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712

C H E M I S T R Y atom, we should find them varying within narrow limits on each so slightly in properties is not after all an argument of side of the mean (Trans. Cliem. Soc. 1888, p. 491). real weight, as it cannot be contended that differences Exception may be taken to this view, if only on such as have been observed are insufficient to characterize the ground that it is somewhat premature. Belief in an element. Our powers of perception seem, indeed, to atomic weights as constants was never more firmly held have been blunted by constantly dealing with elements than at the present time, the refinements introduced by widely different in general properties, and we are conStas and later workers who have followed in his footsteps sequently unprepared to give willing recognition to species having, in all cases, led to results which serve to confirm which cannot well be distinguished by chemical tests. and in no wise to weaken the conception. In fact, Crookes favours the opinion that there would be a difthe views expressed by Clerk Maxwell in the article ficulty in finding place within the periodic system for the Molecule (Ency. 'Brit. vol. xvi.) still represent current large number of elements of which the existence opinion. Then, although much weight must be given in the rare earths is foreshadowed. But is this the to his arguments, it is in no way certain that the case ? It is true that the latest table put forward eiements. complexity of the rare earths is so great as Crookes byMendeleeffin his Faraday lecture (Trans. Chem. would have us believe. As he and others have shown, Soc. 1889, p. 656) contains only a small number of blank the spectra on which he relies are excessively sen- spaces, but as he remarked on that occasion, “ although but sitive, traces of a foreign substance, and even the as- a recent scientific generalization, it has already stood the sociation of two earths, often sufficing to produce marked test of laboratory verification, and appears as an instrument changes in them. But until the question has been far of thought which has not yet been compelled to undergo more thoroughly worked out from the chemical side, no modification; but it needs not only new applications, but valid conclusion can be drawn; the resolution of didymia also improvements, further development, and plenty of and the recent discovery of victorium, etc., show that the fresh energy.” Now that so many new elements are means at our disposal are not yet exhausted. Moreover, being discovered, the time for its development is at least the fact that the reputed elements in the rare earths differ approaching, if not already at hand. Table of the Elements. l H 2 He 3 4 18 19 F 20 A 17 34 35 Cl 36 33

53

78

98

125

54

79

99

126

55 Mn I 56 Fe 57 58 Co 59 Ni

80 Br 81

100

127 I

5 21 37

60

82

101 102 Ru 103 Rh 104 105 Pd 106

128

129

191 Os 192 193 Ir 194 195 Pt 196

6 22 38

61

83

7 Li

23 Na 39 K

62

84 85 Rb

24 Mg 40 Ca

63 Cu 64 65 Zn

86 87 Sr

107 108 Ag 109 110 111 112 Cd

9 Be 25 41

66

88

113

130 131 132 133 Cs 134 135 136 137 Ba fl38 La 140 Ce 141 Pr ,144 Nd

197 198 Au 199 200 Hg ? R

10 Ne 11 B 26 27 A1 42 Kr 43 Sc

67 X

89

12 C j 13 28 Si 29 44 45 ! 46 47 48 Ti 49

14 N 30

15 31 P

16 0 32 S

50

51 V

52 Cr

68 69 70 Ga 71 72 Ge 73

74

75 As

76

77 Se

90 Yt! 91 Zr ! 92 ! 93

94

95

96 Nb

97 Mo

114 In 115 | H6 117 Vc 118 Sn 119 120 121 Sb 122

123

[150 Sm 156 Gd 163 Tb 166 Er 173 Yb] 183 Ta

[204 Tl 207 Pb 208 Bi] | I 232 Tb I

124 Te

184 W

240 U