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==CHAPTER  X - THE  SPECTRA  OF  ISOTOPES==
==CHAPTER  X - THE  SPECTRA  OF  ISOTOPES==
 
[[Aston 1922/Chapter 10]]
108.  The  Spectra  of  isotopes.  As  has  already  been
stated^  the  first  experimental  work  on  the  spectra  of  isotopes
was  that  of  Russell  and  Rossi  in  1912  who  failed  to  distinguish=
 
any  difference  between  the  spectrum  of  thorium  and  that  of  a
mixture  of  thorium  and  ionium  containing  a  considerable
percentage  of  the  latter.  The  same  negative  result  was
obtained  by  Exner  and  Haschek.^  During  the  fractional
diffusion  of  neon^  no  spectroscopic  difference  was  detected
between  the  heaviest  and  the  lightest  fraction,  though  as  the
separation  was  small  this  negative  evidence  was  not  very
strong.  In  1914  Soddy  and  Hyman  showed  that  the  spectrum
of  lead  derived  from  thorium  was  identical  with  that  of  ordinary=
 
lead.*  Furthermore  in  the  same  year  the  experiments  of
Richards  and  Lembert,^  Honigschmidt  and  HoroAvitz,*^  and
Merton '' proved  the  same  result.  Merton  concluded  from  his
1914  experiments  that  the  difference  in  wave-length  for  the
A  4058  line  must  be  less  than  0-003  A.  Before  going  on  to
consider  the  more  recent  results  it  will  be  as  well  to  discuss  =
the
magnitude  of  the  difference  to  be  expected  from  theory.
 
109.  The  magnitude  of  the  Gravitational  effect.  In
 
the  Bohr  theory  of  spectra  the  planetary  electrons  of  the  atom
rotate  round  the  central  positively  charged  nucleus  in  various
 
1  F.  p.  9.
 
2  Exiier  and  Haschek,  Sitz.  Akad.  Wiss.  Wien,  iia,  121,  175,    =
1912.
 
3  V.  p.  39.
 
*  Soddy  and  Hyman,  Jour.  Chem.  Soc,  105,  1402,    1914.
^  Richards  and  Lembert,  Jour.  Amer.  Chem.  Soc,  36,  1329,    1914.=
 
^  Honigschmidt  and  Horowitz,  Sitz.  Akad.    Wiss.    Wien,  iia,  =
123,
1914.
 
'  Merton,  Proc.  Roy.  Soc,  91A,  198,    1914.
 
121
 
 
122  ISOTOPES
 
stable  orbits.  The  frequencies  of  the  spectral  lines  emitted
by  the  element  are  associated  in  an  absolutely  definite  manner
with  the  rotational  frequencies  of  these  orbits  which  are
calculated  by  what  is  known  as  a  "  quantum "  relation.
Without  going  further  into  the  theory  it  will  be  seen  at  once
that  if  we  alter  the  force  acting  between  the  central  nucleus
and  its  planetary  electrons  these  orbits  will  change  and  with
them  the  frequency  of  the  light  emitted.  It  is  therefore  of
interest  to  examine  the  magnitude  of  the  change,  to  be  expected=
 
from  this  theory,  when  we  alter  the  mass  of  the  nucleus  without=
 
changing  its  charge,  and  so  pass  from  one  isotope  to  another.
 
The  difference  in  the  system  which  will  first  occur  to  one  is
that  although  the  electrical  force  remains  the  same  the  gravi-
tational force  must  be  altered.  The  order  of  magnitude  of
the  change  expected  in  the  total  force  will  clearly  be  given  by=
 
considering  the  ratio  between  the  electrical  and  gravitational
forces  acting,  to  take  the  simplest  case,  between  the  protou
and  the  electron  in  a  neutral  hydrogen  atom.
 
Assuming  the  law  of  force  to  be  the  same  in  both  cases,  this
ratio  is  simply  e^/GMm  ;  where  e  is  the  electronic  charge
4-77  X  10~i",  G  the  universal  gravitational  constant  6-6  x  10"^,=
 
M  the  mass  of  the  proton  1-66  x  lO"^*^  and  m  the  mass  of  the=
 
electron  9-0  x  10~  2^.  Putting  in  these  numerical  values  we
obtain  the  prodigious  ratio  2-3  x  10  ^9.  In  other  words  the
effect  of  doubling  the  mass  of  the  nucleus  without  altering  its=
 
charge  would  give  the  same  percentage  increase  in  the  total
pull  on  the  planetary  electron,  as  would  be  produced  in  the
pull  between  the  earth  and  the  moon  by  a  quantity  of  meteoric
dust  weighing  less  than  one  million  millionth  of  a  gramme
falling  upon  the  surface  of  the  former  body.  The  gravitational
effect  may  therefore  be  dismissed  as  entirely  negligible.
 
110.  Deviation  of  the  Bohr  orbits  due  to  change  in
the  position  of  the  centre  of  gravity  of  the  rotating
system.  Although  we  may  neglect  the  gravitational  effect
there  is  another,  of  quite  a  different  order,  which  arises  in  th=
e
following  manner.  The  mass  of  the  electron  compared  with
that  of  the  nucleus  is  small  but  not  absolutely  negligible,  hence=
 
it  will  not  rotate  about  the  nucleus  as  though  that  were  a
 
 
THE  SPECTRA  OF  ISOTOPES  123
 
fixed  point,  but  both  will  rotate  about  their  common  centre
of  gravity.  The  position  of  this  centre  of  gravity  will  be
shifted  by  any  alteration  in  the  mass  of  the  nucleus.  If  E,  M=
 
and  e,  m  are  the  respective  charge  and  mass  of  the  nucleus  and=
 
the  rotating  electron,  the  equation  of  motion  is
 
rM        ,      Ee
 
M  +  m  r^
 
where  r  is  the  distance  between  the  two  charges  and  w  the
angular  velocity.  Bohr  ^  introduced  this  effect  of  the  mass  of
the  nucleus  in  order  to  account  for  the  results  obtained  by
Fowler.  2    The  Bohr  expression  for  the  frequency  then  becomes
 
where  e,  E  and  m,  M  are  the  charges  and  masses  of  the  electron=
 
and  nucleus  respectively.  If  we  suppose  that  the  atomic
weight  of  lead  from  radium  to  be  one  unit  less  than  that  of
ordinary  lead,  this  theory  predicts  a  difference  in  wave-length,
for  the  principle  line,  of  000005  A  between  the  two,  a  quantity=
 
beyond  the  reach  of  the  most  delicate  methods  of  spectrum
analysis  used  up  to  the  present.
 
111.  Later  experiments  of  Aronberg  and  Merton.
 
In  1917  Aronberg,^  applying  the  extremely  high  dispersion
derived  from  the  spectrum  of  the  sixth  order  of  a  Michelson
10-inch  grating  to  the  line  A  4058  emitted  from  a  specimen  of
radio-lead  of  atomic  weight  206-318,  observed  a  difiference  of
0-0044  A  between  this  and  ordinary  lead,  of  atomic  weight
207-20.  This  remarkable  result  has  been  since  confirmed  by
Merton  of  Oxford*  who  gives  the  difference  of  wave-length
between  radio-lead  from  pitchblende  and  ordinary  lead  as
0-0050^2 0-0007,  Merton  made  use  of  a  totally  different  optical
system,  namely  a  Fabry  and  Perot  etalon,  so  that  the  agreement
is  very  striking.
 
It  is  to  be  noticed  that  the  effect  observed  was  not  a  mere
 
1  Bohr,  Nature,  92,  231,    1913.
 
2  Fowler,  Nature,  92,  95,    1913.
 
3  Aronberg,  Proc.  Nat.  Acad.  Sci.,  Z,  710,    1917,  and  Ast=
rophys,
Jour.,  47,  96,    1918.
 
4  Merton,  Proc.  Boy.  Soc,  96A,  388,      920.
 
 
124
 
 
ISOTOPES
 
 
broadening  of  the  line  but  a  definite  shift,  and  that,  though
of  the  same  sign,  it  is  about  one  hundred  times  greater  than
that  predicted  by  the  Bohr  theory,  Merton  also  found  a  shift
of  0-0022 =C2=B10-0008  A  between  the  wave-length  of  thorite-lead
and  ordinary  lead,  differing  in  atomic  weight  by  about  0-6.
The  heavier  atom  shows  the  higher  frequency  in  all  cases.
This  remarkable  discrepancy  between  the  shift  predicted  by
theory  and  that  actually  observed  has  been  discussed  by
Harkins  and  Aronberg.^
 
At  a  recent  discussion  on  isotopes  at  the  Royal  Society  ^
Merton  commented  upon  the  line  6708  A  emitted  by  the
element  lithium,  which  consists  of  two  components  0-151  A
apart.  If  lithium  is  accepted  as  a  mixture  of  isotopes  6  and  7,=
^
he  calculated  that  each  of  these  components  should  be  accom-
panied by  a  satellite,  some  sixteen  times  as  faint,  displaced  by=
 
0-087  A.  So  far  he  had  not  been  able  to  observe  such  satellites=
.
Previous  experiments  of  Merton  and  Lindemann*  on  the
expected  doubling  in  the  case  of  neon  had  given  no  conclusive
results  on  account  of  the  physical  width  of  the  lines.  It  was
hoped  that  this  difficulty  could  be  overcome  by  the  use  of
liquid  hydrogen  temperatures.
 
StiU  more  recently  Merton^  has  repeated  his  experiments  on
lead,  using  a  very  pure  sample  of  uranium  lead  from  Australian
Carnotite.  His  final  results  are  indicated  in  the  following
table  :
 
 
A
 
(Carnotite  lead)"!
.  ^(ordinary  lead)  J
 
r    Wave  niimber  (ordinary  lead) '
.  Wave-number  (Carnotite  lead).
 
4058
3740
3684
3640
3573
 
0-011  =C2=B10-0008
0-0074=C2=B10-0011
0-0048=C2=B10-0007
0-0070=C2=B10-0003
0-0048=C2=B10-0005
 
0-065=C2=B10-005
0-053=C2=B10-008
0-035=C2=B10-005
0-C52=C2=B10-002
0-037=C2=B10-004
 
1  Harkiiis  and  Aronberg,  Jour.  Am.  Chem.  Soc,  42,  1328,
 
Merton,  Proc.  Roy.  Soc.=C2=BB  99A,  87,    1921.
 
=C2=BB  V.  p.  86.
 
*  Lindemann,  ibid.
 
  Merton,  Roy.  Soc.  Proc,  lOOA,  84,    1921.
 
 
1920.
 
 
THE  SPECTRA  OF  ISOTOPES  125
 
It  will  be  noticed  that  the  shift  for  the  line  A  4058  is  rathe=
r
more  than  twice  that  obtained  before.  Merton  suggests  that
the  most  probable  explanation  of  this  difference  is  evidently
that  the  Carnotite  lead  used  is  a  purer  sample  of  uranium  lead=
 
than  that  obtained  from  the  pitchblende  residues.  It  is  also
apparent  that  the  differences  are  not  the  same  for  different
lines,  an  interesting  and  somewhat  surprising  result.
 
112.  "Isotope"  effect  on  the  Infra-red  spectrum  of
molecules.  The  extreme  smaUness  of  the  isotope  "  shift  "=
 
described  above  in  the  case  of  line  spectra  emitted  by  atoms  is=
 
due  to  the  fact  that  one  of  the  particles  concerned  in  the
vibration  is  the  electron  itself,  whose  mass  is  minute  compared
with  that  of  the  nucleus.  Very  much  larger  effects  should  be
expected  for  any  vibration  in  which  two  atoms  or  nuclei  are
concerned,  instead  of  one  atom  and  an  electron.  Such  a
vibration  would  be  in  the  infra-red  region  of  the  spectrum.
 
This  effect  was  first  observed  by  Imes^  when  mapping  the
fine  structure  of  the  infra-red  absorption  bands  of  the  halogen
acids.  In  the  case  of  the  HCl  "  Harmonic  "  band  at  1-76^,
mapped  with  a  20,000  line  grating,  the  maxima  were  noticed
to  be  attended  by  satellites.  Imes  remarks  :  "  The  apparent
tendency  of  some  of  the  maxima  to  resolve  into  doublets  in  the=
 
case  of  the  HCl  harmonic  may  be  due  to  errors  of  observation,
but  it  seems  significant  that  the  small  secondary  maxima  are
all  on  the  long-wave  side  of  the  principal  maxima  they  accom-
pany. It  is,  of  course,  possible  that  still  higher  dispersion
applied  to  the  problem  may  show  even  the  present  curves  to
be  composite."
 
Loomis^  pointed  out  that  these  satellites  could  be  attributed
to  the  recently  discovered  isotopes  of  chlorine.  In  a  later
paper ^  he  has  shown  that,  if  mi  is  the  mass  of  the  hydrogen
nucleus,  and  ma  the  mass  of  the  charged  halogen  atom,  the
 
difference  should  be  expressed  by  the  quanity  ^  =
~  the
 
square  root  of  which  occurs  in  the  denominator  of  the  expression=
 
 
^  Imes,  Astrophysical  Journal,  50,  251,    1919.
 
2  Loomis,  Nature,  Oct.  7,  179,    1920.
 
^  Loomis,  Astrophysical  Journal,  52,  248,    1920.
 
 
126  ISOTOPES
 
for  frequency.  "  Consequently  the  net  difference  between
the  spectra  of  isotopes  will  be  that  the  wave-lengths  of  lines
in  the  spectrum  of  the  heavier  isotope  will  be  longer  than  the=
 
corresponding  lines  for  the  lighter  isotope  in  the  ratio
1  +  1/1330  :  1  for  chlorine  and  1  -f  1/6478  :  1  for  bromine.=
 
Since  the  average  atomic  weight  of  chlorine  is  35-46  the  amounts=
 
of  CP^  and  CP'  present  in  ordinary  chlorine  must  be  as
1-54  :  0-46  or  as  3-35  :  1  and,  if  the  lines  were  absolutely  =
sharp
and  perfectly  resolved,  the  absorption  spectrum  of  ordinary
HCl  should  consist  of  pairs  of  lines  separated  by  1/1330  of
their  frequency  and  the  one  of  shorter  wave-length  should  have
about  3-35  the  intensity  of  the  other.  The  average  atomic
weight  of  bromine  is  79-92,  hence  the  two  isotopes  are  present
in  nearly  equal  proportions  and  the  absorption  spectrum  of
HBr  should  consist  of  lines  of  nearly  equal  intensity  separated
by  1/6478  of  their  frequency."
 
The  latter  will  be  too  close  to  be  observed  with  the  dispersion=
 
employed.  In  the  case  of  the  HCl  band  at  IIQ  ju  the  difference=
 
of  wave  number  on  this  view  should  be  4-3.  The  mean  differ-
ence of  wave  number  given  by  Loomis'  measurements  of  13
lines  on  Imes'  original  curves  for  this  band  is  4-5  ^  0-4  corre=
-
sponding to  14  A  in  wave-length.
 
The  spectroscopic  confirmation  of  the  isotopes  of  chlorine
has  also  been  discussed  by  Kratzer,!  who  considers  that  the
oscillation-rotation  bands  of  hydrogen  chloride  due  to  Imes^
are  in  complete  accordance  with  the  theory.
 
1  H.  Ivratzer,  Zeit.  Physik.,  3,  60,    1920.
*  Loc.  cit.
 


==CHAPTER  XI - THE  SEPARATION  OF  ISOTOPES==
==CHAPTER  XI - THE  SEPARATION  OF  ISOTOPES==

Revision as of 18:23, 3 July 2025

ISOTOPES[1]

F. W. ASTON, M.A., D.Sc, A.I.C., F.R.S.

Fellow of Trinity College, Cambridge

LONDON

EDWARD. ARNOLD & CO.

1922

[All rights reserved]

Printed in Great Britain

PREFACE

I have undertaken the preparation of this book on isotopes in response to many requests made to me by teachers of physics and chemistry and others working in these subjects that I should publish the results obtained by means of the mass spectrograph in a form more convenient to the public than that in which they first appeared. This is one of the reasons why the space allotted to the inactive isotopes may appear, in the light of the general title of the book, somewhat disproportion- ately large. Another is that the subject of radioactive isotopes really requires a book to itself, and I am in the hope that the inadequacy of my account may stimulate the production of such a volume by hands more competent than mine to deal with this very special and remarkable field of modern science. The logical order of exposition of a scientific subject is to start with the simple and from that build up the more complex. Unfortunately the sequence of events in experimental research is the exact opposite of this so that a compromise must be effected, unless one is content to sacrifice historical treatment altogether. The latter seems very undesirable in a new subject. I have endeavoured in Chapters I, II and IV, and elsewhere when possible, to adhere strictly to the historical order of events even at the cost of some reiteration.

I wish to take this opportunity of expressing my indebted- ness to Mr. C. G. Darwin for his timely criticism and unfailing assistance throughout the work, and also to Mr. R. H. Fowler for help with the proofs. My thanks are also due to Professor Soddy for his diagram of the radioactive isotopes, to Mr. A. J. Dempster for kindly sending me the illustrations of his work, to the proprietors of the Philosophical Magazine and to the Council of the Chemical Society for permission to use the plates and figures of my original papers, and to Messrs. Macmillan & Co., for the diagram of the radioactive trans- formations.

F. W. Aston
Cambridge,
January, 1922.

CONTENTS

Aston 1922/Contents

CHAPTER I - INTRODUCTION

Aston 1922 Chapter 1

CHAPTER II - THE RADIOACTIVE ISOTOPES

Aston 1922/Chapter 2

CHAPTER III - POSITIVE RAYS

Aston 1922/Chapter 3

CHAPTER IV - NEON

Aston 1922/Chapter 4

CHAPTER V - THE MASS-SPECTROGRAPH

Aston 1922/Chapter 5

CHAPTER VI - ANALYSIS OF THE ELEMENTS

Aston 1922/Chapter 6

CHAPTER VII - ANALYSIS OF THE ELEMENTS (Continued)

Aston 1922/Chapter 7

CHAPTER VIII - THE ELECTRICAL THEORY OF MATTER

Aston 1922/Chapter 8

CHAPTER IX - ISOTOPES AND ATOMIC NUMBERS

Aston 1922/Chapter 9

CHAPTER X - THE SPECTRA OF ISOTOPES

Aston 1922/Chapter 10

CHAPTER XI - THE SEPARATION OF ISOTOPES

Aston 1922/Chapter 11

APPENDIX I

Table of atomic weights and isotopes of the elements. 

 The  elements  are  given  in  order  of  their  atomic=
 numbers.  The

different periods are indicated by gaps after the inert gases. A curious relation, pointed out by Rydberg, is that the atomic numbers of all the inert gases are given by taking the series 2 (P + 2^ + 22 + 3^ + 3^ + 4^ + = ) and stoppmg the summation at any term. This gives the numbers used by Langmuir (p. 95).

The atomic weights given are the International ones except in the cases marked with an asterisk, where the figures are taken f= rom some of the recent determinations given below.

The isotopes where known are given in order of their atomic masses. The proportion of an isotope in a complex element is indicated by the index letters a, 6, c ... in descending order.=

In the case of isotopes of the radioactive elements 81-92 the ro= man numeral gives the number of them believed to exist. The nomen- clature of some of the rare earths 69-72 is not yet standardised.=

The names here are those used by Moseley. Some of these elements= , though detected by their X-ray spectra, have never been isolated.=

The elements corresponding to atomic numbers 43, 61, 75, 85, 87=

(all odd) have not yet been discovered.

Recent atomic weight determinations. The following is a list of some of the elements whose atomic weights have been re-=

determined quite recently, together with references to the papers in which they were published. Where more than one value is given different methods were used  :

Fluorine 19-001. Moles and Batuecas, Jour. Chim. Phys., 18, 35= 3,

1920. Aluminium 26*963. Richards and Krepelka, Journ. Am. Chem. Soc,=


42, 2221, 1920. Silicon 28-111. Baxter, Weatherelland Holmes, ibid., 42, 1194, = 

1920.

Scandium 45-10. Honigschmid, Zeit. Electrochem., 25, 93, 1919.=

Tin 118-703. Baxter and Starkweather, Journ. Am. Chem. Soc, 42,=


905, 1920.

118-699. Brauner and Krepelka, ibid., 42, 917, 1920.

141


142


APPENDIX I


Tellurium 127-73, 127-79. Bruylants and Michielsen, Bull= . Acad.

Bdg., 119, 1919. Samarium 150 "43. Owens, Balke and Kremers, Journ. Am. Chem= .

Soc, 42, 515, 1920. Thtdium 169-44, 169-66. James and Stewart, ibid., 42, 2022, = 1920. Bismuth 209-02. Honigschmid, Zeit. Electrochem., 26, 403, 1920= .

208-9967. Classen and Wey, Ber., 53, 2267, 1920. Antimony 121-773. Willard and McAlpine, Jouryi. Am. Chem. Soc, = 43,

797, 1921. Lanthanum 138-912. Baxter, Tani and Chapin, Journ. Am. Chem.=


Soc, 43, 1085, 1921. Germanium 72-418. Miller, Journ. Am. Chem. Soc, 43, 1085, 19= 21. Zinc 65-38. Baxter and Hodges, i&id., 43, 1242, 1921. Cadmium 112-411. Baxter and Wilson, ibid., 43, 1230, 1921.


-Q

" m

o^

Element.

2

a

if

Masses of isotopes.

=C2=A3 -2 *^ Hydrogen . .

H

1

1-008

1

1-008

f^^'o Helium . . .

He

2

4-00

1

4

&> 1"

00 Lithivim .

Li

3

6-94

2

-

" Beryllium

Be

4

91

1

9

r^ Boron

B

5

10-9

2

10=C2=BB 11"

3 Carbon .

C

6

12-00

1

12

S Nitrogen .

N

7

14-008

1

14

^ Oxygen . . .

0

8

16-00

1

16

0 Fluorine .

F

9

19-00

1

19

^ Neon ....

Ne

10

20-20

2

20" 22* 23

oQ Sodium .

Na

11

2300

1

^ Magnesium .

Mg

12

24-32*

3

24-=3D 25* 26^

Aluminium .

Al

13

26-96*

_o Silicon

Si

14

28-3

2

28" 29* (30)

3 Phosphorus .

P

15

31-04

1

31

^ Sulphur . . .

s

16

3206

1

32

'S Chlorine . . .

CI

17

35-46

2

35" 37* (39)

^ Argon . . .

A

18

39-9

2

36* 40" 39" 41*

Potassium

K

19

39-10

2

Calcium .

Ca

20

40-07

(2)

40 (44)

Scandium

Sc

21

45-1*

Titanium .

Ti

22

48-1

Vanadium

V

23

510

0

2 Chromium .

Cr

24

52-0

H Manganese .

Mn

25

54-93

' Iron ....

Fe

26

55-84

n

^ Cobalt . . .

Co

27

58-97

J Nickel

Ni

28

58-68

2

58" 60*

P

n Copper .

Cu

29

63-57

J

=3D Zinc ....

Zn

30

65-37

(4)

(64=C2=B0 66* 68 7O<0

  • Galliimi . . .

Ga

31

70-10

Germanivmi .

Ge

32

72-5

Arsenic .

As

33

74-96

1

75

Seleniima .

Se

34

79-2

Bromine .

Br

35

79-92

2

79" 81*

Krypton .

Kr

36

82-92

6

78/ 80 82'^ 83-^ 84=C2=BB

86*

APPENDIX I


143


"S .

^

o *^

O^i

o ^^

Element

o

X!

E >,

00

Masses of Isotopes.

Rubidium

Rb

37

85-45

2

85" 87*

Strontium

Sr

38

87-63

Yttrium .

Y

39

89-33

Zirconium

Zr

40

90-6

Niobium .

Nb

41

93-1

00 Molybdenum

Mo

42

96-0

  • H _ ~


43


'-' Ruthenium .

Ru

44

101-7

'o Rhodium.

Rh

45

102-9

=C2=A7 Palladium

Pd

46

106-7

An Silver ....

Ag

47

107-88

X Cadmium

Cd

48

112-40

"O Indiimi .

In

49

114-8

Tin ... .

Sn

50

118-7

Antimony

Sb

51

120-2

Tellurium

Te

52

127-5

Iodine

I

53

126-92

1

127

L Xenon

X

54

130-2

(7)5

(128) 129" (130) 13P 132=C2=BB 134 136"

Caesium .

Cs

55

132-81

1

133

Barium .

Ba

56

137-37

Lanthanum .

La

57

139-0

Cerium

Ce

58

140-25

Praseodymium .

Pr

59

140-6

Neodymiimi .

Nd

60

144-3



61


Samarium

Sm

62

150-4

Europium

Eu

63

152-0

Gadolinium .

Gd

64

157-3

Terbium .

Tb

65

159-2

Dysprosium .

Ds

66

162-5

c

5 Holmium

Ho

67

163-5

J, Erbium .

Er

68

167-7

=C2=B0 Thulium . . .

Tu

69

168-5

1 Ytterbiiun . .

Yb

70

173-5

'C Lutecuim

Lu

71

175

Pm (Keltium) . .

(Kt)

72

ji Tantalum

Ta

73

181-5

<=C2=BB Tungsten.

W

74

1840



75


Osmium .

Os

76

190-9

Iridium .

Ir

77

193-1

Platinimi .

Pt

78

195-2

1

Gold ....

Au

79

197-2

Mercury .

Hg

80

200-6

(6)

(197-200) 202 204

Thallium . . .

Tl

81

204-0

IV

Lead ....

Pb

82

207-2

XI

Bismuth .

Bi

83

209-0*

V

Poloniuna

Po

84 85

z

VII

L Emanation

Em

86

222-0

III

i

87

.2 Radium . =C2=AE Actinium.

Ra

88

226-0

IV

Ac

89


II

^ Thorium . . .

Th

90

23215

VI

^ Uranium X .

UX

91

II

t_ Uranium

Ur

92

238-2

II

APPENDIX II

The Periodic Table of the Elements. The atomic numbers ar= e given in bold type, the atomic weights in italics and the isotopes, where = known, in ordinary numerals. The roman ntmierals indicate the chemical groups and the most important associated valencies are given below them. Elem= ents are placed to the left or to the right of the columns according= to their chemical properties, those in the same vertical line as each other have s= trong chemical similarities. The Rare Earth group is surrounded by a thick line.= Elements 59-72 have no properties pronounced enough to give them definite = places in the table. The properties of the missing elements can be p= redicted with

PERIODIC TABLE OF


IH

1-008


Valency

0

I

+ 1

II

+ 2

III

+ 3

IV

+ 4

2 He

4-00 4

3 Li

6-94 6, 7

4 Be

9-1

9

5B 10-9 10, 11

60

12-00 12

10 Ne

20-2 20, 22

11 Na

23-00 23

12 Mg

24-32

24, 25, 26

13 AI

26-96

14 Si 28-3 28,29

18 A

39-9 36, 40

19 K

39-1 39, 41

29 Cu

63-57

20 Ca

40-07

30 Zn

65-37

21 Sc 45-1

31 G

70-1

22 Ti 48-1

32 Ge

72-5

36 Kr

82-92

78, 80, 82, 83, 84, 86

37 Rb

85-45

85, 87

47 Ag 107-88

38 Sr

87-83

48 Cd 112-40

39 Y

89-33

49 In

114-8

40 Zr

90-6

50 Sn

118-7

54 Xe

130-2

129, 131, 132, 134, 136

55 Cs

132-81

133

56 Ba

137-37

57 La 58 Ce 139-0 140-25

59 Pr eONd 61 62 Sm 63 Eu = 

    64  Gd           65  Tb

140-6 144-3 150-4 152-0 = 

     157-3           159-2

66 Ds 67 Ho 68 Ev 69 Tu 70 Yb 7= 1 Lu 72 (Kt) 162-5 163-5 1677 168-5 173-5 = 

175

79 Au

197-2

80 Hg

200-6 197-204

81 Tl

204-0

82 Pb

207-2

86 Em

222-0

87-

88 Ra

226-0

89 Ac

90 Th

232-15

144

considerable certainty from the positions of their atomic numbers. From the point of view of the construction of the atom the inert gas= es should mark the end of the periods as they are shown to do ua the hst of = atomic weights in Appendix I, on the other hand it is more usual in chemistry = to start with valency 0. From principles of general convenience of arrangement t= he latter plan is adopted in this table, which is intended to give = the maximum amount of chemical information. Hydrogen, which belongs equally wel= l to group I or group VII, is best omitted from the. table altoget= her.

THE ELEMENTS


V

VI

VII

VIII

3

2

-

-1

7N

80

9F

14-01

16-00

1900

14

16

19

15 P

16 S

17 CI

31-04

32-06

35-46

31

32

35, 37

23 V

24 Cr

25 Mn

26 Fe

27 Co

28 Ni

Sl-O

33 As

74-96 75

52-0

34 Se

79-2

54-93

35 Br

79-92 79, 81

55-85

58-97

58-68 58.60

41 Nb

42 Mo

43

44 Ru

45 Rh

46 Pd

93-5

51 Sb 120-2

96-0

52 Te 127-5

531

126-92 127

101-7

102-9

106-7

73 Ta

74 W

7&-

76 0a

77 Ir

78 Pt

181-5

83 Bi

209-0

184-0

84 Po

85

190-9

1931

195-2

91 UX

ii

92 U

238-2

145

Recent results obtained by Dempster. Thanks to a private=

communication the writer is able to include some further results=

obtained by Dempster and a diagram of his apparatus for obtaining=


Fig. 19. Diagram of Anode in Dempster's latest apparatus.=


positive rays from metals. A full account is to appear in the Physical Review. Fig. 19 shows the new arrangement of vaporising furnace A and ionising filament C. The analysing apparatus has already been described on p, 31 and the results wi= th


.4F


5-9


f

'

1

k

Lithium.

\

1

\

1

\

)

J

[

<=3D/

v..

^^

/

K

9

30


ZO


10


60


6-1


6-9

Atomic Weight.


7-0


7-1


Fig. 20. Curve for Lithium. 146

APPENDIX III

147


magnesium on p. 81. Fig. 20 shows one of the curves obtained with lithium. It will be seen that the relative intensities of t= he isotopes is entirely different from that found by the writer (p. = 

86)

and also disagrees very definitely with the chemical atomic weight= . Dempster describes these relative intensities as varying very considerably. This is a most remarkable phenomenon and further information upon it is very desirable. There seems just a possibi= lity that the 6 line is enhanced by doubly charged carbon but it is = 

not

easy to see where such particles could be produced.

l/oltS 943 928 913-5 899-5 886 873 860 847-5=


J

\

Zinc.

1

t

\

1

\

1

\

f

\

r

\

\

1

1

\

\i

1

1

\

/

\

I

/

1

=C2=AE

l/

\

1

i^

\

^^

62 63 64 65 66 67 Atomic Weight.

Fig. 21. Curve for Zinc.


68 69


70


Fig. 21 gives a remarkable curve obtained from zinc. This indicates three strong isotopes and a faint fourth. The absolute=

scale of atomic weight is not known with certainty, and the valu= es 63, 65, 67, 69 are given by Dempster as those in best agreement=

with the atomic weight 65-37. Considering that the error in th= e


148 APPENDIX III

mean atomic weight of lithium, when calculated on these lines, is about 5 per cent, it would appear possible that these might = be a unit too high or too low. The probability of this is strengthene= d very much by the rule given on p. 110 connecting even atomic number with even atomic weight.

Results with calcium show only one line. This makes it extremely=

probable that this is a simple element of atomic weight 40 and=

therefore an isobare of argon. ^

Note. In a still later communication Dempster states that = 

he

has been successful in using an anode of calcium to which a sma= U quantity of zinc had been added. By this means he is able to compare the masses of the zinc isotopes with the strong calcium=

maximum, assumed as 40. This gives the atomic weights as 64, 66, 68 and 70. The intensities are quite different to those in = the curve given above for zinc. 64 is now the strongest, 66 and 68=

fainter, while 70 is very faint indeed. No explanation is yet advanced for these remarkable irregularities in relative intensity.=


He has also observed a small maximum at 44 invariably accom- panying the strong calcium maximum 40. This he considers to be probably due to an isotope of that element present in smaU quant= ity as suggested by the atomic weight 40 07.

The above values are included provisionally in the tables on pages 89 and 142.

" V. p. 88.


INDEX

Abnormal hydrides, 98

Abundance of the elements, 111

Accuracy of mass-spectrograph, 60

Actinivim chain, 14, 15

Additive law of mass, 99

Alkali metals, mass-spectra of, 83

Alpha ray changes, 13

Analysis of the elements, 63

Andrade and Rutherford, 11

Anode, composite, 80, 86 

      hot,  80,  83,  84

Anticathode, silica, 48

Antimony, 78

Argon, 66

Aronbeeg, 123

,, and Harkins, 124

Atmolysis, separation by, 127

Atomic number, 13, 93 

      theory,  2

,, volume of isotopes, 18 

      weights,  tables  of,  89,  141
      weights  of  radio -elements,  13,

141

Atoms, structure of, 90

Balke, Owens and Kremers, 142 Barkla, 93

Batuecas and Moles, 141 Baxter and Hodges, 142 and Parsons, 113 and Starkweather, 141 and Wilson, 142 Tani and Chapin, 142 Weatherell and Holmes, 73, 142 Beryllium, 88 Beta ray change, 13 Bohr, 94, 95, 121, 122, 123

,, atom, 95 BOLTWOOD, 1, 7 Boron, 72 

     anomalous  atomic  weight  of,

114 

     trifluoride,  73

Bracketing, method of, 59, 69 Brauner and Krepelka, 141 Broek, Van den, 93, 94, 116 Bromine, 76


Bronsted and Hevesy, 135, 136, 139

Brosslera, 102, 104

Bruylants and Michielson, 142

Caesium, 87

,, anomalous atomic weight of, 114 Calcium, 88, 148 Calibration curve, 55 Camera of mass-spectrograph, 51 

      positive  ray,  26

Canalstrahlen, 22 Carbon, 63

Carnotite, lead from, 124 Cathode rays, 22, 24 Chadwick, 94 

 and  Rutherford,  103

Chapin, Baxter and Tani, 142 Chapman, 130 

        and  DooTSON,  130

Chemical action, separation by, 133 

       law  of  radioactive  change,

11 Chlorine, 65, 113 

       separation  of   the  isotopes

of, 136 Classen, 31

and Wey, 142 Claude, 35 Cleveite, lead from, 17 Coincidence, method of, 57 Composite anode, 80, 86 Constancy of chemical atomic weights,

22 Cosmical effect of change of mass, 103 Crookes, 3, 4, 24, 115, 117 ,, dark space, 24, 35 

       theory  of  the  evolution  of

elements, 117 Curie, Mlle. I., 113 

    M.,  18

Dalton's hypothesis, 2 Darwin, 15

Davies and Horton, 68 Deflection of positive rays, 27 Dempster, 31, 80, 81, 86, 114, 146


149


150


INDEX


Dempster's method of analysis, 31,146 Density balance, 35

,, of isotopic leads, 17, 18 Diffusion of neon, 39

separation by, 127 velocity, determination of, 20 Disintegration theory of the evolu- tion of elements, 116 Distillation of neon, 37 Distribution of lines on mass-

spectrum, 64 DooTSON and Chapman, 130 Du Bois magnet, 61

Eddington, 104

Einstein's theory of relativity, 103 Electrical theory of matter, 90 Electric discharge in gases, 23

,, field of mass-spectrograph, 50 Electricity as an element, 115 Electrochemical properties of isotopes,

10 Electron, the, 91

Element, meaning of the word, 115 Enskog, 130 Epstein, 95 ExNER and Haschek, 121

Fa JANS, 11

First order lines, 61

Fleck, 12

Fluorine, 72, 97

Focussing positive rays, 44

FOWLEB, 123 

      and  Aston,  45

Fractional distillation, separation by,

133 Fbanck and Knipping, 68

Gehrcke, 102

,, and Reichenheim, 80, 83, 88 Geigek and Nuttall, 10, 13 Goldstein, 22 Gravitation effect on spectra, 121 

       separation  by,  131

Groh and Hevesy, 20, 135

Hahn, 8 

       and  Meitner,  8

Halation effect, 60 Half-tone plates, 25 Hall and Harkins, 116 Harkins, 102, 111, 116, 129 

        and  Aronberg,  124

        and  Hall,  116

,, and Wilson, 116 Haschek and Exner, 121 Helium, 67, 69, 106


Hevesy, 10, 12, 19 

      and  Bronsted,  136,  136,

139 

      and  Groh,  20,  135
      and  Paneth,  11
      and  Zechmeisteb,  20

Hodges and Baxter, 142 Holmes, Baxteb and Weathebell,

73, 141 Honigschmid, 17, 18, 141, 142 

 and     Horovitz,     18,

121 Horovitz and Honigschmid, 18, 121 HoBTON and Davies, 68 Hot anode, 80, 83, 84 Hydrochloric acid, diffusion of, 129 Hydrogen, 67, 69, 106 Hyman and Soddy, 17, 121

Ibbs, 130

Imes, 125, 126

Indicators, radioactive, 19

Infra-red spectrum of isotopes, 125

Intensity of positive rays, 44

Iodine, 78

Ionic dissociation theory, proof of, 20

lonisation in discharge tube, 24

Ionium, 1, 7, 9, 18

,, atomic weight of, 18 Isobares, 12, 13, 97, 110 Isotopes, definition of, 12

diagrams of, 97

discovery of, 5

melting point of, 18

refractive index of, 18

separation of, 127

solubility of, 18

table of, 89, 141

James and Stewabt, 142 JoLY and Poole, 133

Keetman, 7

Kernel of atom, 98

Kibchoff, 116

Knipping and Franck, 68

kohlweiler, 116

Kratzer, 126

Kremers, Owens and Balke, 142

Krepelka and Bbaun, 141

,, and RiCHABDS, 141

Krypton, 70

,, anomalous atomic weight of, 114

Landaueb and Wendt, 70 Langmuib, 95, 96, 99 Lead, atomic weight of, 16

,, from carnotite, 124

,, from thorite, 17 

     isotopes  of,  14,  15


INDEX


15)


Lembert and Richards, 17, 121 Lewis-Langmuir atom, 95 LmDEMANN, 102, 124, 134, 139

,, and Aston, 131

Lines of first and second order, 61, 76 

     of  reference,  55,  64

Lithium, 86, 97, 146 LooMis, 125, 126

LUDLAM, 129

McAxpiNE and Willard, 142

Magnesimn, 80

Magnetic field of mass-spectrograph,

51 Marckwald, 7, 8 Mass, change of, 100 

     deduced  from  parabolas,  28

    deduced  from  mass -spectrum,

55 Mass-spectrograph, 43 Mass-spectrum, 47, 54 Measurement of lines on mass-

spectrum, 59 Meitner, 21

,, and Hahn, 8 Melting point of isotopes, 18 Mercury, 72, 80 

 parabolas  of,  30

        separation  of  the  isotopes

of, 134 Merton, 121, 123, 124, 125 Mesothorium, 8, 10 Meta-elements, 4

Metallic elements, mass-spectra of, 80 Meteoric nickel, 113 MiCHiELSON and Bruylants, 142 Microbalance for density, 35 MiLLIKAN, 22, 91

Molecular lines of second order, 75 Moles and Batuecas, 141 MOSELEY, 11, 93, 115 Mtjller, 142 Multiply charged rays, 30

Natural numbers and atomic weights,

111 Negatively charged rays, 29, 62 Negative mass-spectra, 62, 66 Neon, 1, 33, 64, 97 Neuberger, 21 Nickel, 79 

     meteoric,  113

Nitrogen, 67, 110 Nomenclature of isotopes, 61 Nucleus atom, 10, 92, 97, 125 

       structure  of,  101

Ntjttall and Geiger, 10, 13

Order, lines of first and second, 61 Owens, Balke and Kremers, 142 Oxygen, 63


Packing effect, 100 Paneth and Hevesy, 11 Parabola method of analysis, 25 Parsons and Baxter, 113 Perforated electrodes, 22, 24 Periodic law, 11, 12, 34 

       table  of  the  elements,  144,

145 Period of radio-elements, 13 Perrin, 104 Phosphonas, 77

Photochemical separation, 137 Photographic plates for positive rays,

25 Planck's quantum, 95 Planetary electrons, 92 Poole, 133 

     and  JoLY,  133

Positive ray paraljolas, 28 

       rays,  22

     separation    by,    136

Potassium, 87 Pressure diffusion, 131 Proton, the, 92 Protyle, 90, 118 Prout's hypothesis, 2, 90, 100


Radioactive isotopes, 7, 14 

       classification  of,

21 

 transformations,  13,  14,

15 Radium B and lead, 11 

       D  and  lead,  11

Ramsay, 115 

        and  Collie,  39
        and  Travers,  33

Ratner, 24 Rayleigh, 127 Reference lines, 55, 64 Refractive index of isotopes, 18 Reichenheim and Gehrcke, 80, 83,

88 Renz, 139

Resolving power of mass-spectro- graph, 60 Richards 17 

        and  Krepelka,  141
        and  Lembert,   17,   121
        and  Wads  WORTH,  17

Richardson, 85 Rossi and Russell, 9, 120 Rubidium, 87 Russell, U 

       and  Rossi,  9,  120

Rutherford, Sir E., 7, 9, 13, 92, 93, 102 

 and  Chadwick,  103

 and  Andrade,  11

Rydberg, 141


162


INDEX


SCHUTZENBERGER, 3

Screens, willemite, 25

Secondary rays, 29

Second order, lines of the, 61

Selenium, 77

Separation of isotopes, 127

Silicon, 72 

      fluoride,  74

Skaupy, 139

Slit system of mass-spectrograph, 49 Smith and Van Haagen, 72 SoDDY, 6, 8, 10, 11, 12, 13, 14, 16, 17, 35 

      and  Hyman,  17,  121

Sodium, 86 Solubility of isotopes, 18

SOMMERFEIiD, 95

Spectra of isotopes, 9, 121,

Spectrum lines, form of, 53

Spencer, 91

Starkweather and Baxter, 141

Stas, 91

Statistical relation of isotopes, 109

Stewart, 11, 12 

        and  James,  142

Sulphur, 76

Tani, Baxter and Chapin, 142 Tellurium, 77 Thermal diffusion, 129 Third order line of argon, 67 

      lines  of,  61

Thomson, G. P., 86, 88

Sir J. J., 1, 22, 29, 33, 62, 70, 72, 75, 84, 91, 129 Thorite, 17, 18 Thorium, 7, 9, 14, 15, 18, 120


Thorium, chain, 17, 18, 116

,, atomic weight of, 18

Tin, 78 Travers, 39 

       and  Ramsay,  33

Triatomic hydrogen, 70

Unitary theory of matter, 90 Uranium, 10, 120 ,, chain, 15

Valency electrons, 98

Van Haagen and Smith, 72

Wadsworth and Richards, 17 Watson, 33 

       and  Aston,  24,  35

Weatherell, Baxter and Holmes,

73, 141 Welsbach, 8

Wendt and Landaueb, 70 Wey and Classen, 142 Whole number rule, 90 WiEN, 22

WiLLARD and McAlpine, 142 Willemite screens, 25 Wilson and Baxter, 142 

       and  Harkins,  116

Xenon, 70

anomalous atomic weight of, 114

X-ray spectra of isotopes, 1 1

Zechmeister and Hevesy, 20 Zinc, 147

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