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.
[[File:Aston 1922 Figure 19.jpg|thumb|400 px|right|Fig. 19. Diagram of Anode in Dempster's latest apparatus.]]
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.<ref>V. p. 88.</ref>
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.
''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.
[[File:Aston 1922 Figure 20.jpg|thumb|400 px|left|Fig. 20. Curve for Lithium.]]
==APPENDIX II==
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 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.<ref>V. p. 88.</ref>
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
[[File:Aston 1922 Figure 21.jpg|thumb|400 px|right|Fig. 21. Curve for Zinc.]]
''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.
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
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 :
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 with 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.
APPENDIX III
Recent results obtained by Dempster.
Fig. 19. Diagram of Anode in Dempster's latest apparatus.
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.
Fig. 20. Curve for Lithium.
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 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.[1]
Fig. 21. Curve for Zinc.
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.
