Leipzig: Johann Ambrosius Barth, 1829. 1st Edition. FIRST EDITION OF DOBEREINER’S LAW OF TRIADS. In this paper, Johann Wolfgang Dobereiner, a German scientist, was the first to classify elements into groups based on John Dalton’s assertions that the atoms of an element have a characteristic mass. In an attempt to classify elements on the basis of Dalton’s proposed atomic mass, Dobereiner grouped the elements with similar chemical properties into clusters of three, later termed 'Triads'. The distinctive feature of a triad was the atomic mass of the middle element. When elements were arranged in order of their increasing atomic mass, the atomic mass of the middle element was approximately the arithmetic mean of the other two elements of the triad.
For example, “Dobereiner found that some groups of three elements that have similar properties, for example lithium, sodium and potassium, the atomic mass (mass number) for the second element was the average of the first and third element. For example, lithium has a mass number of 7 and potassium has a mass number of 39. The average is (7 + 39) ÷ 2 = 23. The mass number of sodium is 23. The same was found for some other groups of three elements for example carbon (12), nitrogen (14) and oxygen (16)” (GC Science, The Periodic Table). Item #521
CONDITION & DETAILS: Leipzig: Johann Ambrosius Barth. Ex-libris, only an occasional small stamp within; no exterior marks whatsoever. Octavo (8 x 5 inches; 200 x 125mm). Full volume, 634 pages. 5 fold-out plates and illustrated throughout. Handsomely rebound in half-calf over marbled paper boards. Pristine; tightly and solidly bound. New endpapers. Occasional light age toning. Very good + condition.