, lead, rock, etc. t 1 n fti i 144 PHYSICAL SCIENCE. If the solid is soluble in water, its specific gravity may Ikj obtained by finding, as above, the ratio of its weight to that of an equal volume of some liquid in which it is not soluble, and then multiplying the result by the specific gravity of this liquid. 2. To Find the Specific Gravity of a Solid lighter than Water. Method 1^ Experiment 4. Weigh a piece of wood. Weight (W) = gm. 1 By means of a needle, or a piec3 of fine wire, sink it in a graduated tube partially filled with water (Fig. 99). Observe the volume of the water displaced by it. Volume (V) = c.cm. 1 But 1 c.cm. of water weighs 1 gram. Therefore V gni. = weight of water equal in volume to the wood. Specific gravity of the wood its weight Fio. 99. not weight of an equal volume of water, W _ --= ? "~ V If the solid is soluble in water, another liquid in which it is soluble may be used in the graduated tube. Method 2, Experiment 5. Weigh a piece of wood. Weight (W)= $ m SPECIFIC GllAVlTY. U5 ' Tie r„ piece of lead to the wood and weigh the two together when, surrounded with water. Weight (Wj)== 1 Now weigh the led, it will receive sufficient heat to cause the water to boil and to eject the cork. Explain the reason, [153] :i . t! 154 Experiment 2. niVSlCAL SCIKNCK. (2) From Percussion. Place a piece of lojul ajK»r and pound on tlie j)lios- pliorus. What takes j)lace '( Moat chemical clian^^os aio aecompaiiiod by chan^fs in the (iuantities of licat posst'ss(>(l by the bodies takin<^ part in them. This is tlie source of the heat resul tin <^ from combustion, wliicli is but a particular case of chemical action. 3. Heat tiom an Electric Current. Experiment 6. Connect three or four Buiisou or (Jrenet cells as shown in Fig. 108. Attach a copper wire tv) each pole, and conipU^e the circuit by attaching to the free end of one of the copper wires a piece of fine j^lutinuin or iron wire four or five inches Fio. 108. long, and touching the end of the other copper wire to the end of the platinum or iron wire. (The fine iron wire used by florists answers well) Slide the copper wire along the iron wire up towards the other copper wire. What evidence have you of the production of heat ? I. \ 11 i It? 156 PHYRICAL SCIENCE. Whenever an electric current meets with resistance in a conductor heat results. Tlie fine iron wire offers con- siderable resistance, and if a suffieientlv stroni;' current be made to pass tlu'ough it, tlie wire will become white hot and burn up. How are the filaiuents in incandescent electric lamps heated? The relation between heat and the Qnergy of an electric current will be more fully discussed under Electricity, Part II. 4. Heat from Radiant Energy from the Sun. This is by far our most important source of heat. We shall consider at a later stage the theory regarding the transmission of the sun's heat to us in the form of Radiant Energy. In the following chapters we shall discuss some of the effects of heat, viz.: expansion, change of temperature, and change of state. 1 1 l«r CHAPTER XVI. EXPANSION THROUGH HEAT. 1. In Solids. Experiment 1. Take a brass ball and ring (Fig. 109), such that ordinarily the ball will just pass through the ring. Heat the ball intensely in the flame of a Bunsen burner and try to pass it through the ring. 1. "What change has taken place in the vol- ume of the ball ? 2. Will it pass through the ring wlien it has cooled ? _ Pio. 109. 3. How could you make the hall pass through when hot ? Experiment 2. ^.rran^e apparatus as in Fig. 110. A metal rod is fixed at Fl». 110. one end while the other presses against a compound lever so arranged that the slightest elongation of the rod is indicated [157] ■S '»![ ') I s 158 PHYSICAL SCIENCE. on a scale. Apply heat to the rod and watch the end of the pointer on the scale. 1. What do you observe ? 2. What does the experiment prove ? 3. Allow the rod to cool, and what is the result ? Experiment 3. Prepare a compound bar made up of two strips, one of iron and the other of copper, riveted together as shown in Fig. 111. Heat this bar strongly in the flame of a Bunsen burner. Fia. 111. 1. What is the result ? 2. Which metid is on the con:ive side ? 3. Which metid is the more elongated through heat ? 4. What result would you expect if the compound bar were made very cold ? Try. From these experiments we see that solids expand through heat, and some expand more than others. 2. In Liquids. Experiment 4. Fill a flask with water, insert a perforated rubber stopper through which has been thrust a "mall glass tid)e open at both ends, and attach a paper scale j the tube as shown in EXPANSION TIIKOUGH HEAT. 159 Fig. 112. Apply heat to the flask and watch the column of water in the glass tube. 1. What is the result ? 2. Which expands the more rapidly through heat, water or glass? 3. Prepare auotlier flask and tube identical with tlie first, filling it with alcohol instead of water. Place the two in the sanie bath of hot water and watch the result. It is found that liquids as weU as soUds expand through heat, and liquids in general expand more rapidly than solids, while some liquids expand more rapidly than others. Fig. 112. 3. In Gases. Experiment 5. Arrange apparatus as in Fig. 112. A is a glass flask filled with air connected by a tube open at both ends with a '/ f 160 fItYSICAL SCIENCE. :\ 9 i; t' bottl© B partly filled with water. Apply heat to A and watch the end of the tube below the surface of the water in B. 1. What is the result ? 2. What does it prove ? 3. Allow A to cool and watch the water. What follows ? 4. What does this result prove ? We find that gases expand very rapidly through heat. m ''ii',i QUESTIONS. 1. A glass stopper stuck in the neck of a hottlo may he loosened by subjecting the neck to violent friction by means of a string. Explain. 2. Pipes of cast iron for conveying steam or gas, if of consider- able length, must have expansion joints. Explain the reason. 3. Why does a blacksmith heat a waggon tire before adjusting it to the wheel ? 4. The rate at which a clock runs depends on the length of its pendulum. Would you expect it to keep accurate time both in sunnner and in winter ? 5. If a large leaden bullet is cast in a mould a small cavity is found near its centre. What is the reason of this ? 6. Why must the water used in Experiment 1, page lOH, he tjiken at the temperature of the room ? 7. WHiat variatieen for some time in contact witli the same air, have the iron and the wood diflferent temperatures ? 2. Do you experience the same sensation on touching them ? 3. Which leels the colder ? From this experiment it is seen that our estimation of the temperature of a body by means of our heat sense depends on the material of the body as well as upon its temperature. Therefore for various reasons we cannot depend upon the heat sense for the accurate determina- tion of temperature. Change of temperature in a body is accompanied by other changes, and by observing some of these we may indirectly determine the temperature. Any instrument constructed to thus enable us to estimate the tempera- ture of a body is called a thermometer. Of all the changes accompanying change of temperature, change of volume is generally the most convenient for estimating change of temperature, since it can be observed by means of our sense of sight, perhaps the most exact of all our senses. 3. Mercury Thermometer— Oonstruction. Procure a glass tube of very fine uniform bore, blow a bulb on one end, and a funnel on the other (Fig. 113). Pour some mercury in the funnel and gently heat the bulb. The air expands and a part of it bubbles out through the mercury in the funnel. Allow the bulb to cool. The air pressure on the surface of the mercury in the funnel forces some of the mercury through the tube into the bulb. Now heat the bulb above the flame of a Bunseu burner until the mercury TEMPERATURE. 165 air rin on the the jury boils long enough to expel all the remaining air. As the bulb cools the mercury vapour will condense and mercury will run down the tube and completely fill the bulb and tube. Again heat the bulb, and the contained mercury will expand, causing some to overflow at the open end of the tube. While the mercury is overflowing, direct a blow-pipe flame upon the open end and seal it up, at the same instant removing the bulb from above the flame. The instiniment now contains a fixed mass of mer- cury, which is free to contract or to expand within cer- tain limits, and the construction is such tliat a small change in tlie volume of the liquid is easily observed. Mi & 1 r- ht ^ i 1 ^ ^ Fig. n3. Fio. 114. 4. Findlxis the Freezing Point. On a convenient support place a funnel, fill it with snow or melting ice, and place in it the bulb of your thermometer, as shown in Fig. 114. The mercury, contracting faster than the glass, will drop down the tube. When the mercury ceases t If ■W il i 1 166 PHYSICAL SCIENCE. r>» to fall, indicating that its temperature is no longer changing, and hence that it has reached the temperature of the melting ice, mark with a file on the tube the position of the upper sur- face of the mercury. 5. Finding the Boiling Point. Next expose the bulb and tube to the steam rising from pure water boiling under a pressure of 760 mm. of mercury, as in Fig. 115, taking care that the bulb is not plunged into the water, but remains suspended above it. Mark with a file on the tube the termination of the mercury column. 6. Oraduation. Having thus marked the freezing and the boiling points, the next thing is to graduate the instrument. Fio. 115. If you wish to make a Fahrenheit ther- mometer, mark the freezing point 32" and the , •_ boiling point 212°, and divide the intervening portion of the stem into 180 equal parts, ex- tending the graduations above the boiling point and below the freezing point. If you wish to make a Centigrade thermometer, mark the freezing point 0" and the boiling point 100°, 32- and divide the intervening portion of the stem into 100 equal parts, extending the graduations °""' as in the previous case. In Fig. 116 both methods of graduation are represented. Fio. 116. 1. Why is it necessary that the bore of the tube should be of uniform size throughout ? 2. Why should the bore bo very small ? TKMPKKATUIIE. 167 7. Oomparison of Scales. 1. What tein])emture on the Contignulo hchIo in tho Hiiiiie as 0° (zoro) on tho Fahrenlieit kcjiIo 't 2. What temperature on the Centit^ratle scale i» the Humo Jis 100° on the Fahrenheit scale ? 3. How many Fahrenheit degrees above freezing point is 41° on the Fahrenheit scale (41" F.) ? How many Centigrade degrees then is it ? Wliat is its reading on the Centigrade thermometer ? 4. How many Centigrade degrees is 10° C. from the freezing point ? How many Fahreidieit degrees is it ? How many Fahren- heit degrees is it from the Fahrenheit zero ? What is its reading on the Fahrenheit scale ? 5. Find the Fahrenheit residings corresponding to the following Centigrade readings : 12\ 76°, - 10% - 40^ 6. Find the Centigrade readings corresponding to the following Fahrenheit readings : m\ 180^ - 5^ - :M)\ 7. The temperature of a room is T° C. What is its reading on the Fahrenheit scale ? 8. The temperature of a room is T° F. What is its reading '<3d and its volume kept ccm- stant, what change may take place iii («) its mass, (b) its density, (c) its absolute temperature ? 3. If the pressure of a gas is lessened so that it becojuea one- half the original pressure, while the t( mperaturo is kept constant, what change takes place in (a) the v«)lun e, (h) the density of the gas 1 4. If the volume of a given mass of gas is IX) c.cm. at 27° C , what will the vohnne become at — 2'i° C if tiie pressure is kept constant ? 5. If the volume of a given mass of gas is 1 litre at a temj)era- ture 0" what will be its volume at a tem})erature of («)100° C, (h) — 13° C, the pressure remaining constant 'i G. At what temperature will a gas, the volunie of w'nicli is 1 litre at a temperature of 0^ C, become 12tMJ c.cm. in ^'olume, the pres- sure remaining constant ? 7. What change will be produced in the ]>res8ure of a gas "hy changing its temperature from 0° C. to 27«'i° (^'.y the volume remain- ing constant ? 8. What will be the volume of a mass of air measuring 1 litre at 0'' C, if the temperature is raised to 273" C. and the pressure doubled^ io 174 PHYSICAL SCIENCE. If" } ! ' ! t i! 9 1)1 Nil ^i i 9. A closed tul)e filled witli air at 0° and under atmospheric j)reHsure is gradually heated. If the tube can safely stand a pres- sure of 4 atmospheres, to what temperature may it be lieated ? 10. Find the volume at 45" C. and under a pressure of 1500 mm. of mercury, of a mass of air whicli, at 27° C. and under a pressure of 760 mm., occupies 10 c. ft. 1 Since the volume varies directly as the absolute temperature, and the temperature is reduced from 45° C. to 27" C. the volume will be reduced and become 273 + 27 = 300 27S4-45 'TlS '^^ ^^^^ original volume when the pressure remains constant ; but since the volume varies inversely as the pi-essure, and the pressure is reduced from 1500 mm. to 700 mm. of mercury the volume will be increased and liecomo 15(X) -,.^ of the original volume. Hence the volume required will ))e Lq 300 1500 \ \ ^3l8^~7(iO ^) '^' 11. The volume of a certain mass of gas at a temperature of 17° C, and under a pressure of 600 gm. per s([. cm. is 10(X> c.cm. ; what will be its volume at a temperature of 27° C, and under a pressure of 1000 gm. per sq. cm. ? 12. A mass of gas occupies a volume of 22.4 litres at the tempera- ture 10° C. when the barometer stands at 70 cm. , what volume will it occupy at the temperature 0° C. when the barometer stands at 76 cm. ? 13. To what temperature must a gas be heated in order that its volume nuiy become double of what it is at 20° C. i 14. A litre of hydrogen weighs 0.0896 gm. at 0° and 760 mm. barometric pressure. Find the weight of a litre at 20° C. and 766 mm. pressure. 15. The density of air at 0° C. and 760 uun. pressure is 1.29 grams per litre. What is its density at 273" C. and ](X)0 una. pressure ? , ft. CHAPTER XVIII. CHANGE OF STATE. I.— Solid to Liquid and Liquid to Solid. 1. Fusion. Experiment 1. * Partly fill a large vessel with water at a higli temperature, say 90° C, and in it place a small vessel partly filled with water at a low temperature, say 10° C, and place a ther- mometer in each. 0]>serve the chan-es of temperatu.-e in the two vessels for a minute or two. Now fill the smaller vessel with wet snow or finely broken ice at 0^ and observe the change of temperature in the two vessels while the snow is meltin<^^ 1. What change occurs in the temperature of the water in the large vessel in the first case ? 2. What in the temperature of the water in the small vessel ? 3. Which body loses heat ? 4. Where does this heat m^'i 5. What does this heat do ? 0. What change takes place in the teuiperature of the Avater in the large vessel in the second case 'i 7. What in the temi^erature of the contents of the small vessel / 8. Does a change of any kind take phice in the contents of the small vessel ? 9. ^^^lich body h)ses heat? 10, Where does it go ? 11. WJiat does this heat do ? I 17a I 1 ll'l I*: 1 i ■ ! ;■ ( i P t r 4; 17() 1'hysic'al sciknoh:. Experiment 2. Heat a tliiii «^lass tuln! about 5 min. in (liumoter and draw it out into a fine tliroad, as sli()wn in Fi«'. 120. ir<'at some •^1 nMW'iiir --■ *^^' Fid. 1-JO. parafiin wax in a test-tulje and l)y .suction draw somo jf the liijuid paiatfiu into the line i)art of the tube. Close the point by fusinijf the extremity in the flame. A]l(jw the paraliin to solidify, and fasten, by means of a rul)ber band or til read, the tube to a chemical thermometer (Fig. 121). Place the tu])e and thermometer in a beaker of water, and gradually warm the water. Stir the water constantly and notice its temperature when the j)aiafhn in the thin tube melts. Allow the water to cool and note the tem])erature at which the paraffin solidifies. 1. At what teniperiituro does the paraffin melt !■ 2. At what temperature doos it solidify ? 8. Find the melting points of other bodies in the same way. 4. IIow do their melting pohits compare with their points of solidification ? 2. Solidification. Experiment 3. ;Melt some paraffin wax in a beaker, ard when it is all melted place the beaker in another vessel slightly larger and Fio. 121. CflAN'CK Ol' STATE. 177 lei* oi all jtnrtially ilUrd m itli t'(»l(l water". Oliscrve the tcimx'i-ature of the Nvater from time to time. 1. What cliange takes place in the paraffni ? 2. What change takes place in the teniperatnn; of the water ? 3. Is any heat given out by the paraftin while it is solidifying? How do yon know ? 3. Laws of Fusion. The alK)ve .and similar experiments prove the following law\s : — - (1) A substance begins to melt at a temperature which is constant for the same substance, if the pressure is constant. (2) The. temperature of a solid remains unchanged while fusion is taking place. (3) The temperature of solidification is the same as the tem- perature of fusion. (4) If a substance expands on solidifying, like ice, its melting point is lowered by pressure; if it contracts, like wax, its melting is raised by pressure. 4. Solution. Experiment 4. Partly fill a beaker with water and note the temperature. Measure out two or tin-ee grams of auimonium nitrate and note its temperature. Put the ammonium nitrate in the water and stir the mixture with a thermometer. 1. What is the tenipemture of the water at first? 2. What is the temperature of the atumonium nitrate ? 3. What teTiii>orature dfM>s ihe mixture reach ? 4. What change uo you observe besides chan^i vi Lcniperature ? 5. What form <»f energy disapptvars ? 0. What is the result pi^Kbuvd by tins energy ? n I ' ' 178 PHYSICAL Science. K h4 ffi li f i K \ ! * k J, j\ t 'V I iM Experiment 5. Break some pieces of ice into small fragments and mix with common salt. Place a thermometer in the mixture. 1. What is the temperature of the ice and of the suit hefore the mixture ? 2. What temperature does the mixture reach ] .3. What change besides change of temperature takoa place 1 4. What energy disappears ? 5. What result does this energy produce ? 6. Does this energy cease to exist ? 7. If not, where can it be ? 8. If a stone is thrown upwards it moves slower and slower as it rises and at last stops. Wl.at has become of the energy due to the velocity with which it started ? II. — Vapourization and Liquefaction. 5- Ebullition. Experiment 1- Partly fill a flask with cold water and insert a perforated stopper containing a tube open at both ends, and a thermometer, as represented in Fig. 122. Place the flask over the flame of a Bunsen burner and let it remain until the water has boiled for some time, carefully watching the thermometer mean- while. 1. What change takes place in the tem- perature of the water at first ? 2. Where does the heat come from that effects this change ? 3. At what temperature does tlie water begin to boil ? 4. After the water has begun to boil, what change takes place in its temperature 'i Fia. 122. CHANGES OP STATE. 179 5. Does tho Water continue to receive heat after it lias l>e«^iin to boil? 6. If so, what does this heat do ? Experiment 2. 1. With the apparatus shown in Fig. 122 determine (a) the temperature of pure wator wlien boiling, (b) the tempera- ture of the steam rising from it. 2. Determine these temperatures in the case of water having some common salt in solution. 3. Mix three parts of water with one of alcohol and deter- mine the temperature of the billing liquid and also of the steam. 4. Sprinkle some iron filings in the flask with pure water and repeat the experiment. Experiment 3. Arrange apparatus as in Fig. 123. Heat the water in the flask containing the thermometer until it begins to boil. bem- FiG. 123. Then, removing the lamp, by means of the attached air-pump exhaust the air from the apparatus, thus lessening the pressure on the surface of the hot water. 180 PHYSICAL SCIKNCE. 1. WliJit takes place wlinn y<»u Ixj'^iii to work tlus air-pinin)? 2. What cliango of toniiH;ratiiro do yoii ohservo '{ 3. What is the lowest teiiiperatiiro at wliicli ytiu can make the water boil ? M Experiment 4. Half fill H fljisk with water and boil for a niinuto or two so that llie escaping steam may oxjxd all the air. Wliilo it is boiling vigorously, remove the ilame and at tlie same instant close the flask with a rublxn* stopper. Tnv(U't the flask and siip2X)rt it on a retort stand as in Fig. 121. Pour cold water over the flask and watch the result. Kow pour very hot water over the flask and see what happens. Again pour cold water over the flask or, still better, immerse the j.'m p,4. flask in cold w»ter. 1. What happens when cold water is first poured over the flask ? 2. What when the hot water is poured on ? 3. What takes place when the cold water is again poured on, or the flask is immersed in cold water ? 4. With a theruKniieter determine the temperature of the water in the flask at the end of the experiment. 5. What does the flask contain after it has been closed by the stopper I 6. What change in its contents is produced by pouring cold water on it ? 7. Can you see any connection ])etween the result of this experi- ment and that of the previous one ? t'IIAN(;K <»F STATK. ISl 6. Evaporation. Experiment 5. Wrap a piece of muslin about tlio flask A of tlio air- thermometer (Fig. 11-) and set the instruiiieiit in an open window where there i.s a draiii,'ht. Pour ether on the muslin drop l)y drop and wateh the result. 1. What becomes (tf the ether ? . 2. What cluingo in tuiupuraturo does the air-theruiouietor indicate i Experiment 6. Pps of (;ther on the back of your hand. 1. What change of state takes place ? 2. What evidence have yoti that your hand loses heat ? 3. What does this heat do ? 4. What eftect on the rate of evaporation follows from an increase in the temperature of a licpiid, other conditions remaining the same '^ 5. From which will a given volume of water evaporate more (piickly, a narrow deep dish or a broad shallow one ? 6. Wliy do we set the apparatus in a draught in Experiment 5 ? The quiet vapoiirization tnkinor place at the surface of a liipiid i.s called evaporation. The rate at whicli evaporation takes place depends upon the nature of the li(piid, its temperature, the amount of tlio vapour of the liijuid in the surroundino- space, and also the presence in the surrounding space of other gases. 7. Saturation— Dew Point. The quantity of a pai'tieular vapour which a given space can hohl dei)ends upcju the vapour and the tem- perature, but is independent of the presence of other .^vV. IMAGE EVALUATION TEST TARGET (MT-3) k A -i ^/ '•^'<^4is y. 4v f/. f/. 1.0 1= 11.25 140 ||U|2.0 m 1.4 11 1.6 Hiotographic Sciences UDiporation )3 WEST MAIN STREET WEBSTER, N.Y. 14580 (7(6)872-4503 V V [v %^ N> ^ O ?C^' <^ <' o^ 182 PHYSICAL SCIENCE. f^ases. A space containing all of a particular vapour which it is cajmblc of holding is said to be saturated with that vapour. The tein[)erature at which the water vapour present in the atinasphere would saturate the space it occupies is called the dew point. 8. LiquefiEUitioii. Experiment 7. Prepare the apparatus slujwn in Fig. 125. Two flasks are connected by a long tul)e, the greater part of which is sur- rounded by a much larger tube so arranged that cold water may be made to circulate in the space between the two tubes. Fio. 126. Partly fill the higher flask with a mixture of alcohol and water in the ratio of one of alcohol to three of water. Boil the mixture. The steam in passing through the cold tube is condensed, and the resulting li(|uid is caught in the lower flask. After you have collected a suiall quantity of liquid in the lower flask, take away the flame. Cool both flasks and CHANGE OF STATE. 183 pour jKirt of the cont<'tits sopanitoly into two evaporating dishes. Try to set fire to the h(|ui(ls with a Hjrhted niateh. 1. Are the two liquids the same? 2. Which contains the greater proportion of water ? 3. How could you ohtain fresh water from sea water ] 4. How could you obtain salt from sea water ? 5. What change takes place in the temperature of tho water used to cool the tube ? 6. Whence comes tlie heat required to i>roduce this change ? Tliese and otlier experiiiiuutM CHtablish laws of ebulli- tion as fol'ows : — (1 ) A liquid begins to boil at a temperature which is approxi- mately constant for the same substance if the pressure is con- stant. (2) The temperature of the boiling liquid remains unchanged until the whole is vapourized- (3) Increase in pressure raises the boiling point of all liquids. (4) The boiling point of water is raised by the presence of salts in solution. Tijese experiments also show that heat is expended in chan<^ing the state of a body from a solid to a li(iuimisen flamo in t sccrdMls = 500 (100 -T) calories. Quantity of heat received from the llunsen flanuj in l^ seconds =^ -j- 50') (100 - T) calorii.'s. But this heat evaporates (500 -m) jnrrams of water at 100". Then^fore th(^ <|uantity of heat re A until the water in it boilrt freely and Hteani is esca[)ing from the open tul>e. Now care- fully note the temperature of the water in C, wrap it in flannel, and place it as shown in the diagram. Keep stirring the water in with a thernnimeter, observing the tempeni- ture from time to time. Allow the Ixjiling to c a flat circular vessel to the dcj>th of about an inch. After the pai'affin has cooled, remove the cake and support it as shown in Fig. 128. Procure a number of balls of different materials, lead, tin, copper, zinc, iron, etc., and of the same mass. Heat the balls to the same temperature in a vessel of boiling Fio. 128. 199 PIIYSIfAf, SCIKNCK. n f t i wattT. Takiii;; (Ih'iii from IIm; vv.itri-, plucn tlirm mi l\m rakn of parallin aiul waicti tlit; ri'sult. 1. Wimt tiikuH phicu HH each ImiII givuH u\t H4»iiiu of itH liuut to tliu ixiratlin ? 2. Aro tho balls C4M)led tliroii^h tho miiiu) luiialiur of ilugrues bvfore cuaHing to givu up heat to tho parattin t 3. Ih tho roHult tlio Haiau in all autOH ? 4. What produces tho roHuIt in each case ? 5. Wliicli l)all gives up tho greatest (juantity of lioat in C(»oIing from tho temperature of the water iMtth to that of tlie parufliu ? Tlio al)()Vo oxporiiiient indicates tluit cmjuhI inaHsc^s of diftbruiit su]).stanc('H jjjive out iliH'crent <|uantitios of li(3at in coolinj^ tlirou^^di tlio sanio ran^o of temperature, but it does not t;na])le us to compare those (juantities with any degree of accuracy. The quantity of heat required to change the tem- perature of a unit mass of any substance 1 ' is called the capacity for heat of that substance. 5. The Calorimeter. To determine accurately tho quantity of lieat given out by a particular lK>dy in cooling through a known range of temperature, an instrument called a calori- meter is used. One form of calorimeter is shown in Fig. 129. It consists of three metal vessels separated from one another by layera of broken ice. A pipe leads from the middle vessel to the outside, through which the water formed by the melting of any of the ice in this vessel will run. The inner vessel is to contain the liot body, and the layer of ice between the outer and middle MKAHUK»i:MKNT <»F HEAT. 193 t]iu vt'Hsels is to prrvt'iit any <»l' tlio ico in tho iiu/iTs) calories. 1. What is the specific heat of the lead in the above experiment ? 2. Determine the specific heat of zinc, iron, sand, etc. Experiment 3. Determine the mass of some shot. Mass (?«) = grams? Heat the shot in steam to a temperature of 100'' as in Experi- ment 2. MEASUREMENT OF HEAT. Determine tlie mass and temperature of some water. 195 Mass (wij) Temperature (T^) ^^ = grams? 1 Place the water in a beaker, or better in a tliin metal vessel polished on the outside (a lemonade shakor answers mcII), surround the beaker with some wool or batting. Pour the shot into the water, stir the two to^'other, and when the two have reached the same temperature determine tli<^ temperature. Temperature T.> s=s o? Heat gained })y water = m^ (T, - TJ calories. Heat lost by shot = m (100 - T.) x calories if .« is the speciHc heat of the sliot. But heat lost ])y sliot ^^^ luvit gained by water, or, m(100-T,)u:=m^(T,-T,) ^_7/.,(T,-T^__ ;/^(100-T,)- II.— Mechanical Equivalent of Heat. The connection between the unit of lieat (ener^ry of molecular vibration) and the unit of mechanical eiu'rjry (ener^rv of bodily onward motion) is a matter of grc^t 196 PHYSICAL SCIENCB. i [ ' i' importance. This connection was fii-st accnrately deter- mined by Joule, wlio used the a2)paratus illustrated in Fig. 131. , : '',i Fio. 131. ; : "..1^ B is a copper ves.sel filled with water and provided with a brass paddle-wheel, arran<,^ed somewhat like a churn. This paddle is driven by a falling weight sus- pended from a roller connected with a pulley C provided with friction-wheels. A cord wound on this pulley passes round the vertical paddle-shaft A. As the weight E falls the paddle revolves and the water in B is heated by friction. A thermometer T indicates the temperature of the water. With this apparatus Joule learned that the quantit3^of heat required to raise the temperature of one pound of wat'^r one Centigrade degree is the same amount of encigy as is expended in raising a mass of 1,31)0 pounds through a vertical distance of one foot (1,390 foot pounds). MEASUREMENT OP HEAT. 197 The value of the heat unit expressed in units of mechanical energy is called the mechanical equivalent of heat. Fn»in .T( Mile's determination us given above calculate the value of the calorie in gram-centimetres. QUESTIONS. 1. If 10 lbs. of water at 12° C. be mixed with 40 lbs. of water at 90 C, find the temperature of the mixture. 2. Fifty grams of ice are i)laced in 520 grams of water at li)."8 C. If the resulting ^cinperature is 10. 5 C, what is the hvtent heat of fusion of ice ] 3. Steam is passed into a nuiss of 405 grams of water at 15. 2 until the temperature becomes 35. °4. The mass of water and sondensed steam is now 512 grams. What is the latent heat of rapourization of water ? 4. The lat(Uit heat of fusion of ice is 80 ; find ((f) AVhat mass of water at 00 C. will melt 100 grams of ice. (h) AVhat mass of ice must be dissolved in a litre of water at 4° C. to reduce the teuiperature of the v.ater to 2" C ((') The resulting temperature when 30 grams of ice are dropped into 100 grams of water at 50^ C. (d) The specific heat of brass if a j)iece weighing 80 grams, heated t«> 100° C, melts 9 grams of ice when placed in an ice calorimeter. 5. The latent heat of vapouri/ation of water is 537; tind ((») The resulting temperatiu'c when 25 grams of steam at 100° are passed into 300 grams of ice cold water. (/>) How many calories will be required to convert one litre of water at 4" C. into steam at KX) C. (c) How many grams of steam at 100^ C. will just melt 10 Uiams of ice at 0^ C. Is It*; 1 CHAPTER XX. TRAXSMISSION OF HEAT. It is a matter of common experience that heat lias a tendency to pass from a warmer to a colder bo) ice jjitchers, made of substances whicli are poor conductors of heat ? 1. Relatative Conductivities of Solids. Experiment 3- <-.,» n' H Take nxls of copper, glass, iron, bone, etc., and })lace one end of each in a btassium nitrate (salt])etre) and then drying it. Light some of the paper and hold it ahove the flame of a candle, or better, above the chimney of a burning lamp. 1. What are the directions of the air currents which the pnioke renders apparent i 2. What ia the cause of these currents ? Experiment 7. Make a M'ooden or metal box of the form shown lu Fig. 139. The front should be a pane of glass which slides into its place through grooves. Cut two holes in the top of the box and over each hole place a lamp chimney. Rtv move the front, light a candle, place it under one of the chim- neys in the position shown in figure, and replace tlie front. Light some touch paper and hold it over the other chimney. Fio. 139 Describe and explain the currents of air observed. Close the chimney B with your hand. 1. Wliat happens after a short time ? 2. Explain the reason. 208 PHYSICAL SCIENCE. Experiment 8. Place a lighted candle in a large glass jar (a candy jar answers well), and insert a perfor- ated cork into which glass tul)es are placed in the positions shown in Fig. 140. 1. Does the candle continue to burn ? 2. If so, explain how fresh air is supplied to it and how the products of combustion are removed from the jar. Draw the right hand tube up to the position shown in Fig. 141. Observe the burning of the candle for a short time. WliJit takes place ? Explain the reason. 9. Ventilation. Fio. 140. Flo. 141. Experiments 7 and 8 illustrate the modes of produc- ing air currents, and show the necessity of providing a means of ingress as well as egress to any confined space in which the air is being vitiated. The air of dwelling houses is vitiated by the respiration of those living in them and by the combustion of the oil or gas used for lighting. Means of removing the foul air and bringing in fresh air should be provided. The pro- duction of convection currents is the simplest expedient. This principle is taken advantage of in the heating and tlie ventilating of buildings by warm air furnaces. Fig. 142 shows a system of heating and ventilating rooms in which a number of persons are required to I'RANSMISSION OP HKAT. '209 jas ind jro- Int. |es. Pg to femain for a considerable time. Tlie air comes from the outside through the fresli air opening into the fresh air room, passes over tlie furnace, is heated, and ascends through the warm air tube into tlie rooms. After circulating through a room and heating it, the air passes through vents in the wall into foul air spaces under the floor and down through a duct into the foul air Fio, 142. gathering room. From this it is taken to the outside of the building by a vent flue, in which an upward draught is maintained by means of the heat which it receives from the hot smoke flue placed alongside of it. 14 210 PHYSICAL SCIfiNCH. The air passages are so arranged that a part of the cold air from tlie fresh air room may pass through a valve directly into the warm air flue without passing over the furnace, the quantity of this air being regulated by a regulator connected with the valve. In this way the temperature at which the air enters the room is under control. In summer, when the furnace is not in use, the circulation, for the purpose of ventilation, is maintained by keeping the vent flue hot by means of a small stove or a flue heater kept burning at its base. i^a 10. Convection Currents in Nature. Winds are the result of convection. Different parts of the earth's surface become unequally heated, and air currents are consequently set up. Their directions depend mainly on the position of the heated belts and the rota- tion of the earth. I! Ocean currents are to a certain extent the result of convection, but these are also influenced by the action of the prevailing winds. III.— Radiation. Experiment 1. Heat an iron ball to a high temperature and place at a distance of a foot or two from it and on a level with it, the bulb of an air thermometer or one of the bulbs of a diflfer- eutial thermometer (Fig. 143). 1. Wliat change in teini)erature does the tliennometer indicate? TUANSMISSION OP IIKAT. 211 2. Is this change in temperature due to a change in the tempera- ture of the surrounding air 1 To answer this question interpose a screen of glass or tin between the ball and the thermometer. What do you observe 1 The heat is said to be transmitted from the hot ball to the thermo- meter by Radiation. In the same way heat is transmitted to bodies in a room from a hot stove or from an open fire, and from the sun to the earth. This transmission is inde- pendent of the air as it takes place in the most perfect vacuum we can j)roduce. To explain the phe nomena of radiation it is found necessary to suppose that a medium^ called etheTj pervades all space and penetrates between the molecides of all ordinary mattery which are embedded in it and probably connected with one another by its means. llie vibrating molecules of a hot body communicate their motion to the ether which surrounds them, and thus cause vibra- tions to be set up in the ether. These mbrations by a species oj wave motion pass from the heated body in all directions through the ether, and may, on reaching any body of matter, communicate their energy to its m,olecideSf and it in turn is heated. The transmission of heat then by radiation consists in the transformation of the energy of molecular vibra- tion, or heat, into the energy of ether vibration, or FlQ. 143 212 PHYSICAL SCIENCE. ; I '.' lit;^ radiant energy; and the retransformation of radiant energy into heat. The first transf on nation is generally called Emission, the second Absorption. 10. The Emissive Power of a Body. Our most coiumoii experiences teach us that the emissive power of a body — tliat is its power to transform heat into radiant energy — varies with its temperature. A hot stove radiates more heat tlian a cold one. But the emissive power does not depend on the temperature alone. Experiment 2- Fio. 144. Blacken the bulbs of a differential thermo- meter by smoking thorn ovor a candle flame, turn them up as shown in Fig. 144. Blacken one of the faces of a cubical tin box about four or fi'" inches wide, fill it with boiling water and place it midway between the bulbs, with the blackened surface facing one of the bulbs and the opposite bright suiface facing the other bulb. 1. At what temperature is eacli of the surfaces of the cube '( 2. Which bulb of the thennouieter absorbs the most radiant energy { * 3. Which surface, the blackened or the bright one, has the highest emissive power i Repeat the experiment, roughening with sand-paper one of the surfaces, and leaving the opposite one polished . Which has the higher emissive power, the polished surface (»r the roughened one ? TRANSMISSION OP HEAT. 213 bhe [ht of he Experiment 3. Take two snuill tin cans of tlie same size furuishod with lids, cut a hole in each lid through which, a stirrer and a thermometer can be inserted. lilacken the outside of one and polish that of the other. Pour the same quantity of water heated to the same temperature (70° or 80° C.) into each, and place them on some non-conducting material. Stir the water in each can at intervals and take the toin})erature. 1. Wliich can loses lie;it the more rapidly ? 2. Which has the higher emissive power ? The emissive power of Ji l)ody depends upon 1. Its temperature. ^ The nature of its surface- Dull, black surfaces have the higliest emissive pDwer uiid bright polished ones the lowest. 11. Absorptive Power. Experiment 2. Place an iron ball heated to a high tem- perature (Fig. 1 45) midway between the bulbs of a differential thermometer, one bulb of which is blackened, the other covered with tinfoil. 1. What change do yon observe in the litiuid levels ? 2. In which bulb is the m(»re radiant energy transformed into heat? This experiment and others of the kind sbow that a body whose emissive power is high possesses great absorptive power, or that, as it is generally stated, good radiators are good absorbers. f,o. 145, 2U PHYSICAL SCIENCE. Mi I 12. Diathermancy or Transmissive Power. Bodies which allow radiant energy to be transmitted through them without much increase in their temperatiues are said to be diathermanous. Rock salt is one of the most diathermanous of solid bodies. Air is also fairly diathermanous, but water vapour is not. 1. How will the presence of water vapour in the air affect the quantity of the earth's heat changed into radiant energy during any particular interval ? 2. When will the surface of the earth at any jiarticuUir place cool the more rapidly, on a clear or on a cloudy evening ? Why ? No body is perfectly diathermanous, nor is any body a perfect absorber. Most bodies exercise what is called selective absorption. For example, glass allows the radiant energy from a highly heated body, like the sun, to pass, but absorbs the radiant energy emitted by a red hot ball or by an open fire. 13. Reflection of Kadiant Energy. Bright polished bodies are as a usual thing neither diathermanous nor good absorbers. The greater part of the radiant energy falling upon them is reflected from their surfaces and sent back into space without transfor- mation. Good reflectors are poor absorbers and good absorbers poor reflectors. Since there can be no loss of energy, the total amount of radiant energy falling on a body equals the amount reflected 4- the amount absorbed -|- the amount trans- mitted by the body. Transmission of heat. 215 Radiant ener) double windows used in houses in winter ? 6. Why, in freezing ice cream, is the freezing mixture put in a wooden vessel and the cream in a metal oim i 7. Water may bo boiled in a paper box placed over a lamp flame without burning the paper. Explain the reason. Make the experi- ment. The paper pails used by oyster dealers will answer. 8. Formerly to ventilate a mine two shafts were provided at opposite ends of the mine and a fire kept burning at the bottom of one of the shafts. Explain the air currents set up. 21G PHYSICAL SCIENCE. : i- i; ■ 4 1^ m I Fio. 140. 0. Wliat is t-luj source of tho hoat given out, by tlio CJulf StroJim to tho British Isles ? Trace its transmission. 10. What effects arc produced upon tho cliuiate of a place and upon tlio variation.^ of temperature in it by the presence of a large body of water near it? Explain the reason. 11. Should a kettle intended to be heated by standing in front of a fire be bright or black ? Give reasons for your answer. 12. The earth absorbs and radiates heat more quickly than the water. In what direction A or B (Fig. 14(i) will the air move (rt) during the day, (h) diu'ing the night ? Explain the cause of land and sea breezes. 13. Should soot be allowed to col- lect on the bottom of a kettle used in heating water over a flame ? Shovdd the remaining ])art of the kettle be kept bright or dull ? Give reasons. 14. Exphiin the advantages of silver plating the outside of a calorimeter. 15. The bulb.s of two identical thermometei's are coated, the one with lamp black, the other with silver ; compare their readings (a) when in a water bath (/>) when exposed to the direct rays of the sun, (c) when exposed on a clear night. Explain why they do not agree on all these occasions. 10. A Norwegian cooking box consists of a wooden box having a thick lining of felt insi«le, so arranged as to leave a central space into which the vessel containing the food is placed. The food is partially cooked, placed in the box, and covered over with the lid. Why will the cooking be completed in the box ? 17. A building is heated with hot water pipes. Explain fully how the heat is transmitted from the furnace of the boiler to a person in the building. What would be the efl'ect on the tempera- ture ()f some distant part of the building of coating the pipes near the boiler with {ensity, definition of, 64; and hardness, 86; maximum, of water, 169 Dew point, 195 Dialysis, 134 Diffusion, 132- 1 38; free of liquids, 132 ; of liquids through a mem- brane, 133 ; free, of gases, 135 ; of gases through a porous par- tition, 136; of gases through a membrane, 137; of gases, law of, 138 Ductility, 86, 87 Ebullition, 178-180 Elasticity, 89 ; of stretch, 47 • of compression, 47 ; of torsion, 47 ; 1 of form, IH) ; of volunu;, 90 ; between force and velocity, 76 ; limit of, IN), 91, 92 ; inoiiHuro of, expansive, of a gas, 117-119 93 Friction, heat from, 153 Electrification, 49 Fusion, 175, 176; laws of, 177 Electric current, heat from, liiS Energy, and work, 35 ; duiined, Gas, defined, 26 ; properties and 35 ; possessed by a l>()dy in vir- laws of gases, 1 15-127; expansive tue of its mass and its velocity. force of, 117, 120; buoyancy of. 38 ; forms of, 38, 39, 40 ; po- 119, 121 ; compressibility of, tential, 40 ; transmutation of, 123-126; free diflFusion of, 135; 41 ; conservation of, 41 ; may diffusion of, through a pofous produce force, 53 ; expended partition, 136 ; diffusion of. only when work is done, 53 ; through a membrane, 137 ; to measurement of, 75-79 ; relation find specific gravity of, 152 ; to mass, 75 ; relation to space, expansion of, through heat. 75, 7G ; unit of, 77 ; relation to 159-160; Charles' law, 170 velocity, 78 Graduate, a, 20 Evaporation, 181 ; laws of, 182 Gram, double meaning of word, 69 Expansion through heat, 157-160 Gravitation, law of, 71 Fact distinguished from theory. Hardness, 85, 86 27 Heat, 153-216; nature of, 153; Fahrenheit degree, 162 sources of, 153-156 ; expansion Flexibility, 91 through, 157-160; heat sense. Flotation, 113 163 ; latent, 183 ; quantity of. Fluid, defined, 25 ; transmission of 185 ; unit of, 185 ; specific, 191- pressure by, 106, 107 195; capacity for, 191, 192; Fluio.ity, 98, 99 mechanical equivalent of, 195- Force, nature of, 43 ; provisional 197 ; transmission of, 198-216 definition of, 43 ; produced by Hydrometers, 147-149 energy, 43, 53 ; counterbalanc- ing, 45 ; recognition of a, 46 ; Latent heat, 185-191; defined, 183; manifestations of, 46-53 ; a con- the«>ry of, 183 ; of fusion of ice. dition, not an objective reality. 186, 187 ; of vapourization of 47; at least two bodies concerned water, 188-190 in a, 48 ; modern view of, 54 ; Law, of nature, 41; of motion, 68, action of a, 54 ; measurement of. 69, 72 ; of gravitation, 7 1 ; of 65-74 ; oquDl forces defined, 65 ; conservation of matter, 84 ; of measured by balancing against conservation of energy, 81 ; of weight of known mass, 67; unit buoyancy, 112, 113; Boyle's or of, 69 ; definition of, 76 ; analogy Mariotte's, 126 ; of diffusion of INDEX. 219 1,68, ; of ;of |1 ; of j'a or m of gaacB, 138 ; of Charles, 170 ; of fusion, 177 ; of ebullition, 182 Liquefaction, 181 Liquid, defined, 2G ; properties and laws of liquids, 98-114; surface of, at rest under the action of gravity, 1 10 ; to find specific gravity of, 14G-151 ; buoyancy of, 111-114; expan- sion of, through heat, 158, 159 MalleabiUty, 87 Mass, defined, 24 ; equal masses defined, 55 ; determination of equal masses, 55 ; metric mea- suremenv of, 59 ; experiments in estimating, 63 ; equal miisses have equal weights, 66 ; of the earth, 72 Matter, and energy, 23 ; defined, 23 ; states of, 24, 28 ; constitu- tion of, 27 ; transmutation of, 80-84 ; indestructibility of, 84 ; law of conservation of, 84 Measure of a quantity, 3 Measurement, general principles of, 1-4; of a quantity, 2; nictiic system of, 4 ; metric, of length, 4 ; of length, experiments in, 9, 10, 11, 12; of surface, 12, 13 ; of surface, experiments in, 14, 15 ; of surface, formulae for, 1 4 ; of volume, 15 ; of volume, for- mulae for, 17 ; of volume, ex- periments in, 18, 19, 20, 21 ; metric, of mass, 59 ; of energy and work, 75-79 ; of elasticity, 93 ; of the pressure of the at- mosphere, 121 Metre, 4 ; sub-divisions of, 5 ; multiples of, 5 ; English i>(|uivii- Ifiita, 5 Metric system, 4 Molecules, 27 Momentum, 79 Motion, 29 ; relative, 30 ; first law of, 69 ; secon