90 
Froceedings of the Royal Irish Academy. 
PART II.— THE THIRD AND FOURTH PERIODS OF SEVEN ELE- 
MENTS FOLLOWING CHLORINE ; OR, TEE TITANIUM- 
GERMANIUM EOUBLE FERIOD. 
[Read May 14, 1888.] 
I NOW proceed to the discussion of the third and fourth periods of 
seven elements each. 
Third Period, or Titanium Period. 
ELEMENT. 
ATOMIC WEIGHT. 
VALENCY. 
1 . Potassium. 
39 
Monad. 
2. Calcium. 
40 
Dyad. 
3. Scandium.^ 
44-45 
Triad. 
4. Titanium. 
48 
Tetrad. 
5. Vanadium. 
51 
Triad. 
6. Chromium. 
52 
Dyad. 
7. Manganese. 
55 
Monad. 
Fourth Period, or Germanium Period. 
ELEMENT. 
ATOMIC WEIGHT. 
VALENCY. 
1. Copper. 
63 
Monad. 
2. Zinc. 
65 
Dyad. 
3. Gallium {Ekaluminium) . 
69 
Triad. 
4. Germanium {Eka Silicium). 
72 
Tetrad. 
5. Arsenic. 
75 
Triad. 
6. Selenium. 
79 
Dyad. 
7. Bromine. 
80 
Monad. 
The atomic weight of scandium lies between 44 and 45, but nearer to 44. 
