Aston 1922/Appendices

Appendices

Francis William Aston (1922), Isotopes, ISBN 978-1016732383, Internet Archive.

• Preface

• Chapter I - Introduction

• Chapter II - The Radioactive Isotopes

• Chapter III - Positive Rays

• Chapter IV - Neon

• Chapter V - The Mass-Spectrograph

• Chapter VI - Analysis of the Elements

• Chapter VII - Analysis of the Elements (Continued)

• Chapter VIII - The Electrical Theory of Matter

• Chapter IX - Isotopes and Atomic Numbers

• Chapter X - The Spectra of Isotopes

• Chapter XI - The Separation of Isotopes

• Appendices

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 (1² + 2² + 2² + 3² + 3² + 4² + ) 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 from 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 roman 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, 353, 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.

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.

Thulium 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, 1921.

Zinc 65.38. Baxter and Hodges, i&id., 43, 1242, 1921.

Cadmium 112.411. Baxter and Wilson, ibid., 43, 1230, 1921.

Element.	Symbol.	Atomic Number.	Atomic Weight.	Number of Isotopes.	Masses of isotopes.
First Period 2 Hydrogen	H	1	I-008	1	1.008
of Helium	He	2	4.00	1	4
Lithium 8	Li	3	6.94	2	6ᵇ 7ª
Beryllium of	Be	4	9.1	1	9
Boron	B	5	10.9	2	10b 11ª
Carbon	C	6	12.00	1	12
Period Nitrogen	N	7	14-008	1	14
Oxygen	O	8	16.00	1	16
2nd Fluorine	F	9	19.00	1	19
Neon	Ne	10	20-20	2	20ᵃ 22b
Sodium 8	Na	11	23.00	1	23
Magnesium of	Mg	12	24.32*	3	24a 25b 26c
Aluminium	Al	13	26.96*
Silicon	Si	14	28.3	2	28ª 29b (30)
Period Phosphorus	P	15	31.04	1	31
Sulphur	S	16	32.06	1	32
3rd Chlorine	Cl	17	35.46	2	35ª 37b (39)
Argon	A	18	39.9	2	36b 40ª
Potassium	K	19	39.10	2	39ª 41b
Calcium	Ca	20	40.07	(2)	40 (44)
Scandium	Sc	21	45.1*
Titanium.	Ti	22	48.1
Vanadium	V	23	51.0
Chromium 18	Cr	24	52.0
Manganese	Mn	25	54.93
of Iron	Fe	26	55.84
Cobalt	Co	27	58.97
Period Nickel	Ni	28	58.68	2	58ª 60b
Copper	Cu	29	63.57
4th Zinc	Zn	30	65.37	(4)	(64ᵃ 66b 68° 70d)
Gallium	Ga	31	70.10
Germanium	Ge	32	72.5
Arsenic	As	33	74.96	1	75
Selenium	So	34	79.2
Bromine	Br	35	79.92	2	79ª 81b
1 Krypton	Kr	36	82.92	6	78' 80e 82c 83ᵈ 84ª 86b

APPENDIX II

The Periodic Table of the Elements.

The atomic numbers are 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. Elements 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 strong 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 predicted withcoiosiderable certainty from the positions of their atomic numbers. From the point of view of the construction of the atom the inert gases 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 the latter plan is adopted in this table, which is intended to give the maximum amount of chemical information. Hydrogen, which belongs equally well to group I or group VII, is best omitted from the. table altogether.

APPENDIX III

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 with magnesium on p. 81. Fig. 20 shows one of the curves obtained with lithium. It will be seen that the relative intensities of the 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 possibility that the 6 line is enhanced by doubly charged carbon but it is not easy to see where such particles could be produced.

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 strengthened 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 small 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 accompanying the strong calcium maximum 40. This he considers to be probably due to an isotope of that element present in smaU quantity as suggested by the atomic weight 40 07. The above values are included provisionally in the tables on pages 89 and 142.

APPENDIX II

The Periodic Table of the Elements. The atomic numbers are 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. Elements are placed to the left or to the right of the columns accordingto their chemical properties, those in the same vertical line as each other have strong 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 predicted 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 71 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 gases 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 the latter plan is adopted in this table, which is intended to give the maximum amount of chemical information. Hydrogen, which belongs equally well to group I or group VII, is best omitted from the. table altogether.

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 with

.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 the 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 possibility 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 values 63, 65, 67, 69 are given by Dempster as those in best agreement with the atomic weight 65-37. Considering that the error in the

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 strengthened 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 smaU 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 quantity 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