,,general ,,science                     
,,by                          ,,bertha  
,m4 ,,clark1 ,,ph4,d4                   
,,head ,,of ,,the ,,science ,,department
             ,,william ,,penn ,,high    
,,school ,,for ,,girls1 ,,philadelphia  
,,new ,,york - ,,cincinnati - ,,chicago 
,,american ,,book ,,company             
#aiab      ,,preface   ,this book is not
 intended to prepare for college        
entrance examinations2 it will not1 in  
fact1 prepare for any of the present-day
 stock examinations in physics1         
chemistry1 or hygiene1 but it should    
prepare the thoughtful reader to meet   
wisely and actively some of life's      
important problems1 and should enable   
him to pass muster on the principles and
 theories underlying scientific1 and    
therefore economic1 management1 whether 
in the shop or in the home4  ,we hear a 
great deal about the conservation of our
 natural resources1 such as forests and 
waterways2 it is hoped that this book   
will show the vital importance of the   

conservation of human strength and      
health1 and the irreparable loss to     
society of energy uselessly dissipated1 
either in idle worry or in aimless      
activity4 ,most of us would reproach    
ourselves for lack of shrewdness if we  
spent for any article more than it was  
worth1 yet few of us consider that we   
daily expend on domestic and business   
tasks an amount of energy far in excess 
of that actually required4 ,the farmer  
who flails his grain instead of         
threshing it wastes time and energy2 the
 housewife who washes with her hands    
alone and does not aid herself by the   
use of washing machine and proper       
bleaching agents dissipates energy sadly
 needed for other duties4  ,the ,chapter
 on machines is intended not only as a  
stimulus to the invention of further    
labor-saving devices1 but also as an eye
 opener to those who1 in the future     
struggle for existence1 must perforce go
 to the wall unless they understand how 
to make use of contrivances whereby     

man's limited physical strength is made 
effective for larger tasks4  ,the       
,chapter on musical instruments is more 
detailed than seems warranted at first  
sight2 but interest in orchestral       
instruments is real and general1 and    
there is a persistent desire for        
intelligent information relative to     
musical instruments4 ,the child of the  
laborer as well as the child of the     
merchant finds it possible to attend    
some of the weekly orchestral concerts1 
with their tiers of cheap seats1 and    
nothing adds more to the enjoyment and  
instruction of such hours than an       
intimate acquaintance with the leading  
instruments4 ,unless this is given in   
the public schools1 a large percentage  
of mankind is deprived of it1 and it is 
for this reason that so large a share of
 the treatment of sound has been devoted
 to musical instruments4  ,the treatment
 of electricity is more theoretical than
 that used in preceding ,chapters1 but  
the subject does not lend itself readily

 to popular presentation2 and1 moreover1
 it is assumed that the information and 
training acquired in the previous work  
will give the pupil power to understand 
the more advanced thought and method4   
,the real value of a book depends not so
 much upon the information given as upon
 the permanent interest stimulated and  
the initiative aroused4 ,the youthful   
mind1 and indeed the average adult mind 
as well1 is singularly non-logical and  
incapable of continued concentration1   
and loses interest under too consecutive
 thought and sustained style4 ,for this 
reason the author has sacrificed at     
times detail to general effect1 logical 
development to present-day interest and 
facts1 and has made use of a popular1   
light style of writing as well as of the
 more formal and logical style common to
 books of science4  ,no claim is made to
 originality in subject matter4 ,the    
actual facts1 theories1 and principles  
used are such as have been presented in 
previous textbooks of science1 but the  

manner and sequence of presentation are 
new and1 so far as ,i know1 untried     
elsewhere4 ,these are such as in my     
experience have aroused the greatest    
interest and initiative1 and such as    
have at the same time given the maximum 
benefit from the informational          
standpoint4 ,in no case1 however1 is    
mental training sacrificed to           
information2 but mental development is  
sought through the student's willing and
 interested participation in the actual 
daily happenings of the home and the    
shop and the field1 rather than through 
formal recitations and laboratory       
experiments4  ,practical laboratory work
 in connection with the study of this   
book is provided for in my ,laboratory  
,manual in ,general ,science1 which     
contains directions for a series of     
experiments designed to make the pupil  
familiar with the facts and theories    
discussed in the textbook4  ,i have     
sought and have gained help from many of
 the standard textbooks1 new and old4   

,the following firms have kindly placed 
cuts at my disposal1 and have thus      
materially aided in the preparation of  
the illustrations3 ,american ,radiator  
,company2 ,commercial ,museum1          
,philadelphia2 ,general ,electric       
,company2 ,hershey ,chocolate ,company2 
,scientific ,american2 ,the ,goulds     
,manufacturing ,company2 ,victor        
,talking ,machine ,company4             
,acknowledgment is also due to          
,professor ,alvin ,davison for figures  
#ai1 #bc1 #bi1 #adb1 and #afa4  ,mr4    
,w4,d4 ,lewis1 ,principal of the        
,william ,penn ,high ,school1 has read  
the manuscript and has given me the     
benefit of his experience and interest4 
,miss4 ,helen ,hill1 librarian of the   
same school1 has been of invaluable     
service as regards suggestions and proof
 reading4 ,miss4 ,droege1 of the        
,baldwin ,school1 ,bryn ,mawr1 has also 
been of very great service4 ,practically
 all of my assistants have given of     
their time and skill to the preparation 

of the work1 but the list is too long   
for individual mention4  ,,bertha ,m4   
,,clark4  ,,william ,,penn ,,high       
,,school4     ,,contents       ,,chapter
        ,i4 ,,heat        ,,ii4         
,,temperature ,,and ,,heat        ,,iii4
 ,,other ,,facts ,,about ,,heat         
,,iv4 ,,burning ,,or ,,oxidation        
,v4 ,,food        ,,vi4 ,,water         
,,vii4 ,,air        ,,viii4 ,,general   
,,properties ,,of ,,gases        ,,ix4  
,,invisible ,,objects        ,x4 ,,light
        ,,xi4 ,,refraction        ,,xii4
 ,,photography        ,,xiii4 ,,color   
,,xiv4 ,,heat ,,and ,,light ,,as        
,,companions        ,,xv4 ,,artificial  
,,lighting        ,,xvi4 ,,man',s ,,way 
,,of ,,helping ,,himself        ,,xvii4 
,,the ,,power ,,behind ,,the ,,engine   
,,xviii4 ,,pumps ,,and ,,their ,,value  
,,to ,,man        ,,xix4 ,,the ,,water  
,,problem ,,of ,a ,,large ,,city        
,,xx4 ,,man',s ,,conquest ,,of          
,,substances        ,,xxi4              
,,fermentation        ,,xxii4           

,,bleaching        ,,xxiii4 ,,dyeing    
,,xxiv4 ,,chemicals ,,as ,,disinfectants
 ,,and ,,preservatives        ,,xxv4    
,,drugs ,,and ,,patent ,,medicines      
,,xxvi4 ,,nitrogen ,,and ,,its          
,,relation ,,to ,,plants        ,,xxvii4
 ,,sound        ,,xxviii4 ,,musical     
,,instruments        ,,xxix4 ,,speaking 
,,and ,,hearing        ,,xxx4           
,,electricity        ,,xxxi4 ,,some     
,,uses ,,of ,,electricity               
,,xxxii4 ,,modern ,,electrical          
,,inventions        ,,xxxiii4 ,,magnets 
,,and ,,currents        ,,xxxiv4 ,,how  
,,electricity ,,may ,,be ,,measured     
,,xxxv4 ,,how ,,electricity ,,is        
,,obtained ,,on ,a ,,large ,,scale      
,,index   ,,general ,,science           
,,chapter ,i  ,,heat   ,i4 ,value of    
,fire4 ,every day1 uncontrolled fire    
wipes out human lives and destroys vast 
amounts of property2 every day1 fire1   
controlled and regulated in stove and   
furnace1 cooks our food and warms our   
houses4 ,fire melts ore and allows of   

the forging of iron1 as in the          
blacksmith's shop1 and of the fashioning
 of innumerable objects serviceable to  
man4 ,heated boilers change water into  
the steam which drives our engines on   
land and sea4 ,heat causes rain and     
wind1 fog and cloud2 heat enables       
vegetation to grow and thus indirectly  
provides our food4 ,whether heat comes  
directly from the sun or from artificial
 sources such as coal1 wood1 oil1 or    
electricity1 it is vitally connected    
with our daily life1 and for this reason
 the facts and theories relative to it  
are among the most important that can be
 studied4 ,heat1 if properly regulated  
and controlled1 would never be injurious
 to man2 hence in the following         
paragraphs heat will be considered      
merely in its helpful capacity4  #b4    
,general ,effect of ,heat4 ,expansion   
and ,contraction4 ,one of the best-known
 effects of heat is the change which it 
causes in the size of a substance4      
,every housewife knows that if a kettle 

is filled with cold water to begin with1
 there will be an overflow as soon as   
the water becomes heated4 ,heat causes  
not only water1 but all other liquids1  
to occupy more space1 or to expand1 and 
in some cases the expansion1 or increase
 in size1 is surprisingly large4 ,for   
example1 if #ajj pints of ice water is  
heated in a kettle1 the #ajj pints will 
steadily expand until1 at the boiling   
point1 it will occupy as much space as  
#ajd pints of ice water4  ,the expansion
 of water can be easily shown by heating
 a flask 7,fig4 ,i7 filled with water   
and closed by a cork through which a    
narrow tube passes4 ,as the water is    
heated1 it expands and forces its way up
 the narrow tube4 ,if the heat is       
removed1 the liquid cools1 contracts1   
and slowly falls in the tube1 resuming  
in time its original size or volume4 ,a 
similar observation can be made with    
alcohol1 mercury1 or any other          
convenient liquid4  ,illustration3      
,,fig4 #a4--;,as the water becomes      

warmer it expands and rise in the narrow
 tube4  ,not only liquids are affected  
by heat and cold1 but solids also are   
subject to similar changes4 ,a metal    
ball which when cool will just slip     
through a ring 7,fig4 #b7 will1 when    
heated1 be too large to slip through the
 ring4 ,telegraph and telephone wires   
which in winter are stretched taut from 
pole to pole1 sag in hot weather and are
 much too long4 ,in summer they are     
exposed to the fierce rays of the sun1  
become strongly heated1 and expand      
sufficiently to sag4 ,if the wires were 
stretched taut in the summer1 there     
would not be sufficient leeway for the  
contraction which accompanies cold      
weather1 and in winter they would snap4 
,illustration3 ,,fig4 #b--,when the ball
 is heated1 it become too large to slip 
through the ring4  ,air expands greatly 
when heated 7,fig4 #c71 but since air is
 practically invisible1 we are not      
ordinarily conscious of any change in   
it4 ,the expansion of air can be readily

 shown by putting a drop of ink in a    
thin glass tube1 inserting the tube in  
the cork of a flask1 and applying heat  
to the flask 7,fig4 #d74 ,the ink is    
forced up the tube by the expanding air4
 ,even the warmth of the hand is        
generally sufficient to cause the drop  
to rise steadily in the tube4 ,the rise 
of the drop of ink shows that the air in
 the flask occupies more space than     
formerly1 and since the quantity of air 
has not changed1 each cubic inch of     
space must hold less warm air than it   
held of cold air2 that is1 one cubic    
inch of warm air weighs less than one   
cubic inch of cold air1 or warm air is  
less dense than cold air4 ,all gases1 if
 not confined1 expand when heated and   
contract as they cool4 ,heat1 in        
general1 causes substances to expand or 
become less dense4  ,illustration3      
,,fig4 #c--;,as the air in ,a is heated1
 it expands and escapes in the form of  
bubbles4  #c4 ,amount of ,expansion and 
,contraction4 ,while most substances    

expand when heated and contract when    
cooled1 they are not all affected       
equally by the same changes in          
temperature4 ,alcohol expands more than 
water1 and water more than mercury4     
,steel wire which measures #a_/d mile on
 a snowy day will gain #be inches in    
length on a warm summer day1 and an     
aluminum wire under the same conditions 
would gain #ej inches in length4        
,illustration3 ,,fig4 #d4--;,as the air 
in ,a is heated1 it expands and forces  
the drop of ink up the tube4  #d4       
,advantages and ,disadvantages of       
,expansion and ,contraction4 ,we owe the
 snug fit of metal tires and bands to   
the expansion and contraction resulting 
from heating and cooling4 ,the tire of a
 wagon wheel is made slightly smaller   
than the wheel which it is to protect2  
it is then put into a very hot fire and 
heated until it has expanded            
sufficiently to slip on the wheel4 ,as  
the tire cools it contracts and fits the
 wheel closely4  ,in a railroad1 spaces 

are usually left between consecutive    
rails in order to allow for expansion   
during the summer4  ,the unsightly      
cracks and humps in cement floors are   
sometimes due to the expansion resulting
 from heat 7,fig4 #e74 ,cracking from   
this cause can frequently be avoided by 
cutting the soft cement into squares1   
the spaces between them giving          
opportunity for expansion just as do the
 spaces between the rails of railroads4 
,illustration3 ,,fig4 #e3 ,a cement walk
 broken by expansion due to sun heat4   
,in the construction of long wire fences
 provision must be made for tightening  
the wire in summer1 otherwise great     
sagging would occur4  ,heat plays an    
important part in the splitting of rocks
 and in the formation of dbris4 ,rocks  
in exposed places are greatly affected  
by changes in temperature1 and in       
regions where the changes in temperature
 are sudden1 severe1 and frequent1 the  
rocks are not able to withstand the     
strain of expansion and contraction1 and

 as a result crack and split4 ,in the   
,sahara ,desert much crumbling of the   
rock into sand has been caused by the   
intense heat of the day followed by the 
sharp frost of night4 ,the heat of the  
day causes the rocks to expand1 and the 
cold of night causes them to contract1  
and these two forces constantly at work 
loosen the grains of the rock and force 
them out of place1 thus producing       
crumbling4  ,illustration3 ,,fig4       
#f4--,splitting and crumbling of rock   
caused by alternating heat and cold4    
,the surface of the rock is the most    
exposed part1 and during the day the    
surface1 heated by the sun's rays1      
expands and becomes too large for the   
interior1 and crumbling and splitting   
result from the strain4 ,with the sudden
 fall of temperature in the late        
afternoon and night1 the surface of the 
rock becomes greatly chilled and colder 
than the rock beneath2 the surface rock 
therefore contracts and shrinks more    
than the underlying rock1 and again     

crumbling results 7,fig4 #f74           
,illustration3 ,,fig4 #g4--;,debris     
formed from crumbled rock4  ,on bare    
mountains1 the heating and cooling      
effects of the sun are very             
striking7,fig4 #g72 the surface of many 
a mountain peak is covered with cracked 
rock so insecure that a touch or step   
will dislodge the fragments and start   
them down the mountain slope4 ,the lower
 levels of mountains are frequently     
buried several feet under dbris which   
has been formed in this way from higher 
peaks1 and which has slowly accumulated 
at the lower levels4  #e4 ,temperature4 
,when an object feels hot to the touch1 
we say that it has a high temperature2  
when it feels cold to the touch1 that it
 has a low temperature2 but we are not  
accurate judges of heat4 ,ice water     
seems comparatively warm after eating   
ice cream1 and yet we know that ice     
water is by no means warm4 ,a room may  
seem warm to a person who has been      
walking in the cold air1 while it may   

feel decidedly cold to some one who has 
come from a warmer room4 ,if the hand is
 cold1 lukewarm water feels hot1 but if 
the hand has been in very hot water and 
is then transferred to lukewarm water1  
the latter will seem cold4 ,we see that 
the sensation or feeling of warmth is   
not an accurate guide to the temperature
 of a substance2 and yet until #aeib1   
one hundred years after the discovery of
 ,america1 people relied solely upon    
their sensations for the measurement of 
temperature4 ,very hot substances cannot
 be touched without injury1 and hence   
inconvenience as well as the necessity  
for accuracy led to the invention of the
 thermometer1 an instrument whose       
operation depends upon the fact that    
most substances expand when heated and  
contract when cooled4  ,illustration3   
,,fig4 #h4--,making a thermometer4  #f4 
,the ,thermometer4 ,the modern          
thermometer consists of a glass tube at 
the lower end of which is a bulb filled 
with mercury or colored alcohol 7,fig4  

#h74 ,after the bulb has been filled    
with the mercury1 it is placed in a     
beaker of water and the water is heated 
by a ,bunsen burner4 ,as the water      
becomes warmer and warmer the level of  
the mercury in the tube steadily rises  
until the water boils1 when the level   
remains stationary 7,fig4 #i74 ,a       
scratch is made on the tube to indicate 
the point to which the mercury rises    
when the bulb is placed in boiling      
water1 and this point is marked #bab4   
,the tube is then removed from the      
boiling water1 and after cooling for a  
few minutes1 it is placed in a vessel   
containing finely chopped ice 7,fig4    
#aj74 ,the mercury column falls rapidly1
 but finally remains stationary1 and at 
this level another scratch is made on   
the tube and the point is marked #cb4   
,the space between these two points1    
which represent the temperatures of     
boiling water and of melting ice1 is    
divided into #ahj equal parts called    
degrees4 ,the thermometer in use in the 

,united ,states is marked in this way   
and is called the ,fahrenheit           
thermometer after its designer4 ,before 
the degrees are etched on the           
thermometer the open end of the tube is 
sealed4  ,illustration3 ,,fig4          
#i4--;,determining one of the fixed     
points of a thermometer4  ,the          
,centigrade thermometer1 in use in      
foreign countries and in all scientific 
work1 is similar to the ,fahrenheit     
except that the fixed points are marked 
#ajj and #j1 and the interval between   
the points is divided into #ajj equal   
parts instead of into #ahj4  ,the       
boiling point of water is #bab ,f4 or   
#ajj ,c4  ,the melting point of ice is  
#cb ,f4 or #j ,c4  ,glass thermometers  
of the above type are the ones most     
generally used1 but there are many      
different types for special purposes4   
,illustration3 ,,fig4                   
#aj4--;,determining the lower fixed     
point of a thermometer4  #g4 ,some ,uses
 of a ,thermometer4 ,one of the chief   

values of a thermometer is the service  
it has rendered to medicine4 ,if a      
thermometer is held for a few minutes   
under the tongue of a normal1 healthy   
person1 the mercury will rise to about  
#ih4d ,f4 ,if the temperature of the    
body registers several degrees above or 
below this point1 a physician should be 
consulted immediately4 ,the temperature 
of the body is a trustworthy indicator  
of general physical condition2 hence in 
all hospitals the temperature of        
patients is carefully taken at stated   
intervals4  ,commercially1 temperature  
readings are extremely important4 ,in   
sugar refineries the temperature of the 
heated liquids is observed most         
carefully1 since a difference in        
temperature1 however slight1 affects not
 only the general appearance of sugars  
and sirups1 but the quality as well4    
,the many varieties of steel likewise   
show the influence which heat may have  
on the nature of a substance4 ,by       
observation and tedious experimentation 

it has been found that if hardened steel
 is heated to about #dej ,f4 and quickly
 cooled1 it gives the fine cutting edge 
of razors2 if it is heated to about #ejj
 ,f4 and then cooled1 the metal is much 
coarser and is suitable for shears and  
farm implements2 while if it is heated  
but #ej ,f4 higher1 that is1 to #eej    
,f41 it gives the fine elastic steel of 
watch springs4  ,illustration3 ,,fig4   
#aa4--;,a well-made commercial          
thermometer4  ,a thermometer could be   
put to good use in every kitchen2 the   
inexperienced housekeeper who cannot    
judge of the heat of the oven would be  
saved bad bread1 etc41 if the           
thermometer were a part of her          
equipment4 ,the thermometer can also be 
used in detecting adulterants4 ,butter  
should melt at #id ,f42 if it does not1 
you may be sure that it is adulterated  
with suet or other cheap fat4 ,olive oil
 should be a clear liquid above #ge ,f42
 if1 above this temperature1 it looks   
cloudy1 you may be sure that it too is  

adulterated with fat4  #h4 ,methods of  
,heating ,buildings4 ,open ,fireplaces  
and ,stoves4 ,before the time of stoves 
and furnaces1 man heated his modest     
dwelling by open fires alone4 ,the      
burning logs gave warmth to the cabin   
and served as a primitive cooking agent2
 and the smoke which usually accompanies
 burning bodies was carried away by     
means of the chimney4 ,but in an open   
fireplace much heat escapes with the    
smoke and is lost1 and only a small     
portion streams into the room and gives 
warmth4  ,when fuel is placed in an open
 fireplace 7,fig4 #ab7 and lighted1 the 
air immediately surrounding the fire    
becomes warmer and1 because of          
expansion1 becomes lighter than the cold
 air above4 ,the cold air1 being        
heavier1 falls and forces the warmer air
 upward1 and along with the warm air    
goes the disagreeable smoke4 ,the fall  
of the colder and heavier air1 and the  
rise of the warmer and hence lighter    
air1 is similar to the exchange which   

takes place when water is poured on oil2
 the water1 being heavier than oil1     
sinks to the bottom and forces the oil  
to the surface4 ,the warmer air which   
escapes up the chimney carries with it  
the disagreeable smoke1 and when all the
 smoke is got rid of in this way1 the   
chimney is said to draw well4           
,illustration3 ,,fig4 #ab4--,the open   
fireplace as an early method of heating4
  ,as the air is heated by the fire it  
expands1 and is pushed up the chimney by
 the cold air which is constantly       
entering through loose windows and      
doors4 ,open fireplaces are very        
healthful because the air which is      
driven out is impure1 while the air     
which rushes in is fresh and brings     
oxygen to the human being4  ,but open   
fireplaces1 while pleasant to look at1  
are not efficient for either heating or 
cooking4 ,the possibilities for the     
latter are especially limited1 and the  
invention of stoves was a great advance 
in efficiency1 economy1 and comfort4 ,a 

stove is a receptacle for fire1 provided
 with a definite inlet for air and a    
definite outlet for smoke1 and able to  
radiate into the room most of the heat  
produced from the fire which burns      
within4 ,the inlet1 or draft1 admits    
enough air to cause the fire to burn    
brightly or slowly as the case may be4  
,if we wish a hot fire1 the draft is    
opened wide and enough air enters to    
produce a strong glow4 ,if we wish a low
 fire1 the inlet is only partially      
opened1 and just enough air enters to   
keep the fuel smoldering4  ,when the    
fire is started1 the damper should be   
opened wide in order to allow the escape
 of smoke2 but after the fire is well   
started there is less smoke1 and the    
damper may be partly closed4 ,if the    
damper is kept open1 coal is rapidly    
consumed1 and the additional heat passes
 out through the chimney1 and is lost to
 use4  #i4 ,furnaces4 ,hot ,air4 ,the   
labor involved in the care of numerous  
stoves is considerable1 and hence the   

advent of a central heating stove1 or   
furnace1 was a great saving in strength 
and fuel4 ,a furnace is a stove arranged
 as in ,figure #ac4 ,the stove ,s1 like 
all other stoves1 has an inlet for air  
and an outlet ,c for smoke2 but in      
addition1 it has built around it a      
chamber in which air circulates and is  
warmed4 ,the air warmed by the stove is 
forced upward by cold air which enters  
from outside4 ,for example1 cold air    
constantly entering at ,e drives the air
 heated by ,s through pipes and ducts to
 the rooms to be heated4  ,the metal    
pipes which convey the heated air from  
the furnace to the ducts are sometimes  
covered with felt1 asbestos1 or other   
non-conducting material in order that   
heat may not be lost during             
transmission4 ,the ducts which receive  
the heated air from the pipes are built 
in the non-conducting walls of the      
house1 and hence lose practically no    
heat4 ,the air which reaches halls and  
rooms is therefore warm1 in spite of its

 long journey from the cellar4          
,illustration3 ,,fig4 #ac4--;,a furnace4
 ,pipes conduct hot air to the rooms4   
,not only houses are warmed by a central
 heating stove1 but whole communities   
sometimes depend upon a central heating 
plant4 ,in the latter case1 pipes       
closely wrapped with a non-conducting   
material carry steam long distances     
underground to heat remote buildings4   
,overbrook and ,radnor1 ,pa41 are towns 
in which such a system is used4  #aj4   
,hot-water ,heating4 ,the heated air    
which rises from furnaces is seldom hot 
enough to warm large buildings well2    
hence furnace heating is being largely  
supplanted by hot-water heating4  ,the  
principle of hot-water heating is shown 
by the following simple experiment4 ,two
 flasks and two tubes are arranged as in
 ,figure #ae1 the upper flask containing
 a colored liquid and the lower flask   
clear water4 ,if heat is applied to ,b1 
one can see at the end of a few seconds 
the downward circulation of the colored 

liquid and the upward circulation of the
 clear water4 ,if we represent a boiler 
by ,b1 a radiator by the coiled tube1   
and a safety tank by ,c1 we shall have a
 very fair illustration of the principle
 of a hot-water heating system4 ,the hot
 water in the radiators cools and1 in   
cooling1 gives up its heat to the rooms 
and thus warms them4  ,illustration3    
,,fig4 #ad4--;,hot-water heating4  ,in  
hot-water heating systems1 fresh air is 
not brought to the rooms1 for the       
radiators are closed pipes containing   
hot water4 ,it is largely for this      
reason that thoughtful people are       
careful to raise windows at intervals4  
,some systems of hot-water heating      
secure ventilation by confining the     
radiators to the basement1 to which cold
 air from outside is constantly admitted
 in such a way that it circulates over  
the radiators and becomes strongly      
heated4 ,this warm fresh air then passes
 through ordinary flues to the rooms    
above4  ,illustration3 ,,fig4 #ae4--,the

 principle of hot-water heating4  ,in   
,figure #af1 a radiator is shown in a   
boxlike structure in the cellar4 ,fresh 
air from outside enters a flue at the   
right1 passes the radiator1 where it is 
warmed1 and then makes its way to the   
room through a flue at the left4 ,the   
warm air which thus enters the room is  
thoroughly fresh4 ,the actual labor     
involved in furnace heating and in      
hot-water heating is practically the    
same1 since coal must be fed to the     
fire1 and ashes must be removed2 but the
 hot-water system has the advantage of  
economy and cleanliness4  ,illustration3
 ,,fig4 #af4--;,fresh air from outside  
circulates over the radiators and then  
rises into the rooms to be heated4  #aa4
 ,fresh ,air4 ,fresh air is essential to
 normal healthy living1 and #bjjj cubic 
feet of air per hour is desirable for   
each individual4 ,if a gentle breeze is 
blowing1 a barely perceptible opening of
 a window will give the needed amount1  
even if there are no additional drafts  

of fresh air into the room through      
cracks4 ,most houses are so loosely     
constructed that fresh air enters       
imperceptibly in many ways1 and whether 
we will or no1 we receive some fresh    
air4 ,the supply is1 however1 never     
sufficient in itself and should not be  
depended upon alone4 ,at night1 or at   
any other time when gas lights are      
required1 the need for ventilation      
increases1 because every gas light in a 
room uses up the same amount of air as  
four people4  ,illustration3 ,,fig4     
#ag4--,the air which goes to the        
schoolrooms is warmed by passage over   
the radiators4  ,in the preceding       
,section1 we learned that many houses   
heated by hot water are supplied with   
fresh-air pipes which admit fresh air   
into separate rooms or into suites of   
rooms4 ,in some cases the amount which  
enters is so great that the air in a    
room is changed three or four times an  
hour4 ,the constant inflow of cold air  
and exit of warm air necessitates larger

 radiators and more hot water and hence 
more coal to heat the larger quantity of
 water1 but the additional expense is   
more than compensated by the gain in    
health4  #ab4 ,winds and ,currents4 ,the
 gentlest summer breezes and the        
fiercest blasts of winter are produced  
by the unequal heating of air4 ,we have 
seen that the air nearest to a stove or 
hot object becomes hotter than the      
adjacent air1 that it tends to expand   
and is replaced and pushed upward and   
outward by colder1 heavier air falling  
downward4 ,we have learned also that the
 moving liquid or gas carries with it   
heat which it gradually gives out to    
surrounding bodies4  ,when a liquid or a
 gas moves away from a hot object1      
carrying heat with it1 the process is   
called convection4  ,convection is      
responsible for winds and ocean         
currents1 for land and sea breezes1 and 
other daily phenomena4  ,the ,gulf      
,stream illustrates the transference of 
heat by convection4 ,a large body of    

water is strongly heated at the equator1
 and then moves away1 carrying heat with
 it to distant regions1 such as ,england
 and ,norway4  ,owing to the shape of   
the earth and its position with respect 
to the sun1 different portions of the   
earth are unequally heated4 ,in those   
portions where the earth is greatly     
heated1 the air likewise will be heated2
 there will be a tendency for the air to
 rise1 and for the cold air from        
surrounding regions to rush in to fill  
its place4 ,in this way winds are       
produced4 ,there are many circumstances 
which modify winds and currents1 and it 
is not always easy to explain their     
direction and velocity1 but one very    
definite cause is the unequal heating of
 the surface of the earth4  #ac4        
,conduction4 ,a poker used in stirring a
 fire becomes hot and heats the hand    
grasping the poker1 although only the   
opposite end of the poker has actually  
been in the fire4 ,heat from the fire   
passed into the poker1 traveled along   

it1 and warmed it4 ,when heat flows in  
this way from a warm part of a body to a
 colder part1 the process is called     
conduction4 ,a flatiron is heated by    
conduction1 the heat from the warm stove
 passing into the cold flatiron and     
gradually heating it4  ,in convection1  
air and water circulate freely1 carrying
 heat with them2 in conduction1 heat    
flows from a warm region toward a cold  
region1 but there is no apparent motion 
of any kind4  ,heat travels more readily
 through some substances than through   
others4 ,all metals conduct heat well2  
irons placed on the fire become heated  
throughout and cannot be grasped with   
the bare hand2 iron utensils are        
frequently made with wooden handles1    
because wood is a poor conductor and    
does not allow heat from the iron to    
pass through it to the hand4 ,for the   
same reason a burning match may be held 
without discomfort until the flame      
almost reaches the hand4  ,stoves and   
radiators are made of metal1 because    

metals conduct heat readily1 and as fast
 as heat is generated within the stove  
by the burning of fuel1 or introduced   
into the radiator by the hot water1 the 
heat is conducted through the metal and 
escapes into the room4  ,hot-water pipes
 and steam pipes are usually wrapped    
with a non-conducting substance1 or     
insulator1 such as asbestos1 in order   
that the heat may not escape1 but shall 
be retained within the pipes until it   
reaches the radiators within the rooms4 
,the invention of the ,fireless ,cooker 
depended in part upon the principle of  
non-conduction4 ,two vessels1 one inside
 the other1 are separated by sawdust1   
asbestos1 or other poor conducting      
material 7,fig4 #ah74 ,foods are heated 
in the usual way to the boiling point or
 to a high temperature1 and are then    
placed in the inner vessel4 ,the heat of
 the food cannot escape through the     
non-conducting material which surrounds 
it1 and hence remains in the food and   
slowly cooks it4  ,illustration3 ,,fig4 

#ah4--;,a fireless cooker4  ,a very     
interesting experiment for the testing  
of the efficacy of non-conductors may be
 easily performed4 ,place hot water in a
 metal vessel1 and note by means of a   
thermometer the rapidity with which the 
water cools2 then place water of the    
same temperature in a second metal      
vessel similar to the first1 but        
surrounded by asbestos or other         
non-conducting material1 and note the   
slowness with which the temperature     
falls4  ,chemical ,change1 an ,effect of
 ,heat4 ,this effect of heat has a vital
 influence on our lives1 because the    
changes which take place when food is   
cooked are due to it4 ,the doughy mass  
which goes into the oven1 comes out a   
light spongy loaf2 the small            
indigestible rice grain comes out the   
swollen1 fluffy1 digestible grain4 ,were
 it not for the chemical changes brought
 about by heat1 many of our present     
foods would be useless to man4 ,hundreds
 of common materials like glass1 rubber1

 iron1 aluminum1 etc41 are manufactured 
by processes which involve chemical     
action caused by heat4     ,,chapter    
,,ii  ,,temperature ,,and ,,heat   #ad4 
,temperature not a ,measure of the      
,amount of ,heat ,present4 ,if two      
similar basins containing unequal       
quantities of water are placed in the   
sunshine on a summer day1 the smaller   
quantity of water will become quite warm
 in a short period of time1 while the   
larger quantity will become only        
lukewarm4 ,both vessels receive the same
 amount of heat from the sun1 but in one
 case the heat is utilized in heating to
 a high temperature a small quantity of 
water1 while in the second case the heat
 is utilized in warming to a lower      
degree a larger quantity of water4      
,equal amounts of heat do not           
necessarily produce equivalent          
temperatures1 and equal temperatures do 
not necessarily indicate equal amounts  
of heat4 ,it takes more heat to raise a 
gallon of water to the boiling point    

than it does to raise a pint of water to
 the boiling point1 but a thermometer   
would register the same temperature in  
the two cases4 ,the temperature of      
boiling water is #ajj ,c4 whether there 
is a pint of it or a gallon4            
,temperature is independent of the      
quantity of matter present2 but the     
amount of heat contained in a substance 
at any temperature is not independent of
 quantity1 being greater in the larger  
quantity4  #ae4 ,the ,unit of ,heat4 ,it
 is necessary to have a unit of heat    
just as we have a unit of length1 or a  
unit of mass1 or a unit of time4 ,one   
unit of heat is called a calorie1 and is
 the amount of heat which will change   
the temperature of #a gram of water #a  
,c4 ,it is the amount of heat given out 
by #a gram of water when its temperature
 falls #a ,c41 or the amount of heat    
absorbed by #a gram of water when its   
temperature rises #a ,c4 ,if #djj grams 
of water are heated from #j to #e ,c41  
the amount of heat which has entered the

 water is equivalent to #e  #djj or     
#bjjj calories2 if #bjj grams of water  
cool from #be to #bj ,c41 the heat given
 out by the water is equivalent to #e   
#bjj or #ajjj calories4  #af4 ,some     
,substances ,heat more readily than     
,others4 ,if two equal quantities of    
water at the same temperature are       
exposed to the sun for the same length  
of time1 their final temperatures will  
be the same4 ,if1 however1 equal        
quantities of different substances are  
exposed1 the temperatures resulting from
 the heating will not necessarily be the
 same4 ,if a basin containing #a lb4 of 
mercury is put on the fire1 side by side
 with a basin containing an equal       
quantity of water1 the temperatures of  
the two substances will vary greatly at 
the end of a short time4 ,the mercury   
will have a far higher temperature than 
the water1 in spite of the fact that the
 amount of mercury is as great as the   
amount of water and that the heat       
received from the fire has been the same

 in each case4 ,mercury is not so       
difficult to heat as water2 less heat   
being required to raise its temperature 
#a than is required to raise the        
temperature of an equal quantity of     
water #a4 ,in fact1 mercury is #cj times
 as easy to heat as water1 and it       
requires only one thirtieth as much fire
 to heat a given quantity of mercury #a 
as to heat the same quantity of water   
#a4  #ag4 ,specific ,heat4 ,we know that
 different substances are differently   
affected by heat4 ,some substances1 like
 water1 change their temperature slowly 
when heated2 others1 like mercury1      
change their temperature very rapidly   
when heated4 ,the number of calories    
needed by #a gram of a substance in     
order that its temperature may be       
increased #a ,c4 is called the specific 
heat of a substance2 or1 specific heat  
is the number of calories given out by  
#a gram of a substance when its         
temperature falls #a ,c4 ,for           
experiments on the determination of     

specific heat1 see ,laboratory ,manual4 
,water has the highest specific heat of 
any known substance except hydrogen2    
that is1 it requires more heat to raise 
the temperature of water a definite     
number of degrees than it does to raise 
the temperature of an equal amount of   
any other substance the same number of  
degrees4 ,practically this same thing   
can be stated in another way3 ,water in 
cooling gives out more heat than any    
other substance in cooling through the  
same number of degrees4 ,for this reason
 water is used in foot warmers and in   
hot-water bags4 ,if a copper lid were   
used as a foot warmer1 it would give the
 feet only 4#jie as much heat as an     
equal weight of water2 a lead weight    
only 4#jca as much heat as water4       
,flatirons are made of iron because of  
the relatively high specific heat of    
iron4 ,the flatiron heats slowly and    
cools slowly1 and1 because of its high  
specific heat1 not only supplies the    
laundress with considerable heat1 but   

eliminates for her the frequent changing
 of the flatiron4  #ah4 ,water and      
,weather4 ,about four times as much heat
 is required to heat a given quantity of
 water one degree as to heat an equal   
quantity of earth4 ,in summer1 when the 
rocks and the sand along the shore are  
burning hot1 the ocean and lakes are    
pleasantly cool1 although the amount of 
heat present in the water is as great as
 that present in the earth4 ,in winter1 
long after the rocks and sand have given
 out their heat and have become cold1   
the water continues to give out the vast
 store of heat accumulated during the   
summer4 ,this explains why lands        
situated on or near large bodies of     
water usually have less variation in    
temperature than inland regions4 ,in the
 summer the water cools the region2 in  
the winter1 on the contrary1 the water  
heats the region1 and hence extremes of 
temperature are practically unknown4    
#ai4 ,sources of ,heat4 ,most of the    
heat which we enjoy and use we owe to   

the sun4 ,the wood which blazes on the  
hearth1 the coal which glows in the     
furnace1 and the oil which burns in the 
stove owe their existence to the sun4   
,without the warmth of the sun seeds    
could not sprout and develop into the   
mighty trees which yield firewood4 ,even
 coal1 which lies buried thousands of   
feet below the earth's surface1 owes its
 existence in part to the sun4 ,coal is 
simply buried vegetation1--vegetation   
which sprouted and grew under the       
influence of the sun's warm rays4 ,ages 
ago trees and bushes grew thick and     
fast1 and the ground was always covered 
with a deep layer of decaying vegetable 
matter4 ,in time some of this vast      
supply sank into the moist soil and     
became covered with mud4 ,then rock     
formed1 and the rock pressed down upon  
the sunken vegetation4 ,the constant    
pressure1 the moisture in the ground1   
and heat affected the underground       
vegetable mass1 and slowly changed it   
into coal4  ,the buried forest and      

thickets were not all changed into coal4
 ,some were changed into oil and gas4   
,decaying animal matter was often mixed 
with the vegetable mass4 ,when the      
mingled animal and vegetable matter sank
 into moist earth and came under the    
influence of pressure1 it was slowly    
changed into oil and gas4  ,the heat of 
our bodies comes from the foods which we
 eat4 ,fruits1 grain1 etc41 could not   
grow without the warmth and the light of
 the sun4 ,the animals which supply our 
meats likewise depend upon the sun for  
light and warmth4  ,the sun1 therefore1 
is the great source of heat2 whether it 
is the heat which comes directly from   
the sun and warms the atmosphere1 or the
 heat which comes from burning coal1    
wood1 and oil4     ,,chapter ,,iii      
,,other ,,facts ,,about ,,heat   #bj4   
,boiling4 ,heat absorbed in ,boiling4   
,if a kettle of water is placed above a 
flame1 the temperature of the water     
gradually increases1 and soon small     
bubbles form at the bottom of the kettle

 and begin to rise through the water4   
,at first the bubbles do not get far in 
their ascent1 but disappear before they 
reach the surface2 later1 as the water  
gets hotter and hotter1 the bubbles     
become larger and more numerous1 rise   
higher and higher1 and finally reach the
 surface and pass from the water into   
the air2 steam comes from the vessel1   
and the water is said to boil4 ,the     
temperature at which a liquid boils is  
called the boiling point4  ,while the   
water is heating1 the temperature       
steadily rises1 but as soon as the water
 begins to boil the thermometer reading 
becomes stationary and does not change1 
no matter how hard the water boils and  
in spite of the fact that heat from the 
flame is constantly passing into the    
water4  ,if the flame is removed from   
the boiling water for but a second1 the 
boiling ceases2 if the flame is         
replaced1 the boiling begins again      
immediately4 ,unless heat is constantly 
supplied1 water at the boiling point    

cannot be transformed into steam4  ,the 
number of calories which must be        
supplied to #a gram of water at the     
boiling point in order to change it into
 steam at the same temperature is called
 the heat of vaporization2 it is the    
heat necessary to change #a gram of     
water at the boiling point into steam of
 the same temperature4  #ba4 ,the       
,amount of ,heat ,absorbed4 ,the amount 
of heat which must be constantly        
supplied to water at the boiling point  
in order to change it into steam is far 
greater than we realize4 ,if we put a   
beaker of ice water 7water at #j ,c47   
over a steady flame1 and note 7#a7 the  
time which elapses before the water     
begins to boil1 and 7#b7 the time which 
elapses before the boiling water        
completely boils away1 we shall see that
 it takes about #e-a_/d times as long to
 change water into steam as it does to  
change its temperature from #j ,c4 to   
#ajj ,c4 ,since1 with a steady flame1 it
 takes #e-a_/d times as long to change  

water into steam as it does to change   
its temperature from #j ,c4 to the      
boiling point1 we conclude that it takes
 #e-a_/d times as much heat to convert  
water at the boiling point into steam as
 it does to raise it from the           
temperature of ice water to that of     
boiling water4  ,the amount of heat     
necessary to raise the temperature of #a
 gram of water #a ,c4 is equal to #a    
calorie1 and the amount necessary to    
raise the temperature #ajj ,c4 is equal 
to #ajj calories2 hence the amount of   
heat necessary to convert #a gram of    
water at the boiling point into steam at
 that same temperature is equal to      
approximately #ebe calories4 ,very      
careful experiments show the exact heat 
of vaporization to be #ecf4a calories4  
7,see ,laboratory ,manual47  #bb4       
,general ,truths4 ,statements similar to
 the above hold for other liquids and   
for solutions4 ,if milk is placed upon a
 stove1 the temperature rises steadily  
until the boiling point is reached2     

further heating produces1 not a change  
in temperature1 but a change of the     
water of the milk into steam4 ,as soon  
as the milk1 or any other liquid food1  
comes to a boil1 the gas flame should be
 lowered until only an occasional bubble
 forms1 because so long as any bubbles  
form the temperature is that of the     
boiling point1 and further heat merely  
results in waste of fuel4  ,we find by  
experiment that every liquid has its own
 specific boiling point2 for example1   
alcohol boils at #gh ,c4 and brine at   
#ajc ,c4 ,both specific heat and the    
heat of vaporization vary with the      
liquid used4  #bc4 ,condensation4 ,if   
one holds a cold lid in the steam of    
boiling water1 drops of water gather on 
the lid2 the steam is cooled by contact 
with the cold lid and condenses into    
water4 ,bottles of water brought from a 
cold cellar into a warm room become     
covered with a mist of fine drops of    
water1 because the moisture in the air1 
chilled by contact with the cold        

bottles1 immediately condenses into     
drops of water4 ,glasses filled with ice
 water show a similar mist4  ,in        
,section #ba1 we saw that #ecf calories 
are required to change #a gram of water 
into steam2 if1 now1 the steam in turn  
condenses into water1 it is natural to  
expect a release of the heat used in    
transforming water into steam4          
,experiment shows not only that vapor   
gives out heat during condensation1 but 
that the amount of heat thus set free is
 exactly equal to the amount absorbed   
during vaporization4 7,see ,laboratory  
,manual47  ,we learn that the heat of   
vaporization is the same whether it is  
considered as the heat absorbed by #a   
gram of water in its change to steam1 or
 as the heat given out by #a gram of    
steam during its condensation into      
water4  #bd4 ,practical ,application4   
,we understand now the value of steam as
 a heating agent4 ,water is heated in a 
boiler in the cellar1 and the steam     
passes through pipes which run to the   

various rooms2 there the steam condenses
 into water in the radiators1 each gram 
of steam setting free #ecf calories of  
heat4 ,when we consider the size of the 
radiators and the large number of grams 
of steam which they contain1 and        
consider further that each gram in      
condensing sets free #ecf calories1 we  
understand the ease with which buildings
 are heated by steam4  ,most of us have 
at times profited by the heat of        
condensation4 ,in cold weather1 when    
there is a roaring fire in the range1   
the water frequently becomes so hot that
 it steams out of open faucets4 ,if1 at 
such times1 the hot water is turned on  
in a small cold bathroom1 and is allowed
 to run until the tub is well filled1   
vapor condenses on windows1 mirrors1 and
 walls1 and the cold room becomes       
perceptibly warmer4 ,the heat given out 
by the condensing steam passes into the 
surrounding air and warms the room4     
,there is1 however1 another reason for  
the rise in temperature4 ,if a large    

pail of hot soup is placed in a larger  
pail of cold water1 the soup will       
gradually cool and the cold water will  
gradually become warmer4 ,a red-hot iron
 placed on a stand gradually cools1 but 
warms the stand4 ,a hot body loses heat 
so long as a cooler body is near it2 the
 cold object is heated at the expense of
 the warmer object1 and one loses heat  
and the other gains heat until the      
temperature of both is the same4 ,now   
the hot water in the tub gradually loses
 heat and the cold air of the room      
gradually gains heat by convection1 but 
the amount given the room by convection 
is relatively small compared with the   
large amount set free by the condensing 
steam4  #be4 ,distillation4 ,if impure1 
muddy water is boiled1 drops of water   
will collect on a cold plate held in the
 path of the steam1 but the drops will  
be clear and pure4 ,when impure water is
 boiled1 the steam from it does not     
contain any of the impurities because   
these are left behind in the vessel4 ,if

 all the water were allowed to boil     
away1 a layer of mud or of other        
impurities would be found at the bottom 
of the vessel4 ,because of this fact1 it
 is possible to purify water in a very  
simple way4 ,place over a fire a large  
kettle closed except for a spout which  
is long enough to reach across the stove
 and dip into a bottle4 ,as the liquid  
boils1 steam escapes through the spout1 
and on reaching the cold bottle         
condenses and drops into the bottle as  
pure water4 ,the impurities remain      
behind in the kettle4 ,water freed from 
impurities in this way is called        
distilled water1 and the process is     
called distillation 7,fig4 #ai74 ,by    
this method1 the salt water of the ocean
 may be separated into pure drinking    
water and salt1 and many of the large   
ocean liners distill from the briny deep
 all the drinking water used on their   
ocean voyages4  ,illustration3 ,,fig4   
#ai4--;,in order that the steam which   
passes through the coiled tube may be   

quickly cooled and condensed1 cold water
 is made to circulate around the coil4  
,the condensed steam escapes at w4      
,commercially1 distillation is a very   
important process4 ,turpentine1 for     
example1 is made by distilling the sap  
of pine trees4 ,incisions are cut in the
 bark of the long-leaf pine trees1 and  
these serve as channels for the escape  
of crude resin4 ,this crude liquid is   
collected in barrels and taken to a     
distillery1 where it is distilled into  
turpentine and rosin4 ,the turpentine is
 the product which passes off as vapor1 
and the rosin is the mass left in the   
boiler after the distillation of the    
turpentine4  #bf4 ,evaporation4 ,if a   
stopper is left off a cologne bottle1   
the contents of the bottle will slowly  
evaporate2 if a dish of water is placed 
out of doors on a hot day1 evaporation  
occurs very rapidly4 ,the liquids which 
have disappeared from the bottle and the
 dish have passed into the surrounding  
air in the form of vapor4 ,in ,section  

#bj1 we saw that water could not pass   
into vapor without the addition of heat2
 now the heat necessary for the         
evaporation of the cologne and water was
 taken from the air1 leaving it slightly
 cooler4 ,if wet hands are not dried    
with a towel1 but are left to dry by    
evaporation1 heat is taken from the hand
 in the process1 leaving a sensation of 
coolness4 ,damp clothing should never be
 worn1 because the moisture in it tends 
to evaporate at the expense of the      
bodily heat1 and this undue loss of heat
 from the body produces chills4 ,after a
 bath the body should be well rubbed1   
otherwise evaporation occurs at the     
expense of heat which the body cannot   
ordinarily afford to lose4  ,evaporation
 is a slow process occurring at all     
times2 it is hastened during the summer1
 because of the large amount of heat    
present in the atmosphere4 ,many large  
cities make use of the cooling effect of
 evaporation to lower the temperature of
 the air in summer2 streets are         

sprinkled not only to lay the dust1 but 
in order that the surrounding air may be
 cooled by the evaporation of the water4
  ,some thrifty housewives economize by 
utilizing the cooling effects of        
evaporation4 ,butter1 cheese1 and other 
foods sensitive to heat are placed in   
porous vessels wrapped in wet cloths4   
,rapid evaporation of the water from the
 wet cloths keeps the contents of the   
jars cool1 and that without expense     
other than the muscular energy needed   
for wetting the cloths frequently4  #bg4
 ,rain1 ,snow1 ,frost1 ,dew4 ,the heat  
of the sun causes constant evaporation  
of the waters of oceans1 rivers1        
streams1 and marshes1 and the water     
vapor set free by evaporation passes    
into the air1 which becomes charged with
 vapor or is said to be humid4          
,constant1 unceasing evaporation of our 
lakes1 streams1 and pools would mean a  
steady decrease in the supply of water  
available for daily use1 if the escaped 
water were all retained by the          

atmosphere and lost to the earth4 ,but  
although the escaped vapor mingles with 
the atmosphere1 hovering near the       
earth's surface1 or rising far above the
 level of the mountains1 it does not    
remain there permanently4 ,when this    
vapor meets a cold wind or is chilled in
 any way1 condensation takes place1 and 
a mass of tiny drops of water or of     
small particles of snow is formed4 ,when
 these drops or particles become large  
enough1 they fall to the earth as rain  
or snow1 and in this way the earth is   
compensated for the great loss of       
moisture due to evaporation4 ,fog is    
formed when vapor condenses near the    
surface of the earth1 and when the drops
 are so small that they do not fall but 
hover in the air1 the fog is said not to
 lift or not to clear4  ,if ice water is
 poured into a glass1 a mist will form  
on the outside of the glass4 ,this is   
because the water vapor in the air      
becomes chilled by contact with the     
glass and condenses4 ,often leaves and  

grass and sidewalks are so cold that the
 water vapor in the atmosphere condenses
 on them1 and we say a heavy dew has    
formed4 ,if the temperature of the air  
falls to the freezing point while the   
dew is forming1 the vapor is frozen and 
frost is seen instead of dew4  ,the     
daily evaporation of moisture into the  
atmosphere keeps the atmosphere more or 
less full of water vapor2 but the       
atmosphere can hold only a definite     
amount of vapor at a given temperature1 
and as soon as it contains the maximum  
amount for that temperature1 further    
evaporation ceases4 ,if clothes are hung
 out on a damp1 murky day they do not   
dry1 because the air contains all the   
moisture it can hold1 and the moisture  
in the clothes has no chance to         
evaporate4 ,when the air contains all   
the moisture it can hold1 it is said to 
be saturated1 and if a slight fall in   
temperature occurs when the air is      
saturated1 condensation immediately     
begins in the form of rain1 snow1 or    

fog4 ,if1 however1 the air is not       
saturated1 a fall in temperature may    
occur without producing precipitation4  
,the temperature at which air is        
saturated and condensation begins is    
called the dew point4  #bh4 ,how ,chills
 are ,caused4 ,the discomfort we feel in
 an overcrowded room is partly due to an
 excess of moisture in the air1         
resulting from the breathing and        
perspiration of many persons4 ,the air  
soon becomes saturated with vapor and   
cannot take away the perspiration from  
our bodies1 and our clothing becomes    
moist and our skin tender4 ,when we     
leave the crowded tea or lecture and    
pass into the colder1 drier1 outside    
air1 clothes and skin give up their load
 of moisture through sudden evaporation4
 ,but evaporation requires heat1 and    
this heat is taken from our bodies1 and 
a chill results4  ,proper ventilation   
would eliminate much of the physical    
danger of social events2 fresh1 dry air 
should be constantly admitted to crowded

 rooms in order to replace the air      
saturated by the breath and perspiration
 of the occupants4  #bi4 ,weather       
,forecasts4 ,when the air is near the   
saturation point1 the weather is        
oppressive and is said to be very humid4
 ,for comfort and health1 the air should
 be about two thirds saturated4 ,the    
presence of some water vapor in the air 
is absolutely necessary to animal and   
plant life4 ,in desert regions where    
vapor is scarce the air is so dry that  
throat trouble accompanied by           
disagreeable tickling is prevalent2     
fallen leaves become so dry that they   
crumble to dust2 plants lose their      
freshness and beauty4  ,the likelihood  
of rain or frost is often determined by 
temperature and humidity4 ,if the air is
 near saturation and the temperature is 
falling1 it is safe to predict bad      
weather1 because the fall of temperature
 will probably cause rapid condensation1
 and hence rain4 ,if1 however1 the air  
is not near the saturation point1 a fall

 in temperature will not necessarily    
produce bad weather4  ,the measurement  
of humidity is of far wider importance  
than the mere forecasting of local      
weather conditions4 ,the close relation 
between humidity and health has led many
 institutions1 such as hospitals1       
schools1 and factories1 to regulate the 
humidity of the atmosphere as carefully 
as they do the temperature4 ,too great  
humidity is enervating1 and not         
conducive to either mental or physical  
exertion2 on the other hand1 too dry air
 is equally harmful4 ,in summer the     
humidity conditions cannot be well      
regulated1 but in winter1 when houses   
are artificially heated1 the humidity of
 a room can be increased by placing pans
 of water near the registers or on      
radiators4  #cj4 ,heat ,needed to ,melt 
,substances4 ,if a spoon is placed in a 
vessel of hot water for a few seconds   
and then removed1 it will be warmer than
 before it was placed in the hot water4 
,if a lump of melting ice is placed in  

the vessel of hot water and then        
removed1 the ice will not be warmer than
 before1 but there will be less of it4  
,the heat of the water has been used in 
melting the ice1 not in changing its    
temperature4  ,if1 on a bitter cold day1
 a pail of snow is brought into a warm  
room and a thermometer is placed in the 
snow1 the temperature rises gradually   
until #cb ,f4 is reached1 when it       
becomes stationary1 and the snow begins 
to melt4 ,if the pail is put on the     
fire1 the temperature still remains     
#cb;,f41 but the snow melts more        
rapidly4 ,as soon as all the snow is    
completely melted1 however1 the         
temperature begins to rise and rises    
steadily until the water boils1 when it 
again becomes stationary and remains so 
during the passage of water into vapor4 
,we see that heat must be supplied to   
ice at #j ,c4 or #cb ,f4 in order to    
change it into water1 and further1 that 
the temperature of the mixture does not 
rise so long as any ice is present1 no  

matter how much heat is supplied4 ,the  
amount of heat necessary to melt #a gram
 of ice is easily calculated4 7,see     
,laboratory ,manual47  ,heat must be    
supplied to ice to melt it4 ,on the     
other hand1 water1 in freezing1 loses   
heat1 and the amount of heat lost by    
freezing water is exactly equal to the  
amount of heat absorbed by melting ice4 
,the number of units of heat required to
 melt a unit mass of ice is called the  
heat of fusion of water4  #ca4 ,climate4
 ,water1 in freezing1 loses heat1 even  
though its temperature remains at #j ,c4
 ,because water loses heat when it      
freezes1 the presence of large streams  
of water greatly influences the climate 
of a region4 ,in winter the heat from   
the freezing water keeps the temperature
 of the surrounding higher than it would
 naturally be1 and consequently the cold
 weather is less severe4 ,in summer     
water evaporates1 heat is taken from the
 air1 and consequently the warm weather 
is less intense4  #cb4 ,molding of      

,glass and ,forging of ,iron4 ,the fire 
which is hot enough to melt a lump of   
ice may not be hot enough to melt an    
iron poker2 on the other hand1 it may be
 sufficiently hot to melt a tin spoon4  
,different substances melt1 or liquefy1 
at different temperatures2 for example1 
ice melts at #j ,c41 and tin at #bcc    
,c41 while iron requires the relatively 
high temperature of #abjj ,c4 ,most     
substances have a definite melting or   
freezing point which never changes so   
long as the surrounding conditions      
remain the same4  ,but while most       
substances have a definite melting      
point1 some substances do not4 ,if a    
glass rod is held in a ,bunsen burner1  
it will gradually grow softer and       
softer1 and finally a drop of molten    
glass will fall from the end of the rod 
into the fire4 ,the glass did not       
suddenly become a liquid at a definite  
temperature2 instead it softened        
gradually1 and then melted4 ,while glass
 is in the soft1 yielding1 pliable      

state1 it is molded into dishes1        
bottles1 and other useful objects1 such 
as lamp shades1 globes1 etc4 7,fig4     
#bj74 ,if glass melted at a definite    
temperature1 it could not be molded in  
this way4 ,iron acts in a similar       
manner1 and because of this property the
 blacksmith can shape his horseshoes1   
and the workman can make his engines and
 other articles of daily service to man4
  ,illustration3 ,,fig4 #bj4--,molten   
glass being rolled into a form suitable 
for window panes4  #cc4 ,strange        
,behavior of ,water4 ,one has but to    
remember that bottles of water burst    
when they freeze1 and that ice floats on
 water like wood1 to know that water    
expands on freezing or on solidifying4  
,a quantity of water which occupies #ajj
 cubic feet of space will1 on becoming  
ice1 need #aji cubic feet of space4 ,on 
a cold winter night the water sometimes 
freezes in the water pipes1 and the     
pipes burst4 ,water is very peculiar in 
expanding on solidification1 because    

most substances contract on solidifying2
 gelatin and jelly1 for example1        
contract so much that they shrink from  
the sides of the dish which contains    
them4  ,if water contracted in freezing1
 ice would be heavier than water and    
would sink in ponds and lakes as fast as
 it formed1 and our streams and ponds   
would become masses of solid ice1       
killing all animal and plant life4 ,but 
the ice is lighter than water and floats
 on top1 and animals in the water       
beneath are as free to live and swim as 
they were in the warm sunny days of     
summer4 ,the most severe winter cannot  
freeze a deep lake solid1 and in the    
coldest weather a hole made in the ice  
will show water beneath the surface4    
,our ice boats cut and break the ice of 
the river1 and through the water beneath
 our boats daily ply their way to and   
fro1 independent of winter and its      
blighting blasts4  ,while most of us are
 familiar with the bursting of water    
pipes on a cold night1 few of us realize

 the influence which freezing water     
exerts on the character of the land     
around us4  ,water sinks into the ground
 and1 on the approach of winter1        
freezes1 expanding about one tenth of   
its volume2 the expanding ice pushes the
 earth aside1 the force in some cases   
being sufficient to dislodge even huge  
rocks4 ,in the early days in ,new       
,england it was said by the farmers that
 rocks grew1 because fields cleared of  
stones in the fall became rock covered  
with the approach of spring2 the rocks  
and stones hidden underground and unseen
 in the fall were forced to the surface 
by the winter's expansion4 ,we have all 
seen fence posts and bricks pushed out  
of place because of the heaving of the  
soil beneath them4 ,often householders  
must relay their pavements and walks    
because of the damage done by freezing  
water4  ,the most conspicuous effect of 
the expansive power of freezing water is
 seen in rocky or mountainous regions   
7,fig4 #ba74 ,water easily finds        

entrance into the cracks and crevices of
 the rocks1 where it lodges until       
frozen2 then it expands and acts like a 
wedge1 widening cracks1 chiseling off   
edges1 and even breaking rocks asunder4 
,in regions where frequent frosts occur1
 the destructive action of water works  
constant changes in the appearance of   
the land2 small cracks and crevices are 
enlarged1 massive rocks are pried up out
 of position1 huge slabs are split off1 
and particles large and small are forced
 from the parent rock4 ,the greater part
 of the debris and rubbish brought down 
from the mountain slopes by the spring  
rains owes its origin to the fact that  
water expands when it freezes4          
,illustration3 ,,fig4 #ba4--,the        
destruction caused by freezing water4   
#cd4 ,heat ,necessary to ,dissolve a    
,substance4 ,it requires heat to        
dissolve any substance1 just as it      
requires heat to change ice to water4   
,if a handful of common salt is placed  
in a small cup of water and stirred with

 a thermometer1 the temperature of the  
mixture falls several degrees4 ,this is 
just what one would expect1 because the 
heat needed to liquefy the salt must    
come from somewhere1 and naturally it   
comes from the water1 thereby lowering  
the temperature of the water4 ,we know  
very well that potatoes cease boiling if
 a pinch of salt is put in the water2   
this is because the temperature of the  
water has been lowered by the amount of 
heat necessary to dissolve the salt4    
,let some snow or chopped ice be placed 
in a vessel and mixed with one third its
 weight of coarse salt2 if then a small 
tube of cold water is placed in this    
mixture1 the water in the test tube will
 soon freeze solid4 ,as soon as the snow
 and salt are mixed they melt4 ,the heat
 necessary for this comes in part from  
the air and in part from the water in   
the test tube1 and the water in the tube
 becomes in consequence cold enough to  
freeze4 ,but the salt mixture does not  
freeze because its freezing point is far

 below that of pure water4 ,the use of  
salt and ice in ice-cream freezers is a 
practical application of this principle4
 ,the heat necessary for melting the    
mixture of salt and ice is taken from   
the cream which thus becomes cold enough
 to freeze4     ,,chapter ,,iv          
,,burning ,,or ,,oxidation   #ce4 ,why  
,things ,burn4 ,the heat of our bodies  
comes from the food we eat2 the heat for
 cooking and for warming our houses     
comes from coal4 ,the production of heat
 through the burning of coal1 or oil1 or
 gas1 or wood1 is called combustion4    
,combustion cannot occur without the    
presence of a substance called oxygen1  
which exists rather abundantly in the   
air2 that is1 one fifth of our          
atmosphere consists of this substance   
which we call oxygen4 ,we throw open our
 windows to allow fresh air to enter1   
and we take walks in order to breathe   
the pure air into our lungs4 ,what we   
need for the energy and warmth of our   
bodies is the oxygen in the air4        

,whether we burn gas or wood or coal1   
the heat which is produced comes from   
the power which these various substances
 possess to combine with oxygen4 ,we    
open the draft of a stove that it may   
draw well3 that it may secure oxygen for
 burning4 ,we throw a blanket over      
burning material to smother the fire3 to
 keep oxygen away from it4 ,burning1 or 
oxidation1 is combining with oxygen1 and
 the more oxygen you add to a fire1 the 
hotter the fire will burn1 and the      
faster4 ,the effect of oxygen on        
combustion may be clearly seen by       
thrusting a smoldering splinter into a  
jar containing oxygen2 the smoldering   
splinter will instantly flare and blaze1
 while if it is removed from the jar1 it
 loses its flame and again burns        
quietly4 ,oxygen for this experiment can
 be produced in the following way4      
,illustration3 ,,fig4 #bb4--,preparing  
oxygen from potassium chlorate and      
manganese dioxide4  #cf4 ,how to        
,prepare ,oxygen4 ,mix a small quantity 

of potassium chlorate with an equal     
amount of manganese dioxide and place   
the mixture in a strong test tube4      
,close the mouth of the tube with a     
one-hole rubber stopper in which is     
fitted a long1 narrow tube1 and clamp   
the test tube to an iron support1 as    
shown in ,figure #bb4 ,fill the trough  
with water until the shelf is just      
covered and allow the end of the        
delivery tube to rest just beneath the  
hole in the shelf4 ,fill a medium-sized 
bottle with water1 cover it with a glass
 plate1 invert the bottle in the trough1
 and then remove the glass plate4 ,heat 
the test tube very gently1 and when gas 
bubbles out of the tube1 slip the bottle
 over the opening in the shelf1 so that 
the tube runs into the bottle4 ,the gas 
will force out the water and will       
finally fill the bottle4 ,when all the  
water has been forced out1 slip the     
glass plate under the mouth of the      
bottle and remove the bottle from the   
trough4 ,the gas in the bottle is       

oxygen4  ,everywhere in a large city or 
in a small village1 smoke is seen1      
indicating the presence of fire2 hence  
there must exist a large supply of      
oxygen to keep all the fires alive4 ,the
 supply of oxygen needed for the fires  
of the world comes largely from the     
atmosphere4  #cg4 ,matches4 ,the burning
 material is ordinarily set on fire by  
matches1 thin strips of wood tipped with
 sulphur or phosphorus1 or both4        
,phosphorus can unite with oxygen at a  
fairly low temperature1 and if          
phosphorus is rubbed against a rough    
surface1 the friction produced will     
raise the temperature of the phosphorus 
to a point where it can combine with    
oxygen4 ,the burning phosphorus kindles 
the wood of the match1 and from the     
burning match the fire is kindled4 ,if  
you want to convince yourself that      
friction produces heat1 rub a cent      
vigorously against your coat and note   
that the cent becomes warm4 ,matches    
have been in use less than a hundred    

years4 ,primitive man kindled his camp  
fire by rubbing pieces of dry wood      
together until they took fire1 and this 
method is said to be used among some    
isolated distant tribes at the present  
time4 ,a later and easier way was to    
strike flint and steel together and to  
catch the spark thus produced on tinder 
or dry fungus4 ,within the memory of    
some persons now living1 the tinder box 
was a valuable asset to the home1       
particularly in the pioneer regions of  
the ,west4  #ch4 ,safety ,matches4      
,ordinary phosphorus1 while excellent as
 a fire-producing material1 is          
dangerously poisonous1 and those to whom
 the dipping of wooden strips into      
phosphorus is a daily occupation suffer 
with a terrible disease which usually   
attacks the teeth and bones of the jaw4 
,the teeth rot and fall out1 abscesses  
form1 and bones and flesh begin to      
decay2 the only way to prevent the      
spread of the disease is to remove the  
affected bone1 and in some instances it 

has been necessary to remove the entire 
jaw4 ,then1 too1 matches made of yellow 
or white phosphorus ignite easily1 and1 
when rubbed against any rough surface1  
are apt to take fire4 ,many destructive 
fires have been started by the          
accidental friction of such matches     
against rough surfaces4  ,for these     
reasons the introduction of the         
so-called safety match was an important 
event4 ,when common phosphorus1 in the  
dangerous and easily ignited form1 is   
heated in a closed vessel to about #bej 
,c41 it gradually changes to a harmless 
red mass4 ,the red phosphorus is not    
only harmless1 but it is difficult to   
ignite1 and1 in order to be ignited by  
friction1 must be rubbed on a surface   
rich in oxygen4 ,the head of a safety   
match is coated with a mixture of glue  
and oxygen-containing compounds2 the    
surface on which the match is to be     
rubbed is coated with a mixture of red  
phosphorus and glue1 to which finely    
powdered glass is sometimes added in    

order to increase the friction4 ,unless 
the head of the match is rubbed on the  
prepared phosphorus coating1 ignition   
does not occur1 and accidental fires are
 avoided4  ,various kinds of safety     
matches have been manufactured in the   
last few years1 but they are somewhat   
more expensive than the ordinary form1  
and hence manufacturers are reluctant to
 substitute them for the cheaper        
matches4 ,some foreign countries1 such  
as ,switzerland1 prohibit the sale of   
the dangerous type1 and it is hoped that
 the ,united ,states will soon follow   
the lead of these countries in demanding
 the sale of safety matches only4  #ci4 
,some ,unfamiliar ,forms of ,burning4   
,while most of us think of burning as a 
process in which flames and smoke occur1
 there are in reality many modes of     
burning accompanied by neither flame nor
 smoke4 ,iron1 for example1 burns when  
it rusts1 because it slowly combines    
with the oxygen of the air and is       
transformed into new substances4 ,when  

the air is dry1 iron does not unite with
 oxygen1 but when moisture is present in
 the air1 the iron unites with the      
oxygen and turns into iron rust4 ,the   
burning is slow and unaccompanied by the
 fire and smoke so familiar to us1 but  
the process is none the less burning1 or
 combination with oxygen4 ,burning which
 is not accompanied by any of the       
appearances of ordinary burning is known
 as oxidation4  ,the tendency of iron to
 rust lessens its efficiency and value1 
and many devices have been introduced to
 prevent rusting4 ,a coating of paint or
 varnish is sometimes applied to iron in
 order to prevent contact with air4 ,the
 galvanizing of iron is another attempt 
to secure the same result2 in this      
process iron is dipped into molten zinc1
 thereby acquiring a coating of zinc1   
and forming what is known as galvanized 
iron4 ,zinc does not combine with oxygen
 under ordinary circumstances1 and hence
 galvanized iron is immune from rust4   
,decay is a process of oxidation2 the   

tree which rots slowly away is          
undergoing oxidation1 and the result of 
the slow burning is the decomposed      
matter which we see and the invisible   
gases which pass into the atmosphere4   
,the log which blazes on our hearth     
gives out sufficient heat to warm us2   
the log which decays in the forest gives
 out an equivalent amount of heat1 but  
the heat is evolved so slowly that we   
are not conscious of it4 ,burning       
accompanied by a blaze and intense heat 
is a rapid process2 burning             
unaccompanied by fire and appreciable   
heat is a slow1 gradual process1        
requiring days1 weeks1 and even long    
years for its completion4  ,another form
 of oxidation occurs daily in the human 
body4 ,in ,section #ce we saw that the  
human body is an engine whose fuel is   
food2 the burning of that food in the   
body furnishes the heat necessary for   
bodily warmth and the energy required   
for thought and action4 ,oxygen is      
essential to burning1 and the food fires

 within the body are kept alive by the  
oxygen taken into the body at every     
breath by the lungs4 ,we see now one    
reason for an abundance of fresh air in 
daily life4  #dj4 ,how to ,breathe4     
,air1 which is essential to life and    
health1 should enter the body through   
the nose and not through the mouth4 ,the
 peculiar nature and arrangement of the 
membranes of the nose enable the        
nostrils to clean1 and warm1 and moisten
 the air which passes through them to   
the lungs4 ,floating around in the      
atmosphere are dust particles which     
ought not to get into the lungs4 ,the   
nose is provided with small hairs and a 
moist inner membrane which serve as     
filters in removing solid particles from
 the air1 and in thus purifying it      
before its entrance into the lungs4  ,in
 the immediate neighborhood of three    
,philadelphia high schools1 having an   
approximate enrollment of over #hjjj    
pupils1 is a huge manufacturing plant   
which day and night pours forth grimy   

smoke and soot into the atmosphere which
 must supply oxygen to this vast group  
of young lives4 ,if the vital importance
 of nose breathing is impressed upon    
these young people1 the harmful effect  
of the foul air may be greatly lessened1
 the smoke particles and germs being    
held back by the nose filters and never 
reaching the lungs4 ,if1 however1 this  
principle of hygiene is not brought to  
their attention1 the dangerous habit of 
breathing through the open1 or at least 
partially open1 mouth will continue1 and
 objectionable matter will pass through 
the mouth and find a lodging place in   
the lungs4  ,there is another very      
important reason why nose breathing is  
preferable to mouth breathing4 ,the     
temperature of the human body is        
approximately #ih ,f41 and the air which
 enters the lungs should not be far     
below this temperature4 ,if air reaches 
the lungs through the nose1 its journey 
is relatively long and slow1 and there  
is opportunity for it to be warmed      

before it reaches the lungs4 ,if1 on the
 other hand1 air passes to the lungs by 
way of the mouth1 the warming process is
 brief and insufficient1 and the lungs  
suffer in consequence4 ,naturally1 the  
gravest danger is in winter4  #da4      
,cause of ,mouth ,breathing4 ,some      
people find it difficult to breathe     
through the nostrils on account of      
growths1 called adenoids1 in the nose4  
,if you have a tendency toward mouth    
breathing1 let a physician examine your 
nose and throat4  ,adenoids not only    
obstruct breathing and weaken the whole 
system through lack of adequate air1 but
 they also press upon the blood vessels 
and nerves of the head and interfere    
with normal brain development4          
,moreover1 they interfere in many cases 
with the hearing1 and in general hinder 
activity and growth4 ,the removal of    
adenoids is simple1 and carries with it 
only temporary pain and no danger4 ,some
 physicians claim that the growths      
disappear in later years1 but even if   

that is true1 the physical and mental   
development of earlier years is lost1   
and the person is backward in the       
struggle for life and achievement4      
,illustration3 ,,fig4                   
#bc4--;,intelligent expression is often 
lacking in children with adenoid        
growths4  #db4 ,how to ,build a ,fire4  
,substances differ greatly as to the    
ease with which they may be made to burn
 or1 in technical terms1 with which they
 may be made to unite with oxygen4 ,for 
this reason1 we put light materials1    
like shavings1 chips1 and paper1 on the 
grate1 twisting the latter and arranging
 it so that air 7oxygen in the air7 can 
reach a large surface2 upon this we     
place small sticks of wood1 piling them 
across each other so as to allow        
entrance for the oxygen2 and finally    
upon this we place our hard wood or     
coal4  ,the coal and the large sticks   
cannot be kindled with a match1 but the 
paper and shavings can1 and these in    
burning will heat the large sticks until

 they take fire and in turn kindle the  
coal4  #dc4 ,spontaneous ,combustion4   
,we often hear of fires starting        
themselves1 and sometimes the statement 
is true4 ,if a pile of oily rags is     
allowed to stand for a time1 the oily   
matter will begin to combine slowly with
 oxygen and as a result will give off   
heat4 ,the heat thus given off is at    
first insufficient to kindle a fire2 but
 as the heat is retained and            
accumulated1 the temperature rises1 and 
finally the kindling point is reached   
and the whole mass bursts into flames4  
,for safety's sake1 all oily cloths     
should be burned or kept in metal       
vessels4  #dd4 ,the ,treatment of       
,burns4 ,in spite of great caution1     
burns from fires1 steam1 or hot water do
 sometimes occur1 and it is well to know
 how to relieve the suffering caused by 
them and how to treat the injury in     
order to insure rapid healing4  ,burns  
are dangerous because they destroy skin 
and thus open up an entrance into the   

body for disease germs1 and in addition 
because they lay bare nerve tissue which
 thereby becomes irritated and causes a 
shock to the entire system4  ,in mild   
burns1 where the skin is not broken but 
is merely reddened1 an application of   
moist baking soda brings immediate      
relief4 ,if this substance is not       
available1 flour paste1 lard1 sweet oil1
 or vaseline may be used4  ,in more     
severe burns1 where blisters are formed1
 the blisters should be punctured with a
 sharp1 sterilized needle and allowed to
 discharge their watery contents before 
the above remedies are applied4  ,in    
burns severe enough to destroy the skin1
 disinfection of the open wound with    
weak carbolic acid or hydrogen peroxide 
is very necessary4 ,after this has been 
done1 a soft cloth soaked in a solution 
of linseed oil and limewater should be  
applied and the whole bandaged4 ,in such
 a case1 it is important not to use     
cotton batting1 since this sticks to the
 rough surface and causes pain when     

removed4  #de4 ,carbon ,dioxide4 ,a     
,product of ,burning4 ,when any fuel1   
such as coal1 gas1 oil1 or wood1 burns1 
it sends forth gases into the           
surrounding atmosphere4 ,these gases1   
like air1 are invisible1 and were       
unknown to us for a long time4 ,the     
chief gas formed by a burning substance 
is called carbon dioxide 7,,co#b7       
because it is composed of one part of   
carbon and two parts of oxygen4 ,this   
gas has the distinction of being the    
most widely distributed gaseous compound
 of the entire world2 it is found in the
 ocean depths and on the mountain       
heights1 in brilliantly lighted rooms1  
and most abundantly in manufacturing    
towns where factory chimneys constantly 
pour forth hot gases and smoke4  ,wood  
and coal1 and in fact all animal and    
vegetable matter1 contain carbon1 and   
when these substances burn or decay1 the
 carbon in them unites with oxygen and  
forms carbon dioxide4  ,the food which  
we eat is either animal or vegetable1   

and it is made ready for bodily use by a
 slow process of burning within the     
body2 carbon dioxide accompanies this   
bodily burning of food just as it       
accompanies the fires with which we are 
more familiar4 ,the carbon dioxide thus 
produced within the body escapes into   
the atmosphere with the breath4  ,we see
 that the source of carbon dioxide is   
practically inexhaustible1 coming as it 
does from every stove1 furnace1 and     
candle1 and further with every breath of
 a living organism4  #df4 ,danger of    
,carbon ,dioxide4 ,when carbon dioxide  
occurs in large quantities1 it is       
dangerous to health1 because it         
interferes with normal breathing1       
lessening the escape of waste matter    
through the breath and preventing the   
access to the lungs of the oxygen       
necessary for life4 ,carbon dioxide is  
not poisonous1 but it cuts off the      
supply of oxygen1 just as water cuts it 
off from a drowning man4  ,since every  
man1 woman1 and child constantly        

breathes forth carbon dioxide1 the      
danger in overcrowded rooms is great1   
and proper ventilation is of vital      
importance4  #dg4 ,ventilation4 ,in     
estimating the quantity of air necessary
 to keep a room well aired1 we must take
 into account the number of lights      
7electric lights do not count7 to be    
used1 and the number of people to occupy
 the room4 ,the average house should    
provide at the minimum #fjj cubic feet  
of space for each person1 and in        
addition1 arrangements for allowing at  
least #cjj cubic feet of fresh air per  
person to enter every hour4  ,in houses 
which have not a ventilating system1 the
 air should be kept fresh by intelligent
 action in the opening of doors and     
windows2 and since relatively few houses
 are equipped with a satisfactory       
system1 the following suggestions       
relative to intelligent ventilation are 
offered4  #a4 ,avoid drafts in          
ventilation4  #b4 ,ventilate on the     
sheltered side of the house4 ,if the    

wind is blowing from the north1 open    
south windows4  #dh4 ,what ,becomes of  
the ,carbon ,dioxide4 ,when we reflect  
that carbon dioxide is constantly being 
supplied to the atmosphere and that it  
is injurious to health1 the question    
naturally arises as to how the air      
remains free enough of the gas to       
support life4 ,this is largely because  
carbon dioxide is an essential food of  
plants4 ,through their leaves plants    
absorb it from the atmosphere1 and by a 
wonderful process break it up into its  
component parts1 oxygen and carbon4     
,they reject the oxygen1 which passes   
back to the air1 but they retain the    
carbon1 which becomes a part of the     
plant structure4 ,plants thus serve to  
keep the atmosphere free from an excess 
of carbon dioxide and1 in addition1     
furnish oxygen to the atmosphere4       
,illustration3 ,,fig4 #bd4--,making     
carbon dioxide from marble and          
hydrochloric acid4  #di4 ,how to ,obtain
 ,carbon ,dioxide4 ,there are several   

ways in which carbon dioxide can be     
produced commercially1 but for          
laboratory use the simplest is to mix in
 a test tube powdered marble1 or chalk1 
and hydrochloric acid1 and to collect   
the effervescing gas as shown in ,figure
 #bd4 ,the substance which remains in   
the test tube after the gas has passed  
off is a solution of a salt and water4  
,from a mixture of hydrochloric acid    
7,h,cl7 and marble are obtained a salt1 
water1 and carbon dioxide1 the desired  
gas4  #ej4 ,a ,commercial ,use of       
,carbon ,dioxide4 ,if a lighted splinter
 is thrust into a test tube containing  
carbon dioxide1 it is promptly          
extinguished1 because carbon dioxide    
cannot support combustion2 if a stream  
of carbon dioxide and water falls upon a
 fire1 it acts like a blanket1 covering 
the flames and extinguishing them4 ,the 
value of a fire extinguisher depends    
upon the amount of carbon dioxide and   
water which it can furnish4 ,a fire     
extinguisher is a metal case containing 

a solution of bicarbonate of soda1 and a
 glass vessel full of strong sulphuric  
acid4 ,as long as the extinguisher is in
 an upright position1 these substances  
are kept separate1 but when the         
extinguisher is inverted1 the acid      
escapes from the bottle1 and mixes with 
the soda solution4 ,the mingling liquids
 interact and liberate carbon dioxide4  
,a part of the gas thus liberated       
dissolves in the water of the soda      
solution and escapes from the tube with 
the outflowing liquid1 while a portion  
remains undissolved and escapes as a    
stream of gas4 ,the fire extinguisher is
 therefore the source of a liquid       
containing the fire-extinguishing       
substance and further the source of a   
stream of carbon dioxide gas4           
,illustration3 ,,fig4 #be4--;,inside    
view of a fire extinguisher4  #ea4      
,carbon4 ,although carbon dioxide is    
very injurious to health1 both of the   
substances of which it is composed are  
necessary to life4 ,we ourselves1 our   

bones and flesh in particular1 are      
partly carbon1 and every animal1 no     
matter how small or insignificant1      
contains some carbon2 while the plants  
around us1 the trees1 the grass1 the    
flowers1 contain a by no means meager   
quantity of carbon4  ,carbon plays an   
important and varied role in our life1  
and1 in some one of its many forms1     
enters into the composition of most of  
the substances which are of service and 
value to man4 ,the food we eat1 the     
clothes we wear1 the wood and coal we   
burn1 the marble we employ in building1 
the indispensable soap1 and the         
ornamental diamond1 all contain carbon  
in some form4  #eb4 ,charcoal4 ,one of  
the most valuable forms of carbon is    
charcoal2 valuable not in the sense that
 it costs hundreds of dollars1 but in   
the more vital sense1 that its use adds 
to the cleanliness1 comfort1 and health 
of man4  ,the foul1 bad-smelling gases  
which arise from sewers can be prevented
 from escaping and passing to streets   

and buildings by placing charcoal       
filters at the sewer exits4 ,charcoal is
 porous and absorbs foul gases1 and thus
 keeps the region surrounding sewers    
sweet and clean and free of odor4 ,good 
housekeepers drop small bits of charcoal
 into vases of flowers to prevent       
discoloration of the water and the odor 
of decaying stems4  ,if impure water    
filters through charcoal1 it emerges    
pure1 having left its impurities in the 
pores of the charcoal4 ,practically all 
household filters of drinking water are 
made of charcoal4 ,but such a device may
 be a source of disease instead of a    
prevention of disease1 unless the filter
 is regularly cleaned or renewed4 ,this 
is because the pores soon become clogged
 with the impurities1 and unless they   
are cleaned1 the water which flows      
through the filter passes through a bed 
of impurities and becomes contaminated  
rather than purified4 ,frequent         
cleansing or renewal of the filter      
removes this difficulty4  ,commercially1

 charcoal is used on a large scale in   
the refining of sugars1 sirups1 and     
oils4 ,sugar1 whether it comes from the 
maple tree1 or the sugar cane1 or the   
beet1 is dark colored4 ,it is whitened  
by passage through filters of finely    
pulverized charcoal4 ,cider and vinegar 
are likewise cleared by passage through 
charcoal4  ,the value of carbon1 in the 
form of charcoal1 as a purifier is very 
great1 whether we consider it a         
deodorizer1 as in the case of the       
sewage1 or a decolorizer1 as in the case
 of the refineries1 or whether we       
consider the service it has rendered man
 in the elimination of danger from      
drinking water4  #ec4 ,how ,charcoal is 
,made4 ,charcoal may be made by heating 
wood in an oven to which air does not   
have free access4 ,the absence of air   
prevents ordinary combustion1           
nevertheless the intense heat affects   
the wood and changes it into new        
substances1 one of which is charcoal4   
,the wood which smolders on the hearth  

and in the stove is charcoal in the     
making4 ,formerly wood was piled in     
heaps1 covered with sod or sand to      
prevent access of oxygen1 and then was  
set fire to2 the smoldering wood1 cut   
off from an adequate supply of air1 was 
slowly transformed into charcoal4       
,scattered over the country one still   
finds isolated charcoal kilns1 crude    
earthen receptacles1 in which wood thus 
deprived of air was allowed to smolder  
and form charcoal4 ,to-day charcoal is  
made commercially by piling wood on     
steel cars and then pushing the cars    
into strong walled chambers4 ,the       
chambers are closed to prevent access of
 air1 and heated to a high temperature4 
,the intense heat transforms the wood   
into charcoal in a few hours4 ,a student
 can make in the laboratory sufficient  
charcoal for art lessons by heating in  
an earthen vessel wood buried in sand4  
,the process will be slow1 however1     
because the heat furnished by a ,bunsen 
burner is not great1 and the wood is    

transformed slowly4  ,a form of charcoal
 known as animal charcoal1 or bone      
black1 is obtained from the charred     
remains of animals rather than plants1  
and may be prepared by burning bones and
 animal refuse as in the case of the    
wood4  ,destructive ,distillation4 ,when
 wood is burned without sufficient air1 
it is changed into soft brittle         
charcoal1 which is very different from  
wood4 ,it weighs only one fourth as much
 as the original wood4 ,it is evident   
that much matter must leave the wood    
during the process of charcoal making4  
,we can prove this by putting some dry  
shavings in a strong test tube fitted   
with a delivery tube4 ,when the wood is 
heated a gas passes off which we may    
collect and burn4 ,other substances also
 come off in gaseous form1 but they     
condense in the water4 ,among these are 
wood alcohol1 wood tar1 and acetic acid4
 ,in the older method of charcoal making
 all these products were lost4 ,can you 
give any uses of these substances8  #ed4

 ,matter and ,energy4 ,when wood is     
burned1 a small pile of ashes is left1  
and we think of the bulk of the wood as 
destroyed4 ,it is true we have less     
matter that is available for use or that
 is visible to sight1 but1 nevertheless1
 no matter has been destroyed4 ,the     
matter of which the wood is composed has
 merely changed its character1 some of  
it is in the condition of ashes1 and    
some in the condition of invisible      
gases1 such as carbon dioxide1 but none 
of it has been destroyed4 ,it is a      
principle of science that matter can    
neither be destroyed nor created2 it can
 only be changed1 or transformed1 and it
 is our business to see that we do not  
heedlessly transform it into substances 
which are valueless to us and our       
descendants2 as1 for example1 when our  
magnificent forests are recklessly      
wasted4 ,the smoke1 gases1 and ashes    
left in the path of a raging forest fire
 are no compensation to us for the      
valuable timber destroyed4 ,the sum     

total of matter has not been changed1   
but the amount of matter which man can  
use has been greatly lessened4  ,the    
principle just stated embodies one of   
the fundamental laws of science1 called 
the law of the conservation of matter4  
,a similar law holds for energy as well4
 ,we can transform electric energy into 
the motion of trolley cars1 or we can   
make use of the energy of streams to    
turn the wheels of our mills1 but in all
 these cases we are transforming1 not   
creating1 energy4  ,when a ball is fired
 from a rifle1 most of the energy of the
 gunpowder is utilized in motion1 but   
some is dissipated in producing a flash 
and a report1 and in heat4 ,the energy  
of the gunpowder has been scattered1 but
 the sum of the various forms of energy 
is equal to the energy originally stored
 away in the powder4 ,the better the gun
 is1 the less will be the energy        
dissipated in smoke and heat and noise4 
,,chapter ,v  ,,food   #ee4 ,the ,body  
as a ,machine4 ,wholesome food and fresh

 air are necessary for a healthy body4  
,many housewives1 through ignorance1    
supply to their hard-working husbands   
and their growing sons and daughters    
food which satisfies the appetite1 but  
which does not give to the body the     
elements needed for daily work and      
growth4 ,some foods1 such as lettuce1   
cucumbers1 and watermelons1 make proper 
and satisfactory changes in diet1 but   
are not strength giving4 ,other foods1  
like peas and beans1 not only satisfy   
the appetite1 but supply to the body    
abundant nourishment4 ,many immigrants  
live cheaply and well with beans and    
bread as their main diet4  ,it is of    
vital importance that the relative value
 of different foods as heat producers be
 known definitely2 and just as the yard 
measures length and the pound measures  
weight the calorie is used to measure   
the amount of heat which a food is      
capable of furnishing to the body4 ,our 
bodies are human machines1 and1 like all
 other machines1 require fuel for their 

maintenance4 ,the fuel supplied to an   
engine is not all available for pulling 
the cars2 a large portion of the fuel is
 lost in smoke1 and another portion is  
wasted as ashes4 ,so it is with the fuel
 that runs the body4 ,the food we eat is
 not all available for nourishment1 much
 of it being as useless to us as are    
smoke and ashes to an engine4 ,the best 
foods are those which do the most for us
 with the least possible waste4  #ef4   
,fuel ,value4 ,by fuel value is meant   
the capacity foods have for yielding    
heat to the body4 ,the fuel value of the
 foods we eat daily is so important a   
factor in life that physicians1         
dietitians1 nurses1 and those having the
 care of institutional cooking acquaint 
themselves with the relative fuel values
 of practically all of the important    
food substances4 ,the life or death of a
 patient may be determined by the       
patient's diet1 and the working and     
earning capacity of a father depends    
largely upon his prosaic three meals4   

,an ounce of fat1 whether it is the fat 
of meat or the fat of olive oil or the  
fat of any other food1 produces in the  
body two and a quarter times as much    
heat as an ounce of starch4 ,of the     
vegetables1 beans provide the greatest  
nourishment at the least cost1 and to a 
large extent may be substituted for     
meat4 ,it is not uncommon to find an    
outdoor laborer consuming one pound of  
beans per day1 and taking meat only on  
high days and holidays4  ,illustration3 
,,fig4 #bf4--,the bomb calorimeter from 
which the fuel value of food can be     
estimated4  ,the fuel value of a food is
 determined by means of the bomb        
calorimeter 7,fig4 #bf74 ,the food      
substance is put into a chamber ,a and  
ignited1 and the heat of the burning    
substance raises the temperature of the 
water in the surrounding vessel4 ,if    
#ajjj grams of water are in the vessel1 
and the temperature of the water is     
raised #b ,c41 the number of calories   
produced by the substance would be      

#bjjj1 and the fuel value would be #bjjj
 calories4,a ,from this the fuel value  
of one quart or one pound of the        
substance can be determined1 and the    
food substance will be said to furnish  
the body with that number of heat units1
 providing all of the pound of food were
 properly digested4  ,footnote ,a3 ,as  
applied to food1 the calorie is greater 
than that used in the ordinary          
laboratory work1 being the amount of    
heat necessary to raise the temperature 
of #ajjj grams of water #a ,c41 rather  
than #a gram #a ,c4      ,,table        
,,showing ,,the ,,number ,,of ,,calories
 ,,furnished ,,by     ,,one ,,pound ,,of
 ,,various ,,foods                      
----------------------------------------
------------   ,,food                   
,,calories,,food         ,,calories     
----------------------------------------
------------   ,leg of lean mutton      
#gij;,carrots           #baj            
----------------------------------------
------------   ,rib of beef             

#aaej,lettuce            #ij            
----------------------------------------
------------   ,shad                    
#chj,onion             #bbe             
----------------------------------------
------------   ,chicken                 
#eje;,cucumber           #hj            
----------------------------------------
------------   ,apples                  
#bij;,almonds          #cjcj            
----------------------------------------
------------   ,bananas                 
#dfj,walnuts          #ccjf             
----------------------------------------
------------   ,prunes                  
#cgj,peanuts          #befj             
----------------------------------------
------------   ,watermelons             
#adj,oatmeal          #dfgc             
----------------------------------------
------------   ,lima beans              
#egj,rolled wheat     #dage             
----------------------------------------
------------   ,beets                   
#bae,macaroni         #affe             

----------------------------------------
------------  #eg4 ,varied ,diet4 ,the  
human body is a much more varied and    
complex machine than any ever devised by
 man2 personal peculiarities1 as well as
 fuel values1 influence very largely the
 diet of an individual4 ,strawberries   
are excluded from some diets because of 
a rash which is produced on the skin1   
pork is excluded from other diets for a 
like reason2 cauliflower is absolutely  
indigestible to some and is readily     
digested by others4 ,from practically   
every diet some foods must be excluded1 
no matter what the fuel value of the    
substance may be4  ,then1 too1 there are
 more uses for food than the production 
of heat4 ,teeth and bones and nails need
 a constant supply of mineral matter1   
and mineral matter is frequently found  
in greatest abundance in foods of low   
fuel value1 such as lettuce1 watercress1
 etc41 though practically all foods     
yield at least a small mineral          
constituent4 ,when fuel values alone are

 considered1 fruits have a low value1   
but because of the flavor they impart to
 other foods1 and because of the        
healthful influence they exercise in    
digestion1 they cannot be excluded from 
the diet4  ,care should be constantly   
exercised to provide substantial foods  
of high fuel value4 ,but the nutritive  
foods should be wisely supplemented by  
such foods as fruits1 whose real value  
is one of indirect rather then direct   
service4  #eh4 ,our ,bodies4 ,somewhat  
as a house is composed of a group of    
bricks1 or a sand heap of grains of     
sand1 the human body is composed of     
small divisions called cells4           
,ordinarily we cannot see these cells   
because of their minuteness1 but if we  
examine a piece of skin1 or a hair of   
the head1 or a tiny sliver of bone under
 the microscope1 we see that each of    
these is composed of a group of         
different cells4 ,a merchant1 watchful  
about the fineness of the wool which he 
is purchasing1 counts with his lens the 

number of threads to the inch2 a        
physician1 when he wishes1 can1 with the
 aid of the microscope1 examine the     
cells in a muscle1 or in a piece of fat1
 or in a nerve fiber4 ,not only is the  
human body composed of cells1 but so    
also are the bodies of all animals from 
the tiny gnat which annoys us1 and the  
fly which buzzes around us1 to the      
mammoth creatures of the tropics4 ,these
 cells do the work of the body1 the bone
 cells build up the skeleton1 the nail  
cells form the finger and toe nails1 the
 lung cells take care of breathing1 the 
muscle cells control motion1 and the    
brain cells are responsible for thought4
  #ei4 ,why we eat so ,much4 ,the cells 
of the body are constantly1 day by day1 
minute by minute1 breaking down and     
needing repair1 are constantly requiring
 replacement by new cells1 and1 in the  
case of the child1 are continually      
increasing in number4 ,the repair of an 
ordinary machine1 an engine1 for        
example1 is made at the expense of      

money1 but the repair and replacement of
 our human cell machinery are           
accomplished at the expense of food4    
,more than one third of all the food we 
eat goes to maintain the body cells1 and
 to keep them in good order4 ,it is for 
this reason that we consume a large     
quantity of food4 ,if all the food we   
eat were utilized for energy1 the       
housewife could cook less1 and the      
housefather could save money on grocer's
 and butcher's bills4 ,if you put a ton 
of coal in an engine1 its available     
energy is used to run the engine1 but if
 the engine were like the human body1   
one third of the ton would be used up by
 the engine in keeping walls1 shafts1   
wheels1 belts1 etc41 in order1 and only 
two thirds would go towards running the 
engine4 ,when an engine is not working1 
fuel is not consumed1 but the body      
requires food for mere existence1       
regardless of whether it does active    
work or not4 ,when we work1 the cells   
break down more quickly1 and the repair 

is greater than when we are at rest1 and
 hence there is need of a larger amount 
of food2 but whether we work or not1    
food is necessary4  #fj4 ,the ,different
 ,foods4 ,the body is very exacting in  
its demands1 requiring certain definite 
foods for the formation and maintenance 
of its cells1 and other foods1 equally  
definite1 but of different character1   
for heat2 our diet therefore must       
contain foods of high fuel value1 and   
likewise foods of cell-forming power4   
,although the foods which we eat are of 
widely different character1 such as     
fruits1 vegetables1 cereals1 oils1      
meats1 eggs1 milk1 cheese1 etc41 they   
can be put into three great classes3 the
 carbohydrates1 the fats1 and the       
proteids4  #fa4 ,the ,carbohydrates4    
,corn1 wheat1 rye1 in fact all cereals  
and grains1 potatoes1 and most          
vegetables are rich in carbohydrates2 as
 are also sugar1 molasses1 honey1 and   
maple sirup4 ,the foods of the first    
group are valuable because of the starch

 they contain2 for example1 corn starch1
 wheat starch1 potato starch4 ,the      
substances of the second group are      
valuable because of the sugar they      
contain2 sugar contains the maximum     
amount of carbohydrate4 ,in the sirups  
there is a considerable quantity of     
sugar1 while in some fruits it is       
present in more or less dilute form4    
,sweet peaches1 apples1 grapes1 contain 
a moderate amount of sugar2 watermelons1
 pears1 etc41 contain less4 ,most of our
 carbohydrates are of plant origin1     
being found in vegetables1 fruits1      
cereals1 and sirups4  ,carbohydrates1   
whether of the starch group or the sugar
 group1 are composed chiefly of three   
elements3 carbon1 hydrogen1 and oxygen2 
they are therefore combustible1 and are 
great energy producers4 ,on the other   
hand1 they are worthless for cell growth
 and repair1 and if we limited our diet 
to carbohydrates1 we should be like a   
man who had fuel but no engine capable  
of using it4  #fb4 ,the ,fats4 ,the     

best-known fats are butter1 lard1 olive 
oil1 and the fats of meats1 cheese1 and 
chocolate4 ,when we test fats for fuel  
values by means of a calorimeter 7,fig4 
#bf71 we find that they yield twice as  
much heat as the carbohydrates1 but that
 they burn out more quickly4 ,dwellers  
in cold climates must constantly eat    
large quantities of fatty foods if they 
are to keep their bodies warm and       
survive the extreme cold4 ,cod liver oil
 is an excellent food medicine1 and if  
taken in winter serves to warm the body 
and to protect it against the rigors of 
cold weather4 ,the average person avoids
 fatty foods in summer1 knowing from    
experience that rich foods make him warm
 and uncomfortable4 ,the harder we work 
and the colder the weather1 the more    
food of that kind do we require2 it is  
said that a lumberman doing heavy       
out-of-door work in cold climates needs 
three times as much food as a city      
clerk4 ,most of our fats1 like lard and 
butter1 are of animal origin2 some of   

them1 however1 like olive oil1 peanut   
butter1 and coconut oil1 are of plant   
origin4  ,illustration3 ,,fig4 #bg4--;a 
is the amount of fat necessary to make  
one calorie2 b is the amount of sugar or
 proteid necessary to make one calorie4 
#fc4 ,the ,proteids4 ,the proteids are  
the building foods1 furnishing muscle1  
bone1 skin cells1 etc41 and supplying   
blood and other bodily fluids4 ,the     
best-known proteids are white of egg1   
curd of milk1 and lean of fish and meat2
 peas and beans have an abundant supply 
of this substance1 and nuts are rich in 
it4 ,most of our proteids are of animal 
origin1 but some protein material is    
also found in the vegetable world4 ,this
 class of foods contains carbon1 oxygen1
 and hydrogen1 and in addition1 two     
substances not found in carbohydrates or
 fats--namely1 sulphur and nitrogen4    
,proteids always contain nitrogen1 and  
hence they are frequently spoken of as  
nitrogenous foods4 ,since the proteids  
contain all the elements found in the   

two other classes of foods1 they are    
able to contribute1 if necessary1 to the
 store of bodily energy2 but their main 
function is upbuilding1 and the diet    
should be chosen so that the proteids do
 not have a double task4  ,for an       
average man four ounces of dry proteid  
matter daily will suffice to keep the   
body cells in normal condition4  ,it has
 been estimated that #cjj1jjj1jjj blood 
cells alone need daily repair or        
renewal4 ,when we consider that the     
blood is but one part of the body1 and  
that all organs and fluids have         
corresponding requirements1 we realize  
how vast is the work to be done by the  
food which we eat4  #fd4 ,mistakes in   
,buying4 ,the body demands a daily      
ration of the three classes of food     
stuffs1 but it is for us to determine   
from what meats1 vegetables1 fruits1    
cereals1 etc41 this supply shall be     
obtained 7,figs4 #bh and #bi74          
,illustration3 ,,fig4 #bh4--,table of   
food values4  ,illustration3 ,,fig4     

#bi4--;,diagram showing the difference  
in the cost of three foods which give   
about the same amount of nutrition each4
  ,generally speaking1 meats are the    
most expensive foods we can purchase1   
and hence should be bought seldom and in
 small quantities4 ,their place can be  
taken by beans1 peas1 potatoes1 etc41   
and at less than a quarter of the cost4 
,the average ,american family eats meat 
three times a day1 while the average    
family of the more conservative and     
older countries rarely eats meat more   
than once a day4 ,the following tables  
indicate the financial loss arising from
 an unwise selection of foods3--        
,,food ,,consumed--,,one ,,week         
,,family ,no4 #a                        
,,family ,no4 #b                        
----------------------------------------
-------------------------- #bj loaves of
 bread          #a4jj #ae lb4 flour1    
bread            #aj to #ab lb4 loin    
steak              home made 7skim milk 
used7  4#de    or meat of similar cost  

#b4jj ,yeast1 shortening1 and           
#bj to #be lb4 rib roast                
skim milk                    4#aj    or 
similar meat           #d4dj #aj lb4    
steak 7round1 ,hamburger #d lb4         
high-priced cereal             and some 
loin7              #a4ej       breakfast
 food1 #bj     4#hj #aj lb4 other meats1
 boiling    ,cake and pastry purchased  
#c4jj    pieces1 rump roast1 etc4       
#a4jj #h lb4 butter1 #cj                
#b4dj  #e lb4 cheese1 #af               
4#hj ,tea1 coffee1 spices1 etc4     4#ge
  #e lb4 oatmeal 7bulk7           4#ae  
,mushrooms                     4#ge  #e 
lb4 beans                    4#be       
,celery                       #a4jj     
,home-made cake and pastry      #a4jj   
,oranges                      #b4jj  #f 
lb4 butter1 #cj             #a4hj       
,potatoes                      4#be  #c 
lb4 home-made shortening     4#be       
,miscellaneous canned goods   #b4jj     
,tea1 coffee1 and spices         4#dj   
,milk                          4#ej     

,apples                          4#ej   
,miscellaneous foods          #b4jj     
,prunes                          4#be #c
 doz4 eggs                   4#fj       
,potatoes                        4#be   
-------,milk                            
#a4jj                            #bc4de 
,miscellaneous foods            #a4jj   
#c doz4 eggs                    4#fj    
------                                  
#aa4cj                                  
----------------------------------------
---------------------------             
----------------------------------------
---------------------------  ,the tables
 show that one family spends over twice 
as much in the purchase of foods as the 
other family1 and yet the one whose food
 costs the less actually secures the    
larger amount of nutritive material and 
is better fed than the family where more
 money is expended4--,from ,human       
,foods1 ,snyder4  ,the ,source of the   
,different ,foods4 ,all of our food     
comes from either the plant world or the

 animal world4 ,broadly speaking1 plants
 furnish the carbohydrates1 that is1    
starch and sugar2 animals furnish the   
fats and proteids4 ,but although        
vegetable foods yield carbohydrates     
mainly1 some of them1 like beans and    
peas1 contain large quantities of       
protein and can be substituted for meat 
without disadvantage to the body4 ,other
 plant products1 such as nuts1 have fat 
as their most abundant food constituent4
 ,the peanut1 for example1 contains #dc 
of fat1 #cj of proteids1 and only #ag of
 carbohydrates2 the ,brazil nut has #fe 
of fat1 #ag of proteids1 and only #i of 
carbohydrates4 ,nuts make a good meat   
substitute1 and since they contain a    
fair amount of carbohydrates besides the
 fats and proteins1 they supply all of  
the essential food constituents and form
 a well-balanced food4     ,,chapter    
,,vi  ,,water   #fe4 ,destructive       
,action of ,water4 ,the action of water 
in stream and sea1 in springs and wells1
 is evident to all2 but the activity of 

ground water--that is1 rain water which 
sinks into the soil and remains         
there--is little known in general4 ,the 
real activity of ground water is due to 
its great solvent power2 every time we  
put sugar into tea or soap into water we
 are using water as a solvent4 ,when    
rain falls1 it dissolves substances     
floating in the atmosphere1 and when it 
sinks into the ground and becomes ground
 water1 it dissolves material out of the
 rock which it encounters 7,fig4 #cj74  
,we know that water contains some       
mineral matter1 because kettles in which
 water is boiled acquire in a short time
 a crust or coating on the inside4 ,this
 crust is due to the accumulation in the
 kettle of mineral matter which was in  
solution in the water1 but which was    
left behind when the water evaporated4  
7,see ,section #be47  ,illustration3    
,,fig4 #cj4--,showing how caves and     
holes are formed by the solvent action  
of water4  ,the amount of dissolved     
mineral matter present in some wells and

 springs is surprisingly great2 the     
famous springs of ,bath1 ,england1      
contain so much mineral matter in       
solution1 that a column #i feet in      
diameter and #adj feet high could be    
built out of the mineral matter         
contained in the water consumed yearly  
by the townspeople4  ,illustration3     
,,fig4 #ca4--,the work of water as a    
solvent4  ,rocks and minerals are not   
all equally soluble in water2 some are  
so little soluble that it is years      
before any change becomes apparent1 and 
the substances are said to be insoluble1
 yet in reality they are slowly         
dissolving4 ,other rocks1 like          
limestone1 are so readily soluble in    
water that from the small pores and     
cavities eaten out by the water1 there  
may develop in long centuries1 caves and
 caverns 7,fig4 #cj74 ,most rock1 like  
granite1 contains several substances1   
some of which are readily soluble and   
others of which are not readily soluble2
 in such rocks a peculiar appearance is 

presented1 due to the rapid             
disappearance of the soluble substance1 
and the persistence of the more         
resistant substance 7,fig4 #ca74  ,we   
see that the solvent power of water is  
constantly causing changes1 dissolving  
some mineral substances1 and leaving    
others practically untouched2 eating out
 crevices of various shapes and sizes1  
and by gradual solution through         
unnumbered years enlarging these        
crevices into wonderful caves1 such as  
the ,mammoth ,cave of ,kentucky4  #ff4  
,constructive ,action of ,water4 ,water 
does not always act as a destructive    
agent2 what it breaks down in one place 
it builds up in another4 ,it does this  
by means of precipitation4 ,water       
dissolves salt1 and also dissolves lead 
nitrate1 but if a salt solution is mixed
 with a lead nitrate solution1 a solid  
white substance is formed in the water  
7,fig4 #cb74 ,this formation of a solid 
substance from the mingling of two      
liquids is called precipitation2 such a 

process occurs daily in the rocks       
beneath the surface of the earth4 7,see 
,laboratory ,manual47  ,illustration3   
,,fig4 #cb4--;,from the mingling of two 
liquids a solid is sometimes formed4    
,suppose water from different sources   
enters a crack in a rock1 bringing      
different substances in solution2 then  
the mingling of the waters may cause    
precipitation1 and the solid thus formed
 will be deposited in the crack and fill
 it up4 ,hence1 while ground water tends
 to make rock porous and weak by        
dissolving out of it large quantities of
 mineral matter1 it also tends under    
other conditions to make it more compact
 because it deposits in cracks1         
crevices1 and pores the mineral matter  
precipitated from solution4  ,these two 
forces are constantly at work2 in some  
places the destructive action is more   
prominent1 in other places the          
constructive action2 but always the     
result is to change the character of the
 original substance4 ,when the mineral  

matter precipitated from the solutions  
is deposited in cracks1 veins are formed
 7,fig4 #cc71 which may consist of the  
ore of different metals1 such as gold1  
silver1 copper1 lead1 etc4 ,man is      
almost entirely dependent upon these    
veins for the supply of metal needed in 
the various industries1 because in the  
original condition of the rocks1 the    
metallic substances are so scattered    
that they cannot be profitably          
extracted4  ,illustration3 ,,fig4       
#cc4--,mineral matter precipitated from 
solution is deposited in crevices and   
forms veins4  ,naturally1 the veins     
themselves are not composed of one      
substance alone1 because several        
different precipitates may be formed4   
,but there is a decided grouping of     
valuable metals1 and these can then be  
readily separated by means of           
electricity4  #fg4 ,streams4 ,streams   
usually carry mud and sand along with   
them2 this is particularly well seen    
after a storm when rivers and brooks are

 muddy4 ,the puddles which collect at   
the foot of a hill after a storm are    
muddy because of the particles of soil  
gathered by the water as it runs down   
the hill4 ,the particles are not        
dissolved in the water1 but are held    
there in suspension1 as we call it      
technically4 ,the river made muddy after
 a storm by suspended particles usually 
becomes clear and transparent after it  
has traveled onward for miles1 because1 
as it travels1 the particles drop to the
 bottom and are deposited there4 ,hence1
 materials suspended in the water are   
borne along and deposited at various    
places 7,fig4 #cd74 ,the amount of      
deposition by large rivers is so great  
that in some places channels fill up and
 must be dredged annually1 and vessels  
are sometimes caught in the deposit and 
have to be towed away4  ,running water  
in the form of streams and rivers1 by   
carrying sand particles1 stones1 and    
rocks from high slopes and depositing   
them at lower levels1 wears away land at

 one place and builds it up at another1 
and never ceases in its work of changing
 the nature of the earth's surface      
7,fig4 #ce74  ,illustration3 ,,fig4     
#cd4--;,deposit left by running water4  
,illustration3 ,,fig4 #ce4--,water by   
its action constantly changes the       
character of the land4  #fh4 ,relation  
of ,water to ,human ,life4 ,water is one
 of the most essential of food          
materials1 and whether we drink much or 
little water1 we nevertheless get a     
great deal of it4 ,the larger part of   
many of our foods is composed of water2 
more than half of the weight of the meat
 we eat is made up of water2 and        
vegetables are often more than nine     
tenths water4 7,see ,laboratory         
,manual47 ,asparagus and tomatoes have  
over #ij per cent4 of water1 and most   
fruits are more than three fourths      
water2 even bread1 which contains as    
little water as any of our common foods1
 is about one third water 7,fig4 #cf74  
,illustration3 ,,fig4 #cf4--;,diagram of

 the composition of a loaf of bread and 
of a potato3 #a4 ash2 #b1 food2 #c1     
water4  ,without water1 solid food      
material1 although present in the body1 
would not be in a condition suitable for
 bodily use4 ,an abundant supply of     
water enables the food to be dissolved  
or suspended in it1 and in solution the 
food material is easily distributed to  
all parts of the body4  ,further1 water 
assists in the removal of the daily     
bodily wastes1 and thus rids the system 
of foul and poisonous substances4  ,the 
human body itself consists largely of   
water2 indeed1 about two thirds of our  
own weight is water4 ,the constant      
replenishing of this large quantity is  
necessary to life1 and a considerable   
amount of the necessary supply is       
furnished by foods1 particularly the    
fruits and vegetables4  ,but while the  
supply furnished by the daily food is   
considerable1 it is by no means         
sufficient1 and should be supplemented  
by good drinking water4  #fi4 ,water and

 its ,dangers4 ,our drinking water comes
 from far and near1 and as it moves from
 place to place1 it carries with it in  
solution or suspension anything which it
 can find1 whether it be animal1        
vegetable1 or mineral matter4 ,the power
 of water to gather up matter is so     
great that the average drinking water   
contains #bj to #ij grains of solid     
matter per gallon2 that is1 if a gallon 
of ordinary drinking water is left to   
evaporate1 a residue of #bj to #ij      
grains will be left4 7,see ,laboratory  
,manual47 ,as water runs down a hill    
slope 7,fig4 #cg71 it carries with it   
the filth gathered from acres of land2  
carries with it the refuse of stable1   
barn1 and kitchen2 and too often this   
impure surface water joins the streams  
which supply our cities4 ,lakes and     
rivers which furnish drinking water     
should be carefully protected from      
surface draining2 that is1 from water   
which has flowed over the land and has  
thus accumulated the waste of pasture   

and stable and1 it may be1 of dumping   
ground4  ,illustration3 ,,fig4          
#cg4--;,as water flows over the land1 it
 gathers filth and disease germs4  ,it  
is not necessary that water should be   
absolutely free from all foreign        
substances in order to be safe for daily
 use in drinking2 a limited amount of   
mineral matter is not injurious and may 
sometimes be really beneficial4 ,it is  
the presence of animal and vegetable    
matter that causes real danger1 and it  
is known that typhoid fever is due      
largely to such impurities present in   
the drinking water4  #gj4 ,methods of   
,purification4 ,water is improved by any
 of the following methods3--  7a7       
,boiling4 ,the heat of boiling destroys 
animal and vegetable germs4 ,hence water
 that has been boiled a few minutes is  
safe to use4 ,this is the most practical
 method of purification in the home1 and
 is very efficient4 ,the boiled water   
should be kept in clean1 corked bottles2
 otherwise foreign substances from the  

atmosphere renter the water1 and the    
advantage gained from boiling is lost4  
7b7 ,distillation4 ,by this method pure 
water is obtained1 but this method of   
purification cannot be used conveniently
 in the home 7,section #be74  7c7       
,filtration4 ,in filtration1 the water  
is forced through porcelain or other    
porous substances which allow the       
passage of water1 but which hold back   
the minute foreign particles suspended  
in the water4 7,see ,laboratory         
,manual47 ,the filters used in ordinary 
dwellings are of stone1 asbestos1 or    
charcoal4 ,they are often valueless1    
because they soon become choked and     
cannot be properly cleaned4  ,the       
filtration plants owned and operated by 
large cities are usually safe2 there is 
careful supervision of the filters1 and 
frequent and effective cleanings are    
made4 ,in many cities the filtration    
system is so good that private care of  
the water supply is unnecessary4  #ga4  
,the ,source of ,water4 ,in the         

beginning1 the earth was stored with    
water just as it was with metal1 rock1  
etc4 ,some of the water gradually took  
the form of rivers1 lakes1 streams1 and 
wells1 as now1 and it is this original  
supply of water which furnishes us all  
that we have to-day4 ,we quarry to      
obtain stone and marble for building1   
and we fashion the earth's treasures    
into forms of our own1 but we cannot    
create these things4 ,we bore into the  
ground and drill wells in order to      
obtain water from hidden sources2 we    
utilize rapidly flowing streams to drive
 the wheels of commerce1 but the total  
amount of water remains practically     
unchanged4  ,the water which flows on   
the earth is constantly changing its    
form2 the heat of the sun causes it to  
evaporate1 or to become vapor1 and to   
mingle with the atmosphere4 ,in time1   
the vapor cools1 condenses1 and falls as
 snow or rain2 the water which is thus  
returned to the earth feeds our rivers1 
lakes1 springs1 and wells1 and these in 

turn supply water to man4 ,when water   
falls upon a field1 it soaks into the   
ground1 or collects in puddles which    
slowly evaporate1 or it runs off and    
drains into small streams or into       
rivers4 ,that which soaks into the      
ground is the most valuable because it  
remains on the earth longest and is the 
purest4  ,illustration3 ,,fig4          
#ch4--;,how springs are formed4 ,a1     
porous layer2 ,b1 non-porous layer2 ,c1 
spring4  ,water which soaks into the    
ground moves slowly downward and after a
 longer or shorter journey1 meets with a
 non-porous layer of rock through which 
it cannot pass1 and which effectually   
hinders its downward passage4 ,in such  
regions1 there is an accumulation of    
water1 and a well dug there would have  
an abundant supply of water4 ,the       
non-porous layer is rarely level1 and   
hence the water whose vertical path is  
obstructed does not back up on the soil1
 but flows down hill parallel with the  
obstructing non-porous layer1 and in    

some distant region makes an outlet for 
itself1 forming a spring 7,fig4 #ch74   
,the streams originating in the springs 
flow through the land and eventually    
join larger streams or rivers2 from the 
surface of streams and rivers           
evaporation occurs1 the water once more 
becomes vapor and passes into the       
atmosphere1 where it is condensed and   
again falls to the earth4  ,water which 
has filtered through many feet of earth 
is far purer and safer than that which  
fell directly into the rivers1 or which 
ran off from the land and joined the    
surface streams without passing through 
the soil4  #gb4 ,the ,composition of    
,water4 ,water was long thought to be a 
simple substance1 but toward the end of 
the eighteenth century it was found to  
consist of two quite different          
substances1 oxygen 7,o7 and hydrogen    
7,h47  ,illustration3 ,,fig4 #ci4--,the 
decomposition of water4  ,if we send an 
electric current through water          
7acidulated to make it a good           

conductor71 as shown in ,figure #ci1 we 
see bubbles of gas rising from the end  
of the wire by which the current enters 
the water1 and other bubbles of gas     
rising from the end of the wire by which
 the current leaves the water4 ,these   
gases have evidently come from the water
 and are the substances of which it is  
composed1 because the water begins to   
disappear as the gases are formed4 ,if  
we place over each end of the wire an   
inverted jar filled with water1 the     
gases are easily collected4 ,the first  
thing we notice is that there is always 
twice as much of one gas as of the      
other2 that is1 water is composed of two
 substances1 one of which is always     
present in twice as large quantities as 
the other4  #gc4 ,the ,composition of   
,water4 ,on testing the gases into which
 water is broken up by an electric      
current1 we find them to be quite       
different4 ,one proves to be oxygen1 a  
substance with which we are already     
familiar4 ,the other gas1 hydrogen1 is  

new to us and is interesting as being   
the lightest known substance1 being even
 lighter than a feather4  ,an important 
fact about hydrogen is that in burning  
it gives as much heat as five times its 
weight of coal4 ,its flame is blue and  
almost invisible by daylight1 but       
intensely hot4 ,if fine platinum wire is
 placed in an ordinary gas flame1 it    
does not melt1 but if placed in a flame 
of burning hydrogen1 it melts very      
quickly4  #gd4 ,how to prepare          
,hydrogen4 ,there are many different    
methods of preparing hydrogen1 but the  
easiest laboratory method is to pour    
sulphuric acid1 or hydrochloric acid1 on
 zinc shavings and to collect in a      
bottle the gas which is given off4 ,this
 gas proves to be colorless1 tasteless1 
and odorless4 7,see ,laboratory         
,manual47     ,,chapter ,,vii  ,,air    
#ge4 ,the ,instability of the ,air4 ,we 
are usually not conscious of the air    
around us1 but sometimes we realize that
 the air is heavy1 while at other times 

we feel the bracing effect of the       
atmosphere4 ,we live in an ocean of air 
as truly as fish inhabit an ocean of    
water4 ,if you have ever been at the    
seashore you know that the ocean is     
never still for a second2 sometimes the 
waves surge back and forth in angry     
fury1 at other times the waves glide    
gently in to the shore and the surface  
is as smooth as glass2 but we know that 
there is perpetual motion of the water  
even when the ocean is in its gentlest  
moods4 ,generally our atmosphere is     
quiet1 and we are utterly unconscious of
 it2 at other times we are painfully    
aware of it1 because of its furious     
winds4 ,then again we are oppressed by  
it because of the vast quantity of vapor
 which it holds in the form of fog1 or  
mist4 ,the atmosphere around us is as   
restless and varying as is the water of 
the sea4 ,the air at the top of a high  
tower is very different from the air at 
the base of the tower4 ,not only does   
the atmosphere vary greatly at different

 altitudes1 but it varies at the same   
place from time to time1 at one period  
being heavy and raw1 at another being   
fresh and invigorating4  ,winds1        
temperature1 and humidity all have a    
share in determining atmospheric        
conditions1 and no one of these plays a 
small part4  #gf4 ,the ,character of the
 ,air4 ,the atmosphere which envelops us
 at all times extends more than fifty   
miles above us1 its height being far    
greater than the greatest depths of the 
sea4 ,this atmosphere varies from place 
to place2 at the sea level it is heavy1 
on the mountain top less heavy1 and far 
above the earth it is so light that it  
does not contain enough oxygen to permit
 man to live4 ,figure #dj illustrates by
 a pile of pillows how the pressure of  
the air varies from level to level4     
,illustration3 ,,fig4 #dj4--,to         
illustrate the decrease in pressure with
 height4  ,sea level is a low portion of
 the earth's surface1 hence at sea level
 there is a high column of air1 and a   

heavy air pressure4 ,as one passes from 
sea level to mountain top a gradual but 
steady decrease in the height of the air
 column occurs1 and hence a gradual but 
definite lessening of the air pressure4 
,illustration3 ,,fig4 #da4--,the water  
in the tube is at the same level as that
 in the glass4  #gg4 ,air ,pressure4 ,if
 an empty tube 7,fig4 #da7 is placed    
upright in water1 the water will not    
rise in the tube1 but if the tube is put
 in water and the air is then drawn out 
of the tube by the mouth1 the water will
 rise in the tube 7,fig4 #db74 ,this is 
what happens when we take lemonade      
through a straw4 ,when the air is       
withdrawn from the straw by the mouth1  
the pressure within the straw is        
reduced1 and the liquid is forced up the
 straw by the air pressure on the       
surface of the liquid in the glass4     
,even the ancient ,greeks and ,romans   
knew that water would rise in a tube    
when the pressure within the tube was   
reduced1 and hence they tried to obtain 

water from wells in this fashion1 but   
the water could never be raised higher  
than #cd feet4 ,let us see why water    
could rise #cd feet and no more4 ,if an 
empty pipe is placed in a cistern of    
water1 the water in the pipe does not   
rise above the level of the water in the
 cistern4 ,if1 however1 the pressure in 
the tube is removed1 the water in the   
tube will rise to a height of #cd feet  
approximately4 ,if now the air pressure 
in the tube is restored1 the water in   
the tube sinks again to the level of    
that in the cistern4 ,the air pressing  
on the liquid in the cistern tends to   
push some liquid up the tube1 but the   
air pressing on the water in the tube   
pushes downwards1 and tends to keep the 
liquid from rising1 and these two       
pressures balance each other4 ,when1    
however1 the pressure within the tube is
 reduced1 the liquid rises because of   
the unbalanced pressure which acts on   
the water in the cistern4               
,illustration3 ,,fig4 #db4--,water rises

 in the tube when the air is withdrawn4 
,illustration3 ,,fig4 #dc4--,the air    
supports a column of mercury #cj inches 
high4  ,the column of water which can be
 raised this way is approximately #cd   
feet1 sometimes a trifle more1 sometimes
 a trifle less4 ,if water were twice as 
heavy1 just half as high a column could 
be supported by the atmosphere4 ,mercury
 is about thirteen times as heavy as    
water and1 therefore1 the column of     
mercury supported by the atmosphere is  
about one thirteenth as high as the     
column of water supported by the        
atmosphere4 ,this can easily be         
demonstrated4 ,fill a glass tube about a
 yard long with mercury1 close the open 
end with a finger1 and quickly insert   
the end of the inverted tube in a dish  
of mercury 7,fig4 #dc74 ,when the finger
 is removed1 the mercury falls somewhat1
 leaving an empty space in the top of   
the tube4 ,if we measure the column in  
the tube1 we find its height is about   
one thirteenth of #cd feet or #cj       

inches1 exactly what we should expect4  
,since there is no air pressure within  
the tube1 the atmospheric pressure on   
the mercury in the dish is balanced     
solely by the mercury within the tube1  
that is1 by a column of mercury #cj     
inches high4 ,the shortness of the      
mercury column as compared with that of 
water makes the mercury more convenient 
for both experimental and practical     
purposes4 7,see ,laboratory ,manual47   
#gh4 ,the ,barometer4 ,since the        
pressure of the air changes from time to
 time1 the height of the mercury will   
change from day to day1 and hour to     
hour4 ,when the air pressure is heavy1  
the mercury will tend to be high2 when  
the air pressure is low1 the mercury    
will show a shorter column2 and by      
reading the level of the mercury one can
 learn the pressure of the atmosphere4  
,if a glass tube and dish of mercury are
 attached to a board and the dish of    
mercury is inclosed in a case for       
protection from moisture and dirt1 and  

further if a scale of inches or         
centimeters is made on the upper portion
 of the board1 we have a mercurial      
barometer 7,fig4 #dd74  ,illustration3  
,,fig4 #dd4--;,a simple barometer4  ,if 
the barometer is taken to the mountain  
top1 the column of mercury falls        
gradually during the ascent1 showing    
that as one ascends1 the pressure       
decreases in agreement with the         
statement in ,section #gf4 ,observations
 similar to these were made by          
,torricelli as early as the sixteenth   
century4 ,taking a barometric reading   
consists in measuring the height of the 
mercury column4  #gi4 ,a ,portable      
,barometer4 ,the mercury barometer is   
large and inconvenient to carry from    
place to place1 and a more portable form
 has been devised1 known as the aneroid 
barometer 7,fig4 #de74 ,this form of    
barometer is extremely sensitive2       
indeed1 it is so delicate that it shows 
the slight difference between the       
pressure at the table top and the       

pressure at the floor level1 whereas the
 mercury barometer would indicate only a
 much greater variation in atmospheric  
pressure4 ,the aneroid barometers are   
frequently made no larger than a watch  
and can be carried conveniently in the  
pocket1 but they get out of order easily
 and must be frequently readjusted4 ,the
 aneroid barometer is an air-tight box  
whose top is made of a thin metallic    
disk which bends inward or outward      
according to the pressure of the        
atmosphere4 ,if the atmospheric pressure
 increases1 the thin disk is pushed     
slightly inward2 if1 on the other hand1 
the atmospheric pressure decreases1 the 
pressure on the metallic disk decreases 
and the disk is not pressed so far      
inward4 ,the motion of the disk is      
small1 and it would be impossible to    
calculate changes in atmospheric        
pressure from the motion of the disk1   
without some mechanical device to make  
the slight changes in motion            
perceptible4  ,illustration3 ,,fig4     

#de4--;,aneroid barometer4  ,in order to
 magnify the slight changes in the      
position of the disk1 the thin face is  
connected with a system of levers1 or   
wheels1 which multiplies the changes in 
motion and communicates them to a       
pointer which moves around a graduated  
circular face4 ,in ,figure #de the real 
barometer is scarcely visible1 being    
securely inclosed in a metal case for   
protection2 the principle1 however1 can 
be understood by reference to ,figure   
#df4  ,illustration3 ,,fig4             
#df4--,principle of the aneroid         
barometer4  #hj4 ,the ,weight of the    
,air4 ,we have seen that the pressure of
 the atmosphere at any point is due to  
the weight of the air column which      
stretches from that point far up into   
the sky above4 ,this weight varies      
slightly from time to time and from     
place to place1 but it is equal to about
 #ae pounds to the square inch as shown 
by actual measurement4 ,it comes to us  
as a surprise sometimes that air        

actually has weight2 for example1 a mass
 of #ab cubic feet of air at average    
pressure weighs #a pound1 and the air in
 a large assembly hall weighs more than 
#a ton4  ,we are practically never      
conscious of this really enormous       
pressure of the atmosphere1 which is    
exerted over every inch of our bodies1  
because the pressure is exerted equally 
over the outside and the inside of our  
bodies2 the cells and tissues of our    
bodies containing gases under           
atmospheric pressure4 ,if1 however1 the 
finger is placed over the open end of a 
tube and the air is sucked out of the   
tube by the mouth1 the flesh of the     
finger bulges into the tube because the 
pressure within the finger is no longer 
equalized by the usual atmospheric      
pressure 7,fig4 #dg74  ,illustration3   
,,fig4 #dg4--,the flesh bulges out4     
,aronauts have never ascended much      
higher than #g miles2 at that height the
 barometer stands at #g inches instead  
of at #cj inches1 and the internal      

pressure in cells and tissues is not    
balanced by an equal external pressure4 
,the unequalized internal pressure      
forces the blood to the surface of the  
body and causes rupture of blood vessels
 and other physical difficulties4  #ha4 
,use of the ,barometer4 ,changes in air 
pressure are very closely connected with
 changes in the weather4 ,the barometer 
does not directly foretell the weather1 
but a low or falling pressure1          
accompanied by a simultaneous fall of   
the mercury1 usually precedes foul      
weather1 while a rising pressure1       
accompanied by a simultaneous rise in   
the mercury1 usually precedes fair      
weather4 ,the barometer is not an       
infallible prophet1 but it is of great  
assistance in predicting the general    
trend of the weather4 ,there are certain
 changes in the barometer which follow  
no known laws1 and which allow of no    
safe predictions1 but on the other hand1
 general future conditions for a few    
days ahead can be fairly accurately     

determined4 ,figure #dh shows a         
barograph or self-registering barometer 
which automatically registers air       
pressure4  ,illustration3 ,,fig4        
#dh4--;,barograph4  ,seaport towns in   
particular1 but all cities1 large or    
small1 and villages too1 are on request 
notified by the ,united ,states ,weather
 ,bureau ten hours or more in advance1  
of probable weather conditions1 and in  
this way precautions are taken which    
annually save millions of dollars and   
hundreds of lives4  ,i recollect a      
summer spent on a ,new ,hampshire farm1 
and know that an old farmer started his 
farm hands haying by moonlight at two   
o'clock in the morning1 because the     
,special ,farmer's ,weather ,forecast of
 the preceding evening had predicted    
rain for the following day4 ,his        
reliance on the weather report was not  
misplaced1 since the storm came with    
full force at noon4 ,sailing vessels1   
yachts1 and fishing dories remain within
 reach of port if the barometer         

foretells storms4  ,illustration3 ,,fig4
 #di4--;,isotherms4  #hb4 ,isobaric and 
,isothermal ,lines4 ,if a line were     
drawn through all points on the surface 
of the earth having an equal barometric 
pressure at the same time1 such a line  
would be called an isobar4 ,for example1
 if the height of barometers in         
different localities is observed at     
exactly the same time1 and if all the   
cities and towns which have the same    
pressure are connected by a line1 the   
curved lines will be called isobars4 ,by
 the aid of these lines the barometric  
conditions over a large area can be     
studied4 ,the ,weather ,bureau at       
,washington relies greatly on these     
isobars for statements concerning local 
and distant weather forecasts1 any shift
 in isobaric lines showing change in    
atmospheric pressure4  ,if a line is    
drawn through all points on the surface 
of the earth having the same temperature
 at the same instant1 such a line is    
called an isotherm 7,fig4 #di74  #hc4   

,weather ,maps4 ,scattered over the     
,united ,states are about #abe          
,government ,weather ,stations1 at each 
of which three times a day1 at the same 
instant1 accurate observations of the   
weather are made4 ,these observations1  
which consist of the reading of         
barometer and thermometer1 the          
determination of the velocity and       
direction of the wind1 the determination
 of the humidity and of the amount of   
rain or snow1 are telegraphed to the    
chief weather official at ,washington4  
,from the reports of wind storms1       
excessive rainfall1 hot waves1 clearing 
weather1 etc41 and their rate of travel1
 the chief officials predict where the  
storms1 etc41 will be at a definite     
future time4 ,in the ,united ,states1   
the general movement of weather         
conditions1 as indicated by the         
barometer1 is from west to east1 and if 
a certain weather condition prevails in 
the west1 it is probable that it will   
advance eastward1 although with decided 

modifications4 ,so many influences      
modify atmospheric conditions that      
unfailing predictions are impossible1   
but the ,weather ,bureau predictions    
prove true in about eight cases out of  
ten4  ,the reports made out at          
,washington are telegraphed on request  
to cities in this country1 and are      
frequently published in the daily       
papers1 along with the forecast of the  
local office4 ,a careful study of these 
reports enables one to forecast to some 
extent the probable weather conditions  
of the day4  ,the first impression of a 
weather map 7,fig4 #ej7 with its various
 lines and signals is apt to be one of  
confusion1 and the temptation comes to  
abandon the task of finding an          
underlying plan of the weather4 ,if one 
will bear in mind a few simple rules1   
the complexity of the weather map will  
disappear and a glance at the map will  
give one information concerning general 
weather conditions just as a glance at  
the thermometer in the morning will give

 some indication of the probable        
temperature of the day4 7,see           
,laboratory ,manual47  ,illustration3   
,,fig4 #ej4 weather ,map  ,on the       
weather map solid lines represent       
isobars and dotted lines represent      
isotherms4 ,the direction of the wind at
 any point is indicated by an arrow     
which flies with the wind2 and the state
 of the weather--clear1 partly cloudy1  
cloudy1 rain1 snow1 etc4--is indicated  
by symbols4  #hd4 ,components of the    
,air4 ,the best known constituent of the
 air is oxygen1 already familiar to us  
as the feeder of the fire without and   
within the body4 ,almost one fifth of   
the air which envelops us is made up of 
the life-giving oxygen4 ,this supply of 
oxygen in the air is constantly being   
used up by breathing animals and glowing
 fires1 and unless there were some      
constant source of additional supply1   
the quantity of oxygen in the air would 
soon become insufficient to support     
animal life4 ,the unfailing constant    

source of atmospheric oxygen is plant   
life 7,section #dh74 ,the leaves of     
plants absorb carbon dioxide from the   
air1 and break it up into oxygen and    
carbon4 ,the plant makes use of the     
carbon but it rejects the oxygen1 which 
passes back into the atmosphere through 
the pores of the leaves4  ,although     
oxygen constitutes only one fifth of the
 atmosphere1 it is one of the most      
abundant and widely scattered of all    
substances4 ,almost the whole earth1    
whether it be rich loam1 barren clay1 or
 granite boulder1 contains oxygen in    
some form or other2 that is1 in         
combination with other substances4 ,but 
nowhere1 except in the air around us1 do
 we find oxygen free and uncombined with
 other substances4  ,a less familiar but
 more abundant constituent of the       
atmosphere is the nitrogen4 ,almost four
 fifths of the air around us is made up 
of nitrogen4 ,if the atmosphere were    
composed of oxygen alone1 the merest    
flicker of a match would set the whole  

world ablaze4 ,the fact that the oxygen 
of the air is diluted as it were with so
 large a proportion of nitrogen1        
prevents fires from sweeping over the   
world and destroying everything in their
 path4 ,nitrogen does not support       
combustion1 and a burning match placed  
in a corked bottle goes out as soon as  
it has used up the oxygen in the bottle4
 ,the nitrogen in the bottle1 not only  
does not assist the burning of the      
match1 but it acts as a damper to the   
burning4  ,free nitrogen1 like oxygen1  
is a colorless1 odorless gas4 ,it is not
 poisonous2 but one would die if        
surrounded by nitrogen alone1 just as   
one would die if surrounded by water4   
,the vast supply of nitrogen in the     
atmosphere would be useless if the      
smaller amount of oxygen were not       
present to keep the body alive4         
,nitrogen is so important a factor in   
daily life that an entire chapter will  
be devoted to it later4  ,another       
constituent of the air with which we are

 familiar is carbon dioxide4 ,in pure   
air1 carbon dioxide is present in very  
small proportion1 being continually     
taken from the air by plants in the     
manufacture of their food4  ,various    
other substances are present in the air 
in very minute proportions1 but of all  
the substances in the air1 oxygen1      
nitrogen1 and carbon dioxide are the    
most important4     ,,chapter ,,viii    
,,general ,,properties ,,of ,,gases     
#he4 ,bicycle ,tires4 ,we know very well
 that we cannot put more than a certain 
amount of water in a tube1 but we know  
equally well that the amount of air     
which can be pumped into a bicycle or   
automobile tire depends largely upon our
 muscular energy4 ,a gallon of water    
remains a gallon of water and requires a
 perfectly definite amount of space1 but
 air can be compressed and compressed1  
and made to occupy less and less space4 
,while it is true that air is easily    
compressed1 it is also true that air is 
elastic and capable of very rapid and   

easy expansion4 ,if a puncture occurs in
 a tire1 the compressed air escapes very
 quickly2 that is1 the compressed air   
within the tube has taken the first     
opportunity offered for expansion4      
,illustration3 ,,fig4 #ea4--;,by        
squeezing the bulb1 air is forced out of
 the nozzle4  ,the fact that air is     
elastic has added materially to the     
comfort of the world4 ,transportation by
 bicycles and automobiles has been      
greatly facilitated by the use of air   
tires4 ,in many hospitals1 air          
mattresses are used in place of hair1   
feather1 or cotton mattresses1 and in   
this way the bed is kept fresher and    
cleaner1 and can be moved with less     
danger of discomfort to the patient4    
,every time we squeeze the bulb of an   
atomizer1 we force compressed or        
condensed air through the atomizer1 and 
the condensed air pushes the liquid out 
of the nozzle 7,fig4 #ea74 ,thus we see 
that in the necessities and conveniences
 of life compressed air plays an        

important part4  #hf4 ,the ,danger of   
,compression4 ,air under ordinary       
atmospheric conditions exerts a pressure
 of #ae pounds to the square inch4 ,if1 
now1 large quantities of air are        
compressed into a small space1 the      
pressure exerted becomes correspondingly
 greater4 ,if too much air is blown into
 a toy balloon1 the balloon bursts      
because it cannot support the great     
pressure exerted by the compressed air  
within4 ,what is true of air is true of 
all gases4 ,dangerous boiler explosions 
have occurred because the boiler walls  
were not strong enough to withstand the 
pressure of the steam 7which is water in
 the form of gas74 ,the pressure within 
the boilers of engines is frequently    
several hundred pounds to the square    
inch1 and such a pressure needs a strong
 boiler4  #hg4 ,how ,pressure is        
,measured in ,buildings4 ,in the        
preceding ,section we saw that undue    
pressure of a gas may cause explosion4  
,it is important1 therefore1 that       

authorities keep strict watch on gases  
confined within pipes and reservoirs1   
never allowing the pressure to exceed   
that which the walls of the reservoir   
will safely bear4  ,illustration3 ,,fig4
 #eb4--;,a pressure gauge4  ,pressure in
 a gas pipe may be measured by a simple 
instrument called the pressure gauge3   
,the gauge consists of a bent glass tube
 containing mercury1 and so made that   
one end can be fitted to a gas jet      
7,fig4 #eb74 ,when the gas cock is      
closed1 the mercury stands at the same  
level in both arms1 but when the cock is
 opened1 the gas whose pressure is being
 measured forces the mercury up the     
opposite arm4 ,if the pressure of the   
gas is small1 the mercury changes its   
level but very little4 ,it is clear that
 the height of a column of mercury is a 
measure of the gas pressure4 ,now it is 
known that one cubic inch of mercury    
weighs about half a pound4 ,hence a     
column of mercury one inch high         
indicates a pressure of about one half  

pound to the square inch2 a column two  
inches high indicates a pressure of     
about one pound to the square inch1 and 
so on4  ,this is a very convenient way  
to measure the pressure of the          
illuminating gas in our homes and       
offices4 ,the gauge is attached to the  
gas burner and the pressure is read by  
means of a scale attached to the gauge4 
7,see ,laboratory ,manual47  ,in order  
to have satisfactory illumination1 the  
pressure must be strong enough to give a
 steady1 broad flame4 ,if the flame from
 any gas jet is flickering and weak1 it 
is usually an indication of insufficient
 pressure and the gas company should    
investigate conditions and see to it    
that the consumer receives his proper   
value4  #hg4 ,the ,gas ,meter4 ,most    
householders are deeply interested in   
the actual amount of gas which they     
consume 7gas is charged for according to
 the number of cubic feet used71 and    
therefore they should be able to read   
the gas meter which indicates their     

consumption of gas4 ,such gas meters are
 furnished by the companies1 and can be 
read easily4  ,illustration3 ,,fig4     
#ec4--,the gas meter indicates the      
number of cubic feet of gas consumed4   
,the instrument itself is somewhat      
complex4 ,it will suffice to say that   
within the meter box are thin disks     
which are moved by the stream of gas    
that passes them4 ,this movement of the 
disks is recorded by clockwork devices  
on a dial face4 ,in this way1 the number
 of cubic feet of gas which pass through
 the meter is automatically registered4 
#hi4 ,the ,relation between ,pressure   
and ,volume4 ,it was long known that as 
the pressure of a gas increases1 that   
is1 as it becomes compressed1 its volume
 decreases1 but ,robert ,boyle was the  
first to determine the exact relation   
between the volume and the pressure of a
 gas4 ,he did this in a very simple     
manner4  ,pour mercury into a ,u-shaped 
tube until the level of the mercury in  
the closed end of the tube is the same  

as the level in the open end4 ,the air  
in the long arm is pressing upon the    
mercury in that arm1 and is tending to  
force it up the short arm4 ,the air in  
the short closed arm is pressing down   
upon the mercury in that arm and tending
 to send it up the long arm4 ,since the 
mercury is at the same level in the two 
arms1 the pressure in the long arm must 
be equal to the pressure in the short   
arm4 ,but the long arm is open1 and the 
pressure in that arm is the pressure of 
the atmosphere4 ,therefore the pressure 
in the short arm must be one atmosphere4
 ,measure the distance bc between the   
top of the mercury and the closed end of
 the tube4  ,illustration3 ,,figs4 #ed1 
#ee4--;,as the pressure on the gas      
increases1 its volume decreases4  ,pour 
more mercury into the open end of the   
tube1 and as the mercury rises higher   
and higher in the long arm1 note        
carefully the decrease in the volume of 
the air in the short arm4 ,pour mercury 
into the tube until the difference in   

level bd is just equal to the barometric
 height1 approximately #cb inches4 ,the 
pressure of the air in the closed end   
now supports the pressure of one        
atmosphere1 and in addition1 a column of
 mercury equal to another atmosphere4   
,if now the air column in the closed end
 is measured1 its volume will be only   
one half of its former volume4 ,by      
doubling the pressure we have reduced   
the volume one half4 ,similarly1 if the 
pressure is increased threefold1 the    
volume will be reduced to one third of  
the original volume4  #ij4 ,heat due to 
,compression4 ,we saw in ,section #hi   
that whenever the pressure exerted upon 
a gas is increased1 the volume of the   
gas is decreased2 and that whenever the 
pressure upon a gas is decreased1 the   
volume of the gas is increased4 ,if the 
pressure is changed very slowly1 the    
change in the temperature of the gas is 
imperceptible2 if1 however1 the pressure
 is removed suddenly1 the temperature   
falls rapidly1 or if the pressure is    

applied suddenly1 the temperature rises 
rapidly4 ,when bicycle tires are being  
inflated1 the pump becomes hot because  
of the compression of the air4  ,the    
amount of heat resulting from           
compression is surprisingly large2 for  
example1 if a mass of gas at #j ,c4 is  
suddenly compressed to one half its     
original volume1 its temperature rises  
#hg ,c4  #ia4 ,cooling by ,expansion4   
,if a gas expands suddenly1 its         
temperature falls2 for example1 if a    
mass of gas at #hg ,c4 is allowed to    
expand rapidly to twice its original    
volume1 its temperature falls to #j ,c4 
,if the compressed air of a bicycle tire
 is allowed to expand and a sensitive   
thermometer is held in the path of the  
escaping air1 the thermometer will show 
a decided drop in temperature4  ,the low
 temperature obtained by the expansion  
of air or other gases is utilized       
commercially on a large scale4 ,by means
 of powerful pistons air is compressed  
to one third or one fourth its original 

volume1 is passed through a coil of pipe
 surrounded with cold water1 and is then
 allowed to escape into large           
refrigerating vaults1 which thereby have
 their temperatures noticeably lowered1 
and can be used for the permanent       
storage of meats1 fruits1 and other     
perishable material4 ,in summer1 when   
the atmospheric temperature is high1 the
 storage and preservation of foods is of
 vital importance to factories and cold 
storage houses1 and but for the low     
temperature obtainable by the expansion 
of compressed gases1 much of our food   
supply would be lost to use4  #ib4      
,unexpected ,transformations4 ,if the   
pressure on a gas is greatly increased1 
a sudden transformation sometimes occurs
 and the gas becomes a liquid4 ,then1 if
 the pressure is reduced1 a second      
transformation occurs1 and the liquid   
evaporates or returns to its original   
form as a gas4  ,in ,section #bc we saw 
that a fall of temperature caused water 
vapor to condense or liquefy4 ,if       

temperature alone were considered1 most 
gases could not be liquefied1 because   
the temperature at which the average gas
 liquefies is so low as to be out of the
 range of possibility2 it has been      
calculated1 for example1 that a         
temperature of #beb ,c4 below zero would
 have to be obtained in order to liquefy
 hydrogen4  ,some gases can be easily   
transformed into liquids by pressure    
alone1 some gases can be easily         
transformed into liquids by cooling     
alone2 on the other hand1 many gases are
 so difficult to liquefy that both      
pressure and low temperature are needed 
to produce the desired result4 ,if a gas
 is cooled and compressed at the same   
time1 liquefaction occurs much more     
surely and easily than though either    
factor alone were depended upon4 ,the   
air which surrounds us1 and of whose    
existence we are scarcely aware1 can be 
reduced to the form of a liquid1 but the
 pressure exerted upon the portion to be
 liquefied must be thirty-nine times as 

great as the atmospheric pressure1 and  
the temperature must have been reduced  
to a very low point4  #ic4 ,artificial  
,ice4 ,ammonia gas is liquefied by      
strong pressure and low temperature and 
is then allowed to flow into pipes which
 run through tanks containing salt      
water4 ,the reduction of pressure causes
 the liquid to evaporate or turn to a   
gas1 and the fall of temperature which  
always accompanies evaporation means a  
lowering of the temperature of the salt 
water to #af or #ah below zero4 ,but    
immersed in the salt water are molds    
containing pure water1 and since the    
freezing point of water is #j ,c1 the   
water in the molds freezes and can be   
drawn from the mold as solid cakes of   
ice4  ,illustration3 ,,fig4             
#ef4--;,apparatus for making artificial 
ice4  ,ammonia gas is driven by the pump
 ,c into the coil ,d 7,fig4 #ef7 under a
 pressure strong enough to liquefy it1  
the heat generated by this compression  
being carried off by cold water which   

constantly circulates through ,b4 ,the  
liquid ammonia flows through the        
regulating valve ,v into the coil ,e1 in
 which the pressure is kept low by the  
pump ,c4 ,the accompanying expansion    
reduces the temperature to a very low   
degree1 and the brine which circulates  
around the coil ,e acquires a           
temperature below the freezing point of 
pure water4 ,the cold brine passes from 
,a to a tank in which are immersed cans 
filled with water1 and within a short   
time the water in the cans is frozen    
into solid cakes of ice4     ,,chapter  
,,ix  ,,invisible ,,objects   #id4 ,very
 ,small ,objects4 ,we saw in ,section   
#hd that gases have a tendency to       
expand1 but that they can be compressed 
by the application of force4 ,this      
observation has led scientists to       
suppose that substances are composed of 
very minute particles called molecules1 
separated by small spaces called pores2 
and that when a gas is condensed1 the   
pores become smaller1 and that when a   

gas expands1 the pores become larger4   
,the fact that certain substances are   
soluble1 like sugar in water1 shows that
 the molecules of sugar find a lodging  
place in the spaces or pores between the
 molecules of water1 in much the same   
way that pebbles find lodgment in the   
chinks of the coal in a coal scuttle4   
,an indefinite quantity of sugar cannot 
be dissolved in a given quantity of     
liquid1 because after a certain amount  
of sugar has been dissolved all the     
pores become filled1 and there is no    
available molecular space4 ,the         
remainder of the sugar settles at the   
bottom of the vessel1 and cannot be     
dissolved by any amount of stirring4    
,if a piece of potassium permanganate   
about the size of a grain of sand is put
 into a quart of water1 the solid       
disappears and the water becomes a deep 
rich red4 ,the solid evidently has      
dissolved and has broken up into minute 
particles which are too small to be     
seen1 but which have scattered          

themselves and lodged in the pores of   
the water1 thus giving the water its    
rich color4  ,there is no visible proof 
of the existence of molecules and       
molecular spaces1 because not only are  
our eyes unable to see them directly1   
but even the most powerful microscope   
cannot make them visible to us4 ,they   
are so small that if one thousand of    
them were laid side by side1 they would 
make a speck too small to be seen by the
 eye and too small to be visible under  
the most powerful microscope4  ,we      
cannot see molecules or molecular pores1
 but the phenomena of compression and   
expansion1 solubility and other equally 
convincing facts1 have led us to        
conclude that all substances are        
composed of very minute particles or    
molecules separated by spaces called    
pores4  #ie4 ,journeys ,made by         
,molecules4 ,if a gas jet is turned on  
and not lighted1 an odor of gas soon    
becomes perceptible1 not only throughout
 the room1 but in adjacent halls and    

even in distant rooms4 ,an uncorked     
bottle of cologne scents an entire room1
 the odor of a rose or violet permeates 
the atmosphere near and far4 ,these     
simple everyday occurrences seem to show
 that the molecules of a gas must be in 
a state of continual and rapid motion4  
,in the case of the cologne1 some       
molecules must have escaped from the    
liquid by the process of evaporation and
 traveled through the air to the nose4  
,we know that the molecules of a liquid 
are in motion and are continually       
passing into the air because in time the
 vessel becomes empty4 ,the only way in 
which this could happen would be for the
 molecules of the liquid to pass from   
the liquid into the surrounding medium2 
but this is really saying that the      
molecules are in motion4  ,from these   
phenomena and others it is reasonably   
clear that substances are composed of   
molecules1 and that molecules are not   
inert1 quiet particles1 but that they   
are in incessant motion1 moving rapidly 

hither and thither1 sometimes traveling 
far1 sometimes near4 ,even the log of   
wood which lies heavy and motionless on 
our woodpile is made up of countless    
billions of molecules each in rapid     
incessant motion4 ,the molecules of     
solid bodies cannot escape so readily as
 those of liquids and gases1 and do not 
travel far4 ,the log lies year after    
year in an apparently motionless        
condition1 but if one's eyes were keen  
enough1 the molecules would be seen     
moving among themselves1 even though    
they cannot escape into the surrounding 
medium and make long journeys as do the 
molecules of liquids and gases4  #if4   
,the ,companions of ,molecules4 ,common 
sense tells us that a molecule of water 
is not the same as a molecule of        
vinegar2 the molecules of each are      
extremely small and in rapid motion1 but
 they differ essentially1 otherwise one 
substance would be like every other     
substance4 ,what is it that makes a     
molecule of water differ from a molecule

 of vinegar1 and each differ from all   
other molecules8 ,strange to say1 a     
molecule is not a simple object1 but is 
quite complex1 being composed of one or 
more smaller particles1 called atoms1   
and the number and kind of atoms in a   
molecule determine the type of the      
molecule1 and the type of the molecule  
determines the substance4 ,for example1 
a glass of water is composed of untold  
millions of molecules1 and each molecule
 is a company of three still smaller    
particles1 one of which is called the   
oxygen atom and two of which are alike  
in every particular and are called      
hydrogen atoms4  #ig4 ,simple           
,molecules4 ,generally molecules are    
composed of atoms which are different in
 kind4 ,for example1 the molecule of    
water has two different atoms1 the      
oxygen atom and the hydrogen atoms2     
alcohol has three different kinds of    
atoms1 oxygen1 hydrogen1 and carbon4    
,sometimes1 however1 molecules are      
composed of a group of atoms all of     

which are alike4 ,now there are but     
seventy or eighty different kinds of    
atoms1 and hence there can be but       
seventy or eighty different substances  
whose molecules are composed of atoms   
which are alike4 ,when the atoms        
comprising a molecule are all alike1 the
 substance is called an element1 and is 
said to be a simple substance4          
,throughout the length and breadth of   
this vast world of ours there are only  
about eighty known elements4 ,an element
 is the simplest substance conceivable1 
because it has not been separated into  
anything simpler4 ,water is a compound  
substance4 ,it can be separated into    
oxygen and hydrogen4  ,gold1 silver1 and
 lead are examples of elements1 and     
water1 alcohol1 cider1 sand1 and marble 
are complex substances1 or compounds1 as
 we are apt to call them4 ,everything1  
no matter what its size or shape or     
character1 is formed from the various   
combinations into molecules of a few    
simple atoms1 of which there exist about

 eighty known different kinds4 ,but few 
of the eighty known elements play an    
important part in our everyday life4    
,the elements in which we are most      
interested are given in the following   
table1 and the symbols by which they are
 known are placed in columns to the     
right3    ,oxygen       ,o    ,copper   
,cu     ,phosphorus ,p     ,hydrogen    
,h    ,iodine   ,i      ,potassium  ,k  
,carbon       ,c    ,iron     ,fe       
,silver     ,ag    ,aluminium ,al ,lead 
,pb       ,sodium ,na                   
,calcium      ,ca   ,nickel   ,ni       
,sulphur    ,s     ,chlorine     ,cl    
,nitrogen ,n      ,tin        ,sn   ,we 
have seen in an earlier experiment that 
twice as much hydrogen as oxygen can be 
obtained from water4 ,two atoms of the  
element hydrogen unite with one atom of 
the element oxygen to make one molecule 
of water4 ,in symbols we express this   
,h#b,o4 ,a group of symbols1 such as    
this1 expressing a molecule of a        
compound is called a formula4 ,na,cl is 

the formula for sodium chloride1 which  
is the chemical name of common salt4    
,,chapter ,x  ,,light   #ih4 ,what      
,light ,does for ,us4 ,heat keeps us    
warm1 cooks our food1 drives our        
engines1 and in a thousand ways makes   
life comfortable and pleasant1 but what 
should we do without light8 ,how many of
 us could be happy even though warm and 
well fed if we were forced to live in   
the dark where the sunbeams never       
flickered1 where the shadows never stole
 across the floor1 and where the soft   
twilight could not tell us that the day 
was done8 ,heat and light are the two   
most important physical factors in life2
 we cannot say which is the more        
necessary1 because in the extreme cold  
or arctic regions man cannot live1 and  
in the dark places where the light never
 penetrates man sickens and dies4 ,both 
heat and light are essential to life1   
and each has its own part to play in the
 varied existence of man and plant and  
animal4  ,light enables us to see the   

world around us1 makes the beautiful    
colors of the trees and flowers1 enables
 us to read1 is essential to the taking 
of photographs1 gives us our moving     
pictures and our magic lanterns1        
produces the exquisite tints of         
stained-glass windows1 and brings us the
 joy of the rainbow4 ,we do not always  
realize that light is beneficial1       
because sometimes it fades our clothing 
and our carpets1 and burns our skin and 
makes it sore4 ,but we shall see that   
even these apparently harmful effects of
 light are in reality of great value in 
man's constant battle against disease4  
#ii4 ,the ,candle4 ,natural heat and    
light are furnished by the sun1 but the 
absence of the sun during the evening   
makes artificial light necessary1 and   
even during the day artificial light is 
needed in buildings whose structure     
excludes the natural light of the sun4  
,artificial light is furnished by       
electricity1 by gas1 by oil in lamps1   
and in numerous other ways4 ,until      

modern times candles were the main      
source of light1 and indeed to-day the  
intensity1 or power1 of any light is    
measured in candle power units1 just as 
length is measured in yards2 for        
example1 an average gas jet gives a #aj 
candle power light1 or is ten times as  
bright as a candle2 an ordinary         
incandescent electric light gives a #af 
candle power light1 or furnishes sixteen
 times as much light as a candle4 ,very 
strong large oil lamps can at times     
yield a light of #fj candle power1 while
 the large arc lamps which flash out on 
the street corners are said to furnish  
#abjj times as much light as a single   
candle4 ,naturally all candles do not   
give the same amount of light1 nor are  
all candles alike in size4 ,the candles 
which decorate our tea tables are of    
wax1 while those which serve for general
 use are of paraffin and tallow4        
,illustration3 ,,fig4 #eg4--;,a         
photograph at a receives four times as  
much light as when held at b4  #ajj4    

,fading ,illumination4 ,the farther we  
move from a light1 the less strong1 or  
intense1 is the illumination which      
reaches us2 the light of the street lamp
 on the corner fades and becomes dim    
before the middle of the block is       
reached1 so that we look eagerly for the
 next lamp4 ,the light diminishes in    
brightness much more rapidly than we    
realize1 as the following simple        
experiment will show4 ,let a single     
candle 7,fig4 #eg7 serve as our light1  
and at a distance of one foot from the  
candle place a photograph4 ,in this     
position the photograph receives a      
definite amount of light from the candle
 and has a certain brightness4  ,if now 
we place a similar photograph directly  
behind the first photograph and at a    
distance of two feet from the candle1   
the second photograph receives no light 
because the first one cuts off all the  
light4 ,if1 however1 the first          
photograph is removed1 the light which  
fell on it passes outward and spreads   

itself over a larger area1 until at the 
distance of the second photograph the   
light spreads itself over four times as 
large an area as formerly4 ,at this     
distance1 then1 the illumination on the 
second photograph is only one fourth as 
strong as it was on a similar photograph
 held at a distance of one foot from the
 candle4  ,the photograph or object     
placed at a distance of one foot from a 
light is well illuminated2 if it is     
placed at a distance of two feet1 the   
illumination is only one fourth as      
strong1 and if the object is placed     
three feet away1 the illumination is    
only one ninth as strong4 ,this fact    
should make us have thought and care in 
the use of our eyes4 ,we think we are   
sixteen times as well off with our      
incandescent lights as our ancestors    
were with simple candles1 but we must   
reflect that our ancestors kept the     
candle near them1 at their elbow1 so to 
speak1 while we sit at some distance    
from the light and unconcernedly read   

and sew4  ,as an object recedes from a  
light the illumination which it receives
 diminishes rapidly1 for the strength of
 the illumination is inversely          
proportional to the square of distance  
of the object from the light4 ,our      
ancestors with a candle at a distance of
 one foot from a book were as well off  
as we are with an incandescent light    
four feet away4  #aja4 ,money ,value of 
,light4 ,light is bought and sold almost
 as readily as are the products of farm 
and dairy2 many factories1 churches1 and
 apartments pay a definite sum for      
electric light of a standard strength1  
and naturally full value is desired4 ,an
 instrument for measuring the strength  
of a light is called a photometer1 and  
there are many different varieties1 just
 as there are varieties of scales which 
measure household articles4 ,one        
light-measuring scale depends upon the  
law that the intensity of illumination  
decreases with the square of the        
distance of the object from the light4  

,suppose we wish to measure the strength
 of the electric light bulbs in our     
homes1 in order to see whether we are   
getting the specified illumination4 ,in 
front of a screen place a black rod     
7,fig4 #eh7 which is illuminated by two 
different lights2 namely1 a standard    
candle and an incandescent bulb whose   
strength is to be measured4 ,two shadows
 of the rod will fall on the screen1 one
 caused by the candle and the other     
caused by the incandescent light4 ,the  
shadow due to the latter source is not  
so dark as that due to the candle4 ,now 
let the incandescent light be moved away
 from the screen until the two shadows  
are of equal darkness4 ,if the          
incandescent light is four times as far 
away from the screen as the candle1 and 
the shadows are equal1 we know1 by      
,section #ajj1 that its strength is     
sixteen candle power4 ,if the           
incandescent light is four times as far 
away from the screen as the candle is1  
its power must be sixteen times as      

great1 and we know the company is       
furnishing the standard amount of light 
for a sixteen candle power electric     
bulb4 ,if1 however1 the bulb must be    
moved nearer to the rod in order that   
the two shadows may be similar then the 
light given by the bulb is less than    
sixteen candle power1 and less than that
 due the consumer4  ,illustration3      
,,fig4 #eh4--,the two shadows are       
equally dark4  #ajb4 ,how ,light        
,travels4 ,we never expect to see around
 a corner1 and if we wish to see through
 pinholes in three separate pieces of   
cardboard1 we place the cardboards so   
that the three holes are in a straight  
line4 ,when sunlight enters a dark room 
through a small opening1 the dust       
particles dancing in the sun show a     
straight ray4 ,if a hole is made in a   
card1 and the card is held in front of a
 light1 the card casts a shadow1 in the 
center of which is a bright spot4 ,the  
light1 the hole1 and the bright spot are
 all in the same straight line4 ,these  

simple observations lead us to think    
that light travels in a straight line4  
,illustration3 ,,fig4 #ei4--,the candle 
cannot be seen unless the three pinholes
 are in a strait line4  ,we can always  
tell the direction from which light     
comes1 either by the shadow cast or by  
the bright spot formed when an opening  
occurs in the opaque object casting the 
shadow4 ,if the shadow of a tree falls  
towards the west1 we know the sun must  
be in the cast2 if a bright spot is on  
the floor1 we can easily locate the     
light whose rays stream through an      
opening and form the bright spot4 ,we   
know that light travels in a straight   
line1 and following the path of the beam
 which comes to our eyes1 we are sure to
 locate the light4  #ajc4 ,good and ,bad
 ,mirrors4 ,as we walk along the street1
 we frequently see ourselves reflected  
in the shop windows1 in polished metal  
signboards1 in the metal trimmings of   
wagons and automobiles2 but in mirrors  
we get the best image of ourselves4 ,we 

resent the image given by a piece of    
tin1 because the reflection is distorted
 and does not picture us as we really   
are2 a rough surface does not give a    
fair representation2 if we want a true  
image of ourselves1 we must use a smooth
 surface like a mirror as a reflector4  
,if the water in a pond is absolutely   
still1 we get a clear1 true image of the
 trees1 but if there are ripples on the 
surface1 the reflection is blurred and  
distorted4 ,a metal roof reflects so    
much light that the eyes are dazzled by 
it1 and a whitewashed fence injures the 
eyes because of the glare which comes   
from the reflected light4 ,neither of   
these could be called mirrors1 however1 
because although they reflect light1    
they reflect it so irregularly that not 
even a suggestion of an image can be    
obtained4  ,most of us are sufficiently 
familiar with mirrors to know that the  
image is a duplicate of ourselves with  
regard to size1 shape1 color1 and       
expression1 but that it appears to be   

back of the mirror1 while we are        
actually in front of the mirror4 ,the   
image appears not only behind the       
mirror1 but it is also exactly as far   
back of the mirror as we are in front of
 it2 if we approach the mirror1 the     
image also draws nearer2 if we withdraw1
 it likewise recedes4  #ajd4 ,the ,path 
of ,light4 ,if a mirror or any other    
polished surface is held in the path of 
a sunbeam1 some of the light is         
reflected1 and by rotating the mirror   
the reflected sunbeam may be made to    
take any path4 ,school children amuse   
themselves by reflecting sunbeams from a
 mirror into their companions' faces4   
,if the companion moves his head in     
order to avoid the reflected beam1 his  
tormentor moves or inclines the mirror  
and flashes the beam back to his        
victim's face4  ,if a mirror is held so 
that a ray of light strikes it in a     
perpendicular direction1 the light is   
reflected backward along the path by    
which it came4 ,if1 however1 the light  

makes an angle with the mirror1 its     
direction is changed1 and it leaves the 
mirror along a new path4 ,by observation
 we learn that when a beam strikes the  
mirror and makes an angle of #cj with   
the perpendicular1 the beam is reflected
 in such a way that its new path also   
makes an angle of #cj with the          
perpendicular4 ,if the sunbeam strikes  
the mirror at an angle of #cb with the  
perpendicular1 the path of the reflected
 ray also makes an angle of #cb with the
 perpendicular4 ,the ray 7,,ac1 ,fig4   
#fj7 which falls upon the mirror is     
called the incident ray1 and the angle  
which the incident ray 7,,ac7 makes with
 the perpendicular 7,,bc7 to the mirror1
 at the point where the ray strikes the 
mirror1 is called the angle of          
incidence4 ,the angle formed by the     
reflected ray 7,,cd7 and this same      
perpendicular is called the angle of    
reflection4 ,observation and experiment 
have taught us that light is always     
reflected in such a way that the angle  

of reflection equals the angle of       
incidence4 ,light is not the only       
illustration we have of the law of      
reflection4 ,every child who bounces a  
ball makes use of this law1 but he uses 
it unconsciously4 ,if an elastic ball is
 thrown perpendicularly against the     
floor1 it returns to the sender2 if it  
is thrown against the floor at an angle 
7,fig4 #fa71 it rebounds in the opposite
 direction1 but always in such a way    
that the angle of reflection equals the 
angle of incidence4  ,illustration3     
,,fig4 #fj4--,the ray ,,ac is reflected 
as ,,cd4  ,illustration3 ,,fig4         
#fa4--;,a bouncing ball illustrates the 
law of reflection4  #aje4 ,why the      
,image seems to be behind the ,mirror4  
,if a candle is placed in front of a    
mirror1 as in ,figure #fb1 one of the   
rays of light which leaves the candle   
will fall upon the mirror as ,,ab and   
will be reflected as ,,bc 7in such a way
 that the angle of reflection equals the
 angle of incidence74 ,if an observer   

stands at ,c1 he will think that the    
point ,a of the candle is somewhere     
along the line ,,cb extended4 ,such a   
supposition would be justified from     
,section #ajb4 ,but the candle sends out
 light in all directions2 one ray       
therefore will strike the mirror as ,,ad
 and will be reflected as ,,de1 and an  
observer at ,e will think that the point
 ,a of the candle is somewhere along the
 line ,,ed4 ,in order that both         
observers may be correct1 that is1 in   
order that the light may seem to be in  
both these directions1 the image of the 
point ,a must seem to be at the         
intersection of the two lines4 ,in a    
similar manner it can be shown that     
every point of the image of the candle  
seems to be behind the mirror4          
,illustration3 ,,fig4 #fb4--,the image  
is a duplicate of the object1 but       
appears to be behind the mirror4  ,it   
can be shown by experiment that the     
distance of the image behind the mirror 
is equal to the distance of the object  

in front of the mirror4  #ajf4 ,why     
,objects are ,visible4 ,if the beam of  
light falls upon a sheet of paper1 or   
upon a photograph1 instead of upon a    
smooth polished surface1 no definite    
reflected ray will be seen1 but a glare 
will be produced by the scattering of   
the beam of light4 ,the surface of the  
paper or photograph is rough1 and as a  
result1 it scatters the beam in every   
direction4 ,it is hard for us to realize
 that a smooth sheet of paper is by no  
means so smooth as it looks4 ,it is     
rough compared with a polished mirror4  
,the law of reflection always holds1    
however1 no matter what the reflecting  
surface is1--the angle of reflection    
always equals the angle of incidence4   
,in a smooth body the reflected beams   
are all parallel2 in a rough body1 the  
reflected beams are inclined to each    
other in all sorts of ways1 and no two  
beams leave the paper in exactly the    
same direction4  ,illustration3 ,,fig4  
#fc4--,the surface of the paper1        

although smooth in appearance1 is in    
reality rough1 and scatters the light in
 every direction4  ,hot coals1 red-hot  
stoves1 gas flames1 and candles shine by
 their own light1 and are self-luminous4
 ,objects like chairs1 tables1 carpets1 
have no light within themselves and are 
visible only when they receive light    
from a luminous source and reflect that 
light4 ,we know that these objects are  
not self-luminous1 because they are not 
visible at night unless a lamp or gas is
 burning4 ,when light from any luminous 
object falls upon books1 desks1 or      
dishes1 it meets rough surfaces1 and    
hence undergoes diffuse reflection1 and 
is scattered irregularly in all         
directions4 ,no matter where the eye is1
 some reflected rays enter it1 and the  
various objects are clearly seen4       
,,chapter ,,xi  ,,refraction   #ajg4    
,bent ,rays of ,light4 ,a straw in a    
glass of lemonade seems to be broken at 
the surface of the liquid1 the handle of
 a teaspoon in a cup of water appears   

broken1 and objects seen through a glass
 of water may seem distorted and changed
 in size4 ,when light passes from air   
into water1 or from any transparent     
substance into another of different     
density1 its direction is changed1 and  
it emerges along an entirely new path   
7,fig4 #fd74 ,we know that light rays   
pass through glass1 because we can see  
through the window panes and through our
 spectacles2 we know that light rays    
pass through water1 because we can see  
through a glass of clear water2 on the  
other hand1 light rays cannot pass      
through wood1 leather1 metal1 etc4      
,illustration3 ,,fig4 #fd4--;,a straw or
 stick in water seems broken4  ,whenever
 light meets a transparent substance    
obliquely1 some of it is reflected1     
undergoing a change in its direction2   
and some of it passes onward through the
 medium1 but the latter portion passes  
onward along a new path4 ,the ray ,,ro  
7,fig4 #fe7 passes obliquely through the
 air to the surface of the water1 but1  

on entering the water1 it is bent or    
refracted and takes the new path ,,os4  
,the angle ,,aor is called the angle of 
incidence4 ,the angle ,,pos is called   
the angle of refraction4  ,illustration3
 ,,fig4 #fe4--,when the ray ,,ro enters 
the water1 its path changes to ,,os4    
,the angle of refraction is the angle   
formed by the refracted ray and the     
perpendicular to the surface at the     
point where the light strikes it4  ,when
 light passes from air into water or    
glass1 the refracted ray is bent toward 
the perpendicular1 so that the angle of 
refraction is smaller than the angle of 
incidence4 ,when a ray of light passes  
from water or glass into air1 the       
refracted ray is bent away from the     
perpendicular so that the angle of      
refraction is greater than the angle of 
incidence4  ,the bending or deviation of
 light in its passage from one substance
 to another is called refraction4  #ajh4
 ,how ,refraction ,deceives us4         
,refraction is the source of many       

illusions2 bent rays of light make      
objects appear where they really are    
not4 ,a fish at ,a 7,fig4 #ff7 seems to 
be at ,b4 ,the end of the stick in      
,figure #fd seems to be nearer the      
surface of the water than it really is4 
,illustration3 ,,fig4 #ff4--;,a fish at 
,a seems to be at ,b4  ,the light from  
the sun1 moon1 and stars can reach us   
only by passing through the atmosphere1 
but in ,section #gf1 we learned that the
 atmosphere varies in density from level
 to level2 hence all the light which    
travels through the atmosphere is       
constantly deviated from its original   
path1 and before the light reaches the  
eye it has undergone many changes in    
direction4 ,now we learned in ,section  
#ajb1 that the direction of the rays of 
light as they enter the eye determines  
the direction in which an object is     
seen2 hence the sun1 moon1 and stars    
seem to be along the lines which enter  
the eye1 although in reality they are   
not4  #aji4 ,uses of ,refraction4 ,if it

 were not for refraction1 or the        
deviation of light in its passage from  
medium to medium1 the wonders and       
beauties of the magic lantern and the   
camera would be unknown to us2 sun1     
moon1 and stars could not be made to    
yield up their distant secrets to us in 
photographs2 the comfort and help of    
spectacles would be lacking1 spectacles 
which have helped unfold to many the    
rare beauties of nature1 such as a clear
 view of clouds and sunset1 of humming  
bee and flying bird4 ,books with their  
wealth of entertainment and information 
would be sealed to a large part of      
mankind1 if glasses did not assist weak 
eyes4  ,by refraction the magnifying    
glass reveals objects hidden because of 
their minuteness1 and enlarges for our  
careful contemplation objects otherwise 
barely visible4 ,the watchmaker1        
unassisted by the magnifying glass1     
could not detect the tiny grains of dust
 or sand which clog the delicate wheels 
of our watches4 ,the merchant1 with his 

lens1 examines the separate threads of  
woolen and silk fabrics to determine the
 strength and value of the material4    
,the physician1 with his invaluable     
microscope1 counts the number of        
infinitesimal corpuscles in the blood   
and bases his prescription on that      
count2 he examines the sputum of a      
patient to determine whether            
tuberculosis wastes the system4 ,the    
bacteriologist with the same instrument 
scrutinizes the drinking water and      
learns whether the dangerous typhoid    
germs are present4 ,the future of       
medicine will depend somewhat upon the  
additional secrets which man is able to 
force from nature through the use of    
powerful lenses1 because as lenses have1
 in the past1 been the means of         
revealing disease germs1 so in the      
future more powerful lenses may serve to
 bring to light germs yet unknown4 ,how 
refraction accomplishes these results   
will be explained in the following      
,sections4  #aaj4 ,the ,window ,pane4   

,we have seen that light is bent when it
 passes from one medium to another of   
different density1 and that objects     
viewed by refracted light do not appear 
in their proper positions4  ,when a ray 
of light passes through a piece of plane
 glass1 such as a window pane 7,fig4    
#fg71 it is refracted at the point ,b   
toward the perpendicular1 and continues 
its course through the glass in the new 
direction ,,bc4 ,on emerging from the   
glass1 the light is refracted away from 
the perpendicular and takes the         
direction ,,cd1 which is clearly        
parallel to its original direction4     
,hence1 when we view objects through the
 window1 we see them slightly displaced 
in position1 but otherwise unchanged4   
,the deviation or displacement caused by
 glass as thin as window panes is too   
slight to be noticed1 and we are not    
conscious that objects are out of       
position4  ,illustration3 ,,fig4        
#fg4--,objects looked at through a      
window pane seem to be in their natural 

place4  #aaa4 ,chandelier ,crystals and 
,prisms4 ,when a ray of light passes    
through plane glass1 like a window pane1
 it is shifted somewhat1 but its        
direction does not change2 that is1 the 
emergent ray is parallel to the incident
 ray4 ,but when a beam of light passes  
through a triangular glass prism1 such  
as a chandelier crystal1 its direction  
is greatly changed1 and an object viewed
 through a prism is seen quite out of   
its true position4  ,whenever light     
passes through a prism1 it is bent      
toward the base of the prism1 or toward 
the thick portion of the prism1 and     
emerges from the prism in quite a       
different direction from that in which  
it entered 7,fig4 #fh74 ,hence1 when an 
object is looked at through a prism1 it 
is seen quite out of place4 ,in ,figure 
#fh1 the candle seems to be at ,s1 while
 in reality it is at ,a4  ,illustration3
 ,,fig4 #fh4--,when looked at through   
the prism1 ,a seems to be at ,s4  #aab4 
,lenses4 ,if two prisms are arranged as 

in ,figure #fi1 and two parallel rays of
 light fall upon the prisms1 the beam ,a
 will be bent downward toward the       
thickened portion of the prism1 and the 
beam ,b will be bent upward toward the  
thick portion of the prism1 and after   
passing through the prism the two rays  
will intersect at some point ,f1 called 
a focus4  ,illustration3 ,,fig4         
#fi4--,rays of light are converged and  
focused at ,f4  ,if two prisms are      
arranged as in ,figure #gj1 the ray ,a  
will be refracted upward toward the     
thick end1 and the ray ,b will be       
refracted downward toward the thick end2
 the two rays1 on emerging1 will        
therefore be widely separated and will  
not intersect4  ,illustration3 ,,fig4   
#gj4--,rays of light are diverged and do
 not come to any real focus4  ,lenses   
are very similar to prisms2 indeed1 two 
prisms placed as in ,figure #fi1 and    
rounded off1 would make a very good     
convex lens4 ,a lens is any transparent 
material1 but usually glass1 with one or

 both sides curved4 ,the various types  
of lenses are shown in ,figure #ga4     
,illustration3 ,,fig4 #ga4--,the        
different types of lenses4  ,the first  
three types focus parallel rays at some 
common point ,f1 as in ,figure #fi4     
,such lenses are called convex or       
converging lenses4 ,the last three      
types1 called concave lenses1 scatter   
parallel rays so that they do not come  
to a focus1 but diverge widely after    
passage through the lens4  #aac4 ,the   
,shape and ,material of a ,lens4 ,the   
main or principal focus of a lens1 that 
is1 the point at which rays parallel to 
the base line ,,ab meet 7,fig4 #ga71    
depends upon the shape of the lens4 ,for
 example1 a thick lens1 such as ,a      
7,fig4 #gb71 focuses the rays very near 
to the lens2 ,b1 which is not so thick1 
focuses the rays at a greater distance  
from the lens2 and ,c1 which is a very  
thin lens1 focuses the rays at a        
considerable distance from the lens4    
,the distance of the principal focus    

from the lens is called the focal length
 of the lens1 and from the diagrams we  
see that the more convex the lens1 the  
shorter the focal length4               
,illustration3 ,,fig4 #gb4--,the more   
curved the lens1 the shorter the focal  
length1 and the nearer the focus is to  
the lens4  ,the position of the         
principal focus depends not only on the 
shape of the lens1 but also on the      
refractive power of the material        
composing the lens4 ,a lens made of ice 
would not deviate the rays of light so  
much as a lens of similar shape composed
 of glass4 ,the greater the refractive  
power of the lens1 the greater the      
bending1 and the nearer the principal   
focus to the lens4  ,there are many     
different kinds of glass1 and each kind 
of glass refracts the light differently4
 ,flint glass contains lead2 the lead   
makes the glass dense1 and gives it     
great refractive power1 enabling it to  
bend and separate light in all          
directions4 ,cut glass and toilet       

articles are made of flint glass because
 of the brilliant effects caused by its 
great refractive power1 and imitation   
gems are commonly nothing more than     
polished flint glass4  #aad4 ,how       
,lenses ,form ,images4 ,suppose we place
 an arrow1 ,a1 in front of a convex lens
 7,fig4 #gc74 ,the ray ,,ac1 parallel to
 the principal axis1 will pass through  
the lens and emerge as ,,de4 ,the ray is
 always bent toward the thick portion of
 the lens1 both at its entrance into the
 lens and its emergence from the lens4  
,illustration3 ,,fig4 #gc4--,the image  
is larger than the object4 ,by means of 
a lens1 a watchmaker gets an enlarged   
image of the dust which clogs the wheels
 of his watch4  ,in ,section #aje1 we   
saw that two rays determine the position
 of any point of our image2 hence in    
order to locate the image of the top of 
the arrow1 we need to consider but one  
more ray from the top of the object4    
,the most convenient ray to choose would
 be one passing through ,o1 the optical 

center of the lens1 because such a ray  
passes through the lens unchanged in    
direction1 as is clear from ,figure #gd4
 ,the point where ,,ac and ,,ao meet    
after refraction will be the position of
 the top of the arrow4 ,similarly it can
 be shown that the center of the arrow  
will be at the point ,t1 and we see that
 the image is larger than the object4   
,this can be easily proved              
experimentally4 ,let a convex lens be   
placed near a candle 7,fig4 #ge72 move a
 paper screen back and forth behind the 
lens2 for some position of the screen a 
clear1 enlarged image of the candle will
 be made4  ,illustration3 ,,fig4        
#gd4--,rays above ,o are bent downward1 
those below ,o are bent upward1 and rays
 through ,o emerge from the lens        
unchanged in direction4  ,if the candle 
or arrow is placed in a new position1   
say at ,,ma 7,fig4 #gf71 the image      
formed is smaller than the object1 and  
is nearer to the lens than it was       
before4 ,move the lens so that its      

distance from the candle is increased1  
and then find the image on a piece of   
paper4 ,the size and position of the    
image depend upon the distance of the   
object from the lens 7,fig4 #gg74 ,by   
means of a lens one can easily get on a 
visiting card a picture of a distant    
church steeple4  ,illustration3 ,,fig4  
#ge4--,the lens is held in such a       
position that the image of the candle is
 larger than the object4  ,illustration3
 ,,fig4 #gf4--,the image is smaller than
 the object4  #aae4 ,the ,value of      
,lenses4 ,if it were not for the fact   
that a lens can be held at such a       
distance from an object as to make the  
image larger than the object1 it would  
be impossible for the lens to assist the
 watchmaker in locating the small       
particles of dust which clog the wheels 
of the watch4 ,if it were not for the   
opposite fact--that a lens can be held  
at such a distance from the object as to
 make an image smaller than the object1 
it would be impossible to have a        

photograph of a tall tree or building   
unless the photograph were as large as  
the tree itself4 ,when a photographer   
takes a photograph of a person or a     
tree1 he moves his camera until the     
image formed by the lens is of the      
desired size4 ,by bringing the camera   
7really the lens of the camera7 near1 we
 obtain a large-sized photograph2 by    
increasing the distance between the     
camera and the object1 a smaller        
photograph is obtained4 ,the mountain   
top may be so far distant that in the   
photograph it will not appear to be     
greater than a small stone4             
,illustration3 ,,fig4 #gg4--,the lens is
 placed in such a position that the     
image is about the same size as the     
object4  ,many familiar illustrations of
 lenses1 or curved refracting surfaces1 
and their work1 are known to all of us4 
,fish globes magnify the fish that swim 
within4 ,bottles can be so shaped that  
they make the olives1 pickles1 and      
peaches that they contain appear larger 

than they really are4 ,the fruit in     
bottles frequently seems too large to   
have gone through the neck of the       
bottle4 ,the deception is due to        
refraction1 and the material and shape  
of the bottle furnish a sufficient      
explanation4  ,by using combinations of 
two or more lenses of various kinds1 it 
is possible to have an image of almost  
any desired size1 and in practically any
 desired position4  #aaf4 ,the ,human   
,eye4 ,in ,section #aad1 we obtained on 
a movable screen1 by means of a simple  
lens1 an image of a candle4 ,the human  
eye possesses a most wonderful lens and 
screen 7,fig4 #gh72 the lens is called  
the crystalline lens1 and the screen is 
called the retina4 ,rays of light pass  
from the object through the pupil ,p1 go
 through the crystalline lens ,l1 where 
they are refracted1 and then pass onward
 to the retina ,r1 where they form a    
distinct image of the object4           
,illustration3 ,,fig4 #gh4--,the eye4   
,we learned in ,section #aad that a     

change in the position of the object    
necessitated a change in the position of
 the screen1 and that every time the    
object was moved the position of the    
screen had to be altered before a clear 
image of the object could be obtained4  
,the retina of the eye cannot be moved  
backward and forward1 as the screen was1
 and the crystalline lens is permanently
 located directly back of the iris4     
,how1 then1 does it happen that we can  
see clearly both near and distant       
objects2 that the printed page which is 
held in the hand is visible at one      
second1 and that the church spire on the
 distant horizon is visible the instant 
the eyes are raised from the book8 ,how 
is it possible to obtain on an immovable
 screen by means of a simple lens two   
distinct images of objects at widely    
varying distances8  ,the answer to these
 questions is that the crystalline lens 
changes shape according to need4 ,the   
lens is attached to the eye by means of 
small muscles1 m1 and it is by the      

action of these muscles that the lens is
 able to become small and thick1 or     
large and thin2 that is1 to become more 
or less curved4 ,when we look at near   
objects1 the muscles act in such a way  
that the lens bulges out1 and becomes   
thick in the middle and of the right    
curvature to focus the near object upon 
the screen4 ,when we look at an object  
several hundred feet away1 the muscles  
change their pull on the lens and       
flatten it until it is of the proper    
curvature for the new distance4 ,the    
adjustment of the muscles is so quick   
and unconscious that we normally do not 
experience any difficulty in changing   
our range of view4 ,the ability of the  
eye to adjust itself to varying         
distances is called accommodation4 ,the 
power of adjustment in general decreases
 with age4  #aag4 ,farsightedness and   
,nearsightedness4 ,a farsighted person  
is one who cannot see near objects so   
distinctly as far objects1 and who in   
many cases cannot see near objects at   

all4 ,the eyeball of a farsighted person
 is very short1 and the retina is too   
close to the crystalline lens4 ,near    
objects are brought to a focus behind   
the retina instead of on it1 and hence  
are not visible4 ,even though the       
muscles of accommodation do their best  
to bulge and thicken the lens1 the rays 
of light are not bent sufficiently to   
focus sharply on the retina4 ,in        
consequence objects look blurred4       
,farsightedness can be remedied by      
convex glasses1 since they bend the     
light and bring it to a closer focus4   
,convex glasses1 by bending the rays and
 bringing them to a nearer focus1       
overbalance a short eyeball with its    
tendency to focus objects behind the    
retina4  ,illustration3 ,,fig4          
#gi4--,the farsighted eye4              
,illustration3 ,,fig4 #hj4--,the defect 
is remedied by convex glasses4  ,a      
nearsighted person is one who cannot see
 objects unless they are close to the   
eye4 ,the eyeball of a nearsighted      

person is very wide1 and the retina is  
too far away from the crystalline lens4 
,far objects are brought to a focus in  
front of the retina instead of on it1   
and hence are not visible4 ,even though 
the muscles of accommodation do their   
best to pull out and flatten the lens1  
the rays are not separated sufficiently 
to focus as far back as the retina4 ,in 
consequence objects look blurred4       
,nearsightedness can be remedied by     
wearing concave glasses1 since they     
separate the light and move the focus   
farther away4 ,concave glasses1 by      
separating the rays and making the focus
 more distant1 overbalance a wide       
eyeball with its tendency to focus      
objects in front of the retina4         
,illustration3 ,,fig4 #ha4--,the        
nearsighted eye4 ,the defect is remedied
 by concave glasses4  #aah4 ,headache   
and ,eyes4 ,ordinarily the muscles of   
accommodation adjust themselves easily  
and quickly2 if1 however1 they do not1  
frequent and severe headaches occur as a

 result of too great muscular effort    
toward accommodation4 ,among young      
people headaches are frequently caused  
by over-exertion of the crystalline     
muscles4 ,glasses relieve the muscles of
 the extra adjustment1 and hence are    
effective in eliminating this cause of  
headache4  ,an exact balance is required
 between glasses1 crystalline lens1 and 
muscular activity1 and only those who   
have studied the subject carefully are  
competent to treat so sensitive and     
necessary a part of the body as the eye4
 ,the least mistake in the curvature of 
the glasses1 the least flaw in the type 
of glass 7for example1 the kind of glass
 used71 means an improper focus1        
increased duty for the muscles1 and     
gradual weakening of the entire eye1    
followed by headache and general        
physical discomfort4  #aai4 ,eye        
,strain4 ,the extra work which is thrown
 upon the nervous system through seeing1
 reading1 writing1 and sewing with      
defective eyes is recognized by all     

physicians as an important cause of     
disease4 ,the tax made upon the nervous 
system by the defective eye lessens the 
supply of energy available for other    
bodily use1 and the general health      
suffers4 ,the health is improved when   
proper glasses are prescribed4          
,possibly the greatest danger of eye    
strain is among school children1 who are
 not experienced enough to recognize    
defects in sight4 ,for this reason1 many
 schools employ a physician who examines
 the pupils' eyes at regular intervals4 
,the following general precautions are  
worth observing3--  #a4 ,rest the eyes  
when they hurt1 and as far as possible  
do close work1 such as writing1 reading1
 sewing1 wood carving1 etc41 by         
daylight4  #b4 ,never read in a very    
bright or a very dim light4  #c4 ,if the
 light is near1 have it shaded4  #d4 ,do
 not rub the eyes with the fingers4  #e4
 ,if eyes are weak1 bathe them in       
lukewarm water in which a pinch of borax
 has been dissolved4     ,,chapter ,,xii

  ,,photography   #abj4 ,the ,magic of  
the ,sun4 ,ribbons and dresses washed   
and hung in the sun fade2 when washed   
and hung in the shade1 they are not so  
apt to lose their color4 ,clothes are   
laid away in drawers and hung in closets
 not only for protection against dust1  
but also against the well-known power of
 light to weaken color4  ,many          
housewives lower the window shades that 
the wall paper may not lose its         
brilliancy1 that the beautiful hues of  
velvet1 satin1 and plush tapestry may   
not be marred by loss in brilliancy and 
sheen4 ,bright carpets and rugs are     
sometimes bought in preference to more  
delicately tinted ones1 because the     
purchaser knows that the latter will    
fade quickly if used in a sunny room1   
and will soon acquire a dull mellow     
tone4 ,the bright and gay colors and the
 dull and somber colors are all affected
 by the sun1 but why one should be      
affected more than another we do not    
know4 ,thousands of brilliant and dainty

 hues catch our eye in the shop and on  
the street1 but not one of them is      
absolutely permanent2 some may last for 
years1 but there is always more or less 
fading in time4  ,sunlight causes many  
strange1 unexplained effects4 ,if the   
two substances1 chlorine and hydrogen1  
are mixed in a dark room1 nothing       
remarkable occurs any more than though  
water and milk were mixed1 but if a     
mixture of these substances is exposed  
to sunlight1 a violent explosion occurs 
and an entirely new substance is formed1
 a compound entirely different in       
character from either of its components4
  ,by some power not understood by man1 
the sun is able to form new substances4 
,in the dark1 chlorine and hydrogen are 
simply chlorine and hydrogen2 in the    
sunlight they combine as if by magic    
into a totally different substance4 ,by 
the same unexplained power1 the sun     
frequently does just the opposite work2 
instead of combining two substances to  
make one new product1 the sun may       

separate or break down some particular  
substance into its various elements4    
,for example1 if the sun's rays fall    
upon silver chloride1 a chemical action 
immediately begins1 and as a result we  
have two separate substances1 chlorine  
and silver4 ,the sunlight separates     
silver chloride into its constituents1  
silver and chlorine4  #aba4 ,the ,magic 
,wand in ,photography4 ,suppose we coat 
one side of a glass plate with silver   
chloride1 just as we might put a coat of
 varnish on a chair4 ,we must be very   
careful to coat the plate in the dark   
room1,b otherwise the sunlight will     
separate the silver chloride and spoil  
our plan4 ,then lay a horseshoe on the  
plate for good luck1 and carry the plate
 out into the light for a second4 ,the  
light will separate the silver chloride 
into chlorine and silver1 the latter of 
which will remain on the plate as a thin
 film4 ,all of the plate was affected by
 the sun except the portion protected by
 the horseshoe which1 because it is     

opaque1 would not allow light to pass   
through and reach the plate4 ,if now the
 plate is carried back to the dark room 
and the horseshoe is removed1 one would 
expect to see on the plate an impression
 of the horseshoe1 because the portion  
protected by the horseshoe would be     
covered by silver chloride and the      
exposed unprotected portion would be    
covered by metallic silver4 ,but we are 
much disappointed because the plate1    
when examined ever so carefully1 shows  
not the slightest change in appearance4 
,the change is there1 but the unaided   
eye cannot detect the change4 ,some     
chemical1 the so-called developer1 must 
be used to bring out the hidden change  
and to reveal the image to our unseeing 
eyes4 ,there are many different         
developers in use1 any one of which will
 effect the necessary transformation4   
,when the plate has been in the         
developer for a few seconds1 the silver 
coating gradually darkens1 and slowly   
but surely the image printed by the     

sun's rays appears4 ,but we must not    
take this picture into the light1       
because the silver chloride which was   
protected by the horseshoe is still     
present1 and would be strongly affected 
by the first glimmer of light1 and1 as a
 result1 our entire plate would become  
similar in character and there would be 
no contrast to give an image of the     
horseshoe on the plate4  ,footnote ,b3  
,that is1 a room from which ordinary    
daylight is excluded4  ,but a photograph
 on glass1 which must be carefully      
shielded from the light and admired only
 in the dark room1 would be neither     
pleasurable nor practical4 ,if there    
were some way by which the hitherto     
unaffected silver chloride could be     
totally removed1 it would be possible to
 take the plate into any light without  
fear4 ,to accomplish this1 the unchanged
 silver chloride is got rid of by the   
process technically called fixing2 that 
is1 by washing off the unreduced silver 
chloride with a solution such as sodium 

thiosulphite1 commonly known as hypo4   
,after a bath in the hypo the plate is  
cleansed in clear running water and left
 to dry4 ,such a process gives a clear  
and permanent picture on the plate4     
,illustration3 ,,fig4 #hb4--;,a camera4 
#abb4 ,the ,camera4 ,a camera 7,fig4    
#hb7 is a light-tight box containing a  
movable convex lens at one end and a    
screen at the opposite end4 ,light from 
the object to be photographed passes    
through the lens1 falls upon the screen1
 and forms an image there4 ,if we       
substitute for the ordinary screen a    
plate or film coated with silver        
chloride or any other silver salt1 the  
light which falls upon the sensitive    
plate and forms an image there will     
change the silver chloride and produce a
 hidden image4 ,if the plate is then    
removed from the camera in the dark1 and
 is treated as described in the         
preceding ,section1 the image becomes   
visible and permanent4 ,in practice some
 gelatin is mixed with the silver salt1 

and the mixture is then poured over the 
plate or film in such a way that a thin1
 even coating is made4 ,it is the       
presence of the gelatin that gives      
plates a yellowish hue4 ,the sensitive  
plates are left to dry in dark rooms1   
and when the coating has become         
absolutely firm and dry1 the plates are 
packed in boxes and sent forth for sale4
  ,glass plates are heavy and           
inconvenient to carry1 so that celluloid
 films have almost entirely taken their 
place1 at least for outdoor work4  #abc4
 ,light and ,shade4 ,let us apply the   
above process to a real photograph4     
,suppose we wish to take the photograph 
of a man sitting in a chair in his      
library4 ,if the man wore a gray coat1 a
 black tie1 and a white collar1 these   
details must be faithfully represented  
in the photograph4 ,how can the almost  
innumerable lights and shades be        
produced on the plate8  ,the white      
collar would send through the lens the  
most light to the sensitive plate2 hence

 the silver chloride on the plate would 
be most changed at the place where the  
lens formed an image of the collar4 ,the
 gray coat would not send to the lens so
 much light as the white collar1 hence  
the silver chloride would be less       
affected by the light from the coat than
 by that from the collar1 and at the    
place where the lens produced an image  
of the coat the silver chloride would   
not be changed so much as where the     
collar image is4 ,the light from the    
face would produce a still different    
effect1 since the light from the face is
 stronger than the light from the gray  
coat1 but less than that from a white   
collar4 ,the face in the image would    
show less changed silver chloride than  
the collar1 but more than the coat1     
because the face is lighter than the    
coat1 but not so light as the collar4   
,finally1 the silver chloride would be  
least affected by the dark tie4 ,the    
wall paper in the background would      
affect the plate according to the       

brightness of the light which fell      
directly upon it and which reflected to 
the camera4 ,when such a plate has been 
developed and fixed1 as described in    
,section #aba1 we have the so-called    
negative 7,fig4 #hc74 ,the collar is    
very dark1 the black tie and gray coat  
white1 and the white tidy very dark4    
,illustration3 ,,fig4 #hc4--;,a         
negative4  ,the lighter the object1 such
 as tidy or collar1 the more salt is    
changed1 or1 in other words1 the greater
 the portion of the silver salt that is 
affected1 and hence the darker the stain
 on the plate at that particular spot4  
,the plate shows all gradations of      
intensity--the tidy is dark1 the black  
tie is light4 ,the photograph is true as
 far as position1 form1 and expression  
are concerned1 but the actual           
intensities are just reversed4 ,how this
 plate can be transformed into a        
photograph true in every detail will be 
seen in the following ,section4  #abd4  
,the ,perfect ,photograph4 ,bright      

objects1 such as the sky or a white     
waist1 change much of the silver        
chloride1 and hence appear dark on the  
negative4 ,dark objects1 such as        
furniture or a black coat1 change little
 of the chloride1 and hence appear light
 on the negative4 ,to obtain a true     
photograph1 the negative is placed on a 
piece of sensitive photographic paper1  
or paper coated with a silver salt in   
the same manner as the plate and films4 
,the combination is exposed to the      
light4 ,the dark portions of the        
negative will act as obstructions to the
 passage of light1 and but little light 
will pass through that part of the      
negative to the photographic paper1 and 
consequently but little of the silver   
salt on the paper will be changed4 ,on  
the other hand1 the light portion of the
 negative will allow free and easy      
passage of the light rays1 which will   
fall upon the photographic paper and    
will change much more of the silver4    
,thus it is that dark places in the     

negative produce light places in the    
positive or real photograph 7,fig4 #hd71
 and that light places in the negative  
produce dark places in the positive2 all
 intermediate grades are likewise       
represented with their proper gradations
 of intensity4  ,illustration3 ,,fig4   
#hd4--;,a positive or true photograph4  
,if properly treated1 a negative remains
 good for years1 and will serve for an  
indefinite number of positives or true  
photographs4  #abe4 ,light and ,disease4
 ,the far-reaching effect which light   
has upon some inanimate objects1 such as
 photographic films and clothes1 leads  
us to inquire into the relation which   
exists between light and living things4 
,we know from daily observation that    
plants must have light in order to      
thrive and grow4 ,a healthy plant       
brought into a dark room soon loses its 
vigor and freshness1 and becomes yellow 
and drooping4 ,plants do not all agree  
as to the amount of light they require1 
for some1 like the violet and the       

arbutus1 grow best in moderate light1   
while others1 like the willows1 need the
 strong1 full beams of the sun4 ,but    
nearly all common plants1 whatever they 
are1 sicken and die if deprived of      
sunlight for a long time4 ,this is      
likewise true in the animal world4      
,during long transportation1 animals are
 sometimes necessarily confined in dark 
cars1 with the result that many deaths  
occur1 even though the car is well aired
 and ventilated and the food supply     
good4 ,light and fresh air put color    
into pale cheeks1 just as light and air 
transform sickly1 yellowish plants into 
hardy green ones4 ,plenty of fresh air1 
light1 and pure water are the watchwords
 against disease4  ,illustration3 ,,fig4
 #he--,stems and leaves of oxalis       
growing toward the light4  ,in addition 
to the plants and animals which we see1 
there are many strange unseen ones      
floating in the atmosphere around us1   
lying in the dust of corner and closet1 
growing in the water we drink1 and      

thronging decayed vegetable and animal  
matter4 ,everyone knows that mildew and 
vermin do damage in the home and in the 
field1 but very few understand that1 in 
addition to these visible enemies of    
man1 there are swarms of invisible      
plants and animals some of which do far 
more damage1 both directly and          
indirectly1 than the seen and familiar  
enemies4 ,all such very small plants and
 animals are known as microorganisms4   
,not all microrganisms are harmful2 some
 are our friends and are as helpful to  
us as are cultivated plants and         
domesticated animals4 ,among the most   
important of the microrganisms are      
bacteria1 which include among their     
number both friend and foe4 ,in the     
household1 bacteria are a fruitful      
source of trouble1 but some of them are 
distinctly friends4 ,the delicate flavor
 of butter and the sharp but pleasing   
taste of cheese are produced by         
bacteria4 ,on the other hand1 bacteria  
are the cause of many of the most       

dangerous diseases1 such as typhoid     
fever1 tuberculosis1 influenza1 and la  
grippe4  ,by careful observation and    
experimentation it has been shown       
conclusively that sunlight rapidly kills
 bacteria1 and that it is only in       
dampness and darkness that bacteria     
thrive and multiply4 ,although sunlight 
is essential to the growth of most      
plants and animals1 it retards and      
prevents the growth of bacteria4 ,dirt  
and dust exposed to the sunlight lose   
their living bacteria1 while in damp    
cellars and dark corners the bacteria   
thrive1 increasing steadily in number4  
,for this reason our houses should be   
kept light and airy2 blinds should be   
raised1 even if carpets do fade2 it is  
better that carpets and furniture should
 fade than that disease-producing       
bacteria should find a permanent abode  
within our dwellings4 ,kitchens and     
pantries in particular should be        
thoroughly lighted4 ,bedclothes1 rugs1  
and clothing should be exposed to the   

sunlight as frequently as possible2     
there is no better safeguard against    
bacterial disease than light4 ,in a sick
 room sunlight is especially valuable1  
because it not only kills bacteria1 but 
keeps the air dry1 and new bacteria     
cannot get a start in a dry atmosphere4 
,,chapter ,,xiii  ,,color   #abf4 ,the  
,rainbow4 ,one of the most beautiful and
 well-known phenomena in nature is the  
rainbow1 and from time immemorial it has
 been considered ,jehovah's signal to   
mankind that the storm is over and that 
the sunshine will remain4 ,practically  
everyone knows that a rainbow can be    
seen only when the sun's rays shine upon
 a mist of tiny drops of water4 ,it is  
these tiny drops which by their         
refraction and their scattering of light
 produce the rainbow in the heavens4    
,the exquisite tints of the rainbow can 
be seen if we look at an object through 
a prism or chandelier crystal1 and a    
very simple experiment enables us to    
produce on the wall of a room the exact 

colors of the rainbow in all their      
beauty4  ,illustration3 ,,fig4          
#hf4--,white light is a mixture of      
lights of rainbow colors4  #abg4 ,how to
 produce ,rainbow ,colors4 ,the         
,spectrum4 ,if a beam of sunlight is    
admitted into a dark room through a     
narrow opening in the shade1 and is     
allowed to fall upon a prism1 as shown  
in ,figure #hf1 a beautiful band of     
colors will appear on the opposite wall 
of the room4 ,the ray of light which    
entered the room as ordinary sunlight   
has not only been refracted and bent    
from its straight path1 but it has been 
spread out into a band of colors similar
 to those of the rainbow4  ,whenever    
light passes through a prism or lens1 it
 is dispersed or separated into all the 
colors which it contains1 and a band of 
colors produced in this way is called a 
spectrum4 ,if we examine such a spectrum
 we find the following colors in order1 
each color imperceptibly fading into the
 next3 violet1 indigo1 blue1 green1     

yellow1 orange1 red4  #abh4 ,sunlight or
 ,white ,light4 ,white light or sunlight
 can be dispersed or separated into the 
primary colors or rainbow hues1 as shown
 in the preceding ,section4 ,what seems 
even more wonderful is that these       
spectral colors can be recombined so as 
to make white light4  ,if a prism ,b    
7,fig4 #hg7 exactly similar to ,a in    
every way is placed behind ,a in a      
reversed position1 it will undo the     
dispersion of ,a1 bending upward the    
seven different beams in such a way that
 they emerge together and produce a     
white spot on the screen4 ,thus we see1 
from two simple experiments1 that all   
the colors of the rainbow may be        
obtained from white light1 and that     
these colors may be in turn recombined  
to produce white light4  ,illustration3 
,,fig4 #hg4--,rainbow colors recombined 
to form white light4  ,white light is   
not a simple light1 but is composed of  
all the colors which appear in the      
rainbow4  #abi4 ,color4 ,if a piece of  

red glass is held in the path of the    
colored beam of light formed as in      
,section #abg1 all the colors on the    
wall will disappear except the red1 and 
instead of a beautiful spectrum of all  
colors there will be seen the red color 
alone4 ,the red glass does not allow the
 passage through it of any light except 
red light2 all other colors are absorbed
 by the red glass and do not reach the  
eye4 ,only the red ray passes through   
the red glass1 reaches the eye1 and     
produces a sensation of color4  ,if a   
piece of blue glass is substituted for  
the red glass1 the blue band remains on 
the wall1 while all the other colors    
disappear4 ,if both blue and red pieces 
of glass are held in the path of the    
beam1 so that the light must pass       
through first one and then the other1   
the entire spectrum disappears and no   
color remains4 ,the blue glass absorbs  
the various rays with the exception of  
the blue ones1 and the red glass will   
not allow these blue rays to pass       

through it2 hence no light is allowed   
passage to the eye4  ,an emerald looks  
green because it freely transmits green1
 but absorbs the other colors of which  
ordinary daylight is composed4 ,a       
diamond appears white because it allows 
the passage through it of all the       
various rays2 this is likewise true of  
water and window panes4  ,stained-glass 
windows owe their charm and beauty to   
the presence in the glass of various    
dyes and pigments which absorb in       
different amounts some colors from white
 light and transmit others4 ,these      
pigments or dyes are added to the glass 
while it is in the molten state1 and the
 beauty of a stained-glass window       
depends largely upon the richness and   
the delicacy of the pigments used4      
#acj4 ,reflected ,light4 ,opaque        
,objects4 ,in ,section #ajf we learned  
that most objects are visible to us     
because of the light diffusely reflected
 from them4 ,a white object1 such as a  
sheet of paper1 a whitewashed fence1 or 

a table cloth1 absorbs little of the    
light which falls upon it1 but reflects 
nearly all1 thus producing the sensation
 of white4 ,a red carpet absorbs the    
light rays incident upon it except the  
red rays1 and these it reflects to the  
eye4  ,any substance or object which    
reflects none of the rays which fall    
upon it1 but absorbs all1 appears black2
 no rays reach the eye1 and there is an 
absence of any color sensation4 ,coal   
and tar and soot are good illustrations 
of objects which absorb all the light   
which falls upon them4  #aca4 ,how and  
,why ,colors ,change4 ,matching ,colors4
 ,most women prefer to shop in the      
morning and early afternoon when the    
sunlight illuminates shops and          
factories1 and when gas and electricity 
do not throw their spell over colors4   
,practically all people know that       
ribbons and ties1 trimmings and dresses1
 frequently look different at night from
 what they do in the daytime4 ,it is not
 safe to match colors by artificial     

light2 cloth which looks red by night   
may be almost purple by day4 ,indeed1   
the color of an object depends upon the 
color of the light which falls upon it4 
,strange sights are seen on the ,fourth 
of ,july when variously colored         
fireworks are blazing4 ,the child with a
 white blouse appears first red1 then   
blue1 then green1 according as his      
powders burn red1 blue1 or green4 ,the  
face of the child changes from its      
normal healthy hue to a brilliant red   
and then to ghastly shades4  ,suppose1  
for example1 that a white hat is held at
 the red end of the spectrum or in any  
red light4 ,the characteristics of white
 objects is their ability to reflect all
 the various rays that fall upon them4  
,here1 however1 the only light which    
falls upon the white hat is red light1  
hence the only light which the hat has  
to reflect is red light and the hat     
consequently appears red4 ,similarly1 if
 a white hat is placed in a blue light1 
it will reflect all the light which     

falls upon it1 namely1 blue light1 and  
will appear blue4 ,if a red hat is held 
in a red light1 it is seen in its proper
 color4 ,if a red hat is held in a blue 
light1 it appears black2 it cannot      
reflect any of the blue light because   
that is all absorbed and there is no red
 light to reflect4  ,a child wearing a  
green frock on ,independence ,day seems 
at night to be wearing a black frock1 if
 standing near powders burning with red1
 blue1 or violet light4  #acb4 ,pure1   
,simple ,colors--,things as they ,seem4 
,to the eye white light appears a       
simple1 single color4 ,it reveals its   
compound nature to us only when passed  
through a prism1 when it shows itself to
 be compounded of an infinite number of 
colors which ,sir ,isaac ,newton grouped
 in seven divisions3 violet1 indigo1    
blue1 green1 yellow1 orange1 and red4   
,we naturally ask ourselves whether     
these colors which compose white light  
are themselves in turn compound8 ,to    
answer that question1 let us very       

carefully insert a second prism in the  
path of the rays which issue from the   
first prism1 carefully barring out the  
remaining six kinds of rays4 ,if the red
 light is compound1 it will be broken up
 into its constituent parts and will    
form a typical spectrum of its own1 just
 as white light did after its passage   
through a prism4 ,but the red rays pass 
through the second prism1 are refracted1
 and bent from this course1 and no new  
colors appear1 no new spectrum is       
formed4 ,evidently a ray of spectrum red
 is a simple color1 not a compound      
color4  ,if a similar experiment is made
 with the remaining spectrum rays1 the  
result is always the same3 the          
individual spectrum colors remain       
simple1 pure colors4 ,the individual    
spectrum colors are groups of simple1   
pure colors4  ,illustration3 ,,fig4     
#hh4--,violet and green give blue4      
,green1 blue1 and red give white4  #acc4
 ,colors not as they ,seem--,compound   
,colors4 ,if one half of a cardboard    

disk 7,fig4 #hh7 is painted green1 and  
the other half violet1 and the disk is  
slipped upon a toy top1 and spun        
rapidly1 the rotating disk will appear  
blue2 if red and green are used in the  
same way instead of green and violet1   
the rotating disk will appear yellow4 ,a
 combination of red and yellow will give
 orange4 ,the colors formed in this way 
do not appear to the eye different from 
the spectrum colors1 but they are       
actually very different4 ,the spectrum  
colors1 as we saw in the preceding      
,section1 are pure1 simple colors1 while
 the colors formed from the rotating    
disk are in reality compounded of       
several totally different rays1 although
 in appearance the resulting colors are 
pure and simple4  ,if it were not that  
colors can be compounded1 we should be  
limited in hue and shade to the seven   
spectral colors2 the wealth and beauty  
of color in nature1 art1 and commerce   
would be unknown2 the flowers with their
 thousands of hues would have a poverty 

of color undreamed of2 art would lose   
its magenta1 its lilac1 its olive1 its  
lavender1 and would have to work its    
wonders with the spectral colors alone4 
,by compounding various colors in       
different proportions1 new colors can be
 formed to give freshness and variety4  
,if one third of the rotating disk is   
painted blue1 and the remainder white1  
the result is lavender2 if fifteen parts
 of white1 four parts of red1 and one   
part of blue are arranged on the disk1  
the result is lilac4 ,olive is obtained 
from a combination of two parts green1  
one part red1 and one part black2 and   
the soft rich shades of brown are all   
due to different mixtures of black1 red1
 orange1 or yellow4  #acd4 ,the         
,essential ,colors4 ,strange and        
unexpected facts await us at every turn 
in science6 ,if the rotating cardboard  
disk 7,fig4 #hh7 is painted one third   
red1 one third green1 and one third     
blue1 the resulting color is white4     
,while the mixture of the spectral      

colors produces white1 it is not        
necessary to have all of the spectral   
colors in order to obtain white2 because
 a mixture of the following colors      
alone1 red1 green1 and blue1 will give  
white4 ,moreover1 by the mixture of     
these three colors in proper            
proportions1 any color of the spectrum1 
such as yellow or indigo or orange1 may 
be obtained4 ,the three spectral colors1
 red1 green1 and blue1 are called       
primary or essential hues1 because all  
known tints of color may be produced by 
the careful blending of blue1 green1 and
 red in the proper proportions2 for     
example1 purple is obtained by the      
blending of red and blue1 and orange by 
the blending of red and yellow4  #ace4  
,color ,blindness4 ,the nerve fibers of 
the eye which carry the sensation of    
color to the brain are particularly     
sensitive to the primary colors--red1   
green1 blue4 ,indeed1 all color         
sensations are produced by the          
stimulation of three sets of nerves     

which are sensitive to the primary      
colors4 ,if one sees purple1 it is      
because the optic nerves sensitive to   
red and blue 7purple equals red plus    
blue7 have carried their separate       
messages to the brain1 and the blending 
of the two distinct messages in the     
brain has given the sensation of purple4
 ,if a red rose is seen1 it is because  
the optic nerves sensitive to red have  
been stimulated and have carried the    
message to the brain4  ,a snowy field   
stimulates equally all three sets of    
optic nerves--the red1 the green1 and   
the blue4 ,lavender1 which is one part  
blue and three parts white1 would       
stimulate all three sets of nerves1 but 
with a maximum of stimulation for the   
blue4 ,equal stimulation of the three   
sets would give the impression of white4
  ,a color-blind person has some defect 
in one or more of the three sets of     
nerves which carry the color message to 
the brain4 ,suppose the nerve fibers    
responsible for carrying the red are    

totally defective4 ,if such a person    
views a yellow flower1 he will see it as
 a green flower4 ,yellow contains both  
red and green1 and hence both the red   
and green nerve fibers should be        
stimulated1 but the red nerve fibers are
 defective and do not respond1 the green
 nerve fibers alone being stimulated1   
and the brain therefore interprets      
green4  ,a well-known author gives an   
amusing incident of a dinner party1 at  
which the host offered stewed tomato for
 apple sauce4 ,what color nerves were   
defective in the case of the host8  ,in 
some employments color blindness in an  
employee would be fatal to many lives4  
,engineers and pilots govern the        
direction and speed of trains and boats 
largely by the colored signals which    
flash out in the night's darkness or    
move in the day's bright light1 and any 
mistake in the reading of color signals 
would imperil the lives of travelers4   
,for this reason a rigid test in color  
is given to all persons seeking such    

employment1 and the ability to match    
ribbons and yarns of all ordinary hues  
is an unvarying requirement for         
efficiency4     ,,chapter ,,xiv  ,,heat 
,,and ,,light ,,as ,,companions         
,the night has a thousand eyes1         
,and the day but one2     ,yet the light
 of the bright world dies       ,with   
the dying sun4   #acf4 ,most bodies     
which glow and give out light are hot2  
the stove which glows with a warm red is
 hot and fiery2 smoldering wood is black
 and lifeless2 glowing coals are far    
hotter than black ones4 ,the            
stained-glass window softens and mellows
 the bright light of the sun1 but it    
also shuts out some of the warmth of the
 sun's rays2 the shady side of the      
street spares our eyes the intense glare
 of the sun1 but may chill us by the    
absence of heat4 ,our illumination1     
whether it be oil lamp or gas jet or    
electric light1 carries with it heat2   
indeed1 so much heat that we refrain    
from making a light on a warm summer's  

night because of the heat which it      
unavoidably furnishes4  #acg4 ,red a    
,warm ,color4 ,we have seen that heat   
and light usually go hand in hand4 ,in  
summer we lower the shades and close the
 blinds in order to keep the house cool1
 because the exclusion of light means   
the exclusion of some heat2 in winter we
 open the blinds and raise the shades in
 order that the sun may stream into the 
room and flood it with light and warmth4
 ,the heat of the sun and the light of  
the sun seem boon companions4  ,we can  
show that when light passes through a   
prism and is refracted1 forming a       
spectrum1 as in ,section #abg1 it is    
accompanied by heat4 ,if we hold a      
sensitive thermometer in the violet end 
of the spectrum so that the violet rays 
fall upon the bulb1 the reading of the  
mercury will be practically the same as 
when the thermometer is held in any dark
 part of the room2 if1 however1 the     
thermometer is slowly moved toward the  
red end of the spectrum1 a change occurs

 and the mercury rises slowly but       
steadily1 showing that heat rays are    
present at the red end of the spectrum4 
,this agrees with the popular notion1   
formed independently of science1 which  
calls the reds the warm colors4 ,every  
one of us associates red with warmth2 in
 the summer red is rarely worn1 it looks
 hot2 but in winter red is one of the   
most pleasing colors because of the     
sense of warmth and cheer it brings4    
,all light rays are accompanied by a    
small amount of heat1 but the red rays  
carry the most4  ,what seems perhaps the
 most unexpected thing1 is that the     
temperature1 as indicated by a sensitive
 thermometer1 continues to rise if the  
thermometer is moved just beyond the red
 light of the spectrum4 ,there actually 
seems to be more heat beyond the red    
than in the red1 but if the thermometer 
is moved too far away1 the temperature  
again falls4 ,later we shall see what   
this means4  #ach4 ,the ,energy of the  
,sun4 ,it is difficult to tell how much 

of the energy of the sun is light and   
how much is heat1 but it is easy to     
determine the combined effect of heat   
and light4  ,illustration3 ,,fig4       
#hi4--,the energy of the sun can be     
measured in heat units4  ,suppose we    
allow the sun's rays to fall            
perpendicularly upon a metal cylinder   
coated with lampblack and filled with a 
known quantity of water 7,fig4 #hi72 at 
the expiration of a few hours the       
temperature of the water will be        
considerably higher4 ,lampblack is a    
good absorber of heat1 and it is used as
 a coating in order that all the light  
rays which fall upon the cylinder may be
 absorbed and none lost by reflection4  
,light and heat rays fall upon the      
lampblack1 pass through the cylinder1   
and heat the water4 ,we know that the   
red light rays have the largest share   
toward heating the water1 because if the
 cylinder is surrounded by blue glass   
which absorbs the red rays and prevents 
their passage into the water1 the       

temperature of the water begins to fall4
 ,that the other light rays have a small
 share would have been clear from the   
preceding ,section4  ,all the energy of 
the sunshine which falls upon the       
cylinder1 both as heat and as light1 is 
absorbed in the form of heat1 and the   
total amount of this energy can be      
calculated from the increase in the     
temperature of the water4 ,the energy   
which heated the water would have passed
 onward to the surface of the earth if  
its path had not been obstructed by the 
cylinder of water2 and we can be sure   
that the energy which entered the water 
and changed its temperature would       
ordinarily have heated an equal area of 
the earth's surface2 and from this1 we  
can calculate the energy falling upon   
the entire surface of the earth during  
any one day4  ,computations based upon  
this experiment show that the earth     
receives daily from the sun the         
equivalent of #cda1jjj1jjj1jjj horse    
power--an amount inconceivable to the   

human mind4  ,professor ,young gives a  
striking picture of what this energy of 
the sun could do4 ,a solid column of ice
 #ic1jjj1jjj miles long and #b-a_/d     
miles in diameter could be melted in a  
single second if the sun could          
concentrate its entire power on the ice4
  ,while the amount of energy received  
daily from the sun by the earth is      
actually enormous1 it is small in       
comparison with the whole amount given  
out by the sun to the numerous heavenly 
bodies which make up the universe4 ,in  
fact1 of the entire outflow of heat and 
light1 the earth receives only one part 
in two thousand million1 and this is a  
very small portion indeed4  #aci4 ,how  
,light and ,heat ,travel from the ,sun  
to ,us4 ,astronomers tell us that the   
sun--the chief source of heat and       
light--is #ic1jjj1jjj miles away from   
us2 that is1 so far distant that the    
fastest express train would require     
about #agf years to reach the sun4 ,how 
do heat and light travel through this   

vast abyss of space8  ,illustration3    
,,fig4 #ij4--,waves formed by a pebble4 
,a quiet pool and a pebble will help to 
make it clear to us4 ,if we throw a     
pebble into a quiet pool 7,fig4 #ij71   
waves or ripples form and spread out in 
all directions1 gradually dying out as  
they become more and more distant from  
the pebble4 ,it is a strange fact that  
while we see the ripple moving farther  
and farther away1 the particles of water
 are themselves not moving outward and  
away1 but are merely bobbing up and     
down1 or are vibrating4 ,if you wish to 
be sure of this1 throw the pebble near a
 spot where a chip lies quiet on the    
smooth pond4 ,after the waves form1 the 
chip rides up and down with the water1  
but does not move outward2 if the water 
itself were moving outward1 it would    
carry the chip with it1 but the water   
has no forward motion1 and hence the    
chip assumes the only motion possessed  
by the water1 that is1 an up-and-down   
motion4 ,perhaps a more simple          

illustration is the appearance of a     
wheat field or a lawn on a windy day2   
the wind sweeps over the grass1         
producing in the grass a wave like the  
water waves of the ocean1 but the blades
 of grass do not move from their        
accustomed place in the ground1 held    
fast as they are by their roots4  ,if a 
pebble is thrown into a quiet pool1 it  
creates ripples or waves which spread   
outward in all directions1 but which    
soon die out1 leaving the pool again    
placid and undisturbed4 ,if now we could
 quickly withdraw the pebble from the   
pool1 the water would again be disturbed
 and waves would form4 ,if the pebble   
were attached to a string so that it    
could be dropped into the water and     
withdrawn at regular intervals1 the     
waves would never have a chance to      
disappear1 because there would always be
 a regularly timed definite disturbance 
of the water4 ,learned men tell us that 
all hot bodies and all luminous bodies  
are composed of tiny particles1 called  

molecules1 which move unceasingly back  
and forth with great speed4 ,in ,section
 #ie we saw that the molecules of all   
substances move unceasingly2 their      
speed1 however1 is not so great1 nor are
 their motions so regularly timed as are
 those of the heat-giving and the       
light-giving particles4 ,as the         
particles of the hot and luminous bodies
 vibrate with great speed and force they
 violently disturb the medium around    
them1 and produce a series of waves     
similar to those produced in the water  
by the pebble4 ,if1 however1 a pebble is
 thrown into the water very gently1 the 
disturbance is slight1 sometimes too    
slight to throw the water into waves2 in
 the same way objects whose molecules   
are in a state of gentle motion do not  
produce light4  ,the particles of       
heat-giving and light-giving bodies are 
in a state of rapid vibration1 and      
thereby disturb the surrounding medium1 
which transmits or conveys the          
disturbance to the earth or to other    

objects by a train of waves4 ,when these
 waves reach their destination1 the     
sensation of light or heat is produced4 
,we see the water waves1 but we can     
never see with the eye the heat and     
light waves which roll in to us from    
that far-distant source1 the sun4 ,we   
can be sure of them only through their  
effect on our bodies1 and by the visible
 work they do4  #adj4 ,how ,heat and    
,light ,differ4 ,if heat and light are  
alike due to the regular1 rapid motion  
of the particles of a body1 and are     
similarly conveyed by waves1 how is it1 
then1 that heat and light are apparently
 so different8  ,light and heat differ  
as much as the short1 choppy waves of   
the ocean and the slow1 long swell of   
the ocean1 but not more so4 ,the sailor 
handles his boat in one way in a choppy 
sea and in a different way in a rolling 
sea1 for he knows that these two kinds  
of waves act dissimilarly4 ,the long1   
slow swell of the ocean would correspond
 with the longer1 slower waves which    

travel out from the sun1 and which on   
reaching us are interpreted as heat4    
,the shorter1 more frequent waves of the
 ocean would typify the short1 rapid    
waves which leave the sun1 and which on 
reaching us are interpreted as light4   
,,chapter ,,xv  ,,artificial ,,lighting 
#ada4 ,we seldom consider what life     
would be without our wonderful methods  
of illumination which turn night into   
day1 and prolong the hours of work and  
pleasure4 ,yet it was not until the     
nineteenth century that the marvelous   
change was made from the short-lived    
candle to the more enduring oil lamp4   
,before the coming of the lamp1 even in 
large cities like ,paris1 the only      
artificial light to guide the belated   
traveler at night was the candle        
required to be kept burning in an       
occasional window4  ,with the invention 
of the kerosene lamp came more efficient
 lighting of home and street1 and with  
the advent of gas and electricity came a
 light so effective that the hours of   

business1 manufacture1 and pleasure     
could be extended far beyond the setting
 of the sun4  ,the production of light  
by candle1 oil1 and gas will be         
considered in the following paragraphs1 
while illumination by electricity will  
be reserved for a later ,chapter4  #adb4
 ,the ,candle4 ,candles were originally 
made by dipping a wick into melting     
tallow1 withdrawing it1 allowing the    
adhered tallow to harden1 and repeating 
the dipping until a satisfactory        
thickness was obtained4 ,the more modern
 method consists in pouring a fatty     
preparation into a mold1 at the center  
of which a wick has been placed4  ,the  
wick1 when lighted1 burns for a brief   
interval with a faint1 uncertain light2 
almost immediately1 however1 the        
intensity of the light increases and the
 illumination remains good as long as   
the candle lasts4 ,the heat of the      
burning tallow melts more of the tallow 
near it1 and this liquid fat is quickly 
sucked up into the burning wick4 ,the   

heat of the flame is sufficient to      
change most of this liquid into a gas1  
that is1 to vaporize the liquid1 and    
furthermore to set fire to the gas thus 
formed4 ,these heated gases burn with a 
bright yellow flame4  #adc4 ,the ,oil   
,lamp4 ,the simple candle of our        
ancestors was now replaced by the oil   
lamp1 which gave a brighter1 steadier1  
and more permanent illumination4 ,the   
principle of the lamp is similar to that
 of the candle1 except that the wick is 
saturated with kerosene or oil rather   
than with fat4 ,the heat from the       
burning wick is sufficient to change the
 oil into a gas and then to set fire to 
the gas4 ,by placing a chimney over the 
burning wick1 a constant and uniform    
draught of air is maintained around the 
blazing gases1 and hence a steady1      
unflickering light is obtained4 ,gases  
and carbon particles are set free by the
 burning wick4 ,in order that the gases 
may burn and the solid particle glow1 a 
plentiful supply of oxygen is necessary4

 ,if the quantity of air is             
insufficient1 the carbon particles      
remain unburned and form soot4 ,a lamp  
smokes when the air which reaches the   
wick is insufficient to burn the rapidly
 formed carbon particles2 this explains 
the danger of turning a lamp wick too   
high and producing more carbon particles
 than can be oxidized by the air        
admitted through the lamp chimney4  ,one
 great disadvantage of oil lamps and oil
 stoves is that they cannot be carried  
safely from place to place4 ,it is      
almost impossible to carry a lamp       
without spilling the oil4 ,the flame    
soon spreads from the wick to the       
overflowing oil and in consequence the  
lamp blazes and an explosion may result4
 ,candles1 on the other hand1 are safe  
from explosion2 the dripping grease is  
unpleasant but not dangerous4  ,the     
illumination from a shaded oil lamp is  
soft and agreeable1 but the trimming of 
the wicks1 the refilling of bowls1 and  
the cleaning of chimneys require time   

and labor4 ,for this reason1 the        
introduction of gas met with widespread 
success4 ,the illumination from an      
ordinary gas jet is stronger than that  
from an ordinary lamp1 and the stronger 
illumination added to the greater       
convenience has made gas a very popular 
source of light4  #add4 ,gas ,burners   
and ,gas ,mantles4 ,for a long time1 the
 only gas flame used was that in which  
the luminosity resulted in heating      
particles of carbon to incandescence4   
,recently1 however1 that has been widely
 replaced by use of a ,bunsen flame upon
 an incandescent mantle1 such as the    
,welsbach4 ,the principle of the        
incandescent mantle is very simple4     
,when certain substances1 such as       
thorium and cerium1 are heated1 they do 
not melt or vaporize1 but glow with an  
intense bright light4 ,welsbach made use
 of this fact to secure a burner in     
which the illumination depends upon the 
glowing of an incandescent1 solid       
mantle1 rather than upon the blazing of 

a burning gas4 ,he made a cylindrical   
mantle of thin fabric1 and then soaked  
it in a solution of thorium and cerium  
until it became saturated with the      
chemical4 ,the mantle thus impregnated  
with thorium and cerium is placed on the
 gas jet1 but before the gas is turned  
on1 a lighted match is held to the      
mantle in order to burn away the thin   
fabric4 ,after the fabric has been      
burned away1 there remains a coarse     
gauze mantle of the desired chemicals4  
,if now the gas cock is opened1 the     
escaping gas is ignited1 the heat of the
 flame will raise the mantle to         
incandescence and will produce a        
brilliant light4 ,a very small amount of
 burning gas is sufficient to raise the 
mantle to incandescence1 and hence1 by  
the use of a mantle1 intense light is   
secured at little cost4 ,the mantle     
saves us gas1 because the cock is       
usually turned on full whether we use a 
plain burner or a mantle burner4 ,but1  
nevertheless1 gas is saved1 because when

 the mantle is adjusted to the gas jet1 
the pressure of the gas is lessened by a
 mechanical device and hence less gas   
escapes and burns4 ,by actual           
experiment1 it has been found that an   
ordinary burner consumes about five     
times as much gas per candle power as   
the best incandescent burner1 and hence 
is about five times as expensive4 ,one  
objection to the mantles is their       
tendency to break4 ,but if the mantles  
are carefully adjusted on the burner and
 are not roughly jarred in use1 they    
last many months2 and since the best    
quality cost only twenty-five cents1 the
 expense of renewing the mantles is     
slight4  #ade4 ,gas for ,cooking4 ,if a 
cold object is held in the bright flame 
of an ordinary gas jet1 it becomes      
covered with soot1 or particles of      
unburned carbon4 ,although the flame is 
surrounded by air1 the central portion  
of it does not receive sufficient oxygen
 to burn up the numerous carbon         
particles constantly thrown off by the  

burning gas1 and hence many carbon      
particles remain in the flame as        
glowing1 incandescent masses4 ,that some
 unburned carbon is present in a flame  
is shown by the fact that whenever a    
cold object is held in the flame1 it    
becomes smoked or covered with soot4 ,if
 enough air were supplied to the flame  
to burn up the carbon as fast as it was 
set free1 there would be no deposition  
of soot on objects held over the flame  
or in it1 because the carbon would be   
transformed into gaseous matter4        
,unburned carbon would be objectionable 
in cooking stoves where utensils are    
constantly in contact with the flame1   
and for this reason cooking stoves are  
provided with an arrangement by means of
 which additional air is supplied to the
 burning gas in quantities adequate to  
insure complete combustion of the       
rapidly formed carbon particles4 ,an    
opening is made in the tube through     
which gas passes to the burner1 and as  
the gas moves past this opening1 it     

carries with it a draft of air4 ,these  
openings are visible on all gas stoves1 
and should be kept clean and free of    
clogging1 in order to insure complete   
combustion4 ,so long as the supply of   
air is sufficient1 the flame burns with 
a dull blue color1 but when the supply  
falls below that needed for complete    
burning of the carbon1 the blue color   
disappears1 and a yellow flame takes its
 place1 and with the yellow flame the   
deposition of soot is inevitable4  #adf4
 ,by-products of ,coal ,gas4 ,many      
important products besides illuminating 
gas are obtained from the distillation  
of soft coal4 ,ammonia is made from the 
liquids which collect in the condensers2
 anilin1 the source of exquisite dyes1  
is made from the thick1 tarry           
distillate1 and coke is the residue left
 in the clay retorts4 ,the coal tar     
yields not only anilin1 but also        
carbolic acid and naphthalene1 both of  
which are commercially valuable1 the    
former as a widely used disinfectant1   

and the latter as a popular moth        
preventive4  ,from a ton of good        
gas-producing coal can be obtained about
 #aj1jjj cubic feet of illuminating gas1
 and as by-products #f pounds of        
ammonia1 #ab gallons of coal tar1 and   
#acjj pounds of coke4  #adg4 ,natural   
,gas4 ,animal and vegetable matter      
buried in the depth of the earth        
sometimes undergoes natural             
distillation1 and as a result gas is    
formed4 ,the gas produced in this way is
 called natural gas4 ,it is a cheap     
source of illumination1 but is found in 
relatively few localities and only in   
limited quantity4  #adh4 ,acetylene4 ,in
 #ahib it was discovered that lime and  
coal fused together in the intense heat 
of the electric furnace formed a        
crystalline1 metallic-looking substance 
called calcium carbide4 ,as a result of 
that discovery1 this substance was soon 
made on a large scale and sold at a     
moderate price4 ,the cheapness of       
calcium carbide has made it possible for

 the isolated farmhouse to discard oil  
lamps and to have a private gas system4 
,when the hard1 gray crystals of calcium
 carbide are put in water1 they give off
 acetylene1 a colorless gas which burns 
with a brilliant white flame4 ,if bits  
of calcium carbide are dropped into a   
test tube containing water1 bubbles of  
gas will be seen to form and escape into
 the air1 and the escaping gas may be   
ignited by a burning match held near the
 mouth of the test tube4 ,when chemical 
action between the water and carbide has
 ceased1 and gas bubbles have stopped   
forming1 slaked lime is all that is left
 of the dark gray crystals which were   
put into the water4  ,when calcium      
carbide is used as a source of          
illumination1 the crystals are          
mechanically dropped into a tank        
containing water1 and the gas generated 
is automatically collected in a small   
sliding tank1 whence it passes through  
pipes to the various rooms4 ,the slaked 
lime1 formed while the gas was          

generated1 collects at the bottom of the
 tanks and is removed from time to time4
  ,the cost of an acetylene generator is
 about #ej for a small house1 and the   
cost of maintenance is not more than    
that of lamps4 ,the generator does not  
require filling oftener than once a     
week1 and the labor is less than that   
required for oil lamps4 ,in a house in  
which there were twenty burners1 the    
tanks were filled with water and carbide
 but once a fortnight4 ,acetylene is    
seldom used in large cities1 but it is  
very widely used in small communities   
and is particularly convenient in more  
or less remote summer residences4       
,electric ,lights4 ,the most recent and 
the most convenient lighting is that    
obtained by electricity4 ,a fine1       
hairlike filament within a glass bulb is
 raised to incandescence by the heat of 
an electric current4 ,this form of      
illumination will be considered in      
connection with electricity4            
,,chapter ,,xvi  ,,man',s ,,way ,,of    

,,helping ,,himself   #adi4             
,labor-saving ,devices4 ,to primitive   
man belonged more especially the arduous
 tasks of the out-of-door life3 the     
clearing of paths through the           
wilderness2 the hauling of material2 the
 breaking up of the hard soil of barren 
fields into soft loam ready to receive  
the seed2 the harvesting of the ripe    
grain1 etc4  ,illustration3 ,,fig4      
#ia4--,prying a stone out of the ground4
  ,the more intelligent races among men 
soon learned to help themselves in these
 tasks4 ,for example1 our ancestors in  
the field soon learned to pry stones out
 of the ground 7,fig4 #ia7 rather than  
to undertake the almost impossible task 
of lifting them out of the earth in     
which they were embedded2 to swing      
fallen trees away from a path by means  
of rope attached to one end rather than 
to attempt to remove them single-handed2
 to pitch hay rather than to lift it2 to
 clear a field with a rake rather than  
with the hands2 to carry heavy loads in 

wheelbarrows 7,fig4 #ib7 rather than on 
the shoulders2 to roll barrels up a     
plank 7,fig4 #ic7 and to raise weights  
by ropes4 ,in every case1 whether in the
 lifting of stones1 or the felling of   
trees1 or the transportation of heavy   
weights1 or the digging of the ground1  
man used his brain in the invention of  
mechanical devices which would relieve  
muscular strain and lighten physical    
labor4  ,if all mankind had depended    
upon physical strength only1 the world  
to-day would be in the condition        
prevalent in parts of ,africa1 ,asia1   
and ,south ,america1 where the natives  
loosen the soil with their hands or with
 crude implements 7,fig4 #id71 and      
transport huge weights on their         
shoulders and heads4  ,illustration3    
,,fig4 #ib4--,the wheelbarrow lightens  
labor4  ,any mechanical device 7,figs4  
#ie and #if71 whereby man's work can be 
more conveniently done1 is called a     
machine2 the machine itself never does  
any work--it merely enables man to use  

his own efforts to better advantage4    
,illustration3 ,,fig4 #ic4--,rolling    
barrels up a plank4  #aej4 ,when do we  
,work8 ,whenever1 as a result of effort 
or force1 an object is moved1 work is   
done4 ,if you lift a knapsack from the  
floor to the table1 you do work because 
you use force and move the knapsack     
through a distance equal to the height  
of the table4 ,if the knapsack were     
twice as heavy1 you would exert twice as
 much force to raise it to the same     
height1 and hence you would do double   
the work4 ,if you raised the knapsack   
twice the distance1--say to your        
shoulders instead of to the level of the
 table1--you would do twice the work1   
because while you would exert the same  
force you would continue it through     
double the distance4  ,illustration3    
,,fig4 #id4--;,crude method of farming4 
,lifting heavy weights through great    
distances is not the only way in which  
work is done4 ,painting1 chopping wood1 
hammering1 plowing1 washing1 scrubbing1 

sewing1 are all forms of work4 ,in      
painting1 the moving brush spreads paint
 over a surface2 in chopping wood1 the  
descending ax cleaves the wood asunder2 
in scrubbing1 the wet mop rubbed over   
the floor carries dirt away2 in every   
conceivable form of work1 force and     
motion occur4  ,a man does work when he 
walks1 a woman does work when she rocks 
in a chair--although here the work is   
less than in walking4 ,on a windy day   
the work done in walking is greater than
 normal4 ,the wind resists our progress1
 and we must exert more force in order  
to cover the same distance4 ,walking    
through a plowed or rough field is much 
more tiring than to walk on a smooth    
road1 because1 while the distance       
covered may be the same1 the effort put 
forth is greater1 and hence more work is
 done4 ,always the greater the          
resistance encountered1 the greater the 
force required1 and hence the greater   
the work done4  ,the work done by a boy 
who raises a #e-pound knapsack to his   

shoulder would be #ex#d1 or #bj1        
providing his shoulders were #d feet    
from the ground4  ,the amount of work   
done depends upon the force used and the
 distance covered 7sometimes called     
displacement71 and hence we can say that
         ,work  force multiplied by     
distance1   or  ,w  f  d4  #aea4        
,machines4 ,a glance into our machine   
shops1 our factories1 and even our homes
 shows how widespread is the use of     
complex machinery4 ,but all machines1   
however complicated in appearance1 are  
in reality but modifications and        
combinations of one or more of four     
simple machines devised long ago by our 
remote ancestors4 ,these simple devices 
are known to-day1 as 7#a7 the lever1    
represented by a crowbar1 a pitchfork2  
7#b7 the inclined plane1 represented by 
the plank upon which barrels are rolled 
into a wagon2 7#c7 the pulley1          
represented by almost any contrivance   
for the raising of furniture to upper   
stories2 7#d7 the wheel and axle1       

represented by cogwheels and coffee     
grinders4  ,illustration3 ,,fig4        
#ie4--,primitive method of grinding     
corn4  ,suppose a #fjj-pound bowlder    
which is embedded in the ground is      
needed for the tower of a building4 ,the
 problem of the builder is to get the   
heavy bowlder out of the ground1 to load
 it on a wagon for transportation1 and  
finally to raise it to the tower4       
,obviously1 he cannot do this alone2 the
 greatest amount of force of which he is
 capable would not suffice to accomplish
 any one of these tasks4 ,how then does 
he help himself and perform the         
impossible8 ,simply1 by the use of some 
of the machine types mentioned above1   
illustrations of which are known in a   
general way to every schoolboy4 ,the    
very knife with which a stick is        
whittled is a machine4  ,illustration3  
,,fig4 #if4--,separating rice grains by 
flailing4  ,illustration3 ,,fig4        
#ig4--,the principle of the lever4      
#aeb4 ,the ,lever4 ,balance a foot rule1

 containing a hole at its middle point  
,f1 as shown in ,figure #ig4 ,if now a  
weight of #a pound is suspended from the
 bar at some point1 say #ab1 the balance
 is disturbed1 and the bar swings about 
the point ,f as a center4 ,the balance  
can be regained by suspending an        
equivalent weight at the opposite end of
 the bar1 or by applying a #b-pound     
weight at a point #c inches to the left 
of ,f4 ,in the latter case a force of #a
 pound actually balances a force of #b  
pounds1 but the #a-pound weight is twice
 as far from the point of suspension as 
is the #b-pound weight4 ,the small      
weight makes up in distance what it     
lacks in magnitude4  ,such an           
arrangement of a rod or bar is called a 
lever4 ,in any form of lever there are  
only three things to be considered3 the 
point where the weight rests1 the point 
where the force acts1 and the point     
called the fulcrum about which the rod  
rotates4  ,the distance from the force  
to the fulcrum is called the force arm4 

,the distance from the weight to the    
fulcrum is called the weight arm2 and it
 is a law of levers1 as well as of all  
other machines1 that the force          
multiplied by the length of the force   
arm must equal the weight multiplied by 
the length of the weight arm4    ,force 
force arm  weight  weight arm4  ,a force
 of #a pound at a distance of #f1 or    
with a force arm #f1 will balance a     
weight of #b pounds with a weight arm   
#c2 that is1    #a  #f  #b  #c4         
,similarly a force of #aj pounds may be 
made to sustain a weight of #ajj pounds1
 providing the force arm is #aj times   
longer than the weight arm2 and a force 
arm of #hjj pounds1 at a distance of #aj
 feet from the fulcrum1 may be made to  
sustain a weight of #hjjj pounds1       
providing the weight is #a foot from the
 fulcrum4  #aec4 ,applications of the   
,lever4 ,by means of a lever1 a         
#fjj-pound bowlder can be easily pried  
out of the ground4 ,let the lever1 any  
strong metal bar1 be supported on a     

stone which serves as fulcrum2 then if a
 man exerts his force at the end of the 
rod somewhat as in ,figure #ia 7p4      
#aed71 the force arm will be the        
distance from the stone or fulcrum to   
the end of the bar1 and the weight arm  
will be the distance from the fulcrum to
 the bowlder itself4 ,the man pushes    
down with a force of #ajj pounds1 but   
with that amount succeeds in prying up  
the #fjj-pound bowlder4 ,if1 however1   
you look carefully1 you will see that   
the force arm is #f times as long as the
 weight arm1 so that the smaller force  
is compensated for by the greater       
distance through which it acts4  ,at    
first sight it seems as though the man's
 work were done for him by the machine4 
,but this is not so4 ,the man must lower
 his end of the lever #c feet in order  
to raise the bowlder #f inches out of   
the ground4 ,he does not at any time    
exert a large force1 but he accomplishes
 his purpose by exerting a small force  
continuously through a correspondingly  

greater distance4 ,he finds it easier to
 exert a force of #ajj pounds           
continuously until his end has moved #c 
feet rather than to exert a force of    
#fjj pounds on the bowlder and move it  
#f inches4  ,by the time the stone has  
been raised the man has done as much    
work as though the stone had been raised
 directly1 but his inability to put     
forth sufficient muscular force to raise
 the bowlder directly would have        
rendered impossible a result which was  
easily accomplished when through the    
medium of the lever he could extend his 
small force through greater distance4   
#aed4 ,the ,wheelbarrow as a ,lever4    
,the principle of the lever is always   
the same2 but the relative position of  
the important points may vary4 ,for     
example1 the fulcrum is sometimes at one
 end1 the force at the opposite end1 and
 the weight to be lifted between them4  
,illustration3 ,,fig4 #ih4--;,a slightly
 different form of lever4  ,suspend a   
stick with a hole at its center as in   

,figure #ih1 and hang a #d-pound weight 
at a distance of #a foot from the       
fulcrum1 supporting the load by means of
 a spring balance #b feet from the      
fulcrum4 ,the pointer on the spring     
balance shows that the force required to
 balance the #d-pound load is but #b    
pounds4  ,the force is #b feet from the 
fulcrum1 and the weight 7#d7 is #a foot 
from the fulcrum1 so that    ,force     
distance  ,weight  distance1   or       
#b  #b  #d  #a4  ,move the #d-pound     
weight so that it is very near the      
fulcrum1 say but #f inches from it2 then
 the spring balance registers a force   
only one fourth as great as the weight  
which it suspends4 ,in other words a    
force of #a at a distance of #bd inches 
7#b feet7 is equivalent to a force of #d
 at a distance of #f inches4            
,illustration3 ,,fig4 #ii4--,the        
wheelbarrow lightened labor4  ,one of   
the most useful levers of this type is  
the wheelbarrow 7,fig4 #ii74 ,the       
fulcrum is at the wheel1 the force is at

 the handles1 the weight is on the      
wheelbarrow4 ,if the load is halfway    
from the fulcrum to the man's hands1 the
 man will have to lift with a force     
equal to one half the load4 ,if the load
 is one fourth as far from the fulcrum  
as the man's hands1 he will need to lift
 with a force only one fourth as great  
as that of the load4  ,illustration3    
,,fig4 #ajj4--;,a modified wheelbarrow4 
,this shows that in loading a           
wheelbarrow1 it is important to arrange 
the load as near to the wheel as        
possible4  ,illustration3 ,,fig4        
#aja4--,the nutcracker is a lever4  ,the
 nutcracker 7,fig4 #aja7 is an          
illustration of a double lever of the   
wheelbarrow kind2 the nearer the nut is 
to the fulcrum1 the easier the cracking4
  ,illustration3 ,,fig4 #ajb4--,the hand
 exerts a small force over a long       
distance and draws out a nail4  ,hammers
 7,fig4 #ajb71 tack-lifters1 scissors1  
forceps1 are important levers1 and if   
you will notice how many different      

levers 7fig4 #ajc7 are used by all      
classes of men1 you will understand how 
valuable a machine this simple device   
is4  #aee4 ,the ,inclined ,plane4 ,a man
 wishes to load the #fjj-pound bowlder  
on a wagon1 and proceeds to do it by    
means of a plank1 as in ,figure #ic4    
,such an arrangement is called an       
inclined plane4  ,the advantage of an   
inclined plane can be seen by the       
following experiment4 ,select a smooth  
board #d feet long and prop it so that  
the end ,a 7,fig4 #ajd7 is #a foot above
 the level of the table2 the length of  
the incline is then #d times as great as
 its height4 ,fasten a metal roller to a
 spring balance and observe its weight4 
,then pull the roller uniformly upward  
along the plank and notice what the pull
 is on the balance1 being careful always
 to hold the balance parallel to the    
incline4  ,when the roller is raised    
along the incline1 the balance registers
 a pull only one fourth as great as the 
actual weight of the roller4 ,that is1  

when the roller weighs #ab1 a force of  
#c suffices to raise it to the height ,a
 along the incline2 but the smaller     
force must be applied throughout the    
entire length of the incline4 ,in many  
cases1 it is preferable to exert a force
 of #cj pounds1 for example1 over the   
distance ,,ca than a force of #abj      
pounds over the shorter distance ,,ba4  
,illustration3 ,,fig4 #ajc4--,primitive 
man tried to lighten his task by        
balancing his burden4  ,prop the board  
so that the end ,a is #b feet above the 
table level2 that is1 arrange the       
inclined plane in such a way that its   
length is twice as great as its height4 
,in that case the steady pull on the    
balance will be one half the weight of  
the roller2 or a force of #f pounds will
 suffice to raise the #ab-pound roller4 
,illustration3 ,,fig4 #ajd4--,less force
 is required to raise the roller along  
the incline than to raise it to ,a      
directly4  ,the steeper the incline1 the
 more force necessary to raise a weight2

 whereas if the incline is small1 the   
necessary lifting force is greatly      
reduced4 ,on an inclined plane whose    
length is ten times its height1 the     
lifting force is reduced to one tenth   
the weight of the load4 ,the advantage  
of an incline depends upon the relative 
length and height1 or is equal to the   
ratio of the length to the height4      
#aef4 ,application4 ,by the use of an   
inclined plank a strong man can load the
 #fjj-pound bowlder on a wagon4 ,suppose
 the floor of the wagon is #b feet above
 the ground1 then if a #f-;foot plank is
 used1 #bjj pounds of force will suffice
 to raise the bowlder2 but the man will 
have to push with this force against the
 bowlder while it moves over the entire 
length of the plank4  ,since work is    
equal to force multiplied by distance1  
the man has done work represented by    
#bjj  #f1 or #abjj4 ,this is exactly the
 amount of work which would have been   
necessary to raise the bowlder directly4
 ,a man of even enormous strength could 

not lift such a weight 7#fjj lb47 even  
an inch directly1 but a strong man can  
furnish the smaller force 7#bjj7 over a 
distance of #f feet2 hence1 while the   
machine does not lessen the total amount
 of work required of a man1 it creates a
 new distribution of work and makes     
possible1 and even easy1 results which  
otherwise would be impossible by human  
agency4  #aeg4 ,railroads and ,highways4
 ,the problem of the incline is an      
important one to engineers who have     
under their direction the construction  
of our highways and the laying of our   
railroad tracks4 ,it requires tremendous
 force to pull a load up grade1 and most
 of us are familiar with the struggling 
horse and the puffing locomotive4 ,for  
this reason engineers1 wherever         
possible1 level down the steep places1  
and reduce the strain as far as         
possible4  ,illustration3 ,,fig4        
#aje4--;,a well-graded railroad bed4    
,the slope of the road is called its    
grade1 and the grade itself is simply   

the number of feet the hill rises per   
mile4 ,a road a mile long 7#ebhj feet7  
has a grade of #acb if the crest of the 
hill is #acb feet above the level at    
which the road started4  ,illustration3 
,,fig4 #ajf4--;,a long1 gradual ascent  
is better than a shorter1 steeper one4  
,in such an incline1 the ratio of length
 to height is #ebhj  #acb1 or #dj2 and  
hence in order to pull a train of cars  
to the summit1 the engine would need to 
exert a continuous pull equal to one    
fortieth of the combined weight of the  
train4  ,if1 on the other hand1 the     
ascent had been gradual1 so that the    
grade was #ff feet per mile1 a pull from
 the engine of one eightieth of the     
combined weight would have sufficed to  
land the train of cars at the crest of  
the grade4  ,because of these facts1    
engineers spend great sums in grading   
down railroad beds1 making them as      
nearly level as possible4 ,in           
mountainous regions1 the topography of  
the land prevents the elimination of all

 steep grades1 but nevertheless the     
attempt is always made to follow the    
easiest grades4  #aeh4 ,the ,wedge4 ,if 
an inclined plane is pushed underneath  
or within an object1 it serves as a     
wedge4 ,usually a wedge consists of two 
inclined planes 7,fig4 #ajg74           
,illustration3 ,,fig4 #ajg4--;,by means 
of a wedge1 the stump is split4  ,a     
chisel and an ax are illustrations of   
wedges4 ,perhaps the most universal form
 of a wedge is our common pin4 ,can you 
explain how this is a wedge8  #aei4 ,the
 ,screw4 ,another valuable and          
indispensable form of the inclined plane
 is the screw4 ,this consists of a metal
 rod around which passes a ridge1 and   
,figure #ajh shows clearly that a screw 
is simply a rod around which 7in effect7
 an inclined plane has been wrapped4    
,illustration3 ,,fig4 #ajh--;,a screw as
 a simple machine4  ,the ridge          
encircling the screw is called the      
thread1 and the distance between two    
successive threads is called the pitch4 

,it is easy to see that the closer the  
threads and the smaller the pitch1 the  
greater the advantage of the screw1 and 
hence the less force needed in          
overcoming resistance4 ,a corkscrew is a
 familiar illustration of the screw4    
#afj4 ,pulleys4 ,the pulley1 another of 
the machines1 is merely a grooved wheel 
around which a cord passes4 ,it is      
sometimes more convenient to move a load
 in one direction rather than in        
another1 and the pulley in its simplest 
form enables us to do this4 ,in order to
 raise a flag to the top of a mast1 it  
is not necessary to climb the mast1 and 
so pull up the flag2 the same result is 
accomplished much more easily by        
attaching the flag to a movable string1 
somewhat as in ,figure #aji1 and pulling
 from below4 ,as the string is pulled   
down1 the flag rises and ultimately     
reaches the desired position4  ,if we   
employ a stationary pulley1 as in       
,figure #aji1 we do not change the      
force1 because the force required to    

balance the load is as large as the load
 itself4 ,the only advantage is that a  
force in one direction may be used to   
produce motion in another direction4    
,such a pulley is known as a fixed      
pulley4  ,illustration3 ,,fig4          
#aji4--;,by means of a pulley1 a force  
in one direction produces motion in the 
opposite direction4  #afa4 ,movable     
,pulleys4 ,by the use of a movable      
pulley1 we are able to support a weight 
by a force equal to only one half the   
load4 ,in ,figure #aji1 the downward    
pull of the weight and the downward pull
 of the hand are equal2 in ,figure #aaj1
 the spring balance supports only one   
half the entire load1 the remaining half
 being borne by the hook to which the   
string is attached4 ,the weight is      
divided equally between the two parts of
 the string which passes around the     
pulley1 so that each strand bears only  
one half of the burden4  ,we have seen  
in our study of the lever and the       
inclined plane that an increase in force

 is always accompanied by a decrease in 
distance1 and in the case of the pulley 
we naturally look for a similar result4 
,if you raise the balance 7,fig4 #aaj7  
#ab feet1 you will find that the weight 
rises only #f feet2 if you raise the    
balance #bd inches1 you will find that  
the weight rises #ab inches4 ,you must  
exercise a force of #ajj pounds over #ab
 feet of space in order to raise a      
weight of #bjj pounds a distance of #f  
feet4 ,when we raise #ajj pounds through
 #ab feet or #bjj pounds through #f feet
 the total work done is the same2 but   
the pulley enables those who cannot     
furnish a force of #bjj pounds for the  
space of #f feet to accomplish the task 
by furnishing #ajj pounds for the space 
of #ab feet4  ,illustration3 ,,fig4     
#aaj4--;,a movable pulley lightens      
labor4  #afb4 ,combination of ,pulleys4 
,a combination of pulleys called block  
and tackle is used where very heavy     
loads are to be moved4 ,in ,figure #aaa 
the upper block of pulleys is fixed1 the

 lower block is movable1 and one        
continuous rope passes around the       
various pulleys4 ,the load is supported 
by #f strands1 and each strand bears one
 sixth of the load4 ,if the hand pulls  
with a force of #a pound at ,p1 it can  
raise a load of #f pounds at ,w1 but the
 hand will have to pull downward #f feet
 at ,p in order to raise the load at ,w 
#a foot4 ,if #h pulleys were used1 a    
force equivalent to one eighth of the   
load would suffice to move ,w1 but this 
force would have to be exerted over a   
distance #h times as great as that      
through which ,w was raised4            
,illustration3 ,,fig4 #aaa4--;,an       
effective arrangement of pulleys known  
as block and tackle4  #afc4 ,practical  
,application4 ,in our childhood many of 
us saw with wonder the appearance and   
disappearance of flags flying at the    
tops of high masts1 but observation soon
 taught us that the flags were raised by
 pulleys4 ,in tenements1 where there is 
no yard for the family washing1 clothes 

often appear flapping in mid-air4 ,this 
seems most marvelous until we learn that
 the lines are pulled back and forth by 
pulleys at the window and at a distant  
support4 ,by means of pulleys1 awnings  
are raised and lowered1 and the use of  
pulleys by furniture movers1 etc41 is   
familiar to every wide-awake observer on
 the streets4  #afd4 ,wheel and ,axle4  
,the wheel and axle consists of a large 
wheel and a small axle so fastened that 
they rotate together4  ,illustration3   
,,fig4 #aab4--,the wheel and axle4      
,when the large wheel makes one         
revolution1 ,p falls a distance equal to
 the circumference of the wheel4 ,while 
,p moves downward1 ,w likewise moves1   
but its motion is upward1 and the       
distance it moves is small1 being equal 
only to the circumference of the small  
axle4 ,but a small force at ,p will     
sustain a larger force at ,w2 if the    
circumference of the large wheel is #dj 
inches1 and that of the small wheel #aj 
inches1 a load of #ajj at ,w can be     

sustained by a force of #be at ,p4 ,the 
increase in force of the wheel and axle 
depends upon the relative size of the   
two parts1 that is1 upon the            
circumference of wheel as compared with 
circumference of axle1 and since the    
ratio between circumference and radius  
is constant1 the ratio of the wheel and 
axle combination is the ratio of the    
long radius to the short radius4  ,for  
example1 in a wheel and axle of radii   
#bj and #d1 respectively1 a given weight
 at ,p would balance #e times as great a
 load at ,w4  #afe4 ,application4       
,windlass1 ,cogwheels4 ,in the          
old-fashioned windlass used in farming  
districts1 the large wheel is replaced  
by a handle which1 when turned1         
describes a circle4 ,such an arrangement
 is equivalent to wheel and axle 7,fig4 
#aab72 the capstan used on shipboard for
 raising the anchor has the same        
principle4 ,the kitchen coffee grinder  
and the meat chopper are other familiar 
illustrations4  ,cogwheels are          

modifications of the wheel and axle4    
,teeth cut in ,a fit into similar teeth 
cut in ,b1 and hence rotation of ,a     
causes rotation of ,b4 ,several         
revolutions of the smaller wheel1       
however1 are necessary in order to turn 
the larger wheel through one complete   
revolution2 if the radius of ,a is one  
half that of ,b1 two revolutions of ,a  
will correspond to one of ,b2 if the    
radius of ,a is one third that of ,b1   
three revolutions of ,a will correspond 
to one of ,b4  ,illustration3 ,,fig4    
#aac4--;,cogwheels4  ,experiment        
demonstrates that a weight ,w attached  
to a cogwheel of radius #c can be raised
 by a force ,p1 equal to one third of ,w
 applied to a cogwheel of radius #a4    
,there is thus a great increase in      
force4 ,but the speed with which ,w is  
raised is only one third the speed with 
which the small wheel rotates1 or       
increase in power has been at the       
decrease of speed4  ,this is a very     
common method for raising heavy weights 

by small force4  ,cogwheels can be made 
to give speed at the decrease of force4 
,a heavy weight ,w attached to ,b will  
in its slow fall cause rapid rotation of
 ,a1 and hence rapid rise of ,p4 ,it is 
true that ,p1 the load raised1 will be  
less than ,w1 the force exerted1 but if 
speed is our aim1 this machine serves   
our purpose admirably4  ,an extremely   
important form of wheel and axle is that
 in which the two wheels are connected  
by belts as in ,figure #aad4 ,rotation  
of ,w induces rotation of w1 and a small
 force at ,w is able to overcome a large
 force at w4 ,an advantage of the belt  
connection is that power at one place   
can be transmitted over a considerable  
distance and utilized in another place4 
,illustration3 ,,fig4 #aad4--;,by means 
of a belt1 motion can be transferred    
from place to place4  #aff4 ,compound   
,machines4 ,out of the few simple       
machines mentioned in the preceding     
,sections has developed the complex     
machinery of to-day4 ,by a combination  

of screw and lever1 for example1 we     
obtain the advantage due to each device1
 and some compound machines have been   
made which combine all the various kinds
 of simple machines1 and in this way    
multiply their mechanical advantage many
 fold4  ,a relatively simple complex    
machine called the crane 7,fig4 #aaf7   
maybe seen almost any day on the street1
 or wherever heavy weights are being    
lifted4 ,it is clear that a force       
applied to turn wheel #a causes a slower
 rotation of wheel #c1 and a still      
slower rotation of wheel #d1 but as #d  
rotates it winds up a chain and slowly  
raises ,q4 ,a very complex machine is   
that seen in ,figure #aag4              
,illustration3 ,,fig4 #aae4--;,a simple 
derrick for raising weights4            
,illustration3 ,,fig4 #aaf4--;,a        
traveling crane4  #afg4 ,measurement of 
,work4 ,in ,section #aej1 we learned    
that the amount of work done depends    
upon the force exerted1 and the distance
 covered1 or that ,w  force  distance4  

,a man who raises #e pounds a height of 
#e feet does far more work than a man   
who raises #e ounces a height of #e     
inches1 but the product of force by     
distance is #be in each case4 ,there is 
difficulty because we have not selected 
an arbitrary unit of work4 ,the unit of 
work chosen and in use in practical     
affairs is the foot pound1 and is       
defined as the work done when a force of
 #a pound acts through a distance of #a 
foot4 ,a man who moves #h pounds through
 #f feet does #dh foot pounds of work1  
while a man who moves #h ounces 7#a_/b  
pound7 through #f inches 7#a_/b foot7   
does only one fourth of a foot pound of 
work4  ,illustration3 ,,fig4 #aag4--;,a 
farm engine putting in a crop4  #afh4   
,the ,power or the ,speed with which    
,work is ,done4 ,a man can load a wagon 
more quickly than a growing boy4 ,the   
work done by the one is equal to the    
work done by the other1 but the man is  
more powerful1 because the time required
 for a given task is very important4 ,an

 engine which hoists a #ej-pound weight 
in #a second is much more powerful than 
a man who requires #ej seconds for the  
same task2 hence in estimating the value
 of a working agent1 whether animal or  
mechanical1 we must consider not only   
the work done1 but the speed with which 
it is done4  ,the rate at which a       
machine is able to accomplish a unit of 
work is called power1 and the unit of   
power customarily used is the horse     
power4 ,any power which can do #eej foot
 pounds of work per second is said to be
 one horse power 7,h4,p474 ,this unit   
was chosen by ,james ,watt1 the inventor
 of a steam engine1 when he was in need 
of a unit with which to compare the new 
source of power1 the engine1 with his   
old source of power1 the horse4         
,although called a horse power it is    
greater than the power of an average    
horse4  ,an ordinary man can do one     
sixth of a horse power4 ,the average    
locomotive of a railroad has more than  
#ejj ,h4,p41 while the engines of an    

ocean liner may have as high as #gj1jjj 
,h4,p4  #afi4 ,waste ,work and          
,efficient ,work4 ,in our study of      
machines we omitted a factor which in   
practical cases cannot be ignored1      
namely1 friction4 ,no surface can be    
made perfectly smooth1 and when a barrel
 rolls over an incline1 or a rope passes
 over a pulley1 or a cogwheel turns its 
neighbor1 there is rubbing and slipping 
and sliding4 ,motion is thus hindered1  
and the effective value of the acting   
force is lessened4 ,in order to secure  
the desired result it is necessary to   
apply a force in excess of that         
calculated4 ,this extra force1 which    
must be supplied if friction is to be   
counteracted1 is in reality waste work4 
,if the force required by a machine is  
#aej pounds1 while that calculated as   
necessary is #ajj pounds1 the loss due  
to friction is #ej pounds1 and the      
machine1 instead of being thoroughly    
efficient1 is only two thirds efficient4
  ,machinists make every effort to      

eliminate from a machine the waste due  
to friction1 leveling and grinding to   
the most perfect smoothness and         
adjustment every part of the machine4   
,when the machine is in use1 friction   
may be further reduced by the use of    
lubricating oil4 ,friction can never be 
totally eliminated1 however1 and        
machines of even the finest construction
 lose by friction some of their         
efficiency1 while poorly constructed    
ones lose by friction as much as one    
half of their efficiency4  #agj4 ,man's 
,strength not ,sufficient for ,machines4
 ,a machine1 an inert mass of metal and 
wood1 cannot of itself do any work1 but 
can only distribute the energy which is 
brought to it4 ,fortunately it is not   
necessary that this energy should be    
contributed by man alone1 because the   
store of energy possessed by him is very
 small in comparison with the energy    
required to run locomotives1            
automobiles1 sawmills1 etc4 ,perhaps the
 greatest value of machines lies in the 

fact that they enable man to perform    
work by the use of energy other than his
 own4  ,illustration3 ,,fig4            
#aah4--,man's strength is not sufficient
 for heavy work4  ,figure #aah shows one
 way in which a horse's energy can be   
utilized in lifting heavy loads4 ,even  
the fleeting wind has been harnessed by 
man1 and1 as in the windmill1 made to   
work for him 7,fig4 #aai74 ,one sees    
dotted over the country windmills large 
and small1 and in ,holland1 the country 
of windmills1 the landowner who does not
 possess a windmill is poor indeed4     
,for generations running water from     
rivers1 streams1 and falls has served   
man by carrying his logs downstream1 by 
turning the wheels of his mill1 etc42   
and in our own day running water is used
 as an indirect source of electric      
lights for street and house1 the energy 
of the falling water serving to rotate  
the armature of a dynamo 7,section      
#caj74  ,illustration3 ,,fig4           
#aai4--,the windmill pumps water into   

the troughs where cattle drink4  ,a more
 constant source of energy is that      
available from the burning of fuel1 such
 as coal and oil4 ,the former is the    
source of energy in locomotives1 the    
latter in most automobiles4  ,in the    
following ,chapter will be given an     
account of water1 wind1 and fuel as     
machine feeders4     ,,chapter ,,xvii   
,,the ,,power ,,behind ,,the ,,engine   
#aga4 ,small boys soon learn the power  
of running water2 swimming or rowing    
downstream is easy1 while swimming or   
rowing against the current is difficult1
 and the swifter the water1 the easier  
the one and the more difficult the      
other2 the river assists or opposes us  
as we go with it or against it4 ,the    
water of a quiet pool or of a gentle    
stream cannot do work1 but water which  
is plunging over a precipice or dam1 or 
is flowing down steep slopes1 may be    
made to saw wood1 grind our corn1 light 
our streets1 run our electric cars1 etc4
 ,a waterfall1 or a rapid stream1 is a  

great asset to any community1 and for   
this reason should be carefully guarded4
 ,water power is as great a source of   
wealth as a coal bed or a gold mine4    
,the most tremendous waterfall in our   
country is ,niagara ,falls1 which every 
minute hurls millions of gallons of     
water down a #afc-;foot precipice4 ,the 
energy possessed by such an enormous    
quantity of water flowing at such a     
tremendous speed is almost beyond       
everyday comprehension1 and would       
suffice to run the engines of many      
cities far and near4 ,numerous attempts 
to buy from the ,united ,states the     
right to utilize some of this apparently
 wasted energy have been made by various
 commercial companies4 ,it is fortunate 
that these negotiations have been       
largely fruitless1 because much         
deviation of the water for commercial   
uses and the installation of machinery  
in the vicinity of the famous falls     
would greatly detract from the beauty of
 this world-known scene1 and would rob  

our country of a natural beauty         
unequaled elsewhere4  ,illustration3    
,,fig4 #abj4--;,a mountain stream turns 
the wheels of the mill4  #agb4 ,water   
,wheels4 ,in ,figure #abj the water of a
 small but rapid mountain stream is made
 to rotate a large wheel1 which in turn 
communicates its motion through belts to
 a distant sawmill or grinder4 ,in more 
level regions huge dams are built which 
hold back the water and keep it at a    
higher level than the wheel2 from the   
dam the water is conveyed in pipes      
7flumes7 to the paddle wheel which it   
turns4 ,cogwheels or belts connect the  
paddle wheel with the factory machinery1
 so that motion of the paddle wheel     
insures the running of the machinery4   
,illustration3 ,,fig4 #aba4--,the       
,pelton water wheel4  ,one of the most  
efficient forms of water wheels is that 
shown in ,figure #aba1 and called the   
,pelton wheel4 ,water issues in a narrow
 jet similar to that of the ordinary    
garden hose and strikes with great force

 against the lower part of the wheel1   
thereby causing rotation of the wheel4  
,belts transfer this motion to the      
machinery of factory or mill4  #agc4    
,turbines4 ,the most efficient form of  
water motor is the turbine1 a strong    
metal wheel shaped somewhat like a pin  
wheel1 inclosed in a heavy metal case4  
,illustration3 ,,fig4 #abb--;,a turbine 
at ,niagara ,falls4  ,water is conveyed 
from a reservoir or dam through a pipe  
7penstock7 to the turbine case1 in which
 is placed the heavy metal turbine wheel
 7,fig4 #abb74 ,the force of the water  
causes rotation of the turbine and of   
the shaft which is rigidly fastened to  
it4 ,the water which flows into the     
turbine case causes rotation of the     
wheel1 escapes from the case through    
openings1 and flows into the tail water4
  ,the power which a turbine can furnish
 depends upon the quantity of water and 
the height of the fall1 and also upon   
the turbine wheel itself4 ,one of the   
largest turbines known has a horse power

 of about #bj1jjj2 that is1 it is       
equivalent1 approximately1 to #bj1jjj   
horses4  #agd4 ,how much is a ,stream   
,worth8 ,the work which a stream can    
perform may be easily calculated4       
,suppose1 for example1 that #ej1jjj     
pounds of water fall over a #bb-;foot   
dam every second2 the power of such a   
stream would be #a1ajj1jjj foot pounds  
per second or #bjjj ,h4,p4 ,naturally1 a
 part of this power would be lost to use
 by friction within the machinery and by
 leakage1 so that the power of a turbine
 run by a #bjjj ,h4,p4 stream would be  
less than that value4  ,of course1 the  
horse power to be obtained from a stream
 determines the size of the paddle wheel
 or turbine which can be run by it4 ,it 
would be possible to construct a turbine
 so large that the stream would not     
suffice to turn the wheel2 for this     
reason1 the power of a stream is        
carefully determined before machine     
construction is begun1 and the size of  
the machinery depends upon the estimates

 of the water power furnished by expert 
engineers4  ,a rough estimate of the    
volume of a stream may be made by the   
method described below3--  ,suppose we  
allow a stream of water to flow through 
a rectangular trough2 the speed with    
which the water flows through the trough
 can be determined by noting the time   
required for a chip to float the length 
of the trough2 if the trough is #aj feet
 long and the time required is #e       
seconds1 the water has a velocity of #b 
feet per second4  ,illustration3 ,,fig4 
#abc4--;,estimating the quantity of     
water which flows through the trough    
each second4  ,the quantity of water    
which flows through the trough each     
second depends upon the dimensions of   
the trough and the velocity of the      
water4 ,suppose the trough is #e feet   
wide and #c feet high1 or has a cross   
section of #ae square feet4 ,if the     
velocity of the water were #a foot per  
second1 then #ae cubic feet of water    
would pass any given point each second1 

but since the velocity of the water is  
#b feet per second1 #cj cubic feet will 
represent the amount of water which will
 flow by a given point in one second4   
#age4 ,quantity of ,water ,furnished by 
a ,river4 ,drive stakes in the river at 
various places and note the time        
required for a chip to float from one   
stake to another4 ,if we know the       
distance between the stakes and the time
 required for the chip to float from one
 stake to another1 the velocity of the  
water can be readily determined4  ,the  
width of the stream from bank to bank is
 easily measured1 and the depth is      
obtained in the ordinary way by         
sounding2 it is necessary to take a     
number of soundings because the bed of  
the river is by no means level1 and     
soundings taken at only one level would 
not give an accurate estimate4 ,if the  
soundings show the following depths3    
#cj1 #be1 #bj1 #cb1 #bh1 the average    
depth could be taken as #cj  #be  #bj   
#cb  #bh  #e1 or #bg feet4 ,if1 as a    

result of measuring1 the river at a     
given point in its course is found to be
 #bg feet deep and #fj feet wide1 the   
area of a cross section at that spot    
would be #afbj square feet1 and if the  
velocity proved to be #f feet per       
second1 then the quantity of water      
passing in any one second would be #afbj
  #f1 or #igbj cubic feet4 ,by          
experiment it has been found that #a cu4
 ft4 of water weighs about #fb4e lb4    
,the weight of the water passing each   
second would therefore be #fb4e  #igbj1 
or #fjg1ejj lb4 ,if this quantity of    
water plunges over a #aj-;ft4 dam1 it   
does #fjg1ejj  #aj1 or #f1jge1jjj foot  
pounds of work per second1 or #aa1jde   
,h4,p4 ,such a stream would be very     
valuable for the running of machinery4  
#agf4 ,windmills4 ,those of us who have 
spent our vacation days in the country  
know that there is no ready-made water  
supply there as in the cities1 but that 
as a rule the farmhouses obtain their   
drinking water from springs and wells4  

,in poorer houses1 water is laboriously 
carried in buckets from the spring or is
 lifted from the well by the windlass4  
,in more prosperous houses1 pumps are   
installed2 this is an improvement over  
the original methods1 but the quantity  
of water consumed by the average family 
is so great as to make the task of      
pumping an arduous one4  ,the average   
amount of water used per day by one     
person is #be gallons4 ,this includes   
water for drinking1 cooking1 dish       
washing1 bathing1 laundry4 ,for a family
 of five1 therefore1 the daily          
consumption would be #abe gallons2 if to
 this be added the water for a single   
horse1 cow1 and pig1 the total amount   
needed will be approximately #aej       
gallons per day4 ,a strong man can pump 
that amount from an ordinary well in    
about one hour1 but if the well is deep1
 more time and strength are required4   
,the invention of the windmill was a    
great boon to country folks because it  
eliminated from their always busy life  

one task in which labor and time were   
consumed4  #agg4 ,the ,principle of the 
,windmill4 ,the toy pin wheel is a      
windmill in miniature4 ,the wind strikes
 the sails1 and causes rotation2 and the
 stronger the wind blows1 the faster    
will the wheel rotate4 ,in windmills1   
the sails are of wood or steel1 instead 
of paper1 but the principle is          
identical4  ,illustration3 ,,fig4       
#abd4--,the toy pin wheel is a miniature
 windmill4  ,as the wheel rotates1 its  
motion is communicated to a mechanical  
device which makes use of it to raise   
and lower a plunger1 and hence as long  
as the wind turns the windmill1 water is
 raised4 ,the water thus raised empties 
into a large tank1 built either in the  
windmill tower or in the garret of the  
house1 and from the tank the water flows
 through pipes to the different parts of
 the house4 ,on very windy days the     
wheel rotates rapidly1 and the tank     
fills quickly2 in order to guard against
 an overflow from the tank a mechanical 

device is installed which stops rotation
 of the wheel when the tank is nearly   
full4 ,the supply tank is usually large 
enough to hold a supply of water        
sufficient for several days1 and hence a
 continuous calm of a day or two does   
not materially affect the house flow4   
,when once built1 a windmill practically
 takes care of itself1 except for       
oiling1 and is an efficient and cheap   
domestic possession4  ,illustration3    
,,fig4 #abe4--,the windmill pumps water 
into the tank4  #agh4 ,steam as a       
,working ,power4 ,if a delicate vane is 
held at an opening from which steam     
issues1 the pressure of the steam will  
cause rotation of the vane 7,fig4 #abf71
 and if the vane is connected with a    
machine1 work can be obtained from the  
steam4  ,when water is heated in an open
 vessel1 the pressure of its steam is   
too low to be of practical value1 but if
 on the contrary water is heated in an  
almost closed vessel1 its steam pressure
 is considerable4 ,if steam at high     

pressure is directed by nozzles against 
the blades of a wheel1 rapid rotation of
 the wheel ensues just as it did in     
,figure #aba1 although in this case     
steam pressure replaces water pressure4 
,after the steam has spent itself in    
turning the turbine1 it condenses into  
water and makes its escape through      
openings in an inclosing case4 ,in      
,figure #abg the protecting case is     
removed1 in order that the form of the  
turbine and the positions of the nozzles
 may be visible4  ,illustration3 ,,fig4 
#abf4--,steam as a source of power4     
,illustration3 ,,fig4 #abg4--,steam     
turbine with many blades and #d nozzles4
  ,a single large turbine wheel may have
 as many as #hjj1jjj sails or blades1   
and steam may pour out upon these from  
many nozzles4  ,the steam turbine is    
very much more efficient than its       
forerunner1 the steam engine4 ,the      
installation of turbines on ocean liners
 has been accompanied by great increase 
in speed1 and by an almost corresponding

 decrease in the cost of maintenance4   
#agi4 ,steam ,engines4 ,a very simple   
illustration of the working of a steam  
engine is given in ,figure #abh4 ,steam 
under pressure enters through the       
opening ,f1 passes through ,n1 and      
presses upon the piston ,m4 ,as a result
 ,m moves downward1 and thereby induces 
rotation in the large wheel ,l4         
,illustration3 ,,fig4 #abh4--,the       
principle of the steam engine4  ,as ,m  
falls it drives the air in ,d out       
through ,o and ,p 7the opening ,p is not
 visible in the diagram74  ,as soon as  
this is accomplished1 a mechanical      
device draws up the rod ,e1 which in    
turn closes the opening ,n1 and thus    
prevents the steam from passing into the
 part of ,d above ,m4  ,but when the rod
 ,e is in such a position that ,n is    
closed1 ,o on the other hand is open1   
and steam rushes through it into ,d and 
forces up the piston4 ,this up-and-down 
motion of the piston causes continuous  
rotation of the wheel ,l4 ,if the fire  

is hot1 steam is formed quickly1 and the
 piston moves rapidly2 if the fire is   
low1 steam is formed slowly1 and the    
piston moves less rapidly4  ,the steam  
engine as seen on our railroad trains is
 very complex1 and cannot be discussed  
here2 in principle1 however1 it is      
identical with that just described4     
,figure #abi shows a steam harvester at 
work on a modern farm4  ,illustration3  
,,fig4 #abi4--,steam harvester at work4 
,in both engine and turbine the real    
source of power is not the steam but the
 fuel1 such as coal or oil1 which       
converts the water into steam4  #ahj4   
,gas ,engines4 ,automobiles have been   
largely responsible for the gas engine4 
,to carry coal for fuel and water for   
steam would be impracticable for most   
motor cars4 ,electricity is used in some
 cars1 but the batteries are heavy1     
expensive1 and short-lived1 and are not 
always easily replaceable4 ,for this    
reason gasoline is extensively used1 and
 in the average automobile the source of

 power is the force generated by        
exploding gases4  ,it was discovered    
some years ago that if the vapor of     
gasoline or naphtha was mixed with a    
definite quantity of air1 and a light   
was applied to the mixture1 an explosion
 would result4 ,modern science uses the 
force of such exploding gases for the   
accomplishment of work1 such as running 
of automobiles and launches4  ,in       
connection with the gasoline supply is a
 carburetor or sprayer1 from which the  
cylinder ,c 7,fig4 #acj7 receives a fine
 mist of gasoline vapor and air4 ,this  
mixture is ignited by an automatic1     
electric sparking device1 and the       
explosion of the gases drives the piston
 ,p to the right4 ,in the #d-;cycle type
 of gas engines 7,fig4 #acj7--the kind  
used in automobiles--the four strokes   
are as follows3 #a4 ,the mixture of     
gasoline and air enters the cylinder as 
the piston moves to the right4 #b4 ,the 
valves being closed1 the mixture is     
compressed as the piston moves to the   

left4 #c4 ,the electric spark ignites   
the compressed mixture and drives the   
piston to the right4 #d4 ,the waste gas 
is expelled as the piston moves to the  
left4 ,the exhaust valve is then closed1
 the inlet valve opened1 and another    
cycle of four strokes begins4           
,illustration3 ,,fig4 #acj4--,the gas   
engine4  ,the use of gasoline in        
launches and automobiles is familiar to 
many4 ,not only are launches and        
automobiles making use of gas power1 but
 the gasoline engine has made it        
possible to propel aroplanes through the
 air4     ,,chapter ,,xviii  ,,pumps    
,,and ,,their ,,value ,,to ,,man   #aha4
 ,as difficult as for water to run up a 
hill6 ,is there any one who has not     
heard this saying8 ,and yet most of us  
accept as a matter of course the stream 
which gushes from our faucet1 or give no
 thought to the ingenuity which devised 
a means of forcing water upward through 
pipes4 ,despite the fact that water     
flows naturally down hill1 and not up1  

we find it available in our homes and   
office buildings1 in some of which it   
ascends to the fiftieth floor2 and we   
see great streams of it directed upon   
the tops of burning buildings by firemen
 in the streets below4  ,in the country1
 where there are no great central       
pumping stations1 water for the daily   
need must be raised from wells1 and the 
supply of each household is dependent   
upon the labor and foresight of its     
members4 ,the water may be brought to   
the surface either by laboriously       
raising it1 bucket by bucket1 or by the 
less arduous method of pumping4 ,these  
are the only means possible2 even the   
windmill does not eliminate the         
necessity for the pump1 but merely      
replaces the energy used by man in      
working it4  ,in some parts of our      
country we have oil beds or wells4 ,but 
if this underground oil is to be of     
service to man1 it must be brought to   
the surface1 and this is accomplished1  
as in the case of water1 by the use of  

pumps4  ,an old tin can or a sponge may 
serve to bale out water from a leaking  
rowboat1 but such a crude device would  
be absurd if employed on our huge       
vessels of war and commerce4 ,here a    
rent in the ship's side would mean      
inevitable loss were it not possible to 
rid the ship of the inflowing water by  
the action of strong pumps4  ,another   
and very different use to which pumps   
are put is seen in the compression of   
gases4 ,air is forced into the tires of 
bicycles and automobiles until they     
become sufficiently inflated to insure  
comfort in riding4 ,some present-day    
systems of artificial refrigeration     
7,section #ic7 could not exist without  
the aid of compressed gases4            
,compressed air has played a very       
important role in mining1 being sent    
into poorly ventilated mines to improve 
the condition of the air1 and to supply 
to the miners the oxygen necessary for  
respiration4 ,divers and men who work   
under water carry on their backs a tank 

of compressed air1 and take from it1 at 
will1 the amount required4  ,there are  
many forms of pumps1 and they serve     
widely different purposes1 being        
essential to the operation of many      
industrial undertakings4 ,in the        
following ,sections some of these forms 
will be studied4  ,illustration3 ,,fig4 
#aca4--;,carrying water home from the   
spring4  #ahb4 ,the ,air as ,man's      
,servant4 ,long before man harnessed    
water for turbines1 or steam for        
engines1 he made the air serve his      
purpose1 and by means of it raised water
 from hidden underground depths to the  
surface of the earth2 likewise1 by means
 of it1 he raised to his dwelling on the
 hillside water from the stream in the  
valley below4 ,those who live in cities 
where running water is always present in
 the home cannot realize the hardship of
 the days when this ready-made supply   
did not exist1 but when man laboriously 
carried to his dwelling1 from distant   
spring and stream1 the water necessary  

for the daily need4  ,what are the      
characteristics of the air which have   
enabled man to accomplish these feats8  
,they are well known to us and may be   
briefly stated as follows3--  7#a7 ,air 
has weight1 and #a cubic foot of air1 at
 atmospheric pressure1 weighs #a-a_/d   
ounces4  7#b7 ,the air around us presses
 with a force of about #ae pounds upon  
every square inch of surface that it    
touches4  7#c7 ,air is elastic2 it can  
be compressed1 as in the balloon or     
bicycle tire1 but it expands immediately
 when pressure is reduced4 ,as it       
expands and occupies more space1 its    
pressure falls and it exerts less force 
against the matter with which it comes  
in contact4 ,if1 for example1 #a cubic  
foot of air is allowed to expand and    
occupy #b cubic feet of space1 the      
pressure which it exerts is reduced one 
half4 ,when air is compressed1 its      
pressure increases1 and it exerts a     
greater force against the matter with   
which it comes in contact4 ,if #b cubic 

feet of air are compressed to #a cubic  
foot1 the pressure of the compressed air
 is doubled4 7,see ,section #hi47       
,illustration3 ,,fig4 #acb4--,the       
atmosphere pressing downward on a pushes
 water after the rising piston b4  #ahc4
 ,the ,common ,pump or ,lifting ,pump4  
,place a tube containing a close-fitting
 piston in a vessel of water1 as shown  
in ,figure #acb4 ,then raise the piston 
with the hand and notice that the water 
rises in the piston tube4 ,the rise of  
water in the piston tube is similar to  
the raising of lemonade through a straw 
7,section #gg74 ,the atmosphere presses 
with a force of #ae pounds upon every   
square inch of water in the large       
vessel1 and forces some of it into the  
space left vacant by the retreating     
piston4 ,the common pump works in a     
similar manner4 ,it consists of a piston
 or plunger which moves back and forth  
in an air-tight cylinder1 and contains  
an outward opening valve through which  
water and air can pass4 ,from the bottom

 of the cylinder a tube runs down into  
the well or reservoir1 and water from   
the well has access to the cylinder     
through another outward-moving valve4   
,in practice the tube is known as the   
suction pipe1 and its valve as the      
suction valve4  ,in order to understand 
the action of a pump1 we will suppose   
that no water is in the pump1 and we    
will pump until a stream issues from the
 spout4 ,the various stages are         
represented diagrammatically by ,figure 
#acc4 ,in 7#a7 the entire pump is empty 
of water but full of air at atmospheric 
pressure1 and both valves are closed4   
,in 7#b7 the plunger is being raised and
 is lifting the column of air that rests
 on it4 ,the air and water in the inlet 
pipe1 being thus partially relieved of  
downward pressure1 are pushed up by the 
atmospheric pressure on the surface of  
the water in the well4 ,when the piston 
moves downward as in 7#c71 the valve in 
the pipe closes by its own weight1 and  
the air in the cylinder escapes through 

the valve in the plunger4 ,in 7#d7 the  
piston is again rising1 repeating the   
process of 7#b74 ,in 7#e7 the process of
 7#c7 is being repeated1 but water      
instead of air is escaping through the  
valve in the plunger4 ,in 7#f7 the      
process of 7#b7 is being repeated1 but  
the water has reached the spout and is  
flowing out4  ,illustration3 ,,fig4     
#acc4 ,diagram of the process of        
pumping4  ,after the pump is in         
condition 7#f71 motion of the plunger is
 followed by a more or less regular     
discharge of water through the spout1   
and the quantity of water which gushes  
forth depends upon the speed with which 
the piston is moved4 ,a strong man      
giving quick strokes can produce a large
 flow2 a child1 on the other hand1 is   
able to produce only a thin stream4     
,whoever pumps must exert sufficient    
force to lift the water from the surface
 of the well to the spout exit4 ,for    
this reason the pump has received the   
name of lifting pump4  ,illustration3   

,,fig4 #acd4--;,force pump4  #ahd4 ,the 
,force ,pump4 ,in the common pump1 water
 cannot not be raised higher than the   
spout4 ,in many cases it is desirable to
 force water considerably above the pump
 itself1 as1 for instance1 in the fire  
hose2 under such circumstances a type of
 pump is employed which has received the
 name of force pump4 ,this differs but  
little from the ordinary lift pump1 as a
 reference to ,figure #acd will show4   
,here both valves are placed in the     
cylinder1 and the piston is solid1 but  
the principle is the same as in the     
lifting pump4  ,an upward motion of the 
plunger allows water to enter the       
cylinder1 and the downward motion of the
 plunger drives water through ,e4 7,is  
this true for the lift pump as well87   
,since only the downward motion of the  
plunger forces water through ,e1 the    
discharge is intermittent and is        
therefore not practical for commercial  
purposes4 ,in order to convert this     
intermittent discharge into a steady    

stream1 an air chamber is installed near
 the discharge tube1 as in ,figure #ace4
 ,the water forced into the air chamber 
by the downward-moving piston compresses
 the air and increases its pressure4    
,the pressure of the confined air reacts
 against the water and tends to drive it
 out of the chamber4 ,hence1 even when  
the plunger is moving upward1 water is  
forced through the pipe because of the  
pressure of the compressed air4 ,in this
 way a continuous flow is secured4      
,illustration3 ,,fig #ace4--,the air    
chamber ,a insures a continuous flow of 
water4  ,the height to which the water  
can be forced in the pipe depends upon  
the size and construction of the pump   
and upon the force with which the       
plunger can be moved4 ,the larger the   
stream desired and the greater the      
height to be reached1 the stronger the  
force needed and the more powerful the  
construction necessary4  ,the force pump
 gets its name from the fact that the   
moving piston drives or forces the water

 through the discharge tube4  #ahe4     
,irrigation and ,drainage4 ,history     
shows that the lifting pump has been    
used by man since the fourth century    
before ,christ2 for many present-day    
enterprises this ancient form of pump is
 inconvenient and impracticable1 and    
hence it has been replaced in many cases
 by more modern types1 such as rotary   
and centrifugal pumps 7,fig4 #acf74 ,in 
these forms1 rapidly rotating wheels    
lift the water and drive it onward into 
a discharge pipe1 from which it issues  
with great force4 ,there is neither     
piston nor valve in these pumps1 and the
 quantity of water raised and the force 
with which it is driven through the     
pipes depends solely upon the size of   
the wheels and the speed with which they
 rotate4  ,irrigation1 or the artificial
 watering of land1 is of the greatest   
importance in those parts of the world  
where the land is naturally too dry for 
farming4 ,in the ,united ,states1       
approximately two fifths of the land    

area is so dry as to be worthless for   
agricultural purposes unless            
artificially watered4 ,in the ,west1    
several large irrigating systems have   
been built by the federal government1   
and at present about ten million acres  
of land have been converted from        
worthless farms into fields rich in     
crops4 ,many irrigating systems use     
centrifugal pumps to force water over   
long distances and to supply it in      
quantities sufficient for vast          
agricultural needs4 ,in many regions1   
the success of a farm or ranch depends  
upon the irrigation furnished in dry    
seasons1 or upon man's ability to drive 
water from a region of abundance to a   
remote region of scarcity4              
,illustration3 ,,fig4                   
#acf4--;,centrifugal pump with part of  
the casing cut away to show the wheel4  
,illustration3 ,,fig4                   
#acg4--;,agriculture made possible by   
irrigation4  ,the draining of land is   
also a matter of considerable           

importance2 swamps and marshes which    
were at one time considered useless have
 been drained and then reclaimed and    
converted into good farming land4 ,the  
surplus water is best removed by        
centrifugal pumps1 since sand and sticks
 which would clog the valves of an      
ordinary pump are passed along without  
difficulty by the rotating wheel4       
,illustration3 ,,fig4 #ach4--,rice for  
its growth needs periodical flooding1   
and irrigation often supplies the       
necessary water4  #ahf4 ,camping4--,its 
,pleasures and its ,dangers4 ,the       
allurement of a vacation camp in the    
heart of the woods is so great as to    
make many campers ignore the vital      
importance of securing a safe water     
supply4 ,a river bank may be beautiful  
and teeming with diversions1 but if the 
river is used as a source of drinking   
water1 the results will almost always be
 fatal to some4 ,the water can be       
boiled1 it is true1 but few campers are 
willing to forage for the additional    

wood needed for this apparently         
unnecessary requirement2 then1 too1     
boiled water does not cool readily in   
summer1 and hence is disagreeable for   
drinking purposes4  ,the only safe      
course is to abandon the river as a     
source of drinking water1 and if a      
spring cannot be found1 to drive a well4
 ,in many regions1 especially in the    
neighborhood of streams1 water can be   
found ten or fifteen feet below the     
surface4 ,water taken from such a depth 
has filtered through a bed of soil1 and 
is fairly safe for any purpose4 ,of     
course the deeper the well1 the safer   
will be the water4 ,with the use of such
 a pump as will be described1 campers   
can1 without grave danger1 throw dish   
water1 etc41 on the ground somewhat     
remote from the camp2 this may not      
injure their drinking water because the 
liquids will slowly seep through the    
ground1 and as they filter downward will
 lose their dangerous matter4 ,all the  
water which reaches the well pipes will 

have filtered through the soil bed and  
therefore will probably be safe4  ,but  
while the careless disposal of wastes   
may not spoil the drinking water 7in the
 well to be described71 other laws of   
health demand a thoughtful disposal of  
wastes4 ,the malarial mosquito and the  
typhoid fly flourish in unhygienic      
quarters1 and the only way to guard     
against their dangers is to allow them  
neither food nor breeding place4  ,the  
burning of garbage1 the discharge of    
waters into cesspools1 or1 in temporary 
camps1 the discharge of wastes to       
distant points through the agency of a  
cheap sewage pipe will insure safety to 
campers1 will lessen the trials of flies
 and mosquitoes1 and will add but little
 to the expense4  #ahg4 ,a ,cheap ,well 
for ,campers4 ,a two-inch galvanized    
iron pipe with a strong1 pointed end    
containing small perforations is driven 
into the ground with a sledge hammer4   
,after it has penetrated for a few feet1
 another length is added and the whole  

is driven down1 and this is repeated    
until water is reached4 ,a cheap pump is
 then attached to the upper end of the  
drill pipe and serves to raise the      
water4 ,during the drilling1 some soil  
particles get into the pipe through the 
perforations1 and these cloud the water 
at first2 but after the pipe has once   
been cleaned by the upward-moving water1
 the supply remains clear4 ,the flow    
from such a well is naturally small2    
first1 because water is not abundant    
near the surface of the earth1 and      
second1 because cheap pumps are poorly  
constructed and cannot raise a large    
amount4 ,but the supply will usually be 
sufficient for the needs of simple camp 
life1 and many a small farm uses this   
form of well1 not only for household    
purposes1 but for watering the cattle in
 winter4  ,if the cheapness of such     
pumps were known1 their use would be    
more general for temporary purposes4    
,the cost of material need not exceed #e
 for a #aj-;foot well1 and the driving  

of the pipe could be made as much a part
 of the camping as the pitching of the  
tent itself4 ,if the camping site is    
abandoned at the close of the vacation1 
the pump can be removed and kept over   
winter for use the following summer in  
another place4 ,in this way the actual  
cost of the water supply can be reduced 
to scarcely more than #c1 the removable 
pump being a permanent possession4 ,in  
rocky or mountain regions the driven    
well is not practicable1 because the    
driving point is blunted and broken by  
the rock and cannot pierce the rocky    
beds of land4  ,illustration3 ,,fig4    
#aci--;,a driven well4  ,illustration3  
,,fig4 #adj4--;,diagram showing how     
supplying a city with good water lessens
 sickness and death4 ,the lines b show  
the relative number of people who died  
of typhoid fever before the water was   
filtered2 the lines a show the numbers  
who died after the water was filtered4  
,the figures are the number of typhoid  
deaths occurring yearly out of #ajj1jjj 

inhabitants4  #ahh4 ,our ,summer        
,vacation4 ,it has been asserted by some
 city health officials that many cases  
of typhoid fever in cities can be traced
 to the unsanitary conditions existing  
in summer resorts4 ,the drinking water  
of most cities is now under strict      
supervision1 while that of isolated     
farms1 of small seaside resorts1 and of 
scattered mountain hotels is left to the
 care of individual proprietors1 and in 
only too many instances receives no     
attention whatever4 ,the sewage disposal
 is often inadequate and badly planned1 
and the water becomes dangerously       
contaminated4 ,a strong1 healthy person1
 with plenty of outdoor exercise and    
with hygienic habits1 may be able to    
resist the disease germs present in the 
poor water supply2 more often the summer
 guests carry back with them to their   
winter homes the germs of disease1 and  
these gain the upper hand under the     
altered conditions of city and business 
life4 ,it is not too much to say that   

every man and woman should know the     
source of his summer table water and the
 method of sewage disposal4 ,if the     
conditions are unsanitary1 they cannot  
be remedied at once1 but another resort 
can be found and personal danger can be 
avoided4 ,public sentiment and the loss 
of trade will go far in furthering an   
effort toward better sanitation4  ,in   
the driven well1 water cannot reach the 
spout unless it has first filtered      
through the soil to the depth of the    
driven pipe2 after such a journey it is 
fairly safe1 unless very large          
quantities of sewage are present2       
generally speaking1 such a depth of soil
 is able to filter satisfactorily the   
drainage of the limited number of people
 which a driven well suffices to supply4
  ,illustration3 ,,fig4 #ada4--;,a deep 
well with the piston in the water4      
,abundant water is rarely reached at    
less than #ge feet1 and it would usually
 be impossible to drive a pipe to such a
 depth4 ,when a large quantity of water 

is desired1 strong machines drill into  
the ground and excavate an opening into 
which a wide pipe can be lowered4 ,i    
recently spent a summer in the ,pocono  
,mountains and saw such a well          
completed4 ,the machine drilled to a    
depth of #bej feet before much water was
 reached and to over #cjj feet before a 
flow was obtained sufficient to satisfy 
the owner4 ,the water thus obtained was 
to be the sole water supply of a hotel  
accommodating #aej persons2 the         
proprietor calculated that the          
requirements of his guests1 for bath1   
toilet1 laundry1 kitchen1 etc41 and the 
domestics employed to serve them1       
together with the livery at their       
disposal1 demanded a flow of #aj gallons
 per minute4 ,the ground was full of    
rock and difficult to penetrate1 and it 
required #f weeks of constant work for  
two skilled men to drill the opening1   
lower the suction pipe1 and install the 
pump1 the cost being approximately #gjj4
  ,illustration3 ,,fig4 #adb4--,showing 

how drinking water can be contaminated  
from cesspool 7c7 and wash water 7w74   
,the water from such a well is safe and 
pure except under the conditions        
represented in ,figure #adb4 ,if sewage 
or slops be poured upon the ground in   
the neighborhood of the well1 the liquid
 will seep through the ground and some  
may make its way into the pump before it
 has been purified by the earth4 ,the   
impure liquid will thus contaminate the 
otherwise pure water and will render it 
decidedly harmful4 ,for absolute safety 
the sewage discharge should be at least 
#ge feet from the well1 and in large    
hotels1 where there is necessarily a    
large quantity of sewage1 the distance  
should be much greater4 ,as the sewage  
seeps through the ground it loses its   
impurities1 but the quantity of earth   
required to purify it depends upon its  
abundance2 a small depth of soil cannot 
take care of an indefinite amount of    
sewage4 ,hence1 the greater the number  
of people in a hotel1 or the more       

abundant the sewage1 the greater should 
be the distance between well and sewer4 
,by far the best way to avoid           
contamination is to see to it that the  
sewage discharges into the ground below 
the well2 that is1 to dig the well in   
such a location that the sewage drainage
 will be away from the well4  ,in cities
 and towns and large summer communities1
 the sewage of individual buildings     
drains into common tanks erected at     
public expense2 the contents of these   
are discharged in turn into harbors and 
streams1 or are otherwise disposed of at
 great expense1 although they contain   
valuable substances4 ,it has been       
estimated that the drainage or sewage of
 ,england alone would be worth          
#hj1jjj1jjj a year if used as           
fertilizer4  ,a few cities1 such as     
,columbus and ,cleveland1 ,ohio1 realize
 the need of utilizing this source of   
wealth1 and by chemical means deodorize 
their sewage and change it into         
substances useful for agricultural and  

industrial purposes4 ,there is still a  
great deal to be learned on this        
subject1 and it is possible that        
chemically treated sewage may be made a 
source of income to a community rather  
than an expense4  #ahi4 ,pumps which    
,compress ,air4 ,the pumps considered in
 the preceding ,sections have their     
widest application in agricultural      
districts1 where by means of them water 
is raised to the surface of the earth or
 is pumped into elevated tanks4 ,from a 
commercial and industrial standpoint a  
most important class of pump is that    
known as the compression type2 in these1
 air or any other gas is compressed     
rather than rarefied4  ,air brakes and  
self-opening and self-closing doors on  
cars are operated by means of           
compression pumps4 ,the laying of bridge
 and pier foundations1 in fact all work 
which must be done under water1 is      
possible only through the agency of     
compression pumps4 ,those who have      
visited mines1 and have gone into the   

heart of the underground labyrinth1 know
 how difficult it is for fresh air to   
make its way to the miners4 ,compression
 pumps have eliminated this difficulty1 
and to-day fresh air is constantly      
pumped into the mines to supply the     
laborers there4 ,agricultural methods   
also have been modified by the          
compression pump4 ,the spraying of trees
 7,fig4 #adc71 formerly done slowly and 
laboriously1 is now a relatively simple 
matter4  ,illustration3 ,,fig4          
#adc4--,spraying trees by means of a    
compression pump4  #aij4 ,the ,bicycle  
,pump4 ,the bicycle pump is the best    
known of all compression pumps4 ,here1  
as in other pumps of its type1 the      
valves open inward rather than outward4 
,when the piston is lowered1 compressed 
air is driven through the rubber tubing1
 pushes open an inward-opening valve in 
the tire1 and thus enters the tire4     
,when the piston is raised1 the lower   
valve closes1 the upper valve is opened 
by atmospheric pressure1 and air from   

outside enters the cylinder2 the next   
stroke of the piston drives a fresh     
supply of air into the tire1 which thus 
in time becomes inflated4 ,in most cheap
 bicycle pumps1 the piston valve is     
replaced by a soft piece of leather so  
attached to the piston that it allows   
air to slip around it and into the      
cylinder1 but prevents its escape from  
the cylinder 7,fig4 #add74              
,illustration3 ,,fig4 #add4--,the       
bicycle foot pump4  #aia4 ,how a ,man   
works under ,water4 ,place one end of a 
piece of glass tube in a vessel of water
 and notice that the water rises in the 
tube 7,fig4 #ade74 ,blow into the tube  
and see whether you can force the water 
wholly or partially down the tube4 ,if  
the tube is connected to a small        
compression pump1 sufficient air can be 
sent into the tube to cause the water to
 sink and to keep the tube permanently  
clear of water4 ,this is1 in brief1 the 
principle employed for work under water4
 ,a compression pump forces air through 

a tube into the chamber in which men are
 to work 7,fig4 #adf74 ,the air thus    
furnished from above supplies the       
workmen with oxygen1 and by its pressure
 prevents water from entering the       
chamber4 ,when the task has been        
completed1 the chamber is raised and    
later lowered to a new position4        
,illustration3 ,,fig4 #ade4--,water does
 not enter the tube as long as we blow  
into it4  ,figure #adg shows men at work
 on a bridge foundation4 ,workmen1      
tools1 and supplies are lowered in      
baskets through a central tube ,,bc     
provided with an air chamber ,l1 having 
air-tight gates at ,a and ,a'4 ,the gate
 ,a is opened and workmen enter the air 
chamber4 ,the gate ,a is then closed and
 the gate ,a' is opened slowly to give  
the men time to get accustomed to the   
high pressure in ,b1 and then the men   
are lowered to the bottom4 ,excavated   
earth is removed in a similar manner4   
,air is supplied through a tube ,,dd4   
,such an arrangement for work under     

water is called a caisson4 ,it is held  
in position by a mass of concrete ,,ee4 
,illustration3 ,,fig4 #adf--,the        
principle of work under water4          
,illustration3 ,,fig4 #adg--,showing how
 men can work under water4  ,in many    
cases men work in diving suits rather   
than in caissons2 these suits are made  
of rubber except for the head piece1    
which is of metal provided with         
transparent eyepieces4 ,air is supplied 
through a flexible tube by a compression
 pump4 ,the diver sometimes carries on  
his back a tank of compressed air1 from 
which the air escapes through a tube to 
the space between the body and the suit4
 ,when the air has become foul1 the     
diver opens a valve in his suit and     
allows it to pass into the water1 at the
 same time admitting a fresh supply from
 the tank4 ,the valve opens outward from
 the body1 and hence will allow of the  
exit of air but not of the entrance of  
water4 ,when the diver ceases work and  
desires to rise to the surface1 he      

signals and is drawn up by a rope       
attached to the suit4  #aib4            
,combination of ,pumps4 ,in many cases  
the combined use of both exhaust and    
compression pumps is necessary to secure
 the desired result2 as1 for example1 in
 pneumatic dispatch tubes4 ,these are   
employed in the transportation of       
letters and small packages from building
 to building or between parts of the    
same building4 ,a pump removes air from 
the part of the tube ahead of the       
package1 and thus reduces the           
resistance1 while a compression pump    
forces air into the tube behind the     
package and thus drives it forward with 
great speed4     ,,chapter ,,xix  ,,the 
,,water ,,problem ,,of ,a ,,large ,,city
   #aic4 ,it is by no means unusual for 
the residents of a large city or town to
 receive through the newspapers a       
notification that the city water supply 
is running low and that economy should  
be exercised in its use4 ,the problem of
 supplying a large city with an         

abundance of pure water is among the    
most difficult tasks which city         
officials have to perform1 and is one   
little understood and appreciated by the
 average citizen4  ,intense interest in 
personal and domestic affairs is        
natural1 but every citizen1 rich or     
poor1 should have an interest in civic  
affairs as well1 and there is no better 
or more important place to begin than   
with the water supply4 ,one of the most 
stirring questions in ,new ,york to-day 
has to do with the construction of huge 
aqueducts designed to convey to the     
residents of the city1 water from the   
distant ,catskill ,mountains4 ,the      
growth of the population has been so    
phenomenally rapid that the combined    
output of all available near-by sources 
does not suffice to meet the increasing 
consumption4  ,where does your city     
obtain its water8 ,does it bring it to  
its reservoirs in the most economic way 
possible1 and is there any legitimate   
excuse for the scarcity of water which  

many communities face in dry seasons8   
#aid4 ,two ,possibilities4 ,sometimes a 
city is fortunate enough to be situated 
near hills and mountains through which  
streams flow1 and in that case the water
 problem is simple4 ,in such a case all 
that is necessary is to run pipes1      
usually underground1 from the elevated  
lakes or streams to the individual      
houses1 or to common reservoirs from    
which it is distributed to the various  
buildings4  ,illustration3 ,,fig4       
#adh4--,the elevated mountain lake      
serves as a source of water4  ,figure   
#adh illustrates in a simple way the    
manner in which a mountain lake may     
serve to supply the inhabitants of a    
valley4 ,the city of ,denver1 for       
example1 is surrounded by mountains     
abounding in streams of pure1 clear     
water2 pipes convey the water from these
 heights to the city1 and thus a cheap  
and adequate flow is obtained4 ,such a  
system is known as the gravity system4  
,the nearer and steeper the elevation1  

the greater the force with which the    
water flows through the valley pipes1   
and hence the stronger the discharge    
from the faucets4  ,relatively few      
cities and towns are so favorably       
situated as regards water2 more often   
the mountains are too distant1 or the   
elevation is too slight1 to be of       
practical value4 ,cities situated in    
plains and remote from mountains are    
obliged to utilize the water of such    
streams as flow through the land1       
forcing it to the necessary height by   
means of pumps4 ,streams which flow     
through populated regions are apt to be 
contaminated1 and hence water from them 
requires public filtration4 ,cities     
using such a water supply thus have the 
double expense of pumping and           
filtration4  #aie4 ,the ,pressure of    
,water4 ,no practical business man would
 erect a turbine or paddle wheel without
 calculating in advance the value of his
 water power4 ,the paddle wheel might be
 so heavy that the stream could not turn

 it1 or so frail in comparison with the 
water force that the stream would       
destroy it4 ,in just as careful a       
manner1 the size and the strength of    
municipal reservoirs and pumps must be  
calculated4 ,the greater the quantity of
 water to be held in the reservoir1 the 
heavier are the walls required2 the     
greater the elevation of the houses1 the
 stronger must be the pumps and the     
engines which run them4  ,in order to   
understand how these calculations are   
made1 we must study the physical        
characteristics of water just as we     
studied the physical characteristics of 
air4  ,when we measure water1 we find   
that #a cubic foot of it weighs about   
#fb4e pounds2 this is equivalent to     
saying that water #a foot deep presses  
on the bottom of the containing vessel  
with a force of #fb4e pounds to the     
square foot4 ,if the water is #b feet   
deep1 the load supported by the vessel  
is doubled1 and the pressure on each    
square foot of the bottom of the vessel 

will be #abe pounds1 and if the water is
 #aj feet deep1 the load borne by each  
square foot will be #fbe pounds4 ,the   
deeper the water1 the greater will be   
the weight sustained by the confining   
vessel and the greater the pressure     
exerted by the water4  ,illustration3   
,,fig4 #adi4--,water #a foot deep exerts
 a pressure of #fb4e pounds a square    
foot4  ,since the pressure borne by #a  
square foot of surface is #fb4e pounds1 
the pressure supported by #a square inch
 of surface is #a_/add of #fb4e pounds1 
or 4#dc pound1 nearly #a_/b pound4      
,suppose a vessel held water to the     
depth of #aj feet1 then upon every      
square inch of the bottom of that vessel
 there would be a pressure of #d4cd     
pounds4 ,if a one-inch tap were inserted
 in the bottom of the vessel so that the
 water flowed out1 it would gush forth  
with a force of #d4cd pounds4 ,if the   
water were #bj feet deep1 the force of  
the outflowing water would be twice as  
strong1 because the pressure would be   

doubled4 ,but the flow would not remain 
constant1 because as the water leaves   
the outlet1 less and less of it remains 
in the vessel1 and hence the pressure   
gradually sinks and the flow drops      
correspondingly4  ,in seasons of        
prolonged drought1 the streams which    
feed a city reservoir are apt to contain
 less than the usual amount of water1   
hence the level of the water supply     
sinks1 the pressure at the outlet falls1
 and the force of the outflowing water  
is lessened 7,fig4 #aej74               
,illustration3 ,,fig4 #aej4--,the       
pressure at an outlet decreases as the  
level of the water supply sinks4  #aif4 
,why the ,water ,supply is not uniform  
in ,all ,parts of the ,city4 ,in the    
preceding ,section1 we saw that the flow
 from a faucet depends upon the height  
of the reserve water above the tap4     
,houses on a level with the main supply 
pipes 7,figs4 #adh and #aea7 have a     
strong flow because the water is under  
the pressure of a column ,a2 houses     

situated on elevation ,b have less flow1
 because the water is under the pressure
 of a shorter column ,b2 and houses at a
 considerable elevation ,c have a less  
rapid flow corresponding to the         
diminished depth 7,c74  ,not only does  
the flow vary with the elevation of the 
house1 but it varies with the location  
of the faucet within the house4 ,unless 
the reservoir is very high1 or the pumps
 very powerful1 the flow on the upper   
floors is noticeably less than that in  
the cellar1 and in the upper stories of 
some high building the flow is scarcely 
more than a feeble trickle4             
,illustration3 ,,fig4 #aea4--,water     
pressure varies in different parts of a 
water system4  ,when the respective     
flows at ,a1 ,b1 and ,c 7,fig4 #aea7 are
 measured1 they are found to be far     
lower than the pressures which columns  
of water of the heights ,a1 ,b1 and ,c  
have been shown by actual demonstration 
to exert4 ,this is because water1 in    
flowing from place to place1 expends    

force in overcoming the friction of the 
pipes and the resistance of the air4    
,the greater the distance traversed by  
the water in its journey from reservoir 
to faucet1 the greater the waste force  
and the less the final flow4  ,in       
practice1 large mains lead from the     
reservoir to the city1 smaller mains    
convey the water to the various sections
 of the city1 and service pipes lead to 
the individual house taps4 ,during this 
long journey1 considerable force is     
expended against friction1 and hence the
 flow at a distance from the reservoir  
falls to but a fraction of its original 
strength4 ,for this reason1 buildings   
situated near the main supply have a    
much stronger flow 7,fig4 #aeb7 than    
those on the same level but remote from 
the supply4 ,artificial reservoirs are  
usually constructed on the near         
outskirts of a town in order that the   
frictional force lost in transmission   
may be reduced to a minimum4            
,illustration3 ,,fig4 #aeb4--,the more  

distant the fountain1 the weaker the    
flow4  ,in the case of a natural        
reservoir1 such as an elevated lake or  
stream1 the distance cannot be planned  
or controlled4 ,new ,york1 for example1 
will secure an abundance of pure water  
from the ,catskill ,mountains1 but it   
will lose force in transmission4 ,los   
,angeles is undertaking one of the      
greatest municipal projects of the day4 
,huge aqueducts are being built which   
will convey pure mountain water a       
distance of #bej miles1 and in          
quantities sufficient to supply two     
million people4 ,according to           
calculations1 the force of the water    
will be so great that pumps will not be 
needed4  #aig4 ,why ,water does not     
always flow from a ,faucet4 ,most of us 
have at times been annoyed by the       
inability to secure water on an upper   
story1 because of the drawing off of a  
supply on a lower floor4 ,during the    
working hours of the day1 immense       
quantities of water are drawn off from  

innumerable faucets1 and hence the      
quantity in the pipes decreases         
considerably unless the supply station  
is able to drive water through the vast 
network of pipes as fast as it is drawn 
off4 ,buildings at a distance from the  
reservoir suffer under such             
circumstances1 because while the        
diminished pressure is ordinarily       
powerful enough to supply the lower     
floors1 it is frequently too weak to    
force a continuous stream to high       
levels4 ,at night1 however1 and out of  
working hours1 few faucets are open1    
less water is drawn off at any one time1
 and the intricate pipes are constantly 
full of water under high pressure4 ,at  
such times1 a good flow is obtainable   
even on the uppermost floors4  ,in order
 to overcome the disadvantage of a      
decrease in flow during the day1        
standpipes 7,fig4 #aec7 are sometimes   
placed in various sections4 ,these are  
practically small steel reservoirs full 
of water and connecting with the city   

pipes4 ,during rush hours1 water passes 
from these into the communicating pipes 
and increases the available supply1     
while during the night1 when the faucets
 are turned off1 water accumulates in   
the standpipe against the next emergency
 7,figs4 #aea and #aed74 ,the service   
rendered by the standpipe is similar to 
that of the air cushion discussed in    
,section #ahd4  ,illustration3 ,,fig4   
#aec4--;,a standpipe4  #aih4 ,the ,cost 
of ,water4 ,in the gravity system1 where
 an elevated lake or stream serves as a 
natural reservoir1 the cost of the      
city's waterworks is practically limited
 to the laying of pipes4 ,but when the  
source of the supply is more or less on 
a level with the surrounding land1 the  
cost is great1 because the supply for   
the entire city must either be pumped   
into an artificial reservoir1 from which
 it can be distributed1 or else must be 
driven directly through the mains 7,fig4
 #aed74  ,illustration3 ,,fig4          
#aed4--,water must be got to the houses 

by means of pumps4  ,a gallon of water  
weighs approximately #h4c pounds1 and   
hence the work done by a pump in raising
 a gallon of water to the top of an     
average house1 an elevation of #ej feet1
 is #h4c  #ej1 or #dae foot pounds4 ,a  
small manufacturing town uses at least  
#a1jjj1jjj gallons daily1 and the work  
done by a pump in raising that amount to
 an elevation of #ej feet would be #h4c 
#a1jjj1jjj  #ej1 or #dae1jjj1jjj foot   
pounds4  ,the total work done during the
 day by the pump1 or the engine driving 
the pump1 is #dae1jjj1jjj foot pounds1  
and hence the work done during one hour 
would be #a_/bd of #dae1jjj1jjj1 or     
#ag1bia1fff foot pounds2 the work done  
in one minute would be #a_/fj of        
#ag1bia1fff1 or #bhh1aid foot pounds1   
and the work done each second would be  
#a_/fj of #bhh1aid1 or #dhjc foot       
pounds4  ,a #a-;,h4,p4 engine does #eej 
foot pounds of work each second1 and    
therefore if the pump is to be operated 
by an engine1 the strength of the latter

 would have to be #h4g ,h4,p4 ,an       
#h4g-;,h4,p4 pumping engine working at  
full speed every second of the day and  
night would be able to supply the town  
with the necessary amount of water4     
,when1 however1 we consider the actual  
height to which the water is raised     
above the pumping station1 and the extra
 pumping which must be done in order to 
balance the frictional loss1 it is easy 
to understand that in actual practice a 
much more powerful engine would be      
needed4 ,the larger the piston and the  
faster it works1 the greater is the     
quantity of water raised at each stroke1
 and the stronger must be the engine    
which operates the pump4  ,in many large
 cities there is no one single pumping  
station from which supplies run to all  
parts of the city1 but several pumping  
stations are scattered throughout the   
city1 and each of them supplies a       
restricted territory4  #aii4 ,the       
,bursting of ,dams and ,reservoirs4 ,the
 construction of a safe reservoir is one

 of the most important problems of      
engineers4 ,in ,october1 #aiaa1 a town  
in ,pennsylvania was virtually wiped out
 of existence because of the bursting of
 a dam whose structure was of           
insufficient strength to resist the     
strain of the vast quantity of water    
held by it4 ,a similar breakage was the 
cause of the fatal ,johnstown flood in  
#ahhi1 which destroyed no less than     
seven towns1 and in which approximately 
#bjjj persons are said to have lost     
their lives4  ,water presses not only on
 the bottom of a vessel1 but upon the   
sides as well2 a bucket leaks whether   
the hole is in its side or its bottom1  
showing that water presses not only     
downward but outward4 ,usually a leak in
 a dam or reservoir occurs near the     
bottom4 ,weak spots at the top are rare 
and easily repaired1 but a leak near the
 bottom is usually fatal1 and in the    
case of a large reservoir the outflowing
 water carries death and destruction to 
everything in its path4  ,if the leak is

 near the surface1 as at a 7,fig4 #aee71
 the water issues as a feeble stream1   
because the pressure against the sides  
at that level is due solely to the      
relatively small height of water above a
 7,section #aie74 ,if the leak is lower1
 as at b1 the issuing stream is stronger
 and swifter1 because at that level the 
outward pressure is much greater than at
 a1 the increase being due to the fact  
that the height of the water above b is 
greater than that above a4 ,if the leak 
is quite low1 as at c1 the issuing      
stream has a still greater speed and    
strength1 and gushes forth with a force 
determined by the height of the water   
above c4  ,illustration3 ,,fig4         
#aee4--,the flow from an opening depends
 upon the height of water above the     
opening4  ,the dam at ,johnstown was    
nearly #a_/b mile wide1 and #dj feet    
high1 and so great was the force and    
speed of the escaping stream that within
 an hour after the break had occurred1  
the water had traveled a distance of #ah

 miles1 and had destroyed property to   
the value of millions of dollars4  ,if a
 reservoir has a depth of #ajj feet1 the
 pressure exerted upon each square foot 
of its floor is #fb4e  #ajj1 or #fbej   
pounds2 the weight therefore to be      
sustained by every square foot of the   
reservoir floor is somewhat more than #c
 tons1 and hence strong foundations are 
essential4 ,the outward lateral pressure
 at a depth of #be feet would be only   
one fourth as great as that on the      
bottom--hence the strain on the sides at
 that depth would be relatively slight1 
and a less powerful construction would  
suffice4 ,but at a depth of #ej feet the
 pressure on the sides would be one half
 that of the floor pressure1 or #a-a_/b 
tons4 ,at a depth of #ge feet1 the      
pressure on the sides would be three    
quarters that on the bottom1 or #b-a_/d 
tons4 ,as the bottom of the reservoir is
 approached1 the pressure against the   
sides increases1 and more powerful      
construction becomes necessary4  ,small 

elevated tanks1 like those of the       
windmill1 frequently have heavy iron    
bands around their lower portion as a   
protection against the extra strain4    
,before erecting a dam or reservoir1 the
 maximum pressure to be exerted upon    
every square inch of surface should be  
accurately calculated1 and the structure
 should then be built in such a way that
 the varying pressure of the water can  
be sustained4 ,it is not sufficient that
 the bottom be strong2 the sides        
likewise must support their strain1 and 
hence must be increased in strength with
 depth4 ,this strengthening of the walls
 is seen clearly in the reservoir shown 
in ,figure #aeb4 ,the bursting of dams  
and reservoirs has occasioned the loss  
of so many lives1 and the destruction of
 so much property1 that some states are 
considering the advisability of federal 
inspection of all such structures4      
,illustration3 ,,fig4 #aef4--,the lock  
gates must be strong in order to        
withstand the great pressure of the     

water against them4  #bjj4 ,the         
,relation of ,forests to the ,water     
,supply4 ,when heavy rains fall on a    
bare slope1 or when snow melts on a     
barren hillside1 a small amount of the  
water sinks into the ground1 but by far 
the greater part of it runs off quickly 
and swells brooks and streams1 thus     
causing floods and freshets4  ,when1    
however1 rain falls on a wooded slope1  
the action is reversed2 a small portion 
runs off1 while the greater portion     
sinks into the soft earth4 ,this is due 
partly to the fact that the roots of    
trees by their constant growth keep the 
soil loose and open1 and form channels1 
as it were1 along which the water can   
easily run4 ,it is due also to the      
presence on the ground of decaying      
leaves and twigs1 or humus4 ,the        
decaying vegetable matter which covers  
the forest floor acts more or less as a 
sponge1 and quickly absorbs falling rain
 and melting snow4 ,the water which thus
 passes into the humus and the soil     

beneath does not remain there1 but      
slowly seeps downward1 and finally after
 weeks and months emerges at a lower    
level as a stream4 ,brooks and springs  
formed in this way are constant feeders 
of rivers and lakes4  ,in regions where 
the land has been deforested1 the rivers
 run low in season of prolonged drought1
 because the water which should have    
slowly seeped through the soil1 and then
 supplied the rivers for weeks and      
months1 ran off from the barren slopes  
in a few days4  ,forests not only lessen
 the danger of floods1 but they conserve
 our waterways1 preventing a dangerous  
high-water mark in the season of heavy  
rains and melting snows1 and then       
preventing a shrinkage in dry seasons   
when the only feeders of the rivers are 
the underground sources4 ,in the summer 
of #aiaa1 prolonged drought in ,north   
,carolina lowered the rivers to such an 
extent that towns dependent upon them   
suffered greatly4 ,the city of          
,charlotte was reduced for a time to a  

practically empty reservoir2 washing and
 bathing were eliminated1 machinery     
dependent upon water-power and steam    
stood idle1 and every glass of water    
drunk was carefully reckoned4 ,thousands
 of gallons of water were brought in    
tanks from neighboring cities1 and were 
emptied into the empty reservoir from   
whence it trickled slowly through the   
city mains4 ,the lack of water caused   
not only personal inconvenience and     
business paralysis1 but it occasioned   
real danger of disease through unflushed
 sewers and insufficiently drained      
pipes4  ,the conservation of the forest 
means the conservation of our waterways1
 whether these be used for              
transportation or as sources of drinking
 water4     ,,chapter ,,xx  ,,man',s    
,,conquest ,,of ,,substances   #bja4    
,chemistry4 ,man's mechanical inventions
 have been equaled by his chemical      
researches and discoveries1 and by the  
application he has made of his new      
knowledge4  ,the plain cotton frock of  

our grandmothers had its death knell    
sounded a few years ago1 when ,john     
,mercer showed that cotton fabrics      
soaked in caustic soda assumed under    
certain conditions a silky sheen1 and   
when dyed took on beautiful and varied  
hues4 ,the demonstration of this simple 
fact laid the foundation for the        
manufacture of a vast variety of        
attractive dress materials known as     
mercerized cotton4  ,possibly no        
industry has been more affected by      
chemical discovery than that of dyeing4 
,those of us who have seen the old      
masterpieces in painting1 or            
reproductions of them1 know the         
softness1 the mellowness1 the richness  
of tints employed by the old masters4   
,but if we look for the brilliancy and  
variety of color seen in our own day1   
the search will be fruitless1 because   
these were unknown until a half century 
ago4 ,up to that time1 dyes were few in 
number and were extracted solely from   
plants1 principally from the indigo and 

madder plants4 ,but about the year #ahef
 it was discovered that dyes in much    
greater variety and in purer form could 
be obtained from coal tar4 ,this        
chemical production of dyes has now     
largely supplanted the original method1 
and the industry has grown so rapidly   
that a single firm produced in one year 
from coal tar a quantity of indigo dye  
which under the natural process of plant
 extraction would have required a       
quarter million acres of indigo plant4  
,the abundance and cheapness of         
newspapers1 coarse wrapping papers1     
etc41 is due to the fact that man has   
learned to substitute wood for rags in  
the manufacture of paper4 ,investigation
 brought out the fact that wood         
contained the substance which made rags 
valuable for paper making4 ,since the   
supply of rags was far less than the    
demand1 the problem of the extraction   
from wood of the paper-forming substance
 was a vital one4 ,from repeated trials1
 it was found that caustic soda when    

heated with wood chips destroyed        
everything in the wood except the       
desired substance1 cellulose2 this could
 be removed1 bleached1 dried1 and       
pressed into paper4 ,the substitution of
 wood for rags has made possible the    
daily issue of newspapers1 for the      
making of which sufficient material     
would not otherwise have been available4
 ,when we reflect that a daily paper of 
wide circulation consumes ten acres of  
wood lot per day1 we see that all the   
rags in the world would be inadequate to
 meet this demand alone1 to say nothing 
of periodicals1 books1 tissue paper1    
etc4  ,chemistry plays a part in every  
phase of life2 in the arts1 the         
industries1 the household1 and in the   
body itself1 where digestion1 excretion1
 etc41 result from the action of the    
bodily fluids upon food4 ,the chemical  
substances of most interest to us are   
those which affect us personally rather 
than industrially2 for example1 soap1   
which cleanses our bodies1 our clothing1

 our household possessions2 washing     
soda1 which lightens laundry work2 lye1 
which clears out the drain pipe clogged 
with grease2 benzine1 which removes     
stains from clothing2 turpentine1 which 
rids us of paint spots left by careless 
workmen2 and hydrogen peroxide1 which   
disinfects wounds and sores4  ,in order 
to understand the action of several of  
these substances we must study the      
properties of two groups of             
chemicals--known respectively as acids  
and bases2 the first of these may be    
represented by vinegar1 sulphuric acid1 
and oxalic acid2 and the second1 by     
ammonia1 lye1 and limewater4  #bjb4     
,acids4 ,all of us know that vinegar and
 lemon juice have a sour taste1 and it  
is easy to show that most acids are     
characterized by a sour taste4 ,if a    
clean glass rod is dipped into very     
dilute acid1 such as acetic1 sulphuric1 
or nitric acid1 and then lightly touched
 to the tongue1 it will taste sour4 ,but
 the best test of an acid is by sight   

rather than by taste1 because it has    
been found that an acid is able to      
discolor a plant substance called       
litmus4 ,if paper is soaked in a litmus 
solution until it acquires the          
characteristic blue hue of the plant    
substance1 and is then dried thoroughly1
 it can be used to detect acids1 because
 if it comes in contact with even the   
minutest trace of acid1 it loses its    
blue color and assumes a red tint4      
,hence1 in order to detect the presence 
of acid in a substance1 one has merely  
to put some of the substance on blue    
litmus paper1 and note whether or not   
the latter changes color4 ,this test    
shows that many of our common foods     
contain some acid2 for example1 fruit1  
buttermilk1 sour bread1 and vinegar4    
,the damage which can be done by strong 
acids is well known2 if a jar of        
sulphuric acid is overturned1 and some  
of it falls on the skin1 it eats its way
 into the flesh and leaves an ugly sore2
 if it falls on carpet or coat1 it eats 

its way into the material and leaves an 
unsightly hole4 ,the evil results of an 
accident with acid can be lessened if we
 know just what to do and do it quickly1
 but for this we must have a knowledge  
of bases1 the second group of chemicals4
  #bjc4 ,bases4 ,substances belonging to
 this group usually have a bitter taste 
and a slimy1 soapy feeling4 ,for our    
present purposes1 the most important    
characteristic of a base is that it will
 neutralize an acid and in some measure 
hinder the damage effected by the       
former4 ,if1 as soon as an acid has been
 spilled on cloth1 a base1 such as      
ammonia1 is applied to the affected     
region1 but little harm will be done4   
,in your laboratory experiments you may 
be unfortunate enough to spill acid on  
your body or clothing2 if so1 quickly   
apply ammonia4 ,if you delay1 the acid  
does its work1 and there is no remedy4  
,if soda 7a base7 touches black         
material1 it discolors it and leaves an 
ugly brown spot2 but the application of 

a little acid1 such as vinegar or lemon 
juice1 will often restore the original  
color and counteract the bad effects of 
the base4 ,limewater prescribed by      
physicians in cases of illness is a     
well-known base4 ,this liquid           
neutralizes the too abundant acids      
present in a weak system and so quiets  
and tones the stomach4  ,the interaction
 of acids and bases may be observed in  
another way4 ,if blue litmus paper is   
put into an acid solution1 its color    
changes to red2 if now the red litmus   
paper is dipped into a base solution1   
caustic soda1 for example1 its original 
color is partially restored4 ,what the  
acid does1 the base undoes1 either      
wholly or in part4 ,bases always turn   
red litmus paper blue4  ,bases1 like    
acids1 are good or bad according to     
their use2 if they come in contact with 
cloth1 they eat or discolor it1 unless  
neutralized by an acid4 ,but this       
property of bases1 harmful in one way1  
is put to advantage in the home1 where  

grease is removed from drainpipe and    
sink by the application of lye1 a strong
 base4 ,if the lye is too concentrated1 
it will not only eat the grease1 but    
will corrode the metal piping2 it is    
easy1 however1 to dilute base solutions 
to such a degree that they will not     
affect piping1 but will remove grease4  
,dilute ammonia is used in almost every 
home and is an indispensable domestic   
servant2 diluted sufficiently1 it is    
invaluable in the washing of delicate   
fabrics and in the removing of stains1  
and in a more concentrated form it is   
helpful as a smelling salt in cases of  
fainting4  ,some concentrated bases are 
so powerful in their action on grease1  
cloth1 and metal that they have received
 the designation caustic1 and are       
ordinarily known as caustic soda1       
caustic potash 7lye71 and caustic lime4 
,these more active bases are generally  
called alkalies in distinction from the 
less active ones4  #bjd4 ,neutral       
,substances4 ,to any acid solution add  

gradually a small quantity of a base1   
and test the mixture from time to time  
with blue litmus paper2 at first the    
paper will turn red quickly1 but as more
 and more of the base is added to the   
solution1 it has less and less effect on
 the blue litmus paper1 and finally a   
point is reached when a fresh strip of  
blue paper will not be affected4 ,such a
 result indicates infallibly the absence
 of any acid qualities in the solution4 
,if now red litmus paper is tested in   
the same solution1 its color also will  
remain unchanged2 such a result         
indicates infallibly the absence of any 
basic quality4 ,the solution has the    
characteristic property of neither acid 
nor base and is said to be neutral4  ,if
 to the neutral solution an extra       
portion of base is added1 so that there 
is an excess of base over acid1 the     
neutralization is overbalanced and the  
red paper turns blue4 ,if to the neutral
 solution an extra portion of acid is   
added1 so that there is an excess of    

acid over base1 the neutralization is   
overbalanced in the opposite direction1 
and the solution acquires acid          
characteristics4  ,most acids and bases 
will eat and corrode and discolor1 while
 neutral substances will not2 it is for 
this reason that soap1 a slightly       
alkaline substance1 is the safest       
cleansing agent for laundry1 bath1 and  
general work4 ,good soaps1 being        
carefully made1 are so nearly neutral   
that they will not fade the color out of
 clothing2 the cheap soaps are less     
carefully prepared and are apt to have a
 strong excess of the base ingredient2  
such soaps are not safe for delicate    
work4  #bje4 ,soap4 ,if we gather       
together scrapings of lard1 butter1 bits
 of tallow from burned-out candles1     
scraps of waste fat1 or any other sort  
of grease1 and pour a strong solution of
 lye over the mass1 a soft soapy        
substance is formed4 ,in colonial times1
 every family made its own supply of    
soap1 utilizing1 for that purpose1      

household scraps often regarded by the  
housekeeper of to-day as worthless4     
,grease and fat were boiled with water  
and hardwood ashes1 which are rich in   
lye1 and from the mixture came the soft 
soap used by our ancestors4 ,in         
practice1 the wood ashes were boiled in 
water1 which was then strained off1 and 
the resulting filtrate1 or lye1 was     
mixed with the fats for soap making4    
,most fats contain a substance of an    
acid nature1 and are decomposed by the  
action of bases such as caustic soda and
 caustic potash4 ,the acid component of 
the grease partially neutralizes the    
base1 and a new substance is formed1    
namely1 soap4  ,with the advance of     
civilization the labor of soap making   
passed from the home to the factory1    
very much as bread making has done in   
our own day4 ,different varieties of    
soaps appeared1 of which the hard soap  
was the most popular1 owing to the ease 
with which it could be transported4     
,within the last few years liquid soaps 

have come into favor1 especially in     
schools1 railroad stations1 and other   
public places1 where a cake of soap     
would be handled by many persons4 ,by   
means of a simple device 7,fig4 #aeg71  
the soap escapes from a receptacle when 
needed4 ,the mass of the soap does not  
come in contact with the skin1 and hence
 the spread of contagious skin diseases 
is lessened4  ,illustration3 ,,fig4     
#aeg4--,liquid soap container4          
,commercial soaps are made from a great 
variety of substances1 such as tallow1  
lard1 castor oil1 coconut oil1 olive    
oil1 etc42 or in cheaper soaps1 from    
rosin1 cottonseed oil1 and waste grease4
 ,the fats which go to waste in our     
garbage could be made a source of       
income1 not only to the housewife1 but  
to the city4 ,in ,columbus1 ,ohio1      
garbage is used as a source of revenue2 
the grease from the garbage being sold  
for soap making1 and the tankage        
7,section #ahh7 for fertilizer4  #bjf4  
,why ,soap ,cleans4 ,the natural oil of 

the skin catches and retains dust and   
dirt1 and makes a greasy film over the  
body4 ,this cannot be removed by water  
alone1 but if soap is used and a        
generous lather is applied to the skin1 
the dirt is cut and passes from the body
 into the water4 ,soap affects a grease 
film and water very much as the white of
 an egg affects oil and water4 ,these   
two liquids alone do not mix1 the oil   
remaining separate on the surface of the
 water2 but if a small quantity of white
 of egg is added1 an emulsion is formed1
 the oil separating into minute droplets
 which spread through the water4 ,in the
 same way1 soap acts on a grease film1  
separating it into minute droplets which
 leave the skin and spread through the  
water1 carrying with them the dust and  
dirt particles4 ,the warmer the water1  
the better will be the emulsion1 and    
hence the more effective the removal of 
dirt and grease4 ,this explanation holds
 true for the removal of grease from any
 surface1 whether of the body1 clothing1

 furniture1 or dishes4  #bjg4 ,washing  
,powders4 ,sometimes soap refuses to    
form a lather and instead cakes and     
floats as a scum on the top of the      
water2 this is not the fault of the soap
 but of the water4 ,as water seeps      
through the soil or flows over the land1
 it absorbs and retains various soil    
constituents which modify its character 
and1 in some cases1 render it almost    
useless for household purposes4 ,most of
 us are familiar with the rain barrel of
 the country house1 and know that the   
housewife prefers rain water for laundry
 and general work4 ,rain water1 coming  
as it does from the clouds1 is free from
 the chemicals gathered by ground water1
 and is hence practically pure4 ,while  
foreign substances do not necessarily   
injure water for drinking purposes      
7,section #fi71 they are often of such a
 nature as to prevent soap from forming 
an emulsion1 and hence from doing its   
work4 ,under such circumstances the     
water is said to be hard1 and soap used 

with it is wasted4 ,even if water is    
only moderately hard1 much soap is lost4
 ,the substances which make water hard  
are calcium and magnesium salts4 ,when  
soap is put into water containing one or
 both of these1 it combines with the    
salts to form sticky insoluble scum4 ,it
 is therefore not free to form an       
emulsion and to remove grease4 ,as a    
cleansing agent it is valueless4 ,the   
average city supply contains so little  
hardness that it is satisfactory for    
toilet purposes2 but in the laundry1    
where there is need for the full effect 
of the soap1 and where the slightest    
loss would aggregate a great deal in the
 course of time1 something must be done 
to counteract the hardness4 ,the        
addition of soda1 or sodium carbonate to
 the water will usually produce the     
desired effect4 ,washing soda combines  
with calcium and magnesium and prevents 
them from uniting with soap4 ,the soap  
is thus free to form an emulsion1 just  
as in ordinary water4 ,washing powders  

are sometimes used instead of washing   
soda4 ,most washing powders contain1 in 
addition to a softening agent1 some     
alkali1 and hence a double good is      
obtained from their use2 they not only  
soften the water and allow the soap to  
form an emulsion1 but they also1 through
 their alkali content1 cut the grease   
and themselves act as cleansers4 ,in    
some cities where the water is very     
hard1 as in ,columbus1 ,ohio1 it is     
softened and filtered at public expense1
 before it leaves the reservoirs4 ,but  
even under these circumstances1 a       
moderate use of washing powder is       
general in laundry work4  ,if washing   
powder is put on clothes dry1 or is     
thrown into a crowded tub1 it will eat  
the clothes before it has a chance to   
dissolve in the water4 ,the only safe   
method is to dissolve the powder before 
the clothes are put into the tub4 ,the  
trouble with our public laundries is    
that many of them are careless about    
this very fact1 and do not take time to 

dissolve the powder before mixing it    
with the clothes4  ,the strongest       
washing powder is soda1 and this cheap  
form is as good as any of the more      
expensive preparations sold under fancy 
names4 ,borax is a milder powder and is 
desirable for finer work4  ,one of the  
most disagreeable consequences of the   
use of hard water for bathing is the    
unavoidable scum which forms on the     
sides of bathtub and washbowl4 ,the     
removal of the caked grease is          
difficult1 and if soap alone is used1   
the cleaning of the tub requires both   
patience and hard scrubbing4 ,the labor 
can be greatly lessened by moistening   
the scrubbing cloth with turpentine and 
applying it to the greasy film1 which   
immediately dissolves and thus can be   
easily removed4 ,the presence of the    
scum can be largely avoided by adding a 
small amount of liquid ammonia to the   
bath water4 ,but many persons object to 
this2 hence it is well to have some     
other easy method of removing the       

objectionable matter4  #bjh4 ,to remove 
,stains from ,cloth4 ,while soap is1    
generally speaking1 the best cleansing  
agent1 there are occasions when other   
substances can be used to better        
advantage4 ,for example1 grease spots on
 carpet and non-washable dress goods are
 best removed by the application of     
gasoline or benzine4 ,these substances  
dissolve the grease1 but do not remove  
it from the clothing2 for that purpose a
 woolen cloth should be laid under the  
stain in readiness to absorb the benzine
 and the grease dissolved in it4 ,if the
 grease is not absorbed while in        
solution1 it remains in the clothing and
 after the evaporation of the benzine   
reappears in full force4  ,cleaners     
frequently clean suits by laying a      
blotter over a grease spot and applying 
a hot iron2 the grease1 when melted by  
the heat1 takes the easiest way of      
spreading itself and passes from cloth  
to blotter4  #bji4 ,salts4 ,a neutral   
liquid formed as in ,section #bjd1 by   

the action of hydrochloric acid and the 
alkali solution of caustic soda1 has a  
brackish1 salty taste1 and is1 in fact1 
a solution of salt4 ,this can be        
demonstrated by evaporating the neutral 
liquid to dryness and examining the     
residue of solid matter1 which proves to
 be common salt4  ,when an acid is mixed
 with a base1 the result is a substance 
more or less similar in its properties  
to common salt2 for this reason all     
compounds formed by the neutralization  
of an acid with a base are called salts4
 ,if1 instead of hydrochloric acid      
7,h,cl71 we use an acid solution of     
potassium tartrate1 and if instead of   
caustic soda we use bicarbonate of soda 
7baking soda71 the result is a brackish 
liquid as before1 but the salt in the   
liquid is not common salt1 but ,rochelle
 salt4 ,different combinations of acids 
and bases produce different salts4 ,of  
all the vast group of salts1 the most   
abundant as well as the most important  
is common salt1 known technically as    

sodium chloride because of its two      
constituents1 sodium and chlorine4  ,we 
are not dependent upon neutralization   
for the enormous quantities of salt used
 in the home and in commerce4 ,it is    
from the active1 restless seas of the   
present1 and from the dead seas of the  
prehistoric past that our vast stores of
 salt come4 ,the waters of the          
,mediterranean and of our own ,great    
,salt ,lake are led into shallow basins1
 where1 after evaporation by the heat of
 the sun1 they leave a residue of salt4 
,by far the largest quantity of salt1   
however1 comes from the seas which no   
longer exist1 but which in far remote   
ages dried up and left behind them their
 burden of salt4 ,deposits of salt      
formed in this way are found scattered  
throughout the world1 and in our own    
country are found in greatest abundance 
in ,new ,york4 ,the largest salt deposit
 known has a depth of one mile and      
exists in ,germany4  ,salt is           
indispensable on our table and in our   

kitchen1 but the amount of salt used in 
this way is far too small to account for
 a yearly consumption of #d1jjj1jjj tons
 in the ,united ,states alone4 ,the     
manufacture of soap1 glass1 bleaching   
powders1 baking powders1 washing soda1  
and other chemicals depends on salt1 and
 it is for these that the salt beds are 
mined4  #baj4 ,baking ,soda4 ,salt is by
 all odds the most important sodium     
compound4 ,next to it come the so-called
 carbonates3 first1 sodium carbonate1   
which is already familiar to us as      
washing soda2 and second1 sodium        
bicarbonate1 which is an ingredient of  
baking powders4 ,these are both obtained
 from sodium chloride by relatively     
simple means2 that is1 by treating salt 
with the base1 ammonia1 and with carbon 
dioxide4  ,washing soda has already been
 discussed4 ,since baking powders in    
some form are used in almost all homes  
for the raising of cake and pastry      
dough1 it is essential that their       
helpful and harmful qualities be clearly

 understood4  ,the raising of dough by  
means of baking soda--bicarbonate of    
soda--is a very simple process4 ,when   
soda is heated1 it gives off carbon     
dioxide gas2 you can easily prove this  
for yourself by burning a little soda in
 a test tube1 and testing the escaping  
gas in a test tube of limewater4 ,when  
flour and water alone are kneaded and   
baked in loaves1 the result is a mass so
 compact and hard that human teeth are  
almost powerless to crush and chew it4  
,the problem is to separate the mass of 
dough or1 in other words1 to cause it to
 rise and lighten4 ,this can be done by 
mixing a little soda in the flour1      
because the heat of the oven causes the 
soda to give off bubbles of gas1 and    
these in expanding make the heavy mass  
slightly porous4 ,bread is never        
lightened with soda because the amount  
of gas thus given off is too small to   
convert heavy compact bread dough into a
 spongy mass2 but biscuit and cake1     
being by nature less compact and heavy1 

are sufficiently lightened by the gas   
given off from soda4  ,but there is one 
great objection to the use of soda alone
 as a leavening agent4 ,after baking    
soda has lost its carbon dioxide gas1 it
 is no longer baking soda1 but is       
transformed into its relative1 washing  
soda1 which has a disagreeable taste and
 is by no means desirable for the       
stomach4  ,man's knowledge of chemicals 
and their effect on each other has      
enabled him to overcome this difficulty 
and1 at the same time1 to retain the    
leavening effect of the baking soda4    
#baa4 ,baking ,powders4 ,if some cooking
 soda is put into lemon juice or        
vinegar1 or any acid1 bubbles of gas    
immediately form and escape from the    
liquid4 ,after the effervescence has    
ceased1 a taste of the liquid will show 
you that the lemon juice has lost its   
acid nature1 and has acquired in        
exchange a salty taste4 ,baking soda1   
when treated with an acid1 is           
transformed into carbon dioxide and a   

salt4 ,the various baking powders on the
 market to-day consist of baking soda   
and some acid substance1 which acts upon
 the soda1 forces it to give up its gas1
 and at the same time unites with the   
residue to form a harmless salt4  ,cream
 of tartar contains sufficient acid to  
act on baking soda1 and is a convenient 
and safe ingredient for baking powder4  
,when soda and cream of tartar are mixed
 dry1 they do not react on each other1  
neither do they combine rapidly in cold 
moist dough1 but as soon as the heat of 
the oven penetrates the doughy mass1 the
 cream of tartar combines with the soda 
and sets free the gas needed to raise   
the dough4 ,the gas expands with the    
heat of the oven1 raising the dough     
still more4 ,meanwhile1 the dough itself
 is influenced by the heat and is       
stiffened to such an extent that it     
retains its inflated shape and spongy   
nature4  ,many housewives look askance  
at ready-made baking powders and prefer 
to bake with soda and sour milk1 soda   

and buttermilk1 or soda and cream of    
tartar4 ,sour milk and buttermilk are   
quite as good as cream of tartar1       
because the lactic acid which they      
contain combines with the soda and      
liberates carbon dioxide1 and forms a   
harmless residue in the dough4  ,the    
desire of manufacturers to produce cheap
 baking powders led to the use of cheap 
acids and alkalies1 regardless of the   
character of the resulting salt4 ,alum  
and soda were popular for some time2 but
 careful examination proved that the    
particular salt produced by this        
combination was not readily absorbed by 
the stomach1 and that its retention     
there was injurious to health4 ,for this
 reason1 many states have prohibited the
 use of alum in baking powders4  ,it is 
not only important to choose the        
ingredients carefully2 it is also       
necessary to calculate the respective   
quantities of each1 otherwise there will
 be an excess of acid or alkali for the 
stomach to take care of4 ,a standard    

powder contains twice as much cream of  
tartar as of bicarbonate of soda1 and   
the thrifty housewife who wishes to     
economize1 can make for herself1 at     
small cost1 as good a baking powder as  
any on the market1 by mixing tartar and 
soda in the above proportions and adding
 a little corn starch to keep the       
mixture dry4  ,the self-raising flour1  
so widely advertised by grocers1 is     
flour in which these ingredients or     
their equivalent have been mixed by the 
manufacturer4  #bab4 ,soda ,mints4      
,bicarbonate of soda is practically the 
sole ingredient of the soda mints       
popularly sold for indigestion4 ,these  
correct a tendency to sour stomach      
because they counteract the surplus acid
 in the stomach1 and form with it a safe
 neutral substance4  ,seidlitz powder is
 a simple remedy consisting of two      
powders1 one containing bicarbonate of  
soda1 and the other1 some acid such as  
cream of tartar4 ,when these substances 
are dissolved in water and mixed1       

effervescence occurs1 carbon dioxide    
escapes1 and a solution of ,rochelle    
salt remains4  #bab;a4 ,source of ,soda4
 ,an enormous quantity of sodium        
carbonate1 or soda1 as it is usually    
called1 is needed in the manufacture of 
glass1 soap1 bleaching powders1 and     
other commercial products4 ,formerly1   
the supply of soda was very limited     
because man was dependent upon natural  
deposits and upon ashes of sea plants   
for it4 ,common salt1 sodium chloride1  
is abundant1 and in #agge a prize was   
offered to any one who would find a way 
to obtain soda from salt4 ,as a result  
of this1 soda was soon manufactured from
 common salt4 ,in the most recent       
methods of manufacture1 salt1 water1    
ammonia1 and carbon dioxide are made to 
react4 ,baking soda is formed from the  
reaction4 ,the baking soda is then      
heated and decomposed into washing soda 
or the soda of commerce4     ,,chapter  
,,xxi  ,,fermentation   #bac4 ,while    
baking powder is universally used for   

biscuits and cake1 it is seldom1 if     
ever1 used for bread1 because it does   
not furnish sufficient gas to lighten   
the tough heavy mass of bread dough4    
,then1 too1 most people prefer the taste
 of yeast-raised bread4 ,there is a     
reason for this widespread preference1  
but to understand it1 we must go        
somewhat far afield1 and must study not 
only the bread of to-day1 but the bread 
of antiquity1 and the wines as well4    
,if grapes are crushed1 they yield a    
liquid which tastes like the grapes2 but
 if the liquid is allowed to stand in a 
warm place1 it loses its original       
character1 and begins to ferment1       
becoming1 in the course of a few weeks1 
a strongly intoxicating drink4 ,this is 
true not only of grape juice but also of
 the juice of all other sweet fruits2   
apple juice ferments to cider1 currant  
juice to currant wine1 etc4 ,this       
phenomenon of fermentation is known to  
practically all races of men1 and there 
is scarcely a savage tribe without some 

kind of fermented drink2 in the tropics 
the fermented juice of the palm tree    
serves for wine2 in the desert regions1 
the fermented juice of the century      
plant2 and in still other regions1 the  
root of the ginger plant is pressed into
 service4  ,the fermentation which      
occurs in bread making is similar to    
that which is responsible for the       
transformation of plant juices into     
intoxicating drinks4 ,the former process
 is not so old1 however1 since the use  
of alcoholic beverages dates back to the
 very dawn of history1 and the authentic
 record of raised or leavened bread is  
but little more than #cjjj years old4   
#bad4 ,the ,bread of ,antiquity4 ,the   
original method of bread making and the 
method employed by savage tribes of     
to-day is to mix crushed grain and water
 until a paste is formed1 and then to   
bake this over a camp fire4 ,the result 
is a hard compact substance known as    
unleavened bread4 ,a considerable       
improvement over this tasteless mass is 

self-raised bread4 ,if dough is left    
standing in a warm place a number of    
hours1 it swells up with gas and becomes
 porous1 and when baked1 is less compact
 and hard than the savage bread4        
,exposure to air and warmth brings about
 changes in dough as well as in fruit   
juices1 and alters the character of the 
dough and the bread made from it4 ,bread
 made in this way would not seem        
palatable to civilized man of the       
present day1 accustomed1 as he is1 to   
delicious bread made light and porous by
 yeast2 but to the ancients1 the least  
softening and lightening was welcome1   
and self-fermented bread1 therefore1    
supplanted the original unleavened      
bread4  ,soon it was discovered that a  
pinch of this fermented dough acted as a
 starter on a fresh batch of dough4     
,hence1 a little of the fermented dough 
was carefully saved from a batch1 and   
when the next bread was made1 the       
fermented dough1 or leaven1 was worked  
into the fresh dough and served to raise

 the mass more quickly and effectively  
than mere exposure to air and warmth    
could do in the same length of time4    
,this use of leaven for raising bread   
has been practiced for ages4  ,grape    
juice mixed with millet ferments quickly
 and strongly1 and the ,romans learned  
to use this mixture for bread raising1  
kneading a very small amount of it      
through the dough4  #bae4 ,the ,cause of
 ,fermentation4 ,although alcoholic     
fermentation1 and the fermentation which
 goes on in raising dough1 were known   
and utilized for many years1 the cause  
of the phenomenon was a sealed book     
until the nineteenth century4 ,about    
that time it was discovered1 through the
 use of the microscope1 that fermenting 
liquids contain an army of minute plant 
organisms which not only live there1 but
 which actually grow and multiply within
 the liquid4 ,for growth and            
multiplication1 food is necessary1 and  
this the tiny plants get in abundance   
from the fruit juices2 they feed upon   

the sugary matter and as they feed1 they
 ferment it1 changing it into carbon    
dioxide and alcohol4 ,the carbon        
dioxide1 in the form of small bubbles1  
passes off from the fermenting mass1    
while the alcohol remains in the liquid1
 giving the stimulating effect desired  
by imbibers of alcoholic drinks4 ,the   
unknown strange organisms were called   
yeast1 and they were the starting point 
of the yeast cakes and yeast brews      
manufactured to-day on a large scale1   
not only for bread making but for the   
commercial production of beer1 ale1     
porter1 and other intoxicating drinks4  
,the grains1 rye1 corn1 rice1 wheat1    
from which meal is made1 contain only a 
small quantity of sugar1 but1 on the    
other hand1 they contain a large        
quantity of starch which is easily      
convertible into sugar4 ,upon this the  
tiny yeast plants in the dough feed1    
and1 as in the case of the wines1       
ferment the sugar1 producing carbon     
dioxide and alcohol4 ,the dough is thick

 and sticky and the gas bubbles expand  
it into a spongy mass4 ,the tiny yeast  
plants multiply and continue to make    
alcohol and gas1 and in consequence1 the
 dough becomes lighter and lighter4     
,when it has risen sufficiently1 it is  
kneaded and placed in an oven2 the heat 
of the oven soon kills the yeast plants 
and drives the alcohol out of the bread2
 at the same time it expands the        
imprisoned gas bubbles and causes them  
to lighten and swell the bread still    
more4 ,meanwhile1 the dough has become  
stiff enough to support itself4 ,the    
result of the fermentation is a light1  
spongy loaf4  #baf4 ,where does ,yeast  
come ,from8 ,the microscopic plants     
which we call yeast are widely          
distributed in the air1 and float around
 there until chance brings them in      
contact with a substance favorable to   
their growth1 such as fruit juices and  
moist warm batter4 ,under the favorable 
conditions of abundant moisture1 heat1  
and food1 they grow and multiply        

rapidly1 and cause the phenomenon of    
fermentation4 ,wild yeast settles on the
 skin of grapes and apples1 but since it
 does not have access to the fruit      
juices within1 it remains inactive very 
much as a seed does before it is        
planted4 ,but when the fruit is crushed1
 the yeast plants get into the juice1   
and feeding on it1 grow and multiply4   
,the stray yeast plants which get into  
the sirup are relatively few1 and hence 
fermentation is slow2 it requires       
several weeks for currant wine to       
ferment1 and several months for the     
juice of grapes to be converted into    
wine4  ,stray yeast finds a favorable   
soil for growth in the warmth and       
moisture of a batter2 but although the  
number of these stray plants is very    
large1 it is insufficient to cause rapid
 fermentation1 and if we depended upon  
wild yeast for bread raising1 the result
 would not be to our liking4  ,when our 
remote ancestors saved a pinch of dough 
as leaven for the next baking1 they were

 actually cultivating yeast1 although   
they did not know it4 ,the reserved     
portion served as a favorable breeding  
place to the yeast plants within it2    
they grew and reproduced amazingly1 and 
became so numerous1 that the small mass 
of old dough in which they were gathered
 served to leaven the entire batch at   
the next baking4  ,as soon as man       
learned that yeast plants caused        
fermentation in liquors and bread1 he   
realized that it would be to his        
advantage to cultivate yeast and to add 
it to bread and to plant juices rather  
than to depend upon accidental and slow 
fermentation from wild yeast4 ,shortly  
after the discovery of yeast in the     
nineteenth century1 man commenced his   
attempt to cultivate the tiny organisms4
 ,their microscopic size added greatly  
to his trouble1 and it was only after   
years of careful and tedious            
investigation that he was able to       
perfect the commercial yeast cakes and  
yeast brews universally used by bakers  

and brewers4 ,the well-known compressed 
yeast cake is simply a mass of live and 
vigorous yeast plants1 embedded in a    
soft1 soggy material1 and ready to grow 
and multiply as soon as they are placed 
under proper conditions of heat1        
moisture1 and food4 ,seeds which remain 
on our shelves do not germinate1 but    
those which are planted in the soil do2 
so it is with the yeast plants4 ,while  
in the cake they are as lifeless as the 
seed2 when placed in dough1 or fruit    
juice1 or grain water1 they grow and    
multiply and cause fermentation4        
,,chapter ,,xxii  ,,bleaching   #bag4   
,the beauty and the commercial value of 
uncolored fabrics depend upon the purity
 and perfection of their whiteness2 a   
man's white collar and a woman's white  
waist must be pure white1 without the   
slightest tinge of color4 ,but all      
natural fabrics1 whether they come from 
plants1 like cotton and linen1 or from  
animals1 like wool and silk1 contain    
more or less coloring matter1 which     

impairs the whiteness4 ,this coloring   
not only detracts from the appearance of
 fabrics which are to be worn uncolored1
 but it seriously interferes with the   
action of dyes1 and at times plays the  
dyer strange tricks4  ,natural fibers1  
moreover1 are difficult to spin and     
weave unless some softening material    
such as wax or resin is rubbed lightly  
over them4 ,the matter added to         
facilitate spinning and weaving         
generally detracts from the appearance  
of the uncolored fabric1 and also       
interferes with successful dyeing4 ,thus
 it is easy to see that the natural     
coloring matter and the added foreign   
matter must be entirely removed from    
fabrics destined for commercial use4    
,exceptions to this general fact are    
sometimes made1 because unbleached      
material is cheaper and more durable    
than the bleached product1 and for some 
purposes is entirely satisfactory2      
unbleached cheesecloth and sheeting are 
frequently purchased in place of the    

more expensive bleached material4       
,formerly1 the only bleaching agent     
known was the sun's rays1 and linen and 
cotton were put out to sun for a week2  
that is1 the unbleached fabrics were    
spread on the grass and exposed to the  
bleaching action of sun and dew4        
,illustration3 ,,fig4 #aeh4--,preparing 
chlorine from hydrochloric acid and     
manganese dioxide4  #bah4 ,an           
,artificial ,bleaching ,agent4 ,while   
the sun's rays are effective as a       
bleaching agent1 the process is slow2   
moreover1 it would be impossible to     
expose to the sun's rays the vast       
quantity of fabrics used in the         
civilized world of to-day1 and the huge 
and numerous bolts of material which    
daily come from our looms and factories 
must therefore be whitened by artificial
 means4 ,the substance almost           
universally used as a rapid artificial  
bleaching agent is chlorine1 best known 
to us as a constituent of common salt4  
,chlorine is never free in nature1 but  

is found in combination with other      
substances1 as1 for example1 in         
combination with sodium in salt1 or with
 hydrogen in hydrochloric acid4  ,the   
best laboratory method of securing free 
chlorine is to heat in a water bath a   
mixture of hydrochloric acid and        
manganese dioxide1 a compound containing
 one part of manganese and two parts of 
oxygen4 ,the heat causes the manganese  
dioxide to give up its oxygen1 which    
immediately combines with the hydrogen  
of the hydrochloric acid and forms      
water4 ,the manganese itself combines   
with part of the chlorine originally in 
the acid1 but not with all4 ,there is   
thus some free chlorine left over from  
the acid1 and this passes off as a gas  
and can be collected1 as in ,figure     
#aeh4 ,free chlorine is heavier than    
air1 and hence when it leaves the exit  
tube it settles at the bottom of the    
jar1 displacing the air1 and finally    
filling the bottle4  ,chlorine is a very
 active substance and combines readily  

with most substances1 but especially    
with hydrogen2 if chlorine comes in     
contact with steam1 it abstracts the    
hydrogen and unites with it to form     
hydrochloric acid1 but it leaves the    
oxygen free and uncombined4 ,this       
tendency of chlorine to combine with    
hydrogen makes it valuable as a         
bleaching agent4 ,in order to test the  
efficiency of chlorine as a bleaching   
agent1 drop a wet piece of colored      
gingham or calico into the bottle of    
chlorine1 and notice the rapid          
disappearance of color from the sample4 
,if unbleached muslin is used1 the moist
 strip loses its natural yellowish hue  
and becomes a clear1 pure white4 ,the   
explanation of the bleaching power of   
chlorine is that the chlorine combines  
with the hydrogen of the water and sets 
oxygen free2 the uncombined free oxygen 
oxidizes the coloring matter in the     
cloth and destroys it4  ,chlorine has no
 effect on dry material1 as may be seen 
if we put dry gingham into the jar2 in  

this case there is no water to furnish  
hydrogen for combination with the       
chlorine1 and no oxygen to be set free4 
#bai4 ,bleaching ,powder4 ,chlorine gas 
has a very injurious effect on the human
 body1 and hence cannot be used directly
 as a bleaching agent4 ,it attacks the  
mucous membrane of the nose and lungs1  
and produces the effect of a severe cold
 or catarrh1 and when inhaled1 causes   
death4 ,but certain compounds of        
chlorine are harmless1 and can be used  
instead of chlorine for destroying      
either natural or artificial dyes4 ,one 
of these compounds1 namely1 chloride of 
lime1 is the almost universal bleaching 
agent of commerce4 ,it comes in the form
 of powder1 which can be dissolved in   
water to form the bleaching solution in 
which the colored fabrics are immersed4 
,but fabrics immersed in a bleaching    
powder solution do not lose their color 
as would naturally be expected4 ,the    
reason for this is that the chlorine gas
 is not free to do its work1 but is     

restricted by its combination with the  
other substances4 ,by experiment it has 
been found that the addition to the     
bleaching solution of an acid1 such as  
vinegar or lemon juice or sulphuric     
acid1 causes the liberation of the      
chlorine4 ,the chlorine thus set free   
reacts with the water and liberates     
oxygen2 this in turn destroys the       
coloring matter in the fibers1 and      
transforms the material into a bleached 
product4  ,the acid used to liberate the
 chlorine from the bleaching powder1 and
 the chlorine also1 rot materials with  
which they remain in contact for any    
length of time4 ,for this reason1       
fabrics should be removed from the      
bleaching solution as soon as possible1 
and should then be rinsed in some       
solution1 such as ammonia1 which is     
capable of neutralizing the harmful     
substances2 finally the fabric should be
 thoroughly rinsed in water in order    
that all foreign matter may be removed4 
,the reason home bleaching is so seldom 

satisfactory is that most amateurs fail 
to realize the necessity of immediate   
neutralization and rinsing1 and allow   
the fabric to remain too long in the    
bleaching solution1 and allow it to dry 
with traces of the bleaching substances 
present in the fibers4 ,material treated
 in this way is thoroughly bleached1 but
 is at the same time rotten and         
worthless4 ,chloride of lime is         
frequently used in laundry work2 the    
clothes are whiter than when cleaned    
with soap and simple washing powders1   
but they soon wear out unless the       
precaution has been taken to add an     
antichlor or neutralizer to the         
bleaching solution4  #bbj4 ,commercial  
,bleaching4 ,in commercial bleaching the
 material to be bleached is first       
moistened with a very weak solution of  
sulphuric acid or hydrochloric acid1 and
 is then immersed in the bleaching      
powder solution4 ,as the moist material 
is drawn through the bleaching solution1
 the acid on the fabric acts upon the   

solution and releases chlorine4 ,the    
chlorine liberates oxygen from the      
water4 ,the oxygen in turn attacks the  
coloring matter and destroys it4        
,illustration3 ,,fig4 #aei4--,the       
material to be bleached is drawn through
 an acid a1 then through a bleaching    
solution b1 and finally through a       
neutralizing solution c4  ,the bleached 
material is then immersed in a          
neutralizing bath and is finally rinsed 
thoroughly in water4 ,strips of cotton  
or linen many miles long are drawn by   
machinery into and out of the various   
solutions 7,fig4 #aei71 are then passed 
over pressing rollers1 and emerge snow  
white1 ready to be dyed or to be used as
 white fabric4  #bba4 ,wool and ,silk   
,bleaching4 ,animal fibers like silk1   
wool1 and feathers1 and some vegetable  
fibers like straw1 cannot be bleached by
 means of chlorine1 because it attacks  
not only the coloring matter but the    
fiber itself1 and leaves it shrunken and
 inferior4 ,cotton and linen fibers1    

apart from the small amount of coloring 
matter present in them1 contain nothing 
but carbon1 oxygen1 and hydrogen1 while 
animal fibers contain in addition to    
these elements some compounds of        
nitrogen4 ,the presence of these        
nitrogen compounds influences the action
 of the chlorine and produces           
unsatisfactory results4 ,for animal     
fibers it is therefore necessary to     
discard chlorine as a bleaching agent1  
and to substitute a substance which will
 have a less disastrous action upon the 
fibers4 ,such a substance is to be had  
in sulphurous acid4 ,when sulphur burns1
 as in a match1 it gives off            
disagreeable fumes1 and if these are    
made to bubble into a vessel containing 
water1 they dissolve and form with the  
water a substance known as sulphurous   
acid4 ,that this solution has bleaching 
properties is shown by the fact that a  
colored cloth dipped into it loses its  
color1 and unbleached fabrics immersed  
in it are whitened4 ,the harmless nature

 of sulphurous acid makes it very       
desirable as a bleaching agent1         
especially in the home4  ,silk1 lace1   
and wool when bleached with chlorine    
become hard and brittle1 but when       
whitened with sulphurous acid1 they     
retain their natural characteristics4   
,this mild form of a bleaching substance
 has been put to uses which are now     
prohibited by the pure food laws4 ,in   
some canneries common corn is whitened  
with sulphurous acid1 and is then sold  
under false representations4 ,cherries  
are sometimes bleached and then colored 
with the bright shades which under      
natural conditions indicate freshness4  
,bleaching with chlorine is permanent1  
the dyestuff being destroyed by the     
chlorine2 but bleaching with sulphurous 
acid is temporary1 because the milder   
bleach does not actually destroy the    
dyestuff1 but merely modifies it1 and in
 time the natural yellow color of straw1
 cotton1 and linen reappears4 ,the      
yellowing of straw hats during the      

summer is familiar to everyone2 the     
straw is merely resuming its natural    
color which had been modified by the    
sulphurous acid solution applied to the 
straw when woven4  #bbb4 ,why the ,color
 ,returns4 ,some of the compounds formed
 by the sulphurous acid bleaching       
process are gradually decomposed by     
sunlight1 and in consequence the        
original color is in time partially     
restored4 ,the portion of a hat         
protected by the band retains its fresh 
appearance because the light has not had
 access to it4 ,silks and other fine    
fabrics bleached in this way fade with  
age1 and assume an unnatural color4 ,one
 reason for this is that the dye used to
 color the fabric requires a clear white
 background1 and loses its              
characteristic hues when its foundation 
is yellow instead of white4 ,then1 too1 
dyestuffs are themselves more or less   
affected by light1 and fade slowly under
 a strong illumination4  ,materials     
which are not exposed directly to an    

intense and prolonged illumination      
retain their whiteness for a long time1 
and hence dress materials and hats which
 have been bleached with sulphurous acid
 should be protected from the sun's     
glare when not in use4  #bbc4 ,the      
,removal of ,stains4 ,bleaching powder  
is very useful in the removal of stains 
from white fabrics4 ,ink spots rubbed   
with lemon juice and dipped in bleaching
 solution fade away and leave on the    
cloth no trace of discoloration4        
,sometimes these stains can be removed  
by soaking in milk1 and where this is   
possible1 it is the better method4      
,bleaching solution1 however1 while     
valuable in the removal of some stains1 
is unable to remove paint stains1       
because paints owe their color to       
mineral matter1 and on this chlorine is 
powerless to act4 ,paint stains are best
 removed by the application of gasoline 
followed by soap and water4             
,,chapter ,,xxiii  ,,dyeing   #bbd4     
,dyes4 ,one of the most important and   

lucrative industrial processes of the   
world to-day is that of staining and    
dyeing4 ,whether we consider the        
innumerable shades of leather used in   
shoes and harnesses and upholstery2 the 
multitude of colors in the paper which  
covers our walls and reflects light     
ranging from the somber to the gay1 and 
from the delicate to the gorgeous2 the  
artificial scenery which adorns the     
stage and by its imitation of trees and 
flowers and sky translates us to the    
,forest of ,arden2 or whether we        
consider the uncounted varieties of     
color in dress materials1 in carpets1   
and in hangings1 we are dealing with    
substances which owe their beauty to    
dyes and dyestuffs4  ,the coloring of   
textile fabrics1 such as cotton1 wool1  
and silk1 far outranks in amount and    
importance that of leather1 paper1 etc41
 and hence the former only will be      
considered here2 but the theories and   
facts relative to textile dyeing are    
applicable in a general way to all other

 forms as well4  #bbe4 ,plants as a     
,source of ,dyes4 ,among the most       
beautiful examples of man's handiwork   
are the baskets and blankets of the     
,north ,american ,indians1 woven with a 
skill which cannot be equaled by        
manufacturers1 and dyed in mellow colors
 with a few simple dyes extracted from  
local plants4 ,the magnificent rugs and 
tapestries of ,persia and ,turkey1 and  
the silks of ,india and ,japan1 give    
evidence that a knowledge of dyes is    
widespread and ancient4 ,until recently1
 the vegetable world was the source of  
practically all coloring matter1 the    
pulverized root of the madder plant     
yielding the reds1 the leaves and stems 
of the indigo plant the blues1 the      
heartwood of the tropical logwood tree  
the blacks and grays1 and the fruit of  
certain palm and locust trees yielding  
the soft browns4 ,so great was the      
commercial demand for dyestuffs that    
large areas of land were given over to  
the exclusive cultivation of the more   

important dye plants4 ,vegetable dyes   
are now1 however1 rarely used because   
about the year #ahef it was discovered  
that dyes could be obtained from coal   
tar1 the thick sticky liquid formed as a
 by-product in the manufacture of coal  
gas4 ,these artificial coal-tar1 or     
aniline1 dyes have practically          
undisputed sway to-day1 and the vast    
areas of land formerly used for the     
cultivation of vegetable dyes are now   
free for other purposes4  #bbf4 ,wool   
and ,cotton ,dyeing4 ,if a piece of wool
 is soaked in a solution of a coal-tar  
dye1 such as magenta1 the fiber of the  
cloth draws some of the dye out of the  
solution and absorbs it1 becoming in    
consequence beautifully colored4 ,the   
coloring matter becomes part and parcel1
 as it were1 of the wool fiber1 because 
repeated washing of the fabric fails to 
remove the newly acquired color2 the    
magenta coloring matter unites          
chemically with the fiber of the wool1  
and forms with it a compound insoluble  

in water1 and hence fast to washing4    
,but if cotton is used instead of wool1 
the acquired color is very faint1 and   
washes off readily4 ,this is because    
cotton fibers possess no chemical       
substance capable of uniting with the   
coloring matter to form a compound      
insoluble in water4  ,if magenta is     
replaced by other artificial dyes1--for 
example1 scarlets1--the result is       
similar2 in general1 wool material      
absorbs dye readily1 and uniting with it
 is permanently dyed4 ,cotton material1 
on the other hand1 does not combine     
chemically with coloring matter and     
therefore is only faintly tinged with   
color1 and loses this when washed4 ,when
 silk and linen are tested1 it is found 
that the former behaves in a general way
 as did wool1 while the linen has more  
similarity to the cotton4 ,that         
vegetable fibers1 such as cotton and    
linen1 should act differently toward    
coloring matter from animal fibers1 such
 as silk and wool1 is not surprising    

when we consider that the chemical      
nature of the two groups is very        
different2 vegetable fibers contain only
 oxygen1 carbon1 and hydrogen1 while    
animal fibers always contain nitrogen in
 addition1 and in many cases sulphur as 
well4  #bbg4 ,the ,selection of ,dyes4  
,when silk and wool1 cotton and linen1  
are tested in various dye solutions1 it 
is found that the former have1 in       
general1 a great affinity for coloring  
matter and acquire a permanent color1   
but that cotton and linen1 on the other 
hand1 have little affinity for          
dyestuffs4 ,the color acquired by       
vegetable fibers is1 therefore1 usually 
faint4  ,there are1 of course1 many     
exceptions to the general statement that
 animal fibers dye readily and vegetable
 fibers poorly1 because certain dyes    
fail utterly with woolen and silk       
material and yet are fairly satisfactory
 when applied to cotton and linen       
fabrics4 ,then1 too1 a dye which will   
color silk may not have any effect on   

wool in spite of the fact that wool1    
like silk1 is an animal fiber2 and      
certain dyestuffs to which cotton       
responds most beautifully are absolutely
 without effect on linen4  ,the nature  
of the material to be dyed determines   
the coloring matter to be used2 in      
dyeing establishments a careful         
examination is made of all textiles     
received for dyeing1 and the particular 
dyestuffs are then applied which long   
experience has shown to be best suited  
to the material in question4 ,where     
mixed goods1 such as silk and wool1 or  
cotton and wool1 are concerned1 the     
problem is a difficult one1 and the     
countless varieties of gorgeously       
colored mixed materials give evidence of
 high perfection in the art of dyeing   
and weaving4  ,housewives who wish to do
 successful home dyeing should therefore
 not purchase dyes indiscriminately1 but
 should select the kind best suited to  
the material1 because the coloring      
principle which will remake a silk waist

 may utterly ruin a woolen skirt or a   
linen suit4 ,powders designed for       
special purposes may be purchased from  
druggists4  #bbh4 ,indirect ,dyeing4 ,we
 have seen that it is practically       
impossible to color cotton and linen in 
a simple manner with any degree of      
permanency1 because of the lack of      
chemical action between vegetable fibers
 and coloring matter4 ,but the varied   
uses to which dyed articles are put make
 fastness of color absolutely necessary4
 ,a shirt1 for example1 must not be     
discolored by perspiration1 nor a waist 
faded by washing1 nor a carpet dulled by
 sweeping with a dampened broom4 ,in    
order to insure permanency of dyes1 an  
indirect method was originated which    
consisted of adding to the fibers a     
chemical capable of acting upon the dye 
and forming with it a colored compound  
insoluble in water1 and hence safe4 ,for
 example1 cotton material dyed directly 
in logwood solution has almost no value1
 but if it is soaked in a solution of   

oxalic acid and alum until it becomes   
saturated with the chemicals1 and is    
then transferred to a logwood bath1 the 
color acquired is fast and beautiful4   
,this method of indirect dyeing is known
 as the mordanting process2 it consists 
of saturating the fabric to be dyed with
 chemicals which will unite with the    
coloring matter to form compounds       
unaffected by water4 ,the chemicals are 
called mordants4  #bbi4 ,how ,variety of
 ,color is ,secured4 ,the color which is
 fixed on the fabric as a result of     
chemical action between mordant and dye 
is frequently very different from that  
of the dye itself4 ,logwood dye when    
used alone produces a reddish brown     
color of no value either for beauty or  
permanence2 but if the fabric to be dyed
 is first mordanted with a solution of  
alum and oxalic acid and is then        
immersed in a logwood bath1 it acquires 
a beautiful blue color4  ,moreover1     
since the color acquired depends upon   
the mordant as well as upon the dye1 it 

is often possible to obtain a wide range
 of colors by varying the mordant used1 
the dye remaining the same4 ,for        
example1 with alum and oxalic acid as a 
mordant and logwood as a dye1 blue is   
obtained2 but with a mordant of ferric  
sulphate and a dye of logwood1 blacks   
and grays result4 ,fabrics immersed     
directly in alizarin acquire a reddish  
yellow tint2 when1 however1 they are    
mordanted with certain aluminium        
compounds they acquire a brilliant      
,turkey red1 when mordanted with        
chromium compounds1 a maroon1 and when  
mordanted with iron compounds1 the      
various shades of purple1 lilac1 and    
violet result4  #bcj4 ,color ,designs in
 ,cloth4 ,it is thought that the        
earliest attempts at making fancy       
materials consisted in painting designs 
on a fabric by means of a brush4 ,in    
more recent times the design was cut in 
relief on hard wood1 the relief being   
then daubed with coloring matter and    
applied by hand to successive portions  

of the cloth4 ,the most modern method of
 design-making is that of machine or    
roller printing4 ,in this1 the relief   
blocks are replaced by engraved copper  
rolls which rotate continuously and in  
the course of their rotation            
automatically receive coloring matter on
 the engraved portion4 ,the cloth is to 
be printed is then drawn uniformly over 
the rotating roll1 receiving color from 
the engraved design2 in this way1 the   
color pattern is automatically printed  
on the cloth with perfect regularity4   
,in cases where the fabrics do not unite
 directly with the coloring matter1 the 
design is supplied with a mordant and   
the impression made on the fabric is    
that of the mordant2 when the fabric is 
later transferred to a dye bath1 the    
mordanted portions1 represented by the  
design1 unite with the coloring matter  
and thus form the desired color         
patterns4  ,unless the printing is well 
done1 the coloring matter does not      
thoroughly penetrate the material1 and  

only a faint blurred design appears on  
the back of the cloth2 the gaudy designs
 of cheap calicoes and ginghams often do
 not show at all on the under side4     
,such carelessly made prints are not    
fast to washing or light1 and soon fade4
 ,but in the better grades of material  
the printing is well done1 and the color
 designs are fairly fast1 and a little  
care in the laundry suffices to         
eliminate any danger of fading4  ,color 
designs of the greatest durability are  
produced by the weaving together of     
colored yarns4 ,when yarn is dyed1 the  
coloring matter penetrates to every part
 of the fiber1 and hence the patterns   
formed by the weaving together of       
well-dyed yarns are very fast to light  
and water4  ,if the color designs to be 
woven in the cloth are intricate1       
complex machinery is necessary and      
skillful handwork2 hence1 patterns      
formed by the weaving of colored yarns  
are expensive and less common than      
printed fabrics4     ,,chapter ,,xxiv   

,,chemicals ,,as ,,disinfectants ,,and  
,,preservatives   #bca4 ,the prevention 
of disease epidemics is one of the most 
striking achievements of modern science4
 ,food1 clothing1 furniture1 and other  
objects contaminated in any way by      
disease germs may be disinfected by     
chemicals or by heat1 and widespread    
infection from persons suffering with a 
contagious disease may be prevented4    
,illustration3 ,,fig4                   
#afj4--,pasteurizing apparatus1 an      
arrangement by which milk is            
conveniently heated to destroy disease  
germs4  ,when disease germs are within  
the body1 the problem is far from       
simple1 because chemicals which would   
effectively destroy the germs would be  
fatal to life itself4 ,but when germs   
are outside the body1 as in water or    
milk1 or on clothing1 dishes1 or        
furniture1 they can be easily killed4   
,one of the best methods of destroying  
germs is to subject them to intense     
heat4 ,contaminated water is made safe  

by boiling for a few minutes1 because   
the strong heat destroys the            
disease-producing germs4 ,scalded or    
,pasteurized milk saves the lives of    
scores of babies1 because the germs of  
summer complaint which lurk in poor milk
 are killed and rendered harmless in the
 process of scalding4 ,dishes used by   
consumptives1 and persons suffering from
 contagious diseases1 can be made       
harmless by thorough washing in thick   
suds of almost boiling water4  ,the     
bedding and clothing of persons         
suffering with diphtheria1 tuberculosis1
 and other germ diseases should always  
be boiled and hung to dry in the bright 
sunlight4 ,heat and sunshine are two of 
the best disinfectants4  #bcb4          
,chemicals4 ,objects1 such as furniture1
 which cannot be boiled1 are disinfected
 by the use of any one of several       
chemicals1 such as sulphur1 carbolic    
acid1 chloride of lime1 corrosive       
sublimate1 etc4  ,one of the simplest   
methods of disinfecting consists in     

burning sulphur in a room whose doors1  
windows1 and keyholes have been closed1 
so that the burning fumes cannot escape1
 but remain in the room long enough to  
destroy disease germs4 ,this is probably
 the most common means of fumigation4   
,for general purposes1 carbolic acid is 
one of the very best disinfectants1 but 
must be used with caution1 as it is a   
deadly poison except when very dilute4  
,chloride of lime when exposed to the   
air and moisture slowly gives off       
chlorine1 and can be used as a          
disinfectant because the gas thus set   
free attacks germs and destroys them4   
,for this reason chloride of lime is an 
excellent disinfectant of drainpipes4   
,certain bowel troubles1 such as        
diarrhoea1 are due to microbes1 and if  
the waste matter of a person suffering  
from this or similar diseases is allowed
 passage through the drainage system1   
much damage may be done4 ,but a small   
amount of chloride of lime in the closet
 bowl will insure disinfection4  #bcc4  

,personal ,disinfection4 ,the hands may 
gather germs from any substances or     
objects with which they come in contact2
 hence the hands should be washed with  
soap and water1 and especially before   
eating4 ,physicians who perform         
operations wash not only their hands1   
but their instruments1 sterilizing the  
latter by placing them in boiling water 
for several minutes4  ,cuts and wounds  
allow easy access to the body2 a small  
cut has been known to cause death       
because of the bacteria which found     
their way into the open wound and       
produced disease4 ,in order to destroy  
any germs which may have entered into   
the cut from the instrument1 it is well 
to wash out the wound with some mild    
disinfectant1 such as very dilute       
carbolic acid or hydrogen peroxide1 and 
then to bind the wound with a clean     
cloth1 to prevent later entrance of     
germs4  #bcd4 ,chemicals as ,food       
,preservatives4 ,the spoiling of meats  
and soups1 and the souring of milk and  

preserves1 are due to germs which1 like 
those producing disease1 can be         
destroyed by heat and by chemicals4     
,milk heated to the boiling point does  
not sour readily1 and successful canning
 consists in cooking fruits and         
vegetables until all the germs are      
killed1 and then sealing the cans so    
that germs from outside cannot find     
entrance and undo the work of the       
canner4  ,some dealers and manufacturers
 have learned that certain chemicals    
will act as food preservatives1 and     
hence they have replaced the safe method
 of careful canning by the quicker and  
simpler plan of adding chemicals to     
food4 ,catchup1 sauces1 and jellies are 
now frequently preserved in this way4   
,but the chemicals which destroy        
bacteria frequently injure the consumer 
as well4 ,and so much harm has been done
 by food preservatives that the pure    
food laws require that cans and bottles 
contain a labeled statement of the kind 
and quantity of chemicals used4  ,even  

milk is not exempt1 but is doctored to  
prevent souring1 the preservative most  
generally used by milk dealers being    
formaldehyde4 ,the vast quantity of milk
 consumed by young and old1 sick and    
well1 makes the use of formaldehyde a   
serious menace to health1 because no    
constitution can endure the injury done 
by the constant use of preservatives4   
,the most popular and widely used       
preservatives of meats are borax and    
boric acid4 ,these chemicals not only   
arrest decay1 but partially restore to  
old and bad meat the appearance of      
freshness2 in this way unscrupulous     
dealers are able to sell to the public  
in one form or other meats which may    
have undergone partial decomposition2   
sausage frequently contains partially   
decomposed meat1 restored as it were by 
chemicals4  ,in jams and catchups there 
is abundant opportunity for             
preservatives2 badly or partially       
decayed fruits are sometimes disinfected
 and used as the basis of foods sold by 

so-called good dealers4 ,benzoate of    
soda1 and salicylic acid are the        
chemicals most widely employed for this 
purpose1 with coal-tar dyes to simulate 
the natural color of the fruit4  ,many  
of the cheap candies sold by street     
venders are not fit for consumption1    
since they are not only made of bad     
material1 but are frequently in addition
 given a light dipping in varnish as a  
protection against the decaying         
influences of the atmosphere4  ,the only
 wise preservatives are those long known
 and employed by our ancestors2 salt1   
vinegar1 and spices are all food        
preservatives1 but they are at the same 
time substances which in small amounts  
are not injurious to the body4 ,smoked  
herring and salted mackerel are         
chemically preserved foods1 but they are
 none the less safe and digestible4     
#bce4 ,the ,preservation of ,wood and   
,metal4 ,the decaying of wood and the   
rusting of metal are due to the action  
of air and moisture4 ,when wood and     

metal are surrounded with a covering    
which neither air nor moisture can      
penetrate1 decay and rust are prevented4
 ,paint affords such a protective       
covering4 ,the main constituent of paint
 is a compound of white lead or other   
metallic substance2 this is mixed with  
linseed oil or its equivalent in order  
that it may be spread over wood and     
metal in a thin1 even coating4 ,after   
the mixture has been applied1 it hardens
 and forms a tough skin fairly          
impervious to weathering4 ,for the sake 
of ornamentation1 various colored       
pigments are added to the paint and give
 variety of effect4  ,railroad ties and 
street paving blocks are ordinarily     
protected by oil rather than paint4     
,wood is soaked in creosote oil until it
 becomes thoroughly saturated with the  
oily substance4 ,the pores of the wood  
are thus closed to the entrance of air  
and moisture1 and decay is avoided4     
,wood treated in this way is very       
durable4 ,creosote is poisonous to      

insects and many small animals1 and thus
 acts as a preservation not only against
 the elements but against animal life as
 well4     ,,chapter ,,xxv  ,,drugs     
,,and ,,patent ,,medicines   #bcf4      
,stimulants and ,narcotics4 ,man has    
learned not only the action of          
substances upon each other1 such as     
bleaching solution upon coloring matter1
 washing soda upon grease1 acids upon   
bases1 but also the effect which certain
 chemicals have upon the human body4    
,drugs and their varying effects upon   
the human system have been known to     
mankind from remote ages2 in the early  
days1 familiar leaves1 roots1 and twigs 
were steeped in water to form medicines 
which served for the treatment of all   
ailments4 ,in more recent times1        
however1 these simple herb teas have    
been supplanted by complex drugs1 and   
now medicines are compounded not only   
from innumerable plant products1 but    
from animal and mineral matter as well4 
,quinine1 rhubarb1 and arnica are       

examples of purely vegetable products2  
iron1 mercury1 and arsenic are equally  
well known as distinctly mineral        
products1 while cod-liver oil is the    
most familiar illustration of an animal 
remedy4 ,ordinarily a combination of    
products best serves the ends of the    
physician4  ,substances which1 like     
cod-liver oil1 serve as food to a       
worn-out body1 or1 like iron1 tend to   
enrich the blood1 or1 like quinine1 aid 
in bringing an abnormal system to a     
healthy condition1 are valuable servants
 and cannot be entirely dispensed with  
so long as man is subject to disease4   
,but substances which1 like opium1      
laudanum1 and alcohol1 are not required 
by the body as food1 or as a systematic1
 intelligent aid to recovery1 but are   
taken solely for the stimulus aroused or
 for the insensibility induced1 are     
harmful to man1 and cannot be indulged  
in by him without ultimate mental1      
moral1 and physical loss4 ,substances of
 the latter class are known as narcotics

 and stimulants4  #bcg4 ,the ,cost of   
,health4 ,in the physical as in the     
financial world1 nothing is to be had   
without a price4 ,vigor1 endurance1 and 
mental alertness are bought by hygienic 
living2 that is1 by proper food1 fresh  
air1 exercise1 cleanliness1 and         
reasonable hours4 ,some people wish     
vigor1 endurance1 etc41 but are         
unwilling to live the life which will   
develop these qualities4 ,plenty of     
sleep1 exercise1 and simple food all    
tend to lay the foundations of health4  
,many1 however1 are not willing to take 
the care necessary for healthful living1
 because it would force them to         
sacrifice some of the hours of pleasure4
 ,sooner or later1 these                
pleasure-seekers begin to feel tired and
 worn1 and some of them turn to drugs   
and narcotics for artificial strength4  
,at first the drugs seem to restore the 
lost energy1 and without harm2 however1 
the cost soon proves to be one of the   
highest ,nature ever demands4  #bch4    

,the ,uncounted ,cost4 ,the first and   
most obvious effect of opium1 for       
example1 is to deaden pain and to arouse
 pleasure2 but while the drug is        
producing these soothing sensations1 it 
interferes with bodily functions4       
,secretion1 digestion1 absorption of    
food1 and the removal of waste matters  
are hindered4 ,continued use of the drug
 leads to headache1 exhaustion1 nervous 
depression1 and heart weakness4 ,there  
is thus a heavy toll reckoned against   
the user1 and the creditor is relentless
 in demanding payment4  ,moreover1 the  
respite allowed by a narcotic is        
exceedingly brief1 and a depression     
which is long and deep inevitably       
follows4 ,in order to overcome this     
depression1 recourse is usually had to a
 further dose1 and as time goes on1 the 
intervals of depression become more     
frequent and lasting1 and the necessity 
to overcome them increases4 ,thus       
without intention one finds one's self  
bound to the drug1 its fast victim4 ,the

 sanatoria of our country are crowded   
with people who are trying to free      
themselves of a drug habit into which   
they have drifted unintentionally if not
 altogether unknowingly4 ,what is true  
of opium is equally applicable to other 
narcotics4  #bci4 ,the ,right ,use of   
,narcotics4 ,in the hands of the        
physician1 narcotics are a great        
blessing4 ,in some cases1 by relieving  
pain1 they give the system the rest     
necessary for overcoming the cause of   
the pain4 ,only those who know of the   
suffering endured in former times can   
fully appreciate the decrease in pain   
brought about by the proper use of      
narcotics4  #bdj4 ,patent ,medicines1   
,cough ,sirups4 ,a reputable physician  
is solicitous regarding the permanent   
welfare of his patient and administers  
carefully chosen and harmless drugs4    
,mere medicine venders1 however1 ignore 
the good of mankind1 and flood the      
market with cheap patent preparations   
which delude and injure those who       

purchase1 but bring millions of dollars 
to those who manufacture4  ,practically 
all of these patent1 or proprietary1    
preparations contain a large proportion 
of narcotics or stimulants1 and hence   
the benefit which they seem to afford   
the user is by no means genuine2        
examination shows that the relief       
brought by them is due either to a      
temporary deadening of sensibilities by 
narcotics or to a fleeting stimulation  
by alcohol and kindred substances4      
,among the most common ailments of both 
young and old are coughs and colds2     
hence many patent cough mixtures have   
been manufactured and placed on the     
market for the consumption of a         
credulous public4 ,such quick cures     
almost invariably contain one or more   
narcotic drugs1 and not only do not     
relieve the cold permanently1 but       
occasion subsequent disorders4 ,even    
lozenges and pastilles are not free from
 fraud1 but have a goodly proportion of 
narcotics1 containing in some cases     

chloroform1 morphine1 and ether4  ,the  
widespread use of patent cough medicines
 is due largely to the fact that many   
persons avoid consulting a physician    
about so trivial an ailment as an       
ordinary cold1 or are reluctant to pay a
 medical fee for what seems a slight    
indisposition and hence attempt to      
doctor themselves4  ,catarrh is a very  
prevalent disease in ,america1 and      
consequently numerous catarrh remedies  
have been devised1 most of which contain
 in a disguised form the pernicious     
drug1 cocaine4 ,laws have been enacted  
which require on the labels a           
declaration of the contents of the      
preparation1 both as to the kind of drug
 used and the amount1 and the choice of 
accepting or refusing such mixtures is  
left to the individual4 ,but the great  
mass of people are ignorant of the      
harmful nature of drugs in general1 and 
hence do not even read the self-accusing
 label1 or if they do glance at it1 fail
 to comprehend the dangerous nature of  

the drugs specified there4 ,in order to 
safeguard the uninformed purchaser and  
to restrict the manufacture of harmful  
patent remedies1 some states limit the  
sale of all preparations containing     
narcotics and thus give free rein to    
neither consumer nor producer4  #bda4   
,soothing ,sirups2 ,soft ,drinks4 ,the  
development of a race is limited by the 
mental and physical growth of its       
children1 and yet thousands of its      
children are annually stunted and       
weakened by drugs1 because most colic   
cures1 teething concoctions1 and        
soothing syrups are merely agreeably    
flavored drug mixtures4 ,those who have 
used such preparations freely1 know that
 a child usually becomes fretful and    
irritable between doses1 and can be     
quieted only by larger and more frequent
 supplies4 ,a habit formed in this way  
is difficult to overcome1 and many a    
child when scarcely over its babyhood   
had a craving which in later years may  
lead to systematic drug taking4 ,and    

even though the pernicious drug craving 
is not created1 considerable harm is    
done to the child1 because its body is  
left weak and non-resistant to diseases 
of infancy and childhood4  ,many of our 
soft drinks contain narcotics4 ,the use 
of the coca leaf and the kola nut for   
such preparations has increased very    
greatly within the last few years1 and  
doubtless legislation will soon be      
instituted against the indiscriminate   
sale of soft drinks4  #bdb4 ,headache   
,powders4 ,the stress and strain of     
modern life has opened wide the door to 
a multitude of bodily ills1 among which 
may be mentioned headache4 ,work must be
 done and business attended to1 and the 
average sufferer does not take time from
 his vocation to investigate the cause  
of the headache1 but unthinkingly grasps
 at any remedy which will remove the    
immediate pain1 and utterly disregards  
later injury4 ,the relief afforded by   
most headache mixtures is due to the    
presence of antipyrin or acetanilid1 and

 it has been shown conclusively that    
these drugs weaken heart action1        
diminish circulation1 reduce the number 
of red corpuscles in the blood1 and     
bring on a condition of chronic anemia4 
,pallid cheeks and blue lips are visible
 evidence of the too frequent use of    
headache powders4  ,the labels required 
by law are often deceptive and convey no
 adequate idea of the amount of drug    
consumed2 for example1 #bdj grains of   
acetanilid to an ounce seems a small    
quantity of drug for a powder1 but when 
one considers that there are only #dhj  
grains in an ounce1 it will be seen that
 each powder is one half acetanilid4    
,powders taken in small quantities and  
at rare intervals are apparently        
harmless2 but they never remove the     
cause of the trouble1 and hence the     
discomfort soon returns with renewed    
force4 ,ordinarily1 hygienic living will
 eliminate the source of the trouble1   
but if it does not1 a physician should  
be consulted and medicine should be     

procured from him which will restore the
 deranged system to its normal healthy  
condition4  #bdc4 ,other ,deceptions4   
,nearly all patent medicines contain    
some alcohol1 and in many1 the quantity 
of alcohol is far in excess of that     
found in the strongest wines4 ,tonics   
and bitters advertised as a cure for    
spring fever and a worn-out system are  
scarcely more than cheap cocktails1 as  
one writer has derisively called them1  
and the amount of alcohol in some widely
 advertised patent remedies is          
alarmingly large and almost equal to    
that of strong whisky4  ,illustration3  
,,fig4 #afa4--;,diagram showing the     
amount of alcohol in some alcoholic     
drinks and in one much used patent      
medicine4  ,some conscientious persons  
who would not touch beer1 wine1 whisky1 
or any other intoxicating drink consume 
patent remedies containing large        
quantities of alcohol and thus          
unintentionally expose themselves to    
mental and physical danger4 ,in all     

cases of bodily disorder1 the only safe 
course is to consult a physician who has
 devoted himself to the study of the    
body and the methods by which a         
disordered system may be restored to    
health4     ,,chapter ,,xxvi  ,,nitrogen
 ,,and ,,its ,,relation ,,to ,,plants   
#bdd4 ,nitrogen4 ,a substance which     
plays an important part in animal and   
plant life is nitrogen4 ,soil and the   
fertilizers which enrich it1 the plants 
which grow on it1 and the animals which 
feed on these1 all contain nitrogen or  
nitrogenous compounds4 ,the atmosphere1 
which we ordinarily think of as a       
storehouse of oxygen1 contains far more 
nitrogen than oxygen1 since four fifths 
of its whole weight is made up of this  
element4  ,nitrogen is colorless1       
odorless1 and tasteless4 ,air is        
composed chiefly of oxygen and nitrogen2
 if1 therefore1 the oxygen in a vessel  
filled with air can be made to unite    
with some other substance or can be     
removed1 there will be a residue of     

nitrogen4 ,this can be done by floating 
on water a light dish containing        
phosphorus1 then igniting the           
phosphorus1 and placing an inverted jar 
over the burning substance4 ,the        
phosphorus in burning unites with the   
oxygen of the air and hence the gas that
 remains in the jar is chiefly nitrogen4
 ,it has the characteristics mentioned  
above and1 in addition1 does not combine
 readily with other substances4  #bde4  
,plant ,food4 ,food is the course of    
energy in every living thing and is     
essential to both animal and plant life4
 ,plants get their food from the        
lifeless matter which exists in the air 
and in the soil2 while animals get their
 food from plants4 ,it is true that man 
and many other animals eat fleshy foods 
and depend upon them for partial        
sustenance1 but the ultimate source of  
all animal food is plant life1 since    
meat-producing animals live upon plant  
growth4  ,plants get their food from the
 air1 the soil1 and moisture4 ,from the 

air1 the leaves take carbon dioxide and 
water and transform them into starchy   
food2 from the soil1 the roots take     
water rich in mineral matters dissolved 
from the soil4 ,from the substances thus
 gathered1 the plant lives and builds up
 its structure4  ,a food substance      
necessary to plant life and growth is   
nitrogen4 ,since a vast store of        
nitrogen exists in the air1 it would    
seem that plants should never lack for  
this food1 but most plants are unable to
 make use of the boundless store of     
atmospheric nitrogen1 because they do   
not possess the power of abstracting    
nitrogen from the air4 ,for this reason1
 they have to depend solely upon        
nitrogenous compounds which are present 
in the soil and are soluble in water4   
,the soluble nitrogenous soil compounds 
are absorbed by roots and are utilized  
by plants for food4  #bdf4 ,the ,poverty
 of the ,soil4 ,plant roots are         
constantly taking nitrogen and its      
compounds from the soil4 ,if crops which

 grow from the soil are removed year    
after year1 the soil becomes poorer in  
nitrogen1 and finally possesses too     
little of it to support vigorous and    
healthy plant life4 ,the nitrogen of the
 soil can be restored if we add to it a 
fertilizer containing nitrogen compounds
 which are soluble in water4 ,decayed   
vegetable matter contains large         
quantities of nitrogen compounds1 and   
hence if decayed vegetation is placed   
upon soil or is plowed into soil1 it    
acts as a fertilizer1 returning to the  
soil what was taken from it4 ,since man 
and all other animals subsist upon      
plants1 their bodies likewise contain   
nitrogenous substances1 and hence manure
 and waste animal matter is valuable as 
a fertilizer or soil restorer4  #bdg4   
,bacteria as ,nitrogen ,gatherers4 ,soil
 from which crops are removed year after
 year usually becomes less fertile1 but 
the soil from which crops of clover1    
peas1 beans1 or alfalfa have been       
removed is richer in nitrogen rather    

than poorer4 ,this is because the roots 
of these plants often have on them tiny 
swellings1 or tubercles1 in which       
millions of certain bacteria live and   
multiply4 ,these bacteria have the      
remarkable power of taking free nitrogen
 from the air in the soil and of        
combining it with other substances to   
form compounds which plants can use4    
,the bacteria-made compounds dissolve in
 the soil water and are absorbed into   
the plant by the roots4 ,so much        
nitrogen-containing material is made by 
the root bacteria of plants of the pea  
family that the soil in which they grow 
becomes somewhat richer in nitrogen1 and
 if plants which cannot make nitrogen   
are subsequently planted in such a soil1
 they find there a store of nitrogen4 ,a
 crop of peas1 beans1 or clover is      
equivalent to nitrogenous fertilizer and
 helps to make ready the soil for other 
crops4  ,illustration3 ,,fig4           
#afb4--,roots of soy bean having        
tubercle-bearing bacteria4  #bdh4       

,artificial ,fertilizers4 ,plants need  
other foods besides nitrogen1 and they  
exhaust the soil not only of nitrogen1  
but also of phosphorus and potash1 since
 large quantities of these are necessary
 for plant life4 ,there are many other  
substances absorbed from the soil by the
 plant1 namely1 iron1 sodium1 calcium1  
magnesium1 but these are used in smaller
 quantities and the supply in the soil  
does not readily become exhausted4      
,commercial fertilizers generally       
contain nitrogen1 phosphorus1 and potash
 in amounts varying with the            
requirements of the soil4 ,wheat        
requires a large amount of phosphorus   
and quickly exhausts the ground of that 
food stuff2 a field which has supported 
a crop of wheat is particularly poor in 
phosphorus1 and a satisfactory          
fertilizer for that land would          
necessarily contain a large percentage  
of phosphorus4 ,the fertilizer to be    
used in a soil depends upon the         
character of the soil and upon the crops

 previously grown on it4  ,illustration3
 ,,fig4 #afc4--,water cultures of       
buckwheat3 #a1 with all the food        
elements2 #b1 without potash2 #c1       
without nitrates4  ,the quantity of     
fertilizer needed by the farmers of the 
world is enormous1 and the problem of   
securing the necessary substances in    
quantities sufficient to satisfy the    
demand bids fair to be serious4 ,but    
modern chemistry is at work on the      
problem1 and already it is possible to  
make some nitrogen compounds on a       
commercial scale4 ,when nitrogen gas is 
in contact with heated calcium carbide1 
a reaction takes place which results in 
the formation of calcium nitride1 a     
compound suitable for enriching the     
soil4 ,there are other commercial       
methods for obtaining nitrogen compounds
 which are suitable for absorption by   
plant roots4  ,phosphorus is obtained   
from bone ash and from phosphate rock   
which is widely distributed over the    
surface of the earth4 ,bone ash and     

thousands of tons of phosphate rock are 
treated with sulphuric acid to form a   
phosphorus compound which is soluble in 
soil water and which1 when added to     
soil1 will be usable by the plants      
growing there4  ,the other important    
ingredient of most fertilizers is       
potash4 ,wood ashes are rich in potash  
and are a valuable addition to the soil4
 ,but the amount of potash thus obtained
 is far too limited to supply the needs 
of agriculture2 and to-day the main     
sources of potash are the vast deposits 
of potassium salts found in ,prussia4   
,although ,germany now furnishes the    
,american farmer with the bulk of his   
potash1 she may not do so much longer4  
,in #aiaa an indirect potash tax was    
levied by ,germany on her best customer1
 the ,united ,states1 to whom #ae       
million dollars' worth of potash had    
been sold the preceding year4 ,this led 
,americans to inquire whether potash    
could not be obtained at home4          
,geologists say that long ages ago      

,germany was submerged1 that the waters 
slowly evaporated and that the various  
substances in the sea water were        
deposited in thick layers4 ,the deposits
 thus left by the evaporation of the sea
 water gradually became hidden by       
sediment and soil1 and lost to sight4   
,from such deposits1 potash is obtained4
 ,geologists tell us that our own       
,western ,states were once submerged1   
and that the waters evaporated and      
disappeared from our land very much as  
they did from ,germany4 ,the ,great     
,salt ,lake of ,utah is a relic of a    
great body of water4 ,if it be true that
 waters once covered our ,western       
,states1 there may be buried deposits of
 potash there1 and to-day the search for
 the hidden treasure is going on with   
the energy and enthusiasm characteristic
 of ,america4  ,another probable source 
of potash is seaweed4 ,the sea is a vast
 reservoir of potash1 and seaweed1      
especially the giant kelp1 absorbs large
 quantities of this potash4 ,a ton of   

dried kelp 7dried by sun and wind7      
contains about #ejj pounds of pure      
potash4 ,the kelps are abundant1        
covering thousands of square miles in   
the ,pacific ,ocean1 from ,mexico to the
 ,arctic ,ocean4     ,,chapter ,,xxvii  
,,sound   #bdi4 ,the ,senses4 ,all the  
information which we possess of the     
world around us comes to us through the 
use of the senses of sight1 hearing1    
taste1 touch1 and smell4 ,of the five   
senses1 sight and hearing are generally 
considered the most valuable4 ,in       
preceding ,chapters we studied the      
important facts relative to light and   
the power of vision2 it remains for us  
to study ,sound as we studied ,light1   
and to learn what we can of sound and   
the power to hear4  #bej4 ,how ,sound is
 ,produced4 ,if one investigates the    
source of any sound1 he will always find
 that it is due to motion of some kind4 
,a sudden noise is traced to the fall of
 an object1 or to an explosion1 or to a 
collision2 in fact1 is due to the motion

 of matter4 ,a piano gives out sound    
whenever a player strikes the keys and  
sets in motion the various wires within 
the piano2 speech and song are caused by
 the motion of chest1 vocal cords1 and  
lips4  ,illustration3 ,,fig4            
#afd4--,sprays of water show that the   
fork is in motion4  ,if a large dinner  
bell is rung1 its motion or vibration   
may be felt on touching it with the     
finger4 ,if a tuning fork is made to    
give forth sound by striking it against 
the knee1 or hitting it with a rubber   
hammer1 and is then touched to the      
surface of water1 small sprays of water 
will be thrown out1 showing that the    
prongs of the fork are in rapid motion4 
7,a rubber hammer is made by putting a  
piece of glass tubing through a rubber  
cork47  ,if a light cork ball on the end
 of a thread is brought in contact with 
a sounding fork1 the ball does not      
remain at rest1 but vibrates back and   
forth1 being driven by the moving       
prongs4  ,illustration3 ,,fig4          

#afe4--,the ball does not remain at rest
  ,these simple facts lead us to        
conclude that all sound is due to the   
motion of matter1 and that a sounding   
body of any kind is in rapid motion4    
#bea4 ,sound is carried by ,matter4 ,in 
most cases sound reaches the ear through
 the air2 but air is not the only medium
 through which sound is carried4 ,a loud
 noise will startle fish1 and cause them
 to dart away1 so we conclude that the  
sound must have reached them through the
 water4 ,an ,indian puts his ear to the 
ground in order to detect distant       
footsteps1 because sounds too faint to  
be heard through the air are            
comparatively clear when transmitted    
through the earth4 ,a gentle tapping at 
one end of a long table can be          
distinctly heard at the opposite end if 
the ear is pressed against the table2 if
 the ear is removed from the wood1 the  
sound of tapping is much fainter1       
showing that wood transmits sound more  
readily than air4 ,we see therefore that

 sound can be transmitted to the ear by 
solids1 liquids1 or gases4  ,matter of  
any kind can transmit sound to the ear4 
,the following experiments will show    
that matter is necessary for            
transmission4 ,attach a small toy bell  
to a glass rod 7,fig4 #aff7 by means of 
a rubber tube and pass the rod through  
one of two openings in a rubber cork4   
,insert the cork in a strong flask      
containing a small quantity of water and
 shake the bell1 noting the sound       
produced4 ,then heat the flask1 allowing
 the water to boil briskly1 and after   
the boiling has continued for a few     
minutes remove the flame and instantly  
close up the second opening by inserting
 a glass stopper4 ,now shake the flask  
and note that the sound is very much    
fainter than at first4 ,as the flask was
 warmed1 air was rapidly expelled2 so   
that when the flask was shaken the      
second time1 less air was present to    
transmit the sound4 ,if the glass       
stopper is removed and the air is       

allowed to reenter the flask1 the       
loudness of the sound immediately       
increases4  ,illustration3 ,,fig4       
#aff4--,sound is carried by the air4    
,since the sound of the bell grows      
fainter as air is removed1 we infer that
 there would be no sound if all the air 
were removed from the flask2 that is to 
say1 sound cannot be transmitted through
 empty space or a vacuum4 ,if sound is  
to reach our ears1 it must be through   
the agency of matter1 such as wood1     
water1 or air1 etc4  #beb4 ,how ,sound  
is transmitted through ,air4 ,we saw in 
,section #bej that sound can always be  
traced to the motion or vibration of    
matter4 ,it is impossible to conceive of
 an object being set into sudden and    
continued motion without disturbing the 
air immediately surrounding it4 ,a      
sounding body always disturbs and throws
 into vibration the air around it1 and  
the air particles which receive motion  
from a sounding body transmit their     
motion to neighboring particles1 these  

in turn to the next adjacent particles1 
and so on until the motion has traveled 
to very great distances4 ,the manner in 
which vibratory motion is transmitted by
 the atmosphere must be unusual in      
character1 since no motion of the air is
 apparent1 and since in the stillness of
 night when not a breath of air is      
stirring1 the shriek of a railroad      
whistle miles distant may be heard with 
perfect clearness4 ,moreover1 the most  
delicate notes of a violin can be heard 
in the remotest corners of a concert    
hall1 when not the slightest motion of  
the air can be seen or felt4  ,in our   
study of the atmosphere we saw that air 
can be compressed and rarefied2 in other
 words1 we saw that air is very elastic4
 ,it can be shown experimentally that   
whenever an elastic body in motion comes
 in contact with a body at rest1 the    
moving body transfers its motion to the 
second body and then comes to rest      
itself4 ,let two billiard balls be      
suspended in the manner indicated in    

,figure #afg4 ,if one of the balls is   
drawn aside and is then allowed to fall 
against the other1 the second ball is   
driven outward to practically the height
 from which the first ball fell and the 
first ball comes to rest4               
,illustration3 ,,fig4 #afg4--;,elastic  
balls4  ,illustration3 ,,fig4           
#afh4--,suspended billiard balls4  ,if a
 number of balls are arranged in line as
 in ,figure #afh or ,figure #afi1 and   
the end ball is raised and then allowed 
to fall1 or if ,a is pushed against ,c1 
the last ball ,b will move outward      
alone1 with a force nearly equal to that
 originally possessed by ,a and to a    
distance nearly equal to that through   
which ,a moved4 ,but there will be no   
visible motion of the intervening balls4
 ,the force of the moving ball ,a is    
given to the second ball1 and the second
 ball in turn gives the motion to the   
third1 and so on throughout the entire  
number1 until ,b is reached4 ,but ,b has
 no ball to give its motion to1 hence ,b

 itself moves outward1 and moves with a 
force nearly equal to that originally   
imparted by ,a and to a distance nearly 
equal to that through which ,a fell4    
,motion at ,a is transmitted to ,b      
without any perceptible motion of the   
balls lying between these points4       
,similarly the particles of air set into
 motion by a sounding body impart their 
motion to each other1 the motion being  
transmitted onward without any          
perceptible motion of the air itself4   
,when this motion reaches the ear1 it   
sets the drum of the ear into vibration1
 and these vibrations are in turn       
transmitted to the auditory nerves1     
which interpret the motion as sound4    
,illustration3 ,,fig4 #afi4--;,elastic  
balls transmit motion4  ,illustration3  
,,fig4 #agj4--,when a ball meets more   
than one ball1 it divides its motion4   
#bec4 ,why ,sound dies away with        
,distance4 ,since the last ball ,b is   
driven outward with a force nearly equal
 to that possessed by ,a1 it would seem 

that the effect on the ear drum should  
be independent of distance and that a   
sound should be heard as distinctly when
 remote as when near4 ,but we know from 
experience that this is not true1       
because the more distant the source of  
sound1 the fainter the impression2 and  
finally1 if the distance between the    
source of sound and the hearer becomes  
too great1 the sound disappears entirely
 and nothing is heard4 ,the explanation 
of this well-known fact is found in a   
further study of the elastic balls      
7,fig4 #agj74 ,if ,a hits two balls     
instead of one1 the energy possessed by 
,a is given in part to one ball1 and in 
part to the other1 so that neither      
obtains the full amount4 ,these balls1  
having each received less than the      
original energy1 have less to transmit2 
each of these balls in turn meets with  
others1 and hence the motion becomes    
more and more distributed1 and distant  
balls receive less and less impetus4    
,the energy finally given becomes too   

slight to affect neighboring balls1 and 
the system comes to rest4 ,this is what 
occurs in the atmosphere2 a moving air  
particle meets not one but many adjacent
 air particles1 and each of these       
receives a portion of the original      
energy and transmits a portion4 ,when   
the original disturbance becomes        
scattered over a large number of air    
particles1 the energy given to any one  
air particle becomes correspondingly    
small1 and finally the energy becomes so
 small that further particles are not   
affected2 beyond this limit the sound   
cannot be heard4  ,if an air particle   
transmitted motion only to those air    
particles directly in line with it1 we  
should not be able to detect sound      
unless the ear were in direct line with 
the source4 ,the fact that an air       
particle divides its motion among all   
particles which it touches1 that is1    
among those on the sides as well as     
those in front1 makes it possible to    
hear sound in all directions4 ,a good   

speaker is heard not only by those      
directly in front of him1 but by those  
on the side1 and even behind him4  #bed4
 ,velocity of ,sound4 ,the transmission 
of motion from particle to particle does
 not occur instantaneously1 but requires
 time4 ,if the distance is short1 so    
that few air particles are involved1 the
 time required for transmission is very 
brief1 and the sound is heard at        
practically the instant it is made4     
,ordinarily we are not conscious that it
 requires time for sound to travel from 
its source to our ears1 because the     
distance involved is too short4 ,at     
other times we recognize that there is a
 delay2 for example1 thunder reaches our
 ears after the lightning which caused  
the thunder has completely disappeared4 
,if the storm is near1 the interval of  
time between the lightning and the      
thunder is brief1 because the sound does
 not have far to travel2 if the storm is
 distant1 the interval is much longer1  
corresponding to the greater distance   

through which the sound travels4 ,sound 
does not move instantaneously1 but      
requires time for its transmission4 ,the
 report of a distant cannon is heard    
after the flash and smoke are seen2 the 
report of a near cannon is heard the    
instant the flash is seen4  ,the speed  
with which sounds travels through the   
air1 or its velocity1 was first measured
 by noting the interval 7#ed4f seconds7 
which elapsed between the flash of a    
cannon and the sound of the report4 ,the
 distance of the cannon from the        
observer was measured and found to be   
#fa1jde feet1 and by dividing this      
distance by the number of seconds1 we   
find that the distance traveled by sound
 in one second is approximately #aaah   
feet4  ,high notes and low notes1 soft  
notes and shrill notes1 all travel at   
the same rate4 ,if bass notes traveled  
faster or slower than soprano notes1 or 
if the delicate tones of the violin     
traveled faster or slower than the tones
 of a drum1 music would be practically  

impossible1 because at a distance from  
the source of sound the various tones   
which should be in unison would be out  
of time--some arriving late1 some early4
  #bee4 ,sound ,waves4 ,practically     
everyone knows that a hammock hung with 
long ropes swings or vibrates more      
slowly than one hung with short ropes1  
and that a stone suspended by a long    
string swings more slowly than one      
suspended by a short string4 ,no two    
rocking chairs vibrate in the same way  
unless they are exactly alike in shape1 
size1 and material4 ,an object when     
disturbed vibrates in a manner peculiar 
to itself1 the vibration being slow1 as 
in the case of the long-roped swing1 or 
quick1 as in the case of the short-roped
 swing4 ,the time required for a single 
swing or vibration is called the period 
of the body1 and everything that can    
vibrate has a characteristic period4    
,size and shape determine to a large    
degree the period of a body2 for        
example1 a short1 thick tuning fork     

vibrates more rapidly than a tall       
slender fork4  ,illustration3 ,,fig4    
#aga4--,the two hammocks swing          
differently4  ,some tuning forks when   
struck vibrate so rapidly that the      
prongs move back and forth more than    
#ejjj times per second1 while other     
tuning forks vibrate so slowly that the 
vibrations do not exceed #ej per second4
 ,in either case the distance through   
which the prongs move is very small and 
the period is very short1 so that the   
eye can seldom detect the movement      
itself4 ,that the prongs are in motion1 
however1 is seen by the action of a pith
 ball when brought in contact with the  
prongs 7see ,section #bej74             
,illustration3 ,,fig4 #agb4--,the pitch 
given out by a fork depends upon its    
shape4  ,the disturbance created by a   
vibrating body is called a wave4  #bef4 
,waves4 ,while the disturbance which    
travels out from a sounding body is     
commonly called a wave1 it is by no     
means like the type of wave best known  

to us1 namely1 the water wave4  ,if a   
closely coiled heavy wire is suspended  
as in ,figure #agc and the weight is    
drawn down and then released1 the coil  
will assume the appearance shown2 there 
is clearly an overcrowding or           
condensation in some places1 and a      
spreading out or rarefaction in other   
places4 ,the pulse of condensation and  
rarefaction which travels the length of 
the wire is called a wave1 although it  
bears little or no resemblance to the   
familiar water wave4 ,sound waves are   
similar to the waves formed in the      
stretched coil4  ,illustration3 ,,fig4  
#agc4--,waves in a coiled wire4  ,sound 
waves may be said to consist of a series
 of condensations and rarefactions1 and 
the distance between two consecutive    
condensations and rarefactions may be   
defined as the wave length4  #beg4 ,how 
,one ,sounding ,body produces ,sound in 
,another ,body4 ,in ,section #bee we saw
 that any object when disturbed vibrates
 in a manner peculiar to itself1--its   

natural period1--a long-roped hammock   
vibrating slowly and a short-roped      
hammock vibrating rapidly4 ,from        
observation we learn that it requires   
but little force to cause a body to     
vibrate in its natural period4 ,if a    
sounding body is near a body which has  
the same period as itself1 the pulses of
 air produced by the sounding body will1
 although very small1 set the second    
body into motion and cause it to make a 
faint sound4 ,when a piano is being     
played1 we are often startled to find   
that a window pane or an ornament       
responds to some note of the piano4 ,if 
two tuning forks of exactly identical   
periods 7that is1 of the same frequency7
 are placed on a table as in ,figure    
#agd1 and one is struck so as to give   
forth a clear sound1 the second fork    
will likewise vibrate1 even though the  
two forks may be separated by several   
feet of air4 ,we can readily see that   
the second fork is in motion1 although  
it has not been struck1 because it will 

set in motion a pith ball suspended     
beside it2 at first the pith ball does  
not move1 then it moves slightly1 and   
finally bounces rapidly back and forth4 
,if the periods of the two forks are not
 identical1 but differ in the slightest 
degree1 the second fork will not respond
 to the first fork1 no matter how long  
or how loud the sound of the first fork4
 ,if we suppose that the fork vibrates  
#bef times each second1 then #bef gentle
 pulses of air are produced each second1
 and these1 traveling outward through   
the air1 reach the silent fork and tend 
to set it in motion4 ,a single pulse of 
air could not move the solid1 heavy     
prongs1 but the accumulated action of   
#bef vibrations per second soon makes   
itself felt1 and the second fork begins 
to vibrate1 at first gently1 then       
gradually stronger1 and finally an      
audible tone is given forth4            
,illustration3 ,,fig4 #agd4--,when the  
first fork vibrates1 the second         
responds4  ,the cumulative power of     

feeble forces acting frequently at      
definite intervals is seen in many ways 
in everyday life4 ,a small boy can      
easily swing a much larger boy1 provided
 he gives the swing a gentle push in the
 right direction every time it passes   
him4 ,but he must be careful to push at 
the proper instant1 since otherwise his 
effort does not count for much2 if he   
pushes forward when the swing is moving 
backward1 he really hinders the motion2 
if he waits until the swing has moved   
considerably forward1 his push counts   
for little4 ,he must push at the proper 
instant2 that is1 the way in which his  
hand moves in giving the push must      
correspond exactly with the way in which
 the swing would naturally vibrate4 ,a  
very striking experiment can be made by 
suspending from the ceiling a heavy     
weight and striking this weight gently  
at regular1 properly timed intervals    
with a small cork hammer4 ,soon the     
pendulum1 or weight1 will be set        
swinging4  ,illustration3 ,,fig4        

#age4--,the hollow wooden box renforces 
the sound4  #beh4 ,borrowed ,sound4     
,picture frames and ornaments sometimes 
buzz and give forth faint murmurs when a
 piano or organ is played4 ,the waves   
sent out by a sounding body fall upon   
all surrounding objects and by their    
repeated action tend to throw these     
bodies into vibration4 ,if the period of
 any one of the objects corresponds with
 the period of the sounding body1 the   
gentle but frequent impulses affect the 
object1 which responds by emitting a    
sound4 ,if1 however1 the periods do not 
correspond1 the action of the sound     
waves is not sufficiently powerful to   
throw the object into vibration1 and no 
sound is heard4 ,bodies which respond in
 this way are said to be sympathetic and
 the response produced is called        
resonance4 ,seashells when held to the  
ear seem to contain the roar of the sea2
 this is because the air within the     
shell is set into sympathetic vibrations
 by some external tone4 ,if the seashell

 were held to the ear in an absolutely  
quiet room1 no sound would be heard1    
because there would be no external      
forces to set into vibration the air    
within the shell4  ,tuning forks do not 
produce strong tones unless mounted on  
hollow wooden boxes 7,fig4 #age71 whose 
size and shape are so adjusted that     
resonance occurs and strengthens the    
sound4 ,when a human being talks or     
sings1 the air within the mouth cavity  
is thrown into sympathetic vibration and
 strengthens the otherwise feeble tone  
of the speaker4  #bei4 ,echo4 ,if one   
shouts in a forest1 the sound is        
sometimes heard a second time a second  
or two later4 ,this is because sound is 
reflected when it strikes a large       
obstructing surface4 ,if the sound waves
 resulting from the shout meet a cliff  
or a mountain1 they are reflected back1 
and on reaching the ear produce a later 
sensation of sound4  ,by observation it 
has been found that the ear cannot      
distinguish sounds which are less than  

one tenth of a second apart2 that is1 if
 two sounds follow each other at an     
interval less than one tenth of a       
second1 the ear recognizes not two      
sounds1 but one4 ,this explains why a   
speaker can be heard better indoors than
 in the open air4 ,in the average       
building1 the walls are so close that   
the reflected waves have but a short    
distance to travel1 and hence reach the 
ear at practically the same time as     
those which come directly from the      
speaker4 ,in the open1 there are no     
reflecting walls or surfaces1 and the   
original sound has no renforcement from 
reflection4  ,if the reflected waves    
reach the ear too late to blend with the
 original sound1 that is1 come later    
than one tenth of a second after the    
first impression1 an echo is heard4     
,what we call the rolling of thunder is 
really the reflection and re-reflection 
of the original thunder from cloud and  
cliff4  ,some halls are so large that   
the reflected sounds cause a confusion  

of echoes1 but this difficulty can be   
lessened by hanging draperies1 which    
break the reflection4  #bfj4 ,motion    
does not always produce ,sound4 ,while  
we know that all sound can be traced to 
motion1 we know equally well that motion
 does not always produce sound4 ,the    
hammock swinging in the breeze does not 
give forth a sound2 the flag floating in
 the air does not give forth a sound    
unless blown violently by the wind2 a   
card moved slowly through the air does  
not produce sound1 but if the card is   
moved rapidly back and forth1 a sound   
becomes audible4  ,motion1 in order to  
produce sound1 must be rapid2 a ball    
attached to a string and moved slowly   
through the air produces no sound1 but  
the same ball1 whirled rapidly1 produces
 a distinct buzz1 which becomes stronger
 and stronger the faster the ball is    
whirled4  #bfa4 ,noise and ,music4 ,when
 the rapid motions which produce sound  
are irregular1 we hear noise2 when the  
motions are regular and definite1 we    

have a musical tone2 the rattling of    
carriage wheels on stones1 the roar of  
waves1 the rustling of leaves are noise1
 not music4 ,in all these illustrations 
we have rapid but irregular motion2 no  
two stones strike the wheel in exactly  
the same way1 no two waves produce      
pulses in the air of exactly the same   
character1 no two leaves rustle in      
precisely the same way4 ,the            
disturbances which reach the ear from   
carriage1 waves1 and leaves are         
irregular both in time and strength1 and
 irritate the ear1 causing the sensation
 which we call noise4  ,the tuning fork 
is musical4 ,here we have rapid1 regular
 motion2 vibrations follow each other at
 perfectly definite intervals1 and the  
air disturbance produced by one         
vibration is exactly like the           
disturbance produced by a later         
vibration4 ,the sound waves which reach 
the ear are regular in time and kind and
 strength1 and we call the sensation    
music4  ,to produce noise a body must   

vibrate in such a way as to give short1 
quick shocks to the air2 to produce     
music a body must not only impart short1
 quick shocks to the air1 but must      
impart these shocks with unerring       
regularity and strength4 ,a flickering  
light irritates the eye2 a flickering   
sound or noise irritates the ear2 both  
are painful because of the sudden and   
abrupt changes in effect which they     
cause1 the former on the eye1 the latter
 on the ear4  ,the only thing essential 
for the production of a musical sound is
 that the waves which reach the ear     
shall be rapid and regular2 it is       
immaterial how these waves are produced4
 ,if a toothed wheel is mounted and     
slowly rotated1 and a stiff card is held
 against the teeth of the wheel1 a      
distinct tap is heard every time the    
card strikes the wheel4 ,but if the     
wheel is rotated rapidly1 the ear ceases
 to hear the various taps and recognizes
 a deep continuous musical tone4 ,the   
blending of the individual taps1        

occurring at regular intervals1 has     
produced a sustained musical tone4 ,a   
similar result is obtained if a card is 
drawn slowly and then rapidly over the  
teeth of a comb4  ,illustration3 ,,fig4 
#agf4--;,a rotating disk4  ,that musical
 tones are due to a succession of       
regularly timed impulses is shown most  
clearly by means of a rotating disk on  
which are cut two sets of holes1 the    
outer set equally spaced1 and the inner 
set unequally spaced 7,fig4 #agf74  ,if1
 while the disk is rotating rapidly1 a  
tube is held over the outside row and   
air is blown through the tube1 a        
sustained musical tone will be heard4   
,if1 however1 the tube is held1 during  
the rotation of the disk1 over the inner
 row of unequally spaced holes1 the     
musical tone disappears1 and a series of
 noises take its place4 ,in the first   
case1 the separate puffs of air followed
 each other regularly and blended into  
one tone2 in the second case1 the       
separate puffs of air followed each     

other at uncertain and irregular        
intervals and the result was noise4     
,sound possesses a musical quality only 
when the waves or pulses follow each    
other at absolutely regular intervals4  
#bfb4 ,the ,effect of the ,rapidity of  
,motion on the ,musical ,tone ,produced4
 ,if the disk is rotated so slowly that 
less than about #af puffs are produced  
in one second1 only separate puffs are  
heard1 and a musical tone is lacking2   
if1 on the other hand1 the disk is      
rotated in such a way that #af puffs or 
more are produced in one second1 the    
separate puffs will blend together to   
produce a continuous musical note of    
very low pitch4 ,if the speed of the    
disk is increased so that the puffs     
become more frequent1 the pitch of the  
resulting note rises2 and at very high  
speeds the notes produced become so     
shrill and piercing as to be            
disagreeable to the ear4 ,if the speed  
of the disk is lessened1 the pitch falls
 correspondingly2 and if the speed again

 becomes so low that less than #af puffs
 are formed per second1 the sustained   
sound disappears and a series of        
intermittent noises is produced4  #bfc4 
,the ,pitch of a ,note4 ,by means of an 
apparatus called the siren1 it is       
possible to calculate the number of     
vibrations producing any given musical  
note1 such1 for example1 as middle ,c on
 the piano4 ,if air is forced           
continuously against the disk as it     
rotates1 a series of puffs will be heard
 7,fig4 #agg74  ,if the disk turns fast 
enough1 the puffs blend into a musical  
sound1 whose pitch rises higher and     
higher as the disk moves faster and     
faster1 and produces more and more puffs
 each second4  ,the instrument is so    
constructed that clockwork at the top   
registers the number of revolutions made
 by the disk in one second4 ,the number 
of holes in the disk multiplied by the  
number of revolutions a second gives the
 number of puffs of air produced in one 
second4 ,if we wish to find the number  

of vibrations which correspond to middle
 ,c on the piano1 we increase the speed 
of the disk until the note given forth  
by the siren agrees with middle ,c as   
sounded on the piano1 as nearly as the  
ear can judge2 we then calculate the    
number of puffs of air which took place 
each second at that particular speed of 
the disk4 ,in this way we find that     
middle ,c is due to about #bef          
vibrations per second2 that is1 a piano 
string must vibrate #bef times per      
second in order for the resultant note  
to be of pitch middle ,c4 ,in a similar 
manner we determine the following       
frequencies3--    do  re  mi  fa  sol la
  si  do     ,c   ,d   ,e   ,f   ,g   ,a
   ,b   ,c'     #bef #bhh #cbj #cda #chd
 #dbg #dhj #eab   ,illustration3 ,,fig4 
#agg4--;,a siren4  ,the pitch of pianos1
 from the lowest bass note to the very  
highest treble1 varies from #bg to about
 #cejj vibrations per second4 ,no human 
voice1 however1 has so great a range of 
tone2 the highest soprano notes of women

 correspond to but #ajjj vibrations a   
second1 and the deepest bass of men     
falls but to #hj vibrations a second4   
,while the human voice is limited in its
 production of sound1--rarely falling   
below #hj vibrations a second and rarely
 exceeding #ajjj vibrations a           
second1--the ear is by no means limited 
to that range in hearing4 ,the chirrup  
of a sparrow1 the shrill sound of a     
cricket1 and the piercing shrieks of a  
locomotive are due to far greater       
frequencies1 the number of vibrations at
 times equaling #ch1jjj per second or   
more4  #bfd4 ,the ,musical ,scale4 ,when
 we talk1 the pitch of the voice changes
 constantly and adds variety and beauty 
to conversation2 a speaker whose tone1  
or pitch1 remains too constant is       
monotonous and dull1 no matter how      
brilliant his thoughts may be4  ,while  
the pitch of the voice changes          
constantly1 the changes are normally    
gradual and slight1 and the different   
tones merge into each other             

imperceptibly4 ,in music1 however1 there
 is a well-defined interval between even
 consecutive notes2 for example1 in the 
musical scale1 middle ,c 7do7 with #bef 
vibrations is followed by ,d 7re7 with  
#bhh vibrations1 and the interval       
between these notes is sharp and well   
marked1 even to an untrained ear4 ,the  
interval between two notes is defined as
 the ratio of the frequencies2 hence1   
the interval between ,c and ,d 7do and  
re7 is #bhh_/bef1 or #i_/h4 ,referring  
to ,section #bfc1 we see that the       
interval between ,c and ,e is #cbj_/bef1
 or #e_/d1 and the interval between ,c  
and ,c' is #eab_/bef1 or #b2 the        
interval between any note and its octave
 is #b4  ,the successive notes in one   
octave of the musical scale are related 
as follows3--    ,key of ,c          ,c 
,d   ,e   ,f   ,g   ,a    ,b   ,c'      
,no4 of vibrations                      
per sec4          #bef #bhh #cbj #cda   
#chd #dbg  #dhj #eab    ,interval       
#i_/h #e_/d #d_/c #c_/b #e_/c #ae_/h #b 

,the intervals of ,f and ,a are not     
strictly #d_/c and #e_/c1 but are nearly
 so2 if ,f made #cda4c vibrations per   
second instead of #cda2 and if ,a made  
#dbf4f instead of #dbg1 then the        
intervals would be exactly #d_/c and    
#e_/c4 ,since the real difference is so 
slight1 we can assume the simpler ratios
 without appreciable error4  ,any eight 
notes whose frequencies are in the ratio
 of #i_/h1 #e_/d1 etc41 will when played
 in succession give the familiar musical
 scale2 for example1 the deepest bass   
voice starts a musical scale whose notes
 have the frequencies #hj1 #ij1 #ajj1   
#ajg1 #abj1 #acc1 #aej1 #afj1 but the   
intervals here are identical with those 
of a higher scale2 the interval between 
,c and ,d1 #hj and #ij1 is #i_/h1 just  
as it was before when the frequencies   
were much greater2 that is1 #bef and    
#bhh4 ,in singing ,home1 ,sweet ,home1  
for example1 a bass voice may start with
 a note vibrating only #acb times a     
second2 while a tenor may start at a    

higher pitch1 with a note vibrating #aih
 times per second1 and a soprano would  
probably take a much higher range still1
 with an initial frequency of #ebh      
vibrations per second4 ,but no matter   
where the voices start1 the intervals   
are always identical4 ,the air as sung  
by the bass voice would be represented  
by ,a4 ,the air as sung by the tenor    
voice would be represented by ,b4 ,the  
air as sung by the soprano voice would  
be represented by ,c4  ,illustration3   
,,fig4 #agh4--;,a song as sung by three 
voices of different pitch4     ,,chapter
 ,,xxviii  ,,musical ,,instruments      
#bfe4 ,musical instruments maybe divided
 into three groups according to the     
different ways in which their tones are 
produced3--  ,first4 ,the stringed      
instruments in which sound is produced  
by the vibration of stretched strings1  
as in the piano1 violin1 guitar1        
mandolin4  ,second4 ,the wind           
instruments in which sound is produced  
by the vibrations of definite columns of

 air1 as in the organ1 flute1 cornet1   
trombone4  ,third4 ,the percussion      
instruments1 in which sound is produced 
by the motion of stretched membranes1 as
 in the drum1 or by the motion of metal 
disks1 as in the tambourines and        
cymbals4  #bff4 ,stringed ,instruments4 
,if the lid of a piano is opened1       
numerous wires are seen within2 some    
long1 some short1 some coarse1 some     
fine4 ,beneath each wire is a small felt
 hammer connected with the keys in such 
a way that when a key is pressed1 a     
string is struck by a hammer and is     
thrown into vibration1 thereby producing
 a tone4  ,if we press the lowest key1  
that is1 the key giving forth the lowest
 pitch1 we see that the longest wire is 
struck and set into vibration2 if we    
press the highest key1 that is1 the key 
giving the highest pitch1 we see that   
the shortest wire is struck4 ,in        
addition1 it is seen that the short     
wires which produce the high tones are  
fine1 while the long wires which produce

 the low tones are coarse4 ,the shorter 
and finer the wire1 the higher the pitch
 of the tone produced4 ,the longer and  
coarser the wire1 the lower the pitch of
 the tone produced4  ,illustration3     
,,fig4 #agi4--,piano wires seen from the
 back4  ,the constant striking of the   
hammers against the strings stretches   
and loosens them and alters their pitch2
 for this reason each string is fastened
 to a screw which can be turned so as to
 tighten the string or to loosen it if  
necessary4 ,the tuning of the piano is  
the adjustment of the strings so that   
each shall produce a tone of the right  
pitch4 ,when the strings are tightened1 
the pitch rises2 when the strings are   
loosened1 the pitch falls4  ,what has   
been said of the piano applies as well  
to the violin1 guitar1 and mandolin4 ,in
 the latter instruments the strings are 
few in number1 generally four1 as       
against eighty-eight in the piano2 the  
hammer of the piano is replaced in the  
violin by the bow1 and in the guitar by 

the fingers2 varying pitches on any one 
string are obtained by sliding a finger 
of the left hand along the wire1 and    
thus altering its length4  ,frequent    
tuning is necessary1 because the fine   
adjustments are easily disturbed4 ,the  
piano is the best protected of all the  
stringed instruments1 being inclosed by 
a heavy framework1 even when in use4    
,illustration3 ,,fig4 #ahj4--;,front    
view of an open piano4  #bfg4 ,strings  
and their ,tones4 ,fasten a violin      
string to a wooden frame or box1 as     
shown in ,figure #aha1 stretching it by 
means of some convenient weight2 then   
lay a yardstick along the box in order  
that the lengths may be determined      
accurately4 ,if the stretched string is 
plucked with the fingers or bowed with  
the violin bow1 a clear musical sound of
 definite pitch will be produced4 ,now  
divide the string into two equal parts  
by inserting the bridge midway between  
the two ends2 and pluck either half as  
before4 ,the note given forth is of a   

decidedly higher pitch1 and if by means 
of the siren we compare the pitches in  
the two cases1 we find that the note    
sounded by the half wire is the octave  
of the note sounded by the entire wire2 
the frequency has been doubled by       
halving the length4 ,if now the bridge  
is placed so that the string is divided 
into two unequal portions such as #a3c  
and #b3c1 and the shorter portion is    
plucked1 the pitch will be still higher2
 the shorter the length plucked1 the    
higher the pitch produced4 ,this movable
 bridge corresponds to the finger of the
 violinist2 the finger slides back and  
forth along the string1 thus changing   
the length of the bowed portion and     
producing variations in pitch4          
,illustration3 ,,fig4 #aha4--,the length
 of a string influences the pitch4      
,illustration3 ,,fig4 #ahb4--,only one  
half of the string is bowed1 but both   
halves vibrate4  ,if there were but one 
string1 only one pitch could be sounded 
at any one time2 the additional strings 

of the violin allow of the simultaneous 
production of several tones4  #bfh4 ,the
 ,freedom of a ,string4 ,some stringed  
instruments give forth tones which are  
clear and sweet1 but withal thin and    
lacking in richness and fullness4 ,the  
tones sounded by two different strings  
may agree in pitch and loudness and yet 
produce quite different effects on the  
ear1 because in one case the tone may be
 much more pleasing than in the other4  
,the explanation of this is1 that a     
string may vibrate in a number of       
different ways4  ,touch the middle of a 
wire with the finger or a pencil 7,fig4 
#ahb71 thus separating it into two      
portions and draw a violin bow across   
the center of either half4 ,only one    
half of the entire string is struck1 but
 the motion of this half is imparted to 
the other half and throws it into       
similar motion1 and if a tiny ,a-shaped 
piece of paper or rider is placed upon  
the unbowed half1 it is hurled off4     
,illustration3 ,,fig4 #ahc4--,the string

 vibrates in three portions4  ,if the   
wire is touched at a distance of one    
third its length and a bow is drawn     
across the middle of the smaller        
portion1 the string will vibrate in     
three parts2 we cannot always see these 
various motions in different parts of   
the string1 but we know of their        
existence through the action of the     
riders4  ,similarly1 touching the wire  
one fourth of its length from an end    
makes it vibrate in four segments2      
touching it one fifth of its length     
makes it vibrate in five segments4  ,in 
the first case1 the string vibrated as a
 whole string and also as two strings of
 half the length2 hence1 three tones    
must have been given out1 one tone due  
to the entire string and two tones due  
to the segments4 ,but we saw in ,section
 #bfg that halving the length of a      
string doubles the pitch of the         
resulting tone1 and produces the octave 
of the original tone2 hence a string    
vibrating as in ,figure #ahc gives forth

 three tones1 one of which is the       
fundamental tone of the string1 and two 
of which are the octave of the          
fundamental tone4 ,hence1 the vibrating 
string produces two sensations1 that of 
the fundamental note and of its octave4 
,illustration3 ,,fig4 #ahd4--,when a    
string vibrates as a whole1 it gives out
 the fundamental note4  ,when a string  
is plucked in the middle without being  
held1 it vibrates simply as a whole     
7,fig4 #ahd71 and gives forth but one   
note2 this is called the fundamental4   
,if the string is made to vibrate in two
 parts1 it gives forth two notes1 the   
fundamental1 and a note one octave      
higher than the fundamental2 this is    
called the first overtone4 ,when the    
string is made to move as in ,figure    
#ahc1 three distinct motions are called 
forth1 the motion of the entire string1 
the motion of the portion plucked1 and  
the motion of the remaining unplucked   
portion of the string4 ,here1 naturally1
 different tones arise1 corresponding to

 the different modes of vibration4 ,the 
note produced by the vibration of one   
third of the original string is called  
the second overtone4  ,the above        
experiments show that a string is able  
to vibrate in a number of different ways
 at the same time1 and to emit          
simultaneously a number of different    
tones2 also that the resulting complex  
sound consists of the fundamental and   
one or more overtones1 and that the     
number of overtones present depends upon
 how and where the string is plucked4   
,illustration3 ,,fig4 #ahe4--;,a string 
can vibrate in a number of different    
ways simultaneously1 and can produce    
different notes simultaneously4  #bfi4  
,the ,value of ,overtones4 ,the presence
 of overtones determines the quality of 
the sound produced4 ,if the string      
vibrates as a whole merely1 the tone    
given out is simple1 and seems dull and 
characterless4 ,if1 on the other hand1  
it vibrates in such a way that overtones
 are present1 the tone given forth is   

full and rich and the sensation is      
pleasing4 ,a tuning fork cannot vibrate 
in more than one way1 and hence has no  
overtones1 and its tone1 while clear and
 sweet1 is far less pleasing than the   
same note produced by a violin or piano4
 ,the untrained ear is not conscious of 
overtones and recognizes only the strong
 dominant fundamental4 ,the overtones   
blend in with the fundamental and are so
 inconspicuously present that we do not 
realize their existence2 it is only when
 they are absent that we become aware of
 the beauty which they add to the music4
 ,a song played on tuning forks instead 
of on strings would be lifeless and     
unsatisfying because of the absence of  
overtones4  ,it is not necessary to hold
 finger or pencil at the points #a3c1   
#a3d1 etc41 in order to cause the string
 to vibrate in various ways2 if a string
 is merely plucked or bowed at those    
places1 the result will be the same4 ,it
 is important to remember that no matter
 where a string of definite length is   

bowed1 the note most distinctly heard   
will be the fundamental2 but the quality
 of the emitted tone will vary with the 
bowing4 ,for example1 if a string is    
bowed in the middle1 the effect will be 
far less pleasing than though it were   
bowed near the end4 ,in the piano1 the  
hammers are arranged so as to strike    
near one end of the string1 at a        
distance of about #a3g to #a3i2 and     
hence a large number of overtones       
combine to renforce and enrich the      
fundamental tone4  #bgj4 ,the           
,individuality of ,instruments4 ,it has 
been shown that a piano string when     
struck by a hammer1 or a violin string  
when bowed1 or a mandolin string when   
plucked1 vibrates not only as a whole1  
but also in segments1 and as a result   
gives forth not a simple tone1 as we are
 accustomed to think1 but a very complex
 tone consisting of the fundamental and 
one or more overtones4 ,if the string   
whose fundamental note is lower ,c 7#abh
 vibrations per second7 is thrown into  

vibration1 the tone produced may        
contain1 in addition to the prominent   
fundamental1 any one or more of the     
following overtones3 ,c'1 ,g''1 ,c''1   
,e''1 ,c'''1 etc4  ,the number of       
overtones actually present depends upon 
a variety of circumstances3 in the      
piano1 it depends largely upon the      
location of the hammer2 in the violin1  
upon the place and manner of bowing4    
,mechanical differences in construction 
account for prominent and numerous      
overtones in some instruments and for   
feeble and few overtones in others4 ,the
 oboe1 for example1 is so constructed   
that only the high overtones are        
present1 and hence the sound gives a    
pungent effect2 the clarinet is so      
constructed that the even-numbered      
overtones are killed1 and the presence  
of only odd-numbered overtones gives    
individuality to the instrument4 ,in    
these two instruments we have vibrating 
air columns instead of vibrating        
strings1 but the laws which govern      

vibrating strings are applicable to     
vibrating columns of air1 as we shall   
see later4 ,it is really the presence or
 absence of overtones which enables us  
to distinguish the note of the piano    
from that of the violin1 flute1 or      
clarinet4 ,if overtones could be        
eliminated1 then middle ,c1 or any other
 note on the piano1 would be            
indistinguishable from that same note   
sounded on any other instrument4 ,the   
fundamental note in every instrument is 
the same1 but the overtones vary with   
the instrument and lend individuality to
 each4 ,the presence of high overtones  
in the oboe and the presence of         
odd-numbered overtones in the clarinet  
enable us to distinguish without fail   
the sounds given out by these           
instruments4  ,the richness and         
individuality of an instrument are due1 
not only to the overtones which         
accompany the fundamental1 but also to  
the forced vibrations of the inclosing  
case1 or of the sounding board4 ,if a   

vibrating tuning fork is held in the    
hand1 the sound will be inaudible except
 to those quite near2 if1 however1 the  
base of the fork is held against the    
table1 the sound is greatly intensified 
and becomes plainly audible throughout  
the room4  ,the vibrations of the fork  
are transmitted to the table top and    
throw it into vibrations similar to its 
own1 and these additional vibrations    
intensify the original sound4 ,any fork1
 no matter what its frequency1 can force
 the surface of the table into          
vibration1 and hence the sound of any   
fork will be intensified by contact with
 a table or box4  ,this is equally true 
of strings2 if stretched between two    
posts and bowed1 the sound given out by 
a string is feeble1 but if stretched    
over a sounding board1 as in the piano1 
or over a wooden shell1 as in the       
violin1 the sound is intensified4 ,any  
note of the instrument will force the   
sounding body to vibrate1 thus          
renforcing the volume of sound1 but some

 tones1 or modes of vibration1 do this  
more easily than others1 and while the  
sounding board or shell always responds1
 it responds in varying degree4 ,here   
again we have not only enrichment of    
sound but also individuality of         
instruments4  #bga4 ,the ,kinds of      
,stringed ,instruments4 ,stringed       
instruments may be grouped in the       
following three classes3--  a4          
,instruments in which the strings are   
set into motion by hammers--piano4  b4  
,instruments in which the strings are   
set into motion by bowing--violin1      
viola1 violoncello1 double bass4  c4    
,instruments in which the strings are   
set into motion by plucking--harp1      
guitar1 mandolin4  ,illustration3 ,,fig4
 #ahf4--a1 violin2 #b1 viola2 #c1       
violoncello2 #d1 double bass4       a4  
,the piano is too well known to need    
comment4 ,in      passing1 it may be    
mentioned that in the construction of   
the      modern concert piano           
approximately #dj1jjj separate pieces of

      material are used4 ,the large     
number of pieces is due1      partly1 to
 the fact that the single string        
corresponding to      any one key is    
usually replaced by no less than three  
or      four similar strings in order   
that greater volume of sound      may be
 obtained4 ,the hammer connected to a   
key strikes      four or more strings   
instead of one1 and hence produces a    
greater volume of tone4       b4 ,the   
viola is larger than the violin1 has    
heavier and      thicker strings1 and is
 pitched to a lower key2 in all other   
respects the two are similar4 ,the      
violoncello1 because of      the length 
and thickness of its strings1 is pitched
 a whole      octave lower than the     
violin2 otherwise it is similar4 ,the   
unusual length and thickness of the     
strings of the double      bass make it 
produce very low notes1 so that it is   
ordinarily looked upon as the bass voice
 of the orchestra4       c4 ,the harp   
has always been considered one of the   

most      pleasing and perfect of       
musical instruments4 ,here the          
skilled performer has absolutely free   
scope for his genius1      because his  
fingers can pluck the strings at will   
and hence      regulate the overtones1  
and his feet can regulate at will       
the tension1 and hence the pitch of the 
strings4       ,guitar and mandolin are 
agreeable instruments for amateurs1     
but are never used in orchestral music4 
,illustration3 ,,fig4 #ahg4--;,a harp4  
#bgb4 ,wind ,instruments4 ,in the       
so-called wind instruments1 sound is    
produced by vibrating columns of air    
inclosed in tubes or pipes of different 
lengths4 ,the air column is thrown into 
vibration either directly1 by blowing   
across a narrow opening at one end of a 
pipe as in the case of the whistle1 or  
indirectly1 by exciting vibrations in a 
thin strip of wood or metal1 called a   
reed1 which in turn communicates its    
vibrations to the air column within4    
,the shorter the air column1 the higher 

the pitch4 ,this agrees with the law of 
vibrating strings which gives high      
pitches for short lengths4              
,illustration3 ,,fig4 #ahh4--,open organ
 pipes of different pitch4  ,the pitch  
of the sound emitted by a column of air 
vibrating within a pipe varies according
 to the following laws3  #a4 ,the       
shorter the pipe1 the higher the pitch4 
#b4 ,the pitch of a note emitted by an  
open pipe is one octave higher than that
 of a closed pipe of equal length4  #c4 
,air columns vibrate in segments just as
 do strings1 and the tone emitted by a  
pipe of given length is complex1        
consisting of the fundamental and one or
 more overtones4 ,the greater the number
 of overtones present1 the richer the   
tone produced4  #bgc4 ,how the ,various 
,pitches are ,produced4 ,with a pipe of 
fixed length1 for example1 the clarinet 
7,fig4 #ahi1 #a71 different pitches are 
obtained by pressing keys which open    
holes in the tube and thus shorten or   
lengthen the vibrating air column and   

produce a rise or fall in pitch4        
,changes in pitch are also produced by  
variation in the player's breathing4 ,by
 blowing hard or gently1 the number of  
vibrations of the reed is increased or  
decreased and hence the pitch is        
altered4  ,illustration3 ,,fig4 #ahi--a1
 clarinet2 #b1 oboe2 #c1 flute4  ,in the
 oboe 7,fig4 #ahi1 #b7 the vibrating air
 column is set into motion by means of  
two thin pieces of wood or metal placed 
in the mouthpiece of the tube4          
,variations in pitch are produced as in 
the clarinet by means of stops and      
varied breathing4 ,in the flute1 the air
 is set into motion by direct blowing   
from the mouth1 as is done1 for         
instance1 when we blow into a bottle or 
key4  ,the sound given out by organ     
pipes is due to air blown across a sharp
 edge at the opening of a narrow tube4  
,the air forced across the sharp edge is
 thrown into vibration and communicates 
its vibration to the air within the     
organ pipe4 ,for different pitches1     

pipes of different lengths are used3 for
 very low pitches long1 closed pipes are
 used2 for very high pitches short1 open
 pipes are used4 ,the mechanism of the  
organ is such that pressing a key allows
 the air to rush into the communicating 
pipe and a sound is produced            
characteristic of the length of the     
pipe4  ,illustration3 ,,fig4 #aij4--a1  
horn2 #b1 trumpet2 #c1 trombone4        
,illustration3 ,,fig4 #aia4--a1         
kettledrum2 #b1 bass drum2 #c1 cymbals4 
,illustration3 ,,fig4 #aib4--,the       
seating arrangement of the ,philadelphia
 orchestra4  ,in the brass wind         
instruments such as horn1 trombone1 and 
trumpet1 the lips of the player vibrate 
and excite the air within4 ,varying     
pitches are obtained partly by the      
varying wind pressure of the musician2  
if he breathes fast1 the pitch rises2 if
 he breathes slowly1 the pitch falls4   
,all of these instruments1 however1     
except the trombone possess some valves 
which1 on being pressed1 vary the length

 of the tube and alter the pitch        
accordingly4 ,in the trombone1 valves   
are replaced by a section which slides  
in and out and shortens or lengthens the
 tube4  #bgd4 ,the ,percussion          
,instruments4 ,the percussion           
instruments1 including kettledrums1 bass
 drums1 and cymbals1 are the least      
important of all the musical            
instruments2 and are usually of service 
merely in adding to the excitement and  
general effect of an orchestra4  ,in    
orchestral music the various instruments
 are grouped somewhat as shown in       
,figure #aib4     ,,chapter ,,xxix      
,,speaking ,,and ,,hearing              
,illustration3 ,,fig4 #aic4--,the       
vibration of the vocal cords produces   
the sound of the human voice4  #bge4    
,speech4 ,the human voice is the most   
perfect of musical instruments4 ,within 
the throat1 two elastic bands are       
attached to the windpipe at the place   
commonly called ,adam's apple2 these    
flexible bands have received the name of

 vocal cords1 since by their vibration  
all speech is produced4 ,in ordinary    
breathing1 the cords are loose and are  
separated by a wide opening through     
which air enters and leaves the lungs4  
,when we wish to speak1 muscular effort 
stretches the cords1 draws them closer  
together1 and reduces the opening       
between them to a narrow slit1 as in the
 case of the organ pipe4 ,if air from   
the lungs is sent through the narrow    
slit1 the vocal cords or bands are      
thrown into rapid vibration and produce 
sound4 ,the pitch of the sound depends  
upon the tension of the stretched       
membranes1 and since this can be altered
 by muscular action1 the voice can be   
modulated at will4 ,in times of         
excitement1 when the muscles of the body
 in general are in a state of great     
tension1 the pitch is likely to be      
uncommonly high4  ,women's voices are   
higher than men's because the vocal     
cords are shorter and finer2 even though
 muscular tension is relaxed and the    

cords are made looser1 the pitch of a   
woman's voice does not fall so low as   
that of a man's voice since his cords   
are naturally much longer and coarser4  
,the difference between a soprano and an
 alto voice is merely one of length and 
tension of the vocal cords4  ,successful
 singing is possible only when the vocal
 cords are readily flexible and when the
 singer can supply a steady1 continuous 
blast of air through the slit between   
the cords4 ,the hoarseness which        
frequently accompanies cold in the head 
is due to the thickening of the mucous  
membrane and to the filling up of the   
slit with mucus1 because when this      
happens1 the vocal cords cannot vibrate 
properly4  ,the sounds produced by the  
vocal cords are transformed into speech 
by the help of the tongue and lips1     
which modify the shape of the mouth     
cavity4 ,some of the lower animals have 
a speaking apparatus similar to our own1
 but they cannot perfectly transform    
sound into speech4 ,the birds use their 

vocal cords to beautiful advantage in   
singing1 far surpassing us in many ways1
 but the power of speech is lacking4    
#bgf4 ,the ,ear4 ,the pulses created in 
the air by a sounding body are received 
by the ear and the impulses which they  
impart to the auditory nerve pass to the
 brain and we become conscious of a     
sound4 ,the ear is capable of marvelous 
discrimination and accuracy4 ,in order  
to form an idea of the extent of this   
power imagine an auditor in a large     
music hall where a full band and chorus 
are performing4 ,here1 there are sounds 
mingled together of all varieties of    
pitch1 loudness1 and quality2 stringed  
instruments1 wood instruments1 brass    
instruments1 and voices1 of many        
different kinds4 ,and in addition to    
these there may be all sorts of         
accidental and irregular sounds and     
noises1 such as the trampling and       
shuffling of feet1 the hum of voices1   
the rustle of dress1 the creaking of    
doors1 and many others4 ,now it must be 

remembered that the only means the ear  
has of becoming aware of these          
simultaneous sounds is by the           
condensations and rarefactions which    
reach it2 and yet when the sound wave   
meets the nerves1 the nerves single out 
each individual element1 and convey to  
the mind of the hearer1 not only the    
tones and notes of every instrument in  
the orchestra1 but the character of     
every accidental noise2 and almost as   
distinctly as if each single tone or    
noise were heard alone4--,,pole4        
,illustration3 ,,fig4 #aid4--,the ear4  
#bgg4 ,the ,structure of the ,ear4 ,the 
external portion of the ear acts as a   
funnel for catching sound waves and     
leading them into the canal1 where they 
strike upon the ear drum1 or tympanic   
membrane1 and throw it into vibration4  
,unless the ear drum is very flexible   
there cannot be perfect response to the 
sound waves which fall upon it2 for this
 reason1 the glands of the canal secrete
 a wax which moistens the membrane and  

keeps it flexible4 ,lying directly back 
of the tympanic membrane is a cavity    
filled with air which enters by the     
,eustachian tube2 from the throat air   
enters the ,eustachian tube1 moves along
 it1 and passes into the ear cavity4    
,the dull crackling noise noticed in the
 ear when one swallows is due to the    
entrance and exit of air in the tube4   
,several small bones stretch across the 
upper portion of the cavity and make a  
bridge1 so to speak1 from the ear drum  
to the far wall of the cavity4 ,it is by
 means of these three bones that the    
vibrations of the ear drum are          
transmitted to the inner wall of the    
cavity4 ,behind the first cavity is a   
second cavity so complex and irregular  
that it is called the labyrinth of the  
ear4 ,this labyrinth is filled with a   
fluid in which are spread out the       
delicate sensitive fibers of the        
auditory nerves2 and it is to these that
 the vibrations must be transmitted4    
,suppose a note of #hjj vibrations per  

second is sung4 ,then #hjj pulses of air
 will reach the ear each second1 and the
 ear drum1 being flexible1 will respond 
and will vibrate at the same rate4 ,the 
vibration of the ear drum will be       
transmitted by the three bones and the  
fluid to the fibers of the auditory     
nerves4 ,the impulses imparted to the   
auditory nerve reach the brain and in   
some unknown way are translated into    
sound4  #bgh4 ,care of the ,ear4 ,most  
catarrhal troubles are accompanied by an
 oversupply of mucus which frequently   
clogs up the ,eustachian tube and       
produces deafness4 ,for the same reason1
 colds and sore throat sometimes induce 
temporary deafness4  ,the wax of the ear
 is essential for flexibility of the ear
 drum2 if an extra amount accumulates1  
it can be got rid of by bathing the ear 
in hot water1 since the heat will melt  
the wax4 ,the wax should never be picked
 out with pin or sharp object except by 
a physician1 lest injury be done to the 
tympanic membrane4  #bgi4 ,the          

,phonograph4 ,the invention of the      
phonograph by ,edison in #ahgh marked a 
new era in the popularity and           
dissemination of music4 ,up to that     
time1 household music was limited to    
those who were rich enough to possess a 
real musical instrument1 and who in     
addition had the understanding and the  
skill to use the instrument4 ,the       
invention of the phonograph has brought 
music to thousands of homes possessed of
 neither wealth nor skill4 ,that the    
music reproduced by a phonograph is not 
always of the highest order does not1 in
 the least1 detract from the interest   
and wonder of the instrument4 ,it can   
reproduce what it is called upon to     
reproduce1 and if human nature demands  
the commonplace1 the instrument will be 
made to satisfy the demand4 ,on the     
other hand1 speeches of famous men1     
national songs1 magnificent opera       
selections1 and other pleasing and      
instructive productions can be          
reproduced fairly accurately4 ,in this  

way the phonograph1 perhaps more than   
any other recent invention1 can carry to
 the shut-ins a lively glimpse of the   
outside world and its doings4           
,illustration3 ,,fig4 #aie4--;,a        
vibrating tuning fork traces a curved   
line on smoked glass4  ,the phonograph  
consists of a cylinder or disk of wax   
upon which the vibrations of a sensitive
 diaphragm are recorded by means of a   
fine metal point4 ,the action of the    
pointer in reporting the vibrations of a
 diaphragm is easily understood by      
reference to a tuning fork4 ,fasten a   
stiff bristle to a tuning fork by means 
of wax1 allowing the end of the point to
 rest lightly upon a piece of smoked    
glass4 ,if the glass is drawn under the 
bristle a straight line will be         
scratched on the glass1 but if the      
tuning fork is struck so that the prongs
 vibrate back and forth1 then the       
straight line changes to a wavy line and
 the type of wavy line depends upon the 
fork used4  ,in the phonograph1 a       

diaphragm replaces the tuning fork and a
 cylinder 7or a disk7 coated with wax   
replaces the glass plate4 ,when the     
speaker talks or the singer sings1 his  
voice strikes against a delicate        
diaphragm and throws it into vibration1 
and the metal point attached to it      
traces on the wax of a moving cylinder a
 groove of varying shape and appearance 
called the record4 ,every variation in  
the speaker's voice is repeated in the  
vibrations of the metal disk and hence  
in the minute motion of the pointer and 
in the consequent record on the         
cylinder4 ,the record thus made can be  
placed in any other phonograph and if   
the metal pointer of this new phonograph
 is made to pass over the tracing1 the  
process is reversed and the speaker's   
voice is reproduced4 ,the sound given   
out in the this way is faint and weak1  
but can be strengthened by means of a   
trumpet attached to the phonograph4     
,illustration3 ,,fig4 #aif4--;,a        
phonograph4 ,in this machine the        

cylinder is replaced by a revolving     
disk4     ,,chapter ,,xxx  ,,electricity
   #bhj4 ,many animals possess the five 
senses1 but only man possesses          
constructive1 creative power1 and is    
able to build on the information gained 
through the senses4 ,it is the          
constructive1 creative power which      
raises man above the level of the beast 
and enables him to devise and fashion   
wonderful inventions4 ,among the most   
important of his inventions are those   
which relate to electricity2 inventions 
such as trolley car1 elevator1          
automobile1 electric light1 the         
telephone1 the telegraph4 ,bell1 by his 
superior constructive ability1 made     
possible the practical use of the       
telephone1 and ,marconi that of wireless
 telegraphy4 ,to these inventions might 
be added many others which have         
increased the efficiency and production 
of the business world and have decreased
 the labor and strain of domestic life4 
,illustration3 ,,fig4 #aig4--;,a simple 

electric cell4  #bha4 ,electricity as   
first ,obtained by ,man4 ,until modern  
times the only electricity known to us  
was that of the lightning flash1 which  
man could neither hinder nor make4 ,but 
in the year #ahjj1 electricity in the   
form of a weak current was obtained by  
,volta of ,italy in a very simple way2  
and even now our various electric       
batteries and cells are but a           
modification of that used by ,volta and 
called a voltaic cell4 ,a strip of      
copper and a strip of zinc are placed in
 a glass containing dilute sulphuric    
acid1 a solution composed of oxygen1    
hydrogen1 sulphur1 and water4 ,as soon  
as the plates are immersed in the acid  
solution1 minute bubbles of gas rise    
from the zinc strip and it begins to    
waste away slowly4 ,the solution        
gradually dissolves the zinc and at the 
same time gives up some of the hydrogen 
which it contains2 but it has little or 
no effect on the copper1 since there is 
no visible change in the copper strip4  

,if1 now1 the strips are connected by   
means of metal wires1 the zinc wastes   
away rapidly1 numerous bubbles of       
hydrogen pass over to the copper strip  
and collect on it1 and a current of     
electricity flows through the connecting
 wires4 ,evidently1 the source of the   
current is the chemical action between  
the zinc and the liquid4  ,mere         
inspection of the connecting wire will  
not enable us to detect that a current  
is flowing1 but there are various ways  
in which the current makes itself       
evident4 ,if the ends of the wires      
attached to the strips are brought in   
contact with each other and then        
separated1 a faint spark passes1 and if 
the ends are placed on the tongue1 a    
twinge is felt4  #bhb4 ,experiments     
which grew out of the ,voltaic ,cell4   
,since chemical action on the zinc is   
the source of the current1 it would seem
 reasonable to expect a current if the  
cell consisted of two zinc plates       
instead of one zinc plate and one copper

 plate4 ,but when the copper strip is   
replaced by a zinc strip so that the    
cell consists of two similar plates1 no 
current flows between them4 ,in this    
case1 chemical action is expended in    
heat rather than in the production of   
electricity and the liquid becomes hot4 
,but if carbon and zinc are used1 a     
current is again produced1 the zinc     
dissolving away as before1 and bubbles  
collecting on the carbon plate4 ,by     
experiment it has been found that many  
different metals may be employed in the 
construction of an electric cell2 for   
example1 current may be obtained from a 
cell made with a zinc plate and a       
platinum plate1 or from a cell made with
 a lead plate and a copper plate4 ,then1
 too1 some other chemical1 such as      
bichromate of potassium1 or ammonium    
chloride1 may be used instead of dilute 
sulphuric acid4  ,almost any two        
different substances will1 under proper 
conditions1 give a current1 but the     
strength of the current is in some cases

 so weak as to be worthless for         
practical use1 such as telephoning1 or  
ringing a door bell4 ,what is wanted is 
a strong1 steady current1 and our choice
 of material is limited to the          
substances which will give this result4 
,zinc and lead can be used1 but the     
current resulting is weak and feeble1   
and for general use zinc and carbon are 
the most satisfactory4  #bhc4           
,electrical ,terms4 ,the plates or      
strips used in making an electric cell  
are called electrodes2 the zinc is      
called the negative electrode 7-71 and  
the carbon the positive electrode 772   
the current is considered to flow       
through the wire from the  to           
the-electrode4 ,as a rule1 each         
electrode has attached to it a binding  
post to which wires can be quickly      
fastened4  ,the power that causes the   
current is called the electromotive     
force1 and the value of the             
electromotive force1 generally written  
,e4,m4,f41 of a cell depends upon the   

materials used4  ,when the cell consists
 of copper1 zinc1 and dilute sulphuric  
acid1 the electromotive force has a     
definite value which is always the same 
no matter what the size or shape of the 
cell4 ,but the ,e4,m4,f4 has a decidedly
 different value in a cell composed of  
iron1 copper1 and chromic acid4 ,each   
combination of material has its own     
specific electromotive force4  #bhd4    
,the ,disadvantage of a ,simple ,cell4  
,when the poles of a simple voltaic cell
 are connected by a wire1 the current   
thus produced slowly diminishes in      
strength and1 after a short time1       
becomes feeble4 ,examination of the cell
 shows that the copper plate is covered 
with hydrogen bubbles4 ,if1 however1    
these bubbles are completely brushed    
away by means of a rod or stick1 the    
current strength increases1 but as the  
bubbles again gather on the  electrode  
the current strength diminishes1 and    
when the bubbles form a thick film on   
the copper plate1 the current is too    

weak to be of any practical value4 ,the 
film of bubbles weakens the current     
because it practically substitutes a    
hydrogen plate for a copper plate1 and  
we saw in ,section #bhb that a change in
 any one of the materials of which a    
cell is composed changes the current4   
,this weakening of the current can be   
reduced mechanically by brushing away   
the bubbles as soon as they are formed2 
or chemically1 by surrounding the copper
 plate with a substance which will      
combine with the free hydrogen and      
prevent it from passing onward to the   
copper plate4  ,illustration3 ,,fig     
#aih4 ,the gravity cell4  ,in           
practically all cells1 the chemical     
method is used in preference to the     
mechanical one4 ,the numerous types of  
cells in daily use differ chiefly in the
 devices employed for preventing the    
formation of hydrogen bubbles1 or for   
disposing of them when formed4 ,one of  
the best-known cells in which weakening 
of the current is prevented by chemical 

means is the so-called gravity cell4    
#bhe4 ,the ,gravity ,cell4 ,a large1    
irregular copper electrode is placed in 
the bottom of a jar 7,fig4 #aih71 and   
completely covered with a saturated     
solution of copper sulphate4 ,then a    
large1 irregular zinc electrode is      
suspended from the top of the jar1 and  
is completely covered with dilute       
sulphuric acid which does not mix with  
the copper sulphate1 but floats on the  
top of it like oil on water4 ,the       
hydrogen formed by the chemical action  
of the dilute sulphuric acid on the zinc
 moves toward the copper electrode1 as  
in the simple voltaic cell4 ,it does not
 reach the electrode1 however1 because1 
when it comes in contact with the copper
 sulphate1 it changes places with the   
copper there1 setting it free1 but      
itself entering into the solution4 ,the 
copper freed from the copper sulphate   
solution travels to the copper          
electrode1 and is deposited on it in a  
clean1 bright layer4 ,instead of a      

deposit of hydrogen there is a deposit  
of copper1 and falling off in current is
 prevented4  ,the gravity cell is cheap1
 easy to construct1 and of constant     
strength1 and is in almost universal use
 in telegraphic work4 ,practically all  
small railroad stations and local       
telegraph offices use these cells4      
,illustration3 ,,fig4 #aii4--;,a dry    
cell4  #bhf4 ,dry ,cells4 ,the gravity  
cell1 while cheap and effective1 is     
inconvenient for general use1 owing to  
the fact that it cannot be easily       
transported1 and the dry cell has       
largely supplanted all others1 because  
of the ease with which it can be taken  
from place to place4 ,this cell consists
 of a zinc cup1 within which is a carbon
 rod2 the space between the cup and rod 
is packed with a moist paste containing 
certain chemicals4 ,the moist paste     
takes the place of the liquids used in  
other cells4  ,illustration3 ,,fig4     
#bjj4--;,a battery of three cells4      
#bhg4 ,a ,battery of ,cells4 ,the       

electromotive force of one cell may not 
give a current strong enough to ring a  
door bell or to operate a telephone4    
,but by using a number of cells1 called 
a battery1 the current may be increased 
to almost any desired strength4 ,if     
three cells are arranged as in ,figure  
#bjj1 so that the copper of one cell is 
connected with the zinc of another cell1
 the electromotive force of the battery 
will be three times as great as the     
,e4,m4,f4 of a single cell4 ,if four    
cells are arranged in the same way1 the 
,e4,m4,f4 of the battery is four times  
as great as the ,e4,m4,f4 of a single   
cell2 when five cells are combined1 the 
resulting ,e4,m4,f4 is five times as    
great4     ,,chapter ,,xxxi  ,,some     
,,uses ,,of ,,electricity   #bhh4 ,heat4
 ,any one who handles electric wires    
knows that they are more or less heated 
by the currents which flow through them4
 ,if three cells are arranged as in     
,figure #bjj and the connecting wire is 
coarse1 the heating of the wire is      

scarcely noticeable2 but if a shorter   
wire of the same kind is used1 the heat 
produced is slightly greater2 and if the
 coarse wire is replaced by a short1    
fine wire1 the heating of the wire      
becomes very marked4 ,we are accustomed 
to say that a wire offers resistance to 
the flow of a current2 that is1 whenever
 a current meets resistance1 heat is    
produced in much the same way as when   
mechanical motion meets an obstacle and 
spends its energy in friction4 ,the flow
 of electricity along a wire can be     
compared to the flow of water through   
pipes3 a small pipe offers a greater    
resistance to the flow of water than a  
large pipe2 less water can be forced    
through a small pipe than through a     
large pipe1 but the friction of the     
water against the sides of the small    
pipe is much greater than in the large  
one4  ,so it is with the electric       
current4 ,in fine wires the resistance  
to the current is large and the energy  
of the battery is expended in heat      

rather than in current4 ,if the heat    
thus produced is very great1 serious    
consequences may arise2 for example1 the
 contact of a hot wire with wall paper  
or dry beams may cause fire4 ,insurance 
companies demand that the wires used in 
wiring a building for electric lights be
 of a size suitable to the current to be
 carried1 otherwise they will not take  
the risk of insurance4 ,the greater the 
current to be carried1 the coarser is   
the wire required for safety4  #bhi4    
,electric ,stoves4 ,it is often         
desirable to utilize the electric       
current for the production of heat4 ,for
 example1 trolley cars are heated by    
coils of wire under the seats4 ,the     
coils offer so much resistance to the   
passage of a strong current through them
 that they become heated and warm the   
cars4  ,illustration3 ,,fig4 #bja4--;,an
 electric iron on a metal stand4  ,some 
modern houses are so built that         
electricity is received into them from  
the great plants where it is generated1 

and by merely turning a switch or       
inserting a plug1 electricity is        
constantly available4 ,in consequence1  
many practical applications of          
electricity are possible1 among which   
are flatiron and toaster4               
,illustration3 ,,fig4 #bjb4--,the fine  
wires are strongly heated by the current
 which flows through them4  ,within the 
flatiron 7,fig4 #bja71 is a mass of fine
 wire coiled as shown in ,figure #bjb2  
as soon as the iron is connected with   
the house supply of electricity1 current
 flows through the fine wire which thus 
becomes strongly heated and gives off   
heat to the iron4 ,the iron1 when once  
heated1 retains an even temperature as  
long as the current flows1 and the      
laundress is1 in consequence1 free from 
the disadvantages of a slowly cooling   
iron1 and of frequent substitution of a 
warm iron for a cold one4 ,electric     
irons are particularly valuable in      
summer1 because they eliminate the      
necessity for a strong fire1 and spare  

the housewife intense heat4 ,in         
addition1 the user is not confined to   
the laundry1 but is free to seek the    
coolest part of the house1 the only     
requisite being an electrical           
connection4  ,illustration3 ,,fig4      
#bjc4--;,bread can be toasted by        
electricity4  ,the toaster 7,fig4 #bjc7 
is another useful electrical device1    
since by means of it toast may be made  
on a dining table or at a bedside4 ,the 
small electrical stove1 shown in ,figure
 #bjd1 is similar in principle to the   
flatiron1 but in it the heating coil is 
arranged as shown in ,figure #bje4 ,to  
the physician electric stoves are       
valuable1 since his instruments can be  
sterilized in water heated by the stove2
 and that without fuel or odor of gas4  
,a convenient device is seen in the     
heating pad 7,fig4 #bjf71 a substitute  
for a hot water bag4 ,embedded in some  
soft thick substance are the insulated  
wires in which heat is to be developed1 
and over this is placed a covering of   

felt4  ,illustration3 ,,fig4 #bjd4--;,an
 electric stove4  #bij4 ,electric       
,lights4 ,the incandescent bulbs which  
illuminate our buildings consist of a   
fine1 hairlike thread inclosed in a     
glass bulb from which the air has been  
removed4 ,when an electric current is   
sent through the delicate filament1 it  
meets a strong resistance4 ,the heat    
developed in overcoming the resistance  
is so great that it makes the filament a
 glowing mass4 ,the absence of air      
prevents the filament from burning1 and 
it merely glows and radiates the light4 
,illustration3 ,,fig4 #bje4--,the       
heating element in the electric stove4  
#bia4 ,blasting4 ,until recently1       
dynamiting was attended with serious    
danger1 owing to the fact that the      
person who applied the torch to the fuse
 could not make a safe retreat before   
the explosion4 ,now a fine wire is      
inserted in the fuse1 and when          
everything is in readiness1 the ends of 
the wire are attached to the poles of a 

distant battery and the heat developed  
in the wire ignites the fuse4           
,illustration3 ,,fig4 #bjf4--;,an       
electric pad serves the same purpose as 
a hot water bag4  #bib4 ,welding of     
,metals4 ,metals are fused and welded by
 the use of the electric current4 ,the  
metal pieces which are to be welded are 
pressed together and a powerful current 
is passed through their junction4 ,so   
great is the heat developed that the    
metals melt and fuse1 and on cooling    
show perfect union4  #bic4 ,chemical    
,effects4 ,the ,plating of ,gold1       
,silver1 and ,other ,metals4 ,if strips 
of lead or rods of carbon are connected 
to the terminals of an electric cell1 as
 in ,figure #bjh1 and are then dipped   
into a solution of copper sulphate1 the 
strip in connection with the negative   
terminal of the cell soon becomes thinly
 plated with a coating of copper4 ,if a 
solution of silver nitrate is used in   
place of the copper sulphate1 the       
coating formed will be of silver instead

 of copper4 ,so long as the current     
flows and there is any metal present in 
the solution1 the coating continues to  
form on the negative electrode1 and     
becomes thicker and thicker4            
,illustration3 ,,fig4 #bjg4--;,an       
incandescent electric bulb4  ,the       
process by which metal is taken out of  
solution1 as silver out of silver       
nitrate and copper out of copper        
sulphate1 and is in turn deposited as a 
coating on another substance1 is called 
electroplating4 ,an electric current can
 separate a liquid into some of its     
various constituents and to deposit one 
of the metal constituents on the        
negative electrode4  ,illustration3     
,,fig4 #bjh4--;,carbon rods in a        
solution of copper sulphate4  ,since    
copper is constantly taken out of the   
solution of copper sulphate for deposit 
upon the negative electrode1 the amount 
of copper remaining in the solution     
steadily decreases1 and finally there is
 none of it left for deposit4 ,in order 

to overcome this1 the positive electrode
 should be made of the same metal as    
that which is to be deposited4 ,the     
positive metal electrode gradually      
dissolves and replaces the metal lost   
from the solution by deposit and        
electroplating can continue as long as  
any positive electrode remains4         
,illustration3 ,,fig4 #bji4--,plating   
spoons by electricity4  ,practically all
 silver1 gold1 and nickel plating is    
done in this way2 machine1 bicycle1 and 
motor attachments are not solid1 but are
 of cheaper material electrically plated
 with nickel4 ,when spoons are to be    
plated1 they are hung in a bath of      
silver nitrate side by side with a thick
 slab of pure silver1 as in ,figure     
#bji4 ,the spoons are connected with the
 negative terminal of the battery1 while
 the slab of pure silver is connected   
with the positive terminal of the same  
battery4 ,the length of time that the   
current flows determines the thickness  
of the plating4  #bid4 ,how ,pure ,metal

 is obtained from ,ore4 ,when ore is    
mined1 it contains in addition to the   
desired metal many other substances4 ,in
 order to separate out the desired      
metal1 the ore is placed in some        
suitable acid bath1 and is connected    
with the positive terminal of a battery1
 thus taking the place of the silver    
slab in the last ,section4 ,when current
 flows1 any pure metal which is present 
is dissolved out of the ore and is      
deposited on a convenient negative      
electrode1 while the impurities remain  
in the ore or drop as sediment to the   
bottom of the vessel4 ,metals separated 
from the ore by electricity are called  
electrolytic metals and are the purest  
obtainable4  #bie4 ,printing4 ,the      
ability of the electric current to      
decompose a liquid and to deposit a     
metal constituent has practically       
revolutionized the process of printing4 
,formerly1 type was arranged and        
retained in position until the required 
number of impressions had been made1 the

 type meanwhile being unavailable for   
other uses4 ,moreover1 the printing of a
 second edition necessitated practically
 as great labor as did the first        
edition1 the type being necessarily set 
afresh4 ,now1 however1 the type is set  
up and a mold of it is taken in wax4    
,this mold is coated with graphite to   
make it a conductor and is then         
suspended in a bath of copper sulphate1 
side by side with a slab of pure copper4
 ,current is sent through the solution  
as described in ,section #bic1 until a  
thin coating of copper has been         
deposited on the mold4 ,the mold is then
 taken from the bath1 and the wax is    
replaced by some metal which gives      
strength and support to the thin copper 
plate4 ,from this copper plate1 which is
 an exact reproduction of the original  
type1 many thousand copies can be       
printed4 ,the plate can be preserved and
 used from time to time for later       
editions1 and the original type can be  
put back into the cases and used again4 

,,chapter ,,xxxii  ,,modern ,,electrical
 ,,inventions   #bif4 ,an ,electric     
,current acts like a ,magnet4 ,in order 
to understand the action of the electric
 bell1 we must consider a third effect  
which an electric current can cause4    
,connect some cells as shown in ,figure 
#bjj and close the circuit through a    
stout heavy copper wire1 dipping a      
portion of the wire into fine iron      
filings4 ,a thick cluster of filings    
will adhere to the wire 7,fig4 #baj71   
and will continue to cling to it so long
 as the current flows4 ,if the current  
is broken1 the filings fall from the    
wire1 and only so long as the current   
flows through the wire does the wire    
have power to attract iron filings4 ,an 
electric current makes a wire equivalent
 to a magnet1 giving it the power to    
attract iron filings4  ,illustration3   
,,fig4 #baj4--;,a wire carrying current 
attracts iron filings4  ,illustration3  
,,fig4 #baa4--;,a loosely wound coil of 
wire4  ,although such a straight current

 bearing wire attracts iron filings1 its
 power of attraction is very small2 but 
its magnetic strength can be increased  
by coiling as in ,figure #baa4 ,such an 
arrangement of wire is known as a helix 
or solenoid1 and is capable of lifting  
or pulling larger and more numerous     
filings and even good-sized pieces of   
iron1 such as tacks4 ,filings do not    
adhere to the sides of the helix1 but   
they cling in clusters to the ends of   
the coil4 ,this shows that the ends of  
the helix have magnetic power but not   
the sides4  ,if a soft iron nail 7,fig4 
#bab7 or its equivalent is slipped      
within the coil1 the lifting and        
attractive power of the coil is         
increased1 and comparatively heavy      
weights can be lifted4  ,illustration3  
,,fig4 #bab4--;,coil and soft iron rod4 
,a coil of wire traversed by an electric
 current and containing a core of soft  
iron has the power of attracting and    
moving heavy iron objects2 that is1 it  
acts like a magnet4 ,such an arrangement

 is called an electromagnet4 ,as soon as
 the current ceases to flow1 the        
electromagnet loses its magnetic power  
and becomes merely iron and wire without
 magnetic attraction4  ,if many cells   
are used1 the strength of the           
electromagnet is increased1 and if the  
coil is wound closely1 as in ,figure    
#bac1 instead of loosely1 as in ,figure 
#baa1 the magnetic strength is still    
further increased4 ,the strength of any 
electromagnet depends upon the number of
 coils wound on the iron core and upon  
the strength of the current which is    
sent through the coils4  ,illustration3 
,,fig4 #bac4--;,an electromagnet4       
,illustration3 ,,fig4 #bad4--;,a        
horseshoe electromagnet is powerful     
enough to support heavy weights4  ,to   
increase the strength of the            
electromagnet still further1 the        
so-called horseshoe shape is used 7,fig4
 #bad74 ,in such an arrangement there is
 practically the strength of two        
separate electromagnets4  #big4 ,the    

,electric ,bell4 ,the ringing of the    
electric bell is due to the attractive  
power of an electromagnet4 ,by the      
pushing of a button 7,fig4 #bae7        
connection is made with a battery1 and  
current flows through the wire wound on 
the iron spools1 and further to the     
screw ,p which presses against the soft 
iron strip or armature ,s2 and from ,s  
the current flows back to the battery4  
,as soon as the current flows1 the coils
 become magnetic and attract the soft   
iron armature1 drawing it forward and   
causing the clapper to strike the bell4 
,in this position1 ,s no longer touches 
the screw ,p1 and hence there is no     
complete path for the electricity1 and  
the current ceases4 ,but the attractive1
 magnetic power of the coils stops as   
soon as the current ceases2 hence there 
is nothing to hold the armature down1   
and it flies back to its former         
position4 ,in doing this1 however1 the  
armature makes contact at ,p through the
 spring1 and the current flows once     

more2 as a result the coils again become
 magnets1 the armature is again drawn   
forward1 and the clapper again strikes  
the bell4 ,but immediately afterwards   
the armature springs backward and makes 
contact at ,p and the entire operation  
is repeated4 ,so long as we press the   
button this process continues producing 
what sounds like a continuous jingle2 in
 reality the clapper strikes the bell   
every time a current passes through the 
electromagnet4  ,illustration3 ,,fig4   
#bae4--,the electric bell4  #bih4 ,the  
,push ,button4 ,the push button is an   
essential part of every electric bell1  
because without it the bell either would
 not ring at all1 or would ring         
incessantly until the cell was          
exhausted4 ,when the push button is     
free1 as in ,figure #baf1 the cell      
terminals are not connected in an       
unbroken path1 and hence the current    
does not flow4 ,when1 however1 the      
button is pressed1 the current has a    
complete path1 provided there is the    

proper connection at ,s4 ,that is1 the  
pressure on the push button permits     
current to flow to the bell4 ,the flow  
of this current then depends solely upon
 the connection at ,s1 which is         
alternately made and broken1 and in this
 way produces sound4  ,illustration3    
,,fig4 #baf4--,push button4  ,the sign  
,bell out of order is usually due to the
 fact that the battery is either        
temporarily or permanently exhausted4   
,in warm weather the liquid in the cell 
may dry up and cause stoppage of the    
current4 ,if fresh liquid is poured into
 the vessel so that the chemical action 
of the acid on the zinc is renewed1 the 
current again flows4 ,another           
explanation of an out-of-order bell is  
that the liquid may have eaten up all   
the zinc2 if this is the case1 the      
insertion of a fresh strip of zinc will 
remove the difficulty and the current   
will flow4 ,if dry cells are used1 there
 is no remedy except in the purchase of 
new cells4  #bii4 ,how ,electricity may 

be lost to ,use4 ,in the electric bell1 
we saw that an air gap at the push      
button stopped the flow of electricity4 
,if we cut the wire connecting the poles
 of a battery1 the current ceases       
because an air gap intervenes and       
electricity does not readily pass       
through air4 ,many substances besides   
air stop the flow of electricity4 ,if a 
strip of glass1 rubber1 mica1 or        
paraffin is introduced anywhere in a    
circuit1 the current ceases4 ,if a metal
 is inserted in the gap1 the current    
again flows4 ,substances which1 like an 
air gap1 interfere with the flow of     
electricity are called non-conductors1  
or1 more commonly1 insulators4          
,substances which1 like the earth1 the  
human body1 and all other moist objects1
 conduct electricity are conductors4 ,if
 the telephone and electric light wires 
in our houses were not insulated by a   
covering of thread1 or cloth1 or other  
non conducting material1 the electricity
 would escape into surrounding objects  

instead of flowing through the wire and 
producing sound and light4  ,in our city
 streets1 the overhead wires are        
supported on glass knobs or are closely 
wrapped1 in order to prevent the escape 
of electricity through the poles to the 
ground4 ,in order to have a steady1     
dependable current1 the wire carrying   
the current must be insulated4  ,lack of
 insulation means not only the loss of  
current for practical uses1 but also    
serious consequences in the event of the
 crossing of current-bearing wires4 ,if 
two wires properly insulated touch each 
other1 the currents flow along their    
respective wires unaltered2 if1 however1
 two uninsulated wires touch1 some of   
the electricity flows from one to the   
other4 ,heat is developed as a result of
 this transference1 and the heat thus   
developed is sometimes so great that    
fire occurs4 ,for this reason1 wires are
 heavily insulated and extra protection 
is provided at points where numerous    
wires touch or cross4  ,conductors and  

insulators are necessary to the         
efficient and economic flow of a        
current1 the insulator preventing the   
escape of electricity and lessening the 
danger of fire1 and the conductor       
carrying the current4  #cjj4 ,the       
,telegraph4 ,telegraphy is the process  
of transmitting messages from place to  
place by means of an electric current4  
,the principle underlying the action of 
the telegraph is the principle upon     
which the electric bell operates2       
namely1 that a piece of soft iron       
becomes a magnet while a current flows  
around it1 but loses its magnetism as   
soon as the current ceases4  ,in the    
electric bell1 the electromagnet1       
clapper1 push button1 and battery are   
relatively near1--usually all are       
located in the same building2 while in  
the telegraph the current may travel    
miles before it reaches the             
electromagnet and produces motion of the
 armature4  ,illustration3 ,,fig4       
#bag4--;,diagram of the electric        

telegraph4  ,the fundamental connections
 of the telegraph are shown in ,figure  
#bag4 ,if the key ,k is pressed down by 
an operator in ,philadelphia1 the       
current from the battery 7only one cell 
is shown for simplicity7 flows through  
the line to ,new ,york1 passes through  
the electromagnet ,m1 and thence back to
 ,philadelphia4 ,as long as the key ,k  
is pressed down1 the coil ,m acts as a  
magnet and attracts and holds fast the  
armature ,a2 but as soon as ,k is       
released1 the current is broken1 ,m     
loses its magnetism1 and the armature is
 pulled back by the spring ,d4 ,by a    
mechanical device1 tape is drawn        
uniformly under the light marker ,p     
attached to the armature4 ,if ,k is     
closed for but a short time1 the        
armature is drawn down for but a short  
interval1 and the marker registers a dot
 on the tape4 ,if ,k is closed for a    
longer time1 a short dash is made by the
 marker1 and1 in general1 the length of 
time that ,k is closed determines the   

length of the marks recorded on the     
tape4 ,the telegraphic alphabet consists
 of dots and dashes and their various   
combinations1 and hence an              
interpretation of the dot and dash      
symbols recorded on the tape is all that
 is necessary for the receiving of a    
telegraphic message4  ,the ,morse       
telegraphic code1 consisting of dots1   
dashes1 and spaces1 is given in ,figure 
#bah4  ,illustration3    ,a 4-   ,h 4444
 ,o 4 4   ,u 44-      ,b -444 ,i 44   ,p
 44444 ,v 444-     ,c 44 4 ,j -4-4 ,q   
44-4  ,w 4--      ,d -44  ,k -4-  ,r 4  
44  ,x 4-44     ,e 4    ,l ---  ,s 444  
,y 44 44    ,f 4-4  ,m - -  ,t -     ,z 
444 4    ,g --4  ,n -4                  
,,fig4 #bah4--,the ,morse telegraphic   
code4  ,the telegraph is now such a     
universal means of communication between
 distant points that one wonders how    
business was conducted before its       
invention in #ahcb by ,s4,f4,b4 ,morse4 
,illustration3 ,,fig4 #bai4--,the       
sounder4  #cja4 ,improvements4 ,the     

,sounder4 ,shortly after the invention  
of telegraphy1 operators learned that   
they could read the message by the click
 of the marker against a metal rod which
 took the place of the tape4 ,in        
practically all telegraph offices of the
 present day the old-fashioned tape is  
replaced by the sounder1 shown in       
,figure #bai4 ,when current flows1 a    
lever1 ,l1 is drawn down by the         
electromagnet and strikes against a     
solid metal piece with a click2 when the
 current is broken1 the lever springs   
upward1 strikes another metal piece and 
makes a different click4 ,it is clear   
that the working of the key which starts
 and stops the current in this line will
 be imitated by the motion and the      
resulting clicks of the sounder4 ,by    
means of these varying clicks of the    
sounder1 the operator interprets the    
message4  ,illustration3 ,,fig4         
#bbj4--;,diagram of a modern telegraph  
system4  ,the ,relay4 ,when a telegraph 
line is very long1 the resistance of the

 wire is great1 and the current which   
passes through the electromagnet is     
correspondingly weak1 so feeble indeed  
that the armature must be made very thin
 and light in order to be affected by   
the makes and breaks in the current4    
,the clicks of an armature light enough 
to respond to the weak current of a long
 wire are too faint to be recognized by 
the ear1 and hence in such long circuits
 some device must be introduced whereby 
the effect is increased4 ,this is       
usually done by installing at each      
station a local battery and a very      
delicate and sensitive electromagnet    
called the relay4 ,under these          
conditions the current of the main line 
is not sent through the sounder1 but    
through the relay which opens and closes
 a local battery in connection with the 
strong sounder4 ,for example1 the relay 
is so arranged that current from the    
main line runs through it exactly as it 
runs through ,m in ,figure #bag4 ,when  
current is made1 the relay attracts an  

armature1 which thereby closes a circuit
 in a local battery and thus causes a   
click of the sounder4 ,when the current 
in the main line is broken1 the relay   
loses its magnetic attraction1 its      
armature springs back1 connection is    
broken in the local circuit1 and the    
sounder responds by allowing its        
armature to spring back with a sharp    
sound4  #cjb4 ,the ,earth an ,important 
,part of a ,telegraphic ,system4 ,we    
learned in ,section #bii that           
electricity could flow through many     
different substances1 one of which was  
the earth4 ,in all ordinary telegraph   
lines1 advantage is taken of this fact  
to utilize the earth as a conductor and 
to dispense with one wire4 ,originally  
two wires were used1 as in ,figure #bag2
 then it was found that a railroad track
 could be substituted for one wire1 and 
later that the earth itself served      
equally well for a return wire4 ,the    
present arrangement is shown in ,figure 
#bbj1 where there is but one wire1 the  

circuit being completed by the earth4   
,no fact in electricity seems more      
marvelous than that the thousands of    
messages flashing along the wires       
overhead are likewise traveling through 
the ground beneath4 ,if it were not for 
this use of the earth as an unfailing   
conductor1 the network of overhead wires
 in our city streets would be even more 
complex than it now is4  #cjc4 ,advances
 in ,telegraphy4 ,the mechanical        
improvements in telegraphy have been so 
rapid that at present a single operator 
can easily send or receive forty words a
 minute4 ,he can telegraph more quickly 
than the average person can write2 and  
with a combination of the latest        
improvements the speed can be enormously
 increased4 ,recently1 #aejj words were 
flashed from ,new ,york to ,boston over 
a single wire in one second4  ,in actual
 practice messages are not ordinarily   
sent long distances over a direct line1 
but are automatically transferred to new
 lines at definite points4 ,for example1

 a message from ,new ,york to ,chicago  
does not travel along an uninterrupted  
path1 but is automatically transferred  
at some point1 such as ,lancaster1 to a 
second line which carries it on to      
,pittsburgh1 where it is again          
transferred to a third line which takes 
it farther on to its destination4       
,,chapter ,,xxxiii  ,,magnets ,,and     
,,currents   #cjd4 ,in the twelfth      
century1 there was introduced into      
,europe from ,china a simple instrument 
which changed journeying on the sea from
 uncertain wandering to a definite1 safe
 voyage4 ,this instrument was the       
compass 7,fig4 #bba71 and because of the
 property of the compass needle 7a      
magnet7 to point unerringly north and   
south1 sailors were able to determine   
directions on the sea and to steer for  
the desired point4  ,illustration3      
,,fig4 #bba4--,the compass4  ,since an  
electric current is practically         
equivalent to a magnet 7,section #bif71 
it becomes necessary to know the most   

important facts relative to magnets1    
facts simple in themselves but of       
far-reaching value and consequences in  
electricity4 ,without a knowledge of the
 magnetic characteristics of currents1  
the construction of the motor would have
 been impossible1 and trolley cars1     
electric fans1 motor boats1 and other   
equally well-known electrical           
contrivances would be unknown4  #cje4   
,the ,attractive ,power of a ,magnet4   
,the magnet best known to us all is the 
compass needle1 but for convenience we  
will use a magnetic needle in the shape 
of a bar larger and stronger than that  
employed in the compass4 ,if we lay such
 a magnet on a pile of iron filings1 it 
will be found on lifting the magnet that
 the filings cling to the ends in tufts1
 but leave it almost bare in the center 
7,fig4 #bbb74 ,the points of attraction 
at the two ends are called the poles of 
the magnet4  ,illustration3 ,,fig4      
#bbb4--;,a magnet4  ,if a delicately    
made magnet is suspended as in ,figure  

#bbc1 and is allowed to swing freely1 it
 will always assume a definite north and
 south position4 ,the pole which points 
north when the needle is suspended is   
called the north pole and is marked ,n1 
while the pole which points south when  
the needle is suspended is called the   
south pole and is marked ,s4  ,a freely 
suspended magnet points nearly north and
 south4  ,a magnet has two main points  
of attraction called respectively the   
north and south poles4  ,illustration3  
,,fig4 #bbc4--,the magnetic needle4     
#cjf4 ,the ,extent of ,magnetic         
,attraction4 ,if a thin sheet of paper  
or cardboard is laid over a strong1     
bar-shaped magnet and iron filings are  
then gently strewn on the paper1 the    
filings clearly indicate the position of
 the magnet beneath1 and if the         
cardboard is gently tapped1 the filings 
arrange themselves as shown in ,figure  
#bbd4 ,if the paper is held some        
distance above the magnet1 the influence
 on the filings is less definite1 and   

finally1 if the paper is held very far  
away1 the filings do not respond at all1
 but lie on the cardboard as dropped4   
,the magnetic power of a magnet1 while  
not confined to the magnet itself1 does 
not extend indefinitely into the        
surrounding region2 the influence is    
strong near the magnet1 but at a        
distance becomes so weak as to be       
inappreciable4 ,the region around a     
magnet through which its magnetic force 
is felt is called the field of force1 or
 simply the magnetic field1 and the     
definite lines in which the filings     
arrange themselves are called lines of  
force4  ,illustration3 ,,fig4           
#bbd4--;,iron filings scattered over a  
magnet arrange themselves in definite   
lines4  ,the magnetic power of a magnet 
is not limited to the magnet1 but       
extends to a considerable distance in   
all directions4  #cjg4 ,the ,influence  
of ,magnets upon ,each ,other4 ,if while
 our suspended magnetic needle is at    
rest in its characteristic              

north-and-south direction another magnet
 is brought near1 the suspended magnet  
is turned2 that is1 motion is produced  
7,fig4 #bbe74 ,if the north pole of the 
free magnet is brought toward the south 
pole of the suspended magnet1 the latter
 moves in such a way that the two poles 
,n and ,s are as close together as      
possible4 ,if the north pole of the free
 magnet is brought toward the north pole
 of the suspended magnet1 the latter    
moves in such a way that the two poles  
,n and ,n are as far apart as possible4 
,in every case that can be tested1 it is
 found that a north pole repels a north 
pole1 and a south pole repels a south   
pole2 but that a north and a south pole 
always attract each other4              
,illustration3 ,,fig4 #bbe4--;,a south  
pole attracts a north pole4  ,the main  
facts relative to magnets may be summed 
up as follows3--  a4 ,a magnet points   
nearly north and south if it is allowed 
to swing freely4  b4 ,a magnet contains 
two unlike poles1 one of which          

persistently points north1 and the other
 of which as persistently points south1 
if allowed to swing freely4  c4 ,poles  
of the same name repel each other2 poles
 of unlike name attract each other4  d4 
,a magnet possesses the power of        
attracting certain substances1 like     
iron1 and this power of attraction is   
not limited to the magnet itself but    
extends into the region around the      
magnet4  #cjh4 ,magnetic ,properties of 
an ,electric ,current4 ,if a            
current-bearing wire is really          
equivalent in its magnetic powers to a  
magnet1 it must possess all of the      
characteristics mentioned in the        
preceding ,section4 ,we saw in ,section 
#bif that a coiled wire through which   
current was flowing would attract iron  
filings at the two ends of the helix4   
,that a coil through which current flows
 possesses the characteristics a1 b1 c1 
and d of a magnet is shown as follows3--
  a1 b4 ,if a helix marked at one end   
with a red string is arranged so that it

 is free to rotate and a strong current 
is sent through it1 the helix will      
immediately turn and face about until it
 points north and south4 ,if it is      
disturbed from this position1 it will   
slowly swing back until it occupies its 
characteristic north and south position4
 ,the end to which the string is        
attached will persistently point either 
north or south4 ,if the current is sent 
through the coil in the opposite        
direction1 the two poles exchange       
positions and the helix turns until the 
new north pole points north4            
,illustration3 ,,fig4 #bbf4--;,a helix  
through which current flows always      
points north and south1 if it is free to
 rotate4  c4 ,if a coil conducting a    
current is held near a suspended magnet1
 one end of the helix will be found to  
attract the north pole of the magnet1   
while the opposite end will be found to 
repel the north pole of the magnet4 ,in 
fact1 the helix will be found to behave 
in every way as a magnet1 with a north  

pole at one end and a south pole at the 
other4 ,if the current is sent through  
the helix in the opposite direction1 the
 north and south poles exchange places4 
,illustration3 ,,fig4 #bbg4--;,a wire   
through which current flows is          
surrounded by a field of magnetic force4
  ,if the number of turns in the helix  
is reduced until but a single loop      
remains1 the result is the same2 the    
single loop acts like a flat magnet1 one
 side of the loop always facing         
northward and one southward1 and one    
face attracting the north pole of the   
suspended magnet and one repelling it4  
d4 ,if a wire is passed through a card  
and a strong current is sent through the
 wire1 iron filings will1 when sprinkled
 upon the card1 arrange themselves in   
definite directions 7,fig4 #bbg74 ,a    
wire carrying a current is surrounded by
 a magnetic field of force4  ,a magnetic
 needle held under a current-bearing    
wire turns on its pivot and finally     
comes to rest at an angle with the      

current4 ,the fact that the needle is   
deflected by the wire shows that the    
magnetic power of the wire extends into 
the surrounding medium4  ,the magnetic  
properties of current electricity were  
discovered by ,oersted of ,denmark less 
than a hundred years ago2 but since that
 time practically all important         
electrical machinery has been based upon
 one or more of the magnetic properties 
of electricity4 ,the motors which drive 
our electric fans1 our mills1 and our   
trolley cars owe their existence        
entirely to the magnetic action of      
current electricity4  ,illustration3    
,,fig4 #bbh4--,the coil turns in such a 
way that its north pole is opposite the 
south pole of the magnet4  #cji4 ,the   
,principle of the ,motor4 ,if a close   
coil of wire is suspended between the   
poles of a strong horseshoe magnet1 it  
will not assume any characteristic      
position but will remain wherever       
placed4 ,if1 however1 a current is sent 
through the wire1 the coil faces about  

and assumes a definite position4 ,this  
is because a coil1 carrying a current1  
is equivalent to a magnet with a north  
and south face2 and1 in accordance with 
the magnetic laws1 tends to move until  
its north face is opposite the south    
pole of the horseshoe magnet1 and its   
south face opposite the north pole of   
the magnet4 ,if1 when the coil is at    
rest in this position1 the current is   
reversed1 so that the north pole of the 
coil becomes a south pole and the former
 south pole becomes a north pole1 the   
result is that like poles of coil and   
magnet face each other4 ,but since like 
poles repel each other1 the coil will   
move1 and will rotate until its new     
north pole is opposite to the south pole
 of the magnet and its new south pole is
 opposite the north pole4 ,by sending a 
strong current through the coil1 the    
helix is made to rotate through a half  
turn2 by reversing the current when the 
coil is at the half turn1 the helix is  
made to continue its rotation and to    

swing through a whole turn4 ,if the     
current could be repeatedly reversed    
just as the helix completed its half    
turn1 the motion could be prolonged2    
periodic current reversal would produce 
continuous rotation4 ,this is the       
principle of the motor4  ,illustration3 
,,fig4 #bbi4--,principle of the motor4  
,it is easy to see that long-continued  
rotation would be impossible in the     
arrangement of ,figure #bbh1 since the  
twisting of the suspending wire would   
interfere with free motion4 ,if the     
motor is to be used for continuous      
motion1 some device must be employed by 
means of which the helix is capable of  
continued rotation around its support4  
,in practice1 the rotating coil of a    
motor is arranged as shown in ,figure   
#bbi4 ,wires from the coil terminate on 
metal disks and are securely soldered   
there4 ,the coil and disks are supported
 by the strong and well-insulated rod   
,r1 which rests upon braces1 but which  
nevertheless rotates freely with disks  

and coil4 ,the current flows to the coil
 through the thin metal strips called   
brushes1 which rest lightly upon the    
disks4  ,when the current which enters  
at ,b flows through the wire1 the coil  
rotates1 tending to set itself so that  
its north face is opposite the south    
face of the magnet4 ,if1 when the helix 
has just reached this position1 the     
current is reversed--entering at ,b'    
instead of ,b--the poles of the coil are
 exchanged2 the rotation1 therefore1    
does not cease1 but continues for       
another half turn4 ,proper reversals of 
the current are accompanied by          
continuous motion1 and since the disk   
and shaft rotate with the coil1 there is
 continuous rotation4  ,if a wheel is   
attached to the rotating shaft1 weights 
can be lifted1 and if a belt is attached
 to the wheel1 the motion of the        
rotating helix can be transferred to    
machinery for practical use4  ,the      
rotating coil is usually spoken of as   
the armature1 and the large magnet as   

the field magnet4  #caj4 ,mechanical    
,reversal of the ,current4 ,the         
,commutator4 ,it is not possible by hand
 to reverse the current with sufficient 
rapidity and precision to insure        
uninterrupted rotation2 moreover1 the   
physical exertion of such frequent      
reversals is considerable4 ,hence1 some 
mechanical device for periodically      
reversing the current is necessary1 if  
the motor is to be of commercial value4 
,illustration3 ,,fig4 #bcj4--,the       
commutator4  ,the mechanical reversal of
 the current is accomplished by the use 
of the commutator1 which is a metal ring
 split into halves1 well insulated from 
each other and from the shaft4 ,to each 
half of this ring is attached one of the
 ends of the armature wire4 ,the brushes
 which carry the current are set on     
opposite sides of the ring and do not   
rotate4 ,as armature1 commutator1 and   
shaft rotate1 the brushes connect first 
with one segment of the commutator and  
then with the other4 ,since the circuit 

is arranged so that the current always  
enters the commutator through the brush 
,b1 the flow of the current into the    
coil is always through the segment in   
contact with ,b2 but the segment in     
contact with ,b changes at every half   
turn of the coil1 and hence the         
direction of the current through the    
coil changes periodically4 ,as a result 
the coil rotates continuously1 and      
produces motion so long as current is   
supplied from without4  #caa4 ,the      
,practical ,motor4 ,a motor constructed 
in accordance with ,section #cji would  
be of little value in practical everyday
 affairs2 its armature rotates too      
slowly and with too little force4 ,if a 
motor is to be of real service1 its     
armature must rotate with sufficient    
strength to impart motion to the wheels 
of trolley cars and mills1 to drive     
electric fans1 and to set into activity 
many other forms of machinery4  ,the    
strength of a motor may be increased by 
replacing the singly coiled armature by 

one closely wound on an iron core2 in   
some armatures there are thousands of   
turns of wire4 ,the presence of soft    
iron within the armature 7,section #bif7
 causes greater attraction between the  
armature and the outside magnet1 and    
hence greater force of motion4 ,the     
magnetic strength of the field magnet   
influences greatly the speed of the     
armature2 the stronger the field magnet 
the greater the motion1 so electricians 
make every effort to strengthen their   
field magnets4 ,the strongest known     
magnets are electromagnets1 which1 as we
 have seen1 are merely coils of wire    
wound on an iron core4 ,for this reason1
 the field magnet is usually an         
electromagnet4  ,when very powerful     
motors are necessary1 the field magnet  
is so arranged that it has four or more 
poles instead of two2 the armature      
likewise consists of several portions1  
and even the commutator may be very     
complex4 ,but no matter how complex     
these various parts may seem to be1 the 

principle is always that stated in      
,section #cji1 and the parts are limited
 to field magnet1 commutator1 and       
armature4  ,illustration3 ,,fig4        
#bca4--;,a modern power plant4          
,illustration3 ,,fig4 #bcb4--,the       
electric street car4  ,the motor is of  
value because by means of it motion1 or 
mechanical energy1 is obtained from an  
electric current4 ,nearly all electric  
street cars 7,fig4 #bcb71 are set in    
motion by powerful motors placed under  
the cars4 ,as the armature rotates1 its 
motion is communicated by gears to the  
wheels1 the necessary current reaching  
the motor through the overhead wires4   
,small motors may be used to great      
advantage in the home1 where they serve 
to turn the wheels of sewing machines1  
and to operate washing machines4 ,vacuum
 cleaners are frequently run by motors4 
,,chapter ,,xxxiv  ,,how ,,electricity  
,,may ,,be ,,measured   #cab4 ,danger of
 an ,oversupply of ,current4 ,if a small
 toy motor is connected with one cell1  

it rotates slowly2 if connected with two
 cells1 it rotates more rapidly1 and in 
general1 the greater the number of cells
 used1 the stronger will be the action  
of the motor4 ,but it is possible to    
send too strong a current through our   
wire1 thereby interfering with all      
motion and destroying the motor4 ,we    
have seen in ,section #bhh that the     
amount of current which can safely flow 
through a wire depends upon the         
thickness of the wire4 ,a strong current
 sent through a fine wire has its       
electrical energy transformed largely   
into heat2 and if the current is very   
strong1 the heat developed may be       
sufficient to burn off the insulation   
and melt the wire itself4 ,this is true 
not only of motors1 but of all electric 
machinery in which there are            
current-bearing wires4 ,the current     
should not be greater than the wires can
 carry1 otherwise too much heat will be 
developed and damage will be done to    
instruments and surroundings4  ,the     

current sent through our electric stoves
 and irons should be strong enough to   
heat the coils1 but not strong enough to
 melt them4 ,if the current sent through
 our electric light wires is too great  
for the capacity of the wires1 the heat 
developed will injure the wires and may 
cause disastrous results4 ,the          
overloading of wires is responsible for 
many disastrous fires4  ,the danger of  
overloading may be eliminated by        
inserting in the circuit a fuse or other
 safety device4 ,a fuse is made by      
combining a number of metals in such a  
way that the resulting substance has a  
low melting point and a high electrical 
resistance4 ,a fuse is inserted in the  
circuit1 and the instant the current    
increases beyond its normal amount the  
fuse melts1 breaks the circuit1 and thus
 protects the remaining part of the     
circuit from the danger of an overload4 
,in this way1 a circuit designed to     
carry a certain current is protected    
from the danger of an accidental        

overload4 ,the noise made by the burning
 out of a fuse in a trolley car         
frequently alarms passengers1 but it is 
really a sign that the system is in good
 working order and that there is no     
danger of accident from too strong a    
current4  #cac4 ,how ,current is        
,measured4 ,the preceding ,section has  
shown clearly the danger of too strong a
 current1 and the necessity for limiting
 the current to that which the wire can 
safely carry4 ,there are times when it  
is desirable to know accurately the     
strength of a current1 not only in order
 to guard against an overload1 but also 
in order to determine in advance the    
mechanical and chemical effects which   
will be produced by the current4 ,for   
example1 the strength of the current    
determines the thickness of the coating 
of silver which forms in a given time on
 a spoon placed in an electrolytic bath2
 if the current is weak1 a thin plating 
is made on the spoon2 if the current is 
strong1 a thick plating is made4 ,if1   

therefore1 the exact value of the       
current is known1 the exact amount of   
silver which will be deposited on the   
spoon in a given time can be definitely 
calculated4  ,illustration3 ,,fig4      
#bcc4--,the principle of the            
galvanometer4  ,current-measuring       
instruments1 or galvanometers1 depend   
for their action on the magnetic        
properties of current electricity4 ,the 
principle of practically all            
galvanometers is as follows3--  ,a      
closely wound coil of fine wire free to 
rotate is suspended as in ,figure #bcc  
between the poles of a strong magnet4   
,when a current is sent through the     
coil1 the coil becomes a magnet and     
turns so that its faces will be towards 
the poles of the permanent magnet4 ,but 
as the coil turns1 the suspending wire  
becomes twisted and hinders the turning4
 ,for this reason1 the coil can turn    
only until the motion caused by the     
current is balanced by the twist of the 
suspending wire4 ,but the stronger the  

current through the coil1 the stronger  
will be the force tending to rotate the 
coil1 and hence the less effective will 
be the hindrance of the twisting string4
 ,as a consequence1 the coil swings     
farther than before2 that is1 the       
greater the current1 the farther the    
swing4 ,usually a delicate pointer is   
attached to the movable coil and rotates
 freely with it1 so that the swing of   
the pointer indicates the relative      
values of the current4 ,if the source of
 the current is a gravity cell1 the     
swing is only two thirds as great as    
when a dry cell is used1 indicating that
 the dry cell furnishes about #a-a_/b   
times as much current as a gravity cell4
  #cad4 ,ammeters4 ,a galvanometer does 
not measure the current1 but merely     
indicates the relative strength of      
different currents4 ,but it is desirable
 at times to measure a current in units4
 ,instruments for measuring the strength
 of currents in units are called        
ammeters1 and the common form makes use 

of a galvanometer4  ,a current is sent  
through a movable coil 7the field magnet
 and coil are inclosed in the case7     
7,fig4 #bcd71 and the magnetic field    
thus developed causes the coil to turn1 
and the pointer attached to it to move  
over a scale graduated so that it reads 
current strengths4 ,this scale is       
carefully graduated by the following    
method4  ,if two silver rods 7,fig4     
#bjh7 are weighed and placed in a       
solution of silver nitrate1 and current 
from a single cell is passed through the
 liquid for a definite time1 we find1 on
 weighing the two rods1 that one has    
gained in weight and the other has lost4
 ,if the current is allowed to flow     
twice as long1 the amount of silver lost
 and gained by the electrodes is        
doubled2 and if twice the current is    
used1 the result is again doubled4  ,as 
a result of numerous experiments1 it was
 found that a definite current of       
electricity will deposit a definite     
amount of silver in a definite time1 and

 that the amount of silver deposited on 
an electrode in one second might be used
 to measure the current of electricity  
which has flowed through the circuit in 
one second4  ,a current is said to be   
one ampere strong if it will deposit    
silver on an electrode at the rate of   
#j4jjaaah gram per second4              
,illustration3 ,,fig4 #bcd4--;,an       
ammeter4  ,in marking the scale1 an     
ammeter is placed in the circuit of an  
electrolytic cell and the position of   
the pointer is marked on the blank card 
which lies beneath and which is to serve
 as a scale 7,fig4 #bce74 ,after the    
current has flowed for about an hour1   
the amount of silver which has been     
deposited is measured4 ,knowing the time
 during which the current has run1 and  
the amount of deposit1 the strength of  
the current in amperes can be           
calculated4 ,this number is written     
opposite the place at which the pointer 
stood during the experiment4  ,the scale
 may be completed by marking the        

positions of the pointer when other     
currents of known strength flow through 
the ammeter4  ,illustration3 ,,fig4     
#bce4--,marking the scale of an ammeter4
  ,all electric plants1 whether for     
heating1 lighting1 or for machinery1 are
 provided with ammeters1 such           
instruments being as important to an    
electric plant as the steam gauge is to 
the boiler4  #cae4 ,voltage and         
,voltmeters4 ,since electromotive force1
 or voltage1 is the cause of current1 it
 should be possible to compare different
 electromotive forces by comparing the  
currents which they produce in a given  
circuit4 ,but two voltages of equal     
value do not give equal currents unless 
the resistances met by the currents are 
equal4 ,for example1 the simple voltaic 
cell and the gravity cell have          
approximately equal voltages1 but the   
current produced by the voltaic cell is 
stronger than that produced by the      
gravity cell4 ,this is because the      
current meets more resistance within the

 gravity cell than within the voltaic   
cell4 ,every cell1 no matter what its   
nature1 offers resistance to the flow of
 electricity through it and is said to  
have internal resistance4 ,if we are    
determining the voltages of various     
cells by a comparison of the respective 
currents produced1 the result will be   
true only on condition that the         
resistances in the various circuits are 
equal4 ,if a very large external        
resistance of fine wire is placed in    
circuit with a gravity cell1 the total  
resistance of the circuit 7made up of   
the relatively small resistance in the  
cell and the larger resistance in the   
rest of the circuit7 will differ but    
little from that of another circuit in  
which the gravity cell is replaced by a 
voltaic cell1 or any other type of cell4
  ,with a high resistance in the outside
 circuit1 the deflections of the ammeter
 will be small1 but such as they are1   
they will fairly accurately represent   
the electromotive forces which produce  

them4  ,voltmeters 7,fig4 #bcf71 or     
instruments for measuring voltage1 are  
like ammeters except that a wire of very
 high resistance is in circuit with the 
movable coil4 ,in external appearance   
they are not distinguishable from       
ammeters4  ,illustration3 ,,fig4        
#bcf4--;,a voltmeter4  ,the unit of     
electromotive force is called the volt4 
,the voltage of a dry cell is           
approximately #a4e volts1 and the       
voltage of a voltaic cell and of a      
gravity cell is approximately #a volt4  
#caf4 ,current1 ,voltage1 ,resistance4  
,we learned in ,section #bhg that the   
strength of a current increases when the
 electromotive force increases1 and     
diminishes when the electromotive force 
diminishes4 ,later1 in ,section #bhh1 we
 learned that the strength of the       
current decreases as the resistance in  
circuit increases4  ,the strength of a  
steady current depends upon these two   
factors only1 the electromotive force   
which causes it and the resistance which

 it has to overcome4  #cag4 ,resistance4
 ,since resistance plays so important a 
rle in electricity1 it becomes necessary
 to have a unit of resistance4 ,the     
practical unit of resistance is called  
an ohm1 and some idea of the value of an
 ohm can be obtained if we remember that
 a #cjj-;foot length of common iron     
telegraph wire has a resistance of #a   
ohm4 ,an approximate ohm for rough work 
in the laboratory may be made by winding
 #i feet #e inches of number #cj copper 
wire on a spool or arranging it in any  
other convenient form4  ,in ,section    
#bii we learned that substances differ  
very greatly in the resistance which    
they offer to electricity1 and so it    
will not surprise us to learn that while
 it takes #cjj feet of iron telegraph   
wire to give #a ohm of resistance1 it   
takes but #ci feet of number #bd copper 
wire1 and but #b4b feet of number #bd   
,german silver wire1 to give the same   
resistance4     ,,note4 ,the number of a
 wire indicates its diameter2 number    

#cj1 for example1 being always of a     
definite fixed diameter1    no matter   
what the material of the wire4  ,if we  
wish to avoid loss of current by        
heating1 we use a wire of low           
resistance2 while if we wish to         
transform electricity into heat1 as in  
the electric stove1 we choose wire of   
high resistance1 as ,german silver wire4
     ,,chapter ,,xxxv  ,,how            
,,electricity ,,is ,,obtained ,,on ,a   
,,large ,,scale   #cah4 ,the ,dynamo4   
,we have learned that cells furnish     
current as a result of chemical action1 
and that the substance usually consumed 
within the cell is zinc4 ,just as coal  
within the furnace furnishes heat1 so   
zinc within the cell furnishes          
electricity4 ,but zinc is a much more   
expensive fuel than coal or oil or gas1 
and to run a large motor by electricity 
produced in this way would be very much 
more expensive than to run the motor by 
water or steam4 ,for weak and infrequent
 currents such as are used in the       

electric bell1 only small quantities of 
zinc are needed1 and the expense is     
small4 ,but for the production of such  
powerful currents as are needed to drive
 trolley cars1 elevators1 and huge      
machinery1 enormous quantities of zinc  
would be necessary and the cost would be
 prohibitive4 ,it is safe to say that   
electricity would never have been used  
on a large scale if some less expensive 
and more convenient source than zinc had
 not been found4  #cai4 ,a ,new ,source 
of ,electricity4 ,it came to most of us 
as a surprise that an electric current  
has magnetic properties and transforms a
 coil into a veritable magnet4 ,perhaps 
it will not surprise us now to learn    
that a magnet in motion has electric    
properties and is1 in fact1 able to     
produce a current within a wire4 ,this  
can be proved as follows3--             
,illustration3 ,,fig4 #bcg4--,the motion
 of a magnet within a coil of wire      
produces a current of electricity4      
,attach a closely wound coil to a       

sensitive galvanometer 7,fig4 #bcg72    
naturally there is no deflection of the 
galvanometer needle1 because there is no
 current in the wire4 ,now thrust a     
magnet into the coil4 ,immediately there
 is a deflection of the needle1 which   
indicates that a current is flowing     
through the circuit4 ,if the magnet is  
allowed to remain at rest within the    
coil1 the needle returns to its zero    
position1 showing that the current has  
ceased4 ,now let the magnet be withdrawn
 from the coil2 the needle is deflected 
as before1 but the deflection is in the 
opposite direction1 showing that a      
current exists1 but that it flows in the
 opposite direction4 ,we learn1         
therefore1 that a current may be induced
 in a coil by moving a magnet back and  
forth within the coil1 but that a magnet
 at rest within the coil has no such    
influence4  ,an electric current        
transforms a coil into a magnet4 ,a     
magnet in motion induces electricity    
within a coil2 that is1 causes a current

 to flow through the coil4  ,a magnet   
possesses lines of force1 and as the    
magnet moves toward the coil it carries 
lines of force with it1 and the coil is 
cut1 so to speak1 by these lines of     
force4 ,as the magnet recedes from the  
coil1 it carries lines of force away    
with it1 this time reducing the number  
of the lines which cut the coil4        
,illustration3 ,,fig4 #bch4--;,as long  
as the coil rotates between the poles of
 the magnet1 current flows4  #cbj4 ,a   
,test of the ,preceding ,statement4 ,we 
will test the statement that a magnet   
has electric properties by another      
experiment4 ,between the poles of a     
strong magnet suspend a movable coil    
which is connected with a sensitive     
galvanometer 7,fig4 #bcg74 ,starting    
with the coil in the position of ,figure
 #bbh1 when many lines of force pass    
through it1 let the coil be rotated     
quickly until it reaches the position   
indicated in ,figure #bch1 when no lines
 of force pass through it4 ,during the  

motion of the coil1 a strong deflection 
of the galvanometer is observed2 but the
 deflection ceases as soon as the coil  
ceases to rotate4 ,if1 now1 starting    
with the position of ,figure #bch1 the  
coil is rotated forward to its starting 
point1 a deflection occurs in the       
opposite direction1 showing that a      
current is present1 but that it flows in
 the opposite direction4 ,so long as the
 coil is in motion1 it is cut by a      
varying number of lines of force1 and   
current is induced in the coil4  ,the   
above arrangement is a dynamo in        
miniature4 ,by rotation of a coil       
7armature7 within a magnetic field1 that
 is1 between the poles of a magnet1     
current is obtained4  ,in the motor1    
current produces motion4 ,in the dynamo1
 motion produces current4  #cba4 ,the   
,dynamo4 ,as has been said1 the         
arrangement of the preceding ,section is
 a dynamo in miniature4 ,every dynamo1  
no matter how complex its structure and 
appearance1 consists of a coil of wire  

which can rotate continuously between   
the poles of a strong magnet4 ,the      
mechanical devices to insure easy       
rotation are similar in all respects to 
those previously described for the      
motor4  ,illustration3 ,,fig4 #bci4--;,a
 modern electrical machine4  ,the       
current obtained from such a dynamo     
alternates in direction1 flowing first  
in one direction and then in the        
opposite direction4 ,such alternating   
currents are unsatisfactory for many    
purposes1 and to be of service are in   
many cases transformed into direct      
currents2 that is1 current which flows  
steadily in one direction4 ,this is     
accomplished by the use of a commutator4
 ,in the construction of the motor1     
continuous motion in one direction is   
obtained by the use of a commutator     
7,section #caj72 in the construction of 
a dynamo1 continuous current in one     
direction is obtained by the use of a   
similar device4  #cbb4 ,powerful        
,dynamos4 ,the power and efficiency of a

 dynamo are increased by employing the  
devices previously mentioned in         
connection with the motor4              
,electromagnets are used in place of    
simple magnets1 and the armature1       
instead of being a simple coil1 may be  
made up of many coils wound on soft     
iron4 ,the speed with which the armature
 is rotated influences the strength of  
the induced current1 and hence the      
armature is run at high speed4          
,illustration3 ,,fig4 #bdj4--,thomas    
,edison1 one of the foremost electrical 
inventors of the present day4  ,a small 
dynamo1 such as is used for lighting    
fifty incandescent lamps1 has a horse   
power of about #cc4e1 and large dynamos 
are frequently as powerful as #gejj     
horse power4  #cbc4 ,the ,telephone4    
,when a magnet is at rest within a      
closed coil of wire1 as in ,section     
#cai1 current does not flow through the 
wire4 ,but if a piece of iron is brought
 near the magnet1 current is induced and
 flows through the wire2 if the iron is 

withdrawn1 current is again induced in  
the wire but flows in the opposite      
direction4 ,as iron approaches and      
recedes from the magnet1 current is     
induced in the wire surrounding the     
magnet4 ,this is in brief the principle 
of the telephone4 ,when one talks into a
 receiver1 ,l1 the voice throws into    
vibration a sensitive iron plate        
standing before an electromagnet4 ,the  
back and forth motion of the iron plate 
induces current in the electromagnet c4 
,the current thus induced makes itself  
evident at the opposite end of the line 
,m1 where by its magnetic attraction1 it
 throws a second iron plate into        
vibrations4 ,the vibrations of the      
second plate are similar to those       
produced in the first plate by the      
voice4 ,the vibrations of the far plate 
thus reproduce the sounds uttered at the
 opposite end4  ,illustration3 ,,fig4   
#bda4--;,diagram of a simple telephone  
circuit4  #cbd4 ,cost of ,electric      
,power4 ,the water power of a stream    

depends upon the quantity of water and  
the force with which it flows4 ,the     
electric power of a current depends upon
 the quantity of electricity and the    
force under which it flows4 ,the unit of
 electric power is called the watt2 it  
is the power furnished by a current of  
one ampere with a voltage of one volt4  
,one watt represents a very small amount
 of electric power1 and for practical   
purposes a unit #ajjj times as large is 
used1 namely1 the kilowatt4 ,by         
experiment it has been found that one   
kilowatt is equivalent to about #a-a_/c 
horse power4 ,electric current is       
charged for by the watt hour4 ,a current
 of one ampere1 having a voltage of one 
volt1 will furnish in the course of one 
hour one watt hour of energy4 ,energy   
for electric lighting is sold at the    
rate of about ten cents per kilowatt    
hour4 ,for other purposes it is less    
expensive4 ,the meters commonly used    
measure the amperes1 volts1 and time    
automatically1 and register the electric

 power supplied in watt hours4          
,,index       ,absorption1 of heat by   
lampblack1 #adc-add4       of gases by  
charcoal1 #eg4       of light waves1    
#ace-ach4      ,accommodation of the    
eye1 #abc4      ,acetanilid1 #bei4      
,acetylene1 as illuminant1 #aeb-aec4    
manufacture of1 #aeb-aec4               
properties of1 #bbj4      ,acid1 boric1 
#bec4       carbolic1 #aeb1 #bea1 #beb4 
hydrochloric1 #ee1 #hj1 #bbg1 #bch1     
#bda4       lactic1 #bcj4       oxalic1 
#bdg1 #bdh4       salicylic1 #bec4      
sulphuric1 #ee1 #hj1 #bdj1 #bda1 #cjg4  
sulphurous1 #bdb4      ,acids1 action on
 litmus1 #bbj4      ,adenoids1 #ea4     
,adulterants1 detection of1 #af4        
,air1 characteristics of1 #ha-hc1 #hf1  
#ahi4       compressibility of1 #ia4    
expansion of1 #aj-aa4       humidity1   
#ch1 #ci4       pumps1 #bja-bje4        
transmits sound1 #bfi4       weight of1 
#hf4      ,see ,atmosphere4             
,alcohol1 #bcd4       in patent         
medicines1 #bfj4      ,alizarin1 #bdh4  

,alkali1 #bbb4      ,alternating        
current1 #cea4      ,alum1 #bdg4        
in baking powder1 #bcj4      ,ammeter1  
#cda1 #cdc4      ,ammonia1 #aeb4       a
 base1 #bba-bbb4       in bath1 #bbf4   
in manufacture of ice1 #ih4             
neutralizing chlorine1 #bdj4            
,ampere1 #cdb4      ,anemia1 #bei4      
,angle1 of incidence1 #aaj4       of    
reflection1 #aaj4       of refraction1  
#aad4      ,aniline1 #aeb1 #bde4        
,animal charcoal1 #eh4      ,animal     
transportation1 #acb4      ,antichlor1  
#bdj4      ,antipyrin1 #bei4            
,armature1 #cai1 #cbj4       dynamo1    
#cej4       motor1 #cce4                
,artificial lighting1 #adh-aec4         
,atmosphere1 #ha4       carbon dioxide  
in1 #ed-ee4       height of1 #ha4       
nitrogen and oxygen in1 #bfb4           
pressure of1 #hb-hf4       water vapor  
in1 #cf-ch4       weight1 #hf4          
,see ,air4      ,atmospheric pressure1  
#hb-hf4      ,atomizer1 #ib4            
,atoms1 #ajb4      ,automobiles1 gas    

engines1 #ahe4      ,axis of a lens1    
#aai4       ,bacteria1 #acc4       as   
nitrogen makers1 #bfc4       destroyed  
by sunlight1 etc41 #acc1 #bej1 #bea4    
diseases caused by1 #acc4       in      
butter and cheese1 #acc4      ,baking   
powder1 #bbi-bcj4      ,baking soda1    
#bbg-bbi4      ,barograph1 #hg4         
,barometer1 aneroid1 #hd-he4            
mercury1 #hd4       use in weather      
predictions1 #hf-hg4      ,bases1 action
 on litmus1 #bba-bbb4       properties1 
#bbj-bbb4      ,battery1 electric1 #caa4
      ,beans1 as food1 #ff4       roots 
take in nitrogen1 #bfc4      ,bell1     
electric1 #cai-cba4      ,benzine1 #aej4
       as a cleaning agent1 #bbg4       
,benzoate of soda1 #bec4                
,bicarbonate of soda1 in fire           
extinguisher1 #ee1 #ef4       in        
,rochelle salt1 #bbg4       in soda     
mints1 #bca4       in seidlitz powder1  
#bca4      ,bicycle pumps1 #bjb4        
,blasting1 by electricity1 #cad4        
,bleaching1 #bcg-bdc4       by chlorine1

 #bch-bdj4      ,bleaching powder1      
#bci-bdj4      ,body1 human1 #fc-fd4    
a conductor of electricity1 #bib4       
,boiling1 #ca4       amount of heat     
absorbed1 #ca-cb4       of milk1 #cb4   
of water1 #gg4       point1 #ae4        
,bomb calorimeter1 #fa4      ,borax1 as 
meat preservative1 #bec4       as       
washing powder1 #bbf4      ,boric acid1 
as meat preservative1 #bec4             
,boyle's law1 #ie-if4      ,bread1      
#bcb-bcc4       unleavened1 #bcc4       
,bread making1 #bcb-bce4                
,breathing1 hygienic habits of1 #ej4    
by mouth1 #ej-ea4      ,burns1 treatment
 of1 #eb-ec4      ,butter1 adulteration 
test1 #af4       bacteria in1 #acc4     
,buttermilk1 #bcj4       ,caisson1      
#bjc-bjd4      ,calcium carbide1        
#aeb-aec4       in making nitrogenous   
fertilizer1 #bfd4      ,calico printing1
 #bdi4      ,calorie1 #bg-bh1 #fa-fb4   
,calorimeter1 #fa4      ,camera1        
#abh-abi4       films1 #abi4       lens1
 #abi4       plates1 #abi4              

,camping1 water supply1 #aie-aig4       
,candle1 #adh-adi4       as standard for
 light-measure1 #ajd-aje4               
,candle-power1 #aje-ajg4      ,carbide1 
calcium1 #aeb-aec1 #bfd4                
,carbohydrates1 #fd-fe1 #adi4           
,carbolic acid1 #aeb4       as          
disinfectant1 #bea4      ,carbon1 #ef1  
#ff4       in voltaic cells1 #cjh4      
,carbon dioxide1 #ec4       as fire     
extinguisher1 #ee-ef4       commercial  
use1 #ee-ef4       in baking soda1 #bbh4
       in fermentation1 #bcd4       in  
health1 #ed4       in plants1 #ee4      
preparation of1 #ee4       source of1   
#ec4       test for1 #bbh4              
,catarrh1 #bei4      ,caustic lime1     
#bbb44      ,caustic potash1 #bbb4      
,caustic soda1 #bah1 #bbb4       to make
 a salt1 #bbg4      ,caves and caverns1 
#ga4      ,cell1 dry1 #caj4             
gravity1 #cji-caj4       voltaic1       
#cjf-cjh1 #caj4      ,cells of human    
body1 #fc1 #fd1 #ff4      ,centigrade   
thermometer1 #ae4      ,central heating 

plant1 #ai4      ,chalk1 in making      
carbon dioxide1 #ee4      ,charcoal as a
 filter1 #eg4       commercially1 #eg4  
preparation1 #eg-eh4      ,chemical     
action1 and electricity1 #cjg1 #cae-cag4
       and light1 #abf1 #abg4           
,chemistry1 in daily life1 #bah1 #bai4  
,chills1 #ch4      ,chloride of lime1 in
 bleaching1 #bdj4       disinfectant1   
#bea4      ,chlorine1 and hydrogen1     
#bci4       effect upon human body1     
#bci4       in bleaching1 #bch-bdj4     
influence of light upon1 #abf4          
presence in salt1 #bbg4      ,circuit1  
electric1 #cba4       local1 in         
telegraph1 #cbe-cbf4      ,city water   
supply1 #bjf-bab4      ,clarinet1 #big4 
,cleaning of material1 #bbf1 #bdc4      
,climate1 influenced by presence of     
water1 #bi1 #dj4      ,clover1 nitrogen 
producers1 #bfc4      ,coal1 #cj4       
,coal gas1 #aej1 #aea4                  
by-products1 #aeb4      ,coal oil1 #adi1
 #aej4      ,coal tar dyes1 #aeb1 #bah1 
#bde4      ,cogwheels1 #agj4      ,coil1

 current-bearing1 #cbj4       magnetic  
field about1 #cca-ccc4      ,coke1 #aeb4
      ,cold storage1 #ig4      ,color1  
#acd-ada4       and heat1 #adb1 #adc4   
influenced by light1 #acg4       of     
opaque bodies1 #acf1 #acg4       of     
transparent bodies1 #ace1 #acf4         
,color blindness1 #adj1 #ada4           
designs in cloth1 #bdh1 #bdi4           
,colors1 compound1 #ach1 #aci4          
essential1 #aci-adj4       primary1     
#ace4       simple1 #ach4               
spectrum1 #acd-ace4       variety in    
dyeing1 #bdg1 #bdh4      ,combustion1   
heat of1 #de4       spontaneous1 #eb4   
,commutator1 #cce4      ,compass1 #cbh4 
,compound colors1 #ach1 #aci4           
,compound machine1 #aga4      ,compound 
substances1 #ajc4      ,compression of  
air1 #ia1 #ib4       cause of heat1 #if4
      ,compression pumps1 #bja1 #bje4   
,concave lens1 #aah4      ,condensation1
 #cc4       heat set free1 #dj4         
,conduction of heat1 #be4               
,conductivity metals1 #cba4             

,conductors1 electric1 #cba1 #cbb4      
,conservation1 of energy1 #eh1 #ei4     
of matter1 #eh1 #ei4      ,convection1  
#bd1 #be4      ,convex lens1 #aah4      
,cooling1 by evaporation1 #ce-cf4       
by expansion1 #ig4      ,copper1 in     
electric cell1 #cjg4      ,core1 iron1  
#cai4      ,corn1 bleached with         
sulphurous acid1 #bdb4      ,cotton1    
mercerized1 #bah4       bleaching1 #bda4
       dyeing1 #bde-bdg4      ,cough    
sirup1 #beh4      ,crane1 compound      
machine1 #agb4      ,cream of tartar1   
#bbi4      ,creosote oil1 #bed4         
,crude petroleum1 #adi1 #aej4           
,current1 electric1 #cjf1 #cab4         
alternating1 #cdi4       induced1       
#cdf-cdg4       measurement of1 #cdj4   
resistance1 #cab1 #cdc1 #cde4           
strength1 #cci1 #cdj1 #cdd4       ,dams1
 #bad-baf4      ,decay1 #di4            
,decomposition of soil by water1 #gj-gd4
      ,degrees ,fahrenheit and          
,centigrade1 #ae4      ,density1 #aa4   
,designs in cloth1 printed1 #bdh1 #bdi4 

woven1 #bdi4      ,developer in         
photography1 #abh4      ,dew1 #cf1 #cg4 
,dew point1 #ch4      ,diarrhea1 #bea4  
,diet1 #fb1 #ff4       economy on table1
 #ff-fi4      ,discord1 reason for1     
#bga4      ,disease1 and surface water1 
#gf4       relation of light to1        
#aca-acb4      ,disease disinfectants1  
#bej1 #bea1 #beb4      ,distillation1   
#cd-ce4       in commerce1 #ce4       of
 petroleum1 #adi-aej4       of soft     
coal1 #aej4       of water1 #cd1 #ce1   
#gg4      ,diving suits1 #bjd4          
,door bells1 #cai-cba4      ,drainage1  
of land1 #aid1 #aie4       sewage1 #aif1
 #aih1 #aii1 #bja4      ,drilled well1  
#aii4      ,drinking water1 #ge-gg4     
in camping1 #aie-aif4       and rural   
supplies1 #aih1 #bja4      ,driven well1
 #aif-aig4      ,drought1 #bag4         
,drugs1 #bee1 #bfj4      ,dry cell1     
#cab4      ,dyeing1 #bdd-bdi4           
color designs1 #bdh4      ,dyeing1      
direct1 #bde4       home1 #bdg4         
indirect1 #bdg4       variety of color1 

#bdg4      ,dyes1 #bah1 #bdd1 #bde4     
,dynamo1 #cdf4       alternating        
current1 #cdi4       source of energy1  
#cdf-cdg4       ,ear1 in man1 #cja-cjc4 
care of1 #cjc4      ,earth1 conductor of
 electricity1 #cbf4      ,echo1 #bgg4   
,economy in buying food1 #ff-fi4        
,effort1 muscular1 #aee1 #afj4          
,electric1 battery1 #caa4       bell1   
#cai-cba4       bread toasters1 #cad4   
conductors and non-conductors1 #cba-cbb4
       cost of1 energy1 #ceb4           
current1 #cjf1 #cab4       flatiron1    
#cac4       heating pad1 #cad4          
lights1 #cad4       street cars1 #ccg4  
,electricity1 heat1 #cab-cae1 #cci4     
as a magnet1 #cai1 #cca-ccc4            
practical uses of1 #cab-cag4            
,electrodes1 of cell1 #cjh4             
,electrolytic metals1 #cag4             
,electromagnets1 #cai4                  
,electromotive force1 #cjh4       unit  
of1 #cdd4      ,electroplating1 #cae4   
,electrotyping1 #cag4      ,elements1   
#ajb-ajc4      ,emulsion1 #bbd4         

,energy1 conservation of1 #eh1 #ei4     
transformations of1 #eh1 #ei4           
,engine1 steam1 #ahc-ahe4       gas1    
#ahe-ahf4       horse power1 #agc4      
,erosion1 #gc-gd4      ,essential       
colors1 #aci-adj4      ,evaporation1    
#ce-ci4       cooling effect1 #ce-cf4   
effect of temperature on1 #ce1 #cf4     
effect of air on1 #ch4       freezing   
by1 #ih4       heat absorbed1 #cf4      
of perspiration1 #ch4      ,expansion1  
of air1 #aj1 #aa4       cooling effect  
of1 #ig4       disadvantage and         
advantage of1 #aa-ac4       of liquids1 
#i-aa4       of solids1 #aj1 #aa4       
of water1 #i1 #aj1 #aa1 #ab4     ,eye1  
#abb-abe4       headache1 #abd1 #abe4   
how focused1 #abb1 #abc4                
nearsighted and farsighted1 #abc4       
strain1 #abe4       ,fahrenheit         
thermometer1 #ae4      ,fats1 #fe4      
in soap making1 #bbc4                   
,fermentation1 #bcb-bcf4       by yeast1
 #bcd-bcf4      ,ferric compounds1 #bdh4
      ,fertilizers1 #bfb-bfe4           

nitrogen1 #bfb4       phosphorus1 #bfc1 
#bfd4       potash1 #bfc-bfe4           
,field magnet1 #ccf4      ,filings1     
iron1 #cbi4      ,film1 photographic1   
#abi4      ,filter1 charcoal1 #eg4      
,filtering water1 #gg4      ,fire1 #i4  
and oxygen1 #de1 #dg4       and tinder  
box1 #dg4       making of1 #ea4         
primitive production of1 #dg4           
produced by friction1 #dg4              
spontaneous combustion1 #eb4       sores
 and burns1 #eb-ec4       extinguisher1 
#ee1 #ef4      ,fireless cooker1 #be1   
#bf4      ,fireplaces1 #ag1 #ah4        
,fixing1 in photography1 #abh4          
,flame1 hydrogen1 #hj4      ,flood1     
,johnstown1 #bad1 #bae4       relation  
to forests1 #bag4      ,flour1          
self-raising1 #bca4      ,flume1 #agg4  
,flute1 #big4      ,focal length1 #aah4 
,focus1 of lens1 #aah4      ,fog1 #cg4  
,food1 #fj-fi4       carbohydrates1 #fd1
 #fe4       economy in buying1 #ff-fi4  
fats1 #fe4       fuel value of1 #fj-fb4 
need of1 #fc1 #fd4       preservatives1 

#beb4       proteids1 #ff4       value1 
#fg4       waste1 #fj4       water in1  
#ge4      ,foot pound1 #agb4      ,force
 and motion1 #aef1 #aeg4       and work1
 #aef1 #aeg4       magnetic lines of1   
#cbi-cca1 #ccd4       muscular1 #aee1   
#afj4      ,force pumps1 #aib1 #aic4    
,forests and water supply1 #baf-bag4    
,forging of iron1 #dj1 #da4             
,formaldehyde1 #bec4      ,freezing1    
effect of salt1 #dd4       effect on    
ground and rocks1 #db4       expansion  
of water on1 #da4       ice cream       
freezer1 #dd4      ,frequency in music1 
#bgc1 #bge4      ,fresh air1 #bb-bd1    
#di4       amount consumed by gas       
burner1 #bb4       and health1 #di1 #ej4
       in underground work1 #bjb4       
in work under water1 #bjc-bje4          
,friction1 #agc1 #agd4       losses by1 
#agd1 #baj4       source of heat and    
fire1 #dg4      ,frost1 #cf1 #cg4       
,fruit1 canned1 bleached with sulphurous
 acid1 #bdb4       colored with coal tar
 dyes1 #bec4      ,fuel value of foods1 

#fj-fb4       table of fuel values1 #fg4
      ,fulcrum1 #aei1 #afj4             
,fumigation1 #bea4      ,fundamental    
tone1 #bij1 #bia1 #bib4      ,furnace1  
hot air1 #ai4      ,fuse1 #cdj4         
,fusion1 heat of1 #dj4                  
,galvanometer1 #cda4      ,gas1         
acetylene1 #aeb1 #aec4       and        
unburned carbon1 #aea4       coal1 #aea1
 #aeb4       effect of heat on volume1  
#if1 #ig4       effect of pressure on   
volume1 #ie-if4       engine1 #ahe-ahf4 
for cooking1 #aea1 #aeb4                
illuminating1 #ib1 #ic1 #aej1 #aea4     
liquefaction1 #ig1 #ih4       meter1    
#ic1 #id4       natural1 #aeb4          
,gasolene1 #adi1 #aej4       as cleaning
 agent1 #bbg1 #bdc4       in gas engine1
 #ahe1 #ahf4      ,gauge1 pressure1     
#ib-id4      ,gelatin1 plate and film1  
#abi4      ,glass1 kinds of1 #aai4      
molding of1 #dj4       non-conductor1   
#cba4      ,grape juice1 fermented with 
millet1 #bcc4      ,gravity cell1 #cji1 
#caj4      ,grease1 and lye1 #bba4      

and soap making1 #bbc4      ,gulf       
,stream1 #bd4       ,hard water1 and    
soap1 #bbe4      ,harp1 #bie4           
,headache1 #abd1 #abe4       powders1   
#bei4      ,health1 effect of diet1 #fb1
 #fd4      ,heat1 #i4       absorbed in 
boiling1 #ca-cb4       and disease      
germs1 #bej4       and food1 #beb4      
and friction1 #dg4       and light1     
#adb1 #adg4       and oxidation1 #de1   
#dh1 #di4       and wave motion1        
#ade-adg4       conduction1 #be4        
convection1 #bd1 #be4       from burning
 hydrogen1 #hj4       from electricity1 
#cab-cae1 #cci4       needed to melt    
substances1 #ci4       of fusion1 #dj4  
of vaporization1 #cb4       produced by 
compression1 #if4       relation of     
water to weather1 #bi1 #dj4       set   
free by freezing water1 #dj4            
sources of1 #bi-cj4       specific1     
#bh-bi4       temperature1 #bg4         
unit of1 #bg1 #bh4      ,heating effect 
of electric current1 #cab-cae4          
,heating of buildings3 central heating  

plant1 #ai4       fireplaces1 #ag-ah4   
,heating1 furnaces1 #ai4       hot      
water1 #ai-bb4      ,helix1 #cah4       
,horse power1 #agc1 #cea4      ,hot     
water heating1 #ai-bb4      ,hues1      
primary1 #ace4      ,humidity1 #ch4     
proper percentage for health and        
comfort1 #ch1 #ci4      ,humus1 #baf1   
#bag4      ,hydrocarbons1 #adi4         
,hydrochloric acid1 composition1 #bbg4  
in bleaching1 #bda4       to make a     
salt1 #bbg4       to make carbon        
dioxide1 #ee4       to make chlorine1   
#bch4       to make hydrogen1 #hj4      
,hydrogen1 #fe1 #ff4       and chlorine1
 #bci4       and water1 #gi4            
chemical conduct1 #abf-abg4       flame1
 #hj4       in voltaic cell1 #cjg4      
peroxide1 #ec1 #beb4       preparation1 
#hj4       to liquefy1 #ig4       ,ice1 
lighter than water1 #db4                
manufacture of1 #ih1 #ii4      ,ice     
cream freezers1 #dd4      ,illuminating 
gas1 manufacture of1 #aej1 #aea4        
measurement of quantity consumed1 #ic1  

#id4       test of pressure1 #ib1 #ic4  
,illumination1 intensity of1 #aje1 #ajf4
      ,image1 in mirror1 #ajh1 #aaa4    
,incandescent lighting1 #ajg1 #cad4     
,incidence1 angle of1 #aaj4             
,inclined plane1 #afb-aff4       screw1 
#aff4       wedge1 #aff4      ,indigo1  
#bah4      ,induced current1 #cdf-cdg4  
,ink spots1 removal of1 #bdc4           
,insoluble substances1 #ga4             
,insulators1 electric1 #cbd4            
,intensity1 of light1 #aje-ajg4       of
 sound1 #bgj-bga4      ,interval1 in    
musical scale1 #bhc4      ,iron1        
forging1 #da4       filings1 #cbi4      
galvanizing1 #di4       oxidation of1   
#dh4      ,irrigation1 #aic-aid4        
,isobaric lines1 #hh1 #ia4              
,isothermal lines1 #hi1 #ia4            
,johnstown flood1 #bad1 #bae4           
,kerosene1 #adi1 #aej4      ,kilowatt1  
#cea4       ,lactic acid1 #bcj4         
,leaves1 #acb1 #bfb4      ,lens1        
#aag-aba4       concave1 #aah4          
converging1 #aah4       crystalline1 of 

eye1 #abb4       focal length1 #aah4    
material1 #aai4       refractive power1 
#aai4      ,lever1 #aeh-afb4            
examples1 #afj-afb4       fulcrum1 #aei1
 #afj4      ,life1 and carbon dioxide1  
#ed4       and nitrogen1 #bfa4       and
 oxygen1 #di1 #ed4      ,lifting pumps1 
#ahi-aib4      ,light1 absorption1      
#ace-ach4       and heat1 #adb-adg4     
a wave motion1 #ade-adg4       bent     
rays1 #aac1 #aad4       chemical action1
 #abf-abg4       disease1 #aca-acb4     
essential to life1 #aca1 #acb4          
fading illumination1 #aje1 #ajf4        
influence on color1 #acd4               
reflection of1 #aji-aab4                
refraction of1 #aac-abe4       travels  
in a straight line1 #ajh4       white1  
composed of colors1 #acd4               
,lighting1 artificial1 #adh-aec4        
,lime1 chloride of1 #bdj1 #bea4         
,limewater1 #bbj4       and carbon      
dioxide1 #bbh4      ,linen1 bleaching1  
#bda4       dyeing1 #bde-bdg4           
,lines1 of force1 #cbi-cca1 #ccd4       

isobaric1 #hh1 #ia4       isothermal1   
#hi1 #ia4      ,liquefaction of gases1  
#ig1 #ih4      ,liquid air1 #ih4        
,liquid soap1 #bbc1 #bbd4      ,litmus1 
action of acids1 #bbj4       action of  
bases1 #bba1 #bbb4       action of      
neutral substance1 #bbb4      ,logwood  
dyes1 #bde1 #bdg1 #bdh4      ,los       
,angeles aqueduct1 #baa4      ,lye1     
#bba1 #bbb4       ,machines1 compound1  
#aga4       inclined plane1 #afb-aff4   
lever1 #aeh-afb4       pulley1 #aff-afi4
       wheel and axle1 #afi-aga4        
,madder1 for dyes1 #bde4      ,magnet1  
#cbh4       electro-1 #cai4       field 
of1 #cbi-cca4       lines of force      
about1 #cbi-cca4       poles of1        
#ccj-ccb4       properties of           
electricity1 #cah4      ,magnetic1      
needle1 #cbh4       poles1 #cbi-cca4    
,magnifying power1 of a lens1 #aae4     
of a microscope1 #aae4       of a       
telescope1 #aae4      ,mammoth ,cave of 
,kentucky1 #ga4      ,manganese dioxide1
 #df4       chlorine made from1 #bch4   

oxygen made from1 #df4      ,marble1 for
 carbon dioxide1 #ee4      ,matches1    
#dg4       safety1 #dg-dh4              
,matching colors1 #acg4      ,matter1   
conservation of1 #eh1 #ei4      ,meat1  
#ff4       preservation of1 #bec4       
,mechanical devices1 #aed1 #aee4        
,melting1 #ci1 #dj4      ,melting point1
 #dj4      ,melting substances without a
 definite melting point1 #dj4           
,mercerized cotton1 #bah4      ,mercury1
 barometer1 #hd4       thermometer1     
#ad-ag4      ,metals1 electroplating1   
#cag4       preservation by paint1      
#bec-bed4       veins deposited by      
precipitation1 #gb1 #gc4       welding1 
#cae4      ,meter1 gas1 #ic1 #id4       
,microrganisms1 #acb1 #acc4             
,microscope1 #aae4      ,milk1 boiling  
point1 #cb4       ,pasteurized1 #bej4   
,minerals1 in foods1 #fb1 #fc4       in 
water1 #gj1 #ga4      ,mirrors1         
#ajh-aab4       distance of image behind
 mirror1 #aaa4       distance of object 
in front of mirror1 #aaa4       image a 

duplicate of object4 #aaa4      ,molding
 of glass1 #dj4      ,molecule1         
#ajj-ajc4      ,mordants1 #bdg1 #bdh1   
#bdi4      ,morphine1 #beg4      ,morse1
 telegraphic code1 #cbd4      ,motion1  
in sound1 #bff1 #bgh1 #bhj4       in    
work1 #aef4      ,motor1 electric1 #ccf4
       principle of1 #ccc4       street 
car1 #ccg4      ,mouth breathing1 #ej4  
cause of1 #ea4      ,movable pulley1    
#afg1 #afh4      ,music1 #bgh4          
,musical instruments1 percussion1 #bii4 
stringed1 #bhd-bie4       wind1 #bie1   
#bii4      ,musical scale1 #bhb4        
,naphtha in gas engines1 #ahe4          
,naphthalene1 #aeb4      ,narcotics1    
#bee4      ,natural gas1 #aeb4          
,needle1 magnetic1 #cbh4      ,negative1
 electrode1 #cjh4       photographic1   
#acj4      ,neutral substance1 #bbb4    
and litmus1 #bbb4      ,neutralization1 
#bbb4      ,niagara ,falls1 #agf4       
,nitrogen1 #ff4       and bacteria1     
#bfc4       and plant life1 #bfa4       
in atmosphere1 #bfa4       in           

fertilizer1 #bfb-bfe4       in food1    
#ff4       preparation of1 #bfa4        
properties of1 #bfa4      ,noise in     
music1 #bhj4      ,non-conductors1 of   
electricity1 #cba-cbb4       of heat1   
#be4      ,nutcracker1 as a lever1 #afb4
       ,oboe1 #big4      ,octave1 #bhd4 
,odors1 #aja4      ,ohm1 unit of        
resistance1 #cde4      ,oil1 gasoline1  
#adi1 #aej4       kerosene1 #adi1 #aej4 
lubricating1 #agd4       olive1 #af4    
,orchestra grouping1 #bii4      ,ore1   
#gb4      ,organ pipes1 #big4           
,overtones1 #bij-bic4      ,oxalic acid1
 #bdg1 #bdh4      ,oxidation1 #de-ei4   
and decay1 #di4       heat the result   
of1 #di-eb4       in human body1 #di1   
#ec4       of iron1 #dh4      ,oxygen1  
#ff4       and bleaching1 #bci4         
and combustion1 #de4       and food1    
#ff4       and plants1 #ee4       and   
the human body1 #ej4       and water1   
#gi1 #hj4       in the atmosphere1 #de4 
preparation of1 #df4       ,paint1 as   
wood and metal preservatives1 #bec1     

#bed4       removal of stains1 #bdc4    
,paper making1 #bai4      ,paraffin1    
#aej1 #cba4      ,pasteurized milk1     
#bej4      ,patent medicines1 #beg-bfj4 
,peas1 sources of nitrogen1 #bfc4       
,pelton wheel1 #agg4      ,percussion   
instruments1 #bii4      ,period of a    
body1 #bgc4      ,peroxide of hydrogen1 
#ec1 #beb      ,petrolatum1 #aej4       
,petroleum1 #adi1 #aej4                 
,phonograph1 #cjc-cje4      ,phosphorus1
 in fertilizer1 #bfc1 #bfd4       in    
making nitrogen1 #bfa4       in matches1
 #dg1 #dh4       poisoning by1 #dg4     
,photography1 #abg-aca4                 
,photometer1 #ajg4      ,pianos1        
#bhd-bib4      ,pin wheel1 #aha4        
,pitch of sound1 #bhj1 #bha4       cause
 of1 #bhb4       in wind instruments1   
#bif-bii4      ,plane1 inclined1        
#afb-aff4      ,plants1 and atmosphere1 
#ee4       and light1 #aca-acb4         
and nitrogen1 #bfa4      ,plate         
developing1 photographic1 #abh4         
,pneumatic dispatch tube1 #bje4         

,poles1 magnetic1 #ccj-ccb4       of    
cell1 #cjh4      ,positive electrode1   
#cjh4      ,potash1 in fertilizer1      
#bfc-bfe4      ,potassium chlorate and  
oxygen1 #df4       permanganate1 #ajj4  
tartrate and ,rochelle salt1 #bbg4      
,power1 candle1 #aje-ajg4               
electric1 #cea4       horse1 #agc1 #cea4
       sources of1 #agd1 #age1 #ahe4    
transmission by belts1 #aga4            
water1 #agf-ahj4      ,precipitation1   
#gb1 #gc4      ,preservatives1 food1    
#beb4       wood and metal1 #bec-bed4   
,pressure1 atmospheric1 #hb-hf4         
calculation of atmospheric1 #hc1 #hd4   
calculation of gas1 #ib1 #ic4           
calculation of water1 #id4       gauge1 
#ib-id4       of illuminating gas1 #ic4 
relation of pressure of gas to volume1  
#ie1 #if4       water pressure1         
#bjh-baa1 #bad-baf4       within the    
body1 #hf4      ,primary colors1 #ace4  
,print1 photographic1 #aca4             
,printing1 color designs in cloth1 #bdh1
 #bdi4       electrotype1 #cag4         

,prisms1 #ace4       refraction through1
 #aag4      ,proteids1 #ff4             
,pulleys1 #aff-afi4       applications  
of1 #afi4      ,pump1 #ahg-bje4         
air1 #bja-bje4       force1 #aib1 #aic4 
lifting1 #ahi-aib4      ,pupil of the   
eye1 #abb4      ,pure food laws1        
bleaching1 #bdb4       preservatives1   
#beb4      ,purification of water1 #gg1 
#aif4      ,push button1 #cba4          
,radiator1 #ai-ba4      ,railroads1     
grading of1 #afe-aff4      ,rain1 #cf1  
#cg4      ,rainbow1 #acd4      ,rain    
water1 #bbe4      ,reflection1 angle of1
 #aaj4       of light1 #aji-aab4        
of sound1 #bgh1 #bgi4      ,refraction1 
angle of1 #aad4       by atmosphere1    
#aad4       of light1 #aac4       uses  
of1 #aae-aaf4      ,relay1 telegraph1   
#cbe4      ,reservoir1 #bad4            
artificial1 #baa4       construction of1
 #bad-baf4       natural1 #baa4         
,resistance1 electrical1 #cab4          
internal1 of cell1 #cdc4       unit of1 
#cde4      ,resonance1 #bgf4            

,river1 volume and value of1 #ahj4      
,roads1 application of inclined plane   
to1 #afe-aff4      ,rochelle salt1 #bbg1
 #bca4      ,rocks1 effect of freezing  
water on1 #db-dc4       water as a      
solvent1 #ga4      ,rosin1 obtained by  
distillation1 #ce4       ,safety        
matches1 #dg-dh4      ,salicylic acid1  
#bec4      ,salt1 #bbg-bbh4      ,salts1
 #bbg4       general properties1 #bbg4  
in ocean1 #bbg4       smelling1 #bbb4   
,saturation of air1 #cg4      ,scale1   
musical1 #bhb4      ,screw1 and inclined
 plane1 #aff4      ,seaweed1 #bfe4      
,seidlitz powder1 #bca4                 
,self-raising flour1 #bca4      ,sewage1
 disposition of1 #aih-aii4       of     
camps1 #aif4       source of revenue1   
#bja4      ,sewer gas1 #eg4      ,silk1 
bleaching1 #bda4       dyeing1 #bde-bdg4
      ,silver chloride1 #abg-aca4       
,simple colors1 #ach4      ,simple      
substances1 #ajc4      ,siren1 #bhj4    
,smelling salts1 #bbb4      ,snow1      
#cf-cg4      ,soap1 #bbb-bbd4       and 

hard water1 #bbe4       liquid1         
#bbc-bbd4       preparation1 #bbc4      
,soda1 baking1 #bbg1 #bbh-bbi4          
benzoate1 #bec4       caustic1 #bah1    
#bbb1 #bbc1 #bbg4       washing1 #bbe1  
#bbf1 #bbi4      ,soda mints1 #bca4     
,sodium1 bicarbonate1 #ef1 #bbg1 #bbh1  
#bcj-bca4       carbonate1 #bbh4        
chloride1 #bbh4      ,soil1 deposited by
 streams1 #gc4      ,solenoid1 #cah4    
,solution1 #gj4      ,soothing sirup1   
#beh4      ,sound1 and motion1 #bff1    
#bgh4       musical1 #bgh4       nature 
of1 #bff4       reflection1 #bgg4       
speed of1 #bga-bgb4       transmission  
of1 #bfg-bga4       velocity of1        
#bga-bgb4       waves1 #bgb-bgd4        
,sounder1 telegraph1 #cbd4              
,sounding board1 #bgg4      ,sour milk  
in cooking1 #bcj4      ,specific heat1  
#bh-bi4      ,spectrum1 #acd-ace4       
,speed1 of sound1 #bga1 #bgb4           
,spontaneous combustion1 #eb4           
,stains1 removal of1 #bbf1 #bdc4        
,standpipes1 #bab4      ,starch1 #fe4   

,steam1 and work1 #ahc-ahd4             
engine1 #ahc-ahe4       heat of         
vaporization1 #cb4       heating by1    
#cc4       turbine1 #ahc-ahd4           
,steel1 forging and annealing1 #af4     
,stoves1 #ah-ai4      ,streams1 carriers
 of mud1 #gc4       volume of1 #agi-ahj4
      ,street cars1 electric1 #ccg4     
,stringed instruments1 #bhd-bie4        
,strings1 vibrating1 #bhf-bij4          
,sugar1 #af1 #fe4       fermented by    
yeast1 #bcd4      ,sulphur1 #ff4        
as disinfectant1 #bea4       in making  
sulphurous acid1 #bdb4      ,sulphuric  
acid1 in bleaching1 #bdj1bda4       in  
fire extinguisher1 #ee4       in making 
of hydrogen1 #hj4       in voltaic cell1
 #cjg4      ,sulphurous acid1 in        
bleaching1 #bdb4       preparation1     
#bdb4      ,sun1 energy derived from1   
#adc-add4       source of heat1 #bi-cj4 
,sunlight1 #ace4       and bacteria1    
#acc4       and chemical action1        
#abf-abg4      ,sympathetic vibrations1 
#bgd-bgg4       ,tallow1 #aje1 #adh4    

,tartar1 cream of1 #bbi4                
,telegraph1 #cbb4       long distance1  
#cbg4       relay1 #cbe4       sounder1 
#cbd4      ,telephone1 #cej-cea4        
,temperature1 #ac-ad4       as          
measurement of heat present1 #bg4       
in detecting adulterants1 #ag4       in 
forging steel1 #af4       in making     
sirups1 #af4       measurement of1      
#ad-ae4      ,thermometer1 #ad-ag4      
,centigrade1 #ae4       ,fahrenheit1    
#ae4      ,tinder box1 #dg4             
,transmission1 of light1 #ade-adg4      
of sound1 #bfg-bga4      ,tuning fork1  
#bff1 #bgc1 #bgh1 #bij4      ,turbine1  
steam1 #ahc4       water1 #agh4         
,turpentine1 and grease1 #bbf4       by 
distillation1 #ce4       ,unleavened    
bread1 #bcc4       ,vacuum1 sound in1   
#bfh4      ,vapor1 in atmosphere1       
#cf-ch4      ,vaporization1 heat of1    
#cb4      ,varnish1 on candies1 #bec4   
,vegetable matter1 and coal1 #cj4       
and gas1 #cj4       and oil1 #cj4       
,veins1 formation in rock1 #gb-gc4      

,velocity1 of sound1 #bga-bgb4          
,ventilation1 #ba-bd1 #ed4       need   
of1 #ch4      ,vibration1 of strings1   
#bhf-bij4       sympathetic1 #bgd-bgg4  
,viola1 #bie4      ,violin1 #bie4       
,violoncello1 #bie4      ,vocal cords1  
#cjj4      ,voice1 #cjj4      ,volt1    
#cdd4      ,voltage1 #cde4      ,voltaic
 cell1 #cjf-cjh1 #caj4      ,voltmeter1 
#cdd4      ,volume1 of a stream1        
#agi-ahj4       relation of pressure of 
a gas1 #ie-if4       ,washing powders1  
#bbd-bbf4       soda1 #bbi4      ,water1
 action in nature1 #gj-gd4       amount 
used daily per person1 #aha4       and  
hydrogen1 #gi4       and oxygen1 #gi1   
#hj4       as solvent1 #gj-ga4          
boiling1 #gg4       boiling point1 #ae4 
composition1 #gi-hj4       condensation1
 #cc4       dams and reservoirs1        
#bad-baf4       density1 #aa4           
distilled1 #cd1 #gg4       drinking1    
#ge-gg1 #aie-bja4       electrolysis1   
#gi-hj4       evaporation1 #cc-cd4      
expansion1 #i-aj1 #da-db4               

filtration1 #gg4       freezing1 #dj-da4
       hard1 #bbe4       heat of fusion1
 #dj4       impurities1 #gf-gg4       in
 atmosphere1 #cf-ch4       in food1 #ge4
       in human body1 #ge4       in     
vegetables1 #ge4       influence on     
climate1 #bi1 #dj4       irrigation1    
#aic-aid4       minerals in1 #gj-ga4    
ocean1 #bfe4       power1 #agf-ahj4     
precipitates1 #gb1 #gc4       pressure1 
#bjh-baa1 #bad-baf4       purification1 
#gg4       rain1 #bbe4       running1   
value of1 #agh-ahj4       source of1    
#gh4       steam1 #cb4       waves1     
#ade-adg4       weight1 #bjh-bji1 #bae4 
wells1 #aie-bja4       wheels1 #agf-ahj4
       work under1 #bjc-bje4      ,water
 supply1 and forests1 #baf-bag4         
cost1 #bab-bad4       of city1 #bjf-bab1
 #bag4      ,watt1 #cea4      ,waves1   
heat1 #ade-adg4       light1 #ade-adg4  
sound1 #bfh1 #bgb-bgd4       water1     
#ade-adg4      ,weather1 bureau1 #hg-ia4
       forecasts1 #ch-ci1 #hf-hh4       
relation of water to1 #bi1 #dj4         

,weather maps1 #hi-ia4      ,wedge1 and 
inclined plane1 #aff4      ,weight1 of  
air1 #hf4       of water1 #bjh-bji1     
#bae4      ,welding1 by electricity1    
#cae4      ,wells1 #aie-bja4            
drilled1 #aii4       driven1 #aif-aig4  
,wheel and axle1 #afi-aga4              
cogwheels1 #agj4       windlass1 #afi4  
,wheelbarrow as lever1 #afj-afa4        
,white light1 nature of1 #ace4          
,wind instruments1 #big-cja4            
,windlass1 #afi4      ,windmill1        
#agd-age1 #ahj-ahb4      ,winds1 #bd4   
,wine1 #bcb1 #bcd4      ,wood1 as source
 of charcoal1 #eh4       ashes in soap  
making1 #bbc4       in paper making1    
#bai4       preservation1 #bec-bed4     
,wool1 bleaching1 #bda4       dyeing1   
#bde-bdg4      ,work1 #aef-ahf4         
and steam1 #ahc-ahd4       and water1   
#agf-ahj4       conservation1 #agd-age4 
formula1 #aeg4       machines1 #aeg-age4
       unit of1 #agb-agc4       waste1  
#agc4      ,woven designs in cloth1     
#bdi4       ,yeast1 #bcd-bcf4           

wild1 #bce-bcf4       ,zinc1 in         
galvanizing iron1 #di4       in making  
hydrogen1 #hj4       in voltaic cell1   
#cjg-cjh4     ,,plant ,,life ,,and      
,,plant ,,uses  ,by ,,john ,,gaylord    
,,coulter1 ,ph4 ,d4  #a4bj   ,an        
elementary textbook providing a         
foundation for the study of agriculture1
 domestic science1 or college botany4   
,but it is more than a textbook on      
botany--it is a book about the          
fundamentals of plant life and about the
 relations between plants and man4 ,it  
presents as fully as is desirable for   
required courses in high schools those  
large facts about plants which form the 
present basis of the science of botany4 
,yet the treatment has in view          
preparation for life in general1 and not
 preparation for any particular kind of 
calling4  ,the subject is dealt with    
from the viewpoint of the pupil rather  
than from that of the teacher or the    
scientist4 ,the style is simple1 clear1 
and conversational1 yet the method is   

distinctly scientific1 and the book has 
a cultural as well as a practical       
object4  ,the text has a unity of       
organization4 ,so far as practicable the
 familiar always precedes the unfamiliar
 in the sequence of topics1 and the     
facts are made to hang together in order
 that the pupil may see relationships4  
,such topics as forestry1 plant         
breeding1 weeds1 plant enemies and      
diseases1 plant culture1 decorative     
plants1 and economic bacteria are       
discussed where most pertinent to the   
general theme rather than in separate   
chapters which destroy the continuity4  
,the questions and suggestions which    
follow the chapters are of two kinds2   
some are designed merely to serve as an 
aid in the study of the text1 while     
others suggest outside study and        
inquiry4 ,the classified tables of terms
 which precede the index are intended to
 serve the student in review1 and to be 
a general guide to the relative values  
of the facts presented4 ,more than #bjj 

attractive illustrations1 many of them  
original1 are included in the book4     
,,american ,,book ,,company     ,a ,,new
 ,,astronomy1 #a4cj  ,by ,,david ,,todd1
 ,m4 ,a41 ,ph4 ,d41 ,professor of       
,astronomy and ,navigation and ,director
 of the ,observatory1 ,amherst ,college4
   ,astronomy is here presented as      
preeminently a science of observation4  
,more of thinking than of memorizing is 
required in its study1 and greater      
emphasis is laid on the physical than on
 the mathematical aspects of the        
science4 ,as in physics and chemistry1  
the fundamental principles are connected
 with tangible1 familiar objects1 and   
the student is shown how he can readily 
make apparatus to illustrate them4 ,in  
order to secure the fullest educational 
value1 astronomy is regarded as an      
inter-related series of philosophic     
principles4         99       99       99
       99       99     ,,mathematical   
,,geography1 #a4jj  ,by ,,willis ,e4    
,,johnson1 ,ph4 ,d41 ,vice-,president   

and ,professor of ,geography and ,social
 ,sciences1 ,northern ,normal and       
,industrial ,school1 ,aberdeen1 ,south  
,dakota4   ,this work explains with     
great clearness and thoroughness that   
portion of the subject which not only is
 most difficult to understand1 but also 
underlies and gives meaning to all      
geographical knowledge4 ,a vast number  
of facts which are much inquired about1 
but little known1 are taken up and      
explained4 ,simple formulas are given so
 that a student unacquainted with       
geometry or trigonometry may calculate  
the heights and distances of objects1   
the latitude and longitude of a place1  
the amount any body is lightened by the 
centrifugal force due to rotation1 the  
deviation of a plumb-line from a true   
vertical1 etc4  ,,american ,,book       
,,company     ,,elements ,,of ,,geology 
,by ,,eliot ,,blackwelder1 ,associate   
,professor of ,geology1 ,university of  
,wisconsin1 and ,,harlan ,h4 ,,barrows1 
,associate ,professor of ,general       

,geology and ,geography1 ,university of 
,chicago4  #a4dj   ,an introductory     
course in geology1 complete enough for  
college classes1 yet simple enough for  
high school pupils4 ,the text is        
explanatory1 seldom merely descriptive1 
and the student gains a knowledge not   
only of the salient facts in the history
 of the earth1 but also of the methods  
by which those facts have been          
determined4 ,the style is simple and    
direct4 ,few technical terms are used4  
,the book is exceedingly teachable4     
,the volume is divided into two parts1  
physical geology and historical geology4
 ,it differs more or less from its      
predecessors in the emphasis on         
different topics and in the arrangement 
of its material4 ,factors of minor      
importance in the development of the    
earth1 such as earthquakes1 volcanoes1  
and geysers1 are treated much more      
briefly than is customary4 ,this has    
given space for the extended discussion 
of matters of greater significance4 ,for

 the first time an adequate discussion  
of the leading modern conceptions       
concerning the origin and early         
development of the earth is presented in
 an elementary textbook4  ,the          
illustrations and maps1 which are       
unusually numerous1 really illustrate   
the text and are referred to definitely 
in the discussion4 ,they are admirably  
adapted to serve as the basis for       
classroom discussion and quizzes1 and as
 such constitute one of the most        
important features of the book4 ,the    
questions at the end of the chapters are
 distinctive in that the answers are in 
general not to be found in the text4    
,they may1 however1 be reasoned out by  
the student1 provided he has read the   
text with understanding4  ,,american    
,,book ,,company     ,,essentials ,,of  
,,biology  ,by ,,george ,,william       
,,hunter1 ,a4 ,m41 ,head of ,department 
of ,biology1 ,de ,witt ,clinton ,high   
,school1 ,new ,york ,city4  #a4be       
,this new first-year course treats the  

subject of biology as a whole1 and meets
 the requirements of the leading        
colleges and associations of science    
teachers4 ,instead of discussing plants1
 animals1 and man as separate forms of  
living organisms1 it treats of fife in a
 comprehensive manner1 and particularly 
in its relations to the progress of     
humanity4 ,each main topic is introduced
 by a problem1 which the pupil is to    
solve by actual laboratory work4 ,the   
text that follows explains and          
illustrates the meaning of each problem4
 ,the work throughout aims to have a    
human interest and a practical value1   
and to provide the simplest and most    
easily comprehended method of           
demonstration4 ,at the end of each      
chapter are lists of references to both 
elementary and advanced books for       
collateral reading4         99       99 
99       99       99     ,,sharpe',s    
,,laboratory ,,manual ,,in ,,biology    
#j4ge   ,in this ,manual the #ef        
important problems of ,hunter's         

,essentials of ,biology are solved2 that
 is1 the principles of biology are      
developed from the laboratory           
standpoint4 ,it is a teacher's detailed 
directions put into print4 ,it states   
the problems1 and then tells what       
materials and apparatus are necessary   
and how they are to be used1 how to     
avoid mistakes1 and how to get at the   
facts when they are found4 ,following   
each problem and its solution is a full 
list of references to other books4      
,,american ,,book ,,company             
,,essentials ,,of ,,physics  ,by        
,,george ,a4 ,,hoadley1 ,c4,e41 ,sc4    
,d41 ,professor of ,physics1 ,swarthmore
 ,college4  #a4be   ,this is the        
author's popular and successful         
,elements of ,physics enriched and      
brought up to date4 ,despite the many   
changes and modifications made in this  
new edition1 it retains the qualities   
which have secured so great a success   
for the previous book4  ,it tells only  
what everyone should know1 and it does  

this in a straightforward1 concise1 and 
interesting manner4 ,it takes into      
consideration the character of high     
school needs and conditions1 and1       
throughout1 lays particular emphasis    
upon the intimate relation between      
physics and everyday life4  ,while the  
subject matter1 as a whole1 is          
unchanged1 the order of topics in many  
cases has been altered to adapt the     
development of the subject to the habits
 of thought of high school pupils4      
,instead of beginning the treatment of a
 subject with the definition and        
proceeding to a discussion of the       
sub-topics1 the author starts with a    
discussion of well-known phenomena and  
leads up to the definition of the       
subject discussed4 ,the text1 wherever  
possible1 has been simplified1 more than
 fifty topics having been amplified1    
expanded1 or reworded4 ,more familiar   
illustrations of the topics treated are 
given1 and the demonstrations of many of
 the experiments are simplified by the  

use of materials that are readily       
obtainable in the classroom4  ,there    
have been added a number of new topics1 
mostly in connection with the recent    
advances in applied science4 ,the number
 both of questions and problems has been
 greatly increased and the data in these
 all relate to actual1 practical1       
physical phenomena4 ,more than one-fifth
 of the illustrations in the book are   
new1 many of the pictures of apparatus  
having been redrawn to show modern      
forms4  ,,american ,,book ,,company