Full text of "High school laboratory manual of physics"

See other formats

HIGH SCHOOL
.KBORKTORY MKNUKL

°f

PHYSICS

INN 5 COMPANY

Southern Branch
of the

University of California

Los Angeles

FormL

35
H33
Cob- 1

This book is DUE on the last date stamped below

F'orm L-9-15m-8,'26

HIGH SCHOOL

LABORATORY MANUAL

PHYSICS

BT
DUDLEY G. HAYS CHARLES D. LOWRY AUSTIN C. RISHEL

TEACHEKS OF PHYSIOS IN THE CHICAGO HIGH SCHOOLS

BOSTON, U.S.A.

GINN & COMPANY, PUBLISHERS
1895

ALL EIGHTS RESERVED

3.5

PREFACE.

~T~N making this Manual two main objects have been kept in
view. First, the teaching of Physics by the Inductive
Method, that is, the presenting of a logically arranged course of
experimental work that shall covej the ground of Elementary
Physics. Second, the providing of sufficient laboratory work to
meet the entrance requirements of any college in the country.

The authors are not so visionary as to suppose that boys and
girls can, unaided, rediscover the laws of Physics, but we know
that, if sufficiently careful directions are given to pupils in the
performance of experiments, and definite instruction is given them
as to the manner of studying results obtained, they will learn
from Nature first-hand many of her great laws. And these will
be much more strongly impressed than when learned from a
text-book or from the teacher's experiments. From the general-
izations made by the pupils, deductions can be made and then
tested for their validity, thus keeping fhe pupil on the border-
land between inductions and deductions, a place where the greatest
mental development is obtained. This plan is the underlying
idea of science study, and the acquiring of this scientific method
is of far more importance than the mere gleaning of facts. The
facts may in time be forgotten, but the method of mind opera-
tion will remain as part of the character developed.

Careful manipulation, accurate observation of phenomena, and
logical deductions or generalizations should be the three steps
kept in mind.

The notes written by the pupils should be neat, terse, and in
good English, and should be logically arranged as shown in the
steps mentioned above. Insist on these three elements of written

work.

iii

IV PREFACE.

In the attainment of our second object, the requirements of
Harvard, as being higher and more definite than those of any
other institution, have been our standard, and we acknowledge
great obligations to the Harvard Pamphlet.

Equivalents of nearly all their exercises will be found in
this Manual.

With regard to the method of laboratory work, that of having
duplicate apparatus so that a whole class may be performing the
same experiment is of course the best. Much of the value of
the work is in the discussion t>f the results in class-room. With
this in view the apparatus selected is of the simplest possible
kind that will secure good results, and most of it may be dupli-
cated at small cost.

In the arrangement of topics, Magnetism has been put first
because the experiments are easy, instructive, and fascinating,
thus giving a very desirable introduction to the laboratory work.
It also gives the teacher time to prepare his laboratory for the
more difficult work which comes later. The other topics are
arranged in about the usual order.

It is of course to be borne in mind that this is in no sense
a text-book, nor intended to supplant one. It is simply a lab-
oratory manual and may be used with any text.

LABORATORY MANUAL.

MAGNETISM.

The beginning work in the laboratory, covering the subject of
Magnetism, can be performed by the pupils working in unison
under the oral directions of the instructor, who can emphasize his
directions in such a way as to leave no doubt as to the way to pro-
ceed. The pupils can thus be given a start in an earnest manner,
and if the instructor is full of life, his pupils will soon gain a
mental momentum that will count. Enthusiastic work coupled
with neatness and accuracy should be xthe first aim. Unison work
calls for but little apparatus here. Let each pupil bring two
knitting needles, and the jeweller will gladly give you a pocket full
of old watch springs which are excellent material for magnets.
The magnetoscopes should be prepared by the instructor before-
hand. Fasten a silk fibre to the bottom of a cork of a small bottle,
such as a Florence flask, and to the lower end of the fibre fasten a
short piece of magnetized watch spring. Clip the magnet with
tinners' shears till it is balanced and is short enough to swing
freely in the bottle. One for each couple of pupils will be enough.
They can be kept throughout the year and will be of frequent use.

Bough notes can be taken in the laboratory and more elaborate
writing can be prepared from them at home for the first few days.
Nothing but neatness and accuracy of statements, based upon facts
observed, should be accepted. A right beginning is half the battle.

EXERCISE 1. — Mix some tacks, some bits of brass, copper, soft
iron wire, and some iron filings on a piece of paper. Stir the
mixture with one end of a knitting needle, and note whether any
of the objects cling to the needle. Now rub the needle from end
to end several times, always in the same direction, on a piece of
natural magnet or one end of a bar magnet — an electro-magnet
arranged by the teacher can be used — and again stir the mixture.

4 LABORATORY MANUAL.

Do any of the objects cling to the needle ? What ones ? Try to
pick up a match ; a pin ; a sewing needle ; a steel pen. What
kinds of material cling to the needle ? How does the needle differ
now from its condition when first tried ?

This attraction it manifests is due to the force called magnetism.
The needle is now a magnet. What substances are attracted and
held by a magnet when touched by it ?

EXERCISE 2. — You have seen that when certain substances
have been touched by a magnet they will cling to it. Ascertain
whether it is necessary to touch these substances in order to show
the attraction of a magnet for them. Cut out a piece of paper
three inches long and two inches wide. Fold the ends together
and crease the paper at the bend. Pin the two ends together with
a soft iron nail parallel to the ends of the strip. Now pass a
thread through the loop above the nail and hang it to any support,
as, for example, over a ruler projecting from the edge of the table,
so that the nail may swing freely. Hold a paper before one end of
a magnet, and bring that end of the magnet near one end of the
nail. Does the nail turn toward the magnet ? Bring it near the
other end of the nail, being careful to keep the paper between
magnet and nail. Does the magnet attract each end of the nail
even though it does not come in contact with it ? How does this
test of the effect of a magnet on soft iron or steel differ from that
in Exercise 1 ? Is contact necessary for a magnet to attract soft
iron?

EXERCISE 3. — Pour a row of iron filings on a piece of paper a
little longer than the knitting needle magnet, so that you can lay
the magnet on the paper and have it rest its entire length in filings.
Eoll the magnet back and forth in the filings and then pick it up
carefully. Note whether the filings cling uniformly along the
entire length of the magnet. Strip the filings off and repeat.
Where do the filings cling? Try to pick up tacks at different
points along the magnet. Stand a book on one end. Lay the
magnet on the book so that one end — nearly half — of the magnet
projects beyond the edge of the book. Now find how many tacks
will hang in line at the end of the magnet. Try it for different
places along the magnet, going from the end toward the center,
the places being about a half inch apart. Kecord the results for
each trial.

6 LABORATORY MANUAL.

The places on a magnet where the filings cling in bunches, or
where the greatest number of tacks cling, are called the poles of
a magnet.

EXERCISE 4. — Get a heavy sewing needle — what is better, a
short piece of Avatch spring one inch long — and dip it into filings
to be sure it is not magnetized. Now lay it 011 a thin cork and float
it in a dish of water. If the dish is small, it is well to oil the cork,
which will then remain in the centre of the dish. When it has
come to rest, with your pencil carefully turn it around so that it
will be at right angles to the position it had when at rest, and note
whether it will stay in about the position in which you put it.
Now remove the needle and stroke it on one end of a magnet,
always from end to end in the same direction. Then place it back
on the cork and repeat the above work. What follows ? Try
other needles so as to be sure of the results. Does the same pole
always seek the same direction ? If one end always seeks the west,
the pole at that end would be called the west-seeking pole. Give
the correct names to the two poles of the magnets you have tried.

EXERCISE 5. — Cork a small clear glass bottle with a cork having
a hole in it, through which passes a small glass tube, having a hook
at the lower end to which is tied a silk fibre, on the lower end of
which is fastened a piece of watch spring which has been magnet-
ized, and which should hang horizontally in the bottle near the
bottom. The tube can be moved up or down in the cork to adjust
the height. The silk fibre allows the magnet to move freely. This
little device is called a magnetoscope. Bring the point of a soft
iron nail near the north-seeking pole of the magnetoscope. What
follows ? Do the same with the head of the nail. What follows ?
Now get a knitting needle magnet or a sewing needle magnet and
try both ends of it the same way. What follows ? How does the
action when the nail was used differ from that when the magnetized
needle was used ? You thus see that the presence of magnetism in
a body may be detected by use of the magnetoscope.

EXERCISE 6. — In the last exercise we saw that a magnetoscope
could be used to detect the presence of magnetism. You saw that
the effect of one end of the magnet on the north-seeking pole of the
magnetoscope was the same as the effect of the point or the head
of the nail, but that the other end of the magnet affected the north-

8 LABORATORY MANUAL.

seeking pole of the magnetoscope in quite a different manner, —
that, instead of the north-seeking pole of the magnetoscope being
attracted in all cases, there was one case in which it was repelled.
This repellent effect is the true gnide to follow in determining
whether or not a body is magnetized. Magnetize a piece of watch
spring and float it on a cork and thus ascertain its north-seeking
pole. Stick this end through a small bit of paper to label it.
Proceed carefully and make the following tests, bringing one pole
of the magnet slowly toward one pole of the magnetoscope, and
record results :

Pole of magnet. Pole of magnetoscope. Effect.
North-seeking. North-seeking. ?

North-seeking. South-seeking. ?

South-seeking. South-seeking. ?

South-seeking. North-seeking. ?

By examining the above, discover a law of the effect of magnetic
poles on each other. State it. How many poles has a magnet ?
What can you say in regard to these poles ?

EXERCISE 7. — Magnetize a knitting needle, and by means of
a magnetoscope determine its poles. Put a paper flag on the
north-seeking pole. Break or cut the magnet in two at the
middle, and roll the half which is labeled in iron filings. Does
it seem to have two poles ? Test this piece for polarity with
the magnetoscope. What do you find ? Now break this piece
at the middle, and repeat the above tests. Results ? You might
continue this dividing process with the same results until you
reached the smallest physical division possible which would give
you a single molecule. What would be the condition of each of
the molecules thus separated from a magnet ? How do you think
the molecules are arranged in a magnet, judging from what you
have found in this experiment ?

Lay one bar magnet on another so that like poles will be
together. Have them project from some support above the table,
— a book will do. Now bring a paper on which are tacks, or
filings, up against the projecting ends. Note the quantity that
clings to the magnets. Now superpose the magnets so that unlike
poles will be together, and repeat the above. Eesults ? Explain.
If you had several flat magnets, how would you fasten them
together so as to make one strong magnet ?

10 LABORATORY MANUAL.

EXERCISE 8. — Magnetize a short piece of watch spring or a
sewing needle by rubbing it from one end to the other, always
in the same way, with the north-seeking pole of the magnet, and
then test the end of the newly made magnet which last left the
old magnet for polarity. Try several and record results. Kepeat
by using the south-seeking pole of the magnet. Kesults ? Can
you discover a law for the arrangement of poles in magnetization ?
State it.

EXERCISE 9. — Make a feeble magnet of a piece of watch
spring by stroking it once or twice with one end of a magnet.
Test it for polarity by means of the magnetoscope. Place it on
the table, and approach its north-seeking pole with the north-
seeking pole of a bar magnet. Make several trials. Does the
north-seeking pole of the small magnet jump towards the north-
seeking pole of the bar magnet ? If it does so several times, again
test it for polarity. How do you account for this result ? From
this experiment do you think any magnet might have its poles
reversed ? Try several magnets made of watch springs, and see
whether or not you can change the polarity at your pleasure.
How can you weaken a strong magnet ? Some magnets have
their poles stamped or marked in the steel when they are pur-
chased. Can we always rely on these marked names for the
poles of a magnet ?

EXERCISE 10. — Select a piece of soft iron wire or soft iron rod
of small diameter (a soft iron nail will do) and test it with a mag-
netoscope to be sure it is not magnetized. Hold one end of the
piece of soft iron in some iron filings. Place your index finger over
the other end of the iron, and with your other hand bring one pole
of a magnet down on the opposite side of the finger from the iron,
the finger thus preventing the magnet from touching the soft iron.
Keeping the objects in the position indicated, withdraw the soft
iron from the filings. Do filings cling to the soft iron ? Does it
seem to be a magnet ? Test it for polarity by means of a mag-
netoscope while the magnet is thus near it. How does the end
of the soft iron farthest away from the magnet compare in polarity
with the pole of the magnet used ? Change ends of the magnet
and try again. Change ends of the soft iron and repeat. If a
piece of soft iron thus used manifests magnetism, it is called an
induced magnet. What can you say about the arrangement of the

12 LABORATORY MANUAL.

poles of an induced magnet in regard to the pole of the magnet
used ? If you should lay several soft iron nails down end to end
in a line, leaving a small space between the ends, and were to hold
the north-seeking pole of a strong magnet near one end of the line,
what would all of the ends pointing towards the magnet be ? All
pointing away from the magnet would be what kind of poles ?

EXERCISE 11. — Lay two rulers on the table about 4 in. apart
and parallel to each other. Place a small magnet beween them,
and cover the three objects with a piece of writing paper. Now
with the thumb and finger sift some fine iron filings on to the paper
from a height of about two feet. The outline of the magnet can
be made more distinct, perhaps, by carefully tapping tne paper
with your lead pencil, being careful not to move the paper. The
filings should show distinct lines radiating from the poles of the
magnet. These lines of filings indicate the lines of magnetic force
which constitute the magnetic field of the magnet. Make a careful
sketch of this field.

Now proceed as before and map out the magnetic fields for
a magnet; for the field when a north-seeking pole is opposite a
north-seeking pole and about 1 in. from it; for the field when a
north-seeking pole is opposite a south-seeking pole and about 1 in.
away from it.

By using several horseshoe and several bar magnets so as to
have the poles arranged around a central point, some interesting
figures may be mapped out with filings.

14 LABORATORY MANUAL.

MEASURING.

EXERCISE 12. — Measure the length and width of your table-
top, and record the measurements in m. and decimals thereof, as,
^===s==^=^==^==^===^=^==^===, L- 2.145 m. Measure the height
J of your table, taking the average
at several points.

Measure the length of this
page, reading to quarters of mm.
F'g- !• and record in cm., and fractions

thereof, as, 27.95 cm. To measure accurately, the measuring rod
must be so placed that the graduated edge will be in contact with the
surface to be measured. It is also best to begin at some division a
little from the end of the measuring rod, as indicated in Fig. 1.

EXERCISE 13. — Apparatus : Metric rule, exterior and interior
calipers, sphere, rectangular prism and cylinder.

With the calipers get the diameter of the sphere, and by placing
the calipers on the metric rule, get the diameter in cm., measuring
to quarters of mm. Lest the ball be not a perfect sphere, take
the average of several diameters. Find the vol. in ccm., using
the formula on p. 150.

Measure the prism, and find its vol. in ccm.

Measure the cylinder, and find its vol. in ccm., using the for-
mula on p. 150.

EXERCISE 14. — Place several thicknesses of paper in the micro-
§meter calipers, and close the calipers upon them, using very gentle
pressure. You will probably need the assistance of your teacher
in reading your calipers. From the thickness of all, find the thick-
ness of a single sheet.

Measure the thickness of the pieces of wire given you.

Measure the thickness of a bit of window glass, a sheet of mica,
a hair, or any other object whose thickness you care to know.

EXERCISE 15. — Clean a small beaker, wipe it dry, place it on
an accurate balance, and counterbalance it accurately by pouring
sand into the other scale pan. Now draw from a burette exactly
25 ccm. of distilled water into the beaker, return the beaker to the
balance, and find the weight of the water in g. What does 1 ccm.
of water weigh ? In case no burette is at hand, use a graduated
vessel, but take a larger quantity of water, say 50 to 75 ccm.

16 LABORATORY MANUAL.

'PROPERTIES OF MATTER.

EXERCISE 16. — Select a two-hole rubber stopper which just fits
a bottle. (If no rubber stoppers are at hand, an ordinary cork will
do, if it be first wet, or, better, boiled in paraffine, to make it air-
tight.)

Through one of the holes pass the neck of a small funnel.
Cover the other hole with a finger, and pour water into the fun-
nel, pouring quite rapidly at first. Does it run into the bottle ?
Kemove the finger an instant. What results? Why? What
does this experiment show concerning water and air?

EXERCISE 17. — Fill a test tube half full of water, then, inclin-
ing the tube a little, slowly pour alcohol into it, letting it run down
the side of the tube, being very careful not to shake the tube.
When full, cover with the thumb and shake vigorously. Notice
any change of volume.

Fill a test tube with water to within 2 cm. of the top. Now
drop in about 2 or 3 ccm. of finely powdered sugar, a little at a time,
and notice the volume when all the sugar is dissolved. Is the
volume of the mixture equal to the sum of the volumes of the
water and sugar ? The same experiment may be tried with salt
instead of sugar. What property of matter have these experi-
ments illustrated?

EXERCISE 18. — Hold a piece of glass tubing, 30 cm. or more
in length and 5 or 6 mm. in diameter, in the flame of a Bunsen
burner so as to heat it about 10 cm. from one end. Hold the tube
with both hands, and turn it steadily so as to heat it equally on
all sides. Try to bend it from time to time to see if it softens.
When thoroughly softened, remove from the flame and quickly
stretch it out into a fine glass thread. When cool, break in the
middle ; or, if you pulled it apart, break off a few cm. of the
finest end, and see if the thread-like part is still a tube. To do
this, insert the small end in water and see if you can blow air
through it. Examine it after withdrawing it from the water.

What property of glass allows you to draw it out thus ?

EXKRCISE 19. — Place a calling card on the top of a cork in a
bottle. Upon the card, immediately over the cork, lay a penny.
Now try to snap the card from under the penny so the penny will

18 LABORATORY MANUAL.

drop upon the cork and remain there. A littls patience will
enable you to do it readily.

Explain why the penny remains behind.

Suspend a bag of sand weighing 2 to 4 Ibs. by a piece of twine
about 50 cm. long. Fasten a hook to the under end of the bag,
and from this suspend about 50 cm. of the same kind of twine.
Now take hold of the lower end of this second cord, and pull
steadily downward till the cord breaks. Which piece of cord
broke ? Arrange as before, and this time break the cord by a
sudden jerk downward. Which piece of cord broke ? Why ?

EXERCISE 20. — Into a flask which contains water to a depth
of 3 or 4 cm. place a close-fitting cork containing a glass tube
with its upper end drawn to a point, and the lower end reaching
about 2 cm. into the water. The tube must be air tight in the cork.

Now blow into the flask until a considerable quantity of air
has bubbled out of the lower end of the tube through the water.
Remove the lips from the tube. What results ? How did the
compression to which you subjected the air affect its density ?
How did it affect the expansive force, or tension ? Why does the
water stop flowing ?

EXERCISE 21. — First Part. Cut off a given length of solid
rubber cord, or rubber tubing, say 40 or 50 cm. Now stretch it
a little, release, and measure again very carefully. Repeat several
times, stretching more each time, always measuring after stretch-
ing, to see if you can reach a point where the rubber does not
return to its original length. A substance which uniformly
resumes its original form is said to be perfectly elastic. Do
you find rubber to be perfectly elastic?

Second Part. For three pupils. Fasten securely one end of
a piece of spring brass wire No. 28, B. & S. gauge, 3 or 4 m. long
to a screw or hook, or other support on the table-top, letting the
wire extend over another table, if one table is too short. To the
other end attach a 30-lb. Chatillon spring-balance.

Near each end of the wire fasten a drop of sealing-wax to serve
as a marker. Lay a metric rule lengthwise under each end of the
wire. Apply a tension of 1 Ib. to the balance. This should stretch
the wire straight. Now adjust each ruler under the wire so the side
of the drop of wax is exactly over one of the divisions of the ruler,
and do not allow the rulers to move throughout the experiment.

LABORATORY MANUAL.

Increase the tension 2 Ibs. (see Note 2). Bead positions of both
drops of wax to quarters of mm. ; the difference between their
movements is the amount the wire has been elongated. Reduce the
force to 1 Ib. and notice if the wire regains its original length.

Make several trials similar to the above, increasing the tension
2 Ibs. at a time until permanent elongation is produced, remember-
ing that after each trial you are to reduce the tension to 1 Ib.

Tabulate your results as follows : —

Material of Wire,

Gauge No., ...

Length,

FOBCE (F).

MOVEMENT
OF IST MARKER.

MOVEMENT
OP 2o MARKER.

ELONGATION (E).

Ibs.

mm.
ii

mm.

Compare F and E, and see if there is any law connecting the
stretching force and the elongation.

NOTE 1. — Very much of your succeeding work will be to derive such laws.
In doing so, there are two general ways of comparing the results of experi-
ments : (1) If the quotients (ratios) of corresponding results are always the
same, then the results are said to be directly proportional to each other j for
example, if in your experiment E -r F (or F -r E), always gives the same quo-
tient, then we say that the stretching force is directly proportional to the elon-
gation. (2) If the products of corresponding results are always the same, then
the results are inversely proportional to each other ; that is, if F x E gives
always the same product, we shall say the stretching force is inversely propor-
tional to the elongation. In most cases the quotients or products will not be
exactly equal, owing to errors in work. If the differences make only a small
part of the whole results, the law may be stated. If the variations are consid-
erable, state what you think the law to be, and say it is approximately proved.
(3) Sometimes one set of results is to be compared in either of the above ways
with the squares or square roots of another set of results, and occasionally with
the cubes or cube roots.

NOTE 2. — The spring-balances are made to be used with the hook hanging
vertically downward ; in any other position the index stands back of the zero
mark. In this case, a "balance correction" must be added to your reading.
To find the balance correction for any position, hook a more delicate balance to
the draw-bar, and see what force is necessary to bring the index to the zero
mark ; or, a cord attached to the hook may be passed over a smooth-running
pulley. To the cord attach a very light scale-pan on which to lay weights suf-
ficient to move the index to the zero point. The weight of the scale-pan and
weights is the correction sought. In all cases where accuracy is sought, the
balance correction should be made.

LABORATORY MANUAL.

EXERCISE 22. — Support two of the prisms described on p. 36
upon blocks 3 or 4 cm. high, so their upper edges shall be 1 m.
apart ; upon these lay a piece of
straight-grained pine or basswood 3 ft.
6 in. long, \ in. thick, and 1 in. wide.
Alongside the middle of the rod sup-
port another of the prisms at the
same height, but parallel to the rod
and 5 cm. from it. Upon this prism,
as a fulcrum, rest a very -light rod
32 cm. long, so its end projects 2 cm.
under the first rod. The arrangement
of the apparatus should be as shown
in Fig. 2.

Fig. 2.

Press downward upon the middle of the rod DE. A will rise ;
and since A C is five times the length of CB, A will rise five times as
far as B is depressed, and the amount of rise at A will serve to
show the depression at B. Consider B as being the point where
the rod DE touches the pointer AB.

Measure the height of A above the table, reading to halves of mm.
Now lay a weight of 200 g. upon DE at B, and again get the height
of A. Kemove the weight and measure again. Now use weights
of 400, 600, 800, and 1000 g., reading the height of the pointer in
every case, as before, and stopping at any time permanent bend-
ing is produced. Great care should be exercised in handling the
weights so the apparatus is not jarred and the position of the
pointer changed.

In case other than flat weights are used, they may be laid on a
pan suspended from the under side of DE by a string which passes
through a hole in the table-top.
Tabulate the results as follows : —

First case. — Rod flat ; supports 100 cm. apart.

LOAD.

READINGS
WITHOUT LOAD.

READINGS
WITH LOAD.

RISE OF
POINTER
IN mm.

DEPRES-
SION
OF ROD
IN mm.

DEPRES-
SION

PER 100 g.

IN mm.

LABORATORY MANUAL.

Second test. — Support the same rod on its narrow side with
supports 100 cm. apart, and load from 500 to 2000 g., increasing
500 at a time, reading as before.

Third test. — Use a rod of same material and grain, but 1 cm.
thick and 1£ cm. wide, laid flat, with the supports 100 cm. apart.
Use weights of 100 to 500 g., increasing 100 g. at a time.

Fourth test. — Use the same rod laid flat with supports' 50 cm.
apart, with forces of 200 to 1,000 g., increasing 200 g. at a time.

A study of your tabulated results should enable you to answer
these questions : —

1. What is the relation between the force employed and the
amount of bending of an elastic rod ? Kefer to Note 1, p. 20.

2. What is the relation between the length of the lod and the
amount of flexure, i. e., depression of its center?

EXERCISE 23. — Arrange apparatus as shown in Fig. 3. A is
a circular board 12 in. in diameter and 1 in. thick. B is a rod of

ash or hickory, \ in. X | in.
in cross section, and 42 in.
long, clamped with its cen-
ter exactly over the center
of A. The support of C
should be adjustable to
heights from 50 to 100 cm.
above A. The rod is firmly
clamped to C. It is best
to have the point of a wire
nail project downward from
the center of A into a hole
bored to receive it in the
table-top, so as to prevent
D is a cardboard with an arc of 60° gradu-
in. or 7 in., and its

Fig. 3.

A from moving about.

ated to single degrees ; the radius should be

center should" coincide with the center of A.

1. Adjust C so there shall be a space of 100 cm. between the
clamped portions of the rod, and apply force with two 4-lb. Chatillon
balances attached to the cords E and F, pulling in opposite direc-
tions, with equal force, and keeping the cords always at right
angles to the line GH. Use forces of 2, 4, 6 and 8 oz. and record
for each force the number of degrees of torsion, as read on the
card Z>.

26 LABORATORY MANUAL.

2. Now lower C so that but 50 cm. of B are exposed to torsion,
and use forces of 4, 8, 16 and 32 oz.

3. Substitute a similar rod of f in. X f in. sectional area, and
with a length of 100 cm. use forces of 1 Ib. to 4 Ibs.

4. Use but 50 cm. of the large rod, and forces of 2 Ibs. to 8
Ibs., using larger balances.

If in any cases the forces suggested are not suited to the
strength of the rods, use forces that are suitable.

Tabulate the results, and from a comparison of results answer
the following questions : —

1. What is the relation between the force employed and the
amount of torsion ?

2. What is the relation between the length of the rod and the
amount of torsion ?

3. How nearly do your results agree with the law, "Torsion
varies inversely as the fourth power of the diameter of the rod " ?

EXERCISE 24. — Apparatus : about 1 m. of spring brass wire,
No. 28 B. & S. gauge, and a 30-lb. ChatiUon spring-balance. The
teacher should prepare the balance for use by slipping an empty
thread spool over the hook so that when in position and the balances
are stretched, the axis of the spool is at right angles to the draw-
bar of the balance. Choose a spool of such length that when
properly cut away at the ends it cannot turn on the hook.

One end of the wire should be wrapped several times around a
cylindrical support, not less than 2 cm. in diameter. A gas-pipe,
water-pipe or table leg will answer. After wrapping the wire
about the cylinder, fasten the end to a tack or screw driven near
the cylinder.

The other end of the wire is to be fastened to the eye in the
end of the draw-bar of the balances, after which the wire should
be wrapped several times around the spool on the hook of the
balance, care being taken all the time not to twist or kink the wire.
Be careful to keep your hands and face out of danger in case the
wire recoils after breaking.

The apparatus being ready, the purpose is to determine the
amount of force necessary to break the wire. Begin with a small
strain on the wire, holding the eyes over the balance so that the
index reading of the balance may be accurately taken. Increase
the force steadily, noting all the time the reading of the balances,

28 LABORATORY MANUAL.

until the wire breaks. Eepeat three or four times, using a different
piece of wire each time, and thus get the average breaking strength
of the wire, making the proper balance correction as noted in
Exercise 21.

Now test a wire of the same thickness but of different material,
as iron, copper, or steel.

Eeturning to the first case, weigh a given length of the brass
wire, as 1 or 2 in., and determine what length of it would just
break of its own weight if suspended by one end.

EXERCISE 25. — Cut a lead bullet or small piece of sheet-lead
in two with a sharp knife, then press the freshly cut surfaces
together with a twisting motion until they cohere. What do the
facts that a smooth surface and pressure are necessary indicate
about the distance through which cohesion acts ?

In same way unite freshly cut surfaces of rubber, paraffine or wax.

Place a small drop of mercury on the table, and note carefully
its shape. Why does not the mercury spread out over the table ?
Would the great weight of mercury hinder or assist it in keeping
a spherical form ?

Place a drop of water on a clean pine board, and account for
the shape of the drop. Now place drops of water on a board
that is covered with powdered rosin. Note and account for the
difference between the shape of these drops and those of water
on a clean surface. What force holds the powder to the surface
of the drop ?

EXERCISE 26. — Suspend a disc of tin or sheet-zinc 5 to 8 cm.
in diameter by means of three threads from the hook on the under
side of the scale-pan of a specific gravity balance. Now support
the balance at such a height that when the beam is horizontal, the
disc rests lightly upon the surface of the water in a battery jar or
tumbler. Be sure there are no air bubbles under the disc. Care-
fully lay weights on the other scale-pan, — do not drop them in —
and find the force necessary to tear the disc away from the water.
Look now at the under side of the disc and decide which is the
greater, the adhesion of the water to the disc, or the cohesion
of the water. Was the force overcome that of cohesion or of
adhesion ?

Wipe the disc dry, coat its under surface with oil, and again
find the force necessary to tear it from the water.

LABORATORY MANUAL.

EXERCISE 27. — (To the teacher: Sets of capillary tubes, cleaned
for use, should be in readiness ; tubes 1, 2 and 5 mm. in diameter
and 20 cm. long are suitable. Liquids for cleaning them should be
in readiness so the pupils lose no time. A rubber bulb with rubber
tube attached will assist in drawing the liquids through the tubes.
To clean the tubes, wash first in dilute nitric acid, rinse in water,
then wash in dilute caustic potash or caustic soda, then rinse in
water.)

In a tumbler or beaker place distilled water about 6 or 8 cm.
deep. Lower the smallest tube to the bottom of the tumbler, so as
to wet the tube inside. First study the form the water takes
around the tube, and around the sides of the tumbler. What form
of attraction is displayed here ? Now lift the tube entirely out of
the water, dry the end, lower it very slowly toward the water and
watch to see if the water jumps to meet the tube. Incline the tube
a little, so one corner approaches the water first.

Now lower the tube about 2 cm. into the water, holding it
vertically, and notice at what height the water stands in the tube.
Lower still more, and see if the water in the tube remains at the
same height above the water in the tumbler. Now lift the tube
entirely out of the water, and notice if any water remains in the
tube, and if so, to what height. Arrange a table similar to the
following, and with the other tubes and liquids determine the
facts : —

DIAMETER OF
TUBE.

HEIGHT
IN COLD WATER.

HEIGHT
IN HOT WATER.

HEIGHT
IN ALCOHOL.

1 mm
2 mm.

6 mm

When the large tube is used, what is the shape of the upper
surface of the water in the tube ?

Pour clean mercury into a test tube to the depth of about 5 cm.,
dry the tubes and place them one at a time into the mercury,
holding the tubes at the side of the test tube so you can see if the
mercury enters the tubes. Record your observations. Make a
sketch showing the shape of the mercury surface within and
around the largest tube.

32 LABORATORY MANUAL.

Take two plates of glass about 3X8 cm. Slips for mounting
microscopic specimens are convenient. Lay the one on top of the
other with a bit of wood 2 mm. thick separating them their entire
length along one edge. Slip a rubber band around them so as to
hold them firmly together, and lower them vertically into the
water. Sketch them, showing the height to which the water
rises between the plates.

These phenomena are said to be due to capillary attraction.
Can you explain them by means of forces already studied ?

LABORATORY MANUAL.

PENDULUMS.

EXERCISE 28. — Suitable pendulums are easily made from lead
bullets by cutting into one side with a knife, inserting a thread
and pinching the lead tight about the thread with a pair of forceps.
Iron balls with holes through them will also serve. These pen-
dulum bobs should be in readiness for the class. The exercise can
be worked by a class in unison if desired.

Measure a pendulum 60 cm. long. In taking its length,
measure from the point of support to the centre of the bob. The
pendulum may be suspended between the thumb and finger, if you
are careful to give it a definite support so it does not change its
length during the experiment. It may also be held in a pair of
forceps, hung over the back of a knife-blade, or suspended in a
variety of ways.

Start the pendulum vibrating through an arc of not over 10 or
15 cm., and count the number of single vibrations in a minute.
Repeat two or three times before recording. Now, keeping the
pendulum still the same length, let it swing through a much larger
arc, say 30 to 40 cm. Repeat and record. What influence has the
length of the arc upon the number of vibrations made in a given
time?

Substitute a cork bob, or other light body for the metal bob,
retain same length as before, and determine whether the material
of which the pendulum is made affects its rate of vibration.

Arrange a table as below, and, using the metal bob, record your
results after two or three trials with pendulums of each length :

NO. VlBB. PER MlN.

PERIOD, i. E. TIME OF 1 VIBR.

LENGTH.

25 cm.

100 "

50 "

200 "

By studying your results determine the law connecting the
period of a pendulum with its length. (Note 1, p. 20.)

36 LABORATORY MAX UAL.

MECHANICS.
^^X

For applying force in mechanics, the Chatillon 4-lb. spring-
balance, graduated to ounces, is recommended. Where weights
have to be provided, bags of sand are both convenient and cheap.
The bag should be made of closely woven material, such as ducking.

Suitable levers may be made from lattice sticks 13 in. long, 1
in. wide and £ in. thick. Half an inch from each end a line should
be drawn across the broad side, and between these, 11 other lines
1 in. apart ; the stick now resembles a foot rule. On the other
broad side, exactly opposite each line, a small notch should be cut
across the lever. A triangular prism 1 in. long and £ in. high,
when lying on one face, will serve as a fulcrum. Where metric
weights are not at hand in sufficient numbers, nickels will serve as
5 g. weights, and 10 g., 15 g., and 20 g. can be cut from sheet-
lead.

Sets of two single, and two double pulleys should be provided ;
also stout linen or cotton cord for same. Fishline is good.

It is recommended that Exercise 40 be performed before the
class, they making their own observations and deriving the laws
unaided so far as possible. A wire 2 or 3 mm. in diameter should
be stretched across the room on a grade of 1 to 16 ; by means of a
turnbuckle it can be stretched very tight. On the wire is a smooth-
running pulley carrying an iron weight of 2 Ibs. so arranged as to
roll down the wire when released. The weight is held in place at
the upper end of the wire by means of an electromagnet. If the
friction prevents the weight from moving 1 foot the first second,
and corresponding integral numbers of feet for each succeeding
second, the inclination of the wire should be increased till these
results are reached. A seconds pendulum, hung by a copper wire,
is so arranged that a very thin wire pointer on the under side of
the bob cuts through a ridge of mercury (a trough 3 mm. wide
heaped full) at the middle of its arc, thereby closing a circuit
which rings a bell or clicks a telegraph instrument once a second.
The ringing of the bell breaks the circuit of the electromagnet,
thus releasing the weight. Above the wire, and parallel to it is
stretched a cord to which are pinned bits of paper 1 foot apart, to
mark the distance the weight moves.

LABORATORY MANUAL.

EXERCISE 29. — For three pupils. On a smooth, square board
rule off a square 12 in. on each side. Divide this square into 36
two-inch squares, and at the intersections of all the lines bore -J in.
holes not quite through the board. Number these holes from 1 to
49. Provide 3 iron pegs fitting the holes pretty closely. (Wire
nails broken off will answer.)

Lay three smooth marbles of equal size upon the table, and
upon these the board, marked side up. Attach a cord a foot long
to each of the pegs, and insert the pegs in three holes in any one
line. Hook a spring-balance into the end of each cord, and apply
forces at right angles to the line on which the pegs stand, so that
when all the balances are stretched, the board will not move. Be
sure the cord does not bear down upon the board, and that it lies
exactly over the line traced on the board. Hold the balance firmly
in both hands, with the knuckles resting upon the table, and keep
the head in such a position that at a given signal all can read the
balances instantly without moving anything but the eyes. Re-
member that the percentage of error is much less if the force
applied is considerable than if it is small.

40 LABORATORY MANUAL.

Now, having produced equilibrium and taken the readings, make
a diagram of the board in your note-book, number the holes, and
record the conditions which produced equilibrium. The record can
be briefly stated in the form of a table, thus : —

HOLE NUMBER.

FORCE.

DIRECTION : N., S., E., OR W.

Now change the distance between the pegs, and record the con-
ditions which produce equilibrium. Be sure that in some of the
trials the pegs are at unequal distances from each other.

Keturn now to the original case of equilibrium; let all the
forces retain the original direction and magnitude, and two of them
the original points of application. Seek a new point of application
for the third force which shall leave the system in equilibrium as
before. Take each of the other two forces as the roving one, and
record the results of your trial, together with any conclusions you
may have reached.

Again, returning to any of the cases of equilibrium, see if the
equilibrium continues while the forces, keeping the same magnitude
and points of application, and still remaining parallel to each other,
are turned about into new directions, i. e., are no longer at right
angles to the line of pegs.

"Now, by referring to your results, answer the following ques-
tions : —

1. What is the direction of the equilibrant of two parallel
forces acting in the same direction ?

2. What is the magnitude of this equilibrant ?

3. What relation exists between the magnitude of the two
forces and the distances of their points of application from the
point of application of the equilibrant ?

EXERCISE 30. — Lay the prism on the table, and on its edge
place the middle notch of the lever. This support on which the
lever turns is called the fulcrum. If the lever does not balance,
lay a lead chip on it at such point as to produce equilibrium. Note

LABORATORY MANUAL.

that this lever balances when neither end shows a tendency to rise
after being depressed.

On the right-hand end of the lever place 5 g. 6 in. from fulcrum ;
in all cases place center of weight exactly over the line on the lever.
Call this 5 g. the weight to be lifted, and find what power must be
applied six in. to left of fulcrum to produce equilibrium. Desig-
nate the weight and power by W and P, the fulcrum by /. The
distance from W to / is called the weight distance, Wd ; that from
P to /, the power distance, Pd. Place your results in the proper
place in the following table, and by use of the lever find all the
missing terms in the table. For convenience, keep Wd to your
right : —

WD.

PD.

6g.

Gin.

6 in.

10"

3 "

? "

15 "

4 "

3 "

V "

2 "

4 "

15 "

? "

6 "

Now place the fulcrum under the notch 4 in. from one end, and
balance the lever with lead chips ; then .find the missing terms in
the following table : —

WD.

PD.

Study these tables to see if you can find a general relation be-
tween P, W, Pd, and Wd.

Moments of Force. The moment of a force is the tendency
of that force to produce rotation about a fixed axis, and is com-
puted by taking the product of the force times the distance of its
point of application from the axis of rotation. Since P and W tend
to produce rotation about the fulcrum in opposite directions, call
that distance positive whose moment tends to motion in a direction
with the hands of a watch, and the other negative. Now, compute
the moments in all the preceding cases., arrange the results as

LABORATORY MANUAL.

indicated below, being careful of algebraic signs, and find the
algebraic sum of the moments in each case : —

Sum of moments.

2. Etc.

Now calculate the moments in the following case : With/ 4 in.
from end, PF 20 g., Wd 4 in., balance by applying two weights of
5 g. and 10 g. at different places on the other arm.

EXEKCISE 31. — Arrange two levers as shown in the figure,
using a loop of thread to connect

/c — D// them. Balance the lever with

~~ lead chips.

^JJ AB is the lever under consid-
eration. Since you learned in the
preceding exercise that a power
applied downward at C exerts an equal upward force at D or A,
you may in each of the succeeding tests treat the power as applied
upward at A, although you apply it over C. On AS place a weight
of 20 g. 6 in. from B. What is the Wd? Pd? Find what power
applied at C will produce equilibrium. Fill out the following table : —

PD.

WD.

no\

1 15J

EXERCISE 32. — Arrange the levers as shown in the figure. A
pin may be driven through the half-inch mark at A, bent into a

hook, which is then hooked into
^| another bent pin driven into the

/>A \<' x/ table-top. Balance the levers. AB

* is the lever under consideration.

Fig- «• Where is its fulcrum? If power

be applied at (7, where does it exert itself upon AB ? Lay a weight

LABORATORY MANUAL.

of 5 g. on the half-inch mark at B, and apply power at C to pro-
duce equilibrium. What is the length of the power arm on tiie
lever AB ? The weight arm ? Arrange yo*ur results in the first
line of the table. Find the other missing terms : —

PD.

WD.

? .

{ &}

r 6

\io

•

Compute the moments.

EXERCISE 33. — Take a wheel and axle device; measure the
diameter of both the wheel and the axle ; call them D and d. What
is the ratio of Dtod? What is the ratio of their circumferences ?
Hang a weight of 3 to 5 Ibs. on the cord passing around the
axle, hook the spring-balance into the cord passing around the
wheel, and raise the weight, pulling vertically downward. Read
the balances to quarter ounces while the weight rises, and add the
balance correction for this position (page 20, Note 2). Now let the
weight slowly descend, reading and making correction as before.
The average of these two readings is the power necessary to support
the weight on the axle. Repeat your readings several times before
recording. Call the power and weight P and W. What is the
ratio of P to W? Compare this ratio with that of the diameters.
Can you see a general relation between P, W, D, and d ?

How far must the power act to raise weight 10 cm. ? Do you
find it necessary to measure to answer this question ?

In this exercise, which is gained, intensity or velocity ? Which
was lost ?

Apply W to wheel and P to axle, and state which is gained and
which lost, intensity or velocity. Calculate the work done by P
in raising W 4 in.* Compare this with the work necessary to
raise W directly upward the same distance.

EXERCISE 34. — Arrange your apparatus as in Fig. 7 (a), using
a weight of 3 to 5 Ibs. Hook a spring-balance which registers to

* The work done by any power is the product of the power times the distance it has
moved.

LABORATORY MANUAL.

ounces into the cord, and raise the weight slowly, applying the
power as nearly vertically downward as you can ; note on the
balances the power used, reading to
half ounces. To this reading add the
balance correction for this position of
the balance. Now allow the weight
to descend slowly and note the power
used as before. Kepeat several times ;
then take the average of the power
used in raising and lowering as
the force necessary to support the
weight.

1. What is the ratio of P to W?

2. How far must P act to raise W 6 in. ?

3. What is the ratio of Pd to Wd ?

4. In this arrangement, how many sections of the cord support
the weight ?

Arrange the pulleys as shown in the other figures, and answer
the above questions for each arrangement. When done, arrange
the results of the four trials in the following table :

Pd.

Wd.

SECTIONS OF CORD.

Can you, by observing P, W and the number of sections of the
cord, discover a general law for the pulley ?

Compute the work done by the power in the last case in raising
the weight 10 in., and compare this with the work necessary to
raise the weight 10 in. directly upward.

EXERCISE 35. — Support a smooth board about 80 cm. long and
30 cm. wide firmly on the table with one end raised from half to
two-thirds the length of the board above the table. The board so
arranged is called an inclined plane.

Measure the length of the plane. Measure its height. This
is the vertical distance from the under edge of the upper end of

50 LABORATORY MANUAL.

the board to the table. Call these L and //. Find the ratio of
H to L.

Place a weight of 2 to 5 Ibs. on the cart, — a roller skate will
do, — and weigh the cart and its load. Call this weight W. Place
the loaded cart on the plane, and apply power with the spring-
balances so as to draw it steadily up the plane, being careful to
apply the power in a direction parallel to the plane. Take very
careful readings — at least to half ounces — as the weight ascends,
making the proper balance correction. Now allow the cart to roll
down the plane, taking readings at it moves. Repeat several
times ; then take the average of the readings while ascending and
descending as the power necessary to support the cart on the plane,
irrespective of friction. Call this P, and find the ratio between
P and W. Compare this with ratio of H to L.

How far must the power act to draw W the full length of the
plane ? How far has W risen vertically in the meantime ? Calcu-
late the work done by P in raising J^ 8 in., and compare with the-
work necessary to raise W 8 in. directly upward.

EXERCISE 36. — Place a smooth pine board about 1 m. long
upon the table. Take a smooth pine block about 2 X 6 X lo in. At
the center of one end of the block fasten a screw-eye with cord
attached.

Place the block with one of its narrow faces upon the board,
and with the balances move it slowly and steadily along the board,
with its fibers parallel to those of the board, being careful to keep
the cord parallel to the table-top. Record the force necessary to
start the block ; now find the force necessary to keep it in motion.
As the force necessary to move the block may vary at different
parts of the board, a place should be sought where for several
inches the force is uniform, and all readings taken there. Repeat
the process several times, take careful readings, make the balance
correction for this position and call the average of these corrected
readings the force necessary to overcome friction. What is the
amount of pressure of the block upon the board ? The ratio of
friction to pressure, i. e., friction divided by pressure, is called the
coefficient of friction. Find the coefficient in the above case.

Lay the board on its broad side, and find the coefficient. Now
place a weight of 2 or 3 Ibs. upon the block, and find the coefficient.

Lay the block upon two round lead-pencils and find the coeffi-
cient of rolling friction.

52 LABORATORY MANUAL.

EXERCISE 37. — Through one corner of a piece of cardboard, 6
or 8 in. across, prick a hole with a pin and enlarge the hole so the
card will revolve freely about the pin. Hang a plumb-line from
the pin, and suspend both the card and plumb-line. It will be well
to drive the pin horizontally into a wooden support. When both
have come to rest, place a mark very carefully back of the plumb-
line just where the line leaves the card. Remove the card, and
with ruler and sharp pencil trace on the card the line of direction
of the pendulum.

Suspend as before from any other position and trace the line as
before. At the intersection of these two lines stick a pin through
the card, bend it into a hook and suspend the hook by a thread.
If the card hangs horizontally, the center of gravity lies half way
between the two surfaces at the intersection of these lines.

Kemove the hook, find a new line of direction and see if it
intersects the two other lines at the point where the hook was.

EXERCISE 38. — Influence of Weight of Lever. Apparatus :
Lever and fulcrum used in Exercise 30 ; metric weights and ruler.

Find the center of gravity of the lever by balancing it over
a knife edge, or other sharp support. Weigh the lever to tenths
of a g. Place the notched face of the lever upward, lay a weight
of 20 g. on the half-inch mark at one end, and carefully adjust the
fulcrum so the lever will balance without using additional weights.
Be sure the fulcrum is exactly cross-wise under the lever. Now
measure very carefully the distance from weight to fulcrum, also
from center of gravity of lever to fulcrum. Compute the moment
on the weight side. Find, by applying the law of moments, at
what distance from the fulcrum the weight of the lever, if applied
at a single point, would have to act to produce the equilibrium
observed.

Now place the weight on the second mark, balance, measure,
and compute as before.

Again, increase the weight to 30 or 40 g., and proceed as before.

Consider now whether in every case the weight of the lever has
acted as if applied at the same point ; and, if so, what is that
point ?

EXERCISE 39. — On a drawing board fastened firmly against a
wall, suspend two spring-balances, reading to ounces, as shown in
Fi. 8.

LABORATORY MANUAL.

On the cord BD hang a weight of 2 to 5 Ibs. With thumb-
tacks or pins fasten a sheet of paper to the board, with the middle

of the paper back of the inter-
section of the cords ; using a ruler
and sharp lead-pencil, trace on the
paper lines parallel to each of the
three cords, being sure the lines
intersect at a common point.

Head the balances, and beside
each line mark the reading in
ounces. Now remove the paper
from the board, decide on some
scale suited to the force used and
size of the paper, and mark off on
each of the three lines a distance
corresponding to the force applied
in that direction. Consider AB
and BC as sides of a parallelogram ;
finish the parallelogram and draw
its diagonal BE. On the scale
adopted, how great a force does the diagonal represent ? Compare
this with BD. Considering AB and BC as components, what are
BE and BD ? What truth does this experiment seem to teach ?

EXERCISE 40.* — Let the weight roll down the wire, and notice
how far it moves in one second. Kepeat several times. Then find
the distance the weight moves in two seconds, etc. Tabulate the
results :

Length of plane ................ ft. Height of plane ................ ft.

Entire distance passed over in
One second ................................ ft.

Two seconds ................................ "

Three " ................................ "

Four " ................................ "

Five " ................................ "

By a comparison of the above results, fill out the following
table: —

Distance passed over in
First second ............................... ft.

Second " ................................ «

Third " ................................ "

Fourth " ................................ "

Fifth " ..... ««

* For directions as to apparatus, see p. 36.

56 LABORATORY MANUAL.

Let the distance passed over during the first second be repre-
sented by d. Now at the right of both the above tables, write
the number of d's passed over in each of the periods of time given
in the tables.

Compare the number of d's passed over in any number of
seconds with that number of seconds, and state a law, if you can.
(Law I.)

In the second table, compare the number of d's passed over
during each second with the number of that second, and state a
law, if you can. (Law II.)

The velocity at the beginning of the first second was 0 ; it
increased uniformly throughout the second ; the average velocity
for the second, therefore, equals half the sum of the velocities
at the beginning and end of the second. But the space passed
over during the first second equals the average velocity for that
second. How many d's represent the velocity at the close of the
first second ?

Now, observing that the velocity at the close of the first second
is also the velocity at the beginning of the second second, and also
that the number of d's passed over during the second second is the
average velocity for the second, find the velocity at the end of the
second second. Proceeding in the same way, make a table for the
velocity at the end of each second.

The velocity gained each second is called the acceleration or
increment of velocity for that second. How many d's represent
the increment for each second ? State a law for the velocity at
the end of any second. (Law III.)

Let S represent the distance passed over in any number of
seconds by a body free to move, acted on by a constant force; s, the
distance passed over in any single second ; t, the time, and d, as
before, the distance passed over during the first second. State
Laws I, II, III by means of formulae ; e. g., S= ? s==? V=?

The force of gravity is the constant force here employed, and
these laws will apply to freely falling bodies, provided you
multiply your value of d by the ratio of the length of the incline
to its height.

LAB OR A TOR Y MANUAL.

HYDROSTATICS.

EXERCISE 41. — Put a wet card on one end of a chimney and
push it down into a glass jar filled with water.
What keeps the card from leaving the chimney ?
Now carefully pour water into the chimney and note
how the height of the water in the chimney compares
with the level of the water outside the chimney when
the card is pushed off. Make several trials, and vary
the depth to which you push the chimney. From
your results, to what is the force which holds the
card against the chimney equal ?

Tie a piece of rubber tissue over one end of a
chimney and after filling it with water cork the other
end with a cork through which pass three glass tubes
as shown in Fig. 9. Be careful to have the centers
of the lower ends of the tubes on the same level.

Note the heigth of the water in the three tubes.
Subject the liquid to pressure by pressing gently on
the rubber. Note the relative heights to which the
water is pushed.

How did the pressure get to the water in the
tubes ?

In what directions did the water move when
entering the tubes ?

What facts does this exercise show in regard to the

Fig. 9.

transmission of pressure to which water is subjected ?

EXERCISE 42. — Use a small brass bucket and
plug. You will notice that the plug exactly fills the
cavity of the bucket. Now hook the plug to the
bottom of the bucket and suspend the bucket from
one scale-pan of a balance, then put weights, or shot,
or sand into the other scale-pan of the balance till
equilibrium is restored. Now place a dish of water
under the plug and elevate the dish (or lower the
upright standard of the balance) till the plug is
entirely submerged when the arms of the balance are
held horizontal. Release your hold. Is the equi-
librium disturbed? Carefully pour water into the
bucket till the arms of the balance are horizontal.

Fig. 10.

The apparent

60 LABORATORY MANUAL.

loss of weight of the plug when it is immersed in the water is
due to the buoyant force of the water which it displaced. How
does th« volume of the water displaced by the plug compare with
the volume poured into the bucket ? Judging from this, the
buoyant force of a fluid upon a body submerged in it is equal to
the weight of what ?

Did the plug lose any of its weight ? Did it lose weight so far
as the balance reading was concerned ? It is customary to speak
of a body as losing weight when it is immersed in a liquid, but
this is a peculiar use of the word "lose."

The truth you have learned in this exercise is called Archimedes'
principle.

LABORATORY MANUAL.

SPECIFIC GRAYITY.

EXERCISE 43. — Measure very carefully a rectangular block
about 3 cm. X 5 cm. X 10 cm. Compute its volume. Weigh it.
What is the weight, in g., of 1 com. of this wood ? This number
is called the density of the wood. Balance, with sand, a beaker,
then pour into it from a graduate as many ccm. of water as will
equal the volume of the wood. Weigh. Divide the weight of the
wood by that of the water. The quotient is called the specific
gravity of the wood. Formulate a definition for specific gravity.

EXERCISE 44. — Weigh an irregular piece of some solid denser
than water and not soluble in it. Tie a fine thread to the solid,
attach it to one side of the balance and let it be immersed in water.
Re-weigh. By Archimedes' principle determine the volume of the
solid. What is the weight of the same volume of water ? What,
then, is the specific gravity of the solid ?

In like manner find the specific gravity of at least 6 substances.

Tabulate as below where W equals weight in air ; W equals
weight in water ; D equals difference between your result and
that given in the table of specific gravity in the back of this book.
This difference is not necessarily an error, as the result given in
the table is the average of many specimens :

NAME.

Loss.

SP. G.

EXERCISE 45. — Weigh a solid less dense than water, e. g., a
piece of paraffine, wood or cork that has been coated with oil or
hot paraffine to make it water-proof. Attach to it a sinker and
weigh them together in water. Weigh sinker in water. From
these three weights find the specific gravity of the body tested.

EXERCISE 46. — Find the specific gravity of a liquid by means
of a specific gravity bottle. The amount of water the bottle will
hold is usually cut in the glass, and need not be tested by the
pupils. If the bottle has no counterpoise, balance it, when per-
fectly dry, with sand. Fill the bottle with the liquid to be tested,

64 LABORATORY MANUAL.

weigh, and calculate the specific gravity. In filling, be sure nv
air bubble is under the stopper ; wipe the outside dry, and be very
careful that none of the liquid is brought in contact with the
scale-pan. If a second liquid is to be tested, rinse out the bottle
with a little of this liquid, then proceed as before.

EXERCISE 47. — Obtain a narrow U tube having arms about 50
cm. long. Pour into it water until it stands about 20 cm. high ic
each arm. Next pour into one arm some liquid that will not mix
with water, as kerosene, mercury, etc. Measure the vertical dis-
tances from the surface where the liquids meet to the free surfaces
of the liquids. In this, as other experiments, measure to the level
of the upper surface, not to the upper edge of the meniscus.

From your measurements, calculate the specific gravity of the
liquid tested.

Alternative : — Connect, by means of rubber tubes, to each arm
of a Y tube, a glass tube about 50 cm. long. Over the stem of the
Y slip a rubber tube about 20 cm. long. Unless the rubber fits the
glass closely, wrap with soft cord. Insert one of the tubes into a
beaker of water ; the other, into a beaker containing some other
liquid. Cause the liquids to rise in the glass tubes by sucking air
out of the rubber tube. Pinch this tube, and measure the height
of each liquid from the level of the liquid in its beaker. Determine
the specific gravity as before.

EXERCISE 48. — Specific Gravity Determined by Meam> of a
Hydrometer. Prepare a stick of pine 1 cm. square and 25 cm. long.
Bore a hole in one end and force bullets into it until the rod will
float in water in a vertical position and with a few cm. projecting
above the surface. Coat with hot paraffine to make it waterproof.
If, before coating the rod, the upper part of it is graduated in mm.,
it will facilitate the work with the instrument.

Moat this hydrometer in water in a suitable vessel, note the
depth to which it sinks. How much water does it displace ? How
much ought it to weigh ? Now float in some other liquid, e. g., salt
water. Note the depth to which it sinks, and from your two
measurements determine the specific gravity of the liquid tested.

66 LABORATORY MANUAL.

PNEUMATICS.

EXERCISE 49. — Fit to a two-liter bottle a rubber stopper
through, which passes a short glass tube. The exact volume of the
bottle should be determined once for all and marked on the bottle ;
this may be done by weighing it when empty and again when full
of water.

Connect this bottle, by means of a thick-walled rubber tube, to
an air-pump having a pressure gauge. Be careful to make all joints
air-tight. Glycerine is useful for this purpose. Exhaust the air
from the bottle. Close the rubber tube with a pinch-cock, and at
the same time record the reading of the gauge. Now weigh bottle,
stopper, tube, and pinch-cock ; then open the pinch-cock, admitting
the air, and again weigh. The difference is the weight of the air
that was removed. Its volume will be found by comparing the
reading of the pressure gauge with that of the barometer at the
time of the experiment. From these data determine the specific
gravity of air.

EXERCISE 50. — (a) Connect to one arm of a Y tube, by means
of a perforated stopper, a glass tube 50 cm. long and about 15 mm.
in diameter ; to the other arm, a tube about 5 mm. in diameter
and 50 cm. long. Over the stem of the Y slip a short rubber
tube. Introduce both glass tubes into a vessel of water. Suck
the air out of the rubber tube. What causes the water to rise
in the glass tubes ? How do the heights of the liquid in the two
tubes compare ?

(b) Measure the height of the mercury in a barometer tube.
What supports the mercury ? What change would it make in the
height of the mercury column, if the cross-section of the column
was 1 scm. ? What would be the weight of such a column, if the
specific gravity of mercury is 13.6 ?

What, then, by your calculation, is the pressure of air per scm. ?

EXERCISE 51. — Work the lifting pump (or force pump), noting
carefully the position of the valves. Make two diagrams of the
pump, one showing the position of the valves during the up
stroke of the piston, the other, during the down stroke of the
piston.

68 LABORATORY MANUAL.

EXERCISE 52. — Make a siphon of a rubber tube. Compare the
velocity of water when the outer end is 2 cm. lower than the sur-
face of water in the vessel with the velocity when the same end is
20 cm. lower.

EXERCISE 53. — Pour a little mercury into a Mariotte's tube,
and adjust by shaking until the mercury stands the same height in
both arms. It is evident that the pressure on the confined air is
the same as external air pressure, or one atmosphere. Also, as the
expansive force of an elastic body is equal to the pressure it sup-
ports, the expansive force of the confined air is one atmosphere.
This may be expressed in g., or, since air pressure is determined
by the height of the barometer, we may represent the pressure and
expansive force of the confined air by this height. Measure the
length of the column of air in the short arm. As the tube should
be of uniform diameter, this length may represent the volume of
the confined air. Pour mercury into the long arm until the vertical
distance between the mercury surfaces in the two arms is about
15 cm. Carefully measure this distance and the height (volume)
of the air in the short arm. Now pour in mercury and measure
as before until you have made five or six measurements, or until
the tube is full. Eecord your results in tabulated form, and by
comparing them, determine the law connecting the variation of
pressure with variation of volume. (See 'Exercise 21. "Note 1.)

70 LABORATORY MANUAL.

HEAT.

In the work in heat it will save much of the pupils' time, if a
vessel is provided for holding water that may be warmed to the
temperature of the room, from which pupils may take water for
experiments when water is needed at that temperature. Also
provide a reservoir for hot water so time will not be taken by the
pupils for heating it. If access can be had to a steam-pipe with a
faucet, the exhaust steam will heat water very quickly.

EXERCISE 54. — Half fill a 4-ounce bottle with water, or mer-
cury. Carefully note its temperature, which should be the same
as that of the room. Close the bottle with a stopper ; wrap in
several thicknesses of paper to protect from the heat of the hand,
and shake vigorously. Note change of temperature. Shake again
for a longer time, and again note the temperature. Evidently
the change has been caused by the shaking. What transforma-
tion of energy is this ? Give three other examples of such trans-
formation.

EXERCISE 55. — Pit to the neck of a 4-ounce bottle a stopper
having two holes. Half fill the bottle with water. Pass through
one hole of the stopper the stem of an air thermometer bulb.
Push it down until the end of the tube is well under water. Now
clasp the bulb with both hands. Explain what occurs. Eemoving
the hands, bring a flame near the bulb. Note the effect. Let the
bulb cool ; then apply cold water, — i-f possible, ice. What effect ?
Explain. Are two holes in the stopper necessary ? Why ?

EXERCISE 56. — Fill an 8-ounce flask (wide test tube) with cold
water. Fit closely to its neck a stopper through which passes a
tube 30 cm. long, having a bore of 1 or 2 mm. The water should
stand in the tube 1 or 2 cm. above the stopper. Clasp the flask
closely with both hands. Note effect on the height of the water in
the tube. Next apply carefully the flame of a Bunsen burner.
Note as before. If you watch closely, you may notice that just
as the flame is applied, the water sinks. Can you account for
this ? What general effect of heat upon water does this experi-
ment show ?

LABORATORY MANUAL.

EXERCISE 57. — To Find the Coefficient of Linear Expansion
of a Solid : Fit up apparatus as indicated in diagram. This
consists (1) of a tin tube 60 cm. long, 2.5 cm. in diameter, open at
both ends. On opposite sides of this tube, near each end, is a short
tube about .6 cm. in diameter. Near the middle is a tube about 1.5
cm. in diameter, into which a thermometer may be fitted. Per-
forated c.orks are fitted to each end of the tube. Through these
passes a brass tube of about .6 cm. diameter, and a little longer
than the large tube. . The whole is mounted so that one end of the
brass tube presses against a screw at the right, the other against
the short arm of a lever whose long arm moves before a ruler

Fig. 11.

fastened vertically. (2) The other piece of apparatus is a boiler
for generating steam. It is a sheet-copper cylindrical vessel 15 cm.
tall and 10 cm. in diameter, mounted on three legs which raise it
about 20 cm. The legs are kept from spreading by a flat ring of
sheet metal connecting them at the bottom. Leading out from
near the top is a tube 5 cm. long and 6 or 7 mm. in diameter,
through which steam may be carried off in a slightly ascending
direction when the top of the vessel is closed. A conical top 30
cm. tall fits the cylindrical vessel as a cover fits a pail. The joint
must be as near steam-tight as possible so the top of the cylinder
is not wired, but is left flexible. The open top of the conical

74 LABORATORY MANUAL.

portion is about' 2.5 cm. in diameter, and of such shape as to be
easily closed with a stopper. A side tube, similar to the one on
the cylindrical portion, leads out from near the top of the cone.
These two admirable pieces, called the "Linear Expansion App."
and "App. A," are described in Hall & Bergen, and are supplied
by most dealers in laboratory materials.

Measure the brass rod when cold, and note reading of ther-
mometer. Adjust the screw so that one edge only of the brass
tube touches the lever. To do this easily it will be well to have
the end of the tube beveled slightly. Now boil the water in App.
A vigorously, and pass the steam through the tin tube. The two
upper openings of App. A are of course closed. Note carefully
the rise of the lever, reading to quarters, or less, of mm. When
the lever ceases to rise, note temperature of steam, i. e., of the
brass tube. Measure carefully the lengths of the two arms of the
lever. From this you can compute the amount of expansion of the
tube. Now determine the ratio of expansion for one degree C. to the
original length of the rod. This is the coefficient of expansion.

EXERCISE 58. — Fasten on a board, as indicated, wires 20 cm.
long, of copper, brass, German silver, iron, etc. Heat at A with a
Bunsen flame. Now beginning at
the ends of the wire farthest from
the flame, slide along each in turn
the head of a match. Note the
point where the match is ignited.
Measure the distance from this
point to the flame, and so make a
list of the metals used, in the order
of their abilities to conduct heat.
Or : Move the tip of a finger care-
fully along each wire toward the
flame until a point is reached which is uncomfortably warm. Mea-
sure the distance from this point to the flame, and thus make a list
of the metals as above.

EXERCISE 59. — Fill a test tube nearly full of water. Incline
it and apply the tip of a flame to it near the top. Take care that
the flame does not touch any part of the glass not covered inside
by the water. Hold in this position until water at the top of the
tube boils. How is the temperature of the lower end of the tube

76 LABORATORY MANUAL.

affected? What does this show as to the ability of water to
conduct heat?

EXERCISE 60. — Fill a large beaker with water. Stir into it a
little fine sawdust. Now gently heat the beaker at the bottom,
close to one side. Watch for evidence of currents. Explain the
cause of these currents from your results in Exercise 56.

Make a rectangle of glass tubing 10 cm. X 15 cm., joining the
ends by using rubber tubes and a Y tube. Fill with water in
which has been stirred a little fine sawdust. Cautiously heat one
of the lower angles of the rectangle. Note and explain. Cool one
of the upper angles by touching with a piece of ice. What occurs ?

This illustrates how water circulates in buildings warmed by
hot water.

Where would you apply heat to water to warm it most quickly?

In what way does the method of heating a metal differ from
that of heating water ? The first is called Conduction ; the second,
Convection.

EXERCISE 61. — " Touch paper " is made by dipping strips of
unsized paper in a solution of saltpetre (potassium nitrate), the
paper being dried before using. It burns with no flame and a
great deal of smoke. Light a strip of this paper, and by means
of the movements of the smoke, study currents of air. Eecollect
that smoke is made up of solid particles which, being visible and
very light, serve to indicate the motions of the "air. Why does the
smoke rise ? Hold it under the mouth of an inverted battery jar.
Note, and explain the motion of the smoke. Light a piece of
candle about 3 cm. long ; set it on the table, and set over it a
student-lamp chimney. Procure a strip of tin that will slip easily
into the chimney. Near the end of this punch two holes, through
which run a stout wire a little longer than the diameter of the
chimney. Drop the strip down the chimney. This will divide the
chimney into two passages. The candle should stand under one of
the passages. Hold the burning paper close above the top of the
other. Note and explain, as before, the movements of the smoke.

EXERCISE 62. — Fill a beaker, or other vessel, with cracked ice
that has been washed clean. Insert in it a thermometer until the
point marked 0° (the instrument is supposed to have the Centi-
grade scale) is just above the surface of the ice. When the mer-

78 LABORATORY MANUAL.

cury column has come to rest, record the reading. In reading the
thermometer in this and other experiments, be careful to stand in
such a position that a line from the centre of the eye to the top of
the mercury column will strike the stem of the thermometer at
right angles. Read to quarters, and, if possible, to tenths of the
smallest division on your instrument. On these two precautions
will depend much of your success in the succeeding work. Now
sprinkle on the ice a little salt. What effect? This shows the
importance of having clean ice.

EXERCISE 63. — Fill App. A with water to the depth of 3 cm.
Close the side tube of the cylinder. Fit a stopper to the top of the
cone. Pass through it a thermometer, pushing it down until the
point marked 100° is about 2 cm. above the stopper. The bulb,
however, must not come within less than 2 or 3 cm. of the water
in the vessel. Boil the water several minutes, read very carefully
your thermometer, and record. In order to find what would be
the boiling point of your thermometer under standard conditions,
consult the barometer. The boiling point will be raised or lowered
one degree for every excess or deficiency of 27 mm. from the
standard 760 mm. What would be the boiling point of your
thermometer under standard pressure? Do not boil the water
violently lest the steam be compressed. Partly close the escape-
pipe a moment with a cloth. Note the effect on the boiling point.
Now lower the bulb into the water and note reading. Dissolve in
the water some salt. What effect on the boiling point ?

EXERCISE 64. — Fit to a wide test tube a stopper. Through
it pass a short glass tube. Over the outer end of this slip a rubber
tube about 10 cm. long. If it does not fit the tube tightly, wrap it
with soft cord. Boil the water in the tube a few seconds ; then,
first removing the flame, pinch the rubber tube, invert the test
tube and pour on it cold water. This condenses the water vapor
in the tube and so lessens the pressure. In the preceding exercise
you noticed how an increase of pressure affected the boiling point.
What do you now find to be the effect of lowering the pressure ?

EXERCISE 65. — Boiling Point of Other Liquids. Fit to a wide
test tube a stopper having two holes. Through one pass a ther-
mometer, and through the other a short glass tube the outer end
of which is bent at right angles. Fill the test tube one-third full

80 LABORATORY MANUAL.

of turpentine. Cork it and press the thermometer down into the
liquid. Boil by means of a sand bath. This may be made by
filling a tin pan 3 or 4 cm. deep by 10 or 15 cm. in diameter, with
fine sand. Immerse the lower end of the test tube in the sand and
apply heat from below. Boil and record temperature. Repeat
with ether. But apply heat by introducing the test tube into a
vessel of water heated to about 70° C. The flame must first be
extinguished to avoid danger of explosion.

EXERCISE 66. - — Fill a beaker with water. Record its tempera-
ture and that of the salt to be used. Stir into the water a handful
of the salt, — better, powdered ammonium chloride. Again note
temperature. What effect, if any, would the stirring have on the
temperature ? What, then, must have produced the change noted ?

Mix snow and salt in portions of about 2 to 1 (the portions are
not very important). Record the temperature. In the first part
of this exercise the fall in temperature was due to the dissolving
of the salt. Is this a similar phenomenon ? You can decide this
by noting which melts the faster, the mixed ice and salt, or the
unused ice or snow.

Pour on the back of your hand a few drops of ether. Then,
after this has evaporated, a few drops of water of about the same
temperature as the ether. Which feels the colder ? Which evapo-
rates the faster ? As both were at the same temperature, to what
may the difference in sensations be due? Repeat by pouring a
little of each liquid in turn on the air thermometer of Exercise 55.

State two other examples of cooling by evaporation.

EXERCISE 67. — Apparatus : A calorimeter ; this must be a
vessel of thin metal about 6 cm. in diameter and 12 cm. tall,
brightly polished ; a nickel-plated "lemonade shaker." Into this
pour water to the depth of a few cm. Cool this gradually by
adding to it ice or snow, — finally salt, if necessary. Stir the
water continually with a thermometer that it may have a uniform
temperature. Watch the outside of the bottom of the vessel for
the appearance of mist. Note the highest temperature of the
water (this is considered the temperature of the metal, and hence
of the air in immediate contact with it) at which the mist appears.
Then gradually warm the vessel. This may be done by pouring
into it a few drops of warm water.

LABORATORY MANUAL.

Note the temperature at which the dew unmistakably begins to
disappear. The average of these two readings gives the dew point
of the atmosphere. Record the temperature of the room, the tem-
perature out of doors, and the kind of weather. How much must
the temperature fall to-day in order that it may rain ?

EXERCISE 68. — Determine how the rate at which a body cools
is affected by the temperature of the surrounding medium, e. g., the
air. Select for the body whose cooling is to be watched a ther-
mometer bulb. One with a large bulb is preferable.

Eemove the top from a tin can of about one liter capacity.
Solder to this can three strips of tin by which it may be tacked
to a board covering the top. Through this cover bore a hole, —
about | in. in diameter. Blacken the inside of the can and the
under side of the cover. This may be done by painting with thin
shellac varnish mixed with dry lamp black. Immerse the can in
a large vessel of water. Note temperature of the water, which
should be the same as the temperature of the room. Slide the
stem of the thermometer through a stopper that fits the hole in
the board. Warm the thermometer to about 80° C. by holding it
above (not in) a flame. Dry the bulb, if it has become moist.
Now introduce the thermometer into the hole in the board and
adjust so the bulb shall be near the centre of the can.

The temperature of the air now around the bulb is assumed to
be that of the water, which you have noted. This will remain
practically constant, since the blackened can will transmit rapidly
to the water any heat received by the air from the thermometer,
and the large body of water will not have its temperature per-
ceptibly raised. Note temperature of thermometer when finally
adjusted, and at the end of each succeeding half-minute. Eecord
results as below :

(1)

TEMPERATURE
OF AIR IN CAN.

(2)
TEMPERATURE
OF THERMOMETER.

(3)
FALL OF TEMP.
OF THERMOMETER.

DIFFERENCE
BETWEEN 1 & 2.

State, by studying last two columns, a rule governing the fall
in temperature of a body. (Page 20, Note 1.)

84 LABORATORY MANUAL.

EXERCISE 69. — Fill a beaker about one-third full of water, and
add about an equal amount of pounded ice or snow. Apply the
heat of a Bunsen flame. Stirring rapidly with a thermometer it
will be noticed that the ice melts, but that the temperature remains
practically the same as long as there is any considerable portion of
ice. Since the vessel is receiving heat from the flame and the sur-
rounding air, the heat so received is said to become latent. That
is, it is used in so altering the cohesion of ice that it becomes liquid.
Determine the amount of heat that becomes latent in turning 1 g.
of ice at 0° to water at 0°. For our unit of heat we will take the
amount of heat needed to warm 1 g. of water 1° C. A heat unit
will, of course, be given up by 1 g. of water in cooling 1° C.

Weigh a dry beaker of, say, 300 ccm. capacity. Pour into it
about 200 g. of water. Warm the water to about 50° and accurately
take the temperature. Drop into the water small pieces of clear
dry ice until about 100 g. have been added, i. e., until the level of
the water is raised about one-half. Stir constantly, but not
violently. Note the temperature when the last piece of ice is
melted. If the ice has not all melted by the time the water has
been cooled to 5°, dip out the remaining ice, taking as little water
as possible. It is also important that the final temperature be
about as much below the temperature of the room as the tempera-
ture at the first was above it, that the influence of the surrounding
air may be disregarded. If the ice put in is not enough to do this,
more may be added, lie-weigh to determine the exact amount of
ice melted. From your results calculate the number of heat units
necessary to melt 1 g. of ice. In doing this, take notice that the
ice is not only melted, but also warmed to the final temperature,
and that the amount of heat used in both these operations is equal
to that given up by the beaker and the water ; — the
amount of heat given up by a g. of glass in cooling
one degree may be taken as .2 of a heat unit. If a
metallic vessel is used, of course its specific heat
will be taken.

EXERCISE 70. — Determine the Latent Heat of
Water Vapor. Fit to the lower delivery tube of
App. A (all the other openings being closed) an
arrangement indicated in the diagram. The delivery
rig. 13. tube should reach nearly to the bottom of a beaker

86 LABORATORY MANUAL.

containing, say, 250 g. of water at about 15° below the temperature
of the room. Accurately take its temperature. Boil water in App.
A. Wait until all the delivery tube is hot and a strong jet of
steam is issuing from it ; then introduce into the water of the
beaker, bringing the end near to the bottom. Condense enough
steam to raise the water to about the same number of degrees
above the temperature of the room as it was at first below it.
Why ? Then remove the delivery tube. Stir the water thoroughly
and note its temperature very carefully. Again weigh and deter-
mine the weight of steam condensed. Now calculate the heat given
up by a g. of steam in condensing to water at 100°. In working
this problem notice that the heat which warms the water and the
beaker comes from two sources, — the condensation of the steam
to water at 100°, and the cooling of the water thus formed from
100° to the final temperature. Allow for the heating of the beaker
as in the previous exercise.

EXERCISE 71. — In our last two exercises we have made use of
the fact that glass in cooling furnishes only .2 as much heat as the
same weight of water ; or, the specific heat of glass is .2.

Determine the specific heat of shot. Place in the dipper of
App. A 500 g. of fine shot. Cover the dipper with a piece of card-
board in which is a small hole through which a thermometer may
be passed. Pour into a calorimeter 100 g. of water cooled to 6° or
8° below the temperature of the room. Place the dipper into App.
A, which should be filled with water nearly to the level of the
bottom of the dipper. Close the side tube of the App. Boil the
water, stirring the shot continually. When the shot has reached
the temperature of 100°, pour it quickly into the calorimeter.
Stir thoroughly and when sure the temperature no longer rises,
record reading of thermometer.

By a similar method to the one used in the two previous experi-
ments, calculate jthe heat yielded by 1 g. of shot cooling 1°, noticing
that in this case the vessel containing the water is of metal and its
specific heat, if brass, is about .09. If the vessel is only partly
filled, consider that only so much as is below the water line is
warmed.

88 LABORATORY MANUAL.

ELECTRICAL ENERGY FROM FRICTION.

EXERCISE 72. — Rub one end of a warm glass tube with a warm
piece of silk, and hold the rubbed end near some bits of tissue
paper and some small pieces of pith. Note carefully what follows.
Repeat several times to be sure of results. Now rub a piece of
sealing-wax with dry, warm flannel and do as you did with the glass
rod. Eesults ? The peculiar action manifested by these rubbed
bodies is due to electrification produced by the rubbing. Did you
do work in producing electrification ? The kind developed on the
glass rod is called positive electrification, and that on the sealing-
wax, negative electrification. Bodies exhibiting these phenomena
are said to have charges of electrification upon them.

Make a paper stirrup large enough to allow the rod or the wax
to pass into it easily, and suspend it by a silk thread. Rub the
rod, and, without touching the rubbed end with the hand, place it
in the stirrup. Now rub another glass rod and hold it near the
rubbed end of the suspended rod. What result do you get ? Try
it several times. Do the same with two sticks of sealing-wax, and
record results.

Now hold a rubbed glass rod near to a suspended stick of wax
on which there is a charge of negative electrification, and record
results. Hold a rubbed stick of wax near a suspended glass rod
011 which there is a charge of positive electrification, and record
results. State the law of action between charges of electrification
covering the phases shown by the above.

EXERCISE 73.. — Suspend a pith-ball by a silk thread. Call
this an electroscope. Develop positive electrification and hold
the rubbed body near the pith-ball. Note fully the action of the
ball. If the ball is attracted to the rod and then flies away
from it, try to touch the ball with the rod, and account for the
result. Now rub the stick of wax, and hold it near the ball.
Are the results the same ? Why ? Rub the wax, hold it near the
ball, and after the ball has touched it and swung away, bring a
rubbed glass rod near the ball, and account for results. Hold an
unelectrified, or neutral, body near a positively charged electro-
scope, and then near a negatively charged electroscope. What is
the action in each case ? If a body has electrification on it, how
would you proceed to find its kind ? Can electrification do work ?

90 LABORATORY MANUAL.

EXERCISE 74. — We have seen that certain bodies, upon coming
in contact with an electrified body, become electrified. Mount two
metallic shells or balls, such as are used on the ends of curtain rods
(or two potatoes may be used) on some short sticks of sealing-wax
so that they will be on about the same level. Some pith-ball
electroscopes can be charged, — one with negative, and the other
with positive electrification, to be ready for any tests you wish to
make, remembering that the repellent action is the true test for
the kind of charge on a body. Hold a rubbed glass rod near one
of the shells, having placed the two shells in contact, and approach
the shells from the opposite direction with the positively charged
electroscope. Result ? Repeat. Result ? Slowly remove the
glass rod and note the action of the electroscope. Test the two
shells for electrification. Result ? Touch the shells and the pith-
ball with your hand. Now re-charge the pith-ball electroscope
positively. Hold the electrified rod as before, being careful that
no sparks pass to the shells, and be sure the shells touch, and
again bring the pith-ball up as before. While the rod is held near
the first shell, carefully remove the shell and the rod. Test the
two shells for the kinds of electrification. Results ? This process
is called Charging by Induction.

EXKKCISE 75. — Place the two insulated shells, having pith-ball
electroscopes, about a foot apart, and connect them by a stick of
wax, as shown in the sketch. Hold an
electrified rod near or against one shell
and note whether the wax conveys the
electrification to the other shell. Try, as
connectors, a glass rod, a ruler, a silk
thread, a piece of rubber tubing, and a
piece of metal, and then try a wet silk
thread. Make a list of those substances

which allow electrification to pass to the second shell. These are
called conductors ; those which do not allow the electrification to
pass are called non-conductors. Name them. Why do the shells rest
on wax ?

EXERCISE 76. — Work an electric machine, and slowly separate
the knobs in front of the wheels. Do you notice any difference in
the frequency of the sparks when the knobs are near or far apart ?
If you get a large spark, it indicates a large charge of electrifica-

92 LABORATORY MANUAL.

tion. Should you desire to increase the electrification on the
machine, how would you have to affect the air space through which
the spark passes from one knob to the other ? In some respects
this action of electrification very much resembles liquid pressure.
If it is desired to have great water pressure throughout the city,
the pipes through which the water passes must be strong ; and if
we desire to have a great charge of electrification on a body, we
must increase the air space between that body and any other body
to which the electrification might pass. The term used in regard
to electrification, as pressure is in liquids, is potential. A body is
said to be at high potential when it must be carefully insulated to
keep its electrification from passing to the earth. Bring one knob
of the electrical machine near an insulated shell provided with a
pith-ball electroscope, and pass some tiny sparks onto it. Does the
number of sparks increase the potential of the shell ? The quan-
tity of electrification on an insulated conductor is called its charge ;
what effect does increasing the charge of a given conductor have on
its potential ? Charge two insulated shells provided with pith-ball
electroscopes with positive electrification so that they will have
different potentials. Now bring them together and note the effect
on the electroscopes. Eepeat several times. This effect will
always be seen when two bodies, at different potentials, are con-
nected by a conductor. The transfer of electrification by means of
a conductor is called a current. The earth is said to be zero poten-
tial. Positively charged bodies would send a current to the earth,
and with negatively charged bodies, the current is said to be in the
opposite direction.

EXERCISE 77. — One end of a narrow strip of board should rest
on an insulated support, and the other on any good conductor, such
as the steam-pipe. Some small screw-eyes can be screwed into the
under side of the strip at equal distances, say 60 cm. ; and from
the screw-eyes suspend double electroscopes by means of No. 36
bare copper wire. The balls should all be of one size ; the wires by
which they are suspended should be the same length, and the ends
of the wires should be tipped with wax. Fasten the wires with a
loop at the upper end so that the balls will be free to swing side-
ways. Now pass sparks from an electrical machine onto the strip
at the insulated end, and watch the balls. Does the electrification
pass the whole length of the strip ? Is it equally distributed

94 LABORATORY MANUAL.

throughout the whole length ? Does all of the electrification which
starts from the insulated end reach the other end ? Whatever
tends to prevent the transference of electrification from one point
to another, is called resistance. Does the strip offer resistance to
the passage of electrification ? Was electrification used up in over-
coming this resistance ? What is that which can overcome resist-
ance and is used up in so doing ? Does electrification seem to be a
form of energy ? What kind of energy is electrification when it is
stationary ? When it moves along a conductor ? Are heat and
light ever produced by the passage of electrical charges ? What
transformation of energy has taken place when a spark is seen ?

EXERCISE 78. — Whatever tends to cause a transference of
electrification from one place to another is called an Electro-
Motive Force, — written E.M.F. A difference of potential between
two points is an E.M.F. Can you think of any way of producing
an E.M.F. without an expenditure of energy ? If a difference of
potential causes an E.M.F., does the E.M.F. probably increase with
an increase of difference of potential ? When you work the elec-
trical machine, one discharging knob becomes positively, and the
other negatively, charged. Is the E.M.F. greater or less between
the two knobs than between either of them and an unelectrified
body ? Try it by holding an unelectrified body as far from one of
the knobs as the knobs are apart, and note the action of the spark.
Results ?

EXERCISE 79. — In the preceding exercises you have found it
necessary to insulate a body in order to electrify it. Now try to
electrify an uninsulated body. A piece of paper, say 5X8 in., is
fastened to one side of a pane of glass by mucilage on the corners
of the paper. Warm the glass slightly and lay it, paper side
down, on the table, and on the glass, just over the paper before
used, place another similar paper. The two are now separated by
the glass. Rub the upper paper with a cat-skin or piece of sheet
rubber. Handle the glass carefully by the corners and bring the
paper surfaces successively near a suspended pith-ball. Does either
paper seem to be electrified ? Hold the glass by one corner, and
pull off the loose paper by the corner and test it to see whether
it is more highly electrified now than it was when on the glass.
Test the other paper now. Results ? Repeat and test each paper
for the kind of electrification on it, and note whether or not the

96 LABORATORY MANUAL.

two have about equal amounts on them. Results ? How did the
lower paper become electrified ? An instrument like this which
enables us to accumulate quantities of electrification is called a
condenser. The most common form consists of a glass jar instead
of a glass plate, and instead of paper coats, it has tinfoil. The
jars so made are called Leyden Jars, and the process of charging
them with electrification is just the same, only, instead of rubbing
either coat, the knob in the cork of the jar is connected to the
inner coat of tinfoil by a little chain, and sparks from the prime
conductor of an electrical machine are passed on to the knob, while
the outer coat is connected with the ground, either by standing the
jar on the table or by holding it in your hand. Do not try to get
a very strong charge, and handle the jar very carefully. (You
would better get the assistance of your instructor). Charge the
jar thus, and having placed it on a glass plate, or cake of paraffine,
connect the outer coating to the knob by means of a metallic con-
nector having an insulator handle. What follows ? Why ? In a
few seconds connect the coats again. Results ?

If there was more of one kind of electrification than of the
other, what will be the condition of the jar after the sparks cease ?
Test the jar by approaching it with an electroscope. Eesults ?

98 LABORATORY MANUAL.

CURRENT ELECTRICAL ENERGY.

EXERCISE 80. — lu your previous work you learned that if two
bodies were at different potentials and were connected by a con-
ductor, there was a transference of electrification from one to the
other. If the bodies could be kept at different potentials, the
transference- of electrification, or current, as it is called, would be
continuous. Such devices have been found, and one of them is
now to be studied.

Make a weak solution of sulphuric acid by pouring about. 2 ccm.
of the acid into a tumbler two-thirds full of water. Stand in this
solution a brightly sand-papered strip of zinc 10 cm. by 4 cm.
Note carefully for a few minutes any changes on the surface of
the metal. Also stand a similar strip of bright sheet-copper in the*
solution, but not in contact with the zinc. Is there any marked
change on its surface ? Kemove the zinc, and while the surface is
still wet with the acid solution, spread a drop of mercury on the
zinc. (Do not let your rings come in contact with the mercury.)
A little cloth may be used to spread the mercury so that the entire
surface of the zinc becomes bright like a mirror. Coating the zinc
thus is called amalgamating it. Keplace the zinc in the solution.
Does the same action appear on its surface ? Keep the bottoms of
the metals apart, but lean the tops together, and watch the surfaces
for the evolution of bubbles. Results ?

EXERCISE 81. — To make it more convenient, you can use a
strip of pine about 2 cm. square, and long enough to rest across
the tumbler, and fasten the metals on opposite sides of the pine by
driving through each strip a tack, around whose head is wound the
bare end of a piece of No. 24 insulated copper wire. Having thus
arranged the metals, stand them in the acid solution and press
together the two free ends of the wire, being careful to have them
scraped bright with a knife or sand-paper. Is any action mani-
fested on either of the metal plates ? Separate the wires Result ?
Repeat several times, and record results. Connecting the wires
thus is called closing the circuit, and separating them is called
breaking the circuit.

Examine two of the strips which have been used for some time,
and tell which one of them the acid solution has acted on the more

100 LABORATORY MANUAL.

vigorously. This "plate" is the one where the electrical energy is
generated, and is called the positive plate. It is at a higher poten-
tial than the other, and the E.M.F. causes the current to pass from
it through the liquid to the other, or negative plate, whence the
current passes through the wire (external path) back to the first
plate. Name in order the substances through which the current
passes in making a complete circuit.

The free end of the wire connected to the negative plate is
called the positive electrode ; while the free end of the wire con-
nected to the positive plate is called the negative electrode. A
vessel containing a pair of metals arranged similarly to the one
you have used, and having in it a solution which will act chemi-
cally on one of the metals, is called a Galvanic or Voltaic cell or
element. When several cells are used and are connected with one
another, they constitute a Galvanic battery. (A single cell is
sometimes called a battery.)

Caution : Never twist the ends of wires when you make connec-
tions ; use double wire couplers. When you are through with the
pieces of wire, wind them carefully onto a spool so as to keep them
from getting twisted or tangled.

EXERCISE 82. — There are many kinds of Galvanic cells, and
among them are some two-fluid cells, one of which is made as fol-
lows : use for materials a strong glass tumbler, about 10 cm. tall,
and 7 or 8 cm. wide ;. a cup of unglazed porcelain, about 10 cm.
tall, and 4 or 5 cm. wide ; about half a liter of dilute sulphuric
acid (20 parts in volume of water to 1 part in volume of concen-
trated acid) ; about half a liter of a saturated solution of copper
sulphate ; a piece of zinc 10 cm. long, 2.5 cm. wide, and .5 cm.
thick, having about 50 cm. of No. 20 insulated copper wire fastened
firmly to it ; a piece of sheet-copper 10 cm. square, and having a
similar wire fastened to it.

Put the zinc into the porous cup, and then pour in dilute acid
until the cup is full to a level, 2 cm. below the top. Now put the
cup into the tumbler and pour into the tumbler the sulphate of
copper solution till the tumbler is full to a level with the acid in
the porous cup. Kemove the zinc and amalgamate it with mercury
and replace it in the porous cup. Put the sheet-copper, bent into
a circular form, into the sulphate of copper solution. Put the cell
in circuit with a galvanometer, and note the deflection when the
needle comes to rest, and then while the current continues to pass

102 LABORATORY MANUAL.

through the galvanometer, note the deflections for periods of 5 min.
each for 30 min., if time permits. Results ? Compare with results
obtained when a single fluid cell is so used. (You may need the
aid of your instructor in using the galvanometer.)

EXERCISE 83. — Among the two-fluid cells the most common is
the so-called Gravity cell. It consists of a zinc plate, a copper
plate, a solution of zinc sulphate, and a solution of copper sulphate,
a jar to hold the solutions and plates. The copper plate is placed
in the bottom of the jar, and is covered with a saturated solution
of copper sulphate ; and from this plate is extended up out of the
jar a copper wire covered with hard rubber. Then a solution of
zinc sulphate is carefully poured in, and in a few minutes is seen
to be resting on the copper sulphate solution. The zinc plate is
now suspended from the top of the jar so as to be immersed in the
light colored solution at the top of the jar, care being taken not to
let it down into the blue solution ; the zinc should be covered with
liquid, — water may be added to get this result.

When the plates are connected by wires, some chemical changes
take place in the molecules of the solutions. The copper sulphate
solution deposits copper on the copper plate, and zinc from the
zinc sulphate takes its place ; and the zinc plate then gives off
more zinc to produce new molecules of zinc sulphate. In time the
copper sulphate will be all used up, and there will be too much zinc
sulphate solution. This is shown by the liquid all becoming clear.
Some of the clear solution must then be poured off, and a handful
of crystals of copper sulphate be poured into the cell. Compare
the strength of the current from this cell with that of the other
two-fluid cell. Kesults ? Why called a Gravity cell ?

EXERCISE 84. — We cannot see the current when a battery is
in action, but we can see some of its effects, and you are now to
study some of them. Use a battery of two or three large cells,
having them connected in series, i. e., the positive plate of one cell
connected to the negative plate of the next, and so on, and then
between the copper wires which connect the last two plates place
a short piece of very fine iron or. platinum wire. Note carefully
any change in color of this fine wire, or, if its color does not change,
carefully touch it with the finger. Eesults ?

Remove the fine wire and connect the two copper wires by a
coupler ; scrape the insulation from a short section of the wire
through which the current is passing, and dip this bare section

104 LABORATORY MANUAL.

into some iron filings. Result ? Break the circuit, and note the
effect on the filings. Repeat several times to be sure of what
happens, and record results. What is here shown to be the con-
dition of a wire carrying a current of electricity ?

Now dip the free ends of the wires coming from the battery
into a solution of potassic iodide (made by dissolving a few crystals
of potassic iodide in water, and then stirring it into a thin starch
paste), and note the effect at the places where the wires touch the
solution. A dark or purple color indicates a chemical change by
which iodine is set free. Do you get this result ? Name the
three effects of current electricity you have seen in this exercise.

EXERCISE 85. — Wind some insulated copper wire No. 24
around a piece of soft iron, such as a wrought iron nail. The

wire should be about 1 in.
long, and shoxild have about
30 cm. free at each end after
winding onto the iron so as
to give freedom of movement
after connecting the free ends
of the wires to a galvanic cell. (The tumbler cell will do.)

Wind two as shown in Fig. 15. ' The figures show the
wire on the side next to you as you wind them. Having
connected the ends of (1) as shown above, dip A and B suc-
cessively into a dish of iron filings. Results ? Approach the
north-seeking pole of a magnetoscope with A and then with B.
Results ? What is the nail now, and what can you say about end
A and end B ? Now disconnect from the cell, and again dip the
ends of the nail into filings. Results ? Under what conditions is
a piece of soft iron a magnet ? If you imagine yourself swimming
in the " current of electricity " in any section of the wire, as at E,
and facing the soft iron, on which side of you is the north-seeking
pole of the magnet which the soft iron becomes ? Now make the
same trials, and answer the questions, using 2, and record your
results.

These devices are called electro-magnets while the current
passes through the insulated wires. The coil is called a helix,
and the soft iron, its core. If you look at the end of 1, as at A,
where the current enters the helix, the current will pass aK>und
the core, as is shown in 3. Compare this direction with the direc-
tion of motion of the hands of a clock. This is a right-hand helix.

106

LABORATORY MANUAL.

Looking at 2 where the current enters at C, the current will travel
around the core, as is shown in 4. Compare this direction with
the direction of the motion of the hands of a clock. Frame a rule
for telling the poles of an electro-magnet when you know the direc-
tion of the current around it.

If you were given an electro-magnet and could not see the
battery to which it is connected, how could you tell the direction
of the current in the wire ?

EXERCISE 86. — You will recall the effect on a freely suspended
magnet when another magnet was brought near it. From what
you saw, when a wire carrying a current was dipped into filings,
what do you think would be the effect on a freely poised magnet,
should a wire carrying a current be held near it ? Use an insulated
copper wire, No. 24, about 1 m. long. Connect the bare ends of
the wire to the poles of a cell and, remembering that the current
is from the negative plate through the wire to the positive plate
(from copper to zinc), hold the wire so that a section of it will
carry the current from the north to the south near a delicately
poised magnet, and get results from each of the following con-
ditions : (Do not turn the wire, even though the needle should
turn when the wire approaches it.)

Current
going
from

' 1. North to south above magnet.

2. South to north below "

3. South to north above "

4. North to south below "

North -seeking
pole deflected
towards east
or west ?

Examine carefully the above results, and, thinking of yourself
as swimming in the " current of electricity " and always facing the
magnet, on which side of you will you find the north-seeking pole
of the magnet deflected ? State the rule clearly and briefly.

EXERCISE 87. — If the wire should be held so that the current
would pass from north to south above a freely-poised magnet, the

Fig. 16.

north-seeking pole would be deflected in what direction ? If from

108 LABORATORY MANUAL.

south to north below, in what direction ? If now you were to hold
the wire so that one section of it would carry the current from
north to south above, and another section, from south to north
below, how would the amount of deflection of the north-seeking
pole compare with either of the first-mentioned cases above ?
Try it (A). Results ? Try by having several coils, as shown
in B, and compare results with the trial in J, and state any
inferences.

Use a larger battery cell, and compare results. Can you think
of any use to which you could put an instrument of this kind ?

Instruments having several coils of wire around a delicately-
poised magnet, under which is a scale graduated in degrees, is
called a galvanometer. How would increasing the number of coils
(other things being the same) affect the deflection ? If the num-
ber of coils remained constant, how would increasing the currenj;
affect the deflection?

EXERCISE 88. — A tangent galvanometer is now to be used. It
should stand on the table so that the coils and the magnet are par-
allel to each other ; this will be true when the pointers are on the
zero marks. The instrument should be level so that the needle is
in the center of the coils, and free to move. There should be no
iron or magnets near, and if the needle tends to stick, tap the base
gently before taking a reading. Be careful not to change the coils
from their north and south position while making tests. The earth
tends to keep the needle in a north and south position, while a cur-
rent passing through the coils tends to turn the needle east and
west, so that when the galvanometer is in use, the needle assumes
a position which is the resultant effect of the two forces acting
upon it. (Some galvanometers have what is called an astatic needle,
i. e., a combination of two magnets, one being placed above the
other, with opposite poles near each other, so that the earth's effect
on one magnet neutralizes the effect of the other, and the influence
of the earth is thus eliminated. Such galvanometers are much
more sensitive than the tangent galvanometers.)

If the number of coils used in the galvanometer be constant, a
greater deflection of the needle indicates what ? Now find the
deflections produced by two or three different cells, and record the
results. It is better to read by reversals, i. e., cause the current to
pass through the coils in one direction, and then, after noting the

110 LABORATORY MANUAL.

deflection, cause the current to pass in the opposite direction, and
note the deflection. The average of the two is the true reading.
(To reverse the current in the galvanometer, a commutator may be
used, or, have two wires, about 30 cm. long, coming from the
galvanometer, and on the free ends have wire couplers, so that
connections may be made without disturbing the instrument.)
Now find the deflections produced by two or three different cells,
and record results ; always get readings accurately to one-fourth of
a degree. The strengths of currents are not proportional to the
degrees of deflection, but are proportional to the tangents of the
degrees, i. e., if one cell gives a deflection of 55°, and another cell
gives a deflection of 35 °, the strengths of the currents are not as
55 : 35, but as tangent 55 to tangent 35. The table of natural tan-
gents is found on p. 150, and by consulting it you will find
tangent 55 to be 1.428, and tangent 35 to be .700, so that the
strengths of the currents are to each other as 1.428 : .700, or about
as 2 : 1.

EXERCISE 89. — Connect one plate of a cell with one post of
a galvanometer, and from the other plate of the cell run a wire
about 30 cm. long, having its free end scraped bright. Connect
a similar wire to the other post of the galvanometer. Now press
these two free bright ends of the wire against or into each of the
following substances, and note the amount of deflection made in
each case, so as to determine which substances allow the current
to pass through them easily : — iron, brass, copper, wood, glass,
carbon, silver, paper, pure water, dilute sulphuric acid and zinc.
Tabulate as follows : —

SUBSTANCE.

GALVANOMETER DEFLECTION.

By examining the list and the deflections, number the sub-
stances in the order of the power to resist a current passing through
them.

Why is copper wire generally used ? Why is it covered with
cotton or silk ? Why is it necessary to remove the insulation in
making connections ?

112 LABORATORY MANUAL.

EXERCISE 90. — You have seen that substances differ in their
ability to resist the passage of an electrical current through them.
To find just how much resistance a certain object offers makes
it necessary to have some standard of measurement. The unit
accepted is called the " ohm," and is the resistance of a column of
mercury 106.3 cm. in height, and of uniform cross-section, and
having a weight of 14.4521 g. at a temperature of 0° C. Instru-
ments consisting of several coils of wires of different known resist-
ances varying from .1 to 500, or more, ohms are now prepared,
and by using such an instrument together with a galvanometer,
you can determine the exact amount of electrical resistance of any
conductor. The resistance box and galvanometer are connected to
a battery or cell so that the current passes through all of them,
thus : Fig. 17. The keys of the resistance box are all placed on the

buttons marked zero, and the de-
flection of the needle noted. Now
introduce more and more of the
coils into the circuit by moving
the keys around on successive but-
tons, thus causing the current to
meet with greater and greater
K resistance to its passage. How

does this affect the current, and

what effect does it have on the needle ? Now, with any resistance,
say 5 ohms, read the deflection. Break the circuit and then place
a bar magnet on the table about 20 or 30 cm. from the coil, and
have it exactly in line with the needle when its pointer is on the
zero mark, having the north-seeking pole of the magnet towards
the south-seeking pole of the needle. Close the circuit and again
note the reading. Does the presence of the magnet increase or
decrease the sensitiveness of the galvanometer ? Reverse the ends
of the bar magnet, and find the effect upon the readings. Vary
the distance of the bar magnet, and record results.

EXERCISE 91. — One method of measuring resistances is as fol-
lows : The object whose resistance is sought is placed in circuit
with a battery and a galvanometer, and the deflection noted. (Use
a magnet and reduce the reading to about 45°.) It is better to
read by reversals, and take the average reading of several trials.
The object is then removed, and a resistance box is substituted in

114

LABORATORY MANUAL.

its place and resistances are introduced in the box till the galva-
nometer gives the same deflection as was obtained when the
former reading was taken (read to quarters of degrees), when the
total resistance introduced by the box will be the resistance of
the object tested. Kecord your results. This is called determin-
ing resistance by substitution. By the process just described,
determine the resistance of several coils of wire and record results
as follows :

NO. OF WlEE,

B. &S.

DIAMETER.

LENGTH.

KIND OF WARE.

KESISTANCE.

22
28

.644 mm.
.321 mm.

10m.
10m.

Copper.

3
4
5

22
28

20m.
20m.
10m.

German silver.

From the above table and the results you obtained, can you see
a definite relation existing between the lengths of conductors of
the same diameters and their resistances ? State it. How do
resistances vary in regard to diameters or sectional areas of wires
of the same length ?

The results from (2) and (5) indicate what in regard to ma-
terial ?

EXERCISE 92. — To measure the resistance of a battery by
means of a tangent galvanometer.

The battery is connected to the galvanometer so that the
deflection is about 45°, and the exact deflection is noted. Now by
means of a resistance box introduce resistance till an angle is
obtained whose tangent is just half of the tangent of the angle of
the former deflection. (Consult the table of angles and their
tangents on p. 151.) The resistances offered by two bodies to
a current are to each other inversely as the tangents of the angles
of deflection on the tangent galvanometer, hence the resistance
introduced by the box above is equal to the resistance of the coils
used in the galvanometer and the resistance of the battery.

If now you deduct the resistance of the coils used in the galva-
nometer from the resistance introduced in the box, you will have
the resistance of the battery. For example, if the battery and
galvanometer in circuit give a deflection of 45° the tangent of

116

LABORATORY MANUAL.

45° is 1.000. Half that tangent is .500. Tangent .500 is that
of angle 27°. The resistance introduced to bring the deflection to
27° is 8.2 ohms. The resistance of the galvanometer coils used is,
say, 1.5 ohms. Then 8.2 — 1.5 = 6.7; therefore, the resistance of
the battery is 6.7 ohms. Measure the resistance of two different
cells thus and record your results.

EXERCISE 93. — Use an astatic galvanometer and a Wheatstone
Bridge. The Wheatstone Bridge presents one of the best known

is.

methods of quickly and accurately measuring resistances. It
works on the following principle : The current starting from the
battery reaches the point marked E on a thick square of wire or a
strip of metal ; here it divides, and if R and R are connected by
a thick copper wire, and X and X are similarly connected, then
equal amounts of the current pass over E, A, L and E, B, L, the two
amounts uniting at L and passing on to the battery. For every
point in E, B, L there is a point in E, A, L having the same poten-
tial, hence should any two such points be connected, there would
be no current through the connecting medium. A and B are
two such points, being equally distant from E, and should you
insert a galvanometer between them, there would be no deflection
of its needle. If, now, you should introduce a coil of wire between
X and X) one division of the current would have to pass through

118 LABORATORY MANUAL.

the path E, B, w, L, and would, therefore, meet more resistance
than it would by passing over the path E, B, G, A, L, so that part
of the current would pass through the galvanometer, as shown
at 1. If you should remove the heavy wire between R and R, and
put it between X and X, and should put the coil w between R and
R, the process would be reversed, and the division of the current
going over the path E, A, L would subdivide at A, part going over
E, A, G, B, L, thus giving a reverse deflection in the galvanometer.
Use No. 16 or 18 wires of about equal lengths to make connec-
tions, and set up the apparatus as shown in the diagram. Have
two keys for closing and breaking the circuits, one between the
point L and the battery, and the other between A and the galva-
nometer. (Always close the battery circuit first.) Close the cir-
cuits and adjust the switches in the resistance box till there is no
deflection of the galvanometer needle. The resistances of the wire
coil and that introduced in the box are now equal. What is the
resistance of the wire tested? Test several different coils, and
record results.

It is better to unplug unequal resistances in the arms of the
bridge marked (a) and (£); for example 10 ohms in (a) and 1 ohm
in (b) if the object to be tested is one of small resistance, and if it
is one of great resistance unplug 10 ohms in one arm and 100 ohms
in the other. Be sure that the plugs marked (P) are in firm con-
tact with the metal strip unless the resistances marked on their
spools are to be thrown into the circuit.

Close the circuits and adjust the switches in the resistance
box till no deflection of the galvanometer needle can be noticed.
Then since it is the principle of the Wheatstone Bridge that when
the above condition is obtained the products of the resistances

be
of the opposite arms are equal, e.g., a '. b :: c : d or d =— , you can

find the numerical value of (d) which will be the resistance sought.
Find the resistances of several coils and record results.

EXERCISE 94. Wind several m. of insulated copper wire, No. 18
or 20, around a pasteboard cylinder about 4 cm, in diameter, and
leave about 2 m. of each end of the wire unwound so as to make
connections with an astatic galvanometer. Place some books on
the wires near the galvanometer, so that in moving the coil you
will not move or disturb the galvanometer, and in your manipula-
tion keep the coil as far from the galvanometer as possible, Slide

120 LABORATORY MANUAL.

the coil suddenly over one end of a bar magnet, as you would a
ring on a finger, and note the effect on the needles of the galvano-
meter. Remove the coil suddenly, and note the effect. Repeat
several times, to be sure of results. Now reverse the ends of the
magnet, and do as before, and note how the deflections compare
with the former ones. How does the direction of the deflection
produced by sliding the coil onto one end of the magnet, compare
with that of the deflection made by removing it from the other end
of the magnet ? Make several trials. Result ?

Hold the coil still while it surrounds the magnet, and note
whether a current is manifested in the galvanometer. 'When
the coil is moving on or off the magnet, the number of lines of
magnetic force passing through the closed circuit of the wire is
varied, i. e., when the coil passes onto the magnet, the number of
lines of magnetic force passing through the closed circuit of wire is
being increased, and while the coil is being withdrawn, the number
of lines of force is being diminished. Will either process cause a
current ? When the number is not being varied, is there a cur-
rent ? How does the deflection made by increasing the number of
lines at one pole of the magnet, compare with decreasing the
number of lines at the other pole ?

How could you arrange a combination of this kind to make
a continuous current in one direction ?

This is the plan of a dynamo. If one is at hand, examine with
the aid of your instructor.

EXERCISE 95. — Wind about half a meter of No. 30 insulated
copper wire around a wrought iron nail, and leave about 1 m. of
each end of the wire free. Suspend
the nail by its "point," as shown in
Pig. 19, connecting the wires to a
battery. Make a similar electro-
magnet which you can use without
suspending it. It can, however, rest
on a cylinder so as to be near B.
Cause the current to pass through A
successively in opposite directions
Flg- 19- by changing the connections at P

and P'. (Simply press the bare ends of the wires from A onto
the posta P and P' and time the connections so as to be in unison,

122

LABORATORY MANUAL.

if possible, with the motion of B, if B moves.) Do you get motion
without touching B or breathing against it ? Why ?

If you could have some electro-magnets arranged on an axle so
that their ends would project like the spokes of a wheel from the

Fig. 20.

hub, as shown in Fig. 20, and have the poles as indicated, what
would the joint action of (1) on (2) and (1) on (3) cause the wheel
to do? If you could continually reverse the currents in the
"wheel" electro-magnets so as to keep the poles in the vicinity of
1 of the polarity indicated, what would happen to the wheel?
This is the plan of an electro-motor, and the connections with the
wheel coils are made through the axle.

124 LABORATORY MANUAL.

SOUND.

EXERCISE 96. — Suspend a solid rubber cord 4 or 5 mm. in
diameter, and 4 or 5 m. long, from a hook in the ceiling, or other
high support, and fasten the lower end to a hook in the
floor so that the cord will be subjected to a very slight
tension. Measure the length of the cord between the two
supports. (The cord may be held to the floor by light
pressure with the foot.)

With a pointer or ruler tap the cord near the bottom ;
a short wave will run up the cord. Continue to tap the
cord at regular intervals, timing the intervals so that
the whole cord will vibrate as one ventral segment, as in
Fig. 21.

When you have learned to keep the cord thus regu-
( larly in motion, count the number of double vibrations in
Fig. 21. gQ seconds. Repeat before recording.

Again, tap the cord at a much faster rate so it will vibrate in
two ventral segments, with a node, i. e., stationary point, at the
middle of the cord. Coiint the number of vibrations now made in
30 seconds.

Similarly, make the cord vibrate in three, then four ventral
segments, and determine the number of vibrations in 30 seconds in
each case. Tabulate the results of the four tests as follows : —

LENGTH OF SEGMENTS.

NITMHKR OF VIBRATIONS
i* 30 SECONDS.

NUMBER OF VIBRATIONS
IN 1 SECOND.

What relation between length of segment and number of vibra-
tions in a given time ?

If on the water four waves, each 30 feet between crests, were
to pass a given point in 1 minute, what would be the velocity per
minute of the onward motion of the wave ?

In your experiment each segment was but one-half the wave
length. Knowing this, find the velocity of the wave motion per
second in each of the above cases. Increase the tension and notice
any effect this has on the rate.

126 LABORATORY MANUAL.

EXERCISE 97. — Cause a bell to sound by striking it with a
pencil or other light body ; and while it is sounding suspend a
small pith-ball or piece of cork from a thread so it rests lightly
against the edge of the bell. What results ? What seems to be
the condition of the bell while sounding ?

Tap a large tuning-fork on a piece of wood, and while sound-
ing, invert it and dip the prongs about 1 mm. into water. What
results ? Sound again, and suspend the pith-ball against the
prongs.

Stretch a short piece of No. 28 brass spring wire, or violin
string, so that when plucked it will yield a musical tone, and
while it is sounding, suspend a card or bit of paper lightly against
the wire. What results ? Why ? Tear a strip of paper 1 cm.
wide and 4 or 5 cm. long ; then fold it so as to make a V-shaped
saddle, technically known as a "rider." Now drop your rider
astride the sounding string. What results ?

Fasten the center of a 6-in. square pane of glass securely
between two corks by means of a clamp. The edges of the glass
should be ground or filed smooth. A brass plate, if not too thin,
vvill answer still better. Sprinkle sand evenly over the surface of
the plate, being careful that the plate is horizontal, then draw a
violin bow across the middle of one edge of the plate so as to make
a musical tone. What results ? What must be the condition of
the plate ? Make a sketch of the plate after sounding a few
times.

EXERCISE 98. — Hold a vibrating tuning-fork, whose pitch is
not lower than middle C, over the mouth of an empty hydrometer
jar about 15 or 16 in. deep. Does the sound appear louder than
when the fork is held away from the jar ? Again, bring the fork
close to the mouth of the jar, and pour water slowly into the jar,
listening carefully for the greatest intensity of sound. Try several
times till you feel certain you have the point of greatest reenforce-
ment ; then measure the length of the column of air from the
surface of the water to the mouth of the jar.

With the air column of the same length, rotate the vibrating
fork slowly on its axis above the jar, and describe the effect.
Now, starting from the position with one prong above the other,
rotate through one-eighth of a turn, and state the effect ; then
through another eighth, etc., till a half-turn is completed. Call

128 LABORATORY MANUAL.

these positions 1, 2, 3, 4 and 5, and designate the loudcess of each.
This change is due to Interference of the sound waves started by
the two prongs.

The length of the air column giving greatest reinforcement,
plus .3 the interior diameter of the jar, is one-fourth of the wave
length of your fork. Knowing this, and the number of vibrations
made by your fork in a second, determine the velocity of sound
per second.

It will be well to repeat the experiment with a fork of different
pitch, and compare with previous velocity.

EXERCISE 99. — To the bob of a heavy seconds pendulum a
white cloth is tied so its vibrations can be seen at a distance.
The pendulum is made to swing through a large arc, and just as
it passes the middle of its arc, a person strikes a sharp rap on a
board with a mallet or hammer, the motion of the hammer also
being made visible by a white cloth. A second person seeks such
a distance from the pendulum that the sound is heard just as the
pendulum crosses the middle of the arc on its return swing. An
opera-glass or spy-glass will be of great assistance. Begin with a
distance of 850 or 900 ft., and increase till the proper point is
found. As this method is at best not very accurate, great care
should be exercised in timing the blows of the hammer to the
swing of the pendulum. What do you find to be the velocity of
sound ? If there is a wind, exchange the positions of observer
and pendulum, and find to what extent the wind increased or
decreased the velocity of sound.

EXERCISE 100. — If a whirling table, with Savart wheel is at
hand, hold the edge of a card against the teeth of the wheel, or
hold the corner of the card so it will rub on the row of holes in
the wheel while the wheel is in motion. A tone, more or less
shrill, should be produced. Vary the rate of the wheel, and decide
how the velocity with which the card is made to vibrate affects
the pitch. If no whirling table is at hand, the escapement may be
removed from an old clock, and a card held against the rapidly
revolving wheel.

Hold a tube immediately over the outer row of holes of a
Savart wheel, and blow steadily through the tube so that when the
wheel is revolved, the air in passing from the tube through the
holes will be broken up into puffs, and produce a musical tone.

130 LABORATORY MANUAL.

How does the speed of revolution, and the consequent number of
puffs per second, affect the pitch ? Try over another row of holes.

Result ?

If you have a good Savart wheel, it will be interesting to
revolve till you bring the pitch in unison with a tuning fork ;
then, turning regularly at this rate for, say, ten seconds, determine
the number of revolutions made by the crank on the wheel per
second, then the number of revolutions made by the Savart wheel
per second, and lastly, by counting the holes in the row used, the
number of puffs per second which produced the tone.

EXERCISE 101. — ^Apparatus : A glass tube about 1.5 m. long
and having an internal diameter of about 4 cm. ; a brass tube or
rod about 2 m. long and 1 cm. in diameter.

Fit to one end of the glass tube a stopper. Scatter through the
tube a small quantity of cork dust. Fasten to the end of the brass
tube, by means of sealing-wax, a thin cork that slides closely in the
glass tube, but moves with slight friction. Push this into the glass
tube about 50 cm. Lay all upon a table, and clamp the brass tube
at its middle point by means of two grooved blocks and an iron
clamp so that it will be held in a horizontal position and in line
with the axis of the glass tube.

Eub a piece of resined leather over the outer end of the brass
tube. A shrill sound should be produced and the cork dust be
violently agitated. By moving the glass tube forward or backward
so as to change the length of the confined air column, a point may
be found where the sound will cause the cork dust to divide into
segments separated by nodes. Find the average length of these
segments.

Now these segments show the way in which the air in the closed
tube is vibrating, and as the distance between two nodes in a vibrat-
ing body is half a wave length, we may thus find the wave length
in air of the sound made by the brass. But the brass tube having
a node in the middle is also half a wave length. By comparing the
wave length in the brass tube with that in air, determine the rela-
tive velocities of sound in the two.

EXERCISE 102. — Apparatus : Sonometer with brass spring wire
Nos. 22 and 28, B. & S. gauge.

Tune two No. 22 wires in unison so they will give a good musi-
cal tone; probably a tension of 15 to 20 Ibs. will be needed. In

132 LABORATORY MANUAL,

sounding a wire, pluck it in the middle, and, with the ear close to
the wire, listen for the fundamental tone, which may for an instant
be obscured by harsh or grating overtones.

Having the wires in unison, place a bridge under one a few cm.
from the end, pluck the longer portion, and note any change of
pitch. (It will be best to press the wire lightly against the bridge
so as to limit the vibrations to the part under consideration.)

Now move the bridge till you find a length of wire whose tone is
an octave above that of the full lengthed wire. Measure now the
length of the wires.

Inasmuch as the higher tone of an octave is produced by twice
as many vibrations per second as the lower tone, find from your
results the relation between the number of vibrations per second
and the length of the wire.

With same wires, apply tension of 6 Ibs. to one, and if it does
not produce a musical tone, place the bridge under both wires at
such a point as will yield a good tone in the first wire. Now place
a tension of 24 Ibs. on the second wire and determine the musical
interval between the tones produced by the two wires. What rela-
tion do you find between ratios of the numbers of vibrations per
second and the ratios of the tensions ?

Substitute a No. 28 wire for one of the No. 22 wires. Place a
tension of 8 Ibs. on each wire, and, if necessary, shorten both wires
equally by means of the bridge so as to get a good tone from the
thicker wire. Compare the vibration rates of the two wires. Com-
pare the diameter of the wires (accurately measured, or taken from
the tables) with the vibration rates.

Inasmuch as the wires are of equal length their weights will
vary as their cross-sections, or as the squares of their diameters.
Now find the relation that exists between the vibration rates and
weights of the wires.

EXERCISE 103. — Tune two No. 22 wires in unison with tension
of 15 to 20 Ibs. While one is vibrating its full length, touch it
lightly with a feather exactly in the middle ; listen for the pitch of
the resulting tone. Eepeat, and drop a little paper rider upon the
middle of the wire just after touching with the feather. What
results ? Try several times. What do you call the stationary points ?

Now touch the wire while sounding its full length at a point one-
third its length from the end. What tone results ? Kepeat, and

134 LABORATORY MANUAL.

place two riders, one at the point touched, and one at the same
distance from the other end, What results? Try several times.
How does the wire seem to vibrate after touching ? These higher
tones are called overtones, or harmonics. What harmonic results
when the wire is touched at one-fourth its length ?

Now, while the wire sounds its fundamental, see if you can
distinguish any of the harmonics without using the feather. Sound
one of the wires vigorously, then stop it with the hand, and listen
to see if any sound issues from the other wire. If so, what tone is
it ? The wires must be tuned exactly in unison to get results.

Two mounted tuning forks of same pitch will answer also.
Sound one ; stop it, and listen for the other. Vibrations thus pro-
duced are called sympathetic vibrations. Can you account for the
way in which they are started ? Now change the tension of one of
the wires, or, if using the forks, fasten a drop of sealing-wax to the
prong of one, and see if you can get the sympathetic vibrations.
Explain.

Now, while the wires or forks are slightly out of tune, sound
the two wires, or the two forks, and listen for beats, i. e., swelling
and diminishing of the tone. Count the number of beats in a
given time, say 10 seconds. Then change the tension still more,
or increase the weight of wax on the prong, and count beats again.
How can you make use of beats in tuning an instrument ?

EXERCISE 104. — Use tuning fork and two Y tubes connected
as in the figure. A is a rubber tube 10 in. long ; B is a bent glass

tube 12 in. long capable of sliding
inside the larger rubber tube C,
which is 13 in. long ; D need not
be more than a few inches, but E
should be 3 or 4 feet long.

Let one person hold the free
Fig- ^ end of the tube E in his ear while

another holds the vibrating fork at the open end of D. At first
A, B, C should be drawn out full length.- Now, seek to adjust
the length of A, B, C, so that no sound is heard when the fork
is held at D. Pinch the tube A shut ; does the sound return ?
Try repeatedly. Having found a length of A, B, C, such that
when A is closed, the fork is heard, but silence results on opening
A, find the difference in the lengths of the two paths from F to G.

136 LABORATORY MANUAL.

Compare this with the wave length of this fork as determined in
Ex. 99. Try to account for the silence when both tubes are open.
The experiment may be varied by connecting both ends of a
rubber tube 1.5 to 2 m. long to the arms of a Ftube ; a second
rubber tube connects with the other arm of the Y tube. While the
free end of this last tube is held to the ear, the base of the vibrat-
ing fork is touched to the wall of the first tube at such a point as
will produce silence. Find the difference in length of the two
parts of this tube and compare this difference with the wave length
of the fork as directed in the first part of this experiment.

138 LABORATORY MANUAL.

LIGHT.

EXERCISE 105. — Shadows. Mount two cardboard screens
about 3 cm. square and 20 cm. square. This may be easily done
by fastening each with sealing-wax on a heavy wire and sticking
this into a square block. Interpose the small screen between a flat
gas jet and the larger screen, and adjust so the entire shadow of
the first falls on the second. The flat flame may be conveniently
obtained by unscrewing the tube from a Bunsen burner and screw-
ing in its place a piece of gas tubing tipped with a regular gas
burner.

Describe or sketch the shadow. Now, make a slight hole in
the lighter part of the shadow called the penumbra. Look through
it at the flame. If you see the flame, state what part of it. Now,
make holes in the darkest part of the shadow, called the umbra ;
next in the line separating the umbra and penumbra ; other places
in the penumbra. State what you see in each case. From your
observations, state the cause of the umbra and the penumbra.

Next turn the edge of the flame toward the small screen.
Sketch the shadow. What sort of shadow would be made if the
light came from a single luminous point ? Test your last conclu-
sion by turning the light very low. What sort of shadow have
you ? What difference have you noticed in the shadows made by
an arc light and by a gas light ? Account for the difference.

EXERCISE 106. — Mount three cardboard screens, 3 cm. (A),
6 cm. (B), and 9 cm. ((7) square, with their centers the same
height. Turn a gas jet very low and set it about 20 cm. from A,
the center of the flame being the same height as that of the screen.
Adjust B until the shadow of A just covers it. If A should now
be removed, it is evident all the light that fell on it would then
fall 011 B ; as this is four times the size of A, the light on B would
be only one-fourth as bright (intense) as on A. Or, representing
the brightness (intensity) of the light on A by 1, the intensity on
B will be .25.

Measure as carefully as possible the distance of the center of
each screen from the center of the flame.

140

LABORATORY MAtfUAL.

Now, take a new distance for A and adjust B as before. Try
A with C ; B with C ; record your results as below, always repre-
senting the intensity of light on the screen nearer the flame by 1 :

SCREENS USED.

INTENSITIES.

DISTANCES.

A and B

m. n.

d. D.

A and S

A and C

B and C

Comparing the results in the last two columns, state a law con-
necting the variation of intensity with variation of distance.

EXERCISE 107. — Make a Bunsen photometer as follows: Cut
out of heavy unsized paper a circle about 10 cm. in diameter ; drop
in the center of it a little hot paraffine. Warm the paper gently
until the paraffine has saturated the paper, making a translucent
spot about 3 cm. in diameter. Mount this as the screens were
mounted in the last Exercise. Do not, however, get .any wax on
the paraffined spot, or allow the wire to cross it. When this paper
is illuminated more brightly on one side than on the other, the
opaque ring appears brighter than the translucent center on the side
of the brighter light, while on the darker side the reverse is true.
When the two sides are equally illuminated, the spot has almost the
same appearance as the rest of the paper. Mount on a block a
candle, on another block four candles in a row close together. Set
•the single candle about 50 cm. from the paper so that the light from
the flame shall fall perpendicularly on the center of the paper.
Similarly on the opposite side set the row of four candles parallel
to the paper, and move them until the paper, as tested by the trans-
lucent spot, appears exactly the same when viewed at the same
angle on each side. Record distance. Make several trials and take
the average. Since the two sides of the paper are now equally
illuminated, how must the light which it receives from each candle
of the four compare with that it receives from the single candle ?
How do their distances compare ? What law does this approxi-
mately verify ?

Compare the intensity of the light of a candle with that of your
gas flame. Adjust them on opposite sides of your photometer until

142 LABORATORY MANUAL.

they illuminate it equally. Measure their respective distances, and
from these calculate the ratio of the intensity of the candle light to
that of the gas light.

EXERCISE 108. — Mount two cardboard screens about 15 cm.
square. Place these about 20 cm. apart and parallel to each other.
Cut in the center of one a hole 2 mm. in diameter. Place 20 cm.
from this a broad gas flame. Describe the image on the second
screen. How does it compare in size with the flame ? Can you
account for its being inverted ? Move either the flame or the
screen. What change in the image ? Why does not the flame
imprint its image on all the surrounding surfaces ? You may
answer this by putting in the place of the screen with one hole
another having many holes.

EXERCISE 109. — Reflection from a Plane Mirror: Through
the middle of a large sheet of paper, say 50 cm. square, draw a
line. On this line and parallel with it stand in a vertical plane a
piece of looking-glass, about 10 cm. by 20 cm. If the glass is
thick, it is well to recollect that the coated surface is the reflector.
Stick a pin upright in the paper in front of the mirror. Sight
along the edge of a ruler laid flat on the paper at the reflection of
the pin. Draw a line AB along this edge ; produce this line to
intersect the line of the reflecting surface. Draw a second line,
BC, from this intersection to the pin, and also from the same
intersection draw a perpendicular to the line of the reflecting
surface. The angle between the line from the pin and perpen-
dicular is called the angle of incidence; the other is the angle
of reflection. How do they compare in size?

Eeplacing the mirror, sight along the ruler from some other
point and draw a line, EF, as before. Produce EF and AB until
they meet. This point is the apparent position of the image of the
pin. How do the distances of the pin and its image from the
reflecting surface compare ?

In front of the mirror draw a diagram, as a triangle, the outline
of a face, etc. Place the pin upright at each of the angles of your
diagram in turn and locate the position of the image of each point.
Connect the points as located. How does the image so formed
compare in size with the diagram ? Since the image in a plane
mirror has no real existence, it is called virtual or imaginary.

144 LABORATORY MANUAL.

EXERCISE 110. — Hold a concave mirror in the sunlight so that
the reflection from it is circular. Move a piece of chalk back and
forth in front of the mirror until the point is found where this
circle is smallest. This point is called the principal focus of the
mirror. Its distance from the mirror is called the focal length of
the mirror ; measure it carefully and record.

Second Method : — Stand alongside of a flat gas jet a cardboard
screen, both being in the same plane. Move the mirror back and
forth in front of these until you obtain a sharp image of the flame
on the screen. The screen, or flame is now very nearly at the
center of the sphere of which the mirror is a part. What is the
radius of this sphere ? Half this is the focal length of the mirror.
Kecord it.

(a) Is the image formed on the screen virtual or real ?

(b) Erect or inverted ?

Place the flame between the center of curvature (center of the
sphere) and principal focus of the mirror, adjust a screen until a
sharp image is formed. Nofe distances of object (flame) and
image from the mirror. Describe the image according to (a), (b)
and (c) above. Without moving the mirror, let flame and screen
change places. Describe image by (a), (b) and (c).

Points near a lens or mirror related to each other, as the
positions of the flame and image in this experiment, are called
conjugate foci. Formulate a definition for them.

Move the flame nearer the mirror than the principal focus.
Can you get any image on a screen? Describe, as before, the
image in the mirror.

Place the flame at any point in front of a convex mirror, and
describe the image obtained.

EXERCISE 111. — Place a bright coin on the bottom of a pan.
Stand in such a position that the coin is just hidden by the side
of the pan. Without moving, watch while another pupil pours
water into the pan. Note the depth of the water when the coin
appears to you, if it does so. Remembering that we see objects
by the rays of light passing from them to our eyes, and that the
rays from the coin could not reach the eye before the water was
poured into the pan, draw a diagram showing what effect the water
must have had on the path of some of the rays from the coin.

146 LABORATORY MANUAL.

EXERCISE 112. — Hold a bi-convex lens in the sunlight so that
a circle of light is cast on a screen behind it. Move the screen
until the circle is the smallest possible ; this is the point to which
the lens by refraction converges the parallel rays of the sun, and is
called the principal focus of the lens, and the distance of this point
from the nearer face of the lens is the focal length. Eecord it.
Obtain on a screen the image of some distant object. How does
the distance of this image from the lens compare with the focal
length previously found ?

Second Method: — Adjust a bright gas flame and a screen on
opposite sides of a lens so that the image of the flame is cast on
the screen, and both are at the same distance from the lens. Both
are now at points called secondary foci of the lens. The principal
focus is midway between the secondary focus and the lens. Record
the focal length of your lens. Compare the image and object in
this Exercise according to (a), (&) and (c) of Exercise 110.

Place the flame between the principal and secondary foci and
move the screen until a sharp image is obtained. Note distance oi
screen and object from the lens, and describe the image as before.

Let screen and flame exchange places. Describe image as
before.

What name may be given to the points where the flame and
image stand ?

Place the flame nearer the lens than the principal focus. Can
you get any image on the screen ? If, by looking through the lens
at the flame, an image of the flame is seen, describe it.

Place the flame anywhere before a concave lens and describe
the image.

EXERCISE 113. — Mount two small bi-convex lenses about 3 cm.
and 5 cm. focus, and 4 cm. diameter, by sticking the edge of each
into a slit in a large cork. Hold some small bright object in front
of and near to the lens of shorter focus. Adjust behind it a screen
so as to obtain a sharp image of the object. Beyond this screen
and nearer to it than the focal distance of the second lens place
the second lens. What sort of an image will a convex lens pro-
duce of anything nearer to it than its principal focus ? Now
remove the screen, and look through the second lens toward the
first. You will now likely see a magnified virtual image of the
true image formed by the first lens ; a little more adjustment of

148

L A B OR A TOR Y MANUA /,.

the lenses may be necessary to make this image distinct. This is
the principle of the compound microscope. The lens nearer the
object is the objective ; the other, the eye-piece.

Adjust as in the previous experiment two lenses, using for the
objective a lens of 40 cm. focus and 10 cm. diameter, and for the
eye piece the lens of 3 cm. focus, and 4 cm. diameter. Obtain on
your screen, however, the image of some distant object ; then place
your eye piece in the proper position and describe the result. This
shows the action of a compound telescope.

AMERICAN WIRE GAUGE. (B. & S.)

No.

DlAM.
IN mm.

RESIST ANC

PER
1000 FT.

E IN OHMS

PER

1000m.

No.

DlAM.

ix nun.

RESISTANC

PER

1000 FT.

E IN OHMS

PER

1000 in.

7.34B

.129

.423

.723

13.323

43.699

6.544

.163

.534

.644

16.799

55.090

5.827

.205

.672

.573

21.185

69.486

5.189

.259

.849

.511

26.713

87.618

4.621

.326

1.059

.455

33.684

110.483

4.115

.411

1.348

.405

42.477

141.324

3.665

.519

1.702

.361

53.563

175.886

3.265

.654

2.145

.321

67.542

221.537

2.907

.824

2.702

.286

85.170

279.357

2.588

1.040

3.411

.255

107.391

352.242

2.305

1.311

4.300

.227

135.402

444.118

2.053

1.653

5.421

.202

170.765

540.109

1.828

2.084

6.835

.180

215.312

706.223

1.628

2.628

8.619

.160

271.583

890.822

1.450

3.314

10.962

.143

342.443

1133.213

1.291

4.179

13.706

.127

431.712

1416.015

1.150

5.269

17.282

.113

544.287

1785.261

1.024

6.645

21.780

.101

686.511

2250.756

.899

8.617

28.265

.090

865.046

2837.350

.812

10.566

34.656

.080

1091.865

3581.317

The resistances given are for pure copper wire at a temperature of 24° C. (75° P.),
Ordinary copper wire lias a resistance 5 or 6 per cent, higher than pure copper.

150

LABORATORY MANUAL.

FORMULAE FOB CALCULATING AREAS AND VOLUMES.

Area of a circle = nil-, it = 3.1416, R = radius.
Volume of a cylinder = area of the base X the altitude.
Volume of a sphere = | ieDa, D = diameter.

TABLE OF SPECIFIC GRAVITIES.

Alcohol, absolute

0.806

Kerosene

0 810

" common .

: 0.833

Lead, sheet

11.400

Alum

1 724

Limestone

3.-180

Ashwood

0.690

Marble

2.720

Beeswax

0.964

Mercury

13.596

Brass, cast

8.400

Milk

1.032

Coal, bituminous...

..1.270 to 1.423

Oak, red

0.850

" anthracite

..1.260 to 1.800

" white

0.779

Cork

0.240

Oil, olive

0.915

Copper

8.850

" turpentine

0 870

Feldspar

2.600

Paraffin

0.820 to 0.940

Galena

7.580

Pine, white

0.554

German Silver

8.432

" pitch

0.660

Glass

2.50 to 3.600

Platinum Wire....

21.530

Gold

19.360

Quartz

2.650

Granite

2.650

Silver, cast

..10.400 to 10.510

Gutta-percha

0.966

Steel

7.816

Ice

0.917

Sulphur, native ..

2.030

Iron, cast

7.230

Sulphuric Acid ..

1.840

" wrought

7.780

Tin, cast

7 290

India-rubber

0.930

Vinegar

1.026

Iron Pyrites

5.000

Zinc, cast

7.000

LABORATORY MANUAL,

151

TABLE OF TRIGONOMETRICAL FUNCTIONS.

BEG.

TANG.

SINE.

DEC.

TANGENT.

SINE.

DEG.

TANGENT.

SINE.

.017

.601

.515

1.80

.875

.035

.625

.530

1.88

.883

.052

.649

.545

1.96

.891

.070

.675

.559

2.05

.899

.087

.700

.574

2.14

.906

.105

.727

.588

2.25

.914

.123

.122

.754

.602

2.36

.921

.141

.139

.781

.616

2.48

.927

.158

.156

.810

.629

2.61

.934

.176

.174

.839

.643

2.75

.940

.194

.191

.869

.656

2.90

.946

.213

.208

.900

.669

3.08

.951

.231

.225

.933

.682

3.27

.956

.249

.242

.966

.695

3.49

.961

.268

.259

1.000

.707

3.73

.966

.287

.276

1.036

.719

4.01

.970

.306

.292

1.070

.731

4.33

.974

.325

.309

1.110

.743

4.70

.978

.344 '

.326

.150

.755

5.14

.982

.364

.342

.190

.766

5.67

.985

.384

.358

.230

.777

6.31

.988

.404

.374

.280

.788

7.12

.990

.424

.390

.330

.799

8.14

.993

.445

.407

.380

.809

9.51

.995

2-5

.466

.423

.430

.819

11.43

.996

.488

.438

.480

.829

14.30

.998

.510

.454

.540

.839

19.08

.999

.532

.469

.600

.848

28.64

.999

.554

.485

.660

.857

57.29

1.000

.577

.500

1.730

.866

Infinite.

1.000

INDEX.

EX MAGNETISM. PAGE

EX.

1. Magnetization

28.

2. Magnetic attraction without

pnntaot

3. Locating the poles of a magnet

29.

4. Naming the poles of a magnet

5. Construction and use of a

30,

magnetoscope

33.

6. Effect of magnetic poles on

34.

each other

35.

7. Effect of breaking a magnet .

36.

8. Arrangement of poles in-mag-

37.

netization

38.

9. Reversal of polarity . . .

10. Induced magnets ....

39.

11. Magnetic fields

40.

MEASURING.

A 1

12. Measuring lengths and plane

41.
42.

surfaces •

13. Measuring volumes ....

14. Using micrometer calipers

43.

15. Weighing

44.

PROPERTIES OP MATTER.

45.

16. Impenetrability

17. Porosity

46.

18. Ductility

19. Inertia

47.

20 Elasticity of air

21. Elasticity of rubber; of

4:0.

stretching wires ....

22. Testing the stiffness of wooden

rods

2:]

49.

23. Elasticity of torsion of wooden

50.

rods

24. Tenacity of wires ....

51.

25, 26» Cohesion and adhesion .

52.

27. Capillary action

53.

PENDULUMS.

28. Pendulums

PAGE
. 34

MECHANICS.

Parallel forces in the same

plane 38

31, 32. Levers .... 40-44

Wheel and axle 46

Pulleys 46

Inclined plane 48

Friction ....... 50

Center of gravity .... 52

Influence of the weight of the

lever 52

Resultant of angular forces . 52

Laws of falling bodies ... 54

HYDROSTATICS .

41. Liquid pressure 58

42. Archimedes' principle ... 68

SPECIFIC GRAVITY.

43. Of a rectangular solid ... 62

44. Of an irregular solid denser

than water 62

45. Of an irregular solid less dense

than water 62

Of a liquid by specific gravity

bottle 62

47. Of aliquid by balanced columns 64

48. Of a liquid by simple hydro-

meter 64

PNEUMATICS.

49. Specific gravity of air . . . 66
Determine the value of air

pressure 66

51. Lifting pump, force pump . 66

52. Siphon 68

53. Mariotte's law 68

164

INDEX.

EX. HEAT. PAGE

54. Heat from mechanical energy 70

55. Expansion of air 70

56. Expansion of water .... 70

57. Coefficient of linear expansion 72

58. Conduction of heat .... 74

59. Conductivity of water ... 74

60. Convection in water ... 76

61. Convection in air .... 76

62. Freezing-point of water . . 76

63. Boiling-point of water ... 78

64. Effect of pressure on boiling-

point 78

65. Boiling-points of ether and

turpentine 78

66. Cooling processes .... 80

67. Dew point 80

68. Law of cooling 82

69. Latent heat of water ... 84

70. Latent heat of steam ... 84

71. Specific heat of shot ... 86

ELECTRICAL ENERGY FROM
FRICTION.

72. Development of two kinds of

electrification ..... 88

73. The electroscope, its construc-

tion and use 88

74. Charging by induction ... 90

75. Conductors and insulators . 90

76. Potential 90

77. Resistance 92

78. Electro-motive force ... 94

79. Condensers, Leyden jar . . 91

CURRENT ELECTRICAL
ENERGY.

80. A galvanic cell 98

-81. Names of plates and electrodes 98

82. A two-fluid cell 100

83. A gravity cell 102

84. Effects of an electrical cur-

rent 102

85. Electro-magnets 104

86. Ampere's law 106

87. The essentials of a galvano-

meter . 106

EX. PAGE

88. A tangent galvanometer . . 108

89. Tests for conductivity of elec-

trical currents . . . .110

90. Effects of a neighboring mag-

net on galvanometer de-
flection 112

91. Measuring resistances by sub-

stitution 112

92. Measuring resistance of a

battery cell 114

93. Resistance by iVheatstone's

bridge 116

94. Induced currents ; idea of the

dynamo 118

95. Development of the idea of

the electro-motor . . . 120

SOUND.

96. Vibrations in a rubber cord . 124

97. Vibrations of a sounding

body 126

98. Reinforcement, interference

and velocity of sound . . 126

99. Velocity of sound . . . .128

100. Determining pitch . . . .128

101. Velocity of sound in a brass

rod 130

102. Laws of vibrating strings . 130

103. Harmonics and beats . . .132

104. Interference of sound . . .134

LIGHT.

105. Shadows 138

106. Law of intensity . . . .138

107. Photometry 140

108. Images through apertures . 142

109. Reflection from a plane mir-

ror 142

1 10. Reflection from spherical mir-

rors 144

111. Refraction by water . . . 144

112. Refraction by spherical lenses 146

113. Principle of the compound

microscope ; principle of
the compound telescope . 146

A 000 938 029 6

5TA

JTENORMALSCHOOU

Internet Archive Audio

Featured

Top

Images

Featured

Top

Software

Featured

Top

Books

Featured

Top

Video

Featured

Top

Mobile Apps

Browser Extensions

Archive-It Subscription

Save Page Now

Full text of "High school laboratory manual of physics"

See other formats